Acta Energetica Power Engineering Qtrly 02/2010 by ENERGA SA

act

nergetica

02/2010

number 4/year 2

Electrical Power Engineering Quarterly

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act

nergetica In this issue

DISTRIBUTION SYSTEM BALANCING SERVICES Paweł Bućko

EVALUATION OF POSSIBILITIES OF THE HVDC CONVERTER STATION UTILISATION FOR REACTIVE POWER COMPENSATION Robert Kowalak Zbigniew Szczerba

ADAPTIVE REGULATION ALGORITHM FOR TRANSFORMERS FEEDING DISTRIBUTION GRIDS Robert Małkowski Zbigniew Szczerba

ANALYSIS OF POSSIBILITIES FOR COORDINATION OF THE UNIT TRANSFORMER REGULATOR AND GENERATOR REGULATOR OPERATION ALGORITHMS Robert Małkowski Zbigniew Szczerba Artur Zbroński

ADVANCEMENT OF WORKS RELATED TO NUCLEAR POWER PROGRAMME COMPLETION IN POLAND Tomasz Minkiewicz

THE PARTICIPATION OF THE FACULTY OF ELECTRICAL AND CONTROL ENGINEERING AT GDAŃSK UNIVERSITY OF TECHNOLOGY IN THE PREPARATORY WORK AIMED AT STARTING THE FIRST NUCLEAR POWER PLANT IN POLAND Andrzej Reński Agnieszka Kaczmarek

VOLTAGE STABILITY OF POWER SUBSYSTEM Ryszard Zajczyk

IMPACT OF CURRENT COMPENSATION SYSTEM ON GENERATOR OPERATION AT VOLTAGE CHANGES IN THE NATIONAL POWER SYSTEM Ryszard Zajczyk Piotr Szczeciński

Our mental approach as humans has not changed at all or has changed very little for decades and centuries. However the environment we live in has been changing significantly. These transformations in the environment, determining the level and quality of our lives, result mainly from technical and technological development, or in actual fact from engineers’ and technicians’ activity. We can quote here the example of changes resulting from the development of transport, telecommunications, IT and - recently - new methods of obtaining energy. The latter will impact our life in the future. We can therefore say that - potentially - it is technical development that determines the level and quality of human life most, although we still should not forget the role of culture and art. The real level - which is always lower than the potential one - results from political or geopolitical conditions including the legal system, economy, history etc. Talking about technical development we always mean people who promote it. In this issue we present profiles of two professors from the Department of Electrical Power Engineering at the Gdańsk University of Technology - prof. zw. dr hab. inż. Jacek Marecki and prof. dr hab. inż. Zbigniew Szczerba. They both celebrate their 80th birthday this year and the beginning of their creative work dates back to over fifty years ago. They are both unusual persons who have had a significant impact on electrical engineering development, and had their share in educating a great number of specialists. Their biographies speak for themselves. The 4th issue of Acta Energetica presents, as our contribution to the anniversary celebration, articles of students from science schools established by both these people celebrating their jubilees. Unfortunately, this is only a presentation of some students’ articles since the issue cannot hold more. prof. dr hab. inż. Zbigniew Lubośny Chief Editor of Acta Energetica

Jacek Marecki, Zbigniew Szczerba

prof. zw. dr hab. inż. Jacek Marecki Gdańsk / Poland Distinguished engineer, academic teacher and master of energy specialists. He has significant value for the Polish economy, related to his scientific and teaching activities. He is regarded as a scientific authority both in Poland and abroad. He is also a Full Member of the Polish Academy of Sciences. His career at the Gdańsk University of Technology has spanned over 55 years. He graduated from the Department of Electrical Engineering of the Gdańsk University of Technology with an M.Sc. Eng. degree (1954) and pursued his scientific career to obtain his Ph.D. degree (1961), Doctor Habilitatus (1966), Associate Professor (1971) and Full Professor (1979). Between 1951 and 1955 he designed power plants (e.g. Gdynia I and II) and combined heat and power plants (e.g. Gdańsk II) as a senior designer at the Institute of Electrical Power Engineering. He also worked at the Czechnica power plant building site in Wrocław. The period between 1958 and 1959 brought him a Ford Foundation scholarship for post-graduate studies in nuclear power engineering in Glasgow. Many years of pursuing a career as an academic teacher (1959-2005) brought him notable successes in educating power energy specialists, particularly in combined heat and power generation in power plants and CHP plants, as well as in complex energy management. Prof. Marecki established his own scientific school at the Department of Electrical Engineering (current Department of Electrical and Control Engineering). He promoted fourteen Doctors of Technical Sciences and five with a Doctor Habilitatus degree. He held a number of functions: Head of Institute (1966-1974), Dean (1969-1973), Director of the Institute of Power and Control Engineering (1974-1984), Vice-President for Research (1984-1987), Head of Institute - again (1987-1991) and Head of the Institute of Power Plants and Power Management (1991-2000). He has a reputation of being an excellent lecturer and teacher and is always at the top of the list in all student rankings. The academic year 2009/2010 still saw him as a lecturer in post-graduate studies. Prof. Marecki’s academic records are truly valuable: over 200 published papers, including 10 monographs, studies and scientific dissertations as well as four academic books and scripts for students. His monograph „Combined Heat and Power Generating Systems” (1988), published in England, was awarded the Award of Ministry of National Education in

1989. Prof. Marecki’s academic book „Foundations for Power Transformations” has already had three issues and has been used at departments of electrical engineering at universities all over Poland for several years. Prof. Marecki also conducted several scientific grants of the State Committee for Scientific Research and made over 200 expert opinions and studies in heat and power generation plants and heat distribution systems. He can be proud of many significant scientific discoveries and of being the initiator of several new scientific trends. His most important achievements that contributed significantly to the development of power engineering as a scientific discipline and whose functional value cannot be underestimated include identifying break-even points of the combined heat and power generation, formulating a criterion for selecting optimum parameters for heat and power generation plants and their use, and developing a method for optimizing the development of power systems with heat generation plants, water plants and nuclear power plants. Prof. Marecki has participated in over 120 conferences and scientific symposiums, including 11 World Energy Council Congresses. He has travelled abroad many times to present his papers and give lectures. He is a member of the International Association for Energy Economics (President of the Polish Affiliate of IAEE: 2000-2003), Senior Member of IEEE in the USA, Fellow of IEE in the UK and a member of the Steering Committee of the Polish and German Scientific Network INCREASE (1997-2003). He was an active member of national scientific organization authorities: Head of the Committee for Energy Issues at the Polish Academy of Sciences, member of the Electrical Engineering Committee, Chief Editor of Archiwum Energetyki and head of the Scientific Council of the Institute of Fluid-flow Machinery (1996-2006), Vice-President (1996-2002), and President (since 2003) of the Gdańsk Branch of the Polish Academy of Sciences and member of the Polish Academy of Sciences Presidium. He was also a member of Atomics Council and President of the Nuclear Power Commission. Prof. Marecki was granted the Siemens scientific award for establishing a research school, many years of scientific activity in the energy field and remarkable achievements in academic teaching (1998). He has been presented with nine ministerial awards and a number of other awards.

Jacek Marecki, Zbigniew Szczerba

prof. dr hab. inż. Zbigniew Szczerba Gdańsk / Poland Distinguished engineer, academic teacher and master of electrical energy specialists. He has significant value for the Polish electric power system, related to his scientific and teaching activities. Author and co-author of over 50 patents and scientific studies, most of which have been employed in practice. Prof. Szczerba received his Engineer’s degree in 1952, after two years of work at the Gdynia power plant and the degree of Master of Technical Sciences four years later. He started his career at the Institute of Power Engineering, where he was the head of his own team that developed a number of excitation systems and voltage controllers for generators ranging in size from several hundreds of kW for shipbuilding purposes up to the rating of 500 MW. ZRE Gdańsk decided to start production of these controllers that controlled almost 75% of the national electrical energy system generators in the peak period. Moreover, his team developed controllers for transformers with tap changers. Most MV grid transformers in Poland are equipped with these tap changers. Several dozen patents were granted for the above-mentioned inventions. In 1963 he received the degree of Doctor of Technical Sciences at the Department of Electrical Engineering at the Gdańsk University of Technology. His posts at the Institute of Power Engineering covered: assistant (until he attained the degree of Assistant Professor), head of laboratory and Vice President of the Gdańsk branch. His professional career led him to the Institute of Power System Control Units in Wrocław (in 1972), where he was appointed Vice-President for Research. During five years of work on this post he managed domestic „research issues” and developed his interests towards system instrumentation, which resulted in his being a co-author of the book „Frequency and Voltage Controlling in Electrical Power Systems”. In 1977 he completed his dissertation „Mathematical Models of Synchronous Generators Control Systems in an Electrical Power System” and received a Doctor Habilitatus degree. Afterwards, upon the request of the Gdańsk University of Technology, he was delegated to academic work and became Head of the Institute of Power Engineering at the Department of Electrical Engineering. Soon afterwards he received the title of Associate Professor and became the department

Dean. He carried out the function for two terms, until 1987, and simultaneously worked as the Head of the Institute of Power Engineering. Between 1987 and 1990 Prof. Szczerba was a visiting professor at the Oran Technical University, where he conducted doctoral studies. When he returned to Poland he established the Institute of Electrical Power Systems at the present Department of Electrical and Control Engineering. Since 1991 he has been an Associate Professor at the Gdańsk University of Technology. Between 1990 and 1996 he was Vice-President for Research. Professor Szczerba is an author and co-author of over 50 patents and over 200 scientific studies, most of which found practical application. He has been a member of the Committee for Energy Issues at the Polish Academy of Sciences, member of the Presidium of Electrical Engineering Committee at the Polish Academy of Sciences and President of the Unit of Electrical Power Systems at this Committee. In 2000 he became a Distinguished Member of CIGRE. The Professor has been a member of the scientific and editor’s board of Wydawnictwa Naukowo-Techniczne and such periodicals as Automatyka Elektroenergetyczna and Acta Energetica. He is a member of Association of Polish Electrical Engineers and Committee for Electrical Power Control Engineering. He has been awarded the Gold Cross for Merits, Polonia Restituta Knight’s Cross and Officer’s Cross, National Education Medal and Gold Emblem for „Merits for Power Science”. Prof. Szczerba has supervised ten Ph. D. programmes. He established a team of scientists famous for their studies in control engineering and automatics in electrical power systems. Two of the team members have already received professor’s degrees. The team received and has been carrying out a number of scientific grants of the State Committee for Scientific Research. The team has done a number of jobs for PSE, distribution companies and power plants. Professor Szczerba has presented his papers at a number of domestic and international conferences and congresses such as CIGRE and IFAC. He was several times the President of the Scientific Committee of the International Scientific Conference Problems in Power Engineering

Paweł Bućko / Gdańsk University of Technology

Authors / Biographies

Paweł Bućko Gdańsk / Poland The area of the author’s research is the power sector’s economics with particular focus on issues of power system development programming in view of market conditions. His professional activity includes analyses of investment in generation sources, and of market mechanisms and rules of billing in energy delivery. The author is also an energy auditor and deals with issues of rational energy use.

Distribution System Balancing Services

DISTRIBUTION SYSTEM BALANCING SERVICES Paweł Bućko / Gdańsk University of Technology

1. DISTRIBUTION SYSTEM OPERATORS AND TRADING COMPANIES AS LOCAL BALANCING MARKET ORGANISERS Distribution system operators (DSO) and local trading companies are passive obligatory participants of balancing markets (BM). This means that they may not (under existing conditions) make price offers to this market. Deviations from contractual positions are billed according to current deviation settlement prices (DSP, DSPs, DSPz), which are set based on system utilities’ balancing offers (CDGU). For the purpose of the balancing market DSO and trading companies set their contractual positions resulting from energy purchases made based on demand forecasts. The forecasting process is of key relevance for such entities. The basic decision variable that rules settlement of the balancing market’s transactions is a proper load forecast that covers a large group of supplied recipients and local generators. No forecast of the power balance in own grid can be very accurate because of the random nature of numerous phenomena affecting the demand. Most trading companies (in particular those serving dispersed recipients) can not forecast with satisfactory accuracy either. In order to minimise their balancing costs, trading companies adopt various strategies, which involve either permanent undercontracting or overcontracting in response to the price levels on the balancing market in previous days. This means deliberate overestimating or underestimating own demand forecasts. This condition results in signiﬁcant costs of trading companies’ participation in the balancing market. As of now the costs account for a few percent of the total costs of energy purchase for trading companies’ needs. Presently, to reduce the costs of their participation in balancing, trading companies employ only various contracting strategies and make diverse attempts at improving the forecasts of demand of supplied recipients and local generators. Trading companies try to discipline larger recipients by enforcing provision of their own demand forecasts. Effectiveness of such efforts is, however, very limited. Where strong economic incentives are lacking, the accuracy of local generators’ and recipient’s forecasts is low. Only large recipients forecast their own loads, since such forecasting of disperse recipients is ineffective. Increasing the share of unsettled recipients and generators in own grid makes the issue of growing balancing costs bigger and bigger. Lacking effective methods of improving the accuracy of forecasting the power balance in own grid, an alternative may be active controlling and shaping the balance by using local recipients’ and generators’ adjustment capacity. A distribution system operator should aim creating a local market of balancing services, the purpose of which should be the following: • improved security of the local grid’s operation, • reduced cost of participation in the system balancing market. • employed local regulation capacities of market entities (generators and recipients), • reduced energy transmission costs, • reduced grid infrastructure extension costs.

Summary There are many obligations imposed on an entity responsible for grid operation management (an operator) for the beneﬁt of all energy market participants. A basic obligation is the duty to ensure the proper quality of electricity and reliability of its supply. System services include the entirety of actions relative to the assurance of electricity quality, power supply reliability, and feasibility of proper deliveries under electricity supply contracts for system interconnections and within systems.

The paper discusses the role of the distribution system operator (DSO) and of energy trading companies as intermediaries in providing the system services, aggregating capacities of disperse entities on the energy market (recipients and directors). Principles of balancing groups’ operation are discussed and acquisition of power reserve among recipients by way of demand side management (DSM) techniques. The paper describes the functional concept of a decentralised system of power reserve and balancing energy acquisition in the system.

Paweł Bućko / Gdańsk University of Technology

As of now operators do not exploit technical opportunities of local balancing. In view of further development of market mechanisms on the energy market and appearing distributed energy sources, inactivity in this respect will have to be compensated by distribution system operators by way of grid infrastructure extensions and increased costs of participation in the balancing market. Local entities may be involved in balancing through the creation by DSOs of local balancing markets or of trading companies establishing so called balancing groups to include, besides unsettled entities, also entities capable of flexible adjustment of their output or demand. Collective entering of such a group to balancing the market as a single balance mechanism unit may be advantageous for members of the balancing group. A trading company should propose a system of distribution of benefits from balancing group operation between its participants. A benefit from an unsettled entity’s participation in a balancing group should result mainly from the reduced cost of its own contractual position’s balancing. Balancing group’s active participants will benefit from the availability of additional income from regulation service provision.

2. USE OF BALANCING SERVICES BY A BALANCING GROUP A balancing group (BG) is a type of agreement between the electricity market’s participants (recipients, generators, trading company) that operate jointly on a balancing market. They submit to TSOs (transmission system operators) a single accumulated trading diagram for the joint balance mechanism unit which is the sum of each entity’s diagrams. The basic purpose of setting up a balancing group is to reduce the cost of settlements on the balancing market of trading companies and other market participants with barely predictable intake/ output plans. The condition of profitability of setting up such a balancing group is availability of a profit big enough to pay all costs incurred in connection with the group’s operations. Moreover a benefit offered to each participant must be attractive enough to make it participate in this venture. The task of an entity that organizes such a balancing group is to set the rules of its operation, including its internal rules, and rules of income and cost allocation between its participants. Typically a balancing group’s organiser and operator is a trading enterprise, although balancing groups may be set up by all balancing market participants that may have recipient balance mechanism units. In order to set up a balancing group, its participants must meet numerous conditions: • entities are connected to a grid (transmission or distribution grid), • they have separate contracts for electricity purchase/ sale and distribution, • they have distribution grid code compliant measurement systems, • they actively participate in electricity purchase/ sale, subject to the TPA rule. Balancing group operator’s tasks include the following: • balancing group management, • incurring the costs of maintenance of the infrastructure necessary for the group’s integral operations, • assuming the risk relative to the group’s leadership, • assuming of the duty to settle accounts with the group members’ DSO and TSO, • settlement of accounts with external entities and within the group. Fig. 1 presents a diagram of a balancing group composition. Typically balancing groups include entities with no significant capacity to adjust own electricity intake or output. In such a case benefits from the group’s operation consist mainly in the effect of anticoincidence of occurrences of unbalancing in group participants and mutual compensation of forecast errors. If a group also includes some entities with the technical capacity to adjust their own intakes or generations, these may provide the balancing service to the group. Benefits from such group operation are then supplemented with the option of active balancing of the balancing group’s energy and significant reduction of the cost of settlements with the balancing market.

Distribution System Balancing Services

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Fig. 1. Example balancing group (BG) structure

Presently active BM participants include: centrally dispatched generating units (CDGU), active balance mechanism units TSO and centrally coordinated generating units (CKGU). Because of using of these units’ availability by TSO within BM, they must be represented by specially defined balance mechanism units and they may not be included to balancing groups. In BG there may be aggregated end recipients and distribution grid participants (DGP), which are connected to distribution grids that are not directly covered by the BM area. DGP may be classified as a recipient and distributor alike (not covered by central coordination). Inclusion of these entities in a BG is possible regardless of their location attributes assigned pursuant to BM rules [9]. In order to aggregate such entities “virtual” power supply locations (PSL), so called off-grid points, are used. Therefore a BG may consist of recipients as well as passive generating units (distributed sources mainly) regardless of their locations in the grid. A BG operates on BM within a declared recipient balancing mechanism unit (JGO). Within this unit supply locations (physical and off-grid) assigned to BG members are aggregated. Inclusion of these entities to a balancing mechanism unit requires agreement with TSO and with relevant DSO (if supply location is in the distribution grid). A BG organiser (managing entity) may be a BM participant that may own the recipient balancing mechanism unit. According to the rules [3] BM members, which may own GUO and effect group balancing therein, include the following: • generators (BMPG), • grid recipients (BMPDG) • end recipients (BMPER) • trading enterprises (BMPTE). In the last three BM participant groups owning at least one recipient balancing mechanism unit is obligatory. Benefits expected as a result of BG operation may be attributed to the following two main causes: • mutual compensation of group participants’ forecasting deviations, resulting in real self-compensation of the group’s balancing mechanism unit, and hence reduced balancing costs, • usage of compensation service provided to the group by generators or recipients with the capacity to adjust own loads and active compensation of resulting unbalancing of the group’s balancing mechanism unit in order to reduce balancing costs. The second effect may be accomplished only in a balancing group consisting of generators or recipients capable of load adjustment. Moreover, organisation of such a BG additionally requires setting rules of controlling power range’s usage by the group’s superior entity and adoption of rules of settlement of accounts due to balancing service provision to the group. It’s easier to organise a BG consisting only of entities that do not use the capacity to adjust their own loads. Benefits are then attained that result from mutual compensation of forecasting deviations. The effects are high with regard to a balancing market that operates under the condition of material divergence of pur-

Paweł Bućko / Gdańsk University of Technology

chase (DSPP) and sale (DSPs) process. A significant difference at positive and negative unbalance results in the natural occurrence within a BG of a possibility of better performance of the entities (than in the case of their independent operation on BM) having unbalance in an adverse direction than that of the whole group’s unbalance. Abolishment of the purchase and sale prices divergence (introduced at the beginning of 2009) justified with the reduction of available speculative behaviours has already made use of this effect impossible. These grounds have been reduced for operation of balancing groups consisting of passive entities alone. Benefits for participants of such a BG result now from reduced personnel and organisational costs of the unbalance settlement process and less demanding requirements with regard to financial security for balancing costs provided for in BM procedures [3]. Balancing groups differ in terms of types of their participating entities, their number, the role of the group operator with regard to their entities, as well as adopted rules of a BG’s internal settlements. The internal settlement of BG participants are typically organised according to one of the following patterns. The simplest way of settlement is based on current assessments of the deviation prices on BM, recalculated with a set coefficient. The coefficient is stipulated in an agreement by and between a BG participant and operator. It is set individually depending on the participant’s energy intake profile and feasibility of its forecasting. This way of settlement was willingly applied in the period of significant divergence between BM prices. The employment of the coefficient effectively reduces the prices divergence for a BG participant and consequently the balancing costs. If a BG operator sells energy to BG participants, then the cost of the participant’s balancing are typically included in the final energy price. A BG operator makes individual calculation of the expected balancing costs depending on the feasibility of accurate forecasting of the demand, its variability in time, and expected impact on the final BG balancing. These account for a premise for pricing the energy offered to BG participant. There are methods of settlement of accounts with BG participants based on complete transfer to them of the final balancing costs. The internal group rules provide for formulas of setting internal settlement prices depending on the concrete settlement situation. The formulas are meant to distribute the profit (along with the risk) among all BG participants. A BG may also operate subject to the so called “settlement tunnel” principles. A BG operator offered preferential rates of unbalance settlement when the participant’s deviation from the position declared in the forecast stayed within a range stipulated in the agreement. In the event of excess (in a direction consistent with the whole BG’s deviation, such a BG participant is billed at BM prices. In terms of the operator role, BGs may be divided into the following categories: • BGs where the operator provides participants with the balancing intermediary service only, • BGs where the operator purchases or sells electricity to/from some participants and provides the other participants with the balancing intermediary service only, • BGs where the operator provides the balancing intermediary service and sells or purchase electricity to/from all participants. The role of the operator of a BG that consists of recipients or generators offering provision of the electricity balancing service to the group includes also current control of the group’s unbalance and dispatch of the controlling power range. In the distribution of benefits from a group’s operation, the group’s active entities that provide it with the regulation services must be privileged. Such regulation service providers incur additional costs that must be compensated with adequate payments. A proposed manner of settlements inside a BG with regard to entities that adjust their intake or output for the purpose of group balancing must provide additional compensation for the balancing service provision. A typical settlement manner may involve the following: • fixed and negotiated (by and between the group operator and service providing participant) price for supply (intake) of the balancing electricity to the group, • set models of balancing benefits’ distribution between the regulating entity and the rest of the group. If the balancing service is provided by the BG operator, the additional benefits from active regulation of the group’s unbalance affect the balancing terms and conditions offered to the group’s other participants and the settlement modes applied are developed subject to the above described principles. Employment of the balancing service provided by a BG participant is justified when internal balancing costs are lower than the actual cost of balancing electricity purchase from BM.

Distribution System Balancing Services

3. DEMAND MANAGEMENT – RECIPIENT INFLUENCING MECHANISMS One of the tasks allocated to contemporary distribution and trading enterprises is Demand Side Management (DSM). The DSM role is to control the demand for electric power and energy in order to minimize the power system development cost. Most of DSM activities are aimed at inspiring recipient attitudes that contribute to electricity consumption rationalisation. Their typical effects include peak power release in the system and avoidance of investment in the generation system and transmission infrastructure. DSM techniques may also be an alternative to system services or reduce demand for reserve power delivered as system services. Basic DSM activities are aimed at triggering changes in recipient demand that are advantageous to the system. Changes in the course of system load variability resulting from DSM application may be classified in a few basic categories (Fig. 2): • peak cut-off – power demand reduction in peak load periods, • off-peak fill-out – electricity consumption increase in off-peak periods, • load relocation – combination of the aforementioned two categories, • strategic saving – total electricity consumption reduction, • strategic load increase – electricity sales increase, • flexible load curve – an option that considers electricity supply reliability and load adjustment to current system conditions.

DSM OBJECTIVES

peak cut-off

strategic saving

off-peak ﬁll-out

strategic load increase

load relocation

ﬂexible load curve

Fig. 2. DSM objectives

The following DSM strategies are adopted: • price response – controlled device is operated so as to minimise the electricity bill, • voluntary limitations – electricity board encourages recipients to limit their consumption in certain periods; participation in the programme is voluntary, • operation scheduling – controlled receiver is operated according to adopted schedule, • device operation duration limit (e.g. maximum number of hours of operation per day), • change at set point – scope of device operation depending on certain factors (e.g. outdoor temperature), • receiver load control • short- and medium-term limitation (in the event of power deﬁcit in the system). The basic and most frequently undertaken action aimed at desirable changes in the system load curve is the price response by way of electricity price differentiation depending on a day’s time zone or the day of the week, and of fees depending on the recipient’s peak power intake. The time zone speciﬁc price differentiation should make recipients lower their consumption in peak periods in order to minimise their electricity bills. Therefore electricity usage rationalisation involves not only consumption reduction but also exploitation of the option of load relocation between time zones.

Paweł Bućko / Gdańsk University of Technology

In many systems the option of electricity intake reduction by end recipients is exercised at the system dispatcher’s order as a system service provided by the recipients. Such recipients’ involvement is most commonly reported in US systems [1, 2, 4, 5, 6, 8]. Tab. 1 speciﬁes the most relevant features of such service in a few selected systems. A quick change in the intake power as a recipient’s quick response to the dispatcher’s order, or by direct power intake reduction in response to an adjustment signal forwarded from the system dispatch centre, is most often considered a service that allows reducing the spinning reserve required in the system on its generating side. Tab. 1. Intake reduction service on selected electricity markets [5] System, service type

Contract type

Advance notice

Minimum requirements Service fee structure

Alberta, Typ 1

Monthly

One hour

1 MW, up to 4 hrs

Fixed monthly per MW rate, regardless of actual number of intake reductions

Alberta, Typ 2

Weekly

One hour

1 MW, up to 4 hrs

Per MWh rate for actual reductions

15 or 30 mins.

1 MW, up to 4 hrs

Monthly per MW rate for availability to provide the service Per MWH rate for actual provision of the service 1 MW – fee as per current rate for spinning reserve 2 MW – fee as per next day market electricity price

California

Long-term

New York

Long-term

10 or 30 mins.

1 MW or 2 MW, up to 1 hr

Taipei, Typ 1

Long-term

One day or one week

5 MW, up to 6 hrs daily

50% reduction of rates for contracted electricity

Taipei, Typ 2

Long-term

One day, 4 hrs, 1 hr

All industrial recipients, up to 6 hrs.

Rate and billing depending on adopted advance notice

Intake power reduction, especially in peak intake periods, allows for reduction of the power reserves required for primary and secondary regulation. With such reserve use, a quick intake power reduction is classified as a second or minute reserve (depending on the time of access to power on the recipient side). Since permanent substitution of primary and secondary regulation reserve with intake reduction is not possible, limits are introduced to the maximum share of reserves acquired on the recipient side in the total second or minute reserve maintained in the system. In the US markets the maximum 25% recipient share in the second and minute regulation service provision is most commonly adopted [9]. Recipients providing the intake reduction service at the system dispatcher’s order participate subject to general rules in the system services market, competing with generators, or they are offered other settlement modes drawn from basic DSM techniques (Tab. 1). Such payments may include fees charged for availability for the service provision and fees for electricity untaken from the system as a result of the demand reduction (such electricity is considered as supplied regulation energy). The electricity billing rate is typically referred to rates charged for regulation electricity supply by generators. The basic DSM implementation objective is to reduce thetotal cost of electricity supply. Benefits from such cost reduction are distributed between recipients, electricity suppliers, and intermediaries (trading enterprises). On top of this basic effect, also additional benefits may be expected such as, for instance [7]: • improved system adjustability, • improved supply availability, • improved demand forecast accuracy, • reduced transit limitations, • better usage of existing system infrastructure, • reduced supplier market power, • recipient implementation of effective electricity cost management programmes, • reduced price risk by way of electricity price fluctuation reduction,

Distribution System Balancing Services

• strengthened market relations of recipients and suppliers, • increased competition of the national economy. All the aforementioned actions translate indirectly to increased energy security. DSM actions should lead to benefits for recipients and suppliers alike. The potential effectiveness of implementing such actions by suppliers and effectiveness following recipients’ appropriate responses depend on both sides’ conviction in the DMS rationale. It should be remembered that benefits from effective DMS implementation to the system are, unfortunately, dispersed: they appear on the sides of generators, transmission system operators, distribution system operators, and trading companies alike. Tariffs and price lists applied to end recipient billing regulate the settlement only between some of these entities (distribution companies and trading companies) and end recipients. DSM implementation in these tariffs and price lists requires, therefore, concurrent development of effective ways to transfer their effects to the other entities (transmission system and generators). Effective DMS implementation, therefore, requires a competitive and efficient gross market that generates appropriate incentives for the retail market. The present gross market in Poland is not yet sufficiently efficient in this respect. The following two conditions must be met for a properly structured tariff to become an effective instrument of DSM implementation: • tariff provisions must ensure profitability of recipients’ appropriate behaviour (adequate differentiation of billing rates and bonuses is necessary), • recipients must be aware how to use the tariff (tariffs must be transparent, as simple as possible, and the knowledge of their usage must be transferred to recipients through marketing and education). The existing tariffs hardly serve the first purpose. The recipient awareness has to be assessed even worse.

4. SUMMARY Gradual decentralisation of market processes and corresponding decentralisation of power control in the system will lead to the creation of local markets of regulation services. DSO may also play the role of system services concentrator with regard to TSO or other participants of the system services market. The scope of services provided to TSO may be limited compared to the system market. Limitations of local services supply to local markets will be significant. Trading companies should actively participate in the creation process of local markets for regulation services by organising so called balancing groups. A balancing group naturally contributes to decentralisation of the electricity balancing process and reduces the demand for balancing energy on BM. Such a group may also play the role of intermediary in the energy balancing service provision by dispersed entities and may aggregate their capacities. Present tariffs hardly serve the purpose of encouraging recipient to implement DMS objectives. The present tariffs’ impact is reduced to some attempts at recipient motivation to advantageous shaping of the active power load curve, reducing peak power intakes, and attempts at disciplining reactive power intake. None of these functions is effectively fulfilled by the present tariffs. Recipient potential is not tapped with respect to the load curve’s active shaping and actions to support regulation procedures in the system, and active participation in its defence under threat, or assistance in the recovery of its normal operation. DSM implementation in the transmission and electricity tariffs should be enabled, meant as active shaping of the load curve, enabling paid-for exploitation of a recipient’s potential to participate in power balance assurance in the system, and in reducing generation cost under the condition of periodic power deficit in the system. Besides tariff billing, recipients’ capacity should be exploited with regard to active and reactive power balances by providing proper conditions for the recipients’ active participation in the provision of selected system services. The above recommendation concerns services from the voltage and reactive power control group as well as recipient participation in active power control (especially in the event of power deficit in the system and threat to the system operation’s security). Services of electricity intake reduction by end recipients at the system dispatcher’s order may be an alternative to reserve power delivery through the provision of regulation services by generators.

Paweł Bućko / Gdańsk University of Technology

Effective DSM implementation in tariff billing for dispersed recipients requires coordination of solutions between transmission tariffs (applied by grid enterprises) and tariffs or price lists (applied by trading enterprises).

This study has been ﬁnanced with funds allocated to science in 2008-2010 as research project N511 376235.

REFERENCES 1. Bolton Zammit M.A., Hill D.J., Kaye R.J., Designing ancillary services markets for power system security, IEEE Transactions on Power Systems, Volume 15, Issue 2, May 2000. 2. Cheung K. W., Shamsollahi P, Sun D., Milligan J., Potishnak M., Energy and ancillary service dispatch for the interim ISO New England electricity market. Proceedings of the 21st 1999 IEEE International Conference: Power Industry Computer Applications, PICA ’99. Jul. 1999. 3. Instrukcja Ruchu i Eksploatacji Sieci Przesyłowej – Bilansowanie systemu i zarządzanie ograniczeniami systemowymi (uniform text effective 1 January 2010). Polskie Sieci Elektroenergetyczne Operator S.A., Warsaw 2010, www.pse-operator.pl 2010. 4. Kun-Yuan Huang, Yann-Chang Huang, Integrating direct load control with interruptible load management to provide instantaneous reserves for ancillary services, IEEE Transactions on Power Systems, Volume 19, Issue 3, Aug. 2004. 5. Le Anh Tuan, Bhattacharya K., Competitive framework for procurement of interruptible load services, IEEE Transactions on Power Systems, Volume 18, May 2003. 6. Le Anh Tuan, Bhattacharya K., Interruptible load management within secondary reserve ancillary service market, IEEE Power Tech Proceedings, Porto 2001. 7. Malko J., Wilczyński A., Oszczędne, racjonalne czy efektywne użytkowanie energii elektrycznej, Energetyka, nr 9/2007 8. Rerkpreedapong D., Feliachi A., Decentralized load frequency control for load following services. Power Engineering Society Winter Meeting, IEEE, Volume 2, 2002. 9. Xingwang Ma, Sun D.I., Cheung KW., Evolution toward standardized market design. IEEE Transactions on Power Systems, Volume 18, Issue 2, May 2003.

Correction In the third issue of Acta Energetica a wrong title was erroneously published of the article by Anna Lisowska-Oleksiak, Andrzej P. Nowak and Monika Wilamowska. The right title is: â&#x20AC;&#x153;Supercapacitors as energy-storage devicesâ&#x20AC;?. We apologise for the mistake. The Editors

Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

Authors / Biographies

Robert Kowalak Gdańsk / Poland

Zbigniew Szczerba Gdańsk / Poland

He graduated from the Faculty of Electrical and Control Engineering at Gdańsk University of Technology (2000). He obtained his PhD in technology at this faculty (2005). Presently, he is working as a lecturer in the Power Engineering Department of the Faculty of Electrical and Control Engineering at Gdańsk University of Technology. His professional interests include: high-voltage power electronics systems (FACTS, HVDC), modelling the operation of power electronics systems in a power system, cooperation of power supply systems with traction power systems.

Obtained his BSc degree in 1952, MSc four years later and PhD in 1963 at the Faculty of Electrical Engineering, Gdańsk University of Technology. At the institute of Power Engineering ran his own team which developed multiple excitation systems and generator voltage regulators with outputs ranging from hundreds kW (for marine industry) to 500 MW. At one point generators controlled by those devices provided 75% of power to the national power grid. In 1972 transferred to the Institute of Power Systems Automation in Wrocław and appointed Deputy Director of Science there. In 1977 obtained his DSc degree. Subsequently appointed Head of the Electrical Engineering Department at the Faculty of Electrical Engineering, GUT, and soon also Assistant Professor. Elected Dean of the Faculty for two terms. In 1987-90 worked as a Visiting Professor at the University of Technology in Oran, Algeria. After returning to Poland organized the Chair of Power Systems at the present-day Faculty of Electrical and Control Engineering. Since 1991, a full Professor at the Gdańsk University of Technology. In 1990-1996 University’s Vice-Rector for Science. Author or co-author of more than 50 patents and more than 200 scientiﬁc studies. Most of that work found practical application.

Evaluation of possibilities of the HVDC converter station utilisation for reactive power compensation

EVALUATION OF POSSIBILITIES OF THE HVDC CONVERTER STATION UTILISATION FOR REACTIVE POWER COMPENSATION Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology 1. INTRODUCTION

Typical devices used for reactive power compensation in system nodes are static compensators in the form of capacitor and choke batteries and the state–of-the-art power electronics compensators of the following types: SVC (Static Var Compensator) and STATCOM (Static Compensator). For compensation purposes, synchronous machines are also used, e.g. water-power station generators. The element operating for several years in the National Power System (KSE) and which can theoretically be used for reactive power regulation is the HVDC (High Voltage Direct Current) circuit. The main task of this system is the transmission of active power between Polish and Swedish power systems. The reactive power issue is also related to the above transmission. It relates directly to the circuit converters which, during operation, draw considerable amounts of reactive power from the systems. Reactive power consumption depends on the active power transmitted through the circuit and the angle of control for the converter semiconducting elements. The authors have investigated the possibility of using HVDC circuit converter stations to regulate this power. The evaluation has been conducted on the basis of simulation tests. This article presents a part of the research conducted and described within the framework of [3].

2. POLAND – SWEDEN HVDC CIRCUIT The Sweden-Poland HVDC transmission system started operating in 2000. The created connection between the Polish and Swedish power systems has greatly enhanced the National Power System operation safety, in particular its northern part which is characterised with a small number of generating systems [8]. The circuit connects the Karlshamn region in south-east Sweden with Wierzbięcin located near Słupsk in Poland. HVDC is connected to the Polish power system in the Słupsk station (voltage 400 kV) and to the Starno station on the Swedish side (voltage also 400 kV). The circuit length is 254 km. The HVDC system diagram is presented in ﬁg. 1. The technical data of the circuit and its individual elements has been obtained from sources [5, 6, 7, 8, 9].

Abstract This paper presents the results of the research related to the evaluation of the possibility of using HVDC circuit converter stations to compensate reactive power in a power system. Proper control of the ignition angle in converters may inﬂuence the value of the reactive power drawn by this converter. By adding the control of the converter voltage transformation ratio, a system is created where the constant ﬂow of active power with changeable reactive power may be maintained. Theoretically speaking, if the controls of reactive power compensation

elements installed in the HVDC station are connected with the controls of the converter system operation (converter + transformer), a system may be obtained which can be successfully used for reactive power compensation in a power system. The conducted research has shown that regulation of the reactive power drawn by the HVDC circuit converters can be obtained, which results in signiﬁcant ranges of changes in this power with maintaining the constant set value of active power transmitted through this circuit.

Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

18 �

SEE 1

DC cable line

SEE 2

Return cable

Fig. 1. HVDC transmission system diagram: PT – 6-pulse thyristor converter; TP – 3-winding converter transformer; D – choke; C – capacitor for reactive power compensation; L – choke for reactive power compensation; F - ﬁlters

The station located in Poland includes the following elements: a converter system, smoothing choke, higher harmonic filters, capacitor batteries and a choke for reactive power compensation. The converter system consists of two 6-pulse thyristor bridging systems connected in series on the DC side. The converter transformer consists of three 3-phase 3-winding units (power 236 MVA each) and the 405/181 kV/kV voltage transformation ratio. Thanks to proper connection of all converters and transformer windings, 12-pulse converter systems have been obtained. The smoothing choke on the DC side (inductance 225 mH, nominal current 1381 A and nominal voltage 450 kV) operates as a rectified voltage filter and as a system reducing the surge values. In order to limit the voltage and current disturbances caused by the converters during operation on the circuit AC side the higher harmonic filters have been installed. The reactive power generated by the filter systems is 95 Mvar with 400 kV voltage, which makes it an additional reactive power source. For the purposes of the HVDC station reactive power compensation, two capacitor batteries (nominal power 95 Mvar each) and a choke (nominal power 117 Mvar) are used. Capacitor batteries are activated as necessary and the choke is used to balance the reactive power of higher harmonic filters in the circuit low load states so as to avoid over-compensation. Both circuit converter stations are similarly created units. The control method for the HVDC circuit operation has been discussed in [2]. In the normal state, the thyristor control angles are within relatively narrow limits. During the rectifier operation, converters operate with the thyristor ignition angle α equal to α = 15° ± 2.5°. However, during the inverter operation, the extinguishing advance angle γ is equal to γ = 18° ± 1°. The regulation of the set current value in the rectifier is effected through changing the voltage transformation ratio of the rectifier system and additionally regulating with the thyristor ignition angle from the given range. However, voltage regulation on the DC side is effected by the inverter and is achieved by changing the voltage transformation ratio of the inverter system and additionally regulating by means of the extinguishing advance angle from the given range.

3. REACTIVE POWER RELATED TO CONVERTERS The change of the thyristor activation angle in converters results in the change of the phase shift angle of the basic current harmonic in the power system in relation to the sinusoidal supply voltage. The increase in the thyristor control angle � is related to the increase in the phase angle of the current run delay in the line in relation to the converter input voltage (ﬁg. 2), which clearly shows that the controlled power electronics converters are the receivers drawing reactive power from the line depending on the control angle [1, 10, 11].

Evaluation of possibilities of the HVDC converter station utilisation for reactive power compensation

Fig. 2. Time runs of current and voltage supplying the rectiﬁer controlled after omitting commutation processes

The elements for reactive power compensation located in the HVDC circuit converter station ensure only discontinuous control of this power. The simultaneous control of the voltage transformation ratio and the thyristor activation angle in the circuit theoretically makes it possible to control the reactive power in an incremental manner which, in connection with the incremental regulation of the capacitor battery and the choke, would make it possible to control the reactive power during the circuit operation in a substantially broader range.

4. EVALUATION OF THE HVDC CIRCUIT STATIONS CAPABILITY FOR REACTIVE POWER REGULATION Model examinations of the circuit operation have been carried out using the DIgSILENT PowerFactory 13.2 program. The circuit static model has been designed for the purposes of the examinations. The model uses ready-made components built into the simulation program. Fig. 3 shows the structure of the designed HVDC circuit model.

�

SEE_2 Shunt/Filter(3) Shunt/Filter(4) Shunt/Filter(5)

SEE_1 Shunt/Filter Shunt/Filter(1) Shunt/Filter(2) ~

Line

AC_R

DC_R+

Dlawik_I

3-W inding..

DC_I2

DC_R2

AC_I2

AC_I1

AC_R2

DC_I+

Dlawik_R

3-W inding..

AC_R1

Terminal

DC_R1

DC_I1

DC_I-

DC_R-

Grounding ..

Line(1)

Fig. 3. Structure of the designed HVDC circuit model

In order to represent the power systems, voltage sources with introduced impedance corresponding to the systems short-circuit power have been used. The circuit AC buses have been ﬁtted, on both sides, with three

Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

capacitor batteries for reactive power compensation (95 Mvar each), two of which model the actual batteries while the remaining one provides the same reactive power as a higher harmonic filter. Depending on the power transmitted through the circuit and voltage levels, the batteries were activated or deactivated during the simulation examinations. Deactivation of the last battery was to represent choke activation with operating higher harmonic filter. While creating the converter system models, a ready-made 3-winding transformer model and bridging thyristor 6-pulse converter models were used. The parameters for these elements have been assumed as for the actual object. Smoothing chokes in a form of inductance itself have been modelled between the converters and the HVDC cable line. In order to represent the circuit cable, ready-made models of the DC cable line have been used and proper parameter values have been inputted to them. As in the model designing stage complete data was not available, it was complemented on the basis of other similar objects. Verification was necessary to check if the designed model corresponds to the actual object. For comparison purposes, the characteristics of the circuit obtained from available sources have been used. For the purposes of the study, they have been represented on diagrams and the characteristics obtained from the designed model have been imposed on them. Fig. 4 shows characteristics Q = f (PDC ) (of the model and the circuit) obtained during rectifier operation and fig. 5 shows these characteristics obtained during inverter operation. �

��

� ��

��

Fig. 4. Q = f (PDC ) characteristics of the HVDC circuit converter system during rectiﬁer operation

�

��

� ��

��

Fig. 5. Q = f (PDC ) characteristics of the HVDC circuit converter system during inverter operation

Evaluation of possibilities of the HVDC converter station utilisation for reactive power compensation

As shown in the presented diagrams, model characteristics do not precisely correspond to the actual object characteristics. The reasons for the differences may be numerous, however, the most signiﬁcant are the assumptions for given circuit parameters and the fact that several model elements are idealised. Taking the above into account, a conclusion has been drawn that the characteristics obtained in the model are precise enough and the model has been designed with the precision allowing conducting the planned examinations. 5. EXAMINATION RESULTS

The simulation examinations were conducted in two stages: the first stage consisted in checking the reactive power regulation range with the station rectifier operation and the second stage consisted in checking the regulation range with the station inverter operation. During both examinations the constant set transmitted power in the circuit was maintained by maintaining the constant DC value in the rectifier and the constant voltage value on the DC side in the inverter. The examinations were carried out for the entire range of transmitted reactive powers set in the circuit assuming that the power change is to be incremental (by 50 MW). Only the extreme analysed power values were inconsistent with the assumed increment. This was related to the current limits in the converter: lower limit equal to 114 A, which corresponded to the transmitted power on the level of 50.46 MW; upper limit equal to 1664 A, which corresponded to the transmitted power equal to 736.54 MW. The results obtained have been presented on diagrams in the form of points. In order to clearly show the change trends, the points have been connected with curves. The points have been coloured to highlight results obtained in slightly altered conditions of converter station operation and the following indications have been introduced in the diagrams: – all three reactive power compensation batteries activated in the station; – two reactive power compensation batteries activated in the station; – one reactive power compensation battery activated in the station (equivalent of higher harmonic filters); – no compensation in the station (equivalent of the situation when the choke compensates reactive power of the higher harmonic filters). Unfilled points show that the voltage on the converter AC side has reached values lower than the ones which are permissible in the long run. Fig. 6-8 shows the results obtained during rectifier examinations and fig. 9-11 shows the results obtained in relation to the inverter. The first figure (6) shows the consumption of reactive power by the rectifier in the function of the location of rectifier transformer taps. The obtained results show that the reactive power regulation range is not small. The figure shows that it was impossible, for any of the set power values in the circuit, to use the full regulation range of the voltage transformation ratio due to the limited possibility of controlling the rectifier. The present reactive power changes are incremental but their increment is much lower than the increment caused by activation of the capacitor battery or the choke. The most extensive changes of the rectifier reactive power have been detected with the highest power values transmitted in the HVDC circuit. The decrease in the power transmitted in the circuit has been accompanied by a decrease in the number of points obtained in the characteristic.

Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

22 � 450

400

736,54 MW

350

700 MW 650 MW

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Q [Mvar]

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300 MW 250 MW

150

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100

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0 -8

-6

-4

-2

TR tap number

Fig. 6. Reactive power drawn by the rectiﬁer in the function of power transmitted by the circuit and the location of the rectiﬁer transformer tap

The next figure (7) shows the value of the converter reactive power in the function of the thyristor activation angle. Regardless of the set value of the transmitted reactive power, the range of the α angle regulation has remained practically constant. This resulted from the fact that, on the one hand, it was limited by the minimum permissible value (5°) and, on the other, the limit resulted from the constant voltage value maintained in the circuit. However, the available reactive power regulation range was significant and made it possible both to increase and decrease its draw in relation to the current value dependant on the ignition angles used. This was related to the fact that the currently used ignition angle is located in the middle of the available range of activation angles. However, fig. 8 shows the dependence of the reactive power value in the function of voltage on the AC side of the rectifier. During transmission of a large amount of power in the circuit, the rectifier draws a large amount of reactive power, which, as a result, causes problems with maintaining the correct voltage on the AC side, which is undoubtedly one of the limits in using this type of reactive power regulation. � 450

400

736,54 MW

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Q [Mvar]

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150

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0 4

Alpha [st.]

Fig. 7. Consumption of reactive power by the rectiﬁer in the function of power transmitted in the circuit and the � angle of activating thyristors in the rectiﬁer

Evaluation of possibilities of the HVDC converter station utilisation for reactive power compensation

Analogously, the examination of the range of the reactive power regulation achieved by the rectifier system of the circuit with inverter operation was conducted. Fig. 9 shows the value of the reactive power drawn by the inverter in the function of the location of the inverter transformer taps. The results obtained also confirmed that the regulation range of the reactive power drawn by the HVDC station converter is significant. Despite the fact that also here, in any analysed case of the circuit operation, it was not possible to use the full range of transformer regulation, the obtained range of reactive power changes was more extensive than for the rectifier operation. Similarly to the rectifier operation, the obtained changes of reactive power were incremental with an increment lower than might result from the activation of the circuit compensator system elements. � 450

400

736,54 MW

350

700 MW 650 MW

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600 MW 550 MW 500 MW

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Q [Mvar]

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0 366

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374

376 378

380

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384

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396 398

400

402

404

406

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UAC [kV]

Fig. 8. Consumption of reactive power by the rectiﬁer in the function of the power transmitted in the circuit and the voltage angle in the 400 kV buses of the rectiﬁer station

� 600

500 736,54 MW 700 MW 650 MW

400

600 MW 550 MW 500 MW 450 MW

Q [Mvar] 300

400 MW 350 MW 300 MW 250 MW

200

200 MW 150 MW 100 MW 50,46 MW

100

0 -8

-6

-4

-2

TR tap number

Fig. 9. Reactive power drawn by the inverter in the function of the power transmitted in the circuit and the location of the inverter transformer tap

Fig. 10 shows the converter reactive power in the function of the thyristor activation angle in the inverter. Depending on the value of the transmitted power set in the circuit, the available regulation angle α changed. This was related to the fact that with the maintained constant value of the γ angle in the inverter the commu-

Robert Kowalak / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

tation angle µ was signiﬁcantly changed together with the changes in the transmitted active power which with the γ angle determined the moment of thyristors activation in the inverter. In this case, the regulation range is limited, on the one hand, by the minimum γ angle and, on the other hand, by the number of transformer taps. The range of control for the inverter thyristors in relation to the one currently utilised during normal operation makes it possible only to increase the reactive power drawn by the inverter as the present range of ignition angles is practically located at the end of the available range of inverter thyristors activation angles. � 600

500 736,54 MW 700 MW 650 MW

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400 MW 350 MW 300 MW 250 MW

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0 125

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Alpha [st.]

Fig. 10. Consumption of reactive power by the inverter in the function of power transmitted in the circuit and the � angle of activating thyristors in the inverters

The last figure (11) shows the value of the inverter reactive power in the function of voltage on the AC side. Similarly to the rectifier operation, during the transmission of high power, the inverter operates with significant difficulties related to maintaining the correct voltage level on the AC buses. Points presenting obtained results in fig. 11 have been grouped according to the number of currently activated capacitor batteries. Deactivation of other batteries has resulted in shifting the voltage range on the AC buses towards the middle of the permissible voltage range and together with decreasing the power transmitted in the circuit the characteristics have systematically shifted towards increasingly higher AC voltage values. A similar tendency has also been observed in the rectifier. � 600

500 736,54 MW 700 MW 650 MW

400

600 MW 550 MW 500 MW 450 MW

Q [Mvar] 300

400 MW 350 MW 300 MW 250 MW

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0 366 368 370 372 374 376 378 380 382 384 386 388 390 392 394 396 398 400 402 404 406 408 410 412 414

UAC [kV]

Fig. 11. Consumption of reactive power by the inverter in the function of the power transmitted in the circuit and the voltage value in the 400 kV buses of the inverter station

Evaluation of possibilities of the HVDC converter station utilisation for reactive power compensation

6. SUMMARY The conducted research has shown that the regulation of the reactive power drawn by the HVDC circuit converters can be obtained while maintaining the constant set value of the active power transmitted through this circuit. The utilisation of the theoretically available range of converter control angles and the range of changes in the converter transformers voltage transmission ratio has made it possible, in relation to the present state, to increase and decrease the reactive power draw with rectiﬁer operation and mainly to increase the draw of this power with inverter operation. The obtained reactive power regulation is incremental, which results from the character of the transformer taps switching. Nevertheless, the change in the converter station reactive power obtained in this manner is achieved with smaller increments than if the currently utilised method is used. The determined range of the rectiﬁer reactive power changes is much broader than the one currently used and has reached the maximum value approaching 140 Mvar, but, taking into account the voltage limit, the maximum available range amounts to approximately 120 Mvar (while maintaining the constant power in the circuit) and has gradually decreased together with the decrease in the value of the power transmitted in the circuit. However, the range of the inverter reactive power changes has also been extended and has reached the maximum value approaching 220 Mvar (while maintaining the constant power in the circuit) and has also gradually decreased together with the decrease in the value of the power transmitted in the circuit. The aim of the research conducted has only been to show that reactive power regulation by means of HVDC circuit converters is possible (which has been demonstrated) and, due to this, it has not included a very precise determination of the available reactive power ranges.

REFERENCES 1. Barlik R., Nowak. M., Technika tyrystorowa, Wydawnictwa Naukowo-Techniczne, edition 3, Warsaw 1994. 2. Kowalak R., Szczeciński P., Modele matematyczne elementów energoelektronicznych – FACTS, ordered research project no PBZ-MEiN-1/2/2006 “Bezpieczeństwo elektroenergetyczne kraju”, Consortium of the Gdańsk, Silesian, Warsaw and Wrocław Universities of Technology, report on the fulfilment of task 3.1.2.c, 2007 (unpublished). 3. Kowalak R., Szczerba Z., Sposób i algorytmy sterowania stacji przekształtnikowej AC/DC dla poprawy bezpieczeństwa napięciowego systemu ee, Consortium of the Gdańsk, Silesian, Warsaw and Wrocław Universities of Technology, report on the fulfilment of task 8. 4.2.F, Gdańsk (unpublished).� 4. Kujszczyk S., Brociek S., Flisowski Z., Gryko J., Kazarko J., Zdun Z., Elektroenergetyczne układy przesyłowe, Wydawnictwa Naukowo-Techniczne, Warsaw 1997. 5. Madajewski K., Modele dynamiczne systemu elektroenergetycznego do badania układów przesyłowych prądu stałego, Prace Instytutu Energetyki, journal 25, Warsaw 2003. 6. Madajewski K., System przesyłowy prądu stałego HVDC Polska – Szwecja, Automatyka Elektroenergetyczna 1/ 2000. 7. ABB company materials: HVDC. Efficient Power Transmission, ABB Power Systems AB, Sweden, Västeras 1998. 8. Website http://www.pse-swepollink.pl/, November 2009. 9. Website http://www.abb.com/hvdc, November 2009. 10. Szczęsny R., Komputerowa symulacja układów energoelektronicznych, Wydawnictwo Politechniki Gdańskiej, Gdańsk 1999. 11. Tunia H., Winiarski B., Podstawy energoelektroniki, Wydawnictwa Naukowo-Techniczne, edition 1, Warsaw 1975.

Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

Autorzy / Biograﬁe

Robert Małkowski Gdańsk / Poland

Zbigniew Szczerba Gdańsk / Poland

Graduate of MSc studies at the Faculty of Electrical and Control Engineering of the Gdańsk University of Technology (1999). In 2003 obtained his PhD degree. Currently works as a lecturer at the Chair of Electrical Engineering, Gdańsk University of Technology. Areas of scientiﬁc interest include wind power, catastrophic disruptions of the power grid, control of voltage levels and reactive power distribution in an electrical grid..

Adaptive Regulation Algorithm for Transformers Feeding Distribution Grids

ADAPTIVE REGULATION ALGORITHM FOR TRANSFORMERS FEEDING DISTRIBUTION GRIDS Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba/ Gdańsk University of Technology

1. ANALYSIS OF NEED FOR BLOCKING TRANSFORMER REGULATORS IN ABNORMAL VOLTAGE CONDITIONS 1.1. Characteristic curve of consumers powered by transformers As in the case of active power, the consumed reactive power is a function of voltage U and frequency f. General variability of reactive power caused by changes of f and U around the operating point, assuming frequency f = const, Δf = 0 can be presented as: � F U , f  Qo  U U

(1)

In fact the linear approach shown above is only valid for small variations of U and f in steady states. For larger voltage variations the function Q = F (U, f) in steady state, for f = const., is non linear, as shown in Fig. 1.

�

��

�

� �

� dQ tgα  o dU ��

��

Fig. 1. Variations of consumer reactive power at variable voltage and f = const. 1, 2, 3, 4 – various responses at signiﬁcant voltage drops.

in some intervals of voltage variations The chart shows that the derivative of reactive power is positive and in others negative. The curves shown in the Fig. 1 can be useful for both qualitative and – in approximation – quantitative interpretation of unsteady states at a system, subsystem or island overloaded with reactive power. Usually at significant voltage drops the relation can have a character similar to curve 1 (Fig. 1). At some types of consumers the curves 2 and 3 can be more correct, and finally – when there is a significant share of asynchronous drives and capacitor banks – the relation will follow the shape of curve 4. In such situations a significant voltage drop causes the reactive power consumption to rise.

Abstract This study describes an example of a new smart transformer regulator. Control system for 110/MV transformers based on the proposed algorithm allows automa-

tically adapting the regulator algorithm for the present condition of the power grid (e.g. cascading failure) and therefore helps to increase the power supply security.

Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

Just like in case of the active power, the higher the voltage change rate – dependant on overload value – is, the more the real characteristic curve differs from those presented in the Fig. 1. This discrepancy is caused by electromagnetic transient states in electric motors, and inﬂuence of spinning masses in drive systems.

1.2. Inﬂuence of transformer voltage control on consumer characteristics At the constant transformer ratio lowering the voltage at the primary winding results in a corresponding drop of voltage on the secondary winding. If, despite lowering primary voltage, the regulator keeps constant voltage at the secondary circuit, the consumed reactive power does not depend on voltage variations in the primary circuit and therefore Q = const. ��

��

Fig. 2. Inﬂuence of transformer regulation on Q = F(U) characteristic curve – discontinuity of the regulation system taken into account.

�

Such a situation will only happen if the tap changer does not reach any of its extreme positions. Otherwise the regulator will be unable to keep the constant voltage at the secondary winding and the Q = F(U) curve will start to follow a no-regulator characteristic with a modiﬁcation caused by the transformer ratio now being different than nominal. In real conditions a transformer regulation system is discontinuous with a neutral zone and considerable delay. This situation is presented in Fig. 2. Characteristic curves shown in Fig. 1 are valid for steady states (after the regulation process is completed). In the presented form they can only be applied for cases of slow voltage change – when the voltage variability is slower than the response of regulation systems. In the case of very large overloads, voltage changes can happen so fast that the regulators do not have enough time to work. Investigation of such cases must therefore be based on characteristic curves which neglect operation of transformer regulation systems and assume voltage ratios ﬁxed at the level observed before the disturbance.

1.3. Adverse effect of transformer voltage regulators at the deﬁcit of reactive power In the case of slow condition changes and growing shortage of reactive power the situation develops as in Fig. 3. �

Consumers with transformer regulation

��

Operation of generator voltage regulators

�

Consumers without transformer regulation

Operation of stator current limiters

��

Cascade after limiters operation

��

Fig. 3. Adverse effect of HV/MV transformer voltage regulation systems at a deﬁciency of reactive power. Symbols: S – stable steady state point without voltage regulator operation; I fpuł – ceiling excitation; grey zone shows discontinuous operation of voltage control.

Adaptive Regulation Algorithm for Transformers Feeding Distribution Grids

Fig. 3 shows a case of adverse effect of transformer voltage regulation systems on the deﬁciency of reactive power. At a constant voltage ratio a stable operating point can be reached still below the threshold of the limiters. Voltage regulation however can trigger the limiters and result in cascade voltage loss. In distribution grids with a large number of asynchronous drives and considerable capacitor power often . This has been conﬁrmed by theoretical studies and investigation presented in the study [1]. This means that while the voltage drops, consumed reactive power actually rises. In such a case the natural characteristic of consumers is obviously less favourable than the one determined by transformer voltage regulator operation, which to some extent manages to maintain constant secondary voltage, resulting in constant reactive power consumption. �

Ug Ugz0

Consumers without transformer regulation

Operation of generator voltage regulators

Operation of stator current limiters

Cascade after triggering limiters

For If =I fpuł Consumers with transformer regulation

Fig. 4. Favourable inﬂuence of HV/MV transformer voltage regulators at a reactive power deﬁciency. Symbols: S – stable (broadened) steady state point with voltage regulator operation; Ifpuł – ceiling excitation; grey area shows discontinuous operation of voltage control system, its inclination results from an increase of current on the primary circuit at constant power.

In The described adverse effect of blocking regulators is explained in Fig. 4. If the characteristic of MV grid’s reactive power consumption is

�dQo < 0. then operation of a voltage regulator allowsreaching stable, dU

broadened operating point S, while blocking regulating systems results in constant reactive power deﬁciency leading to aperiodic instability and voltage cascade. To sum up, the need of blocking (or not) the automatic tap changing on a speciﬁc transformer can only be decided if at least the susceptibility to voltage changes of consumers seen from terminals of that transformer is known. Measurements aimed at estimating voltage stability may be conducted by employees of the distribution grid owner during normal operation. Example results with discussion are presented in the study [1].

1. 4. Smart voltage regulator for 110/MV transformer 1. 4.1. Disadvantages of passive automatic transformer regulation Deciding to block operation of transformer regulator upon offline measurements has significant disadvantages: • It does not address development and changing structures of consumers • It does not address periodic changes related to seasons, weather, working days and weekends • Measurements are made at voltages close to normal operating values. It is not possible to decrease the voltage to a value which would interfere with normal consumer operation. This is significant, as in cases of near-zero susceptibility to voltage changes identified at normal operating voltage it can be expected that at considerably lower voltages the value will turn negative. The disadvantages of passive regulation blocking described above are highlighted by the fact that characteristic curves of reactive power consumption of the MV grid fed from a 110/MV transformer evolve over time. The

Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

number of asynchronous drives and their loading factor vary, just like the powers of capacitor banks etc. This means that a MV grid can, in some situations, have

to determine if

�dQo > 0, dU

�dQo dU

≈ 0 or

�dQo dU

< 0.. Therefore it is not possible

�dQo is positive or negative based on one-time ofﬂine measurements and it cannot be decided dU

if the voltage blockade is beneﬁcial or harmful in general. The described characteristic change cycles can be seasonal, weekly or even daily. In order to correctly decide on blocking – or not – the regulators, it is necessary to identify the current value of

�dQo , for the parameters close to the present voltage value UTd on the MV side of the transformer. dUo

The correct decision on blocking regulators should be based on known characteristics valid for the moment of making that decision. The differential coefﬁcient

�dQo must therefore be determined online. dUo

2. ALGORITHM DESCRIPTION The algorithm proposed by the authors assures adaptation of transformer regulation systems to the changing situation of the grid and therefore it can significantly improve power supply security. In an example application the regulation of 110/MV transformers which supply power to a distribution grid can work as follows: at specified time intervals voltage values on both sides of a transformer – i.e. primary voltage UTg and secondary voltage UTd – are measured together with the current reactive power value at the secondary circuit (i.e. on the side of MV consumers) QTd. Based on those values voltage change susceptibility � dQTd for consumers is determined online. Then – depending on the value of that coefficient, primary voltage dU Td � dU Tg

UTg and current ratio of upper voltage variability

a decision on the transformer regulation mode is made.

Either preset secondary voltage UTd is maintained by tap changing or regulation is stopped. For a distribution grid bus equipped with capacitor banks, if the measured primary voltage is beyond the range determined by the preset minimum primary voltage UTgzm and preset maximum primary voltage UTgzM, the next step is to attempt regulation by appropriate connection or disconnection of capacitor bank sections (Fig. 5).

Adaptive Regulation Algorithm for Transformers Feeding Distribution Grids

Measurement: UT, I T

�

Celculation: � � ��

� Δ� λ�� δ��

� � � ��

��

Connecting capacitor bank .

�

Disconnecting . capacitor bank

�

�� N ��

T �

� � � ��

�� T

“MIN voltage” regulaion

�

��

T �

Fig. 5. Diagram of the algorithm using reactive power sources, e.g. capacitor banks 1 .

If the measured primary voltage UTg stays within the range <UTgzm; UTgzM> then the preset secondary voltage value UTd is maintained by transformer tap changing. If the primary voltage UTg goes beyond the preset permissible range and cannot be brought within it with capacitor banks, the transformer ratio is adjusted to improve voltage stability – to compensate for excess or deﬁciency of reactive power respectively.

1 The process of connecting and disconnecting capacitor banks is not described in detail here..

Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology

32 �

��

�

��

�

��

“Tap” regulation

M-

“Secondary voltage” regulation

��

�

��

� � � > � � ��

M-

“Secondary voltage” regulation

� � �� = � � ��

“Tap” regulation

��

�

��

� � � < � � ��

M-

“Secondary voltage” regulation

� � �� = � � �� “Tap” regulation

“Secondary voltage” regulation

�

Fig. 6. Diagram of adapting algorithm for 110 kV/MV transformer regulation. Case of insufﬁcient voltage value.

For example, at a reactive power deﬁciency situation the regulation is carried out as follows (Fig. 6): • If

�dQo – 0 constant voltage ratio or preset secondary voltage value UTdz is maintained dU �dU Tg

• Constant voltage ratio is maintained if the current primary voltage variation rate �dU Tg

exceeds preset

negative primary voltage variation rate value , otherwise the current preset secondary voltage UTdz is dt M  maintained by tap changing • If

�dQo  0 – constant voltage ratio is maintained or secondary voltage is lowered to the allowed preset dU

minimum UTdzm, and then the UTdzm value is maintained �dU Tg • Constant voltage ratio is maintained if the current rate of primary voltage changes exceeds the preset negative primary voltage change rate

�dU Tg

; if the current primary voltage change rate M

not exceed the preset negative primary voltage change rate

�dU Tg

�dU Tg dt

does

and the measured secondary voltage M

value UTd is higher than the preset minimum UTdzm then the secondary voltage is brought up to the preset minimum by tap changing

Adaptive Regulation Algorithm for Transformers Feeding Distribution Grids

• If

�dQo 0 dU

– the preset secondary voltage value UTdz is maintained or the secondary voltage is

increased to the preset maximum value UTdzM , and then this preset value is maintained • Secondary voltage is increased to the preset maximum value if the present primary voltage change rate �dU Tg dt

does not exceed the preset negative primary voltage change rate

�dU Tg

and the present secondary M

voltage UTd is lower than the preset maximum. UTdM . The proposed algorithm can be carried out automatically by regular sampling of relevant parameters: voltage at both sides of the transformer and reactive power on MV side are recorded at predetermined intervals (set, for example, in the range between several and several tens of seconds). If the preset MV voltage is to be maintained, a signal is sent to the tap changer (the moment of change is recorded). Voltage and power values before and after a tap change (after a stable state is reached) are recorded. Recording and processing voltage and power values measured before and after a tap change allows detecting tendencies for voltage cascade in the power grid and identifying situations in which tap changer blocking is favourable or harmful. 3. SUMMARY As demonstrated in the theoretical part of this paper, 110/SN transformers equipped with tap change regulators maintaining preset MV voltage can have adverse effects when there is a reactive power deﬁciency in the grid, and their operation can precipitate voltage cascade development. This adverse effect happens when lowering MV voltage increases reactive power consumption. Because the type of consumers can change in time, it is not possible to identify situations when a constant tap changer blockade or long-term change of a regulator’s algorithm should be introduced based only on periodic ofﬂine measurements. An adaptive system for regulating 110/MV transformers based on the proposed algorithm can assure automated adaptation of a regulating algorithm to present conditions of the power grid and thus improve power supply security.

REFERENCES 1. Małkowski R., Szczerba Z., Study carried out within PBZ-MEiN-1/2/2006, „Bezpieczeństwo elektroenergetyczne kraju”. Task 8.4.1. 2. Szczerba Z., Czy stosować blokadę napięciową regulatorów transformatorów 110/SN?, conference materials, X Ogólnopolska Konferencja Zabezpieczenia Przekaźnikowe w Energetyce, Automation Committee, Association of Polish Electrical Engineers SEP, Nałęczów, October 2007. 3. Patent application No. P.391598, “Sposób regulacji transformatorów zasilających sieć rozdzielczą” (“Method for controlling transformers supplying power to distribution grid”), June 2010. 4. Małkowski R., Szczerba Z., Wpływ struktury, algorytmów działania oraz nastawień układów regulatorów transformatorów 110/SN na możliwość powstania i przebieg awarii napięciowej, Conference materials APE ’09, Jurata, June 2009.

Robert Małkowski; Zbigniew Szczerba / Gdańsk University of Technology Artur Zbroński / Gdańsk University of Technology

Authors / Biographies

Robert Małkowski Gdańsk / Poland

Zbigniew Szczerba Gdańsk / Poland

Artur Zbroński Gdańsk / Poland Graduated from the Faculty of Electrical and Control Engineering at Gdańsk University of Technology on the basis of the M.A. thesis entitled “Power unit; coordination of the generator control algorithms with unit transformer control algorithms”. He is a doctoral student at the faculty of Electrical and Control Engineering at Gdańsk University of Technology.

Analysis of possibilities for coordination of the unit transformer regulator and generator regulator operation algorithms

ANALYSIS OF POSSIBILITIES FOR COORDINATION OF THE UNIT TRANSFORMER REGULATOR AND GENERATOR REGULATOR OPERATION ALGORITHMS Robert Małkowski / Gdańsk University of Technology Zbigniew Szczerba / Gdańsk University of Technology Artur Zbroński / Gdańsk University of Technology

1. INTRODUCTION The latest legal regulations require that new or modernised power units are equipped with a unit transformer with an on-load tap changer [6]. It is worth considering the advisability of effective utilisation of this regulation possibility. The theoretical bases for coordination of the generator voltage regulator with the transformer regulation system are provided in publication [1, 2]. The aim of this paper is to verify the theoretical considerations on the basis of model examinations. This is vital taking into account the fact that here we deal not only with regulators for two different objects by also two processes differing in terms of the regulation quality. The synchronous generator regulation is of a continuous and rapid character. Unit transformer regulation is discreet and the transformer regulation process is much slower than the generator regulation process. Fig. 1. shows the considerable inﬂuence of the voltage decrease on the available reactive power range [4, 5]. With a certain value of decreased voltage, a generator is neither able to generate nor draw reactive power.

�

P � PM

I gM0,9 I gMn

I fM0,9

δM >90

I fMn Pm

Qm0,9 Qmr0,9 Qmn Qmr

QM0,9 QMr0,9 QMn QMr

-1/Xd

Fig. 1. Available reactive power limits with decreased generator voltage

Abstract Amendments of regulations included in the Instruction on the Operation and Use of the Transmission Grid (IRiESP) obliges the operators) to ﬁt newly constructed or modernised units with a unit transformer equipped with an on-load tap changer. This paper presents the pros and cons of different solutions for coordination of the generator regulator and

unit transformer regulator operation algorithms. The theoretical considerations have been illustrated with model examination results. This made it possible to provide a recommended solution.

Robert Małkowski; Zbigniew Szczerba / Politechnika Gdańska Artur Zbroński / Politechnika Gdańska

PM , Pm – maximum and minimum active power I , If – limit imposed by maximum permissible stator and rotor current with U = U IgM0.9 , IfM0.9 – limit imposed by maximum permissible stator and rotor current with Ug = 0,9Ugn δM – limit imposed by the maximum permissible power angle tt – limit imposed by heating of the extreme stator metal sheet blocks (the area for δ>90º has been marked) Pr – example of active power operation value QMn , Qmn – limits of the actual available reactive power value for P = Pn and U = Un QMr , Qmr – limits of the actual available reactive power value for P = Pr and U = Un QM0.9, Qm0.9 – limits of the actual available reactive power value for P = Pn and U = 0.9Un QM0.9, Qm0.9 – limits of the actual available reactive power value for P = Pr and U = 0.9Un gMn

Fig. 1 shows the influence of the limit caused by the Ig < Ign condition. Due to intensive nonlinearities of dependencies, the approximate limits resulting from the If < Ifn condition have been shown; however, the influence of the voltage decrease on other limits has not been presented. The figure shows that unit transformers of the constant transformation ratio, by interlocking the generator voltage with the mains voltage, impose the available reactive power limits. Using transformers with the controlled transformation ratio makes it possible to fully eliminate the discussed limits, provided the transformation ratio control enables the generator to operate with nominal voltage.

2. COORDINATION OF UNIT TRANSFORMER OPERATION ALGORITHMS WITH A MULTIPARAMETER GENERATOR REGULATOR 2.1. Regulation criteria selection Using the capability of the automatic unit transformer transformation ration regulation in the process of the power unit regulation ﬁrstly requires considering issues related to coordination of this regulator operation with the synchronous generator voltage regulator. In order to ensure the correct regulation process, regulators for two devices (here generator and transformer) must not operate according to the same criterion, i.e. maintain the same value (e.g. voltage on generator or unit taps). Taking the above into account, two methods of regulation criteria division should be considered (Fig. 2): • Method 1 – unit transformer regulator maintains the voltage set on the unit taps and the generator voltage regulator maintains this voltage on the generator taps (Fig. 2a). • Method 2 – unit transformer regulator maintains the voltage set on the generator taps and the generator voltage regulator maintains this voltage on the unit taps (Fig. 2b).

� a) a)

b) b) UBL

UBLz

UBL

UGz

UBLz RG

Fig. 2. Division of the criteria for power unit regulation between the synchronous generator voltage regulator and the unit transformer regulator

Analiza możliwości koordynacji algorytmów działania regulatora transformatora blokowego i regulatora generatora

2.2. Method 1 Adoption of this regulator operation coordination method results in the fact that the generator is perceived as a voltage source with zero internal impedance. Having set the generator voltage regulator current compensation to 0 (Zk = 01), the power unit will be perceived as a source of voltage with internal impedance equal to the unit transformer impedance. One must remember that both the regulation process speed and quality for each regulator is different. These two factors cause that, in normal power system operation, the voltage on generator taps remains constant and, in line with the changes in the reactive power drawn, the unit voltage changes signiﬁcantly as it is decreased to the value set by the unit transformer regulator. Moreover, taking into account the discreet character of the unit transformation ratio and utilisation of the regulator dead band, it is impossible to obtain accurate regulation of the unit voltage value. The phenomena described above are presented in Fig. 3. Runs of the unit voltage Ub, generator voltage Ug and generator reactive power have been recorded with an assumed linear increase in the reactive power draw and incremental change of the power system voltage. a)

Fig. 3. Voltage runs on unit and generator taps and generator reactive power a) with incremental change of the system voltage, b) with linear change of the reactive power drawn

As a result of the voltage drop in the system, the unit voltage changes and not before a longer period of time, it is set in the setpoint value range after switching the transformer tap. The generator voltage is constantly maintained in the setpoint range. The mentioned disadvantages are very signiﬁcant during parallel working of the units. Taking into account the natural differences between parameters of transformers with identical nominal data, the changeability of these parameters in relation to the tap number, measuring converter errors and divergence in the setpoints in regulators may result in the situation presented in Fig. 4. Small differences in both regulators operation have been modelled in the presented example. Switching the tap of one of the generator unit transformers has resulted in the return of the unit voltage (being also the generator parallel cooperation point) to the dead band, which, as a result, stopped the operation of the second transformer regulator.

1 In the National Power System (KSE) the generator current compensation impedance is set to 0.

Robert Małkowski; Zbigniew Szczerba / Politechnika Gdańska Artur Zbroński / Politechnika Gdańska

Time [s]

Fig. 4. Changes in the unit voltage and transformer regulator signals with linear system voltage increase by 2%. Parallel operation of two identical generators

Fig. 4. shows the transformer regulator signals responsible for tap switching. Signal S1 – value of the integral of the unit voltage deviation from the limit value of the transformer regulator 1 dead band, S2 – value of the integral of the unit voltage deviation from the limit value of the transformer regulator 2 dead band 2, S3 – deviation integral setpoint. In order to obtain the divergence in estimating the switching time, the unit voltage measurement error equal to ± 0,05% * Ugn has been assumed. The mutual interaction of unit transformer regulators (resulting in operation with different voltage transformation ratio) has caused the change in the substitute impedance of units operating in parallel, which, as a result, leads to unequal reactive power load in both units – see Fig. 5.

Fig. 5. Changes in the reactive power transmitted to the network by synchronous generators after the linear increase in the system voltage by 2%. Parallel operation of two identical generators Time [s]

This behaviour of units operating in parallel is unacceptable. Moreover, in the discussed case we are dealing with a large (depending on the current tap number) inclination of the unit static characteristic. The transformer short-circuit voltage is equal to several per cent and the changeability (resulting from changing the voltage transformation ratio) may reach a few per cent. Setting the current compensation in such a manner that the voltage drop on the unit transformer impedance is partially compensated will result in less signiﬁcant

Analiza możliwości koordynacji algorytmów działania regulatora transformatora blokowego i regulatora generatora

dependence of the unit voltage on the real generator load; however, the relative voltage transformation ratio inﬂuence on the statism of the external characteristic of the unit will be increased. Taking into account the above, the conclusion is that Method 1 must not be used.

2.3. Method 2 This method of regulation criteria division may be achieved in two voltage measurement variants: a) the generator voltage regulator and unit transformer regulator measures voltage on generator taps; b) the generator voltage regulator measures voltage on unit taps and the unit transformer regulator measures voltage on generator taps. Depending on the adopted variant (a or b) of the voltage measurement method, the power unit will be represented by another substitute impedance. In variant a, the power unit will be perceived as a voltage source of internal impedance equal to the unit transformer impedance. In variant b, the power unit is perceived as a voltage source of zero internal impedance. In the case of variant a, the disadvantage is the high statism of the unit external characteristic determined by the unit transformer impedance. In variant b, one of the generator parallel cooperation conditions is unfulﬁlled, i.e. the condition requiring that units substitute impedances in relation to the parallel cooperation node must be positive. Thus adopting one of the variants (a or b) requires a proper setting of the generator voltage regulator current compensation. In variant a, it will be a negative value to compensate the voltage drops on the unit transformer impedance; in variant b, the current compensation must be set to a positive value. Adopting a proper value of the current compensation impedance will make it possible to shape the unit external characteristic (statism) in any required manner. In both variants, adopting the regulator coordination method according to criterion 2 will make it possible to quickly and precisely (no dead band) regulate the unit voltage value (thanks to the generator regulator operation) – see Fig. 6. a)

Fig. 6. Voltage runs on unit and generator taps and generator reactive power a) with incremental change of the system voltage, b) with linear change of the reactive power drawn

2.3.1. Variant a Taking into account the technical issues related to providing measuring signals, it is simpler to put into practice variant a than variant b. In this variant, the correct regulation process is hindered by the changeability of transformer impedance in the voltage transformation changes function. This disadvantage may be partially corrected by taking into account the influence of the unit transformer voltage transformation ratio change in the current compensation impedance value. This requires an additional regulating signal to be transmitted to the generator regulator, i.e. the number of the current tap. Taking into account the above signal and the defined vector of changes in impedance of a given transformer, it is possible to correct the current compensation settings. Fig. 7 shows the influence of the unit transformer impedance changes on the external characteristics of the unit. In this case, the linear change of the system voltage has been the enforcement.

Robert Małkowski; Zbigniew Szczerba / Politechnika Gdańska Artur Zbroński / Politechnika Gdańska

40 a)

Fig. 7. External characteristics of the unit with linear change of the system voltage 2; a) unit transformer impedance value dependant on the voltage transformation ratio changes, b) constant (independent of the voltage transformation ratio changes) unit transformer impedance

The example assumes that the unit transformer impedance changeability is approx. ±1% x Ukr per tap [3]. The changeability of transformer impedance causing the changes of the external characteristic shown in Fig. 7a has a negative inﬂuence on the unit voltage stability. Moreover, the primary advantage, i.e. a simpler measuring system, is no longer signiﬁcant as a result of the necessity to introduce considerable changes in the generator regulator algorithm. Variant b appears to be a much better solution as, in practice, it is usually impossible to obtain information regarding the dependence of the short-circuit voltage on the transformation voltage transformation ratio. In typical transformer data sheets, the short-circuit voltage value is provided only for the nominal voltage transformation ratio.

2.3.2. Variant b Fig. 8 shows the changes of the unit voltage during the linear change of the system voltage after providing the generator voltage regulator with measurements from the station located by the power plant. The simulation assumes that the unit transformer impedance changeability is approx. ±1% x Ukr per tap [3].

Fig. 8. Unit and generator voltage runs with system voltage linear decrease. Coordination according to method 2, measurements according to variant b

The advantage of this solution is the lack of dependence on the unit transformer impedance changes in the voltage transformation ratio function (ﬁg. 9b). 2 At the beginning of the simulation the present transformer tap is –6, thus the differences in the external characteristic slope in the starting phase of the simulation.

Analiza możliwości koordynacji algorytmów działania regulatora transformatora blokowego i regulatora generatora

Fig. 9. Comparison of static characteristics for different measurement variants (a and b)

As shown in the ﬁgure, the transformer impedance change does not have any inﬂuence on the unit voltage regulation characteristic. This solution requires to: • transmit information from measuring transformers in the station located by the power plant to the power plant; • take into account the location of the generator circuit-breaker in the generator voltage regulator. Both requirements should not be problematic as far as the technical execution is concerned. �

tap

RT Up

TPW

Efd

tap

Fig. 10. Example of an automatic method of changing a voltage and current measurement point depending on the generator circuit-breaker location

Opening of the generator circuit-breaker (Fig. 10) (operation for own purposes: “How to ensure synchronisation?”) should result not only in changing the current and voltage measurement point but changing the regulation criterion as well.

Robert Małkowski; Zbigniew Szczerba / Politechnika Gdańska Artur Zbroński / Politechnika Gdańska

42 3. SUMMARY

Automation of the unit transformer regulation process may significantly enhance the unit regulation possibilities both in normal states and slowly variable emergency states. This paper presents the pros and cons of different solutions for dividing regulation criteria between the generator regulator and the unit transformer regulator. The connection method 2 described in the paper has numerous advantages and no disadvantages resulting from utilisation of method 1, which shows that it should be recommended for implementation. A problematic issue is the selection of the alternative of the voltage measurement taken by the generator regulator fulfilling the function of the unit voltage regulator. Method 1 must be rejected due to the necessity of processing information regarding the current voltage transformation ratio and the unit transformer impedance variable which is difficult to compensate. The voltage measurement method according to variant b has the most advantages and fewest disadvantages so it should be recommended for implementation. In units with unit transformers with controlled voltage transformation ratio, the unit transformer and generator regulation systems should be obligatorily implemented in all newly constructed units: • during modernisation involving unit transformer replacement; • when utilisation of additional unit autotransformers of controlled voltage transformation ratio (with a tap switch) is justified by the system conditions. However, the correct and effective utilisation of the additional regulation method requires changes in the generator regulator operation algorithms utilised up to the present moment and, which is not mentioned in this paper, changes in the superior power plant regulation system algorithms. Unless the above condition is fulfilled, a unit transformer with an on-load tap changer may only become an object with the (unused) possibility of voltage or reactive power regulation.

REFERENCES 1. Szczerba Z., Automatyczna regulacja napięcia i mocy biernej bloków wytwórczych. Wybrane zagadnienia, Archiwum Energetyki, volume XXXIX, Gdańsk 2009. 2. Szczerba Z., Regulator napięcia generatora czy regulator napięcia bloku?, Przegląd Elektrotechniczny, no 10/2009. 3. Pewca W., Napięcia zwarcia w układach uzwojeń transformatorów i autotransformatorów z bezpośrednią regulacją napięcia, II Forum Transformatorowe ABB, 5 November 2007. 4. Hellmann W., Szczerba Z., Regulacja częstotliwości i napięcia w systemie elektroenergetycznym, Wydawnictwa Naukowo-Techniczne, Warsaw 1978. 5. Machowski J., Regulacja i stabilność systemu elektroenergetycznego, Oﬁcyna Wydawnicza Politechniki Warszawskiej, Warsaw 2007. 6. Instrukcja ruchu i eksploatacji sieci przesyłowej PSE – Operator, Warsaw 2007.

Tomasz Minkiewicz / Gdańsk University of Technology

Authors / Biographies

Tomasz Minkiewicz Gdańsk / Poland Graduated from the Department of Electronic and Control Engineering at the Gdańsk University of Technology (2009). At present he is doing his doctorial studies at the same Department and works as an assistant at the Institute of Power Engineering at the Gdańsk University of Technology. His professional interests cover current state and development of the nuclear power industry in Poland and all over the world.

Advancement of Works related to Nuclear Power Programme Completion in Poland

ADVANCEMENT OF WORKS RELATED TO NUCLEAR POWER PROGRAMME COMPLETION IN POLAND Tomasz Minkiewicz / Gdańsk University of Technology 1. INTRODUCTION 1.1. First developments of the nuclear power programme in Poland The ﬁrst plans of developing a nuclear power industry in Poland date back to the middle of the 20th century. The development was stopped by social and economic changes in Poland after 1989 and social protests caused by the Chernobyl disaster. The map below presents a forecast made in 1973, illustrating nuclear power plants that were supposed to be constructed between 1980 and 2000 with power over 300 MW (brown squares). The proposal covered the location of sixteen nuclear power plants [1].

Fig. 1. Map of Poland with the planned locations of nuclear power plants - forecast for 1980–2000

The main investment in Poland related to nuclear power was construction of a power plant in Żarnowiec. The location of the power plant in Kartoszno village at the Żarnowieckie Lake was approved by the Planning Commission at the Board of Ministers at the end of 1972. The proper decision to begin construction work was

Summary The paper presents current (June 2010) state of advancement of works related to nuclear power programme completion in Poland. The ﬁrst nuclear power plant is planned to be open in 2020. In order to complete the project it is necessary to provide legal and technical resources. At present, works on amending the Nuclear Law act, choosing appropriate location for the future nuclear

power plant, establishing collaboration with foreign companies and training programmes for Polish staff who will work in nuclear power centres in Poland are carried out. It is also of paramount importance to select appropriate nuclear reactor technology and handle matters related to radioactive waste storage.

Tomasz Minkiewicz / Gdańsk University of Technology

made at the beginning of 1982. Over 630 different structures were built during almost nine years of construction work. When the decision to close the power plant was made, the plant construction was 36% completed and its auxiliary facilities 85%. Breaking all construction works in 1990 and then decommissioning the nuclear site with the deadline at the end of 1992 entailed substantial ﬁnancial losses, marred the knowledge of many specialists and impeded the nuclear power programme in Poland for many years. 1.2. Renewing work on the nuclear power industry in Poland On 13 January 2008 the Board of Ministers made a decision to develop and implement the Polish Nuclear Power Programme. The return to the concept of nuclear power was ﬁrst mentioned in 2005 when “The Polish Power Policy by 2025” was being established. A subsequent project “Polish Power Policy by 2030” also emphasised the need to make efforts to develop a nuclear power industry in Poland. On 12 May 2009 Hanna Trojanowska was appointed Government Representative for the Polish Nuclear Power Industry, which contributed to developing a schedule of nuclear power activities in Poland (Tab. 1). Table 1. Schedule of activities related to the Polish Nuclear Power Programme [2] Stage

Time frame

Action

by 31 December 2010

Development and approval by the Board of Ministers of the Polish Nuclear Power Programme, making a decision on using nuclear power in Poland

1.01.2011 - 31.12.2013

Selecting location and signing a contract for the ﬁrst power plant construction

III

1.01.2014 - 31.12.2015

Making a technical design and obtaining all legally required permits

1.01.2016 - 31.12.2020

Construction of the ﬁrst power plant

On 28 January 2010 a company called EJ1 was registered at the National Court Register. Its core business will be to prepare the investment, carry out location research and form a consortium to build the ﬁrst nuclear power plant in Poland. The company is a dependant of Polska Grupa Energetyczna Energia Jądrowa (PGE - Polish Power Group - Nuclear Power) registered at the end of 2009 [2].

2. REGULATORY CHANGES RELATED TO INTRODUCING THE NUCLEAR POWER INDUSTRY IN POLAND 2.1. Atomic Law and its Amendments Atomic law is ruled by the act of 29 November 2000, being a collection of regulations on nuclear structures safety (including physical protection) as well as nuclear and radiation safety (not propagating nuclear materials and technology and civil liability for nuclear damage) [3]. Despite the fact that requirements of a number of international and community acts of law were met and a number of directives acquired based on the Treaty establishing European Atomic Energy Community (Euratom) implemented, in the middle of 2009 the National Atomic Energy Agency established a team responsible for amending the Atomic Law act and its executive regulations to adapt the law to the needs of nuclear power programme implementation in Poland. The amendments will be developed based on legal acts of the International Atomic Energy Agency (IAEA). The Atomic Law act makes legal frames for controlling the use of radioactive radiation and use of research reactors. Unfortunately, due to the fact that the act did not contain detailed requirements for a nuclear plant (as industrial and not test facilities) location, design, construction, start-up and operating safety, members of the National Atomic Energy Agency staff were trained to adapt their knowledge to the requirements and tasks that nuclear power supervision staff will have to do, e.g.: issue permits and licences in a process of a nuclear facility approval and assess safety. Therefore on 23 March 2010 the Ministry of Economy concluded an agreement between the President of the National Atomic Energy Agency and the Government Representative for the Polish Nuclear Power Industry to work together towards developing legal acts to complete the nuclear power programme in Poland [4].

Advancement of Works related to Nuclear Power Programme Completion in Poland

Besides requirements concerning location, design, construction, start-up and use of nuclear power plants, there are plans to establish a new supervisory body for nuclear safety and radiological protection – the Nuclear Safety and Radiological Protection Commission consisting of five persons, which will replace the function of the President of the National Atomic Energy Agency. The National Atomic Energy Agency will be transformed into the Office for Nuclear Safety and Radiological Protection that will support the Commission with its actions. At present, the National Atomic Energy Agency monitors the radiological condition of the country, supervises safety of isotope transport to hospitals, provides licences to inspectors and controls safety of operation of all three nuclear facilities in Poland: • Maria research reactor at the POLATOM Nuclear Energy Institute in Otwock-Świerk • Ewa research reactor, being closed down, located at the Radioactive Waste Disposal Plant in Otwock-Świerk • bunkers for burnt nuclear fuel located at the Radioactive Waste Disposal Plant in Otwock-Świerk. It is also important that the Atomic Law according to Council Directive 2009/71/Euratom enters into force (by 22 July 2011) as it will standardise nuclear safety limits (the President of the National Atomic Energy Agency will be held responsible). The end of 2010 is the deadline for implementing the amendments so that the Nuclear Safety and Radioactive Protection Commission is able to issue permits for nuclear plant construction and operation after 1 January 2014 [4, 5]. 2.2. Working on a directive for the burnt nuclear fuel waste repository The European Commission is working on a draft of a new directive for radioactive waste and the burnt nuclear fuel repository. As a result of work on the new directive, each country will have to construct its own repositories for burnt nuclear fuel and remains from its processing and groups of countries will have to construct shared repositories. Moreover, a team responsible for establishing the European Repository Development Organisation (ERDO) was appointed [6]. In relation to SAPIERR II report developed by experts from the EU it was agreed that a shared repository is much cheaper than storing waste individually by each country. If countries from ERDO working groups (including Poland) decide to make one large repository (in the eastern part of Europe), possible savings will amount to 15–25 billion euro. Construction of smaller repositories for two or three countries will also reduce the cost of storing radioactive waste by several billion euro [7]. 2.3. Government decision and acquiring assumptions for draft project amending the Atomic Law act On 22 June 2010 the Board of Ministers acquired assumptions for a draft project amending the Atomic Law act and some other acts, being a transposition of the Council Directive 2009/71/Euratom of 25 June 2009. The new Atomic Law regulations will enter into force on 1 June 2011. They will contribute to increasing safety in nuclear power plants, enhancing supervision of the National Atomic Energy Agency over nuclear facilities and reinforcing its independence in a decision-making process as well as from other organizations involved in nuclear power promotion. Society will be informed on the nuclear supervision decisions, condition of nuclear facilities, their operation, including all factors and events that impact nuclear safety and radiological protection. According to new regulations, to meet the nuclear safety and radiological protection standards it will be necessary to obtain permits for a nuclear facility construction, start-up, operation and closing down. The permits will be granted by the President of the National Atomic Energy Agency. At the same time the investor will have to select state-of-the art technologies conforming to the highest safety standards and with the least harmful impact on the environment. The amended act will also cover all regulations determining safety requirements for location design, construction, start-up, use and closing-down of nuclear facilities. Each person will have the right to obtain written information on the state of nuclear facility safety and radiological protection, its impact on human health and the natural environment. An organisational unit manager (e.g. the entity that operates the plant) will have to put such information on the company website at last once a year. The President of the National Atomic Energy Agency will be obliged to publish information on the submitted applications concerning nuclear facilities and on obtained permits. All abovementioned changes allow society to take part in proceedings related to issuing nuclear facility building permits. Administrative financial fines that can be imposed by the nuclear supervision body for violating nuclear safety requirements on organisational units dealing with nuclear facility operation have also been increased. It

Tomasz Minkiewicz / Gdańsk University of Technology

has been decided that the Minister of Economy, and not the President of the National Atomic Energy Agency as previously, will grant special subsidies from the state budget to secure nuclear safety and radiological protection when ionising radiation is used (the National Atomic Energy Agency should not subsidise operation related to using ionising radiation as it can impact its independence in the decision-making process). The degree of qualiﬁcation and skills of staff responsible for nuclear safety of nuclear facilities has also been agreed [8].

3. SEARCHING LOCATION FOR NUCLEAR POWER PLANTS IN POLAND 3.1. Expert’s opinion on locating nuclear power plants in Poland On 16 March 2010 the Ministry of Economy published a ranking of 28 suggested locations for nuclear power plants in Poland. The ranking was made based on an expert opinion made by Energoprojekt-Warszawa S.A. in cooperation with the Atomic Energy Institute, Central Laboratory for Radiological Protection, National Institute of Geology, Institute of Meteorology and Water Management, EPC Consulting, Hogan and Hardson and PSE Operator. The document called “Expert Opinion on the Location Criteria for Nuclear Plants and Evaluation of the Previously Suggested Location” is based on the recommendations presented in the International Atomic Energy Agency guidelines TECDOC–1513 “Basic Infrastructure for a Nuclear Power Plant Project” (June 2006). Based on the document called “National Power Policy by 2030” approved by the Board of Ministers on 10 November 2009, the nuclear power plant location was evaluated according to seventeen criteria: 1. integration with power system; 2. geological conditions, earthquakes; 3. seismology and seismic engineering; 4. hydrology (including ground water, floods and tsunami); 5. accessibility of cooling water (supply, discharge); 6. demography and land use; 7. meteorology and atmospheric conditions (including direction of wind, tornadoes, hurricanes); 8. studies on plants and animals; 9. nuclear safety and aspects of radiological protection; 10. general environmental effects; 11. risk related to human operation; 12. local infrastructure; 13. cultural and historic places; 14. access and evacuation roads; 15. characteristics of air, land and marine transport; 16. legal aspects; 1 7. social consulting. The results of analysis (Table 2) indicated such places as Żarnowiec, Warta-Klempicz or Kopań as locations for the first power plant. The final decision will be made by the main investor – PGE Polska Grupa Energetyczna S.A., having considered 3-5 of the best locations [9]. 3.2. Żarnowiec as the leading location for the first nuclear power plant in Poland Żarnowiec was already approved in 1990 by the IAEA in the document “Site Safety Review Mission” (26-30 March 1990). According to the document summary: “Żarnowiec is a location with a number of features positive for nuclear power plant construction, including: low seismic level of the area and no sources of events caused by human operation in the nuclear power plant vicinity. Criteria for location selection established by Polish authorities contributed to selecting a location with such characteristics. Generally speaking, characteristics of the Żarnowiec location are comparable to location features of many nuclear power plants in Europe”. According to the information submitted by heads of Gniewino and Krokowa gminas, where the Żarnowiec nuclear power plant is supposed to be built, a vast majority of inhabitants of the area are in favour of building a nuclear power plant in Żarnowiec (70% for, about 12% against, the rest: hard to say). Future social consulting activities can only make their attitude stronger. The Head of Gniewino gmina says that a nuclear power plant would be an opportunity for the region and its inhabitants as well as science.

Advancement of Works related to Nuclear Power Programme Completion in Poland

Tab. 2. Ranking of nuclear power plant locations in Poland [9] Location

Evaluation criteria

TOTAL

Bełchatów

0.3

2.0

3.0

4.5

1.0

3.0

5.0

2.8

5.0

3.0

4.5

5.0

3.0

no data

3.0

53.1

Chełmno

2.0

3.0

5.0

4.0

2.0

3.0

2.0

3.0

1.0

4.7

0.0

3.0

2.5

no data

0.0

42.2

Choczewo

2.3

4.0

5.0

3.5

5.0

2.0

3.2

0.0

3.0

4.5

5.0

2.0

1.5

no data

0.0

51.0

Chotcza

2.0

3.0

5.0

4.5

1.0

5.0

3.0

5.0

2.2

5.0

3.0

4.4.

5.0

0.0

1.5

no data

0.0

49.6

Dębogóra

1.3

4.0

5.0

4.0

1.0

5.0

3.0

2.0

2.6

0.0

3.0

4.8

0.0

3.0

4.5

no data

3.0

46.2

Gościeradów

2.7

3.0

5.0

4.5

1.0

5.0

3.0

1.0

3.0

0.0

3.0

4.4.

0.0

3.0

2.0

no data

3.0

43.6

Karolewo

1.7

4.0

5.0

4.0

5.0

4.0

3.0

1.6

0.0

3.0

4.5

0.0

2.0

no data

0.0

44.8

Kopań

2.0

3.0

5.0

3.5

5.0

2.0

2.6

0.0

3.0

4.7

5.0

3.0

4.0

no data

3.0

55.8

Kozienice

1.7

4.0

5.0

1.0

5.0

3.0

0.0

2.8

0.0

3.0

4.7

5.0

3.0

no data

0.0

48.2

Krzymów

1.3

4.0

5.0

2.0

1.0

5.0

3.0

0.0

2.8

0.0

3.0

4.7

5.0

4.0

no data

3.0

48.8

Krzywiec

1.3

5.0

4.0

0.0

5.0

3.0

1.0

3.2

3.0

4.5

0.0

5.0

4.0

no data

3.0

49.0

Lisowo

1.3

3.0

4.0

0.0

5.0

3.0

1.0

3.0

4.5

0.0

3.0

4.0

no data

3.0

44.8

Lubiatowo -Kopalino

2.0

3.0

5.0

3.5

5.0

1.0

3.0

0.0

3.0

4.7

0.0

2.0

no data

3.0

47.2

Małkinia

3.3

5.0

1.0

5.0

3.0

0.0

3.4

0.0

3.0

4.4

5.0

1.0

no data

0.0

49.1

Nieszawa

1.7

3.0

5.0

4.0

3.0

2.0

1.6

3.0

1.0

4.7

5.0

3.0

no data

3.0

52.0

Nowe Miasto

2.7

4.0

5.0

4.5

1.0

5.0

4.0

5.0

3.2

5.0

3.0

1.9

5.0

3.0

no data

0.0

55.3

Pątnów

1.3

3.0

5.0

0.0

3.0

4.0

0.0

2.6

0.0

3.0

4.7

0.0

5.0

3.0

no data

0.0

39.6

Pniewo

1.3

5.0

2.0

1.0

5.0

3.0

0.0

2.8

0.0

3.0

4.8

5.0

3.0

4.0

no data

3.0

47.9

Pniewo-Krajnik

1.3

5.0

2.0

1.0

5.0

3.0

0.0

2.8

0.0

3.0

4.8

5.0

3.0

4.0

no data

3.0

47.9

Podlasie (no indication)

0.0

no data

0.0

Połaniec

2.0

3.0

4.0

3.0

1.0

5.0

3.0

1.0

3.0

4.7

5.0

3.0

no data

3.0

49.7

Stepnica-1

1.0

3.0

4.0

2.5

1.0

5.0

4.0

0.0

3.0

0.0

2.0

4.8

5.0

3.0

4.0

no data

3.0

45.3

Stepnica-2

1.0

3.0

4.0

2.5

1.0

5.0

4.0

0.0

3.0

0.0

2.0

4.8

5.0

3.0

4.0

no data

3.0

45.3

Tczew

4.0

5.0

1.5

4.0

3.0

1.0

2.0

3.0

4.8

5.0

3.5

no data

0.0

51.8

Warta-Klempicz

4.3

4.0

5.0

4.5

1.0

5.0

3.0

2.0

3.4

3.0

4.7

5.0

3.0

4.0

no data

5.0

59.9

Wiechowo

1.3

4.0

0.0

5.0

3.0

1.0

3.0

4.4

0.0

3.0

3.5

no data

3.0

45.2

Wyszków

3.0

5.0

1.0

3.0

0.0

2.8

0.0

3.0

4.7

5.0

2.5

no data

0.0

48.0

Żarnowiec

4.7

4.0

5.0

3.5

0.0

5.0

3.2

5.0

3.0

4.7

5.0

3.0

4.5

no data

5.0

65.6

The land intended for the nuclear power plant construction belonged some time ago to the Pomerania Special Economic Zone. In February 2010 Energa Invest from Gdańska Grupa Energetyczna Energa S.A. (almost 88% of the company shares belong to the State Treasury) purchased the land with the intention of building a gas power plant there. Both the management of the Pomerania Special Economic Zone and Energa S.A. say that if Żarnowiec is selected for a nuclear power plant location, the land will be made available to complete the construction. In relation to the fact that by the end of 2010 the Ministry of State Treasury wants to sell about 83% of Energa S.A. shares, one of ﬁve investors interested in taking over the Gdańsk corporation and also the main

Tomasz Minkiewicz / Gdańsk University of Technology

investor in the ten first nuclear power plants in Poland, Polska Grupa Energetyczna S.A., declared that they can cash the abovementioned shares (about 6-8 billion PLN). Holding the majority of shares of the current owner of the land intended for the nuclear power plant in Żarnowiec, PGE will significantly accelerate the process of starting the nuclear power plant construction. The area available should be enough to construct two power units. Technical infrastructure (deep water intake, water and sewage system, power system and network of roads suited for overnormative load transport) as well as 400/110 kV Żarnowiec power station located nearby are additional adventures that support selection of Żarnowiec as the first nuclear power plant location. Operation of such a large source of power in Northern Poland would considerably improve the transmission grid operating conditions, reduce transmission losses and improve customer supply reliability. At present, the nuclear power units’ cooling is the largest problem of the location. According to analyses, water from the Żarnowieckie lake will be enough to cool only one large power unit, whereas Warta-Klempicz location, ranked second, is able to cool over three units with EPR grade (over 8000 MJ/s) reactors. Using hybrid cooling systems with a fan cooling system will entail increased power consumption for the facility’s own purposes and large coolers will take up a large part of the land. Another considered solution suggests constructing a channel or pipelines for cooling with sea water, but this solution requires enormous financial resources [10]. A ranking of possible nuclear power plant locations, covering the abovementioned criteria is presented in Table 2.

4. MEMORANDA ON COLLABORATION WITHIN THE NUCLEAR POWER INDUSTRY 4.1. Nuclear reactors suggested for use in Poland The construction of the ﬁrst nuclear power plant in 2020, and of another one after two or three years, planned by PGE, will require not only an appropriate location but also technology. According to EU requirements, stressing safety issues, Poland is only allowed to use III or III+ generation reactors, or reactors with increased safety. The suggested solutions exceed the current safety requirements. They are presented in Table 3. Currently, Areva, Westinghouse and GE Hitachi technologies are most likely to be implemented. PGE formed three teams, each analysing one of the abovementioned solutions for technical, economic and legal aspects of a nuclear power plant construction in Poland. The results of analyses will be ready in July 2010 [11]. Table. 3. III and III+ generation nuclear reactors possible for construction in Poland [11] Manufacturing place

Name of reactor

Reactor manufacturer

France

EPR-1650 (European Pressurized Reactor)

Areva

USA

AP-1000 (Advanced Pressurized)

Westinghouse Electric Company LLC

USA

ESBWR-1550 (European Simpliﬁed Boiling Water Reactor)

General Electric - Hitachi

Russia

WWER-1200/1500 (Wodiano-Wodianyj Energeticzieskij Reaktor)

Gidropress

Japan - USA

APWR-1500 (Advanced Pressurized Water Reactor)

Westinghouse Electric Company LLC - Mitsubishi

South Korea

APR-1400 (Advanced Pressurized Reactor)

Korea Electric Power Corp.

4.2. IAEA examination of nuclear infrastructure in Poland Between 27 and 29 April 2010 a delegation of experts from the International Atomic Energy Agency came to Poland to carry out an Integrated Nuclear Infrastructure Review (INIR). The experts had a meeting with the Government representative for the Polish Nuclear Power Industry and representatives of twenty-three other

Advancement of Works related to Nuclear Power Programme Completion in Poland

institutions from government administration ofﬁces, research institutes, power companies and higher education institutions. The IAEA delegation consisting of a nuclear safety expert and legal specialist assessed all works connected with nuclear power implementation in Poland positively. It was emphasised that Poland should strengthen the National Atomic Agency staff and extend the scope of operation and responsibilities of Polska Grupa Energetyczna. The visit was aimed at making an initial evaluation of works related to the Polish Nuclear Power Programme implementation. It had a review and informative purpose, while a precise assessment and review of all actions will be carried out at the beginning of 2011 [12].

4.3. EPR Reactor A memorandum on collaboration with French companies Areva and EdF was signed on 17 November 2009. It was the first agreement of that kind concluded by PGE. The will of long-term collaboration with Poland was then expressed and examining the possibility of constructing an improved version of an EPR water-pressure reactor in Poland proposed. Information on starting a certification programme for Polish contractors and suppliers from the power sector was also confirmed [17]. Areva, Framatome ANP Inc. and Siemens started working on an EPR reactor in 1992. A French company dealing with power supply – EdF (Électricité de France) and a group of major German power operators joined the project soon afterwards. The project was mainly based on experience gained by the company during operation of French N4 reactors and the German KONVOI series. The EPR reactors suggested by Areva are the only ones that meet all safety requirements for nuclear power stations in Europe (European Utility Requirements). Gross electric power of a nuclear power unit with EPR reactor can reach 1600 MW. When the operation time (over 60 years) was extended and the unit availability (up to 92%) increased, the achieved power generating units showed one of the lowest power generation costs. Compared to some older type reactors, the power unit construction time was shorter, which reduced the period of the power plant expenditure return. Due to the increased fuel burning rate and reduced doses of radiation the staff are exposed to and emitted outside the power plant, an EPR reactor generated less highly-active radioactive waste and is more environmentally friendly. The power plant safety level was also significantly increased by introducing passive safety systems and limiting the number of possible failures [13]. 4.4. ESBWR Reactor A memorandum on collaboration with an American-Japanese corporation GE Hitachi Nuclear Energy Americas (GEH) was signed on 1 March 2010. The agreement is aimed at making a feasibility study for the reactors suggested by GEH: ABWR and ESBWR. Moreover, GEH has established cooperation with Warsaw University of Technology (PW) and other academic centres in Poland. PW obtained five licences for software that allows modelling heat balance in steam turbines installed in nuclear power plants with ESBWR reactors, which will result in educating new engineers who will be able to use the software and quickly identify and solve problems at nuclear power plants. On 27 May 2010 GEH signed an agreement with SNC-Lavalin Polska (engineering service provider) to develop collaboration within the nuclear power industry. An ESBWR type reactor was constructed by General Electric and registered in December 2005 by the United States Nuclear Regulatory Commission – NRC. It was made based on a simplified boiling water reactor - SBWR. At present, BWR type (boiling water reactors) are the second most frequently used nuclear technology in the world. The power plant unit layout was simplified, the number of staff necessary to operate the facility and for maintenance reduced and radiation doses and quantity of radioactive waste limited. The buildings are now smaller and the entire unit structure is simpler, which means a shorter time for nuclear power plant construction (42 months from starting concrete works for the construction of the safety tank for the first fuel loading), reduced costs and improved capital return conditions for investors. The increased height of the reactor tank and reduced height of fuel elements contributed to natural circulation implementation and helped avoid use of re-circulation pumps. Implementation of passive systems allowed for removing pumps from safety systems, and hence some more factors that could cause failure were eliminated. The probability of core damage was reduced to 3x10-8. The power of ESBWR reactors (4500 MW thermal power, 1550 MW electric power) increased by about 15% compared to ABWR reactors (larger core and more fuel elements) [15].

Tomasz Minkiewicz / Gdańsk University of Technology

4.5. AP-1000 Reactor A memorandum on collaboration with American Westinghouse Electric Company LLC was signed on 27 April 2010. The main assumption of the agreement is examining possibilities of using AP-1000 nuclear reactors in Poland. It was pointed out that the product offered by the American company is the only III+ generation reactor certified for design by the American Nuclear Regulatory Commission (NRC) and the Commission for European Utility Requirements (EUR) confirmed compliance of the AP-1000 reactor with its requirements, which means the technology can be implemented in Poland. Design work on the AP-1000 began at the end of 1980s when a document important for the nuclear power industry – URD (Advanced Light Water Reactor Utility Requirements) – containing a list of requirements (of power companies) for advance light water reactors was prepared in the USA. The document included design requirements and principles of American power companies towards next generation nuclear power plants in the USA, which were later on approved by the NRC. In March 2002 Westinghouse filed an application to the NRC for the AP-1000 design approval, which was accepted, and obtained a licence for 15 years in December 2005. Based on AP600 reactor features and using tested solutions, emphasis was placed on ensuring a high degree of reliability and safety. Power density in the core was reduced and water quantity in the reactor tank increased. The main focus was on maximum simplification of the construction, using modular construction and passive safety systems. The safety systems do not use active elements (e.g. pumps, fans, Diesel generators), which are necessary only for reducing the effects of design failures - they were replaced with passive systems whose operation is based on using natural gravity forces, compressed gas pressure or natural circulation. The modular construction allows for manufacturing all 350 modules in a shipbuilding plant or factory – when such modules are sent to the building site the entire construction can be ready within 45 months. The gross electric power of nuclear units with such reactors amounts to 1100 MW [14]. 5. SUMMARY According to an official advertisement of the Minister of Labour and Economy on the country’s power policy by 2030, the gross demand for electrical power in Poland will exceed 200 TWh by 2030, while the installed electrical power in the national electrical power system will be 52 GW. In relation to the fact that the oldest power units are used up (almost 60% of power capacity in Poland dates back to over 30 years ago) and as a result of the fact that modernisation (to reduce emission of harmful substances) of other power units is not profitable from the economic point of view, over 13 GW of the currently used power will have to be withdrawn from operation. Therefore, by the end of 2030 it will be necessary to start new generating units with over 30 GW of power, which means that Poland should theoretically double the currently installed capacity during 20 years [18]. According to an expert opinion issued by the European Renewable Energy Council called “Economic and Legal Aspects of Using Renewable Energy Sources in Poland” (ECBREC, 2000) the technical potential of renewable energy sources in Poland is estimated at about 2500 PJ/a, but to be able to fully use it we should create “appropriate conditions favourable for their development, increase financial resources for research and technological development and develop a system of grants for undertakings related to renewable energy sources” [16]. It all makes energy from renewable resources become much more expensive than nuclear or conventional (coal based) energy, and its generation is related to a number of difficulties. Starting operation of nuclear power plants and reducing the share of carbon power plants in the total power balance, will reduce the quantity of harmful pollution discharged to the air and limit power generation costs. The expected share of each source of electrical energy in Poland by 2030 is presented in Table 4. According to forecasts, the share of renewable energy will increase, but only by 2025. Next, the share of nuclear power (the cheapest source of electric power) and gas power is expected to be high enough to limit the use of renewable energy sources [18, 19, 20].

Advancement of Works related to Nuclear Power Programme Completion in Poland

Table. 4 Electric energy power structure by 2030 [9] Year

Coal

Natural gas

Nuclear power

Pump water power plants

Renewable

2006

90.5%

2.2%

0.0%

4.0%

3.3%

2010

88.4%

2.1%

0.0%

3.9%

5.7%

2015

80.8%

3.2%

0.0%

3.5%

12.4%

2020

70.1%

3.7%

3.6%

3.2%

19.5%

2025

62.7%

4.7%

6.7%

2.9%

23.0%

2030

58.1%

7.2%

9.3%

2.7%

22.7%

There are plans to start operation of five nuclear power units in the eastern part of Europe during the next ten years, the first one – in 2016 – being in Nyeman (Ragnit) (Kaliningrad Region), next in Lithuania, Belarus and finally in Poland. We should then expect offers for participating in building these plants and purchasing electric energy from the plants for the Polish market. There will be a competition for domestic nuclear power. In order to face the challenges and to become independent from imported electric energy, a gradual implementation of the Polish nuclear power industry development programme (suggested in 2009) and opening the first Polish nuclear power plant in 2020 seems absolutely reasonable [21].

Tomasz Minkiewicz / Gdańsk University of Technology

REFERENCES 1. Nuclear power industry in the Republic of Poland – plans, http://atom.edu.pl/index.php/ej-w-polsce/wczoraj/plany-ej-do-1990.html. 2. Nuclear power industry in the Republic of Poland, http://atom.edu.pl/index.php?option=com_content&view=article&id=73&Itemi-d=73#plany. 3. Act of 29 November 2000, Atomic Law (consolidated text, Journal of Laws of 2004, No. 161, item 1689), Legal Department of the National Atomic Agency. 4. Ciepiela D., Trwają zmiany prawne umożliwiające rozwój energetyki jądrowej, http://energetyka.wnp.pl/trwaja-zmia-ny-prawne-umozliwiajace-rozwoj-energetyki-jadrowej,100700_1_0_0.html. 5. Assumptions for the draft act on amending the Atomic Law act and on amendments to some other acts, version of 4 May 2010, http://www.paa.gov.pl/dokumenty/legislacja/zalozenia2.pdf. 6. Stefaniak P. , Będzie nowa dyrektywa składowania odpadów wypalonego paliwa jądrowego, http://energetyka.wnp. pl/bedzie-nowa-dyrektywa-skladowania-odpadow-wypalonego-paliwa-jadrowego,105056_1_0_0.html. 7. ICEM 2009, Shared, regional repositories: developing a practical implementation strategy, http://www.arius-world. org/pages/pdf_2009/02_ICEM_2009_SAPIERR.pdf. 8. Government decision on the assumptions for the draft act on amending the Atomic Law act and on amendments to some other acts, being a transposition for the Council Directive 2009/71/Euratom of 25 June 2009, establishing Community framework for nuclear safety of nuclear power facilities, submitted by the Minister of Environment, http://www.premier. gov.pl/rzad/decyzje_rzadu/id:4972/. 9. Expert opinion on the criteria for nuclear power plant locations and initial evaluation of the agreed locations http:// www.ptf.ps.pl/pliki/Prezentacja_Lok_EJ_1.pdf. 10. Kiełbasa W., Lokalizacja elektrowni jądrowych w Polsce, II Szkoła Energetyki Jądrowej, 3–5 November 2009, Warsaw. 11. PGE wybierze technologię i partnera do budowy elektrowni jądrowej do końca 2013 roku (PGE will select technology and partner for building the future nuclear power plant by the end of 2013), http://www.cire.pl/ite-m,47026,1.html. 12. MAEA bada infrastrukturę jądrową w Polsce (MAEA examines nuclear infrastructure in Poland), http://beta.mg.gov. pl/node/10351. 13. Debontride B., Design of EPR, Areva Framatome ANP Inc., France 2006. 14. Doehnert B., Design of the AP 1000 Power Reactor, Westinghouse Electric, Belgium 2006. 15. Hinds D., Maslak C., Next-generation nuclear energy: The ESBWR, Nuclear News, January 2006. 16. Ministry of Environment, Strategy for renewable energy industry development, Warsaw, September 2010. 17. Current report No. 13/2009, Signing a memorandum on establishing collaboration with EDF in nuclear power, http://www.pgesa.pl/pl/relacjeinwestorskie/raportybiezace/2009/strony/rbnr13_2009.aspx. 18. Marecki J., Perspektywy rozwoju energetyki jądrowej w Polsce, Warsaw 23.01.2007. 19. Marecki J., Duda M., Dlaczego istnieje w Polsce konieczność budowy elektrowni jądrowych, Conference materials. Elektrownie jądrowe dla Polski, Warsaw, June 2006. 20. Strupczewski A., Jaworska K., Patrycy A., Saniewski G., Czemu potrzebujemy energetyki jądrowej w Polsce, PSE Monthly Bulletin, 04/07, pp. 4–15, 2007. 21. Po wyborach Rosja zaproponuje Polsce udział w budowie bałtyckiej elektrowni jądrowej (After elections Russia will invite Poland to take part in building the Baltic nuclear power plant), http://www.cire.pl/item, 47210,1,0,0,0,0,0,po-wyborach-rosja-zaproponuje-polsce-udzial-w-budowie-baltyckiej-elektrowni-jadrowej.html.

Andrzej Reński / Gdańsk University of Technology Agnieszka Kaczmarek / Gdańsk University of Technology

Authors / Biographies

Andrzej Reński Gdańsk / Poland

Agnieszka Kaczmarek Gdańsk / Poland

Andrzej Reński graduated from the Warsaw University of Technology, at the Faculty of Power and Aeronautical Engineering (1969). He got his Ph.D. degree in 1981, at the Faculty of Electrical Engineering at the Gdańsk University of Technology. In 2003, he got his Dr hab. (habilitation) degree, at the Faculty of Power and Aeronautical Engineering of the Warsaw University of Technology. Since 2007, he has been working as an assistant professor, at the Gdańsk University of Technology. His main areas of interest include: heat power engineering – constructing and modelling of power equipment, in power plants and thermal-electric power stations, both standard and nuclear, as well as the optimisation of heat systems’ development.

Graduated from the Faculty of Electrical and Control Engineering at Gdańsk University of Technology, in the ﬁeld of electrical power engineering, specialty of power plants and energy economy. Since 2007, she has been doing her doctoral studies, at the Faculty of Electrical and Control Engineering, in the renewed edition of the Basics of Nuclear Power Industry Postgraduate Studies. Her main areas of interest include: heat and electric combined economy, gas power engineering and nuclear power engineering.

The participation of the Faculty of Electrical and Control Engineering at Gdańsk University of Technology in the preparatory work aimed at starting the ﬁrst nuclear power plant in Poland

INTRODUCTION Nuclear power engineering has its supporters and opponents. One cannot challenge the fact, though, that Poland’s neighbouring countries, as well as the majority of European countries, satisfy the demand for electric energy using the sources of energy based on nuclear fuel. As a result, they gain knowledge and experience in the scope of nuclear power engineering. Although Poland has not yet built a nuclear power plant, Polish engineers have been working in foreign institutions for many years, acquiring valuable experience, thus providing active participation in the process of shaping nuclear power engineering, both in Europe and worldwide.

HISTORY The concept of building the Żarnowiec Nuclear Power Plant required establishing personnel that would prepare the investment, as well as design, start and operate the first Polish nuclear block, which would support the national power system. The Gdańsk University of Technology is proud to be a member of the group of universities, including, among others, the Warsaw University of Technology and the Silesian University of Technology, which have a long-time tradition and great experience in educating in the field of nuclear power engineering. Thanks to the initiative of Professor Kazimierz Kopecki, the first Postgraduate Studies in Nuclear Power Engineering was established in the then Faculty of Electrical Engineering at Gdańsk University of Technology, as early as the first half of the 1970s. The head of this school was Professor Jacek Marecki, who became the director of the postgraduate studies unit many years later, when another postgraduate school in nuclear power engineering was established in Poland. Prof. Jacek Marecki is a supporter of the idea to start nuclear power engineering in Poland, as quickly as possible. He provided patronage and was himself an active participant in the process of training personnel, as required for the nuclear power engineering, both at postgraduate level and as part of full-time studies, for many years. In 1972-1990, there were twelve courses of Nuclear Power Engineering Postgraduate Studies. The commencement of the building of the Żarnowiec Nuclear Power Plant was an important landmark in the development of this field, particularly because since that moment the postgraduate studies have been planned and organised in strict cooperation with the Żarnowiec Nuclear Power Plant, then under construction. The Postgraduate Studies in the Building of Nuclear Power Plants were established in the Faculty of Electrical Engineering, in the academic year 1983/1984. By 1990, there had been three courses of those studies. The Postgraduate Studies in the Designing of Nuclear Power Plants, established at the same faculty, also existed until 1990. The significant role in realising the teaching process was played by the present academic researchers and scientists of the Faculty of Electrical and Control Engineering (formerly the Faculty of Electrical Engineering) at

Summary Educating the personnel that participate in the completing of the construction design of the ﬁrst Polish nuclear power plant, has been going for many years, as the Faculty of Electrical and Control Engineering at Gdańsk University of Technology. This gave birth to the idea of combining the reactivation of the postgraduate

studies in the field of nuclear power engineering and the construction design of the first Polish nuclear power plant itself, with bringing to light the people and actions that played a significant role to popularising the concept to satisfy the national demand for energy using nuclear fuel.

Andrzej Reński / Gdańsk University of Technology Agnieszka Kaczmarek / Gdańsk University of Technology

Gdańsk University of Technology, including, among others: prof. Kazimierz Kosmowski, prof. Andrzej Reński; dr hab. inż. Kazimierz Duzinkiewicz and dr inż. Zdzisław Kusto. Nearly 300 people have received the postgraduate diploma in the afore-mentioned studies. The graduates in the mentioned studies included, among others, the minister, Hanna Trojanowska, who has been the Government Representative for the Polish Nuclear Power Engineering, since 12th May 2009. In 1984-1987, a framework plan was established to prepare personnel required for operating the future nuclear power plant, in cooperation with the management responsible for the construction of the Żarnowiec Nuclear Power Plant. There were also other forms of cooperation: “Course programmes for educating the operation personal of the Żarnowiec NPP” and “Concept for the Nuclear Power Engineering Training and Educating Facility”. 1990 saw the completion of the “Methodological and Programme Concepts for the Broad Social Education in the scope of Nuclear Engineering and Nuclear Power Engineering”. The postgraduate studies is not the only type of experience that the Faculty of Electrical and Control Engineering has had in passing on knowledge and shaping social awareness in the scope of understanding the nature and role of nuclear power engineering in the economic life of a modern country. In the former Polish nuclear programme, the Gdańsk University of Technology, and particularly its Faculty of Electrical and Control Engineering, played the role of a research and education base, intended for the Żarnowiec NPP, which was being built in 1982-1990. The faculty was preoccupied with preparing highly qualified personnel intended for the future nuclear power plant. It organised and ran postgraduate studies in nuclear power engineering, using its own personnel, as well as the academic personnel of other faculties of the Gdańsk University of Technology, and other Polish universities and research institutions, including, among others, the Institute of Atomic Energy POLATOM, in Świerk. The faculty was also particularly involved in completing a broad research programme, as required for nuclear power engineering. Prof. dr hab. inż. Zbigniew Szczerba was one of the initiators and then a coordinator of the cooperation with Żarnowiec NPP. He was supported by dr inż. Wiktor Chotkowski, who took over his role in 1987 when prof. Zbigniew Szczerba left Poland. At that time, the Faculty of Electrical and Control Engineering was the coordinator and contractor for the group of 11 goals of the Central Research and Development Programme 5.3. “Nuclear Power Engineering”. The range of issues addressed was very broad: improving the process of design work and work organisation at the construction site; research into building materials, including research into corrosion processes; learning new technologies of assembly, including new welding technologies; as well as issues related to the modelling of technological systems, taking into account the dynamics of buildings and the issues of optimum controlling, reliable operation and safety of the entire NPP. The then Faculty of Electrical Engineering, later reformed into the Faculty of Electrical and Control Engineering, also entered into cooperation with national scientific and research institutions, universities and design offices, such as: the Institute of Atomic Energy POLATOM, in Otwock-Świerk, the Warsaw University of Technology, the Silesian University of Technology, the Bureau of Power Studies and Engineering “Energoprojekt – Poznań” SA, and first and foremost, with Żarnowiec NPP Under Construction. Unfortunately, that work was interrupted on 17th December 1990, when the government made the decision to terminate the construction of the NPP and put it into liquidation, in 1991. The teaching activities were drastically reduced to individual issues concerning nuclear power engineering, as part of various general power engineering-related subjects, such as the technology of the production of electric energy, taught during full-time studies.

PRESENT ACTIVITIES Nowadays, the global interest in nuclear energy is growing again, given the present economic situation in the world, when it is so important to use the available energy sources in a rational way, while satisfying the requirements concerning the protection of the environment, which have become more and more strict. We can observe the same tendency in Poland. The particular impetus to act was the decision of the Council of Ministers of 13th January 2009, concerning preparing and implementing the Programme for Polish Nuclear Power Engineering, as well as approving “The Framework Schedule of Activities for the Nuclear Power Engineering”, by the Council of Ministers on 11th August 2009. In relation to that, the Faculty of Electrical and Control Engineering has also taken appropriate steps, so as to restore the issues related to nuclear power engineering in the programme

The participation of the Faculty of Electrical and Control Engineering at Gdańsk University of Technology in the preparatory work aimed at starting the ﬁrst nuclear power plant in Poland

of studies, but this time in a much broader scope. Nuclear power engineering has been introduced in the programme of lectures and seminars for the specialty of electrical power engineering, as well as for the specialties of energy markets and power systems, at the inter-faculty subject of power engineering. There are also diploma projects concerning nuclear power engineering being published. Interest in the new subject is conﬁrmed by, among others, the initiative taken by students, aimed at organising a technical inspection at the German Isar 2 NPP, under the supervision of the university teachers of the Department of Nuclear Power Engineering.

Photo 1. Students of the Power Plants and Energy Economy specialty, at the German Isar 2 NPP.

The academic year 2009/2010 saw the reactivation of the postgraduate studies in nuclear power engineering, under the name “The Basics of Nuclear Power Industry Postgraduate Studies”, run by units of the Gdańsk University of Technology, especially the Faculty of Electrical and Control Engineering, as well as teams from the Institute of Atomic Energy POLATOM, in Otwock-Świerk, and the participation of representatives of industry institutions, including, among others, Agencja Rozwoju Energetyki (Agency for Energy Development). In the future it is planned to take advantage of the experience gained by the employees of foreign power companies: CEZ, from the Czech Republic, and Fortum, from Finland. The students of the first renewed edition (photo 2) are graduates from technical universities, characterised by diversified profiles of specialties. Therefore, the programme of studies included general power engineering-related subjects, such as: selected branched of physics, standard and unconventional sources of energy, thermal turbo-machines, power plant operation in a power system, environment protection, and energy markets. As for the specialised studies in the field of nuclear power engineering, they have been completed, among others, at the laboratories of the Institute of Atomic Energy POLATOM, in Otwock-Świerk. The teaching programme will be expanded next year, thanks to the planned starting of an additional Postgraduate Studies in the Preparation for the Operating of Nuclear Power Plants, which will be supported by a much greater involvement of other faculties of the University: Mechanical Engineering, Chemical, Civil and Environmental Engineering, as well as representatives of companies that participate in the construction of foreign nuclear power plants, such as: Elektrobudowa S.A. In the academic year 2010/2011, the Faculty of Electrical and Control Engineering will also start the specialty of nuclear power engineering, as part of II degree studies, initially planned for 30 students. The activities in educating of personnel are synchronised

Andrzej Reński / Gdańsk University of Technology Agnieszka Kaczmarek / Gdańsk University of Technology

with other national universities through the participation of employees of the Department of Nuclear Power Engineering in the work of the Nuclear Power Engineering Committee of the Atomic Energy Council of the National Atomic Energy Agency.

Photo 2. Students of the 1st edition of the reactivated Basics of Nuclear Power Industry Postgraduate Studies, at the Maria reactor hall of the Institute of Atomic Energy POLATOM

Simultaneously, the university plans to prepare educators – young academics – who would bring together their experience in the field of nuclear power engineering at foreign research and scientific institutions. In connection with this, the Department of Nuclear Energy received applications of four candidates who would participate in phase II of the educators’ training course, which is to be completed in three months, at the CAE-SACLAY Nuclear Research Centre in France. It is beyond any doubt that the process of gaining knowledge is greatly supported by proper research tools. For this reason the faculty has submitted a design application concerning the preparation of a calculation and simulation centre of processes and computer systems for the controlling and supporting of decisions made by operators of nuclear power blocks, at the Ministry of Science and Higher Education. Two further applications, concerning the modelling and controlling of a nuclear power plant and its cooperation with the national power system, are being prepared. Another action, this time initiated by the minister, Hanna Trojanowska, was the establishment of a local team of experts in the field of nuclear power engineering to the rector of the Gdańsk University of Technology. Furthermore, the Office of the Marshal of the Pomeranian Voivodeship has a team for preparing the Pomeranian Voivodeship for completion of the “Construction of Nuclear Power Plant” investment, including representatives of the Gdańsk University of Technology, which has been operating for more than a year. The faculty is also involved in initiatives of an educational and informative character. For this reason the faculty tries to take part in discussion panels, aimed at presenting arguments supporting the introduction of nuclear energy in Poland, and particularly in the coastal region, as part of the general educational activity. One such panel was held on TVP channel III as part of the “Forum Gospodarcze” (Economy Forum) series. On 25th November 2009, representatives of the university took part in a meeting held in Gniewin, which was devoted to the issue of cooperation between local governments, related to the preparatory activities before starting

The participation of the Faculty of Electrical and Control Engineering at Gdańsk University of Technology in the preparatory work aimed at starting the ﬁrst nuclear power plant in Poland

the ﬁrst nuclear plant, as well as cooperation in the further operation of the plant. Representatives of local governments from Hungary, Holland and Spain shared their experience at the meeting. On 10th December 2009, a conference on power engineering was held in Gdańsk, Pomerania Voivodeship, organised by the Pomeranian Council of FSNT NOT, during which a representative of the faculty gave a lecture concerning the impact of nuclear power plants on energy security in Poland.

PLANS AND PROSPECTS In the nearest future we will see a continuation of the undertaken teaching activities, i.e. the enrolment for edition II of the Basics of Nuclear Power Industry Postgraduate Studies. Another initiative is the active participation of representatives of the Institute of Atomic Energy POLATOM, as instructors, in the Third School of Nuclear Power Engineering, which is to take place in October 2010, in Gdańsk, with the help of the local scientific and technical circles. Furthermore, it is planned to undertake activities aimed at determining the needs concerning training of personnel and preparing of programmes and schedules of training sessions, at the medium and high technical level. It is also planned to prepare analyses concerning the impact of Żarnowiec NPP on the environment, as well as the safety of the plant, and also analyses concerning factors influencing water management in the vicinity of the NPP, as well as nuclear fuel management. The Faculty of Electrical and Control Engineering will also conduct research into the cooperation between the nuclear power plant and the national power system (KSE), as well as into the possibilities of connecting Żarnowiec NPP to the KSE system. There is also some interest in the issue of a potential adjusting of the nuclear power plant, which would be located on Lake Żarnowiec, to heat-generating operation. Some of the mentioned objectives could be completed as part of the applications for research projects which are being prepared. Research into building materials, factors influencing the setting of the nuclear power plant, as well as studies on the properties of power media, are ever-relevant issues which should be taken up by other faculties of the Gdańsk University of Technology. The test stands that are planned in the Laboratory of Modern Technologies, at the Electrical and Control Engineering, may mark the beginnings of a project to create a research centre, required for nuclear power engineering. The faculty intends to start such a centre in the nearest future.

Ryszard Zajczyk / Gdańsk University of Technology

Authors / Biographies

Ryszard Zajczyk Gdańsk / Polska The author specialises in power systems engineering. The Chair of Power Engineering Department at Faculty of Electric Engineering and Automatics of Gdańsk University of Technology. Graduated in Power Engineering from the Electrical Engineering Faculty of Gdańsk University of Technology in 1978, Professor since 2004. He researches mainly issues of power system operation in adequate and unsteady states, with particular focus on regulation and control processes, impact of renewable sources, including wind generation, on power systems, and power system cooperability with high voltage power-electronic devices. He is the author of numerous publications, scientiﬁc studies, and research projects in this area.

Voltage Stability of Power Subsystem

VOLTAGE STABILITY OF POWER SUBSYSTEM Ryszard Zajczyk / Gdańsk University of Technology

1. REACTIVE POWER OVERLOAD 1.1. Turbo-generator set characteristics In order to describe unsteady states during overloads it is necessary to know the properties of the generating unit, including the synchronous generator, not only at near-rated voltage, but also at voltages much lower that occur in signiﬁcant overloads. An example of generating units consisting of a condensating steam turbine with turbine governor, and asynchronous generator with generator controller is presented in Fig. 1. �

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Pgz Z

 WP WP

PR K

gz

 SP Z

RT g NP

TW GS

U gz

RG UW

If z

SK PIW

Fig. 1. Block diagram of a high-power generating unit [10]

A high-power condensating turbine consists of high-, medium- and low-pressure parts (WP, SP, NP) and an inter-stage steam superheater (PR). The turbine’s quantitative control is accomplished by changing the steam ﬂow through its individual parts by opening adjustment of the high-pressure (Zwp) and low-pressure (Zsp) control valves. The urbine governor consists of a power controller (RP), rotational speed governor (RO), converter (P/ H), and control valves (ZR). A block diagram of turbo-generator set with control system is presented in Fig. 2.

Abstract The paper discusses the issue of power system reactive power overload and presents a methodology of power subsystem voltage stability analysis. In order to conﬁrm the correctness of the adopted assumptions simulation calculations have been made of the subsystem’s voltage stability. The study analyses cases of overloading individual nodes and entire subsystems with active power, reactive power and power with initial tg� retained. The results have conﬁrmed the correctness of the assumptions adopted with regard to the manner of stability boundary in model research.

Ryszard Zajczyk / Gdańsk University of Technology

64 �

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Fig. 2. Turbo-generator set control system RP – active power controller, RO – rotational speed governor, P/H – mechanical/ hydraulic or electro-hydraulic converter, ZR – control valves, SM – valve servo-motor, SL – valve actuator, T – turbine, G – generator [10].

High-power synchronous generators (GS) are provided with static thyristor excitation systems (TW, PW) or machine excitation systems and multi-parameter generator controllers (RG). In either excitation system variant the multi-parameter generator controller consists of the main voltage control circuit, control system limiters, and additional elements. A block diagram of multi-parameter generator controller is presented in Fig. 3. � ��

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Fig. 3. Structural diagram of multi-parameter generator controller [10] TRN – main voltage control circuit, UKP – current compensation system, PSS – system stabiliser, OPS – stator current limiter, OPW – rotor current limiter, OPPW – rotor ceiling current limiter, OKM – power angle limiter.

The generator is controlled by a controller, commonly called a voltage controller, that maintains a set voltage. At large overload the controller fully adjusts the excitation system. As a result the excitation voltage, and – in the steady state – the excitation current, reach their maxima. In this state U = f(Ig) characteristic is not controlled by the controller anymore. From the voltage stability viewpoint, characteristics of some controller components are relevant, such as limiters of stator current, rotor current, and excitation ceiling current. Their shape (time characteristic) may

Voltage Stability of Power Subsystem

govern the course of voltage collapse related phenomena. An example I = f(t) time characteristic provided by excitation ceiling current limiter and excitation maximum current limiter is presented in Fig. 4. ��

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Fig. 4. Current-time characteristic provided by limiters of excitation ceiling and maximum current, kp – ceiling factor (1,6÷2), Ifn – rated excitation current [10]

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Based on measured voltage and current, the RG controller maintains the generator terminal voltage according to the formula:

�U g  Ugzo  I P Rk  I Q X k where Ugz0 – set voltage, Rk , Xk – current compensation impedance. A substitute diagram of a generator with controller is presented in Fig. 5a. The aforementioned characteristic refers to the range from idle run up to the load (in an unsteady state), at which excitation voltage Uf reaches its maximum Ufmax. If, once the maximum excitation voltage has been achieved, the generator voltage is still declining as an overvoltage result, the controller’s action will be ineffective, since it is not able to raise the excitation voltage up to a level necessary to maintain the set generator voltage.

�U g  Uf max  I Q X d A substitute diagram for this state of synchronous generator is presented in Fig. 5b. a)

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Fig. 5. Substitute diagram of generator with controller; a) adequate state, b) at large overload for Uf = Ufmax [5, 6] Superposition of these two characteristics produces a characteristic covering the entire range of generator voltage changes corresponding loads from the idle state up to the maximum generator load (Fig. 6).

Ryszard Zajczyk / Gdańsk University of Technology

66 �

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Fig. 6. Extarbnel characteristic of generator with voltage controller within the linear range (for Uf< Ufmax ) and for the maximum excitation voltage (Uf =Ufmax) [5, 6]

1.2. Receiver characteristics Like active power, reactive power absorbed by receivers is a function of voltage U and frequency f :

�Qo  F (U , f ) In a steady state at f = const, function Qo =F ( U , f ) has the course presented in Fig. 7 � U

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1 2

Fig. 7. Changes in received reactive power at frequency changes and at dQ U = const. �tg�  o dU

Qo Qon

1, 2, 3 – various characteristics at signiﬁcant voltage reductions [5, 6]

Relations shown in the ﬁgure may be useful also for qualitative, and – in approximation – for quantitative interpretation of unsteady states at a system, subsystem, or island overload. The quicker overload related voltage changes, the more the actual characteristic deviates from that presented in Fig. 7. Such a discrepancy is caused by unsteady electromagnetic states in electric motors and by the impact of drive systems’ rotating masses. 1.3. Load level impact To estimate voltage and reactive power changes at overload it is reasonable to explore the relationship between these quantities:

� dU  F (Qg , Qo ) dt If generated and absorbed reactive powers do not balance, a stable or unstable unsteady process occurs. In the case of unstable process – typically aperodic in general – no new steady process may be achieved and a so-called voltage collapse occurs.

Voltage Stability of Power Subsystem

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i 1 n

i 1 m

 Qgi   Qoi  0 then

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 0 and U = const. dt � If  Q gi   Qoi  0 then �dU  0 and U is increasing i 1 i 1 dt n m � �dU  0 and U is decreasing. If  Qgi   Qoi  0 then dt i 1 i 1 If

If the overload is small, then the generator voltage control maintains the voltage near its rated value, causing, however, an excess of the admissible generator current. This excess is not – in the initial period – liquidated by stator current limiters operating with a deliberately set time delay. A new quasi-steady state is accomplished. �

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Fig. 8. Interpretation of small reactive power overloads 1 – quasi-steady state for Xk = 0; 2 – quasi-steady state for Xk> 0; O – receiver characteristic [5, 6]

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However after some time the limiters proceed to limit the current overload and cause a change in the external generator characteristic shown in Fig. 8. The limiter’s action may render the new steady state accomplishment impossible. A voltage collapse develops and the subsystem can not be defended, since the existing unload automatics do not protect against reactive power overload. The ﬁgure presents two points of quasi-steady operation until the current is limited by the limiters. It is also shown that as a result of the limiter’s operation the reactive power demand can not be covered and a voltage collapse develops. At large overload the situation shown in Fig. 9 occurs. It follows from comparison of the generator and receiver characterises that no reactive balance power is available in the system. This results in a voltage collapse that can not be controlled without disconnection of some receivers. Such disconnection moves “O” characteristics to the left thus enabling reactive power balancing. �

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Fig. 9. Interpretation of large reactive power overloads Symbols as in the previous ﬁgures [5, 6].

Ryszard Zajczyk / Gdańsk University of Technology

2. STATISTICAL ANALYSIS OF VOLTAGE STABILITY Voltage stability is determined for a power system’s receiving nodes. Statistical analysis of voltage stability is based on voltage-current equations determined for any power node [10]. A system diagram is presented in Fig. 10.

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Fig. 10. Diagram of current distribution in k node of power system, Ukf – k node voltage, Ulf – l node voltage, Jkl – current between k and l nodes, Jk – current received in k node, Jkg – generator current in k node Zkl , Ykl – impedance and admittance of link between k and l nodes, Yko , Ylo – admittance of Lateran branches in k and l nodes, Yk – substitute admittance of receiver in k node [10]

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Active and reactive powers absorbed in k node are described with the following formulas: n n � Pk  U k2  Gkl   U kU l (Gkl cos φ kl  Bkl sin φ kl ) l 1 l k

l 1 l k

Qk  U k2  Bkl   U kU l ( Bkl cos φ kl  Gkl sin φ kl ) This formula describes active and reactive powers for all receiving nodes of the subject power system for steady and transient states alike. Analysing power changes in the vicinity of the steady operation point deﬁned by (θO, UO) parameters for all nodes, the following active and reactive power changes are determined:

Δ� P(� ,U )  P(θ ,U )  P(θ o ,U o ) Δ Q (� ,U )  Q(� ,U )  Q(� o ,U o ) System linearization and small deviations analysis of power changes ∆P and ∆Q in the function of changes of voltage U and angle between vectors θ produces the following formulas:

� P (θ ,...,θ , U ,...U )   P1 1 1 n 1 n θ 1    ... .....    P  Pn (θ1 ,...,θ n , U1 ,...U n )   θn1     Q1  Q1 (θ1 ,...,θ n , U1 ,...U n )   θ1    ... .....    Qn  Q ( θ ,..., θ , U ,... U )   θ1 n 1 n   n 1

...

P1 θ n

P1 U 1

... ...

Pn θ n Q1 θ n

Pn U 1 Q1 U 1

...

Qn θ n

Qn U 1

i.e.:

� ΔP   P �  ΔQ    Q    �

P U Q U

  Δθ   J P�  x    J  ΔU   Q�

J PU   ΔP  x J QU   ΔQ

  θ1   ...   ...    P ... Unn   θ n  x  Q ... U 1n   U1  ...   ...     Q ... U nn  U n  ...

P1 U n

Voltage Stability of Power Subsystem

Under the assumption that only reactive power changes in the system, ∆P=0, the above formula transforms to:

� 0   J Pθ Q   J    Qθ

J PU   θ  x J QU  U 

Upon transformation and elimination of angle θ, the following relationship is formulated between reactive power changes ∆Q and voltage changes ∆U:





�Δ Q  J QU  J Qθ J P1θ J PU x U  JR U �J R1 matrix entries on the main diagonal determine voltage sensitivity of power system’s receiving nodes For any node k the voltage sensitivity may be determined, as well as the relationship with voltage stability in the node:

� U  J R1 ΔQ

 �diag J �diag J

 (k ) 0 (k ) 0

�diag J R1 (k )  0 voltage-stable node 1 R

stability boundary

1 R

voltage-unstable node

3. DYNAMIC ANALYSIS OF VOLTAGE STABILITY Dynamic analysis of voltage stability involves examination of system response to a preset input function. System components described with differential and algebraic equations account for the basis for unsteady state calculations. System model includes: • Model of the transmission system described with the following equations: x = f(x, U) I (x, U) = YU • Models of generating mode components such as: • synchronous generators • multi-parameter generator controllers • turbines • turbine governors A generating node diagram with modelled components indicated is presented on Fig. 1. For the purpose of stability analysis the system is described with a set of differential equations linearised in the surroundings of the operation point, for which voltage stabiliity is examined. Linearised object’s generic form may be described with: state equation: X(t) = AX(t) + BU(t) output equation: Y(t) = CX(t) + DU(t) where X(t) – state variable vector, U(t) – input Signac vector, Y(t) – output Signac vector, A – state matrix, B – input matrix, C – output matrix, D – matrix tying input signals directly inﬂuencing output.

Ryszard Zajczyk / Gdańsk University of Technology

The synchronous generator is described with the following formulas:

�I (t )  A 1B I (t )  A 1C U (t ) g g g g g g g

state equation:

output equation: �Wg (t )  D g I g (t ) where: �I g (t )  [I d (t ), I q (t ), I f (t ), I kd (t ), I kq (t ), σ (t ), δ (t )] T

�U Tg (t )  [U s (t ), U f (t ), M t (t )] �WgT (t )  [U g (t ), Pg (t )]

– state variable vector

– input value vector

– output value vector

The excitation system and generator controller are described with the following formulas: state equation: output equation: where: vector, �U TRG (t )

�Y RU (t )

A     RU  Y SS (t )   O  

1

O  B x  RU A SS   O

B SS  RU  YRU (t )  A RU x  B SS   YSS (t )   O

1

O  C  x  RU  x URG (t) A SS   C SS 

T �U f (t )  DTRU YRU (t )  EUW U RG (t )

T T �YRU (t ) – voltage control circuit state variable vector, �YSS (t ) – system stabiliser state variable

– input value vector, �U f (t ) – output value – excitation voltage change.

The condensing turbine is described with the following formulas:  1 1 state equation: �DT (t )  ATK BTK DT (t )  ATK CTK UTK (t )

output equation:

�M t (t )  ETT DT (t )

T where: �DT (t ) – turbine state variable vector, �U TTK (t ) – input value vector, �M t (t ) output value – generator driving torque change The turbine governor is described with the following formulas:

state equation:

� Y RE (t ) 

A     RE Y HY (t )  O  

1

O  B x  RE A HY  B EH

O   YRE (t )   A RE x  B HY  YHY (t )  O

1

O  C  x  RE  x URE (t ) A HY   O 

output equation: �Wt (t )  D RT YHY (t ) T where �YRE (t )

T – state variable vector, �YHY (t ) – Valle hydraulic system state variable vector,

�U TRE (t ) – input value vector, �WtT (t )

– output value – control valve opening change.

The other matrices are described in the references cited [10]. After consideration of mutual relations between input and output values of individual objects, a generating unit’s description is obtained in the form of state equations.

Voltage Stability of Power Subsystem

4. VOLTAGE STABILITY CALCULATION METHODOLOGY 4.1. Voltage sensitivity method Voltage sensitivity may be determined for each node of power system as the ratio of voltage change to reactive power supplied to the node.

� U k wkQ  Qk

wkP 

U k Pk

i 1 ik

U k   U ki [h  h]  U ki [h] Qk   Qki [h  h]  Qki [h] ; Pk   Pki [h  h]  Pki [h] ; tgφ k 

Qk Pk

Active and reactive power changes shall be determined in successful steps of determination of power distribution and voltage levels in power system in the process of dynamic simulation. Where factors are positive (positive voltage change increases voltage), the system is voltage-stable. Application of this method is proposed for preliminary calculation of voltage stability in a power system. This will enable determining for a ﬁxed system load (uniquely determined system state) the system nodes exposed to voltage stability loss. In this method constraints may be considered of reactive power generation by synchronous generators • constraint of absorber reactive power Qp (Qpoj) • constraint of generated reactive Power Qg (Qind) and constraints of transformer and autotransformer voltage ratios through consideration of the following boundary values: • minimum transformer voltage ratio min • maximum transformer voltage ratio max and related tap-changer positions.

4.2. Own values method Where boundary characteristics (load impact on voltage stability boundary) have to be procured, analysis of a linearised system’s own values is necessary. Reactive power increment’s dependency on voltage changes in nodes is described by the following formula:

�U  J 1 R Q The Jacobi matrix that appears in the formula may be determined as follows: �J R1  M� 1N , where: M – matrtix of right-side own vectors, N – matrtix of left-side own vectors, Λ – diagonal matrix of own values. 1 After transformation equation 2 assumes the following form: �U  M� NQ or n � mn U   i i Q �i i 1

where: mi – means right-side vector i, ni – left-side vector i, λi – own value i. Own value λi and corresponding vectors: right-side mi and left-side ni make up the system’s mode i.

Ryszard Zajczyk / Gdańsk University of Technology

�m 1  n

�u  nU and q  nQ where u and q – voltage and reactive nU  � nQ � 1 power mode vectors �u  Λ 1q . Formula for mode i: ui  qi . Own value λi reﬂects the mode’s voltage �i Entering to the equations formulas

1

stability (λi>0 – voltage-stable system) where nik – element k of vector ni. Ultimately for node k of power system the relation between the voltage’s reactive power derivative and own values:

�U k Qk

 i 1

mki nik �i

5. SIMULATION EXAMINATION Veriﬁcation of the proposed method of voltage stability determination in receiving nodes of power system – 110 kV grid – for the following three speciﬁc grid nodes: • node A – typical receiving node inside 100 kV grid in rural areas, • node B – typical receiving node inside 100 kV grid in urban agglomeration, • node C – receiving node of 110 kV grid situated near a generating node that supplies the 110 kV grid (generators connected to 400 kV bus bars, 110 kV grid supplied through 400/110 kV transformer with under-load voltage ratio control). The examined sub-grid contained over 80 110 kV receiving nodes and was supplied in a few points from 220 and 400 kV grids through transformers with controlled voltage ratios. A grid diagram is presented in Fig. 11. Voltage stability boundary in the subject sub-area was determined for the following cases: • concurrent change of absorbed reactive and active powers with tgφ maintained in the single subject node of 110 kV grid. Example results for nodes A, B, and C are presented in Fig. 12 • concurrent change of absorbed reactive and active powers with tgφ maintained in the subject subsystem – all nodes of 110 kV grid. Example results for nodes A, B, and C are presented in Fig. 13 • Concurrent change of absorbed reactive power in the subject subsystem - all nodes of 110 kV grid. Example results for nodes A, B, and C are presented in Fig. 14. The PLANS programme was used for the calculations.

�

220 kV 400 kV

� PC ,Q C

�

110 kV

��

� PB,QB

400 kV

��

� PA ,QA

Fig. 11. Diagram of the subject 110 kV power subsystem supplied from 220 and 400 kV grids in a number of points

Voltage Stability of Power Subsystem

�

120

115

110

105

105 100 U [kV]

U [kV]

100 C

70 0

100

200

300

400

500

600

700

800

P [MW]

100

120

140

160

180

Q [Mvar]

Fig. 12. Voltage variability in selected nodes of 110 kV grid in the function of absorbed active power a) and reactive power b). Nodes individually loaded (each node independently).

�

120

115

110

105

100

70 5

100

U [kV]

120

115

P [MW]

Q [Mvar]

Fig. 13. Voltage variability in selected nodes of 110 kV grid in the function of absorbed active power a) and reactive power b). Concurrent loading of receiving nodes of the subject subsystem (at the same power factor).

�

120 115 110 105 C

U [kV]

100

90 85 80 75 70 0

Q [Mvar]

Fig. 14. Voltage variability in selected nodes of 110 kV grid in the function of absorbed reactive power. Concurrent loading of receiving nodes of the subject subsystem (only reactive power loading).

Ryszard Zajczyk / Gdańsk University of Technology

6. CONCLUSIONS These analyses and simulation research enable formulating the following conclusions with regard to the feasibility of various methods of voltage stability calculation in power system’s receiving modes: 1. In global calculations for an entire power system the voltage stability factors method should be applied. Multiple repetition of simulation calculations at variable absorbed power (Q =var) will enable determination of U-Q characteristics for the nodes. 2. Subsystems should be loaded, and not individual nodes. Loading with active and reactive powers at receiver’s set tgφ. 3. In voltage stability analyses the constraints should be considered resulting from the admissible area of generator operation state, the impact of limiters of stator and rotor currents and of stator ceiling current, power angle in generator controller, and the constraints resulting from the impact of generating and transmitting nodes’ group control systems [11]. 4. For voltage stability examination of separated subsystems the own values method for linearised systems may be applied. Ultimately it should be attempted to apply this method for the whole power system. 5. The only effective method of avoiding voltage collapse in cases of reactive power overloading is entering voltage elements to automatic unloading systems. The voltage element, with measurement of time derivative, provides credible reactive power overload information [5, 6, 11].

REFERENCES 1. IEEE Guide for Synchronous Generator Modelling Practices in Stability Analyses. IEEE Std 1110-1991 (American National Standard ANSI). 2. EEE Standard 421.5: IEEE Recommended Practice for Excitation System Models for Power System Stability Studies. August 1992. 3. Kundur P. , Power System Stability and Control. McGraw-Hill, Inc. 1994. 4. Leon O.Chua, Pen-Min Lin, Komputerowa analiza układów elektronicznych. Algorytmy i metody obliczeniowe [Computer analysis of power systems. Algorithms and calculation methods], WNT, Warsaw 1981. 5. Lubośny Z., Szczerba Z., Zajczyk R., Analiza stanu obecnego automatyki odciążającej (SCO) w krajowym systemie elektroenergetycznym – z punktu widzenia operatora systemu [Analysis of the present condition of self-acting frequency unload automatics (SCO) in the national power system – from the operator point of view]. Study by EPS RESEARCH commissioned by PSE S.A., 1999 6. Lubośny Z., Szczerba Z., Zajczyk R., Automatyka realizująca obronę systemu przy awaryjnych przeciążeniach. Opracowanie nowych zasad i programu: stosowania automatyki samoczynnego odciążania w KSE – opartej na nowych algorytmach działania, skoordynowania jej z zabezpieczeniami podczęstotliwościowymi bloków, udziału sieci przesyłowych, sieci rozdzielczych i elektrowni [Automatics that implement power system defend at emergency overloads. Development of new methods and a programme of automatic unloading systems application in KSE national power system – based on new functional algorithms, coordination with sub-frequency protections of generating sets, participation of transmission grids, distribution grids, and utilities]. Stage 1 – 1999, Stage 2 – 2000. Study by EPS RESEARCH commissioned by PSE S.A. 7. Machowski J, Białek J.W., Bumby J.,R.,Power system dynamics and stability. John Wiley & Sons New York 1997. 8. Machowski J., Bernas S., Stany nieustalone i stabilność systemu elektroenergetycznego [Power system unsteady states and stability], Warsaw, WNT, 1989. 9. Van Cutsem T., Vournas C., Voltage stability of electric power systems, Kluwer Academic Publishere, London 1998. 10. Zajczyk R., Modele matematyczne systemu elektroenergetycznego do badania elektromechanicznych stanów nieustalonych i procesów regulacyjnych [Mathematical models of power system for examination of electro-mechanical unsteady states and control processes], Gdańsk University of Technology Publications, 2003. 11. Zajczyk R., Szczerba Z., Lubośny Z., Małkowski R, Klucznik J., Kowalak R., Szczeciński P. , Dobrzyński K., Analiza stanu obecnego i opracowanie zmian w układach regulacji napięcia i mocy biernej w elektrowniach, stacjach sieci przesyłowej i w sieciach rozdzielczych w celu zmniejszenia ryzyka powstania awarii napięciowych w systemie elektroenergetycznym [Analysis of the present condition and development of changes in voltage and reactive power control systems in utilities, transmission grid stations, and distribution grids in order to reduce the risk of voltage failure development in a power system] Gdańsk University of Technology, Study commissioned by PSE Operator, Gdańsk 2007–2008.

Ryszard Zajczyk / Gdańsk University of Technology Piotr Szczeciński / Gdańsk University of Technology

Authors / Biographies

Ryszard Zajczyk Gdańsk / Poland

Piotr Szczeciński Gdańsk / Poland

The author specialises in power systems engineering. The Chair of Power Engineering Department at Faculty of Electric Engineering and Automatics of Gdańsk University of Technology. Graduated in Power Engineering from the Electrical Engineering Faculty of Gdańsk University of Technology in 1978, Professor since 2004. He researches mainly issues of power system operation in adequate and unsteady states, with particular focus on regulation and control processes, impact of renewable sources, including wind generation, on power systems, and power system cooperability with high voltage power-electronic devices. He is the author of numerous publications, scientiﬁc studies, and research projects in this area.

Graduated in Power Systems from the Electrical Engineering and Automatics Faculty of Gdańsk University of Technology. After graduation joined Institute of Power Engineering Gdańsk Branch. After ﬁve years returned to his university, where he develops his interest in DC power transmission, power system stability, excitation systems, and FACTS systems.

Impact of Current Compensation System on Generator Operation at Voltage Changes in the National Power System

IMPACT OF CURRENT COMPENSATION SYSTEM ON GENERATOR OPERATION AT VOLTAGE CHANGES IN THE NATIONAL POWER SYSTEM Ryszard Zajczyk / Gdańsk University of Technology Piotr Szczeciński / Gdańsk University of Technology

1. INTRODUCTION Current compensation systems in use in the national power system, depending on their make and the incorporated solution, enable compensation of voltage loss or drop. Unfortunately, in the majority of turbo-generator sets in the system this opportunity is not exploited, and compensated impedance is set to Zk = 0. Error variable depends then on the generator terminal voltage measurement and on the set value. In such a case the generator controller receives the set generator terminal voltage value, and ARNE group control system, by way of the set value’s change, allows to bring the voltage in nodes to the level indicated by the National Power Dispatch Centre. Because of the problem’s complexity this paper discusses issues of reactive power generation’s sensitivity to grid voltage changes depending on the type of current condensation in place.

2. MATHEMATICAL MODEL A mathematical model describing the operation of two generators (GTHW 360) is used to examine the impact of current compensation on the power system. 1).

�

SEE 400kV

Y52 AFL-8 525 25 km

400kV TB2

TB1 22kV

22kV

G2 Fig. 1. Diagram of the subject power system

Abstract The paper presents the impact of current compensation on generated reactive power changes sensitivity at grid voltage changes. The research results are presented for two different ways of estimating the current compensation signal, which enable the generator controller’s

maintaining the set voltage elsewhere than the generator terminals. The paper discusses necessary changes in ARNE group control at current compensation implementation in generator control systems.

Ryszard Zajczyk / Gdańsk University of Technology Piotr Szczeciński / Gdańsk University of Technology

Set transformers TB1 and TB2 are of TDC - 426000/400 YNd11 type, and the structure of the main voltage control circuit is presented in Fig. 2. Gain KA = 1100 is set in the generator’s main voltage control circuit, as well as time constants TA = 2,4 s, TB = 20,4 s.

�

RA – automatic control

Limiters:

U Nast Ug -



1+sTA 1+sTB

1+sTC 1+sTD OKM [V] OPW [V]

RR – manual control

IfNast Ifg -



Setpoints:

OKM [V]

0-10 [V]

OPW [V]

0-10 [V], I t [A s]

OPS [V]

0-10 [V], I2t [A2s]

OPS [V] KIA

1+sTIA 1+sTIB

LV GATE

RR RA – regulacja automatyczna RR – regulacja ręczna

HV GATE

U st

Fig. 2. Block diagram of the main voltage control circuit

As mentioned in the introduction, the compensated voltage Ugk is calculated depending on the solution in place after the following formulas: Ugk = |Ug + (Rk×Igc − Xk×Igb)+j(Rk×Igb + Xk×Igc)|

(w. Z)

or Ugk = Ug + (Rk×Igc − Xk×Igb)

(w. RX)

Ug – voltage measured on generator busbar Ugk – compensated voltage Zk, Rk, Xk – compensated impedance, resistance, reactance Ig – synchronous generator current (Igc , Igb – generator current’s active and reactive components). In analogue systems installed in the national power system a signal that is input to error variable is calculated after formula w. Z, and in digital systems such signal is typically calculated after formula w. RX. Additionally in Operation and Maintenance Manuals, regardless of the make, ungrounded recommendations may be found, such as to set compensated resistance to Rk= 0. Moreover, the descriptions lack any notice whatsoever on whether the mutual impedance should consider also the transformer’s transverse branch, and whether the input compensated resistances are those determined in cold condition.

3. IMPACT OF CURRENT COMPENSATION SYSTEM ON GENERATOR OPERATION AT VOLTAGE CHANGES IN THE NATIONAL POWER SYSTEM As mentioned in the introduction, current compensation implementation inputs an extra signal to error variable, which enables the generator controller’s maintaining the set voltage elsewhere than the generator terminals. Current compensation impedance Zk = Rk + jXk, which may be set in the complex plane’s four quadrants, enables inputting virtual voltage measurement to the controller and almost unlimited shaping of the set’s substitute diagram (in the steady state) in the power system diagram. The current compensation operating principle has been known for many years [2].

79 Fig. 3 presents the generator’s static characteristics without compensation (a) and with current compensation set to Zk = 0,97 × ZTB.

�

1.1

�

U [p.u.]

1.05

0.95

0.9

0.85

0.85 Q [Mvar]

0.8 -150

-100 -50 Utr12 [400kV]

1.1

0 50 Utr11 [22kV]

100

150

200

U [p.u.]

Q [Mvar]

0.8

250

-150

-100 -50 Utr12 [400kV]

0 50 Utr11 [22kV]

100

150

200

250

Fig. 3. Generator’s static characteristics: a) with no current compensation, b) with current compensation of voltage loss set to Zk = 0,97 × ZTB

The current compensation implementation, as shown in the static characteristics (Fig. 3) maintains fixed voltage as a rule downstream of the set transformer, and not on the generator terminals. It makes the ARNE group control system affect at voltage changes the generator voltage programmers less often in order to maintain the power system voltage. Fig. 4 presents the impact of current compensation on changes of the generator’s voltage and reactive power at changes of the power system voltage. The input disturbance is grid voltage change by +2% within 3 s simulation, then by -2% in 30 s, -1% in 60 s, and +1% in 80 s. Figures 4a) and b) present the research results for a system with no current compensation, while Figures 4 c) and d) present the research results for a system with current compensation. The current compensation considers statism 3%, Rk = (1 - 0,03)RTB, Xk = (1 - 0,03)XTB. Setting of a sufficient current compensation ensures uniform distribution of reactive power between generating units with the same rated powers, supplying a system or a switchgear busbar section. For generating units with various rated powers the system should ensure reactive power distribution pro rata to their respective rated powers, which may be set by sufficient adjustment of Zk. In this case the current compensation enables removal of this function from the ARNE group control system.

�

1.1

�

U [p.u.]

1.1

1.05

0.95

czas [s]

0.9 0 10 Us [400kV]

20 30 Utr12 [400kV]

40 50 Utr11 [22kV]

100

U [p.u.]

czas [s]

0.9 0 10 Us [400kV]

20 30 Utr12 [400kV]

40 50 Utr11 [22kV]

Fig. 4. Voltage and reactive power waveforms: (a, b) with no current compensation, (c, d) with current compensation of voltage loss set to Zk = 0,97 × ZTB

100

Ryszard Zajczyk / Gdańsk University of Technology Piotr Szczeciński / Gdańsk University of Technology

80 b) � 200

d) � 200

Q [Mvar]

150

100

0 -50

Q [Mvar]

100

-100

-50

100

-100

-150

czas [s]

-200 Qg1 [Mvar]

czas [s]

-200 Qg1 [Mvar]

Fig. 4. Voltage and reactive power waveforms: (a, b) with no current compensation, (c, d) with current compensation of voltage loss set to Zk = 0,97 × ZTB

At present the ARNE group control system is responsible for reactive power generation distribution. Upon the generating unit’s connection to system, the system begins to change the generator’s reactive power in order to liquidate the voltage’s deviation from the voltage indicated by the National Power Dispatch Centre and the voltage of the busbar system, to which it is connected. This is done by way of up/down pulse adjustment of the generator voltage programmer. This adjustment causes a one-off change of the reactive power by ca. 2 MVAr (resulting from signal and execution unit discretisation). The ARNE group control system sends pulse signals to the programmers at 5s intervals, regardless of the voltage deviation value. Connecting another generator to parallel operation makes the generators’ reactive powers level ﬁrst, and only then the ARNE group control undertakes the voltage adjustment. Both the voltage adjustment and generator reactive powers levelling by the ARNE system are always done in the same way, i.e. by up/down adjustment of the generator control programmer, and the resulting one-off reactive power change always amounts to ca. 2 MVAr. As mentioned above, where current compensation is in place, the set statism ensures uniform reactive power distribution between generating units. This type of distribution and control may be considered fast compared to the ARNE group control system’s impact. Such voltage programmer adjustment by the ARNE group control system introduces a deviation in the reactive power distribution between generators operating in parallel. In presently applied solutions the reactive power control error should not exceed 2% of the rated power. Where current compensation system is in place the error depends on current compensation setting, and signal and execution unit discretisation. It follows from the study results that absence of current compensation decreases the turbo-generator set’s busbar voltage variability, which in turn increases the grid voltage variability. The absence of compensation means lower sensibility of the generator reactive power to the grid voltage changes, and therefore a change in the set voltage value causes small changes in the generated reactive power. Current compensation implementation and change in ARNE group control system’s functional algorithm enable reﬁnement of these control processes. Moreover, current compensation improves the turbo-generator sets’ local stability conditions. The ARNE group control system does not affect the local stability. The setting of current compensation and increase of the generator sensitivity to grid voltage changes can necessitate a change in the settings of the generator voltage control and system stabiliser. Because of this issue’s complexity these aspects will be addressed in subsequent papers. Fig. 5a) presents the impact of the type of current compensation on the generated reactive power changes’ sensitivity at grid voltage changes. The results are presented in the function of reactive power change referred to compensated impedance. The compensated impedance Zk varies from 0 to ZTB.. Reactive power increment at various Zk values was determined at grid voltage by 2 kV. As can be seen from the study results, controller voltage programmers adjustment should ensure meeting the required group control accuracy at setting voltage controllers’ current compensation. Compensation setting in excess of 60% doubles the generator sensitivity to voltage changes. A one-off change by the generator controller programmer changes the reactive power by ca. 4 MVAr.

81 Implementation of current compensation with statism set at 3% [8] may at various utilities require voltage programmers’ replacement. Current compensation should be implemented gradually at each utility.

�

ΔQ [Mvar]

P [MW] 375

50 40

365

355 20

345

10 Zk [p.u.]

czas [s]

335 0

0.2 0.4 UKP według wzoru RX

0.6 0.8 UKP według wzoru Z

30 32 Pg z UKP Z97%

34 Pg bez UKP

36 Pg z UKP RX97%

Fig. 5. Generator reactive power sensitivity. Generator active power waveforms: with no current compensation, with Z and RX type compensation.

As shown in Fig. 5a), implementation of current compensation after formula w. Z or w. RX does not materially impact the generator reactive power sensitivity. Depending on the compensation type, however, differences may be noticed in the generator active power waveforms (Fig. 5b). In this case the input disturbance is a grid voltage change of –2%. Fig. 6 presents the voltage, active power, and reactive power waveforms of two generators operating in parallel.

a) �

1.1

�

U [p.u.]

1.1

1.05

0.95

czas [s]

0.9 0 Us [400kV]

b) � 200

20 40 60 Utr12 [400kV] Utr11 [22kV]

100

U [p.u.]

czas [s]

0.9

120

0 Us [400kV]

20 40 60 Utr22 [400kV] Utr21 [22kV]

100

120

d) � 380

Q [Mvar]

P [MW]

375

150

370

100

365

360

0 -50

100

120

355 350

-100

345

-150

340

czas [s]

-200

czas [s]

335 0

Qg1 [Mvar]

Qg2 [Mvar]

20 Pg1 [MW]

40 Pg2 [MW]

Fig. 6. Voltage and reactive power waveforms with voltage drop’s current compensation set at Zk = 1,03 × ZTB.

100

120

Ryszard Zajczyk / Gdańsk University of Technology Piotr Szczeciński / Gdańsk University of Technology

The voltage drop’s current compensation is set at Zk = 1,03 × ZTB for the both generators. As can be seen, the input disturbance causes generator stability loss. With the voltage drop’s current compensation in place, the system, at the same input disturbances, loses stability at the transformer’s full compensation.

4. CONCLUSIONS A current compensation system in a generator control system should be set at a non-zero impedance and reactance. This enables fuller exploitation of the generator’s control capacity at a power grid voltage change. A current compensation system in place also improves the generator’s static stability and leads to its increased sensitivity at a voltage change in the National Power System. In a state involving a low voltage in the National Power System, a generator without current compensation gets loaded with reactive power much more slowly, which results in worsening of the voltage conditions in the National Power System.

REFERENCES 1. Model układów wzbudzenia i regulacji napięcia. Struktury układów wzbudzenia. Struktury regulatorów napięcia w KSE [A Model of Excitation Systems and Voltage Control. Voltage Controller Structures in the Nationa Power System] , PBZ-MEiN-1/2/2006, „Bezpieczeństwo elektroenergetyczne kraju”. 2. Hellman W., Szczerba Z., Regulacja częstotliwości i napięcia w systemie elektroenergetycznym [Frequance and Voltage Control in Power System], WNT, Warsaw 1978. 3. Lubośny Z., Małkowski R., Pochyluk R., Siodelski A., Szczerba Z., Wrycza M., Zajczyk R., Hierarchiczny wielopoziomowy układ sterowania poziomami napięć i rozpływem mocy biernej w krajowym systemie elektroenergetycznym. Zadanie nr 1: Struktura oraz zasady sterowania poziomami napięć i rozpływem mocy biernej [Hierarchic Multi-tier Control System of Voltage Levels and Reactive Power Distribution in the National Power System], Dedicated Project 8T10B051 98C/99, Power System Department of Gdańsk Univeristy of Technologt, Gdańsk, June 2001. 4. Zajczyk R., Modele matematyczne systemu elektroenergetycznego do badania elektromechanicznych stanów nieustalonych i procesów regulacyjnych [Mathematical Models of Power System for Examination of Electomechanical Unsteady States and Control Processes, Gdańsk University of Technology Publications, Gdańsk 2003. 5. R. Zajczyk et al., Zintegrowane modele matematyczne dla analiz technicznych różnych stanów systemu elektroenergetycznego [Integrated Mathematical Models for Technical Analysis of Various Power System States], PBZ „Bezpieczeństwo elektroenergetyczne kraju”, 2008. 6. Szczerba Z., Automatyczna regulacja napięcia i mocy biernej bloków wytwórczych [Automatic Control of Turbogenerator Set Voltage and Reactive Power, XIV International Conference Current Problems in Power Engineering APE ’09, Jurata 2009. 7. Communique of PSE-Operator S.A. on Final Report of Examination of Voltage Failure on 26 June 2006 and Program of Actions Undertaken to Prevent Future Threat States. 8. Instrukcja ruchu i eksploatacji sieci przesyłowej; Warunki korzystania, prowadzenia ruchu, eksploatacji i planowania rozwoju sieci [Transmission Grid Operation and Maintenance Code], Issue 1.2; Warsawa, 17 March 2006. 9. R&D Study: Analysis of the Present State and Development of Changes in Voltage and Reactive Power Systems at Utilities, in Transmision Grid Stations and in Distribution Grids in Order to Reduce the Risk of Voltage Failure Development in Power System. Stage II. Commissioned by PSE-Operator S.A.

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