Special Instrument Transformers for Renewable Energy and Rural Electrification

International Journal of Energy and Power, Volume 5 2016 www.ijep.org doi: 10.14355/ijep.2016.05.002

Special Instrument Transformers for Renewable Energy and Rural Electrification Worawut Sae‐Kok1, David Xu*2, Jinyong Chen3, Nicholas S. Powers4, Mathew Paul5 ABB Limited, Thailand, 2, 4, 5ABB Inc., USA, 3ABB Jiangsu Jingke Instrument Transformer Co., Ltd., China

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worawut.sae‐kok@th.abb.com; *2david.xu@us.abb.com; 3jinyong.chen@cn.abb.com; 4nicholas.s.powers@us.abb.com; 5mathew.paul@us.abb.com 1

Abstract This paper presents the solutions provided by Station Service Voltage Transformer (SSVT) for applications in renewable energy and rural electrification. A SSVT is a special hybrid type of instrument transformer product with features of a high voltage inductive voltage transformer and a distribution transformer to offer a compact, reliable power source. Using SSVT for renewable applications, e.g. wind and solar, can provide a reliable, convenient source of control power for independent operations in remote areas. For rural electrification application, SSVT serves as a mini‐substation, stepping down the power supply directly from the high voltage transmission line to low voltage or medium voltage output in one step to provide power source to small residential areas without the large investment, meanwhile reduce the required space and shorten the time duration for construction of a typical substation. ABB has delivered many SSVT products both oil and SF6 in substations around the world. Many of them are used for the above‐mentioned applications which are recommended for wide use in the future grid.

Keywords Control Power Source; Rural Electrification; Renewable Energy; Station Service Voltage Transformer; SSVT

Introduction Nowadays, two of key promising and interesting topics discussed, researched and developed for power systems are related to renewable energy as well as rural electrification. The challenge of the former is how to tap the renewable sources and send the electricity to the users as well as connection to the grid cost effectively with good reliability and availability. And that of the latter is how to cost effectively increase the access to electricity in the specific areas, in particular, where the electrification rate is low, e.g. Africa region.

The renewable energy available to the earth is sufficient to meet the energy demand for all the human beings on earth, saving all natural resources and preventing greenhouse gas generation. Renewable technologies are becoming increasingly cost competitive in a number of countries and circumstances, but public support schemes are still required to support deployment in many others. Renewables‐based power generation capacity is estimated to have increased by 128GW in 2014; this amounted to more than 45% of world power generation capacity additions in 2014, consistent with the general upward trend in recent years [1]. Our focus is to provide technology and products which are efficient, reliable and low initial cost for the energy hungry world, without consuming the world. One of important issues on integration of renewable to the grid is how to provide reliable control power source in the renewable energy substation. In response to this, a cost effective control power source by using oil‐ and SF6 ‐insulated SSVT has been developed. The solution is to apply SSVT to step down the power directly from the high voltage transmission line to low voltage level to feed the substation as control power (see Fig. 1).

Electricity has the undeniable ability to raise the quality of life in any community. It is more so in the developing countries, where electric supply has not reached. Bringing power to many rural villages across the world can have significant impact. According to IEA WORLD ENERGY OUTLOOK 2014 report, “an estimated 620 million people in sub‐Saharan Africa do not have access to electricity.” [2]. ABB has a clear focus to make contributions in helping people living in rural villages to access electricity through many different solutions, as envisioned through its “Access to Electricity” program started in 2002 [3]. In response to this kind of humanitarian need, a cost effective power solution for rural electrification using SSVT is available today.

A typical community electrification application would consist of an electrical network, high voltage fenced substations and many voltage transformations from high voltages down to utilization level to deliver power to the 11

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residential area (see Fig. 2‐left). This normally requires a higher investment, much more space allotment and longer time duration to complete construction and installation. An alternative solution developed by ABB is to apply the SSVT product to serve as a mini‐substation, stepping down the power supply directly from the high voltage transmission line to low voltage or medium voltage output in one step to provide power source to small residential area without the large investment (see Fig. 2‐right).

This paper describes the technical features and parameters for both oil‐ and SF6‐insulated SSVT, as well as examples of their applications for wind farm substation and rural electrification, to illustrate the technology and product to bring benefits to customers in different aspects. Real projects ABB has delivered SSVT in Uruguay to supply control power source for wind farm application and in DR Congo for rural electrification are also presented as good examples for helping population in rural villages to access to electricity and to change their life by improving living environment and standards.

FIG. 1. A TYPICAL WIND FARM SUBSTATION USING SSVT (CIRCLED) TO SUPPLY CONTROL POWER IN A RURAL AREA, REDUCING THE INVESTMENT OF SUBSTATION

FIG. 2. HOW TO DELIVER POWER TO RESIDENTIAL AREA BY: (LEFT) A TYPICAL NETWORK SYSTEM; (RIGHT) USING SSVT FOR RURAL ELECTRIFICATION CONCEPT

Technical Aspect of SSVT Product SSVT is a special hybrid type of instrument transformer product which incorporate features of an inductive voltage instrument transformer with that of a distribution power transformer to offer a compact, reliable power source: Differrent Technology of SSVT Start as early as 1970’s, industry has applied SSVT as a very reliable, convenient means of taking power off the HV bus to satisfy the requirements for available sources of control power within electrical substations.

The SSVT is a line to ground connected single phase that can be used as a single unit or in a three phase bank to power loads (see Fig. 3). This solution provides reliable power from any high voltage (46kV to 500kV) transmission circuit with oil and paper insulated dielectric or SF6 insulated graded dielectric system, with ground shield isolated secondary within a shell form construction. This solution integrated inside the substation gives the user the full control of the energy supply in a limited space and directly from the constantly available transmission grid.

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FIG. 3. SMALL FOOTPRINT OF SSVT WITH EASY INSTALLATION: (LEFT) OIL‐INSULATED TYPE; (RIGHT) SF6‐INSULATED TYPE IN STALLED IN A WIND FARM SUBSTATION

FIG. 4. (LEFT) TYPICAL SF6‐INSULATED SSVT‐TIP; (RIGHT) TIP RURAL INTEGRATED SUBSTATION DESIGN

By using a format which is similar to an inductive voltage transformer to satisfy the dielectric requirement, coupled to a larger format core similar to that used in distribution transformers, and using advanced materials and design, a fully rated dielectric compact design was developed. Given its compact size and ease in siting, along with the low loss single transformation right from HV to LV, this has made the SSVT a preferred source for substation control power in the North American Market since the 1990’s. SSVTs feature rugged transformer designs incorporating high creepage insulators and high over‐voltage capability with impedance protection to limit fault currents. Until now, the hybrid SSVT has been designed, produced and tested per the requirements of the following industry standards: IEEE C57.13 / IEC 60044‐2 (applicable dielectric clauses) and IEEE C57.12 / IEC 60076 (applicable power rating clauses). Beginning in 2016, IEEE is developing a definite purpose standard specific to this product with the following number: IEEE C57.13.8 (all applicable clauses).

Current family of SSVT products continue to evolve with products being developed in both the oil‐filled format, as well as the SF6 insulated units.

1) Oil‐Filled Station Service Voltage Transformers – Type SSVT (LV Output) and Type SSMV (MV Output): The SSVT and SSMV designs are oil‐filled and shipped completely assembled, ready for installation. The SSVT supplies low voltage output for direct utilization without further transformer in either 50Hz or 60Hz. For remote locations farther from the HV connection, SSMV has been designed up to 138kV with a medium voltage output to extend the reach of the power supply to distances as far away as 20 miles (33km). This prevents excessive voltage drop over the conductor run, but will require an additional voltage transformation for use.

SSVT voltage ratings are ranging from 46kV, up to 362kV nominal system voltage, with power ratings as high as 167kVA single, 333kVA single phase at 230kV only.

2) SF6 Insulated Station Service Voltage Transformers – Type TIP (LV and MV Output) and TIP Rural: The TIP can provide LV or MV output on 50Hz or 60Hz systems for close‐in or farther‐out applications. The pressured gas design is shipped with reduced gas pressure and would require a gas cart on site for filling to its operating gas pressure. For cold temperature applications below ‐30 degree Celcius ambient, heaters or mixed gas is used. To provide an integrated substation solution, this design is offered from 69kV to 525kV nominal system ratings, and up to 333kVA power level. ABB also offers a variation of the TIP called the TIP Rural that incorporates the SSVT function with a gas insulated circuit breaker and disconnect switch, along with a low voltage control cabinet to supply power needs to 167kVA power and 420kV nominal system voltage rating. The

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TIP Rural provides a pre‐assembled substation configuration available for easy transport and installation on site in the smallest substation footprint possible (see Fig. 4).

FIG. 5. (LEFT) TIP INSTALLED IN 145KV SUBSTATION FOR CONTROL POWER; (MIDDLE) SSVT INSTALLED IN 145KV SUBSTATION FOR CONTROL POWER; (RIGHT) 230KV SSVT RURAL ELECTRIFICATION SITE WITH ARRESTER/DISCONNECT SWITCH

Typical Applications The power rating of the SSVTs have increased from 25kVA single phase at beginning, to as high as 333kVA today (1MVA three phase) to meet the growing need of the substation control power in size and complexity. Future designs are moving to 500kVA single phase (1.5MVA three phase). Given these higher available power ratings, this has opened the use of the SSVT to other applications, including rural electrification.

SSVT can be used in many areas for reducing initial cost, while increasing the reliability of the power supply.

Applications for their uses are wide‐ranging and include: 1) Switching and Step‐Down Substations: SSVT is mounted onto a pedestal inside the substation, with the primary tied to the incoming transmission line and the output secondary control wiring connected to the station power panel (see Fig. 5‐left and Fig.5‐middle).

This solution saves utilities from having to rely on main power transformer tertiary windings or distribution feeders outside of the substation for low voltage control power. Wind and solar power projects located in far‐ flung regions would also benefit from the SSVT. 2) Substation Auxiliary Power SSVT can eliminate the need for dependency on a power transformer tertiary output to a distribution transformer to provide the low voltage required for control power supply. These two transformer configurations can now be handled with one step transformation, while enhancing the reliability of the control power supply.

3) Rural Electrification In under‐developed or developing countries, transmission systems are in place, but a wide‐spread distribution infrastructure is lacking. SSVT can be used as a compact transformer to greatly reduce the first cost of electrification for small villages or compounds lacking much financial support. SSVT can either be used with its low voltage output to directly supply needed power for in‐close loads near the transmission right of way, or SSMV or TIP Rural for medium voltage output distributed farther and stepped down near the use for a local distribution network (see Fig. 5‐right).

4) Transmission Tower Lighting When high voltage transmission lines cross a large body of water, they are typically taller and require aviation safety hazard lighting. ABB has designed a 46kV, 5 kVA power rating SSVT with hanger brackets for pole‐ mounting and fusing in the control cabinet. These units are mounted atop a transmission pole adjacent to the transmission line, eliminating the need to maintain control supply near the ground level from a distribution feeder.

5) Remote Cell Towers When a cell tower needs to be placed in a remote location and lacks nearby electrical secondary feeders, siting the cell tower adjacent to a high voltage transmission line is an economical option. A tap can be taken from the transmission line to a SSVT placed in a fenced‐in area (a miniature substation) to energize the cell tower. Where permitted, the cell transceiver can be located directly on the transmission tower.

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6) Oil and Gas, Mining Projects, Construction Power, as Well as Defense and Special Applications Power Many oil and gas exploration and mining projects are far away from a distribution network and dependent on portable generator sets for electric power. SSVTs or SSMVs can bring electric power at low cost reliably to such remote sites. This option requires low maintenance and running costs along with a low cost of energy. The SSVT initially used as a power supply for during construction of a substation project, can continue to serve as a second control power source. Additionally, the SSVTs and SSMVs can be relocated to another project site quickly and easily where required.

In addition, small power needs can arise in an emergency situation, with constraints on timeframe, footprint, safety, transportation logistics and reliability. SSVT and SSMV offer a ready, easy solution for managing these situations quickly.

Renewable Energy and Rural Electrification Applications Today, many SSVTs have been delivered for different applications into several countries. For the application of renewable energy and rural electrification, below are using recent actual projects to illustrate the concept and benefits.

SSVT Using for Wind Farm Application Wind power as one of important renewable energy resources has been widely used in several regions/countries.

Based on the estimated increase of renewables‐based power generation capacity by 128GW in 2014, 37% is wind power, almost one‐third solar power and more than a quarter from hydropower. The growth in wind capacity continued to be led by onshore installations (although offshore has also grown rapidly). China remains of having the largest wind power with 20 GW of new capacity. Germany installed more than 5 GW of wind capacity, while US capacity additions bounced back from the very low levels of 2013 to almost 5GW in 2014. Relatively high (but declining) costs for offshore wind and delays in the build‐up of grid connections have resulted in delays to projects in some countries or the cutting of capacity targets (e.g. Germany), though other countries have responded by boosting their support to the industry (e.g. Japan, Korea and China) [1]. Wind power is now an undisputed pillar of the electricity supply in many parts of the world. 370GW of wind power installed worldwide can now contribute close to 5% of the global electricity demand. Several countries, including Denmark, Spain, Portugal, Ireland, the United Kingdom and Germany, have now reached 10% or more of their power coming from wind. In addition, more countries in other parts of the world (i.e. Latin America and Asia) have increased the installed wind capacity such as Brazil and Uruguay [4].

Most of the wind farm substations are located at the rural area and in a good distance away from major distribution network. Wind farm substation can have the following control power supply with some concerns: 

Drawing a distribution feeder for control power is very expensive and is not so reliable. It also may attract higher energy rate.



Using tertiary winding from main power transformer hampers design of main power transformer as well reduces its reliability by adding one more winding. In addition, a second step‐down transformer may be required for low voltage.

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Diesel generator to supply the control power increases unit cost of energy and also requires more maintenance. It adds to carbon footprint and noise pollution.

FIG. 6. SSVT INSTALLED IN A WIND FARM SUBSTATION IN URUGUAY

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SSVT can be used as an alternative to above‐mentioned ways to supply the control power in wind farm substation and have the advantage over their drawbacks. The recent case is supplying three units of oil‐insulated SSVT with 750kV BIL, 67kVA thermal rating (100kVA in 3 phase) connected in three phase to provide control power to the remotely located wind farm substation to supply power in a rural area in Uruguay (See Fig. 6). A delta connected 3‐ phase secondary applied in this project has the additional advantage of maintaining a three phase supply, although at reduced level, even if one SSVT is taken out of service. This can reduce the investment of substation with a reliable power supply from SSVT. It is worth noting that this solution by using SSVT can be applied to other types of renewable applications, e.g. solar and biomass, due to the similarity of how to connect to the grid.

SSVT for Rural Electrification in Africa In Africa, despite many positive efforts to have more access to modern energy services, instead of bioenergy, still more than 620 million people in sub‐Saharan African are without access to electricity. Fig. 7 shows the African countries with the electrification rate less than 40%. The rural electrification is one of key actions to increase the access to the electricity. The challenge for the electricity infrastructure is clear, while grid extension typically serve only urban and peri‐urban population, investment in rural micro‐grids and stand‐alone energy solutions assume the dominant role in reaching the massive populations of rural sub‐Saharan Africa. As the financial constraint is one of key challenges for the rural electrification, using SSVT as a mini‐substation and utilizing the existing infrastructure more efficiently will bring the electricity to the household shows the possibility of achievement for powering the rural areas with the lower cost and provide less negative impacts in environments and other activities.

A simplified model to calculate the total electrification project cost with SSVT as a mini‐substation related to typical substation can be shown as (1).

Z = αX + βY = γ (X+Y) (1) where X, Y, and Z: costs of typical substation with power transformer, distribution transformer and line for substation with power transformer and mini‐substation with SSVT, respectively α and β: reduction factors related cost of substation and distribution transformer and line when using SSVT instead of power transformer, respectively γ: reduction factor related to total cost of rural electrification when using SSVT instead of power transformer Typically, α and β are in the range of 0.1‐0.3 and 0.5‐0.8, respectively, depending on power rating and size of substation as well as distances to load areas. It is clear that cost of the substation construction is reduced from lower number and smaller size of equipment and less required space for the substations. The equipment can be easily transported via existing roads and infrastructures, with no need for further investment. The installation and commissioning time has been much shorter on these mini‐substations due to smaller size of substation.

FIG. 7. ELECTRIFICATION RATE (SOURCE: WORLD ENERGY OUTLOOK 2011)

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FIG. 8. (LEFT) PREPARATION FOR THE MINI‐SUBSTATION, BEFORE THE SSVT INSTALLED ON A SITE; (RIGHT) AFTER THE INSTALLATION OF SSVT AND OTHER EQUIPMENTS

The recent rural electrification project is for the DR Congo by using 7 units of ABB SSVTs to supply power to 7 rural villages located in the southeastern part of the country. This project has been funded by the World Bank to support the rural electrification of these villages near roads and transmission lines in an area that supports mining opportunities. The number of inhabitants in each village ranges from 200 to 1,500 people. There are 220kV high voltage transmission lines passing over or near those villages, but a power substation was financially and logistically beyond their reach. In addition, that the distribution lines need to be built to connect from the power substation to those villages even increase the cost of the electrification. ABB has provided the solution of a mini‐substation at 220kV, which is a single‐phase and consists of a SSVT, disconnector and surge arrester. Each substation is located near each village and is directly connected to the 220kV transmission line which passes over or near the village. The output of the substation is at low voltage level (230V) and is connected to the villages for electricity usage. Fig. 8 shows one of site locations before the project start and after the installation of SSVT and other equipment, respectively.

In term of the required space, comparison of a typical substation for 230kV, with a 20 to 50MVA power transformer, a general space required in the range of 2,000 square meters. To get first power into the site, the traditional sized 230kV substation is too large for the application. By using the SSVT in a single phase installation “right‐sized” for the needs of a small village, the size shrinks to almost 1/10 the size at 250 square meters. This results in dramatic reductions in (1) site preparation for SSVT being roughly 10% of standard substation; (2) fencing smaller space with 66 meters for mini‐substation compared to 180 meters; (3) support structures reduced to 4 from over 21 required for insulators and HV equipments for large substation, plus pouring a major pad for the power transformer; and (4) HV conductor use with about 90% reduction. It is clear that the SSVT min‐substation is the right‐size for many first projects for rural electrification, given it simplicity, small space, less site resources required to install and maintain, and of course the economy in the approach.

Conclusions The various solutions provided by ABB SSVT which is a special hybrid type of instrument transformer combining features of inductive voltage transformer and distribution transformer, for applications in renewable energy and rural electrification are presented in this paper. For renewable energy application, SSVT can provide a reliable and convenient control power source to the independent operation in the remote areas and has advantages comparing to other ways of providing power source. For rural electrification application, the mini‐substation with SSVT can be one of the most economical solutions for rural electrification. It can act as a reliable power source to enable the rural community to access the electricity. Without the SSVT offered by ABB, community electrification would be done by construction of much larger network system which requires high investment and long period of time. Two recent real projects ABB has delivered SSVT for wind farm application in Uruguay and for rural electrification in DR Congo are also elaborated in this paper as good examples of SSVT implementation for such applications which can provide several benefits, including helping population in rural villages to access to electricity and change their life by improving living environments and standards.

REFERENCES

[1]

IEA, “World Energy Outlook Special Report – Energy and Climate Change”, 2015

[2]

IEA, “World Energy Outllook 2014 Factsheet – Energy in Sub‐Saharan Africa Today”, 2014.

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ABB, “Access to Electricity – White Paper on ABB’s Initiative for Access to Electricity”, April 2005

[4]

World Wind Energy Association, “WWEA Quaterly Bulletin”, Issue No. 1, March 2015

Worawut Sae‐Kok received the B.Eng. in electrical engineering from Chulalongkorn University, Thailand in 2000, and the M.Eng. and Ph.D. in electrical engineering from the University of Tokyo, Japan in 2003 and 2006, respectively. He has been with ABB since 2006 and worked mainly in sales and marketing management for power products. He is currently responsible for global product marketing for high voltage instrument transformers and disconnectors and based in Bangkok, Thailand. His experience in the industry includes low/medium/high voltage products and transformers as well as knowledge on power system analysis.

David Zuoqing Xu received the B. Eng in electrical engineering from JiaoTong University, China, the M. Sc. from University of Guelph, Canada and MBA from University of Missouri, St‐Louis, USA. He has been with ABB since 1993, where he has worked as an electrical design engineer, project manager, engineering manager, R&D manager for ABB transformer group for last 20 years and currently as a global product manager and responsible for ABB high voltage instrument transformers business. He is based in Raleigh, NC, USA. His experience in the industry includes various transformer technologies, such as instrument transformer, small distribution transformers and large power transformers.

Jinyong Chen received the B. Eng in electrical engineering from Shandong Polytechnic University, China and worked as an instrument transformer R&D engineer in China. He has been with ABB since 2008, where he has worked as a product engineer, senior project management engineer for ABB power products. He is currently technology manager and product manager for ABB Jiangsu Jingke Instrument Transformers Co., Ltd. and based in Suqian, China. His experience in the industry includes various high voltage instrument transformer technologies and manufacturing, such as ring type and dry type current transformers, liquid insulation current and voltage transformers, gas insulation current and voltage transformers.

Nicholas S. Powers received the B.Sc. in electrical engineering from University of Kentucky, USA in 1978 and has worked with a number of instrument transformer suppliers over the last 35 years in application engineering, business development and marketing management. He has also completed courses of study in marketing and business development at the University of Wisconsin, School of Business, and has been instrumental in developing advanced designs targeted for the rapidly changing electricity utility measurement, protection and control needs. He is currently ABB global product marketing manager for station service voltage transformer (SSVT) and based in ABB Kuhlman Office Lexington, Kentucky, USA Mathew Paul holds a B. Sc. in Physics from Madras University, India, B. Sc. in Electrical Engineering from Bangalore University, and a MBA from School of management at Cochin University, India. He is ABB Station Service Voltage Transformer (SSVT) Global Business Development Manager and resides in Lexington, Kentucky, USA. He has worked in the electric utility industry for over 16 years, much of it in the power transformer market, holding positions from strategic account manager to power generation and export sales manager, as well as utility sales manager. He is currently business Development manager and responsible for promoting SSVT globally.

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