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ISBN: 378 - 26 - 138420 - 5
Placement of Super Conducting Fault Current Limiters to mitigate fault Currents in Smart Grids with different types of Distributed Generation Sources 1
Sai Sowmya Varanasi Ramachandra college of Engineering,4th B.Tech saisowmya.varanasi@gmail.com from all power sources and has no negative effect on the integrated Sources was suggested.
Abstract—
The important application of superconducting fault current limiters (SFCL) for upcoming smart grid is its possible effect on the reduction of abnormal fault current and the suitable location in the micro grids. Due to the grid connection of the micro grids with the current power grids, excessive fault current is a serious problem to be solved. In this paper, a resistive type SFCL model was implemented using Simulink and SimPowerSystem blocks in Matlab. The designed SFCL model could be easily utilized for determining an impedance level of SFCL according to the fault-current-limitation requirements of various kinds of the smart grid systems. In addition, typical smart grid model including generation, transmission and distribution network with different types of DG’s having different ratings such as wind, solar, diesel was modeled to determine the location and the performance of the SFCL. A 10 MVA wind farm, 675 KW solar and 3MVA diesel generator was considered for the simulation. Three phase fault has been simulated at distribution grid and the effect of the SFCL and its location on the wind farm, solar, diesel generator fault currents was evaluated. The SFCL location in Smart Grid with different types Distributed Generation Sources have been proposed and their performances were analyzed.
2. SIMULLINK MODELS SET-UP Matlab/Simulink/SimPowerSystem was selected to design and implement the SFCL model. A complete smart grid power network including generation, transmission, and distribution with an integrated wind farm, solar, diesel generator model [6] was also implemented in it. Simulink /SimPowerSystem have number of advantages over its contemporary simulation software (like EMTP, PSPICE) due to its open architecture, a powerful graphical user interface and versatile analysis. 2.1. Power System Model The modeled power system consists of an electric transmission and distribution power system. Newly developed micro grid model was designed by integrating a 10 MVA wind farm, 675 KW solar, 3MVA diesel generator with the distribution network. Fig.1 shows the power system model designed in Simulink/SimPowerSystem. The power system is composed of a 100 MVA conventional power plant, composed of 3-phase synchronous machine, connected with 200 km long 154 kV distributed-parameters transmission line through a step-up transformer TR1. At the substation (TR2), voltage is stepped down to 22.9 kV from 154 kV. High power industrial load (6 MW) and low power domestic loads (1 MW each) are being supplied by separate distribution branch networks. The 10 MVA wind farm, 675 KW solar, 3MVA diesel generator are connected directly through Step up transformer to the grid in Fig.1 artificial fault three-phase-to-ground fault and locations of SFCL are indicated in distribution grid. Three prospective locations for SFCL installation are marked as Location 1, Location 2 and Location 3. Generally, conventional fault current protection devices are located in Location 1 and Location 2. The output current of wind farm, solar, diesel measured at the output of DG for various SFCL locations have been measured and analyzed.
Index Terms—Fault current, micro grid, smart grid, SFCL, wind farm, solar, diesel.
1.
INTRODUCTION
Conventional protection devices installed for protection of excessive fault current in electric power systems allows initial two or three fault current cycles to pass through before getting activated. But, superconducting fault current limiter (SFCL) is innovative electric equipment [1] which has the capability to reduce fault current level within the first cycle of fault current. The first-cycle suppression of fault current by a SFCL results in an increased transient stability of the power system carrying higher power with greater stability. Smart grid is the novel term used for future power grid which integrates the modern communication technology and renewable energy resources to supply electric power which is cleaner, reliable, resilient and responsive than conventional power system. One of the important aspects of the smart grid is decentralization of the power grid network into smaller grids, which are known as micro grids, having distributed generation sources (DG) connected with them. These micro grids need to integrate various kinds of DGs and loads with safety should be satisfied. The direct connection of DGs with the power grid are the excessive increase in fault current and the islanding issue which is caused, when despite a fault in the power grid, DG keeps on providing power to fault-state network . Solving the problem of increasing fault current in micro grids by using SFCL technology is the main topic of this work. In this paper, the effect of SFCL and its position was investigated considering a wind farm, solar [5], diesel generator [6] integrated with a distribution grid model as one of typical configurations of the smart grid. The impacts of SFCL on the wind farm, solar, diesel generator and the strategic location of SFCL in a micro grid which limits fault current
2.2. Resistive SFCL Model The three phase resistive type SFCL was modeled and considering four fundamental parameters of a resistive SFCL. These parameters and their selected values are 1) Transition or response time 2) minimum impedance and maximum impedance 3) Triggering current and 4) recovery time .Its working voltage is 22.9 kV. Fig. 2 shows the SFCL model developed in Simulink/Simpower System. The SFCL model works as follows. First, SFCL model calculates the RMS value of the passing current and then compares it with the Lookup table. Second, if a passing Current is larger than the triggering current level, SFCL’s resistance increases to maximum impedance level in a pre-defined response time. Finally, when the current level falls below the
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INTERNATIONAL CONFERENCE ON CURRENT INNOVATIONS IN ENGINEERING AND TECHNOLOGY
ISBN: 378 - 26 - 138420 - 5
Fig.1 Power system model designed in Simulink/SimPowerSystem,Fault and SFCL locations are indicated in the diagram
triggering current level the system waits until the recovery time and then goes into normal state. SFCL is located at different locations.
2.4. Solar model The terminal equations of the Voltage, Current and Power [5] used for the devolpement of Solar Simulink model are given by equations 1,2 and 3.
Fig.2 Single phase SFCL model developed in Simulink/SimPowerSystem.
2.3. Wind Turbine Generator Model Where Iph is the light generated current, Is is the cell saturation of dark current, q is the unit electric charge, k is the Boltzman’s constant t is the working temperature of p-n junction, A is the ideal factor. Iph is the current based on cells working temperature and solar irradiation level described in equation.2 . Isc is the cells short circuit current Kt is the temperature coefficient and S is the solar irradiation level in KW/m2. Power delivered by PV array is given by equation(3) and PV array is modeled as single diode circuit . The subsystem can be implemented by using equations 1, 2 and 3.
A 10 MVA wind farm[1] is composed of 5 fixed-speed inductiontype wind turbines,each having a rating of 2MVA at the time of fault the domestic load is being provided with 3MVA out of which 2.7 MVA is provided by the wind farm. The wind farm is directly connected with the branch network B6 through the transformer TR3.Simulink model of wind turbine generator is shown.
Fig.3 Three phase wind turbine generator subsystem model.
Fig.4 Solar model developed in Simulink/SimPowerSystem.
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The output power of pv array is 675KW which is given to the inverter and then the ouput of model is connected directly to the branchnetwork B6 through transformer T3. The PV simulink model is shown in Fig.4.
ISBN: 378 - 26 - 138420 - 5
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A lower order model [6] is used for studying dynamics of internal combustion engines. A self –tuning PID controller is developed for a small size diesel engine and generator set.The output power of diesel generator is 3.125MVA.The ouput of model is connected directly to the branchnetwork B6 through transformer T3.The Simulink model of Governor and diesel engine is shown in Fig.5.
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Three scenarios of SFCL’s possible locations were analyzed for distribution grid fault occurring in the power system. The simulation is carried by placing SFCL in Location 1,2 and 3 by considering one DG at a time at the position shown in fig.1.
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Fault currents of one phase where the severity is more and different locations of SFCL are shown in Fig.7. When a threephase-to-ground fault was initiated in the distribution grid (Fig.1) SFCL located at Location 1 or Location 2, fault current contribution from the wind farm was increased . These critical observations imply that the installation of SFCL in Location 1 and Location 2 instead of reducing, has increased the DG fault current. This sudden increase of fault current from the wind farm is caused by the abrupt change of power system’s impedance. The SFCL at these locations (Location 1 or Location 2) entered into current limiting mode and reduced fault current coming from the conventional power plant due to rapid increase in its resistance. Therefore, wind farm which is the other power source and also closer to the Fault is now forced to supply larger fault current to fault point. In the case when SFCL is installed at the integration point of wind farm with the grid, marked as Location 3 in Fig.1 wind farm fault current has been successfully reduced. SFCL gives 68% reduction of fault current from wind farm and also reduce the fault current coming from conventional power plant because SFCL is located in the direct path of any fault current flowing towards Fault 1.
D.Fault current with SFCL at Location 3
Fig.7 Fault Currents of Wind Turbine Generator.
Comparison of fault currents when SFCL is placed at different Locations in Fig.1 are shown in Fig.8
Fig.8.Comparison of fault currents at different locations
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ISBN: 378 - 26 - 138420 - 5
3.2. Solar model as DG Fault currents of one phase where the severity is more and different locations of SFCL are shown in Fig.9.When a three-phaseto-ground fault was initiated in the distribution grid (in Fig. 1).The fault without SFCL is greater when compared with SFCL placed at different Locations the following results were observed. Once again the best results are obtained when a single SFCL is located at Location 3, when compared with the remaining two locations. Fault current has been successfully reduced.SFCL gives 70% reduction of fault current from Solar module and also reduce the fault current coming from conventional power plant because SFCL is located in the direct path of any fault current flowing towards Fault 1.
Fig.10.Comparison of fault currents at different locations
3.3. Diesel Generator as DG
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Fault currents of one phase where the severity is more and different locations of SFCL are shown in Fig.11. In this case when a three-phase-to-ground fault was initiated in the distribution grid (in Fig. 1).The fault without SFCL is greater when compared with SFCL placed at different Locations the following results were observed. Once again the best results are obtained when a single SFCL is located at Location 3, when compared with the remaining two locations. Diesel fault current has been successfully reduced. SFCL gives 84% reduction of fault current from diesel engine and also reduce the fault current coming from conventional power plant because SFCL is located in the direct path of any fault current flowing towards Fault 1.
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Fig.9 Fault Currents of Solar model.
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Comparison of fault currents when SFCL is placed at different Locations in Fig.1 are shown in Fig.10.
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and diesel. Multiple SFCLs will not used in micro grid because of their inefficiency both in performance and cost. The strategic location of SFCL in a power grid which limits all fault currents and has no negative effect on the DG source is the point of integration of the DG sources with the power grid.
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ISBN: 378 - 26 - 138420 - 5
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REFERENCES
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[1] Umer A.Khan, J.K.seong, S.H.Lee “Feasibility analysis of the Positioning of Super Conducting Fault Current Limiters for the Smart Grid Application using Simulink & Simpower Systems” IEEE Transactions on applied superconductivity, vol.21, No.3 June-2011. [2] S.Sugimoto, J.Kida, H.Aritha “Principle and Characteristics of Fault Current limiters with series compensation” IEEE Trans. on Power Delivery, vol.11,No.2,pp 842-847,Apr 1996. [3] J.Driensen, P.Vermeyen and R.Belmans “Protection issues in micro grids with multiple distributed generation units” in Power conversion conference., Nagoya, April 2007, pp 646-653. [4] K.Maki ,S.Repo and P.Jarventausta “Effect of wind power baSed distributed generation on protection of distribution netwrk Work” in IEEE Developments in Power systems protection, Dec.2004, vol.1, pp 327-330. [5] N.Pandiarajan, Ranganath muth “Modeling of Photo Voltaic Module with Simulink” international conference on electrical Energy system (ICEES-2011), 3-5 Jan-2011. [6] Takyin Takychan Transient analysis of integrated solar/diesel hybrid power System using MATLAB/Simulink . [7] S.N.B.V.Rao Asst Prof. in Ramachandra college of engineering
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Fig.11 Fault Currents of Diesel Engine.
Comparison of fault currents when SFCL is placed at different Locations in Fig.1
Fig.12.Comparison of fault currents at different locations
When the SFCL was strategically located at the point of integration Location 3, the highest fault current reduction was achieved whatever may be the DG source. The multiple SFCLs in a micro grid are not only costly but also less efficient than strategically located single SFCL. Moreover, at Location 3, fault current coming from the conventional power plant was also successfully limited. The results of fault currents at three locations with different DG units are summarized in Table I for comparison. Table I: Percentage change in fault currents of different DG units due to SFCL locations 3-Ph Distribution grid fault DG type
No SFCL
Location 1
Location 2
Location 3
Wind
787A
1020A 30% increased
1020A 30% increased
265A 67% decreased
Solar
2675A
1100A 59% decreased
1100A 59% decreased
800A 70% decreased
Diesel
916A
798A 13% decreased
798A 13% decreased
148A 84% decreased
4. CONCLUSION This paper presented a feasibility analysis of positioning of the SFCL in rapidly changing modern power grid. A complete power system along with a micro grid (having a wind farm, solar, diesel connected with the grid) was modeled and transient analysis for three-phase-to-ground faults at different locations of the grid were performed with SFCL installed at different locations of the grid. This placement of SFCL results in abnormal fault current contribution from the wind farm and other two sources such as solar
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