Determination of the Optimal Location of Superconductive Fault Current Limiter in a Power System with Grid Connection

Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 2013 416 Determination of the Optimal Location of Superconductive Fault Current Limiter in a Power System with Grid Connection Maria Reshel Paul and Dr.M.V. Jayan Abstract Superconducting fault current limiter (SFCL) is an innovative electrical device which is connected in series in power grid for the reduction of abnormal fault current. The existing generating stations in a particular area or locality are not sufficient to provide a continuous supply to the customers. In such a case grid connection helps to solve this issue and to provide supply round the clock. In this paper, a resistive type SFCL was modeled using Simulink, SimPowerSystem blocks in Matlab. In addition, typical power grid model including generation, transmission, distribution network and grid connection was modeled to determine the effect of grid on the positioning of SFCL and its performance. Both symmetrical and unsymmetrical faults were considered at different locations in power grid. The performances of SFCL were studied and the results were compared and analyzed in the power system with grid, with and without SFCL. Keywords Generating Station, Optimal Location, Power Grid, Resistive SFCL, Transmission Line, Superconducting Fault Current Limiter G I. INTRODUCTION RID connection will increase the complexity of the power system. Due to grid connection, the total impedance of the system decreases thereby increasing the fault current. It is possible to draw any amount of electrical energy from the grid. Grid connection has got a lot of advantages such as the reducing the reserve generation capacity in each area. The other advantages are the Random diversity, Savings from time zone, Transmission of peak off power, Flexibility to meet unexpected emergency load. Generation sources and loads are connected via Transmission line. It posses very low impedance. This will helps to maintain a stable fixed system voltage in which the current changes according to the system loads. The advantage of this is that loads are independent of each other, which allows the system to operate stably when loads change. But the major drawback of the low interconnection impedance is that very large fault current (5 to 20 times the rated) will develop in the power system during any fault or disturbances. These faults may lead to power failure. In order to provide the customer a continuous power supply round the clock and to reduce customer downtime a fault current limiter is essential. Superconducting fault current limiter (SFCL) is an innovative electric equipment. It will capable to reduce the fault current within the first cycle of fault [1]. This first-cycle suppression of fault current by a SFCL will results in an increased transient stability of the power system [2]. SFCL also provide the electric power system an effective damping to improve its dynamic response [3]. SFCL is a series device which will offer a very low (almost zero) impedance to current under normal conditions. During a fault, the impedance must rapidly increases to a predefined value to limit the current. It can be treated as a normally closed switch which is in parallel with a resistor. SFCL can be installed in different locations such as generator side, power station auxiliary, network coupling, busbar coupling, shunt current limiting reactor, transformer feeder, coupling closed generating unit, closed ring circuit. The resistive SFCL can improve the reliability of the system [3]. The location and the resistance value of SFCL is very important otherwise it can result in adverse effect. This paper is organized as follows. The simulation set-up of the power system model with grid and resistive SFCL is described in section II. Section III discusses the result and analysis. Finally conclusions are given in section IV. II. SIMULATION SET-UP POWER SYSTEM MODEL Matlab/Simulink/SimPowerSystem was used to design and model the SFCL model. A complete power system with grid connection including generation, transmission, and distribution system was implemented in it. A. Power System Model A portion of the Kerala State Electricity Board (KSEB) network was modeled for the study. The power system model is designed in Simulink/SimPowerSystem. Maria Reshel Paul, M.Tech Student, Dept. of Electrical & Electronics Engg, Govt. Engineering College. Thrissur, Kerala, India. E-mail: mariareshel@gmail.com Dr.M.V. Jayan, Assistant Professor, Dept. of Electrical & Electronics Engg, Govt. Engineering College. Thrissur, Kerala, India. E-mail: jayan@gectcr.ac.in

Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 2013 417 In the power system with grid connection simulation model, consist of 15 numbers of generating station with sixty four energy sources, Sixty power transformer, twenty one 220 kv buses, twenty three 110 kv buses, six 66 kv buses, 11 kv buses, load and a 400 kv grid. The power system is composed of fifteen numbers of power plant, composed of three phase synchronous machine, connected with distributed parameter transmission line through a step up transformer. The single line diagram of the simulation set up for the power system with grid connection is shown in the Fig.1. All the electric power plant produces a voltage of 11 kv. The voltage generated at Idukki, Lower Periyar, Kayamkulam and Sabarigiri generating stations are stepped up to 220kV and transmitted to different substations and generating stations. At the substation, the voltage is either stepped down to 11 kv to supply the high power industrial load and low power domestic load through separate feeders or to 110kV to different substation to transmit the power to different location. The voltage generated at Brahmapuram, Edamalayar, Kuttiady, Nallalam, Neriyamangalam, Poringal and Sholayar generating stations are stepped up to 110 kv and transmitted to different substations and generating stations. At the substation, the voltage is stepped up to 220 kv to transmit the power to different location or it can be stepped down to 11 kv to supply the high power industrial load and low power domestic load through different feeders. The voltage generated at Kallada, Pallivasal, Panniyar and Sengulam generating stations are stepped up to 66 kv and transmitted to different substations and generating stations. At the substation, the voltage is stepped up to 110 kv to transmit Fig. 1 Single line diagram of the power system with grid the power to different location or it can be stepped down to 11 kv to supply the high power industrial load and low power domestic load through separate feeders. B. Resistive SFCL Model A resistive SFCL unit is shown in Fig.2. A resistive SFCL consist of a stabilizer resistance of the nth unit, Rns(t) and the superconductor resistance of the nth unit, Rnc(t), both are connected in parallel; and the coil inductance of the nth unit, Ln [3]. The subscript n denotes the number of units connected. Fig.2 Structure of Resistive SFCL The superconductor resistance of the nth unit, R nc (t), become nonzero time-varying parameters due to the large fault current. The value of L n has to be as small as possible in order to reduce the ac loss under a normal condition. It is a usual practice to have a coil with very low value of inductance. Therefore, the value of L n is very small so that its effect can be neglected. The working of SFCL can be explained as follows. First, SFCL model calculates the root mean square value of the current and then compares it with the constant. Constant is that current which is allowed to flow through the power system safely (permitted rated current). Then, if the passing current is greater than the constant current level, SFCL s resistance will

Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 2013 418 increases to the maximum impedance level in a pre-defined response time. Finally, when the current level falls below the permitted rated current level, then the system waits until the recovery time and then goes into normal state. III. RESULT AND ANALYSIS The internal generation in our state is not sufficient to meet our demand. Normal practice is to purchase electrical energy from the central generating station. Unfortunately both the power from the internal and the central generating station are not sufficient to meet our demand. The remaining energy is purchased either through Power Exchange of India or India Energy Exchange. This electrical energy is transmitted to our state through the grid. If we are having surplus of energy, it can be sold to other state through this grid. Therefore the grid connection play a major role along state wise and country wise in electricity market in order to provide the customer a continuous power supply. It is possible to install SFCL in different locations where it will offer technical and economical benefits. In this work, SFCL is installed in the entire generating stations and the 400 kv grid for different fault location in the power system. Twenty five fault locations were considered, which can be categorized into three. They are the fault at customer grid, transmission line and the generating station. Here the discussion is only three from each category. Both symmetrical and unsymmetrical fault has to be considered. The faults are three phase to ground fault, phase to phase fault and phase to ground fault. In power system with grid, SFCL is installed in the entire generating stations and at the 400kV grid. In this power system, I have considered fifteen numbers of generating stations which will generate a total power of 2916 MVA. At grid a conventional power plant is connected which will generate a power of 830 MVA. Power factor is considered to be 0.85. Therefore the total generation is 3184 MW. Total connected load is 2989 MW. Transmission loss is considered as 3.05% (Information from KSEB load dispatch centre Kalamassery). 92 MW of energy is taken as transmission loss. Sum of load and transmission loss is equal to 3081 MW. Fig.3 The Current waveform for a three phase to ground, phase to phase and phase to ground fault without SFCL and with SFCL at Idukki generating station and fault at Sengulam generating station Rarely occurring fault in the transmission line will result in a very large fault current. The majority of the fault will occur in the distribution section. During the fault in transmission line, the current is drawn from the generating stations will increase. This is mainly due to the change in impedance of the power system network. It is very important that the system has to be stable at this condition. SFCL will reduce the fault current within in the first cycle of the fault itself, which will helps in maintaining the security and stability of the power system. The current waveform for a three phase to ground, phase to phase and phase to ground fault without SFCL and with SFCL at Idukki and the fault occurring at Sengulam generating station is shown in Fig.3. The fault current in different buses with and without SFCL is shown in Table.I. The minimum value of the fault current is shown by bold letters with underlined. The percentage change in fault current in different buses when SFCL is kept at different generating station and 400kV grid is shown in Table.II.

Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 2013 419 Table 1: Fault Current under Normal Condition during three phase to ground fault Without SFCL 1871 280.4 18615 1104 8804 2685 4935 3202.7 527.6 1731 5549 369.7 Bhramapuram 1861 274 18573 1093 8806 2654 4934 3201 526 1729 5537 369 Edamalayar 1867 280 18594 1102 8810 2681 4935 3164 523 1727 5545 369 Idduki 1326 280 1679 1102 8802 2474 4868 2526 372 1709 4898 365 Kallada 1869 284 18607 1108 8801 2691 4934 3177 527 1730 5547 369 Nallalam 1870 280 18615 1103 8813 2684 4935 3175 527 1731 5549 369 Kuttaidy 1870 280 18614 1103 8801 2684 4934 3175 527 1731 5549 369 Lower Periyar 1867 278 18597 1098 8801 2669 4935 3188 527 1730 5544 369 Neriyaangalam 1865 279 18582 1102 8801 2679 4934 3172 526 1731 5539 369 Kayamkulam 1866 281 18595 1066 8801 2718 4934 3183 527 1730 5543 369 Pallivasal 1871 281 17882 1104 8812 2685 4934 3182 527 1311 5088 369 Panniyar 1867 280 18528 1103 8801 2681 4935 3169 526 1721 5531 416 Poringalkuthu 1866 280 18521 1102 8801 2680 4934 3175 526 1720 5529 367 Sabarigiri 1864 301 18583 1110 8811 2709 4934 3184 526 1730 5540 369 Sengulam 1868 280 18172 1103 8135 2683 4934 3175 526 1731 5498 369 Sholayar 1868 280 18544 1103 8810 2721 3302 3176 526 1724 5533 368 Grid 1777 310 18271 1050 10142 2572 5949 3352 513 1727 5451 369 SFCL placed at Table II: the percentage change in fault Current under normal condition during three phase to ground fault Bhramapuram 0.534 2.282 0.226 1.014-0.019 1.158 0.028 0.05308 0.303 0.115 0.220 0.1893 Edamalayar 0.214 0.143 0.113 0.199-0.064 0.153 0.008 1.2083 0.872 0.231 0.076 0.1893 Idduki 29.13 0.143 9.793 0.199 0.026 7.862 1.366 21.129 29.49 1.271 11.73 1.2713 Kallada 0.107-1.283 0.043-0.344 0.037-0.219 0.028 0.8024 0.114 0.058 0.040 0.1893 Nallalam 0.053 0.143 0 0.109-0.098 0.041 0.008 0.8648 0.114 0.0036 0.1893 Kuttaidy.0534.1426.0053.1086.0374.0409.0283 0.8648.1137 0.0036 0.1893 Lower Periyar.2137.8559.0966.5614.0374.5996.0081.4589.1137.0577.0937 0.1893 Neriyaangalam.3206.4992.1772.1992.0374.2271.0284 0.9585.3032 0.1838 0.1893 Kayamkulam.2672-0.213.1074 3.459.0374-1.225.0283 0.6151.1137.0577.1117 0.1893 Pallivasal 0-0.214 3.938.0181-0.087.0037.0283 0.6463.1137 24.26 8.311 0.1893 Panniyar.2137.1426.4673.1087.0374.1526.0081 1.0522.3032.5777.3279-12.523 Poringalkuthu.2672.1426.5049.1992.0374.1899.0283 0.8648.3032.6354.3640 0.7303 Sabarigiri.3741-7.346.1719-0.525-0.076-0.890.0283 0.5838.3032.0577.1657 0.1893 Sengulam.1603.1426 2.379.1086 7.602.0782.0283 0.8648.3032 0.9226 0.1893 Sholayar.1603.1426.3814.1086-0.064-1.337 33.09 0.8336.3032.4043.2919 0.4598 Grid 5.024-10.56 1.848 4.909-15.19 4.212-20.54-4.6619 2.767.2310 1.769 0.1893 From the Table.II it is clear that, best place to keep SFCL at Idukki generating station except some of the fault at 220 kv transmission line. In some cases the fault current with SFCL is greater than the fault current without SFCL. Because of this, it is very essential to do the analysis of the SFCL at two different positions. In this condition a total of 120 cases will be there. From that 6 cases were selected. These 6 cases is obtained from the Table.1 i.e. the optimal location at different fault condition. 1. Idukki Brahmapuram 2. Idukki Grid 3. Idukki Lower Periyar 4. Idukki Pallivasal 5. Idukki Sengulam 6. Idukki Sholayar The fault current in different buses with and without SFCL when SFCL is installed at two different location is shown in Table.III. The minimum value of the fault current is shown by bold letters with underlined. The percentage change in fault current in different buses when SFCL is kept at different generating station and 400 kv grid is shown in Table.IV.

Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 2013 420 The fault current has reduced much more than the current when SFCL is kept at single position. The fault current is always less than the fault current without SFCL. Here we can conclude that the optimal location of the SFCL is found to be at Idukki and grid. As the number of SFCL in the power grid increases, the fault current has reduced very much. But cost is directly proportional to number of SFCL i.e. cost increases with increase in the number of SFCL. Table I: Fault Current under Normal Condition during three phase to ground fault Without SFCL 1871 280.4 1435 2723 1104 1229 773.4 506.1 434.5 1731 5549 370 Idduki - Bhramapuram 1316 227 1413 1735 1080 963 631 377 428 1708 4885 365 Idduki - Grid 1222 280 1274 1677 1003 900 608 370 424 1701 4777 361 Idduki - Lower Periyar 1322 262 1413 1738 1100 942 632 379 428 1708 4893 365 Idduki - Pallivasal 1329 234 1414 1745 1053 935 614 393 429 1429 4460 367 Idduki - Sengulam 1324 235 1414 1741 1017 935 623 371 428 1709 4847 365 Idduki - Sholayar 1323 262 1414 1738 1100 925 624 448 428 1702 4882 364 Table IV: The percentage change in fault Current under normal condition during three phase to ground fault Idduki - Bhramapuram 29.66 19.04 1.547 36.27 2.192 21.66 18.412 25.509 1.496 1.328 11.97 1.271 Idduki - Grid 34.69 0.143 11.23 38.40 9.165 26.80 21.386 26.892 2.417 1.733 13.92 2.353 Idduki - Lower Periyar 29.34 6.562 1.547 36.16 0.380 23.38 18.283 25.12 1.496 1.329 11.83 1.271 Idduki - Pallivasal 28.97 16.55 1.477 35.91 4.637 23.95 20.610 22.35 1.496 17.45 19.63 0.730 Idduki - Sengulam 29.24 16.19 1.477 36.05 7.897 23.95 19.447 26.69 1.266 1.270 12.65 1.271 Idduki - Sholayar 29.29 6.562 1.477 36.16 0.380 24.77 19.317 11.48 1.496 1.675 12.02 1.541 The optimal location of SFCL for the power system with gird is at Idukki generating station. If we are an option for the second SFCL, then it can be placed at the 400 kv grid. IV. CONCLUSION A complete power system with 400 kv grid, containing fifteen numbers of generating stations was modelled and transient analysis for the symmetrical and unsymmetrical faults at different locations were performed with SFCL installed at different generating station. SFCL suppress the fault voltage and reduces the fault current which will decrease the short circuit stress on the network. The best position of the SFCL is found to be at Idukki generating station for the power system with grid connection when we are keeping the SFCL at single position. In some cases it is observed that the fault current with SFCL is greater than the fault current without SFCL. Grid is assumed to be an infinite source of energy which will provide sufficient active and reactive power to the circuit. The fault current has reduced drastically when SFCL is kept at two positions. The fault current is always less than the fault current without SFCL. Here we can conclude that the best position of the SFCL was found to be at Idukki and 400 kv grid. From the analysing of transient behaviour it is very clear that the power system will improve power quality, to decrease energy dissipation and to reduce the stress on system equipment. REFERENCES [1] T.Jamasb, W.J. Nuttall, and M.G. Pollitt, Future Electricity Technologies and Systems. Cambridge: Cambridge Univ. Press,2006, pp. 83-97, 235-246. [2] C. Sung, D. K. Park, J. W. Park, and T. K. Ko, Study on a series resistive SFCL to improve power system transient stability: Modeling, simulation and experimental verification, IEEE Trans. Industrial Electron., vol. 56, no. 7, pp. 2412 2419, Jul. 2009. [3] Byung Chul Sung, Dong Keun Park, Jung-Wood Park and Tae Kuk Ko, Study on Optimal Location of a Resistive SFCL Applied to an electric Power Gid, IEEE Trans. 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