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

Transcription

1 Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 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. mariareshel@gmail.com Dr.M.V. Jayan, Assistant Professor, Dept. of Electrical & Electronics Engg, Govt. Engineering College. Thrissur, Kerala, India. jayan@gectcr.ac.in

2 Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 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

3 Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 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 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.

4 Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF Table 1: Fault Current under Normal Condition during three phase to ground fault Without SFCL Bhramapuram Edamalayar Idduki Kallada Nallalam Kuttaidy Lower Periyar Neriyaangalam Kayamkulam Pallivasal Panniyar Poringalkuthu Sabarigiri Sengulam Sholayar Grid SFCL placed at Table II: the percentage change in fault Current under normal condition during three phase to ground fault Bhramapuram Edamalayar Idduki Kallada Nallalam Kuttaidy Lower Periyar Neriyaangalam Kayamkulam Pallivasal Panniyar Poringalkuthu Sabarigiri Sengulam Sholayar Grid 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.

5 Proceedings of International Conference on Materials for the Future - Innovative Materials, Processes, Products and Applications ICMF 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 Idduki - Bhramapuram Idduki - Grid Idduki - Lower Periyar Idduki - Pallivasal Idduki - Sengulam Idduki - Sholayar Table IV: The percentage change in fault Current under normal condition during three phase to ground fault Idduki - Bhramapuram Idduki - Grid Idduki - Lower Periyar Idduki - Pallivasal Idduki - Sengulam Idduki - Sholayar 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 , [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 , Jul [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. Applied Superconductivity.,vol. 19, no.3, pp , June [4] Umer A. Khan, J.K. Seong, S.H. Lee, S.H. Lim, and B.W. Lee, Feasibility Analysis of the Positioning of Superconducting Fault Current Limiters for the Smart Grid Application Using Simulink and SimPowerSystem, IEEE Trans. Applied Superconductivity.,vol. 21, no.3, pp , June [5] S. Sugimoto, J. Kida, H. Arita, C. Fakui, and T. Yamagiwa, Principle and characteristics of a fault current limiter with series compensation, IEEE Trans. Power Delivery, vol. 11, no. 2, pp , Apr [6] L. Dessaint, K. Al-Haddad, H. Le-Huy, G. Sybille, and P. Brunelle, A power system tool based on simulink, IEEE Trans. Industrial Electron., vol. 46, no. 6, pp , Dec [7] Vinod Gupta, U. C. Trivedi, N. J. Buch, Solid State Electronic Fault Current Limitert to Limit the Fault Current in Power System, Electrical Research & Development Association, Vadodara [8] U.M.Mohana, S.T.Suganthi, Performance Analysis of Superconducting Fault Current Limiter (SFCL) in Single Phase and Three phase Systems, International Journal of Communications and Engineering Volume 01 No.1, Issue: 01 March2012.