Short Circuit Current and Voltage Stability Analysis of a Realistic Generation System Using Fault Current Limiter and SVC

Transcription

1 Short Circuit Current and Voltage Stability Analysis of a Realistic Generation System Using Fault Current Limiter and SVC 1 Ezz Badry, 1 Salah Kamel, 1 Loai S.Nasrat, 1,2 Ziad M. Ali 1 Department of Electrical Engineering, Faculty of Engineering, Aswan University, Aswan, Egypt 2 Electrical Engineering Department, Faculty of Engineering, Prince Sattam Bin Abdualziz University, 54 Wadi eldawaser11991, Kingdom of Saudi Arabia Ezzeldin.badry@khalda-eg.com, skamel@aswu.edu.eg, loaisaad@yahoo.com, dr.ziad.elhalwany@aswu.edu.eg Abstract_ Due to the frequently increasing in loads, the generated power must be upgraded to match this increasing, consequently a new short-circuit level will be developed based on the value of the generation system upgraded, this raising on short-circuit current level could be extremely harmful on the protective equipment. To overcome the problem of the new S.C. level a new approach can be achieved by using the fault current limiter (FCL) which consider the most economical and practical solution. This paper investigates a realistic power plant Khalda Petroleum Company (KPC), which located at Egypt western desert. The main target is to add a new 7 MW Generator to an existing 14 MW power plant drawn by three Generators therefor a short-circuit study will be calculated after and before adding the new Generator. An adequate FCL will be selected to maintain the short-circuit within the previous levels, on the other hand the S.V.C. will be used to maintain the voltage level likewise the existing by carrying out the Load Flow analysis after adding the FCL, all operations will be executed using ETAP 12.6 software. Keywords Fault current limiter, Short Circuit, Load Flow, SVC, ETAP I. INTRODUCTION Catastrophically damage for all components of the power system will be occurs due to frequently increasing of loads which demanding increasing in system generation in the power plant so an increasing in the short circuit level may exceed the equipment breaking capacity. By using larger stepper transformer, the level of the voltage will be increase and so adequate the S.C. level and this will grantee the safety conditions for the equipment of the system, or by readjusting the existing protection scope to be matches with the new S.C. level. Actually, both solutions will be expensive to carry out because of the high equipment fees, so an economical and a practical solution is needed to solve this problem without any change in the existing protection relay scope in the power system. This work illustrates in details a realistic example of power plant consists of three generators and needed to add a new generator as per loading increases therefor Fault Current Limiter are being uses to maintain short circuit level, SVC will also be used as the voltage drops on the 3.3 KV switchgear Bus Bar due to using of the FCL. II. Fault Current Limiter (FCL). FCL is a nonlinear devices works on decreasing the amount of the fault current cause it has a high impedance that can be added to the electric circuit when fault take place. Some of FLC has low impedance at the normal operation change to high impedance device extremely fast once the faults happened, and before a circuit breaker take action to trip a few milliseconds later. The common condition that for different current limiters is the operation should be at the distribution voltage level [1], and the FLC could be classified into two main types as following: A. Passive Limiters: It is permanently connected in series with the circuit of the power system so no need to turn on or using an external signal to control its operation, the series inductors and superconducting fault current limiters are considered passive devices[2-4], Reactors are counted as the most common passive limiter and flexible to be connected anywhere in the distribution circuit. They are a linear inductive reactance; arithmetically the impedance will be added to the system to reduce of the fault currents, a voltage regulation carried out to maintain the distribution system voltage within the limits, due to voltage drop, which exists due to the current flow through the reactors, are in the same quadrature with the load voltage. The case under study with this type of FCL will be investigated in this work. Reference Number: JO-P

2 B. Solid State Limiters(SSL) During the fault case and after a few milliseconds of its action the solid state devices inserted by electronic switches to increase the system impedance and to limit fault currents. [5]. SSL is categorized into two main types: The resonance based devices and the impedance switched bypass limiters. The operation of resonance-based devices is based on that during the fault the voltage sags will be happened and will have a direct effect on the fault current values [6, 7]. The impedance switched bypass limiters connected in series with the main distribution line, a pair of GTO are shunted with it to operate during the voltage alternate half cycles to create a new path of low impedance. The GTO switches are closed due to the fault and a large impedance will be appeared and so limiting the current, but there are some disadvantages due to switching power loss and its reliability cause the switching times effects are under search and study to enhance [8-9]. III. SHORT CIRCUIT STUDY. A short circuit study is modeled to get the values of the Max. and Min., a new generator or Fault Current limiter is added and so the study will be updated and repeat the adding process until optimize the best efficient limiter which will contribute on limiting the fault current to the same values before adding the new generator. All S.C. calculations were carried by using ETAP 12.6 based on IEC [10-13], the associated standards classify short circuit currents according to their magnitudes (maximum and minimum) and classify the fault distances from the generator (far and near). Maximum short circuit currents determine equipment ratings, while minimum currents dictate protective device settings. Near-to-generator and far-from-generator classifications determine which of the AC components decrease in the calculation. IV. STATIC VAR COMPENSATOR OPERATION To provide the fast acting reactive power the static VAR compensator (SVC) is installed on high voltage transmission networks [14-15], SVCs are parts of the Flexible AC transmission system [16-17] device family, regulating voltage, power factor, harmonics and stabilizing the system, and here in our case study the SVC has to be used after adding the adequate fault current limiter to regulate the far end bus voltage which influence in stabilizing the system. V. RESULT AND DISCUSSION The power plant single line diagram is shown in Fig.3 consists of three existing generator, two 2MVA power transformers 11 KV/.4KV, two 2.5MVA power transformer 11KV/3.3KV, 14 medium voltage CBs mounted with its related protective devices, 4 CBs represent as incoming feeders from the 4 generators to the two main bus bars feeding the 11 KV switchgear, when the coupler will maintain always closed the operation of adding new generator of 10 MW will be implemented as per the following steps: A- Calculate the short circuit values on the main four buses and at the far end, six buses are depicted in table (1), from the table (1). The Max. Values of S.C. are KA at BUS 1 & 2. these values should be adequate to the breaking capacity of the protective devices such as the CB, CT and PT. Bus No. Table (1) Short-Circuit Summary GROUND FAULT Voltage B- Calculate the short circuit values for the previous buses after adding the new 7 MW generator which will certainly as a result on increasing the Max. Fault current as shown in table (2). Table (2) Short-Circuit Summary GROUND FAULT Bus No. Voltage Reference Number: JO-P

3 C- Adding the fault current reactor in series with both Generators 3&4 as in Fig. 1 Then calculate the new short circuit values as shown in table (3). The results show that the sufficient values of the Max. Fault current which dropped from8.312 KA to 7.43 KA resulting on adding new fault current limiter reactors. Table (3) Short-Circuit Summary GROUND FAULT Bus No. Voltage D- Preform the load flow analysis to check the voltage stability for all the mentioned buses and found all buses listed on table (4) in under voltage case which resulting of inserting series reactor on the circuit, this problem had been overcome by using Static Var Compensator at the far end bus#48 As shown in Fig. (1) Fig. (2) Shows the amount of current change before and after adding the new generator and after adding the fault current limiter. Fig. (1) SLD after adding the FCL Table (4) LF Marginal Alerts results Bus No. Condition Rating % operating 37 Under voltage Under voltage Under voltage Under voltage Under voltage Under voltage Under voltage Under voltage Under voltage Under voltage Reference Number: JO-P

4 VI. CONCLUSION Fig. (2) Fault current values in the three cases Fig (3) Single line diagram Upgrading generation station is one of the most required operations now days, due to the rapidly increased in loads, some of this stations were not prepared for upgrading and leading to risky rises in the fault current level, all equipment, which are dealing directly with the system current, must withstand this rises in S.C. level. To overcome this problem there are two direction one of them is rise the voltage level of the system and the other is increase the impedance of the faulty circuit, in this paper after adding new 10 MW generator to an existing system of 15 MW we trying to maintain the new fault current level to the same as was before adding the new generator thus we don t have to replace any of the system equipment, this minimizing of the fault current had been achieved by adding Reference Number: JO-P

5 limitation, in Power Engineering Society Winter Meeting, vol. 4. two of passive FLC (reactors / Z= 4 ohm) in series with the IEEE Power Engineering Society, Jan. 2000, pp two Generator 3&4,results show that the adding of FLC is [8] R. K. S. et al., Solid state distribution current limiter and able to control the fault current by increasing the impedance circuit breaker: Application requirements and control strategies, IEEE Transactions on Power Delivery, vol. 8, no. 3, pp of the system without adding or interrupting the circuit. The 1164, July fault current limiter is proved to be and effective technique [9] P. K. C. Meyer and R. W. DeDoncker, Design of a novel low to limit the current in the faulty network without any loss fault current limiter for medium-voltage systems, in Applied physical change in the structure of the network. Power Electronics Conference and Exposition, vol. 3. IEEE APEC, 2004, pp VII. REFERENCES [1] P. G. S. et al., The utility requirements of a fault current limiter, IEEE Transactions on Power Delivery, vol. 7, no. 3, pp , Apr [2] J. F. Amon, P. C. Fernandez, E. H. Rose, A. D Ajuz and A. Castanheira, Brazilian Successful Experience in the Usage of Current Limiting Reactors for Short-Circuit Limitation, International Conference on Power Systems Transients (IPST 05), Montreal, June 2005, pp [3] W. Paul and M. Chen, Superconducting control for surge currents, IEEE Spectrum, pp , May [4] B. W. Lee, J. Sim, K. B. Park and I. S. Oh, Practical Application Issues of Superconducting Fault Current Limiters for Electric Power Systems, IEEE Transactions on Applied Superconductivity, Vol. 18, No. 2, 2008, pp [5] D. Fedasyuk, P. Serdyuk, Y. Semchyshyn and Lviv Polytechnic National University, Resistive Superconducting Fault Current Limiter Simulation and Design, 15th International Conference, Poznan, June 2008, pp [6] Principles of Fault Current Limitation by a Resonant LC Circuit, vol IEE, Jan [7] C. S. Chang and P. C. Loh, Designs synthesis of resonant fault current limiter for voltage sag mitigation and current [10] IEC Short-Circuit Currents in Three-phase a.c. systems - Part 0: Calculation of Currents (including 2002 corrigendum 1) for systems up to 500kV. [11] IEC Short-circuit currents in three-phase a.c. systems - Part 1: Factors for the calculation of short-circuit currents according to IEC [12] IEC Electrical equipment - Data for short-circuit current calculations in accordance with IEC 909 (1988) [13] IEC Short-circuit currents in three-phase a.c. systems Part 4: Examples for the calculation of short-circuit currents [14] De Kock, Jan; Strauss, Cobus (2004). Practical Power Distribution for Industry. Elsevier. pp ISBN [15] Deb, Anjan K. Power Line Ampacity System. CRC Press. pp ISBN [16] Song, Y.H., Johns, A.T. Flexible ac transmission systems. IEE. ISBN [17] Hingorani, N.G. & Gyugyi, L. Understanding FACTS - Concepts and Technology of Flexible AC Transmission Systems. IEEE. ISBN Reference Number: JO-P