DEVELOPMENT OF A TEST PROTOCOL FOR A 15 KV CLASS SOLID-STATE CURRENT LIMITER ABSTRACT Ashok Sundaram Electric Power Research Inc., USA asundara@epri.com The Solid-state Fault Current Limiter (SSFCL) is a new product for which no industry standard exists. This paper gives the overview of the effort to date to develop the test protocol for this new product. It involves the review of existing standards of several legacy electrical gears, survey of the high voltage test facilities, and review of Acceptance test criteria of several leading US-based Electrical Utilities. The resulting test protocol is a comprehensive document to apply to SSFCL to provide a reliable new product. INTRODUCTION Growth in the generation of electrical energy, increased penetration of distributed resources and increased interconnection of the networks leads to higher fault currents. This growth in capacity requires replacing existing circuit breakers with units with higher fault current ratings, incurring a major cost and down time. Higher fault current causes more stress on the system reducing the life of critical components such as transformers. According to Pat Duggan of Con Edison, Fault Current Limiting functionality is a critical enabler for open access for new transmission and generation, and more cost effective infrastructure upgrades and replacements. In addition fault current limiters can mitigate recovery time of superconducting cables and give selected DGs an advanced option to serve peak loads after external faults. [1] The SSFCL is a fault current limiter using solid-state technology providing active control of fault current limiting. In the event of fault SSFCL introduces the current limiting impedance till the fault is cleared. Mahesh Gandhi Silicon Power Corporation, USA mahesh_gandhi@siliconpower.com SSFCL Concept: Figure 1: SSFCL Concept Operation Normally the continuous current flows through the fast speed switch (Main SGTO) as shown in figure 1. Once the fault is sensed by high-speed sensor and declared by FPGA board, the current is commutated to Limiting Inductor (CLI). Introduction of CLI will limit the current to the level below the rating of the downstream breaker. The downstream breaker will trip and open the circuit within 30 cycles as shown in figure 2. Once the fault is cleared the SSFCL can perform Auto/Manual reset. SSFCL Fault Current Limiting Effect Figure 2: SSFCL limiting effect SSFCL Design Features The SSFCL incorporates the following features for ease of
operation, faster response, minimum system impact, improved reliability, better efficiency, and compact footprint. Immediate recovery Fail safe No line current distortions SGTO devices as shown in figure 3 Lower losses Reduced Overall size and weight Modular design expandable to desired Voltage & Current Ratings as shown in figure 4 & 5 Robust construction for outdoor applications with OFAF cooling, No cryogenics as shown in figure 6 Figure 5 SSFCL Power Stack Internal detail Figure 3: R&D100 Award Winner SGTO Device Figure 4 SSFCL Building Block Internal detail Figure 6: 1200A SSFCL Outline - 12 H 11 W 12 D, 40000 lbs
SSFCL Projects SSFCL units are under development for the following projects. 3 phase 15 kv, 1200A SSFCL funded by CEC to be field tested at Southern California Edison on their Avanti Circuit in 2009. 3 phase 15 kv, 4000A SSFCL funded by DHS to be field tested at ConEdison, New York, on their 3G Circuit of the Future in 2010. 1 phase 69 kv, 1000A SSFCL funded by DOE to be tested at an Independent Lab in 2009. SSFCL FIELD TEST CIRCUITS Con-Ed s 3G Circuit of Future SSFCL in 3G Circuit of Future provides fault current limiting in the bus-tie circuit between two substations as shown in figure 7 & 8. Figure 7 Con Edison 3G Application Figure 8 Con Edison 3G Circuit SCE s Avanti circuit of the future SSFCL in SCE s testing is to limit fault current in their innovative feeder circuit Avanti as shown in figure 9. Figure 9 SCE Avanti Circuit 15KV SSFCL PERFORMANCE REQUIREMENTS Parameters [2]-[7] Req t Maximum Voltage, kv rms 15.5 Max. Continuous Current, Ampere rms 1200/4000* Power Frequency, Hz 60 Available fault current, ka Sym. rms 23/11* Let-thru Current, Sym. ka rms 9/5.5* Let-thru Current Duration, cycles 30 Dielectric Withstand Partial discharge pc @19.5kV 100 Power Frequency 1 min, kv rms 50 Impulse, Full-wave, kv peak 110 Impulse, Chopped-wave, kv peak 142 Max. Ambient Temp, Degree C 50/40* Power Efficiency 99.75% Line Harmonic Distortion None Audible Noise 50dBA@20 /58dBA@6 *Application specific requirement POWER TEST LAB CAPABILITIES The capability of various power labs in USA was assessed. The following is the summary of their capabilities to perform the desired tests on the SSFCL. Partial discharge Test [8] Capability: to 40 kv Power Frequency Voltage Withstand Test 150 kv BIL/ Impulse Full-wave Voltage Withstand Test 1000 kv Impulse, Chopped-wave Voltage Withstand Test 1000 kv Max. Continuous Current/ Temp. Rise Test 300 ka at 1300 V AC, 3 phase
Full load Operation/ Power Efficiency/ Line Harmonics Distortions Test 38 kv, 5000 A Fault current limiting Test 1000 MVA (16 kv) or 2250 MVA (16 kv) generators available Audible Noise test Noise Unlimited, Bordentown, NJ EMI test Alion Science & Technology, R&B Lab, Conschohoken, PA 15KV SSFCL TEST PROTOCOL Qualification Testing (subject of this paper) Design Testing Utility Acceptance tests Pre-connection tests Field evaluation tests Production Testing DESIGN TESTING The following tests have been formulated based on review of the industry standards for switchgears used in T&D system. Dielectric Test [9], [12], [13], [14], [16] Insulation test by resistance measurement (Megger test) Insulation test by power factor measurement (Dobble test) Partial Discharge Test Power frequency Voltage Withstand Test Full-wave lightning impulse withstand voltage tests Chopped wave lightning impulse withstand voltage tests CLR resistance & impedance measurement Current Limiting Test Efficiency (power loss) Test Continuous Current Test/ Temperature Rise Test [10], [11] Audible Noise test EMI UTILITY ACCEPTANCE TESTS: The following tests have been derived from consultation with US based Utilities. Insulation test by power factor measurement (Dobble test) Insulation test by resistance measurement (Megger test) Partial Discharge test Full set of dielectric tests PRECONNECTION TESTS AT UTILITY SUBSTATION: The following are the tests US based Utilities prefer to perform before applying power to the SSFCL in the field. Visual Inspection Tank Pressure test Insulation/Dielectric tests Insulation test by power factor measurement (Dobble test) Insulation test by resistance measurement (Megger test) FIELD EVALUATION TESTING In the field SSFCL will be evaluated for it s performance under Steady-State and Transient (at fault) conditions DETAILS OF TEST PROCEDURES : The following sections provide details of the procedures for key tests. POWER FREQUENCY VOLTAGE WITHSTAND TEST Tests SSCL dielectric integrity against the continuous operating voltages [9], [16]. 60Hz sine-wave voltage of rated amplitude is applied for 60 seconds from SSFCL line terminals to ground. Leakage current is monitored as shown in figure 10. Wet test procedure - The wet tests are made only on outdoor SSFCL or on external components such as bushings, in accordance with the procedure described in IEEE Standard C57.19.00-1991 [15]. Note: For those bushings, where their voltage distribution is negligibly influenced by their surroundings, and which have been tested separately as individual bushings in accordance with IEEE Standard C57.19.00-1991, the tests need not be repeated on the assembled SSFCL. Figure 10 Power Frequency Voltage Withstand Test
FULL-WAVE IMPULSE WITHSTAND VOLTAGE TEST Tests to verify system s ability to withstand rated fullwave lightning impulse withstand voltages. Both positive and negative, lightning impulse voltages having a peak value equal or greater than the rated fullwave lightning impulse withstand voltage, as shown in figure 11 & 12, shall be applied between the terminals of the SSFCL and the ground / case as shown in figure 13. Waveform for lightning impulse tests per IEEE Standard 4-1978 [9] Waveform for full-wave Impulse Test Schematic for Full-wave Impulse Test Figure 13: Full wave impulse test CHOPPED-WAVE IMPULSE WITHSTAND VOLTAGE TEST Figure 11: Positive Impulse To verify their ability to withstand their assigned rated chopped wave lightning impulse withstand voltage. The waveforms, figure 14 & 15, and the application of the chopped wave test voltage, and the type of rod gap and its location, shall be as described in IEEE Standard 4-1978 [9]. The voltage shall be applied to the terminals of the SSFCL, without causing damage or producing a flashover, following the same procedure as for full-wave impulse test, as shown in figure 16. Waveform for Chopped-wave Impulse Test Figure 12: Negative Impulse Figure 14: Linearly rising front chopped impulse
RISE TESTS Test conditions Ambient Room temperature. Output 3phase bolted short. Input Voltage Variable low voltage enough to provide 25% and gradual rise to 50%-75% and finally to rated load current. Temperature. Monitoring Built in heatsink temperature. sensors Cooling liquid temperature (Top, Mid, and lower level) Tank (top, bottom, middle on both sides) Figure 15: Lightning Impulse chopped on the tail FAULT CURRENT LIMITING TEST Schematic for Chopped-wave Impulse Test Figure 16 Chopped wave impulse test FULL LOAD/ EFFICIENCY/ HARMONIC DISTORTION TESTS The purpose of the test is to evaluate the SSFCL performance for fault current limiting operation. The SSFCL is connected to the test set up as shown in figure 18 below. Test conditions Set source impedance for required available short circuit current. Set backup breaker for let-thru current for desired duration. Perform test starting with 25/50/75% of desired let-thru before hitting 100% of current. The purpose of the test is to evaluate the SSFCL performance for full load operation, power losses and harmonic distortion at various current levels using the circuit as shown in figure 17 below. Test conditions Input At the lower end of operating voltage range and higher end of input frequency. Output / load At 25%/50%/75% and rated load current and 0.85 lagging power factor. Figure 17 Efficiency Test CONTINUOUS CURRENT / TEMPERATURE Figure 18 Fault current Limiting Test PRECONNECTION TEST Visual Inspection Once received at site an external inspection of the SSFCL tank and fittings will be done which will include the following points: 1. Is there any indication of external damage? 2. Is the paint finish damaged? 3. Are the attached fittings loose or damaged? 4. Is there evidence of fluid leakage on or around the tank coolers? 5. Are any of the bushings broken or damaged?
6. Is there any visible damage to the parts or packaging which shipped separately from the SSFCL? Tank Pressure The tank pressure may be positive or negative when received, depending on liquid temperature. In some cases, the vacuum pressure gauge may read zero, which could indicate a tank leak. In such cases, it is recommended to contact manufacturer before installation. Dielectric tests Dielectric tests are the group of tests during which the SSFCL will be subjected to higher voltage levels and therefore higher voltage stresses than would normally be experienced in service. The purpose is to confirm that the design, manufacture and processing of the SSFCL and insulation structure and materials are adequate to provide many years of satisfactory life. Recommended test is power frequency voltage withstand at reduced level to 75% of rating. FIELD PERFORMANCE EVALUATION The objective of this test is to evaluate the SSFCL performance in the field under Steady-State and transient condition of the system in which the SSFCL is connected (see figure 19 & 20). Test Monitoring Steady state voltage and current sensors. High speed voltage and current sensors. Power Monitor and data recorder Temperature and Pressure Sensors Figure 19 Field Evaluation Sequence of Operation Commissioning: Close Bypass Switch. Close Load Disconnect Switch. Close Line Breaker. Open Bypass switch. Turn-on SSFCL. Decommissioning: Turn-off SSFCL. Close Bypass switch. Open Line Breaker. Open Load Disconnect Switch. Figure 20 Field evaluations Test Real time monitoring Temperature Alarm Pressure alarm Power monitoring - V, I, kva, kvar Gas relay alarm Fault data records Site Requirements AC Aux Power Internet Access for support during field testing Working Space REFERENCES [1] Pat Duggan, Con Edison (private communication) [2] ANSI C37-04 [3] ANSI C57.16 [4] ANSI C57.12.01 [5] ANSI C57.12.90 [6] Con Edison General Engineering Specifications (private communication) [7] SCE Specifications (private communication) [8] KEMA Labs (private communication) [9] IEEE Standard 4-1978 [10] IEEE Standard C37.04-1999 [11] IEEE Standard 119-Aug. 1950 [12] IEEE Standard C57.113-1991 [13] IEEE Standard 454-1973 [14] IEEE Standard C57.12.00-2006 [15] IEEE Standard C57.19.00-1991 [16] IEEE Standard C37.20.2-1993
MISCELLANEOUS Acknowledgments The authors would like to acknowledge the support of the following individuals for their contributions to the SSFCL project and in development of the test protocol. Gil Bindewald, DOE Pat Murphy, DHS Lloyd Cibulka, CIEE Nancy Henderson, AMSC Pat Duggan, Pat Di Lillo, and John Isecke, Con Edison Syed Ahmed, Alan Hood and Ed Kamiab, SCE Professor Keyue Smedley, UCI Dr. Mischa Stuerer, FSU Rob Warren, KEMA Labs