kV Superconducting Fault Current Limiter Research Articles

High Voltage Calculations for a 380 kV Superconducting Fault Current Limiter

High Voltage Calculations for a 380 kV Superconducting Fault Current Limiter

First Russian 220 kV Superconducting Fault Current Limiter (SFCL) For Application in City Grid

The superconducting fault current limiter (SFCL) for a nominal voltage of 220 kV and a rated current of 1200 A was developed by SuperOx company to be applied in high voltage substation in Moscow, Russia. The device is a three-phase dead-tank apparatus and is equipped with a closed-cycle cryocooling system. Liquid nitrogen serves simultaneously as a cooling and an insulating media. The device makes use of about 25 km of 12 mm wide high-performance 2G HTS wire with uniform properties along the length. High-voltage tests of the device were performed at Korea Electrotechnology Research Institute (KERI) in accordance with the IEEE C37.302-2015 test guide and Russian national standards for high voltage electrical equipment. The installation of the SFCL at substation in parallel with the existing air core reactors was completed in 2019. Since then, the device is in a daily operation. Over this period, SFCL has fully confirmed its design specifications including transmitting over 80 million kWh to customers and experiencing three fault current events.

10 kV AC test verification of the high temperature superconducting fault current limiter with bias magnetic field

Under the support of the China State Grid Corporation Science and Technology Project, a set of 10 kV superconducting fault current limiter (SFCL) with bias magnetic field including a high temperature superconducting a low inductance unit, a double split reactor, a fast breaker and its control system is designed and assembled in Hushitai high voltage center of Electric Power Research Institute of State Grid Liaoning Electric Power Co., Ltd. The 10 kV dedicated test including high voltage test, phase to phase short circuiting fault test, quench resistance measurement, quench recovery time measurement were performed in December 2019. The fault current distribution and voltage test results during the phase to phase short-circuit fault of the SFCL are presented and analyzed. Test results indicate that current limiting resistance of SFCL unit is about 1.21 Ω within 10 ms fault time. Those results meet the design requirement.

Comparison of Surface Flashover Characteristics of Rod and Rib Type Post Insulator for Extra-High Voltage Superconducting Fault Current Limiter

One of the most important insulating components for developing a 154 kV superconducting fault current limiter (SFCL) is post insulator, which supports 154-kV SFCL modules in a cryostat. In order to design an optimum post insulator, the top priority is to determine the creepage distance of post insulator. In our previous research, surface flashover voltages along smooth glass fiber reinforced polymer (GFRP) rods immersed in liquid nitrogen (LN2) were experimentally investigated. To reduce the cryostat volume, ribbed post insulators with increased creepage path were then considered. However, due to difficulties with producing ribbed GFRP post insulators, ribbed specimens were made of polytetrafluoroethylene instead. Four kinds of test specimens were prepared to determine the position and the number of ribs attached to the surface. From the experimental results, it was found that the ribbed insulator has shown better insulation performance in LN2 and number of ribs could affect the surface flashover voltage of post insulator. Consequently, ribbed model for 154-kV SFCL post insulator was designed and successfully tested. Finally, real 154-kV SFCL system with newly designed ribbed post insulator was installed and Basic Impulse Level (BIL) test and ac required withstand voltage were successfully carried out.

Development and Test of a Cooling System for a 154 kV Superconducting Fault Current Limiter

The superconducting fault current limiter (SFCL) is an electric power device that limits the fault current immediately in a power grid. Korea Electric Power Corporation (KEPCO) has been developing a 154 kV, 2 kA SFCL since 2011 to protect power grids from increasing fault current and improve the stability and quality of electric power. This SFCL adopts 2G YBCO wires and operates at 71 K and 5 bars. In this paper, a cooling system for the 154 kV SFCL and its cooling test results are reported. This cooling system uses a Stirling-type cooler to make sub-cooled liquid nitrogen (<TEX>$LN_2$</TEX>), which cools the superconductor modules of the SFCL. The <TEX>$LN_2$</TEX> is circulated between the cooler and the cryostat that contains superconductor modules. The <TEX>$LN_2$</TEX> also plays the role of a high voltage insulator between the modules and the cryostat, so the pressure was maintained at 5 bars for high insulation performance. After installation in a test site, the cooling characteristics of the system were tested. In this operation test, some important data were measured such as temperature distribution in <TEX>$LN_2$</TEX>, pressure change, performance of the heat exchanger, and cooling capacity of the total system. Consequently, the results indicate that the cooling system operates well as designed.

Demonstration of a Superconducting Fault Current Limiter in a Real Grid

A 22.9 kV superconducting fault current limiter (SFCL) has been in operation in a real grid in Korea. The SFCL is of hybrid type, in which the fault current is detected by a superconductor and bypassed by a high-speed switch to a reactor in a parallel circuit for current limitation. It has a current rating of 630 A, and has been operated in a distribution line in Icheon Substation, which is located in a suburban area with moderate loads. The SFCL has been operated very stably with no degradation in performance. Temperatures and level of the liquid nitrogen cooling the superconductors have been maintained within 0.1 K and 0.3 cm, respectively, under large daily load variation of about 100 A. Performance of the SFCL was tested by measuring minimum limitation current and impedance of the SFCL, and was proved to maintain the initial level of performance. There was a single line-to-ground fault event in the distribution line where the SFCL has been operated, and the SFCL limited the fault current successfully. Data analysis showed that the SFCL limited the current as designed. These results proved reliability and performance of the SFCL.

배전계통에 전력용 변압기 병렬운전시 22.9 kV SFCL Bus Tie 적용방안에 관한 연구

This paper analyzed the application of Superconducting Fault Current Limiter (SFCL) on 22.9 [㎸] bus tie in a power distribution system. Commonly, the parallel operations of power main transformers offer a lot of merits. However, when a fault occurs in the parallel operation of power main transformer, the fault currents might exceed the interruption capacity of existing protective devices. To resolve this problem, thus, the SFCL has been studied as the fascinating device. In case that, Particularly, the SFCL could be installed to parallel operation of various power main transformers in power distribution system of the Korea Electric Power Corporation (KEPCO) on 22.9 [㎸] bus tie, the effect of the resistance of SFCL could reduce the increased fault currents and meet the interruption capacity of existing protective devices by them. Therefore, we analyzed the effect of application and proposed the proper impedance of the R-type SFCL on 22.9 [㎸] bus tie in a power distribution system using PSCAD/EMTDC.

Analysis model development and specification proposal of hybrid Superconducting Fault Current Limiter (SFCL)

Concentrated power demand can cause a fault current problem in a real power system. The Superconducting Fault Current Limiter (SFCL) application is one of the solutions for this problem. At present, many projects for the development of SFCLs are being done actively throughout the world. In Korea, LS Industrial Systems Co., Ltd. (LSIS) and the Korea Electric Power Research Institute (KEPRI) are jointly developing a 22.9kV hybrid SFCL. It will be installed onto the Icheon 154kV substation for an actual distribution power system operation in 2010. It is very important to carry out some feasibility studies for the application of SFCLs to the real power system. For the accuracy of the results of these studies, it is necessary to develop an analysis model which considers the real operating mechanism of the SFCLs. In this paper, we developed an SFCL analysis model using the PSCAD/EMTDC program, which is commonly used in the transient analysis of power systems. The developed model realizes the operating mechanisms of the SFCL, including the superconductor quenching property, for fault current and temperature, based on the experimental data from the 22.9kV SFCL being developed by LSIS and KEPRI in Korea. This paper then conducts a technical analysis using the model and proposes specifications for the Current Limiting Resistor/Reactor (CLR) used for applying the SFCL to a real distribution power system in Korea.

Design and Experimental Results of Three-Phase Superconducting Fault Current Limiter Using Highly-Resistive YBCO Tapes

As one of the programs in the Ministry of Economy, Trade and Industry (METI) R&D project on coated conductors, we developed a three-phase 6.6 kV superconducting fault current limiter (SFCL) and conducted some evaluation tests. The developed SFCL mainly comprised a set of three-phase current-limiting coils installed in a sub-cooled nitrogen cryostat with a Gifford-McMahon (GM) cryocooler, circuit breakers, and a sequence control circuit. Two tapes were wound in parallel in each limiting coil to obtain a rated current of 72 A rms. AC characteristics of each coil were measured, and relevant performance metrics were obtained. The whole system was installed in a cubicle. Short circuit experiments were then conducted with a short circuit generator. In a three-line ground fault test, the SFCL successfully restricted a short circuit current of over 1.56 kA to about 840 A with an applied voltage of 6.6 kV. The system integration ability and the obtained data show the promise of this approach for practical implementation. The SFCL was ready for user field tests.

AC loss reduction of a 6.6 kV superconducting fault current limiter

The authors have been investigating a 6.6 kV superconducting fault current limiter (SCFCL) for use in power distribution systems. For practical application, heat load at 4.2 K must be reduced to a level which can be compensated by a small refrigerator. This paper describes AC loss reduction of a SCFCL coil, which is comprised of a conductor and junctions. The conductor is a cable of double-twisted multi-filament NbTi strands in a high-resistivity CuNi matrix. The filament diameter in strands and the filament twist pitch were reduced for AC loss reduction. Current junctions made of copper generate eddy current loss because an alternating magnetic field is applied on them by the conductor. It was confirmed experimentally that cylindrical-shaped junctions effectively reduced the loss. A total coil loss of 0.8 W at 1 kA has been achieved, which value is sufficiently low for the development of a closed cryostat of superconducting fault current limiter compensated by a small refrigerator.