Seungje Lee

Stability analysis of a power system with superconducting fault current limiter installed

As a process of developing high temperature superconducting fault current limiter (SFCL), the stability of a power system in which SFCLs were installed was analyzed. For the investigation into the effect of SFCLs to a power system, we have proposed a simple model power system that had SFCL circuits. The modeling parameters of SFCL are obtained by experiment of a prototype SFCL, which is 440 V class and a shielding type model. This electric circuit was solved for transient performance by numerical methods. In case the SFCLs are installed in a power system, it can effectively protect synchronization both in a symmetrical three-phase fault and a single-phase line to ground fault by maintaining synchronism of the synchronous machines for a long time. By this analysis, we found a quantitative effect of SFCLs to a power system. Limiting fault currents means not only an improvement of circuit breaker abilities but also a protection of synchronism. So its synchronism protection property must be considered for a design of superconducting fault current limiters.

Test of DC reactor type fault current limiter using SMES magnet for optimal design

This paper deals with the operational characteristics of a three-phase DC reactor type fault current limiter (FCL) at a short-circuit test. This type FCL consists of transformers,. diodes, and a superconducting coil. In this paper, a superconducting coil, low-Tc SMES magnet, is made of Nb-Ti and the power system of the experimental circuit is 400 V/7 A class. This is a preliminary step to develop its faculties for applications to high voltage transmission line. As the results of the experiment, the values are referred to the limitation rate about 77% and 90% when the turns ratio of transformer was 1 and 2, respectively.

Design, fabrication, and test of high-Tc superconducting DC reactor for inductive superconducting fault current limiter

A high-T/sub c/ superconducting (HTS) DC reactor has been developed as a part of DC reactor type superconducting fault current limiter (SFCL) rated on 6.6 kV/200 A. The DC reactor was a solenoid coil and was wound with a 4-parallel stacked tape. This coil has 5 layers which are connected in series each other. The inductance of the coil is about 84 mH. This paper deals with the design, fabrication and testing of the DC reactor. For this design of the coil, a prototype solenoid coil had been used. Using the experimental result of a prototype solenoid, the number of stacks and the inductance were designed. The winding machine for the HTS solenoid was manufactured. Using this machine, the large-scale HTS solenoid using a Bi-2223 tape was fabricated successfully. Characteristics of the fabricated coil were observed through a measurement of voltage as current transportation.

A variation of impedance of a high-Tc superconducting fault current limiter with an open core

The high-Tc superconducting fault current limiter (SFCL) is studied worldwide to be classified into a resistive type and an inductive type such as a magnetic shielding type and a DC reactor type. The high-Tc SFCL with an open core belongs to the magnetic shielding type SFCL. Unlike conventional magnetic shielding type SFCLs, it uses the open core to reduce the mechanical vibrations and installed space. The high-Tc SFCL with an open core was designed and manufactured by stacking three BSCCO-2212 tubes and it was tested in the maximum source voltage of 400 Vrms and the results such as the reduction of fault current and impedance of the SFCL are described in this paper. The results show that the fault current in the source voltage of 400 Vrms was reduced to be about 123 A peak and it is about 3.9 times as the normal state current. Also, the impedance of the high-Tc SFCL was about 9 /spl Omega/ to be about 9 times the normal state impedance. The impedance of the SFCL appears just after the fault, and the size of it is dependent on the source voltage. From the impedance, the inductance of the SFCL was calculated.

Development of 6.6 kV-200 A DC reactor type superconducting fault current limiter

As a part of the 21st Century Frontier R&D Program in Korea being performed from 2001, a DC reactor type superconducting fault current limiter (SFCL) is being developed. The target of the first phase is to develop a 6.6 kV/200 A class 3-phase SFCL as a prototype for a 154 kV class. This prototype SFCL has a magnet wound with a high-T/sub c/ superconducting wire (Bi-2223) operating at 65 K. The magnet uses solenoid bobbins with grooves for the tape wire. Its inductance is about 84 mH. An AC-DC power converter was made with light trigger thyristor (LTT) having a phase controller. The maximum voltage is 7 kV. The DC reactor, which is cooled by sub-cooled nitrogen, uses a three phase transformer with dual tap for series connection with a power line. Through several experiments this SFCL shows current limiting performance about 50% of short circuit current at short run tests.

Design and characteristic analysis of a rod type high-Tc superconducting fault current limiter through electromagnetic analysis

The existence of large air gaps, between a high-Tc superconducting (HTS) tube and an iron core, or between a primary winding and a HTS tube, possibly causes some undesirable voltage drops under the condition of normal operation. It makes the power system unstable. For this reason, the optimization of air gaps is essential in designing a high-Tc superconducting fault current limiter (SFCL). In this paper, the optimal values of air gaps are determined through electromagnetic analysis, and the comparison between computational and experimental results is provided.

Design and test of modified bridge type superconducting fault current limiter with reverse magnetized core

To develop a DC reactor type Superconducting Fault Current Limiter (SFCL), the most important elements are superconducting magnets or inductors. Recently large size magnets have been developed, according with the improvement of high temperature superconducting wire. In the DC reactor type SFCL, the purpose of a magnet is to store the generated electric energy of the power system immediately after a fault. Therefore most inductors are designed with an air core since the magnetic core inductor is too easy saturated to absorb the energy. Therefore the inductor consumes so much superconducting wire to make a large inductance and these expensive coils are a weak point of the DC reactor type SFCL. To solve this problem, the Reverse Magnetization Bias (RMB) method is introduced. The energy capacity of magnetic core is expanded to several times. With a shorter length of HTC superconducting wire, a much improved effect was obtained in the 40 V prototype SFCL.

Characteristics of critical current of high-T/sub c/ superconducting magnets wound with various tensions

High-T/sub c/ superconducting fault current limiters (SFCLs) with a DC reactor limit fault currents using the inductance of the DC reactor. Therefore, manufacture of the DC reactor is very important in developing this type of SFCL. The DC reactor makes use of high-T/sub c/ superconducting (HTS) magnets. Because high-T/sub c/ superconducting wires are rectangular tape and contain ceramic compounds, the winding method and the tension control of the HTS magnet are different from those of normal conductor magnets. In this research, we design and manufacture a winding machine for HTS magnets. We fabricate four HTS magnets wound with various tension. Characteristics of the fabricated magnets are observed through measurements of critical currents. This paper suggests an optimal winding method of HTS magnets.

Design, fabrication techniques and test results of 1.2 kV/80 A inductive fault current limiter by using conduction-cooled system

Abstract An inductive superconducting fault current limiter protects power system by limiting the amplitude of fault current by the inductance of its dc reactor. Therefore, it is very important to design the dc reactor of high critical current prior to fabrication. At first, the optimal design parameters were calculated by using finite element method and then the superconducting dc reactor for 1.2 kV/80 A rms inductive superconducting fault current limiter was designed by considering the conduction-cooling characteristics. Moreover, the design, fabrication and conduction-cooling method of the superconducting dc reactor were introduced. Actually, the superconducting dc reactor was fabricated and cooled down to 20 K by using GM cryocooler. Finally, the short-circuit test was performed and the experimental results were discussed.

Current sharing in multi-stacked HTS solenoid coil

The high-temperature superconducting (HTS) electric equipment using Bi-2223 wire successfully commercialized 1st generation HTS wire, has been developing by many research groups. HTS coil is one of the most important parts in HTS electric equipment. To enlarge the critical current, the operating temperature of the equipment tends to go down and number of HTS wire tends to increase. Thus, it is very important to determine the whole critical current of HTS coil for the stable operation of HTS equipment. The whole critical current of multi-stacked wire of HTS solenoid coil is not equal to the sum of the critical current of each stacked wire because of nonuniform current sharing occurs in multi-stacked HTS wires and each HTS path does not has the same critical current. In this paper, current sharing in two types of 5-stacked HTS solenoid coils, made up of 1 copper layer which is a current buffer layer of HTS coil and 4 HTS wire layers, was analyzed. One was wound with Bi-2223 wire insulated with polyimide tape and the other was wound with noninsulated Bi-2223 wire. All of the Bi-2223 wires were reinforced with stainless steel. The simulation results of current sharing in multi-stacked HTS coils coincided well with the experimental results. Based on these results, the current sharing ratio of large scale HTS coil was also expected. The copper layer acted as a good current path when all the HTS wires were quenched.