Duck Kweon Bae

Manufacture and Test of Small-Scale Superconducting Fault Current Limiter by Using the Bifilar Winding of Coated Conductor

Superconducting fault current limiters (SFCLs) have been developed by many research groups. However, there is no standard for current limiting device. Recently, YBCO coated conductor (C.C.) which is named as 2nd-generation wire has been developed rapidly. YBCO C.C. has many advantages for applying to fault current limiting material. In this paper, a bifilar winding type SFCL was manufactured using YBCO C.C. The bifilar coil was wound as pancake type, and the length of C.C. tape used was 8 m. The short-circuit test of the SFCL was performed successfully rated on 30V/80A. The SFCL had a very low impedance in normal operation and limited the fault current effectively when a fault occurred. From the result, it could be confirmed that the bifilar winding type FCL using YBCO C.C. is feasible. Large-scale SFCL using C.C. should be developed in the future

The short-circuit characteristics of a DC reactor type superconducting fault current limiter with fault detection and signal control of the power converter

In general case of DC reactor type superconducting fault current limiter (SFCL), a fault current gradually increases during the fault. It takes above 5 cycles to cut off the fault in the existing power system installed the conventional circuit breakers (CBs). Therefore, the fault current increases during the fault even if the SFCL is installed. This paper proposes a technique for decaying the fault current with the function of the fault detection and control of power converter of the SFCL. Using the proposed method, the fault current can decay after 1-2 cycles when the fault occurs. To analyze this technique, three-phase 6.6 kV/200 A SFCL was fabricated. The SFCL has just one DC reactor, an AC to DC power converter which has thyristors as the rectifying device, and a three-phase transformer, which is called magnetic core reactor (MCR). The short-circuit tests of this SFCL were performed successfully. Comparing the result using the proposed technique with the typical result, the fault current is decreased effectively by the proposed technique. This result shows that this SFCL using the fault detection and control of power converter can be applied to the existing power system which has conventional CBs.

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 testing of superconducting DC reactor for 1.2 kV/80 A inductive fault current limiter

A superconducting DC reactor protects a power system by limiting the amplitude of fault current with its inductance. Therefore, it is very important to design and simulate the DC reactor precisely for making the power system stable and effective. In this paper, we designed the superconducting DC reactor of an inductive superconducting fault current limiter conceptually and acquired the optimal design parameters by using Finite Element Method (FEM). We manufactured the superconducting DC reactor and tested its characteristics at cryocooler-cooled 20 K temperature. Moreover, we compared experimental characteristics with simulation results and analyzed them. We introduced the design method of the superconducting DC reactor and the fabrication method of a 1.2 kV/80 A class DC reactor for an inductive superconducting fault current limiter. Finally, we performed the short circuit test and discussed the results.

Characteristic Analysis of HTSC Persistent Current Switch for Maglev Application

This paper deals with the preliminary study on the HTSC persistent current switch (PCS) for MAGLEV in Korea. The onboard HTSC levitation magnet system for high-speed maglev has advantage in power consumption because it can be operated in persistent current mode (PCM). The high speed superconducting maglev operated in PCM does not need the additional electrical energy to provide levitation force. To develop the PCS having good characteristics, it is important to develop a technology to minimize the joint resistance between two superconducting wires. The HTSC levitation magnet system consists of one HTSC magnet wound with Bi-2223 wire and a persistent current switch (PCS). The inductance of the magnet was 18.5 mH and total joint resistance of the magnet was 5.74 x 10-7 Omega. The PCS was experimented with respect to various ramping-up rates and magnitudes of charging current. The experimental results were compared with simulation results using finite different method. Based on these results, the current decay of 1 H class PCS using HTSC wire was calculated.

Characteristics Analysis of a High-Tc Superconducting Power Supply Considering Flux Creep Effect

This paper describes the characteristics analysis of a high-Tc superconducting (HTSC) power supply considering flux creep effect, and also presents its operational characteristics through experiments. The power supply can be employed to charge an HTSC magnet. An HTSC power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid, and a series-connected Bi-2223 pancake load. The pancake load was fabricated by connecting four double pancake coils in series. In the experiments, two cases of the pumping period, which correspond to 8.5 and 17 s, were used with an electromagnet of 331 mH and a dc heater current of 0.8 A. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 22.9 A

An Analysis and Short Circuit Test of Various Types of Bi-2223 Bifilar Winding Fault Current Limiting Module

This paper deals with feasibility of fault current limiter (FCL) by using Bi-2223 high temperature superconducting (HTS) wire. The FCL using HTS wire has some advantages of stability, flexibility of structure and cost compared with existing superconducting FCLs using bulk or thin film. Even if the FCL using HTS wire has zero resistance in normal state, it needs to be wound as a bifilar winding for non inductance. In this paper, four types of FCL module with bifilar winding were suggested, manufactured and experimented with short circuit tests in 77 K. The FCL modules have different fault current limiting characteristic and stability respectively. These types of module are solenoid, pancake, solenoid impregnated with epoxy resin and pancake impregnated with epoxy resin. The FCL module was applied by controllable AC bias during fault duration, 0.1 s, from 0.5 V to 22 V. A process of fault occurrence in this test is very similar to a fault occurrence in real system. In results of tests, the pancake type was more effective to limit a fault current than the solenoid type. Also modules impregnated with epoxy resin showed more efficient current limiting characteristics than nonimpregnated modules. The solenoid type has better characteristic of stability. The feasibility of the FCL by using HTS wire was verified by this paper

Conceptual Design for HTS Coil in Superconducting Electromagnet for Maglev

This study deals with a conceptual design for a high temperature superconductor (HTS) coil fabricated with YBCO wire in a prototype HTS-electromagnet (HTS-EM) model for the electromagnetic suspension (EMS)-based Maglev. Because the size of the HTS coil and the power it consumes during operation are very critical factors in designing the HTS-EM, we focused on the number of coil turns and the operating conditions needed to generate the required magneto-motive force (MMF) effectively. The winding geometry of the sample HTS coil with the largest Ic value was selected for use in this study. To determine the operating condition corresponding to the number of coil turns, we produced the operating profile for the load current of DC current source and the Ic value of HTS coil. From the profile, the optimal number of coil turns to minimize the operating power is determined to be in the range of 1200 to 1400 turns. And the HTS coil should be operated with the current of 37 to 43 A at the cooling temperature of 73 to 76 K.

Experimental Study on the Electrical Breakdown Characteristics of Sub-Cooled Liquid Nitrogen for Designing a High Voltage Superconducting Machine

The electrical breakdown characteristics of liquid nitrogen should be investigated for developing of a high voltage superconducting machine. This paper deals with the experimental study for the verification of dielectric characteristics of sub-cooled in accordance with utilization factors. AC dielectric experiments were carried out by using sphere-plane electrode systems. The utilization factors of simulated electrode systems were controlled by gap distance between two electrodes and diameter of a sphere electrode. Also, dielectric experiments according to various pressures, 1.25, 1.5 and 2 bar, by gaseous nitrogen were carried out. In this paper, the electrical breakdown criteria of sub-cooled conditions are derived with various sphere diameters. In addition, the sub-cooled condition and saturated condition were compared with AC dielectric characteristics. Research results could be applicable to designing of high voltage superconducting applications such as superconducting fault limiters (SFCLs), cables and large-capacity transformers.

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.