• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1082-1084
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• 1998

In this paper, we developed a diagnosis device for ZnO arrester to detect on-line leakage current and acquire data from the power distribution system. The arrester is important power equipment used in power transmission and distribution systems to protect the generator and the main transformer from surge and overvoltage. First of all we developed a diagnosis device for ZnO arrester leakage current. And then we detect the total leakage current by the developed device without disconnecting the arrester ground wire and analysis the 3rd order harmonic by Fast Fourier Transform(FFT) to diagnose the ZnO arrester deterioration. With measuring the total current and the resistive current of power distribution system in operation, we analysis the trend of resistive current component in the total leakage current. We expect the result will be promote the method to protect electrical utility and customer from accident.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.1058-1062
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• 2000

We investigated resistive superconducting fault current limites (SFCLs) fabricated using YBCO thin films on 2-inch diameter sapphire substrates. Nearly identical SFCL units were prepared and tested. The units were connected in series and parallel to increase the current and voltage ratings. A serial connection of the units showed significantly unbalanced power dissipation between the units. This imbalance was removed by introducing a shunt resistor to the firstly quenched unit. Parallel connection of the units increased the current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current 25 A$\_$peak/, was produced and successfully tested at a 220 V$\_$rms/circuit. From the resistance increase, we estimated that the film temperature increased to 200 K in 5 msec, and 300 K in 120 msec. Successive quenches revealed that this system is stable without degradation in the current limiting capability under such thermal shocks as quenches at 220 V$\_$rms/.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.817-821
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• 2017

As a ZnO varistor is subjected to electrical and environmental stresses, it degrades gradually, which may result in power interruption by short circuit. This study investigates changes in the electrical characteristics of ZnO varistors due to deterioration owing to energy absorption, and determines the optimal parameters for on-line diagnosis of the varistor. Two types of varistors were used for an accelerated aging experiment involving the application of the $8/20{\mu}s$ standard lightning impulse current. The electrical characteristics in terms of the reference voltage, total leakage current, resistive leakage current, and third-harmonic component of the total leakage current were measured, and their change rates were analyzed. The results revealed that the total leakage current increased slightly with an increase in the varistor absorbed energy, while the resistive leakage current and the third-harmonic component increased apparently. Therefore, the third-harmonic component of the total leakage current was proposed as the optimal parameter for on-line monitoring of ZnO varistor conditions.

• Progress in Superconductivity
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• v.6 no.2
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• pp.113-117
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• 2005

In this study, electromagnetic analysis of current paths including meander pattern, spiral pattern, and bi-spiral pattern were performed and in order to verity the analysis results, experiments tests including quench test, and insulation tests were performed. In addition, bubble corner concepts were introduced to enhance insulation reliability. From our study, bi-spiral pattern of YBCO thin films were rather effective for quench and insulation than the other patterns. So this current path pattern was adopted for YBCO thin films in order to develop 6.6 kV resistive fault current limiters. Finally YBCO thin films were connected in series and parallel to enhance capacity, and the test results of current limiting characteristics of 6.6kV resistive SFCL were successful. The Progress in Superconductivity is published every six month and serves as a channel for publications on superconductivity and related topics. The author(s) are required to submit THREE copies of the manuscripts along with original figures directly to the Editor.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.1
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• pp.42-46
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• 2003

Arresters are deteriorated by overvoltages or impulse currents, and the resistive leakage current of arresters increases as the deterioration of the arrester progresses, showing an increase in the 3$^{rd}$ harmonic component of the leakage current. In this reason, arrester diagnostic techniques based on the 3$^{rd}$ harmonic leakage current as a reference parameter of deterioration are widely used. The technique, however, includes an error due to the harmonics of power system voltage. Therefore, the influence of the harmonics on arrester diagnostics should be considered. In this paper, we designed a PSpice ZnO arrester model to simulate the influence of the voltage harmonics described above. A pure sinusoidal voltage and its the 3r harmonic voltage were applied to the model, and the leakage current components were analyzed. From the simulation results, it is confirmed that the peak value of resistive leakage current depends not only on the phase of the 3$^{rd}$ harmonic voltage but also on the magnitude of it. Consequently, the errors caused 1)y the harmonic voltage could be minimized by correcting the magnitude of leakage current upon analyzing the harmonics.cs.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.26-31
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• 2007

In recent years. YBCO coated conductor (CC) called as second generation HTS (high temperature superconducting) wire has been developed as a suitable material for resistive superconducting fault current limiter (SFCL). For designing the SFCL. the required length of superconducting wire is inverse proportional to the maximum temperature reached when a fault occurs. Since the required length strongly affects a manufacturing cost, it is the most important parameter to determine the maximum temperature reached. It is necessary to observe the repetitive over-current characteristics of HTS wire. This paper attempts to measure the variation of critical current of YBCO CC after repetitive over-current pulse. No degradation of the critical current of CC sample was observed by applying 100 times over-current pulse which makes temperature above 400 K after 100ms. This study can be useful in designing optimally resistive SFCL employing YBCO CC. The maximum permissible temperature can be set to 400K. so wire length could be reduced by 30% compared in case of 300K-criterion.

• Progress in Superconductivity
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• v.5 no.2
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• pp.136-140
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• 2004

We fabricated and tested a resistive superconducting fault current limiters (SFCL) operated at 3.8 ㎸ based on YBCO thin films. The SFCL was composed of 7 components connected in series. Each component was designed to be capable of current limiting at 600 V, and has a SiC shunt resistor ( $R_{s}$) of 40 Ω in Parallel. Short circuit tests were carried out fur 0 and 90 degree faults lasting fur 5 cycles. The test results showed that the 7 components were quenched simultaneously under the safe quenches and evenly shared the applied voltage. The SFCL successfully suppressed the fault currents below 94 $A_{peak}$ within the quarter cycle after fault.t.t.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.3
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• pp.173-178
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• 1999

In this paper, the characteristics of the shielded inductive superconducting fault current limiter(FCL) were simulated and analyzed. After determining parameters fo design for superconducting tube, iron core and primary coil, simple power system composed of shielded inductive FCL was simulated by the numerical analysis. The currents flowing under the fault condition could be limited below 50 A successfully. It was suggested that as the important factors of operational characteristics, the turns of primary coil and size of iron core play a major role for whether the shielded inductive SCFCL operated as inductive type or resistive type FCL.

• KIEE International Transactions on Power Engineering
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• v.4A no.2
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• pp.69-72
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• 2004

Nowadays, one of the serious problems in the KEPCO system is a much higher fault current than the SCC (Short Circuit Capacity) of the circuit breaker. Since superconductivity technology has become more developed, the HTS-FCL (High Temperature Superconductor-Fault Current Limiter) may become an attractive alternative to solving the fault current problem. In order to achieve the best performance, the parameters of HTS-FCL should be designed optimally. Under this setting, this paper presents the optimal design method of parameters for resistive type HTS-FCL using the Monte Carlo technique.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.11
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• pp.619-623
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• 2004

We proposed the bridge type superconducting fault current limiter(SFCL) using switching operation of high-Tc superconducting(HTSC) thin film. The proposed bridge type SFCL consists of HTSC thin film, a diode bridge and a dc reactor. The controller for the operation of an interrupter is required in the conventional bridge type SFCL to prevent the continuous increase of fault current after a fault happens. On the other hand, the proposed bridge type SFCL can limit the fault current without the interrupter and the controller for its operation by the resistance generated when the gradually increased fault current exceeds HTSC thin film's critical current. We calculated the time when the gradually increased fault current started to be limited by the resistance generated in HTSC thin film after a fault happened and confirmed that it could be dependent on the amplitude of source voltage. The experimental results well agreed with the calculated ones from simulation.