• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.57-61
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• 2007

The current limiting characteristics of hybrid SFCL with additional power electronic devices was investigated in order to improve operation reliabilities. The hybrid SFCL developed consists of a superconducting trigger (S/T) part, a fast switch (F/S) module and a current limiting (C/L) part. Although hybrid SFCL had shown a excellent current limiting characteristics, this device was rather vulnerable to the residual arc currents which could exist during fast switch operation. This undesirable arc should be extinguished as quickly as possible in order to implement perfect fault current commutation. So, in order to eliminate the residual arcs between fast switch contacts, the power electronic devices (IGBT or GTO) were connected in series between the S/T part and the interrupter of the F/S module. According to the fault tests conducting with an input voltage of $270\;V_{rms}$ and a fault current of $5\;kA_{rms}$, The power electronic devices could perfectly remove the arc generated between the contacts of the interrupter within 4 ms after the fault occurred. From the test analysis, it was confirmed that the hybrid SFCL could enhance the operation reliability by adopting additional power electronic devices.

• Progress in Superconductivity and Cryogenics
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• v.5 no.2
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• pp.36-40
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• 2003

Inductive superconducting fault current limiter(SFCL) with DC reator rated on 6.6k $V_{rms}$/200 $A_{rms}$ has been developed in Yonsei University. The development of the DC reactor is the key technology in this type SFCL. This paper deals with the fabrication and characteristic test of the DC reactor. For the development of this magnet, the winding machine for high-Tc superconducting solenoid was manufactured. Using this machine, a large-scale HTS solenoid using Bi-2223 tape was fabricated successfully. This coil has 5 layers which are connected in series each other. The inductance of the DC reactor coil is 84mB. The cooling system was the sub-cooled nitrogen whose temperature is about 65K. The characteristic test of the coil was performed. The full quench current of this coil is about 490A.90A.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1554-1560
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• 2012

In this paper, the even harmonic current(2nd, 4th, 6th, 8th) of the arc fault current and normal current were measured in computer load and analyzed. The BPF with GIC was developed to detection of harmonic, the exact center frequency and a high degree of sharpness could be easily obtained. The total even harmonic distortion due to series arc fault in computer load was 31.2%, this value was increased 3.9 times better than the total even harmonic distortion of normal current. The results of analysis of arc fault current RMS variation rate and Peak variation rate per half-cycle, The RMS average variation rate are as follows ; the 2nd harmonic was 0.24, the 4th harmonic was 0.15, the 6th harmonic was 0.19, the 8th harmonic was 0.25, respectively. The Peak average variation rate are as follows ; the 2nd harmonic was 0.19, the 4th harmonic was 0.12, the 6th harmonic was 0.13, the 8th harmonic was 0.15, respectively. The results of this analysis utilize data to detect of series arc fault on wiring of computer load.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.3
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• pp.155-161
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• 1996

For the condition monitoring of the journal bearing in rotating machinery, a system for their diagnosis by acoustic emission(AE) was developed. AE has been used to detect abnormal conditions in the bearing system. It was found from the field application study as well as the laboratory experiment using a simulated journal bearing system that AE RMS voltage was the most efficient parameter for the purpose of current study. Based on the above results, algorithms and judgement criteria for the diagnosis system was established. The system is composed of four parts as follows: the sensing part including AE sensor and preamplifier, the signal processing part for RMS-to-DC conversion to measure AE ms voltage, the interface part for transferring RMS voltage data into PC using A/D converter, and the software part including the graphic display of bearing conditions and the diagnosis program.

• Progress in Superconductivity and Cryogenics
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• v.6 no.2
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• pp.25-28
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• 2004

Three-phase inductive superconducting fault current limiter (SFCL) with DC reactor rated on 6.6 $KV_{rms}/200 A_{rms}$ has been developed in Korea. This system consists of one DC reactor, AC/DC power converter, and a three-phase transformer, which is called magnetic core reactor (MCR). This paper deals with the short-circuit analysis of the SFCL. The DC reactor was the HTS solenoid coil whose inductance was 84mH. The power converter was performed as the dual-mode operation for dividing voltage between the rectifying devices. The short-term normal operation (1 see) and short-circuit tests (2∼3 cycles) of this SFCL were performed successfully. In regular short-circuit test, the fault current was limited as 30% of rated short-circuit current at 2 cycles after the fault. The experimental results have a very similar tendency to the simulation results. Using the technique for the fault detection and SCR firing control, the fault current limiting rate of the SFCL was improved. From this research, the parameters for design and manufacture of large-scale SFCL were obtained.

• Journal of the Korean Society of Safety
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• v.29 no.2
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• pp.12-17
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• 2014

This paper is aimed to analyze the characteristics of simultaneous voltage, current and temperature signals for poor connection on electrical connector. In order to attain this purpose, detected were the current and voltage signals on electric wire with series arc, named arc signals, and also monitored were the changes of RMS, instantaneous value of waveform in time domain and temperature value with video. Two states are made normal state over $5kgf{\cdot}cm$ and poor connections state below $0.5kgf{\cdot}cm$ by screw gage. In the voltage signal case, the voltage drop was increased with which the current was increased. In the current signal case, poor connections at the time interval 1~4A all showed "shoulder", as distinct difference from the normal state shown waveform pattern. In the temperature signal case, poor connections are twice at 1A and five times at 4A in the normal state. The temperature continues insulation of electrical wiring and connector can be carbonized. The results of this study will be effectively used in developing the preventive devices and system for electric fire by poor connections.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.150-156
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• 1996

Static variations of cutting forces are estimated using spindle motor current. Static sensitivity of spindle motor current is higher than feed motor current. The linear relationship between the cutting force and RMS value of the spindle motor current is obtained. Using cutting force estimation, tool overload in milling process can be well detected, and cutting force is regulated at a constant level by feedrate adaptive control.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.67-69
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• 2002

This paper presents the statistical analysis of the circuit breaker's making current in large sacle industrical loads using EMTDC. Typically, the making current includes DC components as the phase angel of making instances varies and represents as a instantaneous valus not rms. Consequently, in this paper, the statistical analysis results of making current and steady state fault current for typical industrial loads presents.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.3
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• pp.74-81
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• 2008

The control system of high-precision AC power is important in traffic management lighting and beaconing of aerodromes, etc. To control AC power supply in these load characteristics, inverter systems of AC/DC/AC conversion are widely used in high-precision current control. Therefore, in this paper, a inverter system of constant current regulation using improved measuring technique of feedback current is proposed. Proposed measuring techniques improve response and precision in that it use moving average method of instantaneous RMS for measuring current sensing. Results of the computer simulation and experiment prove the effects of proposed system.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.65-71
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• 2015

This paper presents the efficiency analysis of a critical current mode interleaved PFC rectifier, in which each of three different semiconductor switches is employed as the active switch. The Si FET, SiC FET, and GaN FET are consecutively used with the prototype PFC rectifier, and the efficiency of the PFC rectifier with each different semiconductor switch is analyzed. An equivalent circuit model of the PFC rectifier, which incorporates all the internal losses of the PFC rectifier, is developed. The rms values of the current waveforms main circuit components are calculated. By adapting the rms current waveforms to the equivalent model, all the losses are broken down and individually analyzed to assess the conduction loss, switching loss, and magnetic loss in the PFC rectifier. This study revealed that the GaN FET offers the highest overall efficiency with the least loss among the three switching devices. The GaN FET yields 96% efficiency at 90 V input and 97.6% efficiency at 240 V, under full load condition. This paper also confirmed that the efficiency of the three switching devices largely depends on the turn-on resistance and parasitic capacitance of the respective switching devices.