• Journal of Welding and Joining
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• v.17 no.2
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• pp.97-103
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• 1999

The dynamic resistance monitoring in primary circuit is one of the important issues. Because in-process and real time quality assurance of resistance spot weld is needed to increase the product reliability. In this study, new dynamic resistance detecting method is proposed as a practical manner of weld quality assurance using instantaneous current and voltage measured at the primary circuit. and also, various patterns of primary dynamic resistance curve are characterized with the macro photograph and the weldability lobe curve. It is found that the primary dynamic resistance patterns are basically similar to those of the secondary, but there is evident advantage such as no extra devices are needed to obtain the quality information and eventually real time feedback control will be possible.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.1
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• pp.46-51
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• 2008

Extra-high voltage(EHV) disconnecting switch(DS) consists of the electrical contacts and mechanical parts which actuate the contacts. When the short-circuit condition occurs, a large amount of current flows through the electrical contact in disconnecting switches and this causes considerable temperature rise due to Joule heating. If the temperature rise is higher than the melting point of contact material, the DS contact becomes melting and cannot be usable anymore. For this reason, the analysis for capability of carrying short-circuit current in DS contacts must be performed at a design stage. Here, we proposed a numerical technique for evaluating the capability of carrying short-circuit current at electrical contacts in EHV DS. In this numerical approach, the mechanical and thermal analyses were simulated to check the capability of carrying short-circuit current. First, the applied pressure at contact parts was analyzed considering the mechanical properties, and then contact resistance was calculated by an empirical equation. Finally, thermal analysis was performed with resistance variation at electrical contacts. To verify these numerical results, the distributions of temperature in DS were experimentally measured and compared with each other. The results from experiments were agreed well with those from the proposed numerical simulations.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.31-35
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• 2019

The lumped-parameter circuit model for a no- insulation (NI) high temperature superconductor (HTS) magnet has been well understood after many experimental and analytic studies over a decade. It successfully explains the non-linear charging behaviors of NI magnets. Yet, recently, multiple groups reported that the post-quench electromechanical behaviors of an NI HTS magnet may not be well explained by the lumped circuit model. The characteristic resistance of an NI magnet is one of the key parameters to characterize the so-called "NI behaviors" of an NI magnet and recently a few groups reported a potential that the characteristic resistance of an NI magnet may substantially vary during a quench. This paper deals with this issue, the increment of contact resistance of the no-insulation (NI) REBCO magnet during a quench and its impact on the post-quench behaviors. A 7 T 78 mm NI REBCO magnet that was previously built by the MIT Francis Bitter Magnet Laboratory was chosen for our simulation to investigate the increment of contact resistance to better duplicate the post-quench coil voltages in the simulation. The simulation results showed that using the contact resistance value measured in the liquid nitrogen test, the magnitude of the current through the coil must be much greater than the critical current. This indicates that the value of the contact resistance should increase sharply after the quench occurs, depending on the lumped circuit model.

• Progress in Superconductivity and Cryogenics
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• v.5 no.2
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• pp.1-7
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• 2003

Nowadays, one of the serious problems in KEPCO(Korea Electric Power Co-Operation) system is the more higher fault current than the SCC(Short Circuit Capacity) of circuit breaker. There are many alternatives to reduce the increased fault current such as isolations of bus ties, enhancement of SCC of circuit breaker, applications of HVDC-BTB(High Voltage Direct Current-Back to Back) and FCL(fault current limiter). But, these alternatives have some drawbacks in viewpoints of system stability and cost. As the superconductivity technology has been developed, the HTS-FCL(High Temperature Superconductor -Fault Current Limiter) can be one of the attractive alternatives to solve the fault current problem. Under this background, this paper presents the EMTDC(Electro-Magnetic Transient Direct Current) model for resistance type HTS-FCL considering the nonlinear characteristic of final resistance value when quenching phenomena occur.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.638-648
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• 2003

An active capacitance circuit is analyzed in depth and its application to active RF BPF with low noise figure is discussed. The characteristics of the active capacitance circuit made of FET[1] exhibits negative resistance and conventional capacitance, which is easily controlled. However, it is difficult to make the negative resistance adequate in the designated frequency range due to the lack of detailed analysis, which could make an active circuit unstable as the frequency is going higher or lower. In this paper, we analyzed the negative resistance characteristics of active capacitance circuits and also presented the method that the flatness of passband can be controlled. Finally we have designed a 4-stage active BPE, which results in bandwidth of 100 MHz, 0,04 dB insertion loss, 0.2 dB ripple, and noise figure of 2.4 dB at 1.75 GHz band.

• Progress in Superconductivity and Cryogenics
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• v.7 no.2
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• pp.35-38
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• 2005

One of the most serious problems in KEPCO system operation is higher fault current than the SCC(Short Circuit Capacity) of circuit breaker. There are many alternatives to reduce the increased fault current such as isolations of bus ties, enhancement of SCC of circuit breaker, applications of HVDC-BTB(Back to Back) and FCL(fault current limiter). But, these alternatives have some drawbacks in viewpoints of system stability and cost. As the superconductivity technology has been developed, the resistance type HTS-FCL(High Temperature Superconductor Fault Current Limiter) can be one of the most attractive alternatives to solve the fault current problem. To evaluate the accurate transient performance of resistance type HTS-FCL, it is needed that the dynamic simulation model considering transient characteristics during quenching and recovery state. Under this background, this paper presents the EMTDC model for resistance type HTS-FCL considering the nonlinear characteristic of final resistance value when quenching and recovery phenomena by fault current injection and clearing occurs.

• 전기의세계
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• v.24 no.1
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• pp.29-42
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• 1975

In this paper, the electrical angle between two winding axes in the stator of the capacitor motor is put optional angle, deviding the space harmonics in its magnetic field of two windings and the leakage flux into the forward revolving field and the backward one by the revolving-field theory, its equivalent circuit which consider mutual induction between two windings is depicted. In the depicted equivalent circuit, the rotor resistance for the fundamental flux is devided into the resistance for the rotor bar and endring, and the rotor leakage reactance for the fundamental is devided into the skew leadage reactance and the other, and each circuit constants for each harmonics is expressed in terms of the circuit constants for the fundamental, so it mades easy to determine the characteristics for the capacitor motor. As the circuit constant ratios to the magnetizing reactance of the fundamental are used, motors which have same circuit constant ratios should be resembled in their characteristics.

• Journal of the Korean Institute of Telematics and Electronics
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• v.8 no.4
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• pp.7-16
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• 1971

A negative resistance element in the form of current control can be obtained by using a pair transistor circuit. This negative resistance element can be used in the generation of square pulse, and also in the realization of pulse width modulation circuit by superposing signal current on its bias current. The each bias current of pair circuit increases alternatively according to the polarity of the input signal. In order to satisfy this condition, a modified full wave rectification circuit has been adopted for supplying the input signal. Theoritical analysis of pulse times and design guidances for practical modulation circuit parameters are presented.

• 전기의세계
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• v.22 no.3
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• pp.25-34
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• 1973

In this paper, the characteristics of a single phase induction motor which is considered the space harmonic flux by the double revolving field theory is analysed. As the rotor resistance for the fundamental flux is separated from the resistance for the rotor bar and end-ring, and the rotor leakage reactnace is separated from the skew leakage reactance and the other, so the circuit constants for the space harmonic flux is expressed by the circuit constants for the fundamentals. As the ratio of the circuit constants for the magnetizing reactance is used, the generalized equivalent circuit is made up. the characteristic equation which is able to analysis the subdivided characteristics by the above circuit is induced. The ratio of the circuit constants and the skew angle being changed, the variations of the torque-speed characteristics for the fundamentals and harmonics is examined by this equation.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.22-27
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• 2018

Fire fighters are exposed to the risk of many accidents during fire suppression, especially near the high voltage circuit. In order to prevent and analyze the electric shock accidents, measurement of water resistance is crucial. However, this has been one of the overlooked research areas and it has been very difficult to measure the mixed up resistance components separately. In this paper, we measured a total resistance of apparatus and regarded it as a serial resistance of contact resistance and length dependant resistance. Measuring the resistance by varying the length of water stream, the variable resistance and fixed contact resistance appear, which are used to calculate the both components of resistances. In addition, the resistance of fire hose can be calculated from the parallel circuit which is formed by grounding the fire hose with the resistance of water stream. Results show that we can successfully measure the resistance per unit length of water stream and fire hose, thereby proving that this method is a facile way to measure water and fire hose resistance. However, many experiments are still required to obtain the precise contact resistance of ground under various condition and the resistance between the human body and fire hose.