• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.3
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• pp.473-479
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• 2015

Thermal relays are sometimes used instead of long time overcurrent relays for motor protection. But, it is difficult for any relay design engineer to adequately approximate motor heating curves which represent the average of a difficult-to-define thermal zone. Thermal relays frequently may not provide sufficient protection on heavy overloads. Digital multifunction relays are microprocessor-based devices. These relays offer highly reliable and advanced protection of motors. If a situation can be mathematically described, the microprocessor in a digital relay can be programmed to tackle that problem. Today's motor protection is accomplished with digital protective relays. Digital relays offer additional, highly important features to complement protection. The best way to prevent short in motor is to not overheat and degrade the insulation.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.1
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• pp.29-36
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• 2006

The interest for harmonic problems has been increasing due to the increment of nonlinear loads. The loads such as DC power system, personal computers, UPS system, inverters and converters operate as harmonic current sources. In this paper, a new type of the passive filter, Hybrid Harmonic Filter (HHF) is suggested to mitigate harmonic problems in power systems. The HHF is developed for reducing harmonic current, especially on the system that includes 6-pulse bridge rectifiers. Also, it is expected to prevent the overheating of transformers and feeders due to overcurrent and to correct the power factor.

• Progress in Superconductivity and Cryogenics
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• v.21 no.4
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• pp.39-43
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• 2019

The breaking of a circuit in DC grid could pose a challenge because of the absence of zero-crossing instant for both current and voltage when a fault occurs. An additional fault current limiting function will be very helpful for reducing the burden of the DC circuit breaker by limiting the fault current to a reasonable value. In this paper, we studied the overcurrent characteristics of several HTS conductors so that we could use the selected conductors for the basic design work of a resistive type fault current limiting module as a part of the circuit breaking system. According to the short-circuit test results, we suggested and compared two different basic design parameters of the HTS fault current limiting module, which will be connected in series to the DC circuit breaker.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.4
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• pp.226-233
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• 2003

Directional elements are fundamental to protection scheme security and selectivity, performing such critical tasks as supervising distance elements and controlling overcurrent elements. But, conventional operating principles for directional detection based on negative or zero sequence quantify do not satisfy the requirements for improved sensitivity and fast operation under any fault conditions. In this paper, new algorithm for directional elements is proposed. The proposed algorithm use the positive-sequence superimposed voltages and currents in order to be used in all fault conditions. Also, because this algorithm uses a voltage compensation method. it can be well operated under strong source conditions.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.2
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• pp.89-93
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• 2006

Recently as a people recognize a safety more about a high and large buildings the importance of a fire-damper which supplies fresh air into the building in case of fire increases greatly. Therefore, in this paper a fire-damper using a micro-controller is designed and fabricated. In the design of fire-damper a pressure sensor is modeled as a capacitor and the p-spice is used as a circuit simulator PIC16F72 is used as a micro-controller to drive a pressure sensor and to display a pressure value from the pressure sensor and to drive a motor to open and close a damper. A photo-coupler is used to protect a motor from a overcurrent.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.737-739
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• 1996

Abnormal conditions and disturbances in distribution system cause an immediate influence to the customers. Conventional detection schemes for the distribution abnormalities have been applied in limited extents mainly because of their low reliability. In this paper, we developed a disturbance identification system which monitors the load level after a transient, checks the harmonic behavior of the load, and finally makes decision on the cause of the disturbance. This system identifies and discriminates overcurrent faults, arcing ground faults, recloser activities, and foreign object or tree contacts. In the implementation of the identification system, we applied fuzzy logic to better represent some variables whose Quantities are expressed only in non-numerical terms.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.850-852
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• 1996

High impedance fault (HIF) is defined as fault that general overcurrent relay can't detect or interrupt, Especially when HIF occur under 15 kV, energized high voltage conductor results in fire hazard, equipment damage or personal threat. Because most HIF occur arc, HIF detection using arc is to increase. Numerical arc model can be applied in an electromagnetic transients program (EMTP) to reproduce the dynamic and random characteristic of arcs for any insulator arrangement, current and system voltage. It allows the representation of any network configuration to be investigated, so the digital simulation of arc faults through air can be substitute for demanding power arc test.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.156-158
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• 1993

This paper presents several techniques of power spectrum estimation for high impedance fault detection. High impedance faults are those faults with current too low to be reliably cleared by conventional overcurrent protection. So power spectrum estimation is required. AR and MA techniques require optimal order for good performance of power spectrum estimation because these techniques are unstable for order selection. ARMA and Extended techniches are stable for order selection and have very sharp response. So ARMA and Extended Prony techniques are suitable for our purpose.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.127-129
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• 1996

고저항지락사고시 선로의 지락후비보효용인 지락거리계전기 및 변압기 후비보호용 방향지락과 전류계전기의 비협조 문제로 인하여 광범위한 정전이 유발될수 있다. 본 논문에서는 이에 대한 대책으로 고저항지락보호용 과전류계전기의 도입과 적용방안에 대하여 제안한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.152-155
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• 2020

This study proposes an input filter for a gallium-nitride-based direct matrix converter with a stepless current commutation technique. Various current commutation strategies have been adopted for reliable operation of switches. These strategies are complex to be implemented and require additional components. The stepless current commutation technique is simple to operate but causes overcurrent issues due to the occurrence of short circuit on input sources. In this study, to restrict the short circuit current, we utilized GaN devices with fast switching properties and modified the input filter. The proposed input filter was verified by experimental results of induction motor drive.