• 전기의세계
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• 제29권5호
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• pp.315-320
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• 1980

It has been appeared and widely used today SF6 Gas Insulated Substation(Hereafter called GIS) for the power supply to the densely populated area due to the superior insulation withstand ability of SF6 Gas. And to maximize the compact effect of this substation, it is normal practice to connect underground cables. If it is possible to elieminate the redundant lightning arresters using the physical characterestics of travelling waves in underground cables, economical advantages can be obtained together with easy maintenances. It is presented in this paper the possiblity of eliminating the transformer protection lightning arresters under some conditions for the 154kV GIS's (BIL:750kV) which Korea Electric Co. plans to construct using the general purpose digital computer program.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.73-74
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• 2008

When 154kV Line is opened, what happens on generator? What protection relay operates? Therefore through studying on this trouble, the operator will handle well on re-troubling and we would like to re-examine thoroughly the co-ordination of generator and transformer protection system.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.249-250
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• 2007

Applying the AC over-currents over the critical current to Bi-2223/Ag tape having 56 A Ie, resistance increase with the duration of current application was measured and analyzed. In addition, the influence of the tape's electrical insulation on the over-current characteristics was investigated and compared with each other. From the results, we will establish the safe operating condition against the AC over-currents and the protection of the tape for the practical power application such as cable and transformer.

• 비파괴검사학회지
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• 제21권5호
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• pp.542-548
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• 2001

과전류 보호계전기에 사용할 목적으로 광섬유를 센서헤드로 사용하는 광 전류센서를 구성하였다. 전류측정의 원리는 도체 주변에 감겨진 광섬유 코일을 따라 광신호의 선형편광축이 자기장에 의하여 회전하는 정도를 측정하여 이로부터 전류의 값을 산출하는 편광측정 방법이 사용되었다. 센서코일은 $10/125{\mu}m$ 규격의 일반 통신용 광섬유를 미터당 20회전 이상 비틀어 제작하여 온도나 진동 등의 환경적 영향을 최소화하였다. 코일의 한쪽 끝은 Faraday Rotator Mirror를 장착한 반사형으로 설계하여 계통을 해체하지 않은 상태에서도 센서의 탈 부착이 가능하고 코일의 회전수에 따라 센서의 민감도 조절이 용이하며 폐회로형 구조이므로 인근 신호원에 의한 간섭을 차단할 수 있다. 편광 빛가르개 등을 이용한 광학 신호처리부를 구성하고 표준 전류원을 이용한 전류측정 실험을 수행한 결과로 이론적인 해석과 동일한 형태의 출력을 얻을 수 있었다. 본 논문에서는 구성한 광 전류센서의 이론적 모델을 기술하고 전류측정 실험의 결과와 이론치에 대하여 비교 분석한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전력기술부문
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• pp.9-11
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• 2008

A protection current transformer (CT) has been widely used for protection devices. When a fault occurs, a CT should provide the faithful reproduction of the primary fault current. However, a CT may saturates due to the magnitude of fault current, dc component primary time constant and the remanent flux of the iron core, and the secondary current of a CT is distorted. The distorted current can cause mal-operation or the operating time delay of a protection relay. This paper provides a modeling of CT saturation using EMTP-RV. The performance of the proposed CT saturation modeling was investigated under various fault conditions varying the fault distance, fault inception angle, and remanent flux of the iron core. The results indicate that the proposed EMTP-RV modeling can operate correctly, and the reasons for CT saturation are verified by EMTP-RV simulations.

• 전기학회논문지
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• 제61권12호
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• pp.1801-1806
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• 2012

This paper presents a simple and practical method which enables to prevent malfunction of protection relay due to differential current caused by one end CT saturation in case of external fault. This method uses difference of magnitude(instantaneous value) between the both end current just before the occurrence of differential current without a separate method to CT staturation detection. One end CT saturation is simulated by current transformer model using type-96 component and the presented method is verified by using EMTP MODELS with respect to internal and external fault with one end CT staturation. The presented method distinguished rightly bewteen external and internal fault with one end CT saturation. This information can be used to prevent malfunction of current differential protection relay in case of external fault. And this method is not affected by sampling rate and has no calculation burden, so it will be applicable to differential current protection relay with ease.

• 전기학회논문지
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• 제57권6호
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• pp.938-943
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• 2008

Coupling capacitor voltage transformers(CCVTs) have been used in extra or ultra high voltage systems to obtain the standard low voltage signal for protection and measurement. For fast suppression of the phenomenon of ferroresonance, three winding CCVTs are used instead of two winding CCVTs. A tuning reactor is connected between a capacitor voltage divider and a voltage transformer to reduce the phase angle difference between the primary and secondary voltages in the steady state. Slight distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has significant errors due to the transient components such as dc offset component and/or high frequency components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of a three winding CCVT in the time domain. With the values of the measured secondary voltage of the three winding CCVT, the secondary, tertiary and primary currents and voltages are estimated; then the voltages across the capacitor and the tuning reactor are calculated and then added to the measured voltage. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the three winding CCVT irrespective of the fault distance, the fault impedance and the fault inception angle as well as in the steady state.

• 대한전기학회논문지:전력기술부문A
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• 제52권7호
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• pp.387-392
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• 2003

During a fault the remanent flux in a current transformer (CT) may cause severe saturation of its core. The resulting distortion in the secondary current could cause the mal-operation of a protection relay. This paper proposes an algorithm for compensating for the errors in the secondary current caused by CT saturation and the remanent flux. The algorithm compensates the distorted current irrespective of the level of the remanent flux. The second-difference function of the current is used to detect when the CT first starts to saturate. The negative value of the second-difference function at the start of saturation, which corresponds to the magnetizing current, is inserted into the magnetization curve to obtain the core flux at the instant. This value is then used as an initial flux to calculate the actual flux of the CT during the course of the fault with the secondary current. The magnetizing current is then estimated using the magnetization curve and the calculated flux value. The compensated secondary current can be estimated by adding the magnetizing current to the secondary current. Test results indicate that the algorithm can accurately compensate a severely distorted secondary current signal.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전력기술부문
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• pp.12-15
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• 2008

A distance relay has been widely used for transmission line protection. The distance relay detects a fault based on the calculated impedance i.e. the ratio of the voltage to the current measured from a current transformer (CT) and a coupling capacitor voltage transformer (CCVT), respectively. When a fault occurs and a CT saturates due to the magnitude of fault current, dc component, primary time constant, and the remanent flux of the iron core, the secondary current of a CT is distorted On the other hand, non-fundamental components generated during a fault can increase the error of a CCVT, particularly when a fault distance is short. The distortion of the current and voltage can cause mal-operation or the operating time delay of a distance relay. This paper describes the response of a distance relay considering the errors of a CT and a CCVT. The results indicate that the severe distortion of a CT and a CCVT have noticeable effect to a distance relay.

• 전기학회논문지
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• 제58권8호
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• pp.1457-1462
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• 2009

This paper proposes a compensating algorithm for the secondary voltage of a coupling capacitor voltage transformer (CCVT) in the time domain by considering the hysteresis characteristics of the core. The proposed algorithm estimates the three error terms i.e. the voltage across the secondary winding parameters, the voltage across the primary winding parameters, and the voltage across the capacitor and the tuning reactor. These three terms are added to the measured secondary voltage to obtain the correct voltage. The algorithm reduces the errors of the CCVT significantly both in the steady state and during a fault. The performance of the algorithm is verified under the various fault conditions by varying the fault distance, the fault inception angle, and the fault impedance with the EMTP generated data. Test results clearly indicate that the algorithm can increase the accuracy of a CCVT significantly under the fault conditions as well as in the steady state. The algorithm helps improve the performance of a protection relay or a metering device.