• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.216-217
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• 2007

This paper represents the reliability assessment on the mould type combined transformer used in the distribution system by electrical tests. For the reliability assessment, we had tested lightning impulse test, short-circuit withstand capability test, electrical accelerated life test and so on to the mould type combined transformer of Young-Hwa Industrial Electric Co., Ltd.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.319-320
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• 2007

We researched basic study about electrical characteristics of Zinc Selenide (Faraday Cell), which is known for various temperature of good-performance, that applied measuring current or protecting instrument by Optical Current Transducer, on Gas Insulated Switchgear. Measuring System consists of VCSEL produced 850nm IR Laser, Pin Photo Diode made of GaAs surveyed as Optical Power Meter, and Optical Fibers specified Multi-mode. We observed optical output changes during measurement of currents increasing by 100[A] in range from 0[A] to 1,000[A] and set temperature condition increasing by $5[^{\circ}C]$ in a range from $30[^{\circ}C]\;to\;60[^{\circ}C]$.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.501-502
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• 2007

This paper describes a distance relay that operates in conjunction with a current transformer (CT) compensation algorithm. A distance relay detects a fault based on the ratio of the voltage to the current. If a CT saturates, the calculated impedance becomes larger. This causes maloperation or operating time delay of the distance relay. A compensating algorithm estimates the correct secondary current from the severely distorted currents even when the measurement CTs are used. The correct current is estimated by adding the calculated magnetizing current to the measured secondary current. Test results show that the proposed distance relay can detect a fault without the operating time delay even when the secondary currents are extremely distorted because of use of measurement CTs.

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.116-118
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• 2002

This paper presents leakage magnetic field and leakage inductance calculations in current transformer by means of 3-D Integral methods. From the distribution diagram of leakage magnetic flux to be analyzed using program called TRACAL 3, it confirms a parallel to the winding axis direction of the leakage flux lines in the air gap between the windings. The leakage inductances $L_{r1}\;and\;L_{r2}$ of the primary and secondary windings were calculated, their values are 4.23 mH and 0.49 mH, respectively. They are also similar to the measured values of the leakage inductances for the experimental verification, 4.06 mH and 0.47 mH.

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.22-24
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• 2002

지금까지 변전소나 개폐소에서 전류, 전압을 계측하는 수단으로서 주로 철심과 권선으로 구성되어진 변류기(CT), 계기용 변압기(PT, PD)가 사용되어져 왔다. 최근, 2차측의 계측기나 보호 Relay의 Digital화가 진전되어, 또한 이것을 Digital Network으로 총합한 Intelligent 변전소의 구축이 검토되어짐에 따라, Digital Network에 대응한 신형 CT, VD가 요구되어지고 있다. 상기와 같은 요구로 인해 당사에서는 CT는 검출부에 Rogowski Coil을 적용하며 그 후단에 적분기를 설치하였으며, VD는 검출부에 중간 전극을 이용해서 분압하는 방식인 Capacitive Voltage Divider를 사용하고 증폭기를 삽입하여, 각각 요구되는 전압 신호를 얻었다. 이러한 신형 CT/VD의 적용으로 종래의 CT/PT가 차지하는 공간이 필요 없게 되어 컴팩트한 GIS의 구조가 가능하게 되어 있다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.951-953
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• 2005

The current transformer is used for the insulation of measuring instrument, enlargement of measurement scope, standardization of measuring instrument, control of protective device. It's required various performance as the intention of service, site of establishment, insulation. especailly, current transformer has small ratio errors. if current transformer has large ratio error, it's caused a electricity failure. so in this paper, we examine the theory of current transformer, major factor of errors, output performance on over-current.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.20-25
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• 2007

Instrument transformers are a safe measurement device designed to measure high voltage and large current. A current transformer(CT) is a type of instrument transformer designed to provide a current in its secondary winding proportional to the current flowing in its primary. It is commonly used in metering and protective relaying in the electrical power industry where it facilitates the safe measurement of large current. But, care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary, as this will produce a dangerously high voltage across the open secondary, and may permanently affect the accuracy of the transformer. Especially, industrial disaster such as an electric shock and/or a burn accident occurs occasionally by disregard of warning or attention. In this paper, we developed the detector for open of current transformer secondary terminal, and which was tested by the Korea Electrotechnology Research Institute. Test results show that Current Transformer secondary Open Detector(CTOD) interrupted within one second electronically when the 2nd terminal of current transformer opened.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.7
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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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1709-1714
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• 2007

This paper proposes a compensating algorithm for the secondary current of the measurement current transformer (CT) that removes the effects of the hysteresis characteristics of the iron-core. The exciting current resulting from the hysteresis characteristics of the core causes an error between the primary current and the secondary current of the measurement CT. The exciting current can be decomposed into the magnetizing current and the core loss current. The core loss current is obtained from the measured secondary current and the core loss resistance. The core flux linkage is calculated by integrating the measured secondary current, and then inserted into the flux-magnetizing current curve to obtain the magnetizing current. The exciting current at every sampling interval is obtained by summing the core-loss and magnetizing currents and then added to the measured current to obtain the correct current. The performance of the proposed algorithm is validated under various conditions using EMTP generated data. The results indicate that the proposed algorithm can improve the accuracy of the measurement CT significantly, and thus reduce the size and the cost of the measurement CT.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.163-164
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• 2006

A current differential relay has been used for transmission line protection. The relay may maloperate in the case of a failure of the secondary circuit of a current transformer (CT) because the differential current is produced. This paper presents an algorithm to detect a failure of a CT using the zero-sequence current. If the magnitude of the zero-sequence current is the same as the magnitude of the current of the other healthy phases, a failure of a CT is detected and then the blocking signal is activated. The proposed algorithm prohibit the maloperation of a differential relay in the case of a CT failure and thus increase the security of the relay.