• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 C
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• pp.834-836
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• 1998

Current transformer (CT) saturation may cause a variety of protective relays to malfunction. The conventional CT is designed that it can carry up to 20 times the rated current. However, the possibility of CT saturation still remains, because the fault current may have substantial amounts of ac and/or de components. This paper presents a iron-cored CT design method to prevent CT saturation. The proposed method employs the overdimensioning factor $(K_{ta})$ considering dc components contained as well as symmetrical ac components in the fault current.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 A
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• pp.491-494
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• 1992

This paper described the development example of optical CT(Current Transformer) and optical PT (Potential Transformer) which is measurement system of current and voltage of electric power line using Electro-Optic effect and Magneto-Optic effect. We designed the optical CT of 22KV class and 154KV class and an optical PT of 22KV class. And now the filed testing is in progress in a KEPCO's substation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.5-7
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• 2006

Current transformers(CTs) whose rating is selected per a full load current of a feeder in high voltage system can be easily saturated due to high fault current that may be several hundred times of the full load current of the feeder. However, the protective relay shall operate properly at the fault without mis-operation under the CT saturation. So, in selecting the CT rating, it is necessary to consider the behaviour of CT and a performance of protection scheme in condition where CT can be saturated. In this paper, a performance of CT and a degree of saturation are studied and verified whether its ratings are proper for the operation of the protective relay.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.14-15
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• 2006

A saturation of magnetic flux in the core may occur when a large primary current flows when the iron-cored current transformer is used. This saturation makes the distorted secondary current of the CT. the distorted secondary current may cause the mal-operation or operation time delay of protective relays. CT compensation algorithm using The LSQ(Least Square) fitting method has a problem. It needs to acquire enough data for executing this algorithm without an error. In this paper, an enhanced algorithm using interpolation based LSQ(Least Square) Fitting Method is proposed. The Lagrange Interpolation Method is used for the interpolation and CT is simulated by EMTP. The results show that the proposed algorithm can accurately compensate a distorted secondary current more than existing Algorithm when the saturation severely occurs.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.868-869
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• 2008

An automatic excitation characteristics measurement system for the protective relaying current transformer(CT) with accuracy of about 1 % has been developed. The system can be used up to 2 kV and 10 A at power frequency. The developed system can calculate the voltage and current at knee points of $30^{\circ}$ and $45^{\circ}$ tangents in accordance with IEEE standard by the interpolation in log scale. The excitation curve of the CT is plotted in auto-scale simultaneously with measuring rms voltage and current at the secondary of the CT.

• 전기학회논문지
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• 제62권9호
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• pp.1313-1317
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• 2013

With increasing demand of power, the equipment of power system is enlarging and the absolute capacity is going up. As a result, when a fault occurs, the fault current is consistently increasing. Therefore, I suggested some solution for limiting the fault current more efficiently. This study shows the characteristics of superconducting limiting elements and normal conducting elements combined with a transformer. We performed a short-circuit test about the fault current by using SCR switching control system operated from a CT. When short circuit accidents happened in the secondary side of a transformer, fault currents flowed and a SCR switching control system was operated. It resulted in a decrease of the fault current in the limited elements of third winding connected in parallel. For this test, we used YBCO thin films and normal conducting elements as the limited elements. Within a cycle, a superconducting fault current limiter with YBCO thin films reduced more than 90% of fault current because the resistance of superconducting elements sustainedly grew. On the other hand, the limiter with normal conductors limited as much as a set value because its resistance characteristic was linear. Consequently, in case of the limiter with superconductor, limiting range of the circuit was wide but the range of protective detection was undefined. In contrast, as for the limiter with normal conductors, limiting range and protection duty were appropriate.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.255-257
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• 2005

This paper proposes a compensating algorithm of a measurement torrent transformer (CT) using DSP. The core flux is calculated and then magnetizing current is estimated in accordance with the flux-magnetizing current curve. The core loss current is obtained with the core loss resistance and the secondary voltage. The correct secondary current is estimated by adding the exciting current to the measured secondary current. The performance of the proposed algorithm was tested using EMTP generated data. The experiment on the real CT was conducted using the prototype compensated system based on a digital signal processor. The results indicate that the algorithm can increase the accuracy of the measurement CT significantly.

• 대한전기학회논문지:전력기술부문A
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• 제50권6호
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• pp.275-278
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• 2001

This paper presents an algorithm for detecting current transformer (CT) saturation. At the instants of beginning (or end) of saturation, as a magnetizing inductance of the core is changed significantly, the shapes of the secondary current are also changed significantly though secondary currents are continuous the instants. At the instants, the second-order of third-order difference of the secondary current has big values. Thus, the third difference of the current is used to detect the beginning/end of CT saturation in this paper. If the magnitude of third-order difference of the secondary current is larger than a threshold value, the CT begins of ends saturation at the instants. The proposed detection method is unaffected by the amount of residual flux. The results of various tests with residual flux from -80% to +80% indicate satisfactory performance of the method.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권4호
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• pp.256-264
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• 2000

In the conventional method, two CTs have been used to share the load current equally with two converters. A new simle method to find out the current difference between two converters using only one CT as a ZCT is suggested. Two experimental prototype converters were designed and implemented for the evaluation of the load current sharing. The results of experiment show that the newly proposed ZCT method using only one CT could make a good load current sharing than the conventional method required two CT when operating two converters in parallel.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.427-428
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• 2008

We have studied design and application about an self generation equipment for underground power transmission cable. The split CT(Current Transformer), which has the applicable underground power transmission cable, was manufactured through electromagnetic simulation of magnetic core. And manufactured the AC-DC converter that supplied stable DC power for PLC modem when current of power line has more than 150A. An self generation equipment using the CT and AC-DC converter get into operation the PLC modem consistently. As a result, the underground power transmission cable was showed the application possibility through the stable communication and network characteristics.