• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 G
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• pp.2281-2283
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• 1998

In this paper, we propose a digital differential protection of power transformer using intelligent schemes. Intelligent schemes is based on fuzzy logic and neural networks. To enhance the distinction between fault and inrush of conventional approaches, relaying technique by fuzzy logic and neural networks are used. We used transformer inrush currents, external and internal fault signals, which are obtained from EMTP simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.671-673
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• 1996

Simulation methods using EMTP to analyze power transformer transient characteristics and their interesting results are presented in this paper. Because of the transformer saturation including initial inrush, the conventional current differential relay with harmonic restraint module does not provide a clear distinction between internal faults and other conditions. Providing the bases to develop a new relaying concept for power transformer protection, transformer nonlinear transient characteristics are analyzed.

• 센서학회지
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• 제5권4호
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• pp.41-46
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• 1996

변압기 절연유중 용존수소를 감지하기 위해 Pd/Pt 게이트 MISFET 센서를 제조하고 그 특성을 조사하였다. 동일 칩안에 내장형 히터와 온도측정용 다이오드를 제조하고 MISFET의 전압 드리프트를 줄이기 위해 차동형구조로 하였다. 수소유입 드리프트를 줄이기 위해, 양쪽 FET의 게이트 절연층을 실리콘 산화막과 실리콘 질화막의 2중 구조로 하였다. 수소감지막의 블리스터를 줄이기 위해 Pd/Pt 2중 금속층을 증착하였다. 제조된 센서의 변압기 절연유에 대한 수소감지 특성은 40mV/10ppm 감도와 0.14mV/day 안정도를 보였다.

• 대한전기학회논문지:전력기술부문A
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• 제53권9호
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• pp.500-506
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• 2004

This paper proposes a modified current differential relay for transformer protection unaffected by the remanent flux. The relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. To cope with the remanent flux, before saturation, the relay calculates the core-loss current and uses it to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the actual core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay discriminates magnetic inrush and over-excitation from an internal fault and is not affected by the level of remanent flux.

• 전기학회논문지
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• 제67권1호
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• pp.29-37
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• 2018

Inrush current and fault current in a transformer need to be distinguished from one another. In order to do this, KEPCO uses a 2nd harmonic restraint/block method. We use two setting values for 2nd harmonic restraint; 15% and 10%. We also apply per-phase blocking method among various harmonic restraint methods. If the transformer is located at the radial system, we adjust 10% in the 2nd harmonic restraint, but this method is not enough to prevent mal-operations of the current differential relay and let us spend more time to change setting value again as the power system changes. In this paper, a more reasonable setting value for a 2nd harmonic blocking scheme in KEPCO is proposed. To present a proposed method, the fault data of the current differential relays which have occurred since 2009 are analyzed. To evaluate the performance of the proposed method, the results of the RTDS test for the current differential relay of the transformer by KEPCO are analyzed.

• 한국기계가공학회지
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• 제16권3호
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• pp.100-106
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• 2017

A universal outer diameter measurement module was developed using a linear variable differential transformer (LVDT). This outer diameter measurement module enables simultaneous measurement of outer diameter, displacement, and perpendicularity of bench-type high-precision products by combining analogue and digital measurement principles with mechanically precise and fine adjustment functions. The developed module showed a performance of 0.001mm in measurement resolution, 0.001mm in measurement accuracy, reference surface abrasion lower than Ra 0.1864, and measurement stability of 0.002mm. Therefore, we have acquired domestic measurement technology to improve productivity by securing technical competitiveness for universal diameter measurement technology, lower production costs through import substitution, and increased quality of products with more precise measurement technology. Furthermore, a substitution effect is expected for expensive import measurement system equipment used in production, research, and inspection sites in industries that produce precision processing products such as automobile and machine components.

• 전기학회논문지
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• 제56권11호
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• pp.1873-1878
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• 2007

Current differential relays may maloperate during magnetic inrush and over-excitation because a significant differential current is produced. To prevent maloperation, the relays adopt some harmonic components included in the differential current. The harmonic restraints may increase the security of a relay but cause the operating time delay of a relay when an internal fault occurs. Moreover, the operating time delay is more increased if a current transformer (CT) is saturated. This paper describes a current differential relaying algorithm for power transformer protection with a compensating algorithm for the secondary current of a CT. The comparative study was conducted with and without the compensating algorithm. The performance of the proposed algorithm was investigated when the measurement CT (C400) and the protection CT (C400) are used. The proposed algorithm can compensate the distorted current of a CT and thus reduce the operating time delay of the relay significantly for an internal fault with CT saturation.

• 조명전기설비학회논문지
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• 제28권6호
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• pp.99-105
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• 2014

Power transformers are applied throughout the power system to connect systems of different voltage to one another. Since a ratio differential relay offers high sensitivity in detection of internal faults in power transformers, it is widely used in the main protection system. The use of nonlinear devices such as rectifiers and other devices utilizing solid state switching have been increased in industry during recent years. For nonlinear loads, the load current is not proportional to the instantaneous voltage. This situation creates harmonic distortion on the system. The harmonic could differential relay misoperation if not recognized. This paper aims at analyzing and probing into the influences of harmonics on a ratio differential relay for power transformer protection.

• 대한전기학회논문지:전력기술부문A
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• 제55권3호
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• pp.95-101
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• 2006

This paper proposes a modified current differential relay for $Y-{\Delta}$ transformer protection. The relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. A method to estimate the circulating component of the delta winding current is proposed. To cope with the remanent flux, before saturation, the core-loss current is calculated and used to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Test results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation, because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay does not require additional restraining signal and thus cause time delay of the relay.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전력기술부문
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• pp.262-265
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• 2003

During magnetic inrush or over-excitation saturation of the core in a transformer draws a large exciting current. This can cause mal-operation of a differential relay. This paper proposes a modified current differential relay for transformer protection. In order to cope with the remanent flux at the beginning. the start of saturation of the core is detected and the core flux at the instant is estimated by inserting the differential current into a magnetization curve. Then, this core flux value can be used to calculate the core flux. The proposed relay calculates the core-loss current from the induced voltage and the core-loss resistance; the relay calculates the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss current and the magnetizing current from the conventional differential current. The proposed technique not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the speed of the conventional relay.