• Journal of Industrial Technology
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• v.14
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• pp.89-100
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• 1994

The effects of transient inrush currents on the dynamic characteristics of percentage differential relays are studied when the power transformers are reenergized. An algorithm of estimation the nonlinear magnetic property of power transformer and current trnasformer core are developed. Using this method, we can analyze the effect of inrush currents on the trip region of the percentage differential relays corresponding to the variation of the phase angle and the residual magnetism at the instant of switch closing. Test results are used to verify the availibility of the proposed algorithm. Finally a case study is performed to the 110 MVA main transformer in hydraulic power station.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.3
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• pp.33-38
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• 2010

In this paper, the nature of iron loss in electrical steel during alternating field excitation is investigated more precisely. The exact definition of AC iron loss is cleared by accurately measuring the iron loss for conditions of both the sinusoidal magnetic field and sinusoidal magnetic flux density. The results of this approach to iron loss calculations in electrical steel are compared to experimentally-measured losses. In addition, an inverse hysteresis model considering eddy current loss was developed to analyze the iron loss when the input is the voltage source. With this model, the inrush current in the inductor or transformer as well as the iron loss can be calculated.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.194-196
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• 2000

This paper presents a new digital relaying algorithm for protection of a two winding power transformer. The proposed algorithm calculates mutual flux linkages of primary and secondary windings from the currents and voltages of primary and secondary windings. The mutual flux linkage ratio of primary and secondary windings is equal to the turn ratio in case of the steady state and magnetic inrush. On the other hand, the ratio is different from the turn ratio in case of internal winding faults. The algorithm does not require B-H curve. The results of various tests are satisfactory.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.7
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• pp.375-381
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• 2004

This paper describes a three-winding transformer protective relaying algorithm based on the ratio of increments of flux linkages (RIFL). To minimize the approximation errors, the algorithm uses integration approximation. The RIFL of the two windings is equal to the turns ratio for all operating conditions except for an internal fault. For a single-phase and three-phase transformer containing the wye-connected windings, the increments of flux linkages (IFL) are calculated. For a three-phase transformer containing the delta-connected windings, the difference of IFL between the two phases are calculated to use the line currents, because the winding currents are practically unavailable. Their ratios are compared with the turns ratio. The comparative study between the proposed and differential approximation methods was conducted. The test results show that the algorithm can reduce the errors resulting from the conventional methods.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.10
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• pp.524-530
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• 2000

This paper presents a transformer protective relaying algorithm using the ratio of induced voltages. The proposed algorithm calculates primary and secondary voltage from currents and voltages of primary and secondary windings. The ratio of primary and secondary induced voltages is equal to the turn ratio in case of the steady state and magnetic inrush. On the other hand, the ratio is different form the turn ratio in case of internal winding faults. The algorithm does not require B-H curve and can reduce the relay's operating time.

• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.168-170
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• 2000

This paper presents a protective relaying algorithm for transformers using the ratio of induced voltages. The ratio primary and secondary induced voltages calculated calculates from currents and voltages of primary and secondary windings is used. In case of the steady state and magnetic inrush, it is equal to the turn ratio while it is different from the turn ratio in case of internal winding faults. The proposed algorithm operates satisfactorily even large residual flux.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2285-2286
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• 2008

여자돌입전류는 변압기 가압 시 발생하는 과도 전류의 한 형태로서 정격의 수배에 크기를 가지며 변압기에 직접적인 손상을 입히거나 보호계전기에 오동작을 유발 할 수 있다. 또한 전기 품질에 영향을 주어 기기에 충격을 입히거나 고장을 불러일으킬 수 있다. 따라서 여자 돌입전류를 분석하고 파악하는 일은 전력계통의 운영에 있어서 매우 중요하다. 본 논문에서는 과도 해석 프로그램인 EMTP(Electric Magnetic Transient Program)를 이용하여 여자돌입전류를 모델링하고, 여자돌입 전류모델링 검증을 통해 전형적인 여자돌입전류 파형에 대한 분석을 실시하였다.

• Journal of Electrical Engineering and Technology
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• v.5 no.4
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• pp.538-544
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• 2010

This paper proposes an estimation algorithm for the separate primary and secondary leakage inductances of a three phase $Y-\Delta$ transformer using least squares method. The voltage equations from the primary and secondary windings are combined into a differential equation to estimate the separate primary and secondary leakage inductances in order to use the line current of the delta winding. Separate primary and secondary leakage inductances are obtained by applying least squares method to the differential equation. The performance of the proposed algorithm is validated under transient states, such as magnetic inrush and overexcitation, as well as in the steady state with various cut-off frequencies of low-pass filter. The proposed technique can accurately generate separate leakage inductances both in the steady and transient states.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.320-322
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• 2003

This paper describes a current differential relaying algorithm for a three-phase transformer considering the nonlinear magnetization characteristics of the core. The iron-loss current is obtained from the calculated induced voltage and the core-loss resistance. The magnetizing current is calculated from the estimated core flux and the magnetization curve. The proposed algorithm uses the modified differential current, which is obtained by subtracting the iron-loss current and the magnetizing current from the conventional differential current. The various test results show that the algorithm can discriminate internal fault from magnetic inrush, overexcitation and an external fault.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.314-316
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• 2003

To prevent maloperation during magnetic inrush and over-excitation, a current differential relay for power transformers uses harmonic current based restraining or blocking scheme; it also uses dual slope characteristics to prevent maloperation for an external fault with CT saturation. This paper proposes a current differential relaying algorithm for power transformers with an advanced compensation algorithm for the secondary current of CTs. The comparative study was conducted with and without the compensating algorithm. The algorithm can reduce the operating time of the relay in the case of an internal fault and improve security for external faults.