• 전기학회논문지P
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• 제65권2호
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• pp.122-129
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• 2016

Current differential protection relaying with second harmonic restraint is the main protection for large capacity power transformer. PSCAD simulation program is widely used for modeling of dynamic varying transients phenomena. This paper deals with a power transformer model and transients analysis using PSCAD software to develop IED for power transformer. Simulation was carried out using a three phase 40MVA, 154/22.9kV, 60Hz, two-winding transformer with Y-Y connection used in actual fields. The paper analyzed transformer magnetizing inrush, external fault, and internal fault conditions with this model in the time domain. In addition, we performed an analysis in the frequency domain using FFT during several conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
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• pp.9-13
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• 2004

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. The relay correctly discriminates magnetic inrush and over-excitation from an internal fault and is not affected by the level of remanent flux.

• 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.

• 전기학회논문지P
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• 제57권3호
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• pp.236-243
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• 2008

This paper analyses magnetic flux saturation of matching transformer considering characteristic of dynamic voltage restorer(DVR) system to solve voltage sags which are considered the dominant disturbances affecting power quality. This DVR consist of PWM inverter to inject arbitrary voltage, LC low pass filter and matching transformer for isolation and grid connection. However, the matching transformer has an excess of inrush current by magnetic flux saturation in the core of transformer. Due to this inrush current, the rating of matching transformers is double for needed nominal rating for protection of DVR. Therefore, in this paper, an advanced modeling method of magnetic flux saturation is used to analyze a magnitude and characteristic of magnetizing current. Simulation and experimental results considering characteristic of DVR system are provided to demonstrate the validity of the proposed analysis method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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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.

• 대한전기학회논문지:전력기술부문A
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• 제53권7호
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• pp.382-388
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• 2004

The most widely used primary protection for the internal fault detection of power transformers is current percentage differential relaying(PDR). However, the harmonic components could be decreased by magnetizing inrush when there have been changes to the material of iron core or its design methodology. The higher the capacitance of high voltage status and underground distribution, the more differential current includes the second harmonic component during occurrence of an internal fault. Therefore, the conventional harmonic restraint methods need modification. This paper proposes an advanced protective relaying algorithm by fluxt-differential current slope characteristic and trend of voltage and differential current. To evaluate the performance of proposed algorithm, we have made comparative studies of PDR fuzzy relaying, and DWT relaying. The paper is constructed power system model including power transformer, utilizing the WatATP99, and data collection is made through simulation of various internal faults and inrush. As the results of test. the new proposed algorithm was proven to be faster and more reliable.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.274-276
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• 2002

This paper proposes a current differential relaying algorithm for power transformers using the third difference function of a differential current. The algorithm observes the instants when the wave-shape of the differential current is changed due to the change of the magnetization inductance. If the value of the third difference is bigger than the threshold, the output of a current differential relay is blocked for a cycle. In the cases of magnetic inrush and overexcitation, the blocking signal is maintained: however, for internal faults, reset in a cycle. The test results clearly show that the algorithm successfully distinguishes internal faults from magnetizing inrush.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 학술대회 논문집 전문대학교육위원
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• pp.101-105
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• 2005

To comparative analysis of proposed techniques, the paper constructs power system model including power transformer, utilizing the EMTP, and collects data through simulation of various internal faults and magnetizing inrush.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.199-202
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• 2002

This paper presents the new protective relaying scheme as a method for discriminating of power transform's transient state associated with magnetizng inrush state and internal fault using wavelet transforms. The simulation of EMTP with respect to different fault and inrush condition in transformer have been conducted, and the result prove that the preposed method is able to discriminate between inrush magnetizing current and internal fault.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 A
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• pp.229-232
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• 2001

This paper presents the protective relaying scheme as a method for discriminating of power transform's transient state associated with magnetizng inrush state, over-exciting state and internal fault using wavelet based neural networs. The simulation of EMTP with respect to different fault, inrush condition and over-exciting condition in transformer have been conducted, and the result prove that the proposed method is able to discriminate between inrush magnetizing current and internal fault.