• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.5
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• pp.242-250
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• 2005

This paper proposes a new protective relaying algorithm using Neuro-Fuzzy and wavelet transform. To organize advanced nuero-fuzzy algorithm, it is important to select target data reflecting various transformer transient states. These data are made of changing-rates of Dl coefficient and RSM value within half cycle after fault occurrence. Subsequently, advanced neuro-fuzzy algorithm is obtained by converging the target data. As a result of applying the advanced neuro-fuzzy algorithm, discrimination between internal fault and inrush is correctly distinguished within 1/2 after fault occurrence. Accordingly, it is evaluated that the proposed algorithm can effectively protect a transformer by correcting discrimination between winding fault and inrushing state.

• KIEE International Transactions on Power Engineering
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• v.12A no.1
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• pp.26-30
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• 2002

The four fuzzy criteria to distinguish the internal fault from the inrush fur the power transformer protection have been identified. They are based on the wave shape, terminal voltage, fundamental and second harmonic component of differential current. systematic way to determine the associated fuzzy membership function is also proposed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2317-2322
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• 2011

In three-phase power, when the power is supplied to the single phase load, there is the unbalance of load in the three-phase power. So the scott transformer is used in the power system to supply a single phase load in three-phase power without the unbalance of loads. Especially, the scott transformer is used in the AC substation of electric railroad. Two single phase transformers are combined by T-wiring in the scott transformer. So, two single phase voltage is provided by differing $90^{\circ}$ phase in three-phase power. The selection of related equipment and correction of protective relay are not easy from characteristic of the scott transformer when shunt and ground faults occur. In this paper, electric model of the scott transformer is suggested and the current of the scott transformer in shunt and ground faults is analyzed. Also, the scott transformer model is demonstrated by using Sinulink.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1892-1897
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• 2010

In three-phase power, when the power is supplied to the single phase load, there is the unbalance of load in the three-phase power. So the scott transformer is used in the power system to supply a single phase load in three-phase power without the unbalance of loads. Especially, the scott transformer is used in the AC substation of electric railroad. Two single phase transformers are combined by T-wiring in the scott transformer. So, two single phase voltage is provided by differing $90^{\circ}$ phase in three-phase power. The selection of related equipment and correction of protective relay are not easy from characteristic of the scott transformer when shunt and ground faults occur. PSIM(Power Electronics Simulator) is optimal simulation software in field of the power electronics and provide the simple and convenient user interface. In this paper, electric model of the scott transformer is suggested and the current of the scott transformer in shunt and ground faults is analyzed. Also, the scott transformer model is demonstrated by using PSIM.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.229-231
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• 2002

The digital current differential relaying scheme is widely used for primary protection of 765(kV) power transformer. The current differential relay pickup the internal fault at the threshold which is set at 30% of rating current. Margin of 30% include current transformer error 5%, relay error 5%, on load tap changer error 7% and margin factor 140% obtained from the field experience. In this paper transformer protection relay and relay setting rule of high voltage power system are discussed. And we verify the correctness of relay setting rule with current differential relay using Matlab simulation.

• KIEE International Transactions on Power Engineering
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• v.2A no.4
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• pp.153-159
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• 2002

Power transformer protective relay should block the tripping during magnetizing inrush and rapidly operate the tripping during internal faults. Recently, the frequency environment of power system has been made more complicated and the quantity of 2nd frequency component in inrush state has been decreased because of the improvement of core steel. And then, traditional approaches will likely be maloperate in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmonic component. This paper proposes a new relaying algorithm to enhance the fault detection sensitivities of conventional techniques by using a fuzzy logic approach. The proposed fuzzy based relaying algorithm consists of flux-differential current derivative curve, harmonic restraint, and percentage differential characteristic curve. The proposed relaying was tested with relaying signals obtained from EMTP simulation package and showed a fast and accurate trip operation.

• Proceedings of the KIEE Conference
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• 2006.07a
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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.

• Proceedings of the KIEE Conference
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• 2002.07a
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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.

• Proceedings of the KIEE Conference
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• 2001.07a
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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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.9
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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.