• Transactions on Electrical and Electronic Materials
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• v.7 no.6
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• pp.324-329
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• 2006

As the average usage period of transformers increases, it is becoming increasingly necessary to know the internal condition of transformers. It is therefore critically important to establish monitoring and diagnostic techniques that can perform transformer condition assessment. Frequency response analysis, generally known as FRA, is one of the technologies to diagnose transformers. Using case studies, this paper presents the effectiveness of FRA as measurements for detecting transformer failures. This paper introduces the fact that FRA waveforms have useful information about diagnosis of failure on core earths and winding shield, and that the condition outside transformers can affect frequency response characteristics.

• 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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.9
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• pp.1146-1151
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• 2018

Recently, researches on the intelligence of electric power facilities have been trying to apply artificial intelligence techniques as computer platforms have improved. In particular, faults occurring in substation should be able to quickly identify possible faults and minimize power fault recovery time. This paper presents fault location technique for 154kV substation using neural network. We constructed a training matrix based on the operating conditions of the circuit breaker and IED to identify the fault location of each component of the target 154kV substation, such as line, bus, and transformer. After performing the training to identify the fault location by the neural network using Weka software, the performance of fault location discrimination of the designed neural network was confirmed.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.9
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• pp.1103-1111
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• 1999

STACOM will be utilized to control substation voltage in the near future. Although STACOM shows good voltage regulation performance owing to its rapid and continuous response, it needs additional reactive power compensation device to keep control margin for emergency such as fault. ULTC transformer is one of good candidates. This paper presents a Kohonen Neural Network (KNN) based coordination control scheme of ULTC transformer and STACOM. In this paper, the objective function of the coordination control is minimization of both STACOM output and the number of switchings of ULTC transformer while maintaining substation voltage magnitude to the predefined constant value. This coordination, control is performed based on reactive load trend of the substation and KNN which offers optimal tap position in view of STACOM output minimization. The input variables of KNN are active and reactive power of the substation, current tap position, and current STACOM output. The KNN is trained by effective Iterative Condensed Nearest Neighbor (ICNN) rule. This coordination control applied to IEEE 14 bus system and shows satisfactory results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2084-2090
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• 2007

The DGA (Dissolved Gases Analysis) technique has been widely using for fault diagnosis of the power transformers. Some electric power utility company establishes the criteria of DGA to improve reliability, because of difference of operation environment and design of power transformer. In this paper, we introduce intelligent diagnosis system for DGA result of KEPCO (Korea Electric Power Cooperation). This system can classify patterns type of gases ratio that frequently occurs in recent result of gases analysis using Fuzzy Inference. The classification of Patterns let us know that major causes of gases generation based on type of patterns. Finally, Neural Network based on patterns diagnose transformer. NN was trained using result data of DGA of actually faulted transformers recently. Result of intelligent diagnosis system is right well in comparison with actual inner inspection of transformers.

• 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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• 1997.07c
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• pp.864-866
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• 1997

This paper presents fault recognition and interpretation in power transformers using dissolved gas analysis embedded Kohonen feature mapping. The imprecision of gas ratio analysis in dissolved gas analysis are managed by mapping in accordance with learning of Kohonen neural network. To verify the effectiveness of the proposed system, it has been tested by the historical gas records to power transformers of Korea Electric Power Corporation. More appropriate fault types can support the maintenance personnels to increase the disgnostic performance for fault of power transformers.

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.37-39
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• 2004

To restrain abnormal voltage and effective operation in protect system, some of customer in Korea earth their own transformer in 154kV power system. The above ground system has some problems if ground fault occurs in other related area such as ground relay errors, under count register in two element register system. There for most huge customers opens the ground neutral and it causes errors in insulate and protection coordination and register system. In this paper presents the solution for above system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.189-189
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• 2010

The Improved flux-lock type superconducting fault current limiter(SFCL) is composed of a series transformer and superconducting unit of the YBCO coated conductor. The primary and secondary coils in the transformer were wound in series each other through an iron core and the YBCO coated conductor was connected with secondary coil in parallel. In a normal condition, the flux generated from a primary coil is cancelled out by its structure and the zero resistance of the YBCO thin films. When a fault occurs, the resistance of the YBCO coated conductor was generated and the fault current was limited by the SFCL. In this paper, we investigated the fault current limiting characteristics through the spot at the beginning of the fault current in the Improved flux-lock type SFCL. The experiment results that the fault current limiting characteristics was difference according to the point of a fault current started. Through the analysis, it was shown that shorter the time of a phase transition.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.954-957
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• 1997

In this paper, we analyze the voltage sag caused by reclosing on electric power distribution system. When a fault is on the electric system, a reclosing operation brings a voltage sag on the feeders which is supplied with a common substation transformer. By analyzing the fault wave-form measured in the field, it is showed that a voltage sag is in proportion to a fault current. Also, we propose an adaptive reclosing scheme. This scheme changes the number of reclosing as a function of the magnitude of a fault voltage and the fault type. As the proposed scheme is compared with conventional scheme in the side of voltage sag and permanent fault, it is verified that the proposed scheme is more effective than conventional scheme.