• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.541-543
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• 2002

This paper describes the analysis resulates on the P.T ferroresonance at 154kV GIS(Gas Insulated Substation) by EMTP(Electromagnetic transient program). We had simulated the PT ferroresonance between a potential transformer(PT) and open circuit braker's grading capacitance. The ferroresonance leads to very large power frequency overvoltage on PT bus and subsequent insulation failure. The damping circuit connected on the secondary winding were considered in the model. The actual countermeasure include a saturable inductor and a resistor series mounted, but the 2 ohms of damping resistance was used in the computational model.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.9
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• pp.414-420
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• 2005

A method for partial discharge diagnosis based on UHF narrow band type for GIS has been developed and calibrated. In generally, PD cannot be directly measured under on-line condition, but we can indirectly measure the electromagnetic wave made by PD using the high-frequency antenna. Compared with VHF band, electromagnetic waves of UHF band have a low influence for external noise in high-voltage substation. Therefore, we can detect the real abnormality with several pC in GIS using UHF narrow-band type method. For the case of no internal VHF sensor for GIS of the domestic substation, it has applied to use the external UHF sensor attached in spacer in GIS of existing substation. In this paper, we firstly described the technique of partial discharge measurement using frequency analysis and phase analysis in UHF band. Secondly, we presented the results of sensitivity test, the relationship of dBm-pC and diagnosis result of the cause of PD source by phase analysis. And then, we report the diagnosis result of partial discharge on the real GIS in domestic substation. These results make above method applicable for measurement of quantity and cause of PD for real operation GIS in high-voltage substation.

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.36-42
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• 2008

In a gas insulated substation (GIS), Very Fast Transient Over-voltages (VFTOs) are generated due to switching operations and ground faults. These fast transients are associated with high frequency components of the order of a few hundreds of MHz. These transients may cause internal faults i.e., layer-to-layer faults or minor faults in a capacitively graded bushing, which is one of the important pieces of terminal equipment for GIS. In the present study, the PSPICE model has been developed to calculate the voltage distribution across the layers of 420kV graded bushing for high frequency pulses of rise time 1 to 50ns, which simulate the VFTO. For this simulation, an equivalent electrical network of bushing with different equivalent layers has been considered. The effect of different equivalent layers modeling circuits on the non-uniform voltage factor has been analysed. The influence of copper strip inductance on voltage distribution across layers has also been analysed for various rise times of high frequency transients. Finally, the leakage current of the bushing is calculated for evaluating the bushing condition under these transients.

• KIEE International Transactions on Power Engineering
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• v.3A no.4
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• pp.214-221
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• 2003

In view of the fact that gas insulated switchgear (GIS) is an important piece of equipment in a substation, it is highly desirable to continuously monitor the state of equipment by measuring the partial discharge (PD) activity in a GIS, as PD is a symptom of an insulation weakness/breakdown. However, since the PD signal is relatively weak and the external noise makes detection of the PD signal difficult, it therefore requires careful attention in its detection. In this paper, the algorithm for detection of PD in the GIS using the wavelet transform (WT) is proposed. The WT provides a direct quantitative measure of the spectral content and dynamic spectrum in the time-frequency domain. The most appropriate mother wavelet for this application is the Daubechies 4 (db4) wavelet. 'db4', the most commonly applied mother wavelet in the power quality analysis, is very well suited to detecting high frequency signals of very short duration, such as those associated with the PD phenomenon. The proposed algorithm is based on utilizing the absolute sum value of coefficients, which are a combination of D1 (Detail 1) and D2 (Detail 2) in multiresolution signal decomposition (MSD) based on WT after noise elimination and normalization.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1620-1622
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• 2003

Recently, as the technology for the development of high voltage power apparatus using SF6 gas has made remarkable progress, it became possible to develop more compact power apparatus adopting single body substation system. In these gas insulated power apparatus, it is impossible to achieve perfect and safe insulation using only SF6 gas, because some solid insulation parts should be installed to support current-carrying conductor parts for electrical and mechanical safety. When spacers were installed in SF6 gas insulation system, they were exposed to severe electrical intensification which could reduce system insulation performance and restrict the rated operating voltage So, it is necessary to clarify the dielectric characteristics of spacers by analytically and experimentally, in order to design and develop more compact and optimum gas insulated systems. In this paper, the field distribution of three-phase spacers were investigated using three dimensional electrostatic field analysis tool adopting BEM method. And the obtained results were compared to the conventional two dimensional computations. According to these three dimensional calculations, it was possible to find out weak points in the spacer more clearly and these results could be applied to design more compact and optimum three phase spacer developments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.216-221
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• 2000

This paper describes the analysis results on the PT ferroresonance at 154 kV GIS (gas Insulated substation by EMTP(Electro- magnetic Transient Program). We had simulated the PT ferroresonance between a potential transformer(PT) and an open circuit breaker's grading capacitance. The ferroresonance leads to very large power frequency overvoltages on PT bus and subsequent insulation failure. The large power can be supplied to the PT by the high voltage on the opened circuit due to the grading capacitance and equivalent capacitance of the buses during the ferroresonance. The damping circuit connected on the secondary winding were considered in the model. The actual countermeasure include a saturable inductor and a resistor series-mounted, but the 2 ohms of damping resistance was used in the computationl model.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2076-2079
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• 1999

This paper describes the analysis results on the PT ferroresonance at 154 kV GIS (gas Insulated substation by EMTP (Electro-magnetic Transient Program). We had simulated the PT ferroresonance between a potential transformer(PT) and an open circuit breaker's grading capacitance. The ferroresonance leads to very large power frequency overvoltages on PT bus and subsequent insulation failure. The large power can be supplied to the PT by the high voltage on the opened circuit due to the grading capacitance and equivalent capacitance of the buses during the ferroresonance. The damping circuit connected on the secondary winding were considered in the model. The actual countermeasure include a saturable inductor and a resistor series-mounted, but the 2 ohms of damping resistance was used in the computational model.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.12
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• pp.1726-1731
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• 2014

This paper shows the developed new lightning arrester LCM (Leakage Current Measuring device) which is important element of GIS (Gas Insulated Switchgear) Preventive & Diagnostic system and verify its performance though strengthened test standards. The existing lightning arrester LCM was modified to solve measuring errors which happened frequently. At first, we explained the principle of measuring leakage current. Through analyzing some problems which the existing LCM have. we got some improvable items. For the performance verification of the improved LCM, we manufactured prototype LCM which is applied some improvable items such as improving LCM circuit, adding protection circuit, optimizing inner structure of LCM and changing ground design. After then we carried out the performance test. Accredited testing laboratory carried out the performance verification test according to performance test criteria and procedure of reliability test standards, IEC-60225, 61000 and 60068 etc. We confirmed the test results which correspond with the performance test criteria. Also, we confirmed the performance of the improved LCM installed & being operated at G Substation through the immunity test against the normal noise and open/close surge etc.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.12
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• pp.592-596
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• 2005

Recently, substations have been constructed in GIS (Gas Insulated Switchgear) and indoor type because of the increasing difficulties of securing locations. In case of urban substations, it is also common that the substations are exclusively fed by underground cables. Sometimes, the infrastructures in urban area, such as communication facilities, are located near substations to be constructed. In this paper, we examined such a case that a branch office building of KT(Korea Telecom) was located near 154 kV underground GIS substation under construction with about 100 meters of the lateral distance between two facilities. GPR (Ground Potential Rise) at the substation and the transferred earth potential at the KT building through the earth in SLG (Single-Line-to- Ground) fault condition were investigated based on a series of computer simulations. The calculated earth potential at a distance of 100 m from the substation was below 120 V which satisfying the limit value of 650 V.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.5
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• pp.313-319
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• 2000

In order to design the current carrying conductor for GIS, it is important to predict temperature-rise when rated current flows in the bus bar. However, it is not easy to apply the correct heat transfer coefficient on the boundary between different material for the thermal analysis. In this paper, the heat transfer coefficient which depends on parameters such like material constant, model geometry as well as ambient temperature, was calculated by analytic method. The calculated coefficient is used for the temperature rise prediction by F.E.M. The results show good agreement with experimental data.