• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.11a
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• pp.275-278
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• 2007

Dissolved gases analysis (DGA) is one of the most useful techniques to detect incipient faults in power transformers. Criteria interpreting DGA result is the most important. Because of difference of operation environment, construction type, oil volume, and etc, the interpretative criteria of DGA at KEPCO must be different with other standard like IEC-60599, Rogers and Doernenburg. In this paper, we collected the DGA data of the normal condition transformers and the incipient fault transformer to suggest the most appropriate criteria. Using these data, this paper suggests appropriate condition classification algorithm. Suggested algorithm can help to detect incipient fault earlier without unnecessary sampling.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1996.11a
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• pp.101-103
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• 1996

This Paper describes Peak load forecasting technique of pole transformers with correlation equation. While customers are demanding safe energy supply, current correlation equation that is used for load management of pole transformers has some problems. To get accurate correlation equation. several correlation equation were examined using past data and nu data collected using the measuring instrument developed for this study. It was recognized that the quadratic equation was the most accurate for peak load forecasting from working electrical energy.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.251-255
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• 2003

This paper proposes a novel UPQC(unified power quality conditioner) based on H-bridge modules, isolated through single-phase multi-winding transformers. The dynamic performance of proposed system was analyzed by simulation with EMTDC/PSCAD, assuming that the UPQC is connected with the 22.9kV distribution line. The proposed system can be directly connected to the transmission line without series injection transformers. It has flexibility in expanding the operation voltage by increasing the number of H-bridge modules and can compensate reactive power, harmonics, voltage sag and swell, voltage unbalance. The control strategy for the proposing UPQC was derived using the instantaneous power method. The proposing UPQC has the ultimate capability of improving power quality at the point of installation on power distribution systems and can be utilized for the future distribution system.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.938-941
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• 1992

This paper presents an acoustic emission(AE) technique using ultrasonic sensors to diagonize power transformers. Conventional methods detect and measure the electrical signal of the partial discharge(PD) of transformers in operation. The proposed techniques measures the acoustic signal generated by the partial discharge, and counts the number of the waveforms above a threshold to diagonize transformers. Experiments showed that the proposed method improved diagonosis capability over the conventional PD method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.8
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• pp.1382-1387
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• 2010

Recently, there has been a growing interest in the environmental conservation. Accordingly, problems related to the audible noise of transformers have became more frequent. Therefore, it is urgent to find a fundamental solution about the audible noises in the substations. This paper described a sort of fundamental solution to solve the noise problem. As a fundamental solution, we suggested the proper audible noise level of transformers through noise prediction in the substation construction phase. And we applied the low noise transformers which have the predicted noise level. As the result, we are able to satisfy the noise regulation through measuring 43.6dBA at the boundary of substation. It is confirmed that the average error rate of prediction was within 3 percent.

• Journal of Electrical Engineering and Technology
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• v.10 no.6
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• pp.2348-2355
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• 2015

Transformer mineral oil which is normally hydrocarbon based is non- biodegradable and pollutes the environment in all aspects. Though vegetable oils are eco-friendly in nature and potentially could be used in transformers as a replacement for the mineral oil, there usage is restricted because of their oxidative instability. The present work focuses on using rapeseed oil and pongamia (pongamia pinnata) oil as effective alternatives for the traditional mineral oil in power transformer. The oxidative stability of the rapeseed oil and pongamia oil is increased by using combinations of the natural and synthetic anti-oxidants as additives. The parameters like breakdown voltage, viscosity, flash point, fire point are measured for the rapeseed oil and pongamia oil with and without the additives as per IEC and ASTM standards. The results shown encouraging changes in the parameter values and ensures the use of the oils as a potential alternative insulation in power transformers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.649-656
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• 2013

A conventional epoxy-microsilica composite (EMC) and an epoxy-microsilica-nanosilicate composite (EMNC) were prepared in order to apply them to mold-type transformers, current transformers (CT) and potential transformers (PT). Nanosilicate was exfoliated in a epoxy resin using our electric field dispersion process and AC insulation breakdown strength at $30{\sim}150^{\circ}C$, glass transition temperature and viscoelasticity were studied. AC insulation breakdown strength of EMNC was higher than that of EMC and that value of EMNC was far higher at high temperature. Glass transition temperature and viscoelasticity property of EMNC was higher than those of EMC at high temperature. These results was due to the even dispersion of nanosilicates among the nanosilicas, which could be observed using transmission electron microscopy (TEM). That is, the nanosilicates interrupt the electron transfer and restrict the mobility of the epoxy chains.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.388-393
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• 1988

New circuit D-Q transformation concept is introduced to analyze AC converters such as inverters, rectifiers and cyclo-converters with ease. The equivalent linear time invariant circuit is obtained by substituting switches with equivalent turn-ratio variable transformers and changing balanced AC reactors into equivalent DC reactors combined by gyrators. This circuit enables us to utilize the powerful linear system analysis techniques such as Laplace transform otherwise which could not be applied to the time varying switching systems. Direct substitution of switches of DC converters with transformers is shown as a preliminary. Then the modeling procedure is shown for a controlled rectifier-inverter circuit. Finally an analysis example is proposed for a buck-boost inverter and the result is compared with the conventional approach. This approach is applicable to all AC converter families to determine the AC transfer functions and the DC operating points. It is identified that the switching systems are equivalent to the RLC filter circuits with transformers and gyrators.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.547-549
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• 2000

This paper develops phase sensitive detector for diagnosis of distribution transformers. And to detect the $tan{\delta}$ more effectively, this paper used phase sensitive detector. The sensor in oil which could be placed inside of the distribution transformer can measures the $tan{\delta}$ in oil. This could be the important factor and information, and it could be used for the basic information for a precise diagnosis. Establishment of the proposed system helps to build the confidence in monitoring of the oil-filled transformers.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.550-551
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• 2000

This paper suggests the system which monitors and diagnoses the distribution transformers. Moreover, this paper has established the system for the multi diagnoses by all the informations. Through the proven oil sensor, the oil temperature, capacitance and $tan{\delta}$ could be measured throughly, and followed by these informations, detected problems of the distribution transformers, using wireless data communication, could directly reported to the main host. For this, the proposed system is divided into sensor part and controller part. To prove the usefulness of the system, the paper compared and analyzed the system with the existing one, and after studying the correlation of the both, the result proved its goodness.