• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.498-499
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• 2006

Oil-filled transformer technology has been around more than 100 years. The principle of operation in the same today as it has been for the previous decades. But all transformers have their life so it is important to know their useful life and the time for replacement. This paper will address this issue and provide the distribution transformer oil aging test results. Distribution transformer and laboratory specimens were externally heated to their respective maximum temperatures. Sample of oil and paper were removed at convenient intervals for testing. We believe that the results of this study will show the possibility of assessing the life of transformers.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.225-227
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• 2006

Multilayer step down piezoelectric transformers were manufactured using PZN-PMN-PZT and PMN-PNN-PZT ceramics respectively. Sintering temperature of the ceramics was $940^{\circ}C$. And then. their electrical properties were investigated according to the variations of frequency and load resistance. The voltage step-up ratio of multilayer piezoelectric transformer showed the maximum values in the vicinity of 69 and 71kHz, respectively. At the load resistance of $100{\Omega}$, the piezoelectric transformers showed the temperature rises of about 21 and $18^{\circ}C$ at the output power of 15W and 18W, respectively. At the transformer with high effective electromechanical coupling factor($k_{eff}$), lower temperature increase was appeared.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.132-134
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• 2005

This paper represents the criteria of Power Transformers for substation design in Korea. The construction of new substations and expansion of existing facilities are commonplace projects in KEPCO(Korea Electric Power Corporation). The KEPCO has had the only design criteria, which need to be adequate criteria considering the new technology and environment in Korea.

• Transactions on Control, Automation and Systems Engineering
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• 제2권3호
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• pp.214-219
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• 2000

This paper presents a recoil and counter recoil motion measurement system using linear variable differential transformers (LVDT). The output of the LVDT is obtained from the differential voltage of the secondary transformers. Since a transducer core is attached to the motion body, the output is directly proportional to the movement length of the core. Displacement, velocity and acceleration are measured from the LVDT. With a comparison between the measurement result and the reference value obtained by the highly accurate Vernier calipers, it is proved that the measurement system with the LVDT is applicable to the test of the moving part of the mechanism with better accuracy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.159-163
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• 1989

The various degradation phenomena, such as the evolution of gases, tan $\delta$, moisture content and total acid number in power transformer insulation oil, have been measured and analyzed. Mineral oil has been degraded at laboratory by the forced thermal stress of $60^{\circ}C$ and $90^{\circ}C$ respectively. Thermal aging oil has been degraded about 17, 34, 72 days. Also, we extracted insulation oil from working transformers. We measured gases dissolved in samples, tan $\delta$, moisture content, total acid number. Activation energy and resistivity is calculated from them. It is found that gases and tan $\delta$ increases as partial discharge and total acid number increases and that conductivity of the sample increases as activation energy increases.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.590-593
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• 2004

This paper presents recent trends on the on-line monitoring and diagnostic systems for oil-immersed transformers. Specially, our system on YeoSu thermal power plant is introduced for high sensitivity and accuracy of ours. It is combined with communication networks to provide an on-line remote monitoring system. Several alarm criteria are formulated to enable a superimposed monitoring system to perform decisive action. The reasons for monitoring the condition and maintaining the health of electrical apparatus were discussed. The experience at the fields and the criteria for the judgment are also discussed in detail.

• 대한전기학회논문지:전력기술부문A
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• 제51권11호
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• pp.559-567
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• 2002

This paper presents the general recommendations for the overload criterions of mineral-oil-immersed distribution transformers rated 100kVA and less. For this purpose, we analyze the characteristics of top-oil temperature rising for mineral-oil-immersed power distribution transformer rated 100kVA and less, manufactured in Korea, In order to analyze the characteristics of top-oil temperature rising due to the distribution transformer loading, we performed experiments at KERI (Korea Electrical Research Institute) from December 2000 to May 2001. The restraint of ambient temperatures for the experiment results is solved using the results of foreign standards. Finally, we present the overload criterions of distribution transformer for summer and winter season, respectively.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1136-1141
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• 2003

The primary insulation materials used in an oil filled transformer are kraft paper, wood, porcelain and oil. Modern transformers use chemically treated paper to improve its tensile strength and resistance to aging caused by immersion in oil. But these insulation papers are mainly aged by thermal stress. Over the life time of the insulation paper and oil, it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper used in the layer insulation. We made two aging cells in which insulation papers and mineral oil are conducted to test thermal properties. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.16-18
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• 2002

This paper proposes a difference-blocked current differential relaying algorithm for power transformers. The proposed algorithm observes that the shape of the differential current is changed using the difference. If the change is detected, output of current differential relay is blocked for a certain time. In this way, the algorithm distinguishes internal faults from magnetizing inrush. The proposed algorithm uses only currents and is unaffected by the remanent flux.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.406-409
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• 2002

The primary insulation system used in an oil-filled transformer is Kraft paper, wood, porcelain and, of course, oil. Modern transformers use paper that is chemically treated to improve its tensile strength properties and resistance to aging caused by immersion in oil. These insulation papers are mainly aged to thermal stress. Over the course of the insulation paper and oil's life it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper using the layer insulation. We made two aging cell in which thermal aging tests of insulation papers and mineral oil are conducted. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.