• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.962-964
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• 2001

In this paper, the RC filter for mitigating the output overvoltage of the 3-level 3300V 4MW inverter is described. The descriptions on power circuit and overvoltage phenomena are presented. The output transformer which may be used to obtain the higher output voltage, makes the filter design difficult because the parameter measurements are not easy and the accuracy may be poor. So, this paper presents several preliminary results on the output overvoltage with or without transformer to investigate the overall system characteristics. Some experimental results are also provided when the designed filter is applied.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.55-60
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• 2002

$100 A/mm^2$ class Bi-2223 tapes have recently become commercially available. Some important characteristics of the tapes, e .g. critical current, ac loss, characteristics at joint, fault current characteristics, are required for an application such as a power cable or a power transformer. In this paper they have been investigated experimentally. The results indicate that the self-field loss of the high current density tapes is not negligible, compared to resistive loss in a copper wire for the same currents. In a cable, the self-field loss for relatively large currents is much larger than the magnetization loss due to an external field. But in a transformer, the magnetization loss is dominant, compared to the self-field loss. Finally the fault current characteristics show that the high current density tapes are never safe from burn-out even for fault currents with a few cycles.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.821-826
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• 2012

The streaming electrification process of vegetable insulating oils occurring when the oils contacted with solid material in a high power transformer circulation system seems to cause electrical discharge incidents and may cause failures. We therefore measured the dielectric breakdown voltage tendency of vegetable insulating oils flowing on the surface of the charging device with various velocity and temperature. First, the relation between the velocity and breakdown voltage tendency of vegetable oils, can be explained by volume effect and v-t effect. Second, experimental results show that applied voltage have little effect on dielectric breakdown voltage, when vegetable insulating oils used for large power transformer.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.276-278
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• 1999

In this paper, we analyze customers' working electric energy (kWh) which is served pole-transformer in order to reduce peak load current error which is generated in application load correlation equation. The characteristic of electric load which customers are using is classified by customer's working electric energy (kWh) and ratio of cooling equipment possession. For the input data of fuzzy model, we used to kWh on April which represents basic load and kWh which is increased from April to August. The April kWh is used to classify into large, medium, small customer. Also, the increased kWh is used to know information of cooling equipment possession. For the output value of fuzzy model, we can determined peak load current limit in application load correlation equation.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.2 no.4
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• pp.45-51
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• 2009

A hardware implementation of Hilbert transform is indespensible element in DSP system, but it suffers form a high complexity of system level hardware resulted in a large amount of the used gate. In this paper, we implemented the Hilbert transformer using MAG algorithm that reduces the complexity of hardware.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.395-398
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• 2005

A novel full-bridge converter with a new energy-recovery driver implemented a regenerative transformer is proposed to improve the efficiency for wide input voltage range and load variation. The main switches achieve ZVS independent of the load current condition. During the free wheeling period, conduction loss is minimized by recovering the circulating energy to the source. The principle of operation, design consideration and experimental result, including efficiency, are presented in the case of large variation of the input voltage or load. A proposed 1kW converter prototype is compared with a PS-FB converter.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.12
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• pp.691-697
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• 2003

This paper proposes a current differential relay for transformer protection that operates in accordance with a blocking method based on the difference-function of a differential current. For magnetic inrush and over-excitation, discontinuities in the first-difference function of the differential current arise at the points of inflection, which correspond to the start and end of each saturation period of the core. These discontinuities are converted into the pulses in the second- and third-difference functions of the differential current. The magnitudes of the pulses are large enough to detect saturation of the core. A blocking signal is issued if the magnitude of the third-difference function exceeds the threshold and is maintained for three quarters of a cycle. The performance of the relay is assessed under various conditions with magnetic inrush, internal faults and external faults. The proposed blocking method can improve significantly the operating time of a relay and achieve high sensitivity of a relay.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1903-1905
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• 2000

Power transformers have a tendency of ultra-high voltage capacity as power demand increases day after day KEPCO also will have plan to supply transmission power from 345KV to 765KV in the early of 2000. Therefore, the fault by insulation destruction gives rise to large area of power failure in huge capacity transformers. On-line predictive diagnostics is very important in power transformers because of economic loss and its spreading effect. This study presents the algorithm for transformer oil analysis used KEPCO code, IEC code, gas pattern method and Dornenburg & Roger Ratio method. We also describe the MMI display of expert system programmed by Element Expert Tool(Neuron Data Inc.).

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.289-292
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• 2007

The flyback converter is one of the most attractive isolated converters in small power applications because of its simple structure. However, it suffers from high device stress, large transformer size, and high voltage stress across switch and diode. To solve these problems a new cost-effective PWM single-switch isolated converter is proposed. The proposed converter has no output filter inductor, reduced voltage stress on the secondary devices, and reduced transformer size. Moreover, the switch turnoff loss is reduced and no dissipative snubber across the secondary diode is required. Therefore, it features a simple structure, low cost, and high efficiency. The operational principle and characteristics of proposed converter are presented compared with flyback converter and verified experimentally.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2089-2094
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• 2009

The fault current has increased due to growth of distributed generations for the large power demand in power distribution system. To solve some problem such as excess of the circuit breaker's cut-off ratings, the superconducting fault current limiter(SFCL) has been progressed. However, the operational characteristics of the relay is changed by SFCL. Therefore, the proper impedance for the SFCL should be selected to keep protective coordination with the SFCL when SFCL is introduced on the neutral line of main transformer in distribution system. In this paper, the proper normal conducting resistance was suggested to solve the problem in case of the protection coordination with SFCL.