• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.34-41
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• 2016

This study investigates transformer losses caused by current harmonics. Electrical transformers are designed to work under sinusoidal voltage and current waves at a rated frequency. Recently, various nonlinear loads, such as power electronic converters, are connected to a power system; these converters generate current harmonics. Current harmonics increase power loss in transformers, which results in several problems, including temperature increase of the transformer and insulation damage. These problems will eventually shorten the operational life of the transformer. In this study, different types of losses caused by current harmonics in three-phase transformers are studied under linear and nonlinear load conditions. Linear loads are simulated and experimented on using pure resistance load, whereas nonlinear loads are simulated and experimented on using a three-phase twelve-pulse thyristor full-bridge rectifier. The different types of losses in three-phase transformers are evaluated analytically through the experimental result and simulation in PSiM.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.43-48
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• 2000

In this paper, vortical integrated transformers using bondwires are proposed and characterized for MMIC's (Monolithic Microwave Integrated Circuits) In a wide range of frequencies (1∼20 GHz), where full-wave analysis by the FEM (Finite Element Method) was adopted. The electrical characteristics of the proposed transformers are compared with those of the spiral transformer. We extracted mutual inductances from S -parameters. The vertical transformers using bondwires have not only low insertion loss but also reduce parasitic capacitances and dielectric loss due to their separation from substrates. It can be fabricated easily by used of the modern automatic wirebonding technology. It is expected that the proposed transformers are to improve the performance of MMIC's applied to impedance matching, and phase shifting circuits.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.5
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• pp.23-29
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• 2005

The increasing use of nonlinear loads has resulted in an increase in the harmonic content of the load current for power transformers. Transformers subject to harmonic currents have higher losses and need to be derated. This paper presents a simple method for determining the capability of transformers to supply harmonic load currents and shows that the application of capacitor banks with a series connected reactor and harmonic filters will greatly increase the capability of transformers.. The EDSA program was used as a simulation tool for the case study.

• Progress in Superconductivity and Cryogenics
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• v.9 no.1
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• pp.67-71
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• 2007

HTS transformers which have been developed until now had only fundamental structures. Among the auxiliary functions of conventional transformers, voltage regulating is the most important one. For the voltage regulation, conventional transformers are equipped with on load tap changers (OLTCS). In this paper, we describe the possibility of the HTS transformer with OLTC. For the case study, we designed a single phase 33 MVA HTS transformer with OLTC. It is one of three individual HTS transformers which composes a 3 phase, 100 MVA transformer. It is expected to substitute for a 3 phase, 60 MVA conventional transformer in Korea. The parameters of an HTS transformer are varied due to the gap length between primary and secondary windings. The length was decided for the transformer to have the impedance of 12 %. Its size was limited to the one of the conventional transformer. The characteristics of the HTS transformer were analyzed in both case of having OLTC and not.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.497-507
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• 2010

This paper presents current unbalance improved half-bridge LLC resonant converter using the two transformers with different leakage inductances. The proposed converter resonates with the leakage inductance and magnetizing inductance of the transformer and the resonant capacitance. The converter operates in a wide load range and satisfies the zero voltage switching even under the light load. The series-parallel connected two transformers act as the transformers or the resonant inductances according to the operational modes, and the separate output filter inductance in the transformer secondary is not needed using the leakage inductance. The current unbalance of the secondary diode rectifier is improved using the different leakage inductances of the two transformers and the asymmetrical pulse-width modulation (PWM). In this paper, the operational principle of the converter is explained by the modes, and the design example for the prototype is also shown. To validate the performance of the converter, the prototype is implemented as the designed circuit parameters and the good performance of the proposed converter is shown through the experimental results

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.3
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• pp.194-198
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• 2010

Recently as the electronic devices are getting to be more and more smaller, transformers are needed to be micro fabricated using MEMS technology. In this paper transformers have been fabricated and measured by depositing insulation layer to reduce the loss of eddy current and in the middle core a high permeability permalloy was designed based on the turns ratio between primary coil and secondary coil which are 1:1 transformers. (the number of turns of primary coil and secondary coil: 3/3, 5/5, 7/7). The size of the transformers including ground shield are $1mm{\times}1.5mm$, $1mm{\times}1.95mm$, $1mm{\times}2.35mm$ respectively. The line width, pitch and the height of post are 50um. Based on the measured data from the micro fabricated transformers, the 3/3 turns in the primary coil and secondary coil showed the lowest insertion loss with 1.5 dB at 480 MHz and the 7/7 turns in the primary coil and secondary coil showed the highest insertion loss with 2.5 dB at 280 MHz. Also confirmed that the bandwidth goes up as the number of turns goes down. There was some difference between the actual measured data and the HFSS simulation result. It looks as if it is an error of the difference between oxidation of copper or the permeability of SU-8.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.47-55
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• 2008

According to the increase of power demand and expansion of downtown, it is necessary to install transformers additionally in operating substations and construct substations in residential area. But the public complaint has been increased due to the transformer noise of the substation. KEPCO has used a vibration preventing pad, various soundproof walls and an enclosure to transformers in outdoor substations, and a soundproof door, shutter and wind-path soundproof equipment in indoor substations to block the sound propagation from the transformers. But these noise reduction methods are not satisfied. It should be considered to reduce transformer noise itself. To shut out sound emitted from transformers, we developed a soundproof technology that wall up reinforcing bar by steel sheet. For the practical application of it, we analyzed the vibration characteristics of a transformer tank and reduction of noise according to soundproof plate. As a result, it is confirmed that the technology can reduce 11 [dB] of transformer noise.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.694-696
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• 2002

Transformers together with all equipment and accessories shall be designed and constructed to withstand the mechanical and thermal stresses produced by external short circuit which include three phase, single line-to-ground, double line-to-ground and line-to-line faults etc. Generally the Short Circuit Test of transformers is tested according to the ANSI/IEEE, IEC/JEC, KS etc, in domestic. In this study, it will be showed and compared the difference of symmetrical current for short circuit test of a Pad -mounted transformer according to with ANSI /IEEE and IEC.

• Journal of Electrical Engineering and Technology
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• v.7 no.4
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• pp.538-545
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• 2012

In this paper a novel cascaded transformer multilevel inverter is proposed. Each basic unit of the inverter includes two DC sources, single phase transformers and semiconductor switches. This inverter, which operates as symmetric and asymmetric, can output more number of voltage levels in the same number of the switching devices. Besides, the number of gate driving circuits is reduced, which leads to circuit size reduction and lower power consumption in the driving circuits. Moreover, several methods to determination of transformers turn ratio in proposed inverter are presented. Theoretical analysis, simulation results using MATLAB/SIMULINK and experimental results are provided to verify the operation of the suggested inverter.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.2
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• pp.20-25
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• 2016

This paper describes the effectiveness of continuous water removal in oil immersed transformers. Insulation oil in which insulation papers were immersed were prepared for tests and water concentrations in oil with heating time were measured at five oil temperatures. Also, the tests that water dissolved in $100^{\circ}C$ oil was removed at once and continuously at $50^{\circ}C$ and $100^{\circ}C$ were performed for consideration of effective method for water removal. Test results indicated that the oils for water measurement have to be extracted at similar temperatures and water in oil has to be continuously removed at higher temperatures for more effective water management of transformers.