• 조명전기설비학회논문지
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• 제24권9호
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• pp.150-158
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• 2010

We had experienced the several system failures which were concerned about zero sequence voltages at the tertiary side of 345[kV] transformers. In this paper, we had considered the zero sequence voltage and its reduction methods at the 345[kV] auto-transformer tertiary. For analysis, we used EMTP(Electro-Magnetic Transients Program). The calculation results by EMTP were compared with the measured data of the field tests. From the calculation and the field tests, we had verified that it is due to pre-saturation characteristics of the potential transformer. So, we had improved its saturation characteristics and applied it at real site. After improvements, we could reduce the zero sequence voltage below the setting level of the relay.

• 한국전기전자재료학회논문지
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• 제11권10호
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• pp.855-860
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• 1998

This paper presents a new structure for a piezoelectric transformer, operating in thickness extensional vibration mode. Modified $PbTiO_3$ family ceramics were used for the piezoelectric transformer, because it was a material with large anisotropy between elecromechanical coupling factors $K_t$ and $K_p$ . The size of piezoelectric transformer was 20mn long, 20mm wide and 3.1mm thick. The second harmonic resonant frequency of thickness extensional vibration mode was 0.72MHz at loading resistance 100[$\omega$], And Voltage gin of piezoelectric ceramics showed 0.53 at resonant frequency of sencond thickness extensional vibration mode.

• E2M - 전기 전자와 첨단 소재
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• 제10권6호
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• pp.562-569
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• 1997

The resonance characteristics on vibration mode of a transverse type ceramic resonator and the output voltage characteristics of a piezoelectric ceramic transformer are discussed in the effects of partial electrode arrangement (one sided, centered and both sided). A resonance characteristics of resonator depended strongly on both a vibration mode and a electrode structure because of a strain distribution. The maximum resonance current of a piezoelectric ceramic transformer [PCT] with partial centered electrode appeared in λ/2 mode, and that of a PCT with partial both sided electrode appeared in 3λ/2 mode. But the maximum output voltage of those samples appeared in λ/2 mode. In the PCT with partial both sided electrode, the ration of output voltage to input current was highest out of all samples and the poling voltage was a half times of 깬두 type transformer.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.66-70
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• 2003

In a HTS transformer, the perpendicular component of magnetic flux density ($B_r$) applied to HTS tapes of pancake windings becomes larger than that of solenoid winding, thereby decreasing the critical current in the HTS tapes. This paper introduces several methods to reduce $B_r$ applied to the HTS tapes in the transformer with double pancake windings by changing winding arrangements and the relative permeability of flux diverters. We have conducted a winding design for a single-phase 1MVA 22.9kV/6.6kV HTS transformer. We observed a change of $B_r$ due to a variation of gap-length between the high voltage windings and the low voltage windings, reciprocal arrangement and an increase of the number of the high voltage pancake. We also observed a change of Br on the HTS tapes due to variation of the relative permeability of flux diverters placed between the high voltage winding and the low voltage winding. Finally, we have designed a 1MVA 22.9kV/6.6kV HTS transformer winding using suggested methods and calculated transformer parameters by the 3D finite element method.

• 조명전기설비학회논문지
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• 제25권1호
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• pp.113-117
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• 2011

As one of the countermeasures to solve the increase of the fault current in a power system, the superconducting fault current limiter (SFCL) has been noticed together with the development of a various types of SFCL, which has accelerated the researches to apply a SFCL into a power system. Among the developed SFCLs, the transformer type SFCL is expected to be available for adjusting the voltage and the current ratings of the SFCL. In this paper, the fault current limiting and the bus line‘s voltage sag suppressing effect by the transformer type SFCL were investigated and the case without the transformer type SFCL was compared as well. Through the analysis on the results of the short-circuit tests, the fault current limiting and the bus-line voltage suppressing characteristics of the transformer type SFCL could be confirmed to be effectively performed.

• 한국전기전자재료학회논문지
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• 제11권10호
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• pp.849-854
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• 1998

The load characteristics on the voltage gain and efficiency were analyzed using a lumped constant equivalent circuit of the piezoelectric transformer. These analytical results were confirmed by experiments. Theoretical values of voltage gain were nearly constant with experimental ones. However, It was shown that theoretical values of efficiency is higher than experimental ones.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.183-189
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• 1998

In this paper, The load characteristics on the voltage gain and efficiency were analyzed sing an lumped constant equivalent circuit of the piezoelectric transformer. These analytical results are confirmed by experiments. Theoretical values of voltage gain were nearly constant with experimental ones. However, It was shown that theoretical values of efficiency had higher values than experimental ones.

• 전기전자학회논문지
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• 제18권1호
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• pp.31-36
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• 2014

본 논문에서는 트랜스포머의 자가공진 특성에 대하여 분석하였으며, 부유용량과 권선량, 권선비에 따른 변화관계를 수식으로 정리하였다. 일반적으로 트랜스포머에서의 부유용량은 제작과 관련하여 불요인자로 간주되나, 모든 트랜스포머에서 내재하는 특성을 갖는다. 특히 고역의 구동 주파수에서는 해당 특성이 확연하게 나타남은 주지의 사실이며, 자기적 요소와 결합하여 특정주파수에서 공진형상을 유발한다. 출력이득 값이 높아야 하는 소형 고전압기기, 특히 의료용 응용전기기의 경우 트랜스포머의 자가공진 특성을 이용하면 트랜스포머 및 회로의 사이즈를 줄임과 동시에 시스템의 경량화가 가능하여 추가적 설계 기법으로 제안한다.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1883-1890
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• 2017

Transformers are one of the most precious elements of the electric power system. Stability and reliability of the electric power network mainly depend on the working of the transformer. Leakage reactance of the transformer is one of the important factors and accurate calculation of the leakage reactance is necessary for the transformer designers and electric distributors. Leakage reactance of the transformer depends on the geometry of the transformer. There are many different methods for the calculations of the leakage reactance however mostly are usable when the axial heights of the high voltage and low voltage windings are equal. When the axial heights of high voltage and low voltage windings are asymmetric most of the analytical methods are not reliable. In this study, a new analytical method is introduced for the calculation of the leakage reactance. Fourteen different transformers are investigated in this study and four of them are presented in this paper. The results of the new analytical method are compared with the experimental results. Other analytical and numerical methods are also compared with this new method. Results show that this method is more reliable and accurate as compared to the other analytical methods. The maximum relative error between short-circuit test and proposed method for these fourteen transformers was less than 2.8%.

• 산업경영시스템학회지
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• 제31권3호
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• pp.117-124
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• 2008

Ultra-high voltage transformer industry has characteristic of small quantity batch production system by other order processing unlike general mass production systems. In this industry, observance of time deadline is very important in market competitive power security and company continued existence. The transformer winding is a process that rolls a coil is coated with an electric insulation material in order to generate the required voltage using the voltage fluctuation. The winding process is very important production process in the extra-high voltage transformer manufacturing industry because winding process is core process that occupy weight about half of whole process and is process that decide current ratio of transformer. This paper proposes a statistical calculation and control method of planned leadtime on the basis of real data and informations for the A company in transformer winding process. Moreover, we develop unit process scheduling system.