• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권10호
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• pp.683-692
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• 2000

A new primary-side-assisted zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation is proposed. The auxiliary circuit adopted to assist ZCS for the leading leg is composed of only one small transformer and two diodes. It has a simple and robust structure, and load current control capability even in short circuit conditions. Possibility of magnetic saturation due to asymmetricity of circuits or transient phenomena is greatly reduced, which is a very attractive feature in DC/DC converters with transformer isolation. The power rating of the auxiliary transformer is about 10% of that of the main transformer. Operation of a 12.5KW prototype designed for welding application was verified by experiments.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.621-625
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• 1999

Rosen type piezoelectric transformer for LCD backlight operated at high voltage and low current, may not be sucessfully used for illuminating general fluorescent lamps because low voltage and high current are required. In this study, the piezoelectric transformer with width vibration mode operated at low voyage and high current was designed for the application of fluorescent lasso ballast. The step-up ratio and efficiency as a function of the load resistance in the piezoelectric transformer indicated that the transformer can be effectively used for the electronic ballast for low profile fluorescent lamp.

• 한국전기전자재료학회논문지
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• 제16권8호
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• pp.688-692
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• 2003

For high voltage operation, a new type of piezoelectric transformer using radial vibration of disk, poled with the same direction was proposed. The piezoelectric ceramics was composed to PZT-PMN-PSN. The diameter and thickness of a disk type piezoelectric transformer were 45［mm］and 4［mm］, respectively The surface ratio of driving electrode and generating electrode of the piezoelectric transformer was 2 : 1. The resonance characteristics of input admittance, step-up voltage ratio and power transmission efficiency of the piezoelectric transformer were measured by varying the load resistance(0.1∼70［kΩ］). As a result, both resonance frequency and step-up voltage ratio increased with increasing load resistance. The step-up voltage ratio was reached more than 60 times under no load resistance. The maximum efficiency of 97% at load resistance of 2kΩ was obtained.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.742-747
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• 2005

Electric railroad transformer of a supply of Operation power of DC electric cars is intense fluctuation of load and flows the only big short-circuit current as a accident of the power system. it is a peculiarity more severe than general power transformer. Consequently, researches the properties about the rectifier mold transformer of DC substation and applies with data of safety of the electric railroad transformer. This paper analyzed a failure mode, the accident occurrence scenario and the be latent dangerous unit against the rectifier mold transformer of DC railway system.

• 설비공학논문집
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• 제11권2호
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• pp.157-166
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• 1999

Numerical calculations of turbulent natural convection in an enclosure of the 20 kYA oil-immersed transformer model are presented. The transformer is modelled as two concentric cylinders with different heights and diameters. The thermal boundary layers are well represented in the temperature distributions along the wall of the transformer model. The flow stratification between the hot and cold walls can not be seen in the transformer model. The turbulence eddy viscosity has its maximum at the center of the core and its maximum values at the top of the core are larger than those at the bottom of the core.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 추계학술대회 논문집
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• pp.327-330
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• 1999

In this paper, the electrical characteristics of λ vibration-mode piezoelectric transformer for applying to CCFL driving inverter was investigated. Piezoelectric transformer was made of PZT - PMN -0.5wt% N $b_2$ $O_{5}$ composition. As a results of the electrical characteristics of piezoelectric transformer, when applied voltage was 35[ $V_{rms}$] in 100[k$\Omega$] load resistance, output voltage was about 510[ $V_{rms}$] and output power was more than 2[W]. As output power increased, step-up ratio and temperature was very stable until output power was 2.5(W). Also, Efficiency was maximum in 70[k$\Omega$] load resistance, and about 89[%]. Also, when piezoelectric transformer was continuously driven for 10[hrs], output voltage and temperature change ratio was fess than 10[%], and very stable. Conclusively, piezoelectric transformer fabricated in this paper can be applied to piezoelectric inverter for CCFL driving.g.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1245-1249
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• 2017

Recently, unusual transformer failures have been reported in 25kV power systems connected with a VCB and transformer. In this study, performance of the protection system, dielectric strength of the transformers, characteristics of switching surges and resonance phenomena were analysed and assessed. All investigations regarding the insulation breakdown of the transformers were carried out by simulations, laboratory tests, factory tests and on-site measurements in order to thoroughly investigate the root causes. Furthermore, experimental methods for investigating the resonance phenomenon were derived and tests were conducted applying the derived method to recreate the phenomenon in the transformer. It is found that resonance between the transformer and switching surge generated by closing a VCB can initiate the breakdown of internal windings of a transformer.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 하계학술대회 논문집
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• pp.424-427
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• 2007

The LLC series resonant converter with a LLT (Inductor-Inductor-Transformer) transformer for PDP power supply is presented. LLT transformer used to combine the inductor and transformer into one unit has the increased leakage inductance in the primary and secondary due to the winding method and the use of the gaped core. The increased leakage inductance in the primary and secondary of LLT transformer can be impacted on the DC voltage gain characteristics of LLC series resonant converter. In this paper, DC gain characteristics and the experimental results of the LLC series resonant converter with a LLT transformer are verified on the Math-CAD simulation based on the theoretical analysis and the 600W experimental prototype.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 B
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• pp.321-323
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• 2000

This paper describes the construction and test results of a 10kVA single phase HTS transformer. Double pancake windings with BSCCO-2223 HTS tape and GFRP cryostat with room temperature bore are used in the transformer. Two double pancake windings are connected in series to provide 184 turns and two double pancake windings are connected in parallel to conduct the secondary current of 45.4A. Coefficients of the constructed transformer are obtained using the fundamental tests of the transformer. According to the test results, larger leakage reactance than expected is observed due to the bulky core which surrounded the cryostat.

• 한국전기전자재료학회논문지
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• 제23권2호
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• pp.164-168
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• 2010

The transformer is expected to be an essential component of a superconducting fault current limiter (SFCL) for both the increase of its voltage ratings and the simultaneous quench due to different critical current between high-$T_C$ superconducting (HTSC) elements comprising the SFCL. However, in order to perform the effective current limiting operation of the SFCL, the design for the SFCL considering the hysteresis characteristics of the iron core is required. In this paper, the influence of the hysteresis characteristics of the iron core comprising the transformer type SFCL on its current limiting characteristics was investigated. Through the comparative analysis on the hysteresis curves due to the ratio of the turn number between the 1st and the 2nd windings of the transformer, the proper design condition for the ratio of the turn number to achieve the effective current limiting operation of the transformer type SFCL could be obtained.