• 전기의세계
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• v.28 no.11
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• pp.45-51
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• 1979

Finte element methods are developed for the initial distribution problems which contain the surge potential circuits of high voltage transformer windings. The initial distribution of surge voltages in transformer windings are useful to the work to a practical engineering basis. However, the conventional methods of analyzing them so far are much complicated for practical designs. In this paper, the ability to solve surge potential field problems underlies the development of descreting methods to a lodal capacitive distribution-coefficients for determing the surge voltage relationship among a set of transformer coils. A practical example-the modeling of an antioscillation shield coil winding and hisercap winding is used to illustrate and evaluate these methods.

• Electrical & Electronic Materials
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• v.8 no.2
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• pp.217-223
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• 1995

In this paper, we investigated physical properties and electrical characteristics of the fluorocarbon that used as coolants for large power gas-insulated transformer. Volume resistivity of the fluorocarbon was .rho.=1.87*10$^{15}$ [.ohm.cm] at 1 atm, 27.deg. C. Dielectric constant was 1.86 and decreases as temperature increase. The breakdown voltage at 1 atm was higher than that of transformer oil. The breakdown voltage of fluorocarbon vapor was about 18kV when pressure in a test chamber increases over lkg/cm$^{2}$. When fluorocarbon was mixed with SF$_{6}$ gas, breakdown voltage of the mixed was higher than that of fluorocarbon. Then fluorocarbon leads to increase over 4kg/cm$^{2}$ in pressure as temperature increase. Therefore, when a gas-insulated transformer is manufactured, the design must be taken into consideration a high-pressure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.191-194
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• 1998

This Paper present 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 is a material with large anisotropy between electromechanical coupling facters k$\sub$t/ and k$\sub$p/. Piezoelectric transformer was fabricated that is 20mm long, 20mm wide and 3.1mm thick. Resonant frequencies of sencond thickness extensional vibration mode is 1.72MHz at loading resistance 100{$\Omega$]. And Voltage gain of piezoelectric ceramics is showed 0.53 at resonant frequency of sencond thickness extensional vibration mode.

• Progress in Superconductivity and Cryogenics
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• v.13 no.2
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• pp.5-8
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• 2011

This paper shows results of a design work of a program that is to develop a large power single phase high temperature superconducting (HTS) transformer. The program forms a part of a national project in Korea. A target of the design work is an HTS power transformer with rated voltages of 154 kV/22.9 kV and material for windings is supposed to be coated conductor. The design results presents in this paper will include: 1)HTS winding structures for high voltage in liquid nitrogen, 2)design result of continuously transposed coated conductor (CTCC), 3)conceptual design of high voltage bushings, 4)cooling system. A feasibility study will succeed to this design work for construction of a prototype HTS power transformer with capacity/voltage of 33 MVA/154 kV.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.605-608
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• 2001

With the intention of investigating the breakdown properties of oil-immersed transformer oils in temperature range of 20∼100[$^{\circ}C$], we are made researches AC breakdown in the gap of 500∼2,500[$\mu\textrm{m}$]. The classification for the physical properties of oil for oil-immersed transformer by FTH and $^1$H-NMR experiments was confirmed to type of mineral oils. As the dependance of breakdown properties due to electrode gap length variation, breakdown voltage was found increasing according to the increase of gap, while dielectric strength was decreasing. As a result the characteristics for AC breakdown, It goes to prove that the breakdown voltage was increased to 90[$^{\circ}C$] but decreased over 90[$^{\circ}C$] in the temperature range. Also, breakdown voltage was found increasing in the increase of gap and the rising of temperature according to Weibull distribution.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.760-761
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• 2007

Instrument transformers provide the reproduction of the primary current or voltage to the measuring and protecting devices. The errors of an iron-cored transformer are caused by the difference between the primary and secondary currents due to the hysteresis characteristics of the iron-core. An error compensating algorithm for instrument transformer can improve the accuracy of conventional current and voltage transformers. This paper describes the performances of the electronic current and voltage transformers mounted an error compensating algorithm. The test results of the electronic transformers in Korea Electrotechnology Research Institute(KERI) are presented.

• Journal of Power Electronics
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• v.5 no.4
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• pp.257-263
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• 2005

This paper describes the development and testing results of a high density High Voltage Power Supply (HVPS) that drives microwave Traveling Wave Tubes (TWTs) of phased array transmitters for airborne EW systems. The HVPS is designed to consist of a number of modules connected in series. Among them, especially, the high-density pulse transformer module including the resonant circuit is newly designed to make the HVPS much more reliable. In addition, this paper describes the development of high voltage solid-state modulation using fast switching devices (FETs) and also represents the test results of a modulator module.

• Journal of Power Electronics
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• v.8 no.3
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• pp.217-227
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• 2008

The electric power subsystems (EPS) of most remote sensing satellites consist of a solar array as a source of energy, a storage battery, a power management and control (PMC) unit and a charge equalization unit (CEU) for the storage battery. The PMC and CEU use high frequency transformers in their power modules. This paper presents a design, implementation and testing results of a high frequency transformer for the EPS of satellite applications. Two approaches are used in the design process of the transformer based on the pre-determined transformer specifications. The transformer is designed based on an ETD 29 ferrite core. The implemented transformer consists of one center-tapped primary coil with eleven center-tapped secondary coils. The offline calculation results and measured values of R, L for transformer coils are convergence. A test circuit for measuring the transformer parameters like voltage, current and B-H hysteresis was implemented and applied. The test results confirm that the voltage waveforms of both primary and secondary coils were as desired. No overlapping occurred between the control signal and the transformer, which was not saturated during testing even during a short circuit test of the secondary channels. The dynamic B-H loop characteristics of the used transformer cores were measured. The sample test results are given in this paper.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.348-352
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• 2004

The mold transformers have been widely used in underground substations in large building and have some advantages in comparison to oil-transformer, that is low fire risk, excellent environmental compatibility, compact size and high reliability. In addition, the application of mold transformer for outdoor is possible due to development of epoxy resin. The mold transformer generally has cooling duct between low voltage coil and high voltage coil. A mold transformer made by one body molding method has been developed for small size and ow loss, but it needs some cooling method because heat radiation between each winding is difficult. The life of transformer is significantly dependent on the thermal behavior in windings. Many transformer designers have calculated temperature distribution and hot spot point by finite element method(FEM) to analyze winding temperature rise. In this paper, The thermal analysis of pole mount mold transformer with one body molding by duct condition is investigated and the test result of temperature rise is compared with simulation data.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2078-2083
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• 2007

We have analyzed operating characteristics of transformer-type superconducting fault current limiter (SFCL) according to the serial or parallel connections of secondary coils with $YBa_2Cu_3O_7$ (YBCO) thin films. The turn ratio between the primary and secondary coils was 63:21. Transformer-type SFCL using a transformer with secondary winding of serial or parallel coils could reduce the unbalanced quench caused by differences of the critical current density between YBCO thin films. We found that transformer-type SFCL having serial or parallel connections induced simultaneous quench between the superconducting units. The limiting current in the transformer-type SFCL with a parallel connection was lowered to 30 % compared to the SFCL with a serial connection. In the meantime, when the currents generated in the superconducting units were similar, the voltage value in the parallel connection was 60 % as low as that in the serial connection. However, the voltage generated in the primary winding was some higher. In conclusion, we found that transformer-type SFCL with parallel connection of secondary coils was more effective in fault current limiting characteristics and in the reduction of the consumption power for superconducting units compared to those of the transformer-type SFCL with serial connection of secondary coils.