• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.295-300
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• 2007

High temperature superconducting (HTS) windings for an HTS transformer which have been developed have two kinds of type, one is the layer winding and the other is disk winding. The layer winding has adopted for an HTS power transformer so far because of the small AC losses of the HTS windings. The disk windings have surface of the HTS wire. We propose a new winding method for a high voltage HTS transformer which has advantages of both type of HTS windings, and we call it continuous disk winding. This new HTS winding consists of pile of HTS disk windings. The continuous disk winding was fabricated with multi-stacked HTS wires for dover HTS transformer. We can check the potential possibility from the characteristic test of the fabricated winding. The new type HTS windings can be applied to HTS power transformers, especially to the high voltage ones.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.5
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• pp.15-21
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• 2011

This paper presents an analyzing method of the capacitance of the power transformer for initial voltage distribution and insulation design. When a high incoming surge voltage is accidently occurred in windings of transformer, it does not distribute equally in the windings. This phenomenon makes electric field concentration and the insulating material could be break. Initial voltage distribute mostly depends on capacitances between winding to winding or winding to core in the transformer. If the C network can be structuralized into the equivalent circuit model and be calculated each capacitance element value by circuit analysis and FEM(Finite Element Method) simulation program, the transformer designer could know the place where the structure is to be modified or the insulation to be reinforced. This method quickly provides the data of the voltage distribution in each winding to the designer.

• Proceedings of the KIPE Conference
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• 1998.11a
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• pp.55-59
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• 1998

By this time, Diode Rectifier or SCR has been used to gain DC Voltage for Electrolysis Power. Generally DC Voltage is produced from rectifier shall be transformed before rectifier using step-down transformer to obtain adaptable DC Voltage, rectifier output. In the same way, rectifier using SCR shall obtain output voltage after step-down voltage through transformer and control of the SCR firing angle. Transformer shall be used for this two methods to adjust the voltage. But the size and weight of the transformer are increased in accordance with the increase of capacity, and the hardships are accompanied in workspace or transportation. Besides, only the value of input voltage is possible to be regulated, and the expectation of current control is almost impossible during Electrolysis. This study has conducted Design and Simulation to reduce the size and weight of transformer and to be enable voltage and current control of Electrolysis power through high-speed switching using Inverter, Electronics device.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.9
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• pp.541-545
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• 2000

We propose a pulsed $CO_2$laser below 30W by the AC(60Hz) switching control of leakage transformer primary which has some advantages of cost and size compared to a typical pulsed power supply. Pulse repetition rate is adjusted from 5 Hz to 60 to Hz control laser output. In this laser a low voltage open loop control for high voltage pulse discharge circuit is employed to aviod the Hv sampling or switching and high voltage leakage transformer is used to convert low voltage pulse rectified from AC to high voltage one. A ZCS(Zero Crossing Switch) circuit and a PIC(programble one-chip microprocessor are used to control gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to the frequency of AC line and a high leadkage inductance. The maximum laser output was about 23 W at pulse repetition rate of 60Hz total gas mixture of $CO_2$ : $N_2$ : He=1: 9: 15 and total pressure of 18 Torr

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.4
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• pp.366-373
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• 2005

This paper presents two new circuit topologies of the dc busline side active resonant snubber assisted voltage source high frequency link soft switching PWM full-bridge dc-dc power converters acceptable for either utility ac 200V-rms or ac 400V-rms input grid. These high frequency switching dc-dc converters proposed in this paper are composed of a typical voltage source-fed full-bridge PWM inverter, high frequency transformer with center tap, high frequency diode rectifier with inductor input filter and dc busline side series switches with the aid of a dc busline parallel capacitive lossless snubber. All the active switches in the full-bridge arms as well as dc busline snubber can achieve ZCS turn-on and ZVS turn-off transition commutation with the aid of a transformer leakage inductive component and consequently the total switching power losses can be effectively reduced. So that, a high switching frequency operation of IGBTs in the voltage source full bridge inverter can be actually designed more than about 20 kHz. It is confirmed that the more the switching frequency of full-bridge soft switching inverter increases, the more soft switching PWM dc-dc converter with a high frequency transformer link has remarkable advantages for its power conversion efficiency and power density implementations as compared with the conventional hard switching PWM inverter type dc-dc power converter. The effectiveness of these new dc-dc power converter topologies can be proved to be more suitable for low voltage and large current dc-dc power supply as arc welding equipment from a practical point of view.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.830-833
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• 2004

Voltage step-down characteristics of Ring/Dot type piezoelectric transformer were examined with increasing input voltage from $10\;V_{pp}$ to $140V_{pp}$. Then the output load resistance was fixed to $125\;\Omega$. The voltage gain showed constant value till the input voltage of $70\;V_{pp}$. And then it linearly decreased till the input voltage of $140V_{pp}$. The output voltage of fabricated piezoelectric transformer increased with increasing input voltage. And driving frequencies when the output voltage was maximum value were changed according to input voltage. Frequency shifts and temperature rise of fabricated sample showed 2 kHz, $13^{\circ}C$, respectively when input voltage was changed from $10\;V_{pp}$ to $140V_{pp}$. Because of the temperature rise of fabricated piezoelectric transformer, the step-down characteristics of it was deteriorated above the input voltage of $70\;V_{pp}$.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.574-576
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• 2008

Now there are two types Non-contact compensation AC automatic voltage regulator (A.V.R). One is transformer compensation regulator, whose principle is the combination of multiple compensation transformers, do the compensation by turning on and off the connections of the transformer through the multi-full bridge circuit. This method removed the mechanical drive and contacts, which increases the life and the dynamic performance of the A.V.R. However, the compensation is multilevel, and it needs many compensation transformers and switches, the circuit is complex, the compensation precision is low. Another type is PWM switch AC regulator, whose principle is getting the AC voltage from the input, then induce the AC compensation voltage through commutating and high frequency PWM transforming, and phase tracking. Here the compensation is step-less, the compensation precision is high, and the response is fast. But the circuit is complex, and it needs an inverse compensation transformer, which is difficult to realize high-power applications. In this paper, it shows an Automatic Voltage Regulator which use high frequency PWM inverter do compensation. This A.V.R has the function as the custom-power, which make the performance of the power supply in a high level.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.494-498
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• 2002

HTS transformer experimentally. High temperature superconductors can only be applied against an engineering specification that has to be determined for each particular application form the design requirements for economic viability and for operation margins in service. High temperature superconducting(HTS) power apparatus are very promising candidates for application. Especially, these advantages make superconducting transformers very promising candidates for application in electrical power engineering and locomotives. In order to realize the HTS transformer, it is necessary to establish the high voltage insulation technique in cryogenic temperature. So far, insulation research of Pancake type HTS transformer is lacking nothing but insulation research of . solenoid type transformer consisted. Therefore, the composite insulation of double pancake coil type transformer are described and ac breakdown voltage characteristics of liquid nitrogen(LN$_2$) under HTS pancake coil electrode made by Bi-2223/Ag are studied. Breakdown in LN$_2$ is dominated electrode shape and distance. The relation between surface flashover voltage is considered for FRP. This research presented basis information of electrical insulation design for double pancake coil type HTS transformer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.5
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• pp.939-944
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• 2010

A high voltage air-cored helical strip/wire type pulse transformer has been fabricated for charging of a high voltage pulse forming line. As a primary coil, copper strip of 25mm width was wound helically around a MC nylon cylinder. For a secondary coil, copper enameled wire of 1mm diameter was wound around conical cylinder in order to provide insulation between two windings. The coupling coefficient of 0.53 was obtained when two coils were combined coaxially in the insulation oil filled chamber. Voltage gain and energy transfer efficiency were investigated by varying the parameters of primary and secondary circuit. Test results shows that the voltage gain increases up to 17 with increasing the primary capacitance up to 200nF. And highest energy transfer efficiency of 44% was obtained when the dual resonant operation condition was nearly satisfied. The pulse transformer developed in this study can be used for charging the middle conductor of a Blumlein pulse forming line.

• Transactions on Electrical and Electronic Materials
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• v.15 no.1
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• pp.12-15
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• 2014

At the moment of transformer energization by the supply voltage, a high current called transient inrush current, which may rise to ten times the transformer full load current, could be drawn by the primary winding. This paper discusses a microcontroller circuit with the intention of controlling and limiting the inrush current for a transformer, by the method of ramping up the supply voltage feeding to the transformer primary. Simulations and the experimental results show a significant reduction of inrush current, when the ramping up voltage is applied to the three-phase transformer load. The inrush current could be almost eliminated if the correct switching step rate is chosen.