• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.5
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• pp.411-416
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• 2010

A voltage drop characteristics of a transformer-based voltage disturbance generator with series transformers is analysed. It is well known that a voltage disturbance generator with series transformer is cost-effective and reliable compared with other types. The voltage drop depends on the %Z of the transformer, power rating, and output power factor. A wrong design of the transformer results in a severe voltage drop, which can not guarantee the proper performance of the generator. The voltage drop is analysed under the condition of 10kVA output power rating and 4% of %Z with the variation of power factor. It is found through simulations and experiments that the drop increases as the power factor decreases in lagging mode, and the drop is 4% of the rated voltage in case of 0.85 lagging power factor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.821-825
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• 2004

In this paper, in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, PMN-PZT ceramcis using $Li_2CO_3$ and $Bi_2O_3$ as sintering aids were manufactured, and their microstructural, dielectric and piezoelectric properties were investigated. The sintering aids were proved to lower the sintering temperature of piezoelectric ceramics due to the effect of $LiBiO_2$ liquid phase. At 0.1wt% $Li_2CO_3$ added specimen sintered at $970[^{\circ}C]$, electromechanical coupling factor(Kp), mechanical quality factor(Qm) and dielectric constant showed the optimum values of 0.50, 2,413 and 1,245, respectively, for multilayer piezoelectric transformer application.

• Journal of Electrical Engineering and Technology
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• v.7 no.3
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• pp.312-319
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• 2012

The life of a power transformer is dependent on the life of the cellulose paper, which influenced by the hot spot temperature. Thus, the determination of the cellulose paper's life requires identifying the hot spot temperature of the transformer. Currently, however, the power transformer uses a heat run test is used in the factory test to measure top liquid temperature rise and average winding temperature rise, which is specified in its specification. The hot spot temperature is calculated by the winding resistance detected during the heat run test. This paper measures the hot spot temperature in the single-phase, 154kV, 15/20MVA power transformer by the optical fiber sensors and compares the value with the hot spot temperature calculated by the conventional heat run test in the factory test. To measure the hot spot temperature, ten optical fiber sensors were installed on both the high and low voltage winding; and the temperature distribution during the heat run test, three thermocouples were installed. The hot spot temperature shown in the heat run test was $92.6^{\circ}C$ on the low voltage winding. However, the hot spot temperature as measured by the optical fiber sensor appeared between turn 2 and turn 3 on the upper side of the low voltage winding, recording $105.9^{\circ}C$. The hot spot temperature of the low voltage winding as measured by the optical fiber sensor was $13.3^{\circ}C$ higher than the hot spot temperature calculated by the heat run test. Therefore, the hot spot factor (H) in IEC 60076-2 appeared to be 2.0.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.6
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• pp.38-46
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• 2012

In this paper, the necessity for the identification of the absolute phase value is introduced and analyzed for a particular conductor line of a 3-phase type distribution network and the recent methods are also introduced. For the determination of the exact phase value for a specific point in the line, as compared with the phase reference point, the measured phase value must be within a range of ${\pm}60[^{\circ}]$. However, the phase of a particular point can fluctuate depending on the line constant, transformer wiring method, line length, line amperage, etc. A theoretical formulation such as Simulink modeling and analysis for a distribution network are conducted for the identification of phase at a specific point in the line. In particular, through evaluating the effects of unbalanced current loads at the time of determination of the phase value, the limitations of the present method for the determination of phases is described.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.328-335
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• 1999

Three phase full bridge rectifier has been used to obtain dc voltage from three phase ac voltage source. The rectifier system has drawbacks that power factor is low and power flow is unidirectional. Therefore, when dc voltage increases due to regeneration of power the dynamic resister for dissipation of regeneration power must be installed. But three phase PWM converter can be controlled to operate with unity power factor and bidirectional power flow. Therefore when the PWM converter is used as do supply system, the dissipating resistor is not necessary. On this thesis, in order to design a controller having good performance, the hee phase PWM converter is completely modeled by using circuit DQ-transformation and thus a general and simple instructive equivalent circuit is obtained; the inductor set becomes a second order gyrator-coupled system and three phase inverter becomes a transformer as well. Under given phase angle(${\alpha}$) and modulation index(MI) of the three phase inverter, the dc and ac characteristics are obtained by analysis of the transformed equivalent circuit The validity of the equivalent circuit is confirmed through PSPICE simulation. And based on the dc and ac characteristics a controller with unity power factor is proposed.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.598-602
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• 2002

This paper presents the 3-phase hybrid series active power filter with dynamic voltage restorer(DVR) which serve as an energy buffer and current harmonics blocking resistor connected to sensitive loads, such as, to compensate voltage dips and current harmonics in power distribution system. The DVR is to inject a dynamically controlled voltage generated by a forced commutated converter in series to the bus voltage by means of a booster transformer. The momentary amplitudes of the three injected phase voltages are controlled such as to eliminate any detrimental effects of a bus fault to the load voltage. The proposed system is able to simultaneously compensate current harmonics, voltage fluctuating and voltage unbalance in power distribution systems. The reference phase angle detected by synchronized with the positive sequence component of the unbalanced source by using symmetrical component transformation. The effectiveness of proposed system is verified by the computer simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.359-362
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• 2001

Phase shifter has been used as a means of power-flow control and for transient stability improvement in AC transmission system. Until now, phase shifters have been based on an injection transformer. Conventional phase shifters with tap changers require regular maintenance and allow only step-like control of the phase an81e. This paper propose a three-phase phase shifter using PWM AC/AC converter, which can improve system response and control stability in the applications. This paper deals with the circuit topology, operating principle so that the features of the phase shifter will be shown through computer simulation, especially using PSIM software.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.3
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• pp.265-272
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• 2001

The traditional 60[Hz] power supply for during magnetron in microwave oven has disadvantages of heavy weight and low efficiency due to 60[Hz] High Voltage Transformer(HVT), capacitor and th phase control of thyristors. To alleviate these disadvantages, this paper proposes a 20[kHz] phase-shifted Full-Bridge(FB) Zero-Voltage-Switched(ZVS) PWM converter for driving a 600[W] magnetron in an 1[kW] microwave oven. The proposed converter has advantages of light weight and high power density.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.362-364
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• 2006

This paper presents a novel DC-DC Converter for 3 [kW] Fuel Cell System Residential Application. Phase shifted control is employed to regulate the output voltage and achieve soft switching. The transformer leakage inductance is utilized effectively to achieve zero voltage turn on for the power semiconductor switches. The current doubler rectifier has only one diode drop. The transformer secondary winding current rating is one half the load current. The overall effciency of the converter is improved.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.4
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• pp.373-379
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• 2005

In this paper, the control algorithm of DC source device for inverter starting is proposed and the control method for compensating unbalance system source on operating time in the voltage type PWM converter with driving and regenerative faculty is suggested. The maintaining way of balancing condition for converter of AC source is used the compensating unbalanced status by current control loop. Because it is possible that the unbalanced System control is used to leakage transformer not equaled reactance by each phase in rectifier system, the proposed H/W and control algorithm of rectifier system is contributed to minimize of device and rising efficiency.