• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
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• pp.261-264
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• 2003

In this paper, a disk-type piezoelectric transformer for the high power was investigated with the variation of road resistance. The diameter and thickness of a disk-type piezoelectric transformer was 45mm and 4mm, respectively. The piezoelectric ceramics was composed to PZT-PMN-PSN. The ratio of driving electrode and generating electrode is 2:1. The poling direction of driving part and generating part are the same. A voltage step-up ratio increased with increasing the load resistance, $R_L$, so it reached 60 under no road resistance. Also, the maximum efficiency of 97% was obtained.

• International Journal of Advanced Culture Technology
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• 제4권2호
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• pp.47-56
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• 2016

In transformer cooling systems, oil temperature is controlled through the use of a blower and oil pump. For this paper, set-point algorithms, a reset algorithm and control algorithms of the cooling system were developed by neural networks and fuzzy logics. The oil inlet temperature was set by a $2{\times}2{\times}1$ neural network, and the oil temperature difference was set by a $2{\times}3{\times}1$ neural network. Inputs used for these neural networks were the transformer operating ratio and the air inlet temperature. The inlet set temperature was reset by a fuzzy logic based on the transformer operating ratio and the oil outlet temperature. A blower was used to control the inlet oil temperature while the oil pump was used to control the oil temperature difference by fuzzy logics. In order to analysis the performance of these algorithms, the initial start-up test and the step change test were performed by using the dynamic model of a transformer cooling system. Test results showed that algorithms developed for this study were effective in controlling the oil temperature of a transformer cooling system.

• 한국전기전자재료학회논문지
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• 제20권11호
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• pp.948-952
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• 2007

In this study, a low temperature sintering multilayer piezoelectric transformer for a DC-DC converter was manufactured using $(Pb,Ca,Sr,)(Ti,Mn,Sb)O_3$ ceramics. Its electrical properties were investigated according to the variation in frequency and load resistance. The voltage step-up ratio of the multilayer piezoelectric transformer showed a maximum value at a resonant frequency of input part and increased with an increase of load resistance. The efficiency of the multilayer piezoelectric transformer showed the highest value at a load resistance of 17 $\Omega$. The output power was increased with increasing input voltage. Temperature increase of the multilayer piezoelectric transformer was increased with the increase of output power. At the load resistance of 17 $\Omega$, the multilayer piezoelectric transformer showed the temperature rises of about $20^{\circ}C$ at the output power of 18 W, and stable driving characteristics.

• 전기학회논문지
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• 제56권1호
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• pp.88-99
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• 2007

In this paper, a novel new pulse power generator based on IGBT stacks is proposed for pulse power application. Because it can generate up to 60kV pulse output voltage without any step- up transformer or pulse forming network, it has advantages of fast rising time, easiness of pulse width variation and rectangular pulse shape. Proposed scheme consists of series connected 9 power stages to generate maximum 60kV output pulse and one series resonant power inverter to charge DC capacitor voltage. Each power stages are configured as 8 series connected power cells and each power cell generates up to 850VDC pulse. Finally pulse output voltage is applied using total 72 series connected IGBTs. To reduce component for gate power supply, a simple and robust gate drive circuit is proposed. For gating signal synchronization, full bridge invertor and pulse transformer generates on-off signals of IGBT gating with gate power simultaneously and it has very good characteristics of short circuit protection.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권5호
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• pp.259-264
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• 2000

In this paper, the characteristics of piezoelectric transformer is studied for driving CCFL(Cold Cathode Fluorescent Lamp). In order to investigate the effects of geometrical dimensions, λvibration-mode type piezoelectric transformers with different sizes in the length(l), width$(\omega)$ and thickness(t) are made of ceramics with PZT-PMWS compositions. The increases in temperature and aging effect are also measured in the transformer of PT-3 sample under the condition of operation continuously for 10 hrs. As the results of dimensional effects, the output power and voltage step-up ratio are largely affected by the ratio of length to thickness(l/t) rather than that of length to $width(l/\omega)$. The output power and step-up ratio are increased with increasing l/t. On case of PT-3, the output voltages are 510[Vrms] at 36[Vrms] in input voltage, $100[k\Omega]$ in load resistance. Temperature increases and variation of output voltages are $10[^{\circ}C]$ and less than 5[%], respectively.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.106-109
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• 2003

This paper describes an AC voltage regulator using AC chopper and auxiliary transformer which is series connected with main input. It has many advantages such as fast voltage control, high efficiency and low THD. A detail study of step down AC voltage regulator is described and two kinds of novel step-up/down voltage regulator for AVR are proposed. The operation principle and PWM method of the proposed regulator are described. Experimental results show that it can be used as AC voltage regulator for special purpose very efficiently.

• Journal of Power Electronics
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• 제19권2호
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• pp.363-379
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• 2019

Resonant converters have attracted a lot of attention because of their high efficiency due to the soft-switching performance. An isolated high step-up converter with secondary-side resonant loops is proposed and analyzed in this paper. By placing the resonant loops on the secondary side, the current stress for the resonant capacitors is greatly reduced. The power loss caused by the equivalent series resistance of the resonant capacitor is also decreased. Clamp diodes in parallel with the resonant capacitors ensure a unique discontinuous current mode in the converter. Under this mode, the active switches can realize soft-switching during both turn-on and turn-off transitions. Meanwhile, the reverse-recovery problems of diodes are also alleviated by the leakage inductor. The converter is essentially a step-up converter. Therefore, it is helpful for decreasing the transformer turn-ratio when it is applied as a high step-up converter. The steady-state operation principle is analyzed in detail and design considerations are presented in this paper. Theoretical conclusions are verified by experimental results obtained from a 500W prototype with a 35V-42V input and a 400V output.

• 전기학회논문지
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• 제60권1호
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• pp.43-49
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• 2011

A distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, Zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome this problem clearly, this paper describes an improved backup protection coordination scheme using an IEC 61850-based distance relay for transformer backup protection. IEC 61850-based IED(Intelligent Electronic Device) and the network system based on the kernel 2.6 LINUX are realized to verify the proposed method. And laboratory tests to estimate the communication time show that the proposed coordination method is reliable enough for the improved backup protection scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.25-27
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• 2002

This paper describes a new economical voltage sag and swell generator suitable to the evaluations of high power custom power devices such as DVR (Dynamic Voltage Restorer) and DSTATCOM (Distribution Static Compensator). This system was designed to generate the several power quality disturbances in MVA power ratings - voltage sag and swell, under voltage, over voltage and harmonic distortions. The basic idea for voltage sag and swell is to use the voltage drop across a reactor, while the voltage swell is to use the step-up transformer and the TCR(Thyristor Controlled Reactor). In this paper, two identical 3 phase TCRs and a step-up transformer with tap changer are used. Additional harmonic filters are added to reduce the voltage distortion when TCRs are operated. Simulation results are given for several cases of voltage sag and swell generations.

• 조명전기설비학회논문지
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• 제26권10호
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• pp.95-101
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• 2012

Typically, large scale power generation facilities are linked to 345kV transmission line through a step-up transformer. If the value of transient voltage by generating lightning stroke is large more than electric equipment's BIL, devices insulation is destroyed. LA(Lighting Arrester) is used as a main means of prevention. However, the installation of LA takes the constraints of installation place and expensive installation costs. Therefore, we need to carefully study whether installation of installation can be omitted and the most efficient place of installation. In this paper, we simulated the transient voltage detected by lightning stroke at each equipments in the 345kV transmission power grid by using EMTP-RV program.