• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.1
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• pp.67-72
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• 1991

For improving the magnetic properties of the amorphous Fe-B-Si alloy, we annealed the sample in a magnetic field oriented in the plane of the ribbon longitudinal to its long axis. By field annealing, coercive force and total core loss are reduced from 0.04 Oe to 0.02 Oe, and from 0.25 watt/kg to 0.15 watt/kg respectively in comparsion with non-field annealed specimen. These reductions were caused by the formation of 180 dcmain wall parallel to the annealing field due to the induced anisotropy.

• ETRI Journal
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• v.6 no.4
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• pp.31-36
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• 1984

This paper presents an efficient method for real power loss minimization and for improvements in voltage profiles. This method is accomplished by optimal control of reactive power in the system. The problem is formulated as an optimization problem, suitable for solution by linear programming technique. After establishing the objective function for minimizing the system losses with the help of linearised sensitivity relationships of control variables, i. e., the transformer tap position, generator terminal voltages and switchable reactive power sources. The linear programming technique is used to determine the optimal adjustments to the above variables, simultaneously satisfying the constraints. The proposed algorithm has been tested on a sample system and the result is presented and discussed.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.512-513
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• 2015

최근 다양한 형태의 비선형 부하가 계통에 연계됨에 따라 이러한 부하에 적절한 전원을 공급하는 전력변환장치의 보급이 활발히 진행되고 있다. 이러한 전력변환장치들은 전력용반도체소자의 스위칭에 의해 동작하기 때문에 전류의 고조파를 발생시키고, 이때 발생하는 고조파는 변압기의 손실을 증대시키고 역률을 저하시키며 온도의 과도한 상승을 유발하여 결국 변압기의 수명을 단축시킨다. 따라서 본 논문에서는 과열을 방지하면서 비선형 부하에 적절하게 연계하기 위하여 전류 고조파에 의한 변압기에서의 손실을 해석한다.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.171-172
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• 2015

본 논문은 변압기에 부하가 연결 되었을 때 발생하는 전류 고조파에 의한 변압기 손실을 분석한다. 3상 변압기에 대해서 선형 부하와 비선형 부하가 연결되었을 경우 변압기 손실 값을 계산한다. PSIM을 이용하여 부하를 모델링하고 시뮬레이션 수행한다. 시뮬레이션을 통하여 얻어진 데이터를 이용하여 변압기의 손실값을 계산한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.39-48
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• 2020

Since the fire accident of ESS (energy storage system) occurred at Gochang KEPCO Power Testing Center in August 2017, 29 fire cases with significant property losses have occurred in Korea. Although the cause of fire accidents have not been identified precisely, it should be considered battery and PCS (power conditioning system) as well as unbalance issues in the distribution system. In particular, circulating currents in a neutral line of a grid-connected transformer, which can affect a magnetized current, may have a negative effect on the ESS with unintentional core saturation and surge voltages at the secondary side of the transformer. Therefore, this paper proposes the modeling of the distribution system, which was composed of a substation, grid-connected transformer, and customer loads using PSCAD/EMTDC S/W, to analyze the phenomena of circulating current and surge voltages of the transformer with unbalanced currents in the distribution system. This paper presents a countermeasure for a circulating current with the installation of NGR (neutral grounding resistor) in grid-connected transformer. From the simulation results, it is clear that exceeding the circulating current and surge voltage at the secondary side of the transformer can be one of the causes of fire accidents.

• Journal of Power Electronics
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• v.7 no.3
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• pp.181-190
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• 2007

This paper presents a novel circuit topology of a DC bus line series switch and parallel snubbing capacitor-assisted soft-switching PWM full-bridge inverter type DC-DC power converter with a high frequency planar transformer link, which is newly developed for high performance arc welding machines in industry. The proposed DC-DC power converter circuit is based upon a voltage source-fed H type full-bridge soft-switching PWM inverter with a high frequency transformer. This DC-DC power converter has a single power semiconductor switching device in series with an input DC low side rail and loss less snubbing capacitor in parallel with the inverter bridge legs. All the active power switches in the full-bridge arms and DC bus line can achieve ZCS turn-on and ZVS turn-off transition commutation. Consequently, the total switching power losses occurred at turn-off switching transition of these power semiconductor devices; IGBTs can be reduced even in higher switching frequency bands ranging from 20 kHz to 100 kHz. The switching frequency of this DC-DC power converter using IGBT power modules can be realized at 60 kHz. It is proved experimentally by power loss analysis that the more the switching frequency increases, the more the proposed DC-DC power converter can achieve a higher control response performance and size miniaturization. The practical and inherent effectiveness of the new DC-DC converter topology proposed here is actually confirmed for low voltage and large current DC-DC power supplies (32V, 300A) for TIG arc welding applications in industry.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.1-6
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• 2001

In this article, the fundamental concept, characteristics and application potentials of coreless printed-circuit-board (PCB) transformers are described. Coreless PCB transformers do not have the limitations associated with magnetic cores, such as the frequency limitation, magnetic saturation and core losses. In addition, they eliminate the manual winding process and its associated problems, including labor cost, reliability problems and difficulties in ensuring transformer quality in the manufacturing process. The parameters of the printed windings can be precisely controlled in modern PCB technology. Because of the drastic reduction in the vertical dimension, coreless PCB transformers can achieve high power density and are suitable for applications in which stringent height requirements for the circuits have to be met. A transformer's power density of $24W/cm^2$ has been reported in a power conversion application. When used in an isolation amplifier application, coreless PCB transformers tested so far enable the amplifier to achieve a remarkable linear frequency range of 1MHz, which is almost eight times higher than the frequency range of 120kHz in existing Integrated-Circuit products. PCB materials offer extremely high isolation voltage, typically from 15kV to 40kV, which is higher than many other isolation means such as optocouplers. It is envisaged that coreless PCB transformers can replace traditional core-based transformers in some industrial applications. Their application potentials deserve more attention and exploration.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.5
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• pp.1134-1138
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• 2008

In this paper, the synthesis of distributed impedance transformers is presented that is essential for power divider design, whereby a broadband power divider is designed. Transfer functions of distributed transformers are synthesized with Chebyshev approximation, and their element values are calculated for various minimum insertion losses(MIL) and ripples. Desired performance of transformers is obtained by optimizing MIL's and ripples of a transfer function. As an application example, a four-way power divider is designed that operates over 2 to 8GHz frequency range. Experimental results are shown to approach the design performance, so transformer design by distributed network synthesis proves to be useful to power divider design.

• Journal of Power Electronics
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• v.17 no.1
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• pp.20-30
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• 2017

A novel zero-voltage-switching (ZVS) push-pull forward converter with a parallel resonant network is presented in this paper. The novel topology can provide a releasing loop for the energy storage in a leakage inductor for the duration of the power switching by the resonant capacitors paralleled with the primary windings of the transformer. Then the transformer leakage inductor is utilized to be resonant with the parallel capacitor, and the ZVS operation is achieved. This converter exhibits many advantages such as lower duty-cycle losses, limited peak voltage across the rectifier diodes and a higher efficiency. Furthermore, the operating principles and key problems of the converter design are analyzed in detail, and the ZVS conditions are derived. A 500W experimental converter prototype has been built to verify the effectiveness of the proposed converter, and its maximum efficiency reaches 94.8%.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.10
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• pp.1741-1747
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• 2010

The development of overload management systems for distribution transformers offers new opportunities for improving the reliability of distribution systems. It allows network planners to optimize the system resource utilization and investment cost. Such an improvement in the flexibility of the distribution network is only possible if the operator has more accurate knowledge of the realtime conditions of distribution transformers. In this paper, we present an improved overload decision system for distribution transformers using realtime monitoring data. Our study can be categorized into two parts: (a) improvement in the criteria for judging the overload conditions of distribution transformers and (b) development of an overload evaluation system using realtime monitoring data. In order to determine the overload criteria, overload experiments are performed on sample transformers; the results of these experiments are used to define the relationship between the transformer overload and the increase in the top-oil temperature. To verify the accuracy of the experimental results, field tests are performed using specially manufactured transformers, the loads and top-oil temperatures of which can be measured. For arriving at online overload decisions, we propose methods whereby the measured load curve can be converted into an overload characteristic curve and the overload time can be calculated for any load condition. The developed system is able to evaluate the overload for individual distribution transformers and calculate the losses using realtime monitoring data.