• Proceedings of the KIEE Conference
• /
• summer
• /
• pp.1528-1530
• /
• 2004

In this paper, an efficient switching pattern to equalize the size of transformer is proposed for a multi-level inverter employing cascaded transformers. It is based on the prior selected harmonic elimination PWM(SHEPWM) method. Because the maximum magnetic flux imposed on each transformer becomes exactly equal each to each, all transformers can be designed with the same size regardless of their position. Therefore, identical full-bridge inverter units can be utilized, thus improving modularity and manufacturability. The fundamental idea of the proposed switching pattern is illustrated and then analyzed theoretically. The validity of the proposed switching strategy is verified by experimental results.

• KIEE International Transactions on Power Engineering
• /
• v.5A no.1
• /
• pp.40-45
• /
• 2005

Substation facilities have become extremely large and complex parts of electric power systems. The development of condition monitoring and diagnosis techniques has been a very significant factor in the improvement of substation transformer security. This paper presents a method to analyze the cause, the degree, and the aging process power transformers by the Self Organizing Map (SOM) method. Dissolved gas data were non-linearly transformed by the sigmoid function in SOM that works much the same way as the human decision making process. The potential for failure and the degree of aging of normal transformers are identified by using the proposed quantitative criterion. Furthermore, transformer aging is monitored by the proposed criterion for a set of transformers. To demonstrate the validity of the proposed method, a case study is performed and its results are presented.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.14 no.5
• /
• pp.406-414
• /
• 2009

To cope with the high power density and low cost in switching power supply, LLC resonant converters with the two resonant tank circuits composed of resonance capacitors and two transformers are proposed in this paper. Each transformers used for the proposed resonant circuits are parallel connected in the primary and series connected in the secondary to reduce the current unbalance. The proposed LLC resonant converters are described and verified on 300W experimental prototype.

• Proceedings of the KIPE Conference
• /
• 2007.07a
• /
• pp.512-514
• /
• 2007

The number of transformers and the size of transformers in inverter using 3-phase transformer could be reduced compare with a multi-level inverter using single phase transformer. but still the 3-phase transformer inverter needs many switches. In this study, we proposed the isolated multi-level inverter using 3-phase transformers and common arm. Also, the equal-area method is used to calculate conduction angle with switching frequency equal to output fundamental frequency and it can reduce harmonics component of output voltage and switching loss. Finally, We tested multi-level inverter to clarify electric circuit and reasonableness through Matlab simulation and experiment by using prototype inverter.

• Proceedings of the KIEE Conference
• /
• 2007.07a
• /
• pp.1134-1135
• /
• 2007

In this paper, we proposed the isolated multi-level inverter using 3-phase transformers. It makes possible to use a single DC power source due to employing low frequency transformers. In this inverter, the number of transformer could be reduced comparing with an exiting 3-phase multi-level inverter using single phase transformer. Also, using phase angle control method with switching frequency equal to output fundamental frequency, harmonics component of output voltage and switching losses can be reduced. Finally, we made a prototype inverter to clarify the proposed electric circuit and reasonableness of control signal.

• Proceedings of the KIEE Conference
• /
• 2000.11a
• /
• pp.171-173
• /
• 2000

This paper presents a discriminating algorithm between magnetizing inrush and internal faults of transformers using difference of a differential current. Incase of inrush, change of magnetizing inductance repeats. Thus, second difference of differential current periodically shows pulse while periodic pulse is not represented in case of internal winding fault. The proposed algorithm is suitable irrespective of the amount of remanent flux.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2000.11a
• /
• pp.55-59
• /
• 2000

This paper gives various load profiles of power transformers and motors in apartment housing. The load profile of power transformer shows that it is peaked in winter by heating system, and the maximum value of load profiles in power transformer is ranged 25%∼35%, which shows it is operated on over-capacity. The maximum value of demand factor in water supply system is about 60% and this of wastewater treatment system is about 50%.

• Proceedings of the KIEE Conference
• /
• 1990.07a
• /
• pp.3-6
• /
• 1990

The impact of the convected charges, which is caused by the electrification phenomina, in the oil-paper insulation systems of power transformers has been numerically investigated using FEM. The potential distribution of the oil-paper insulation system is assumed to be governed by three equations instead of the classical Laplace equation. When the charge density of oil and the conduction current are kept high, the field distortion or the interrace in a power transformer is considerably distorted due to the convected charges.

• Proceedings of the KIEE Conference
• /
• 2001.07a
• /
• pp.371-373
• /
• 2001

Main functions of Generator Circuit Breaker(GCB) is cut the generator off from the main transformers and the aux. transformers when plant trip or startup. In this paper, the design requirements For GCB of nuclear power plant is examined. NRC presented the area of review, acceptance criteria and review procedures of GCB in the SRP(Standard Review Plan). In Korea, APR1400 adapted the GCB in main power system.

• Proceedings of the KIEE Conference
• /
• 1998.07c
• /
• pp.952-954
• /
• 1998

This paper presents an artificial neural network approach to diagnose and detect faults in oil-filled power transformers based on dissolved gas analysis. The proposed algorithm is used to detect faults with or without cellulose involved. Several neural network topologies have been considered. Good diagnosis accuracy is obtained with the proposed approach.