• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.54-60
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• 2003

Feeding traction loads from the public power system may lead to some current and voltage unbalance and consequently affects the operation of its energy-supply system and other equipment connected with it. This paper introduces an analysis of the current unbalance caused by the demands of an electric railway on a public power system. And the results with compensator and without compensator are simulated, and eventually the formula about the current unbalance is suggested. The Scott-connected transformer is adopted in Korea National Railway System. So Scott-connected transformer among the various transformer connection schemes is analyzed in this paper. Also, the formulas about the unbalance and compensating current can be derived by using two parameters(M-phase and T-phase current) of secondary Scott-connected transformer. So, the practical and accurate simulation can be done through dynamic models by using scheduling of traction.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.93-94
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• 2007

An essential step for SERGI is to show the TRANSFORMER PROTECTOR (TP) efficacy for all transformers and all types of rupture of insulation. Its research program philosophy is thus to maintain a strong connection between experiments and the theoretical developments. Up to now, two TP test campaigns have been performed, both under the worst conditions by creating low impedance faults leading to electrical arcs inside the transformer tank dielectric oil. In 2002, Electricite de France performed 28 TP tests. Then, in 2004, a second campaign of 34 TP tests was carried out by CEPEL, the Brazilian independent High Voltage Laboratory. For the 62 tests, each transformer was equipped with the TP, which reacts directly to the moving dynamic pressure peak, shock wave, caused by the low impedance fault. When an electrical arc occurs, only one pressure peak is generated. The initial energy transfer is almost instantaneous, and so is the phase change. Because of the oil inertia, the gas is very quickly pressurised. As it is more difficult to vaporise a liquid than to crack oil-vapour into smaller molecules, the arc location would mainly remain in the gaseous phase after and less gas will be produced. As a result, when comparing tests for which pressure peaks are respectively equal to 8 bar (116 psi) and 8.8 bar (127 psi), the corresponding arc energies vary by an order 10 of magnitude (0.1 MJ and 1 MJ respectively). The correlation of the results obtained between arc energy and dynamic pressure demonstrates that the arc energy is not the key parameter during transformer tank explosion, which is in opposition with the common electrical engineers belief.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.3
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• pp.414-417
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• 2014

At present, the demand for electric power increases, the electric power system is complicated. The size of the line-to-ground fault and the line-to-line fault occurred with complication of electric power system continue to increase, therefore several issues are raised. To address these issues effectively, the superconducting fault current limiter (SFCL) has been proposed, this study is ongoing. In this paper, we applied the SFCL in three-phase transformer and comparative analysis of the electric power burden to the SFCL. The superconductor is combined to the third winding of transformers in connection structure. In case of a third line-to-line fault, we did comparative analysis of the electric power burden to the SFCL based on the turn ratio of transformer third winding. In this case, we could confirm as the third turn ratio increased, electric power impressed to the superconducting element increased.

• Journal of Power Electronics
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• v.13 no.3
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• pp.329-338
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• 2013

In this paper, the charging characteristics of series resonant type high voltage capacitor chargers considering the transformer stray capacitance have been studied. The principles of operation for the four operational modes and the mode changes for the four different switching frequency sections are explained and analyzed in the range of switching frequency below the resonant frequency. It is confirmed that the average charging currents derived from the above analysis results have non-linear characteristics in each of the four modes. The resonant current, resonant voltage, charging current, and charging time of this capacitor charger as variations of the switching frequency, series parallel capacitance ratio ($k=C_p/C_s$), and output voltage are calculated. From the calculation results, the advantages and disadvantages arising from the parallel connection of this stray capacitance are described. Some methods to minimize charging time of this capacitor charger are suggested. In addition, the results of a comparative test using two transformers whose stray capacitances are different are described. A 1.8 kJ/s prototype capacitor charger is assembled with a TI28335 DSP controller and a 40 kJ, 7 kV capacitor. The analysis results are verified by the experiment.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1398-1406
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• 2018

Owing to the consistent increase in accurate analysis issue for energy consumption of the AC electric railway systems, there is controversy about the adequacy of the present watt-hour metering configuration. Due to the unusual load characteristics and facilities, the discussions have not been active. Therefore, in order to achieve more accurate watt-hour metering for AC electric railway system, this paper proposes numerical formulas for watt-hour metering that reflects the highly-varying characteristics of the railway load and the structural characteristics of the Scott transformer. The proposed formulas have been verified by comparison with site-measured data, and a more suitable metering configuration for AC railway system has been proposed.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.916-917
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• 2001

We investigated the properties of a hybrid type superconducting fault current limiter (SFCL), which consists of a transformer with multiple secondary windings and resistive $YBa_2Cu_3O_7$ (YBCO) thin film stripes. The secondary windings of the transformer were coupled with each other, and a superconducting current limiting unit of YBCO stripes was connected to each of them as a switch. Simple connection in series of SFCL units tends to produce imbalance in power among the units due to slight differences in quench current. In current design, magnetic coupling between the SFCL units provides a solution to power dissipation imbalance, inducing simultaneous quench by current redistribution in the YBCO films.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.551-554
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• 2002

This paper describes a new interactive inverter between a photovoltaic(PV) array and single-phase utility that avoid the bulky input (60Hz) transformer on the AC side. The interface employs a pwm boost converter on the DC side followed by a pwm current-forced single-phase rectifier for injecting the power from the PV array into the mains. The current waveform at the AC side remains sinusoidal and exactly in phase at all time. The circuit also has the advantage of requiring fewer switching device than high-frequency link system. This paper describes modeling of PV array and new system topology. Simulation results on the performance of the connection are also presented.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.71-72
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• 2010

This paper deals with the SCR thyristor switching characteristics of a 3-phase voltage disturbance generator. The series transformers of the generator require bypass SCR thyristors to provide the source voltage to the output terminal in normal operating mode. The SCR thyristor switching characteristics is quite different according to the connection point to the series transformer. The switching characteristics is analysed and verified through simulation results.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.532-533
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• 2010

This paper deals with the SCR thyristor switching characteristics of a 3-phase voltage disturbance generator. The series transformers of the generator require bypass SCR thyristors to provide the source voltage to the output terminal in normal operating mode. The SCR thyristor switching characteristics is quite different according to the connection point to the series transformer. The switching characteristics is analysed and verified through simulation results.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.11
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• pp.645-651
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• 2002

In this paper, a multilevel PWM inverter employing a cascaded transformer is presented to reduce the harmonics of output voltage and load currents. The proposed PWM inverter consists of two full-bridge modules and their corresponding transformers. The secondarics of each transformer are series-connected. So continuous output voltage levels can be synthesized from the suitable selection of the turns ratio of trasformer. And it appears an integral ratio to input DC source. Because of the cascaded connection of transformers, output filter inductor is not necessary. The operational principles and analysis are explained, and it is compared with a conventional isolated H-bridge PWM inverter. The validity of proposed multilevel inverter is verified through simulated and experimental waveform and their FFT results.