• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.2
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• pp.149-156
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• 1990

In DC electric railway systems, the feeding currrnt is not permitted to flow backward in almost all the substations and the pantograph voltages at the regenerating cars rise extremely by the voltage drop of the resistance of the feeder line. In order to prevent the overrise of the pantograph voltage in power regenerating cars, the squeezing circuits for the regenerative current are equipped and this leads to double losses, which are an extra worn-out of the brake-shoes and an ineffective use of regenerative power. In this study, the insertion of resistors in the feeder line system is proposed as a possible method for the effective utilization of the regenerative power in the electric railways. Also it is investigated how the output voltages of substations affect the effective use of regenertive capability. The investigation results show that the energy savings and the reduction of the worn-out of the brake-shoe can be achieved at the same time by the insertion of resistors in the feeder line system.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1083-1084
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• 2006

The wide spread of DC electric railway systems such as urban rapid transits including heavy rail and light rail transits has significant ramification as the stray currents from return conductor rails can cause the electrochemical interference, that is, the electrolytic corrosion of both rails and outside underground metallic infrastructures. The immature understanding of either the railway authority who is responsible for establishing the necessary provisions at the design stage or the affected parties makes it difficult to prepare the optimum range of solutions for the long-pending interference problem. In Japan, however, numerous assessment studies have been carried out on the stray current interference, by which protective guidelines are provided by "Electrolysis Committee". In this paper, we review a guide book from "Tokyo Electrolysis Committee", namely, "Protective Methods for Stray Current Corrosion".

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.6
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• pp.534-539
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• 2015

The DC overhead line voltage of an electric railway substation swings depending on the accelerating and regenerative-braking energy of trains, and it deteriorates the energy quality of the electric facility in the DC railway substation and restricts the powering and braking performance of subway trains. Recently, an energy storage system or a regenerative inverter has been introduced into railway traction substations to diminish both the variance of the overhead line voltage and the peak power consumption. In this study, the variance of the overhead line voltage in a DC railway substation is modelled by RC parallel circuits in each feeder, and the RC parameters are estimated using the recursive least mean square (RLMS) scheme. The forgetting factor values for the RLMS are selected using simulated annealing optimization, and the modelling scheme of the overhead line voltage variation is evaluated through raw data measured in a downtown railway substation.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.446-448
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• 1999

The forced drainage set up to decrease the cathodic protection in each kind of steel conduit laid under the ground is so proscribed to be maintained less than 60V in its output voltage that insulation coordination is easy to be left out of account, on the basis of 60V of working voltage. When railway or subway break down during the service of a subway, 1,500 voltage approximating to line voltage flows through the load terminal of the drainage (rail and underground conduit) though momentary in the worst case. And so, an accident followed by dielectric breakdown, fire and damage by a fire is expected. Therefore, I suggest that insulation coordination should be considered against such a thing on designing, producing and setting up forced drainage.

• Proceedings of the KIEE Conference
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• 2009.04b
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• pp.201-203
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• 2009

This paper presents the real time stray current monitoring techniques on the DC railway system. These techniques are two types. The first one is the rail potential measurement technique between running rail and earthing mats on the important locations such as substation, station, and so on. And the second one is measurement technique of stray current through substation earthing mats and from collection mats, and continuous monitoring of return currents through the running rails. We need to apply these techniques on DC railway system to monitor stray current periodically and maintain the system properly.

• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.270-272
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• 2005

With the wide spread of direct current (DC) electric railroads in Korea, the stray currents from negative return rails become a pending problem to the safety of nearby underground infrastructures, such as gas pipelines, water distribution lines, heat pipelines, POF cables, etc. The mitigation of such interference, however, is mainly dependent on stray current drainage bond methods, which connect the underground metallic structures to the negative feeder cables attached to the rails with diodes (polarized drainage) or thyristors (forced drainage). Despite some merits of these methods, they increase the total amount of stray currents from rails and cause other interference problems. In this paper, we summarize the domestic conditions of stray current interference and describe a conceptual design of other mitigation methods for such interference.

• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.279-281
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• 2005

In DC traction substation with 12-pulse diode rectifiers, the DC line voltage tends to rise above noload voltage because it can't absorb the regenerative power caused by electric brakes of train. To solve this problem, an IGBT regenerative inverter should be installed and thus recycles the surplus regenerative power by delivering it to the supply grid. In this paper, the DC traction substation equipped with a IGBT regenerative inverter is studied using computer simulation. Matlab/simulink is used to simulate the operation of regenerative inverter which injects the regenerative power into the supply grid and stabilizes the DC line voltage. It is confirmed that the high quality regenerative power is delivered to the supply grid thorough computer simulation.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1637-1639
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• 2005

The measurement of magnetic field is performed about DC and AC magnetic field in test track of depot. The test point is cap, on the converter/inverter box, on the traction motor, on the APSE and on the line filter, the height of measurement is bottom and 50 cm height. In case of AC magnetic field, the selected specific frequency is measured on the converter/inverter box. The AC magnetic field is checked and analysis through RS-232C and notebook PC. The DC magnetic field is measured by using the Hall Probe, test result is saved and analysis by PXI system. On the line filter, the maximum value is 1.4 mT in case of DC magnetic field and 0.044 mT in case of AC magnetic field at 50 Hz.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1607-1609
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• 2005

This paper presents capability calculation methods for regenerative inverter in DC electrified transit system. The proposed method uses a train performance and power simulation tool to calculate the regenerative power generated in the DC substation and decide the capability of regenerative inverter. The capability of regenerative inverters for Seoul subway line 5, 6, 7, and 8 has been calculated.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2109-2112
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• 2016

The rate of rise of the fault current in DC grids is very high compared to AC grids because of the low line impedance of DC lines. In AC grids the arc of the circuit breaker under current interruption is extinguished by the zero current crossing which is provided naturally by the system. In DC grids the zero current crossing must be provided by the circuit breaker itself. Unlike AC girds, the magnetic energy of DC grids is stored in the system inductance. The DC circuit breaker must dissipate the stored energy. In addition the DC breaker must withstand the residual overvoltage after the current interruption. The main contents of this paper are to ${\cdot}$ Explain the theoretical background for the design of DC circuit breaker. ${\cdot}$ Develop the simulation model in PSIM of the real scaled DC circuit breaker for 1,800V DC railway. ${\cdot}$ Suggest design guidelines for the DC circuit breaker based on the experimental work, simulations and design process.