It is difficult to detect a high resistance-grounding fault because it is impossible to distinguish the fault current from load current on DC electric railway system. Resistance and reactance of a feeding circuit including rolling stock are detected by injecting harmonic current with a single frequency from a substation. Therefore, the high resistance grounding fault and rolling stock can theoretically be distinguished by the ratio of resistance and reactance. It is however, substantially difficult to distinguish the high resistance-grounding fault and rolling stock, because the resistance of a feeding circuit has a skin effect. We therefore proposed a new method to detect the resistance without any effect due to the skin effect by injecting two harmonic currents with two different frequencies. Therefore this new method can detect the high resistance-grounding fault, because it is possible to distinguish the resistance of grounding fault from a total resistance of feeding circuit. This paper describes the new detection method of high resistance grounding fault by injecting harmonic currents to feeding circuit.

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