Affection of distributed capacitance on and a new method of detecting on detecting DC system earth fault

On the basis of discussing the existing detecting principle of earth faults in a DC system, the paper analyzes relation of earth resistance, signal frequency, and earth distributed capacitance of a DC system. Two mathematical equations are derived for earth resistance as the function of distributed capacitance in criterion on resistance current and that on the comparison between ratios of currents. Explicit data relations are given. At the same time the paper discusses the effect of the principle on undulation coefficient of DC voltage also. Finally, a new method of detecting an earth fault is introduced, which need not feed low frequency AC voltage signal into DC bus by the principle of magnetic modulation.