Insulation resistance detection method and circuit for ungrounded DC power supply system

摘要

An insulation resistance detection method and circuit for an ungrounded DC power supply systems. When the ratio of the voltage of the positive bus to that of the negative bus exceeds a preset range, the DC current is injected into the ungrounded DC power supply systems. DC power supply systems have essentially some grounded stray and external capacitors, so some of the injected DC current will flow into the grounded capacitor, increasing the voltage of the fault bus and the leakage current. The proposed method increases the leakage current by the injection of DC current, so the current sensor can detect the leakage current from which the insulation resistance can be calculated. The DC current injection method can significantly improve the detection of ground insulation faults in ungrounded DC power supply systems.