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Abstract: This paper proposes a novel online insulation fault detection circuit to overcome the shortcomings of ungrounded DC power supply system for being unable to provide high sensitivity leakage current detection. A DC power supply insulation fault detection circuit includes a leakage current detector located in each branch circuit, and a positive voltage transient compensator and a negative voltage transient compensator respectively bridging the positive terminal and negative terminal of the power supply system. The positive and negative voltage transient compensators respectively include a charge circuit to allow an energy storage circuit to be charged. When grounding insulation deterioration takes place at the positive or negative terminal of the leakage current detector, a leakage current loop is formed so that energy storage elements discharge and the leakage current detector detects current variations on the positive and negative terminals, and issue an alarm signal or control cutoff of the circuit breaking elements. The experiment result demonstrates that this novel method is able to detect 1 mA/50 kΩ insulation fault to achieve the high sensitivity detection goal.

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