Abstract: 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.

Abstract: The present invention is a high-sensitivity 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.

Abstract: A DC power supply insulation fault detection circuit includes a plurality of circuit breaking elements located at a positive terminal and a negative terminal of each circuit in a power supply system, at least one leakage current detector located in the circuit, and at least one positive voltage transient compensator and at least one 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/discharge 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.

Abstract: A DC power supply insulation fault detection circuit includes a plurality of circuit breaking elements located at a positive terminal and a negative terminal of each circuit in a power supply system, at least one leakage current detector located in the circuit, and at least one positive voltage transient compensator and at least one 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/discharge 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.