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. In this paper, the capacitor group is used to connect with positive and negative bus and ground the intermediate point of the capacitor group, and that each branch loop is installed with a leakage current detection device. When insulation fault occur in the system, the capacitor is able to provide a leakage current return path and discharge through the stored energy in the capacitor. This will allow the Hall effect current sensor to detect the difference of positive and negative bus current, and deliver warning signal or control the breaker to cut off the power supply. The experiment result demonstrates that this novel method is able to detect 1mA/50kΩ insulation fault to achieve the high sensitivity detection goal.
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