DC system ground fault tester

The utility model discloses a DC system grounding fault tester, which is suitable for on-line grounding fault test of the direct current 220V and negative 110V to positive 110V systems in power plants and transformer substations without external signal. The utility model properly solves the ground testing problem of the direct current system so as to effectively improve the reliability of power supply of the direct current system. A branch drain current testing circuit of a ground testing circuit is formed through that each branch of the direct current system is provided with a Hall transducer; the positive and negative buses of the direct current power respectively pass through the middle part of each Hall transducer after passing through a direct current breaker; a bridge circuit of the ground testing circuit is formed through that the positive and negative buses of the direct current power are provided with Hall bridges; the Hall bridge on the negative bus is connected with a first bridge resistance, and the Hall bridge on the positive bus is connected with a second bridge resistance; the other ends of the first and the second bridge resistances are connected and pass through the center of the Hall transducers used for checking the bus grounding and branch grounding so as to be grounded through a third bridge resistance 7.