Abstract: DC system provides reliable DC power supply for control, signal, relay protection, automatic device and emergency lighting in substation. But also provides reliable operation power supply for operation. Whether the DC system is reliable or not plays an important role in the safe operation of the substation and is an important guarantee for the safe operation of the substation. The DC system is mainly composed of AC distribution unit, charging module, feeder unit, battery pack, monitoring unit, voltage and current detection meter, insulation detection device, battery pack management unit (optional), etc.