The insulation level of DC system is often damaged due to aging of power cable insulation

damaged construction

damp accumulation and faulty wiring

which affects the safe and stable operation of units. In the light of the phenomenon that two sets of DC insulation monitoring devices are given an alarm at the same time but both sets of DC bus voltage are normal during the operation of unit 2 of a power plant

it is found that there is a loop network fault in the DC system

and this phenomenon is theoretically analyzed

the fault rules of DC system loop network are summarized

and some suggestions for reliable operation of DC system are put forward.