It introduces a fault that occurrs in a 220 kV substation

where the 10 kV side circuit breaker trips due to two-point grounding in the DC system.It investigates and analyses on-site faults.It finds that the 72 disconnector mechanism box is not tightly sealed

resulting in water vapor condensation and causing the insulating baffle of the thermocouple relay to creepage and carbonize.The positive voltage of the DC system is connected in series into the operating circuit of the AC disconnector

and then connected to the ground through AC neutral line(N)

resulting in a positive grounding of the DC system.The manufacturing process defect of the control cable head of the superimposed 80 circuit breaker leads to the insulation damage and grounding of the tripping wire core

and the two-point grounding causes the 80 circuit breaker to malfunction.In response to the problems exposed by faults such as insufficient process control of concealed works and loopholes in the acceptance mechanism

it proposes a systematic prevention and control measure covering the early process norms

process quality supervision and full-process responsibility traceability

providing a reference for the prevention and control of grounding faults in the DC system of substations.