The invention belongs to the field of the operation and maintenance monitoring of substation direct-current power source systems and relates to an insulation grounding fault 
simulation unit. The insulation grounding fault 
simulation unit comprises a main control 
chip, a 
voltage acquisition module, a communication module, a 
bus-bar and 
branch input control module, a 
busbar and 
branch insulation reduction and grounding control module, an alternating-current intrusion control module, a 
direct current mutual intrusion control module, and a ground distributed 
capacitance increasing module; the 
voltage acquisition module and the communication module are both connected with the main control 
chip; the 
bus-bar and 
branch input control module is connected with the 
busbar and branch insulation reduction and grounding control module; and the 
busbar and branch insulation reduction and grounding control module, the alternating-current intrusion control module, and the 
direct current mutual intrusioncontrol module are connected with the main control 
chip through an optocoupler isolation module. With the insulation grounding fault 
simulation unit of the invention adopted, the automatic simulationof various faults of a direct-current power source can be realized, the ability of operation and maintenance personnel to check and solve problems can be improved, and the 
safe operation of a substation can be ensured.