For production enterprises, the continuity, reliability and security of power supply are very important. If power failure occurs, it will cause unpredictable losses to the normal production of enterprises.

In the normal operation of the substation, single-phase ground fault occurs frequently. According to the electric power regulations, single-phase ground fault can operate with fault for 2 hours. However, single-phase ground fault will cause the normal phase voltage to rise, which may lead to insulation breakdown and fault expansion, even to interphase short circuit, causing greater harm to the safety of system operation. Therefore, it is necessary to quickly find out the fault line and eliminate it.

However, for some substations, there are many outgoing lines of 10KV and 35KV, and the original design did not design and install a small current grounding line selection device. When a fault occurs, the operation and maintenance personnel cannot find which circuit outgoing line single-phase grounding fault in time, let alone go further and remove the fault; It brings some blindness to the operators, so it is necessary to add small current grounding line selection device to this substation.