The neutral point ungrounded or arc suppression coil grounding mode is usually adopted in 35kV and below system. When the system operates normally, the three voltage to ground is equal to the phase voltage. When single-phase grounding occurs, the ground to ground voltage is less than the phase voltage, and the other two phase to ground voltages are greater than the phase voltages. The grounding point flows through small point current capacitance, so it is called small current grounding system.

The advantage of the small current grounding system is that when the single-phase grounding fault occurs, the symmetry of the system voltage is not damaged, and the fault current value is small, which does not affect the continuous power supply to users, and the system can continue to operate for 1 ~ 2 h. However, in long-term operation, due to the rise of the non fault two phase to ground voltage, the weak link of insulation may be broken down and develop into phase to phase short circuit, which will expand the accident and affect the normal power consumption of users.

At the same time, arc grounding will cause over-voltage of the whole system, which will damage the equipment and damage the safe operation of the system. Therefore, when the single-phase grounding fault occurs, the fault line must be found and removed in time.

The smr-zn09 series small current grounding line selection device developed by our company can accurately find out the fault line and upload the information to the background through alarm relay and communication mode. The device has made significant changes in the design of software and hardware, which makes the device work stably, without debugging, convenient setting and more accurate line selection. It is an important protection equipment for stable operation of power industry.