Small current grounding line selection device can accurately and quickly select grounding line or bus when single-phase grounding fault occurs in the system. Select the line with grounding fault and give the indication signal.

The operation mode of 10kV system in Chongqing 110kV substation is that the neutral point is grounded through arc suppression coil. In the process of operation, when single-phase grounding fault occurs in 10kV small current grounding system, it used to manually pull the line to determine the fault line. Later, a small current grounding line selection device was installed, which was installed in the arc suppression coil control cabinet. By clamping the secondary circuit of the system, the zero sequence voltage and zero sequence current of the system were collected for comprehensive judgment.

Because the advanced relative direction judgment principle is adopted in the line selection of small current grounding, the signal polarity must be ensured to be correct, otherwise misjudgment will occur and the line selection cannot be correct. Therefore, the wiring must be carefully checked. For parallel outgoing double lines in the same interval, the zero sequence current transformer should be threaded on each cable, and then the zero sequence current transformer secondary side with the same end should be connected in parallel and then introduced into the device, For the lines with two different loads in the same interval, lead the zero sequence signal line to the device respectively. After the zero sequence voltage and current signal lines are checked correctly, they will be connected to the terminal block of the corresponding input signal of the device.

As the 10kV system of substation is a small current grounding line selection device recently installed and debugged, the specific small current grounding line selection operation and action line selection rate should be recorded through later observation.