When the small current grounding fault is detected by the small current grounding line selection device, there is no need to trip immediately before a more serious accident is formed, so that the power supply of the power grid will not be interrupted immediately, so as to improve the reliability of continuous power supply. The energy of partial discharge of the cable is very small, which usually does not affect the short-term insulation strength of the cable. However, if partial discharge exists for a long time, the insulation will be damaged slowly, which will lead to insulation breakdown over time.

        Installation of small current grounding line selection without setting, simple debugging, small amount of maintenance, automatic selection display fault line; The line selection scheme is reasonable, accurate and directional, which can distinguish line and bus grounding; Record the initial time and cumulative time of grounding, with strong anti-interference function and high precision of data acquisition; And the device is not affected by the system operation mode, long and short lines, and grounding resistance; It can judge instantaneous grounding fault and configure grounding trip system to realize automatic trip. After use, it greatly facilitates the electrician on duty, reduces the workload of the electrical operator on duty, reduces the fault finding time, and improves the work efficiency.

        The line selection method of the small current grounding line selection device first determines which bus is grounded by measuring the zero sequence voltage of the bus, and then compares the zero sequence current of each line with the zero sequence voltage, and the zero sequence current is 90% behind the zero sequence voltage °， Determine the grounding line.

        Another way of line selection is to judge whether the bus is grounded, through the turn off function and the trip (close) function, the turn off function can be started after the selected line fails to trip. After the reclosing delay, the reclosing action will automatically close the switch. When the zero sequence voltage still exists, it indicates that "the line is not grounded"; When the zero sequence voltage does not exist, it indicates "the line is grounded".

        The application of small current grounding line selection device solves the problem of single-phase grounding line selection of transmission lines outside the power supply system, avoids a large number of switching operations and potential safety hazards caused by safe operation of power plant when single-phase grounding line selection is carried out by pulling wires in the past, greatly improves the safety and reliability of power supply of power plant, and also improves the efficiency of finding grounding point.