When single-phase grounding occurs in small current grounding system, the common faults in distribution system often occur in wet and rainy weather. It is caused by many factors such as tree barrier, single-phase breakdown of insulator on distribution line, single-phase line break and small animal harm. Single phase grounding not only affects the normal power supply of users, but also may produce overvoltage, burn out equipment, and even cause phase to phase short circuit and expand the accident.

The small current grounding line selection device is installed in the substation, which can automatically select the single-phase grounding fault line with short time and high accuracy. It can change the traditional manual line selection method, reduce unnecessary power failure for non fault lines, improve power supply reliability and prevent fault expansion. At present, most of the substations have been installed with this device, and good results have been achieved. In practical application, it should be noted that this device should be used together with the zero sequence current transformer on each outgoing line interval, otherwise it can not play any role.

The fault signals of the system are collected in real-time for line selection of small current grounding, and various line selection methods are applied for comprehensive line selection. The device determines the effective region of various fault line selection methods by rough set theory, and automatically evaluates the reliability of fault line selection results obtained by each method according to the characteristics of fault signals. The evidence theory is applied to integrate various line selection methods to ensure the complementary advantages of various line selection methods. In order to avoid misselection caused by interference of fault signal, continuous line selection method is adopted for small current grounding line selection device, and data are collected again every certain time for analysis. As long as the fault does not disappear, the calculation of line selection will not stop.