As the name implies, the use condition of small current grounding line selection device is small current system. In China's 3KV ~ 66kV system, the neutral point treatment method of power system is generally ungrounded, grounded by arc suppression coil and grounded by resistance. This power system is called small current system. The small current grounding system, especially the small current grounding system of 35kV and below, has many branches, complicated direction and low voltage level, so it is difficult to guarantee the quality in the design and construction, and the probability of ground fault in operation is very high.

The traditional method to find the ground fault line is to gradually disconnect each circuit breaker. After the fault line is disconnected, the system voltage will recover and the grounding signal will disappear, otherwise continue to search. Although most of this method can be remedied by reclosing, the disadvantages of this method are obvious to some customers with high demand for power supply, especially for those lines with heavy load, this method can no longer meet the requirements of safe and stable power supply.

Therefore, fast and accurate fault line selection and timing trip not only help to improve the service life of the equipment, provide power supply reliability, but also help to reduce the burden of maintenance personnel and the outage probability of users, and improve the economic benefits of power supply departments and users. The fault line can be accurately found through the small current grounding line selection device.