In our country, the neutral point of distribution network is widely used, which is not effectively grounded and grounded by arc suppression coil, which is used to be small current grounding mode. When single-phase grounding fault occurs in small current grounding power grid, its fault current is very small, so it is called small current grounding fault. Because the small current grounding fault does little harm to the power equipment, communication and personal, and the line voltage between three phases is basically unchanged, which does not affect the power supply to the load, therefore, the power grid can be allowed to continue to operate for a period of time under the condition of single-phase grounding, so as to avoid the impact of sudden interruption of power supply on users. With the increasing requirements of power supply reliability, the small current grounding mode is more and more respected by the power sector.

Although the small current grounding fault will not affect the normal operation of the power grid, the overvoltage caused by it will harm the insulation of the power grid, which may lead to short circuit fault and expand the accident. Therefore, when the small current grounding fault occurs, it is necessary to select the fault line as soon as possible, so that the operators can take measures to deal with it in time. However, due to the weak fault current and unstable arc at fault point, it is difficult to select single-phase grounding fault line in small current grounding power grid.

For a long time, people have done a lot of work and developed many detection methods and devices, but the actual operation effect is not ideal. Due to the lack of reliable grounding line selection means, power grid operators have to use the method of manual switching to select the fault line. On the basis of summing up the successful experience and failure lessons of various small current grounding line selection schemes, our company applied the new concept and method of current computer measurement and control technology to make major improvements on analog signal processing, a / D conversion, calculation platform and algorithm. According to the requirements of different sites and users, the small current grounding line selection device was improved and upgraded, which solved the problem of power distribution The problem of network operators.