In the substation, the main function of small current grounding line selection device is to select the line accurately. For example: in coal mining enterprises, with the development of mine production, many local substations have been re planned, transformed and so on, which have brought certain pressure to the operation of small current grounding line selection device.

The traditional small current grounding line selection device adopts single line selection principle, and its own accuracy performance is poor, so it is difficult to get good results in line selection work. Some substations have undergone many times of capacity expansion and transformation. The zero sequence current transformer of the new line is inconsistent with the zero sequence current transformer model and transformation ratio of the original other lines. The zero sequence current of the grounding line collected may be smaller than that of the ungrounded line, which will directly cause the wrong selection of the line.

When some substations expand their capacity, arc suppression coils are added to the bus bar in the substation, which makes the capacitive grounding current compensated by the inductive current, and the small current grounding system based on the principle of amplitude and phase comparison of zero sequence current can not be effectively distinguished.

After the circuit transformation, the parallel cable does not pass through the zero sequence current transformer, which makes the zero sequence current monitored too small and leads to the wrong identification of the device. The polarity of zero sequence current transformer in a few circuits was wrongly connected during construction.

In the application process of small current grounding line selection, it has brought a lot of positive effects, but it also needs to take preventive measures. The small current grounding line selection device on the market can not achieve 100% line selection accuracy, so it can better integrate with the substation, and it can deal with different situations more quickly.