Single phase grounding fault is common in small current grounding system, accounting for more than 80% of power grid fault. When single-phase grounding, due to the small fault current, it is difficult to select the fault line.

        In case of grounding fault in small current grounding system, the zero sequence current flowing through the protection of non fault line is the sum of the non fault phase to ground capacitive current of the line itself, and its direction is from the bus to the line. The zero sequence current passed by the protection of the fault line is the sum of the zero sequence currents of all non fault lines, and its direction is from the line to the bus.

        There are many advantages of industrial computer small current grounding line selection device. There are many functional upgrades on the conventional small current line selection device. The wheel cutting line selection technology is a new technology, which is a technical measure taken for the characteristics of weak fault signal and easy interference in the single-phase grounding fault of small current grounding system. This line selection does not completely depend on the result of one-time judgment, but comprehensively considers the whole process. When the fault does not disappear after the first line selection trip, the device will conduct round line selection until the fault disappears.

        With the progress of technology, the small current grounding line selection device is continuously improved, and the function of small current grounding line selection is gradually improved. As long as the equipment with the principle suitable for the system is selected and the error of measurement link is minimized in the actual operation, the accuracy of small current grounding line selection will be further improved.