The invention discloses a method for selecting a wire after single-phase grounding of an underground
system. By adopting the method, after single-phase grounding happens in the ungrounded
system, a fault wire can be selected according to the change of zero sequence current after a neutral point of a
capacitor bank is instantly grounded. The method comprises the following steps: A, additionally installing a
control switch and a medium
resistor between the neutral point of a
capacitor and the ground, and keeping the
control switch on the point position during normal operation; B, judging whether single-phase grounding happens in a circuit or not according to the
voltage change of a
bus bar, and judging that single-phase grounding failure happens when the criterion is that a zero sequence
voltage is more than a certain value, a certain phase
voltage in three-phase voltages is reduced, and voltages of other two phases rise; C, immediately closing the
control switch and putting in a
resistor after single-phase grounding is judged to ensure that the grounding mode of the
system is turned into grounding through the
resistor and the
active component of the zero sequence current of the single-phase grounded circuit is greatly increased; and D,
tripping the circuit switch to clear the failure after the single-phase grounded circuit is determined.