Closed fault: short circuit to ground, broken wire, or their mixture, single phase, two phase or three phase fault. For example, power cable In case of cable fault in operation, if there is only grounding signal, it may be single-phase grounding fault; In case of overcurrent tripping of relay protection, two-phase or three-phase short circuit or mixed fault of short circuit and grounding may occur. According to the preliminary judgment, if the nature of the fault cannot be determined completely, the insulation resistance must be measured and the conduction test must be carried out;
(2) Burnout at fault point. That is, the high resistance fault or flashover fault is changed into low resistance fault through burn through for rough measurement;
(3) Rough measurement. Use an instrument on one side of the cable to measure the fault distance, and use the cable line technical data to calculate the location of the fault point;
(4) The measurement of the path. If the drawings and data are not complete or the cable path is unknown, the audio induction detection method and pulse magnetic field method can be used to find the laying path and burial depth of the faulty cable, so as to carry out fixed-point precision measurement. The audio induction detection method is to inject audio signal current into the wire, and determine the path according to the strength of the audio signal received by the receiver in the receiving coil;
(5) Fine measurement point of fault point. The precise location of the fault point is determined by means of impulse discharge acoustic measurement, audio frequency induction, acoustic magnetic synchronous detection and other methods. The acoustic measurement method is only applicable to cable faults with low resistance grounding, and has poor effect on metallic grounding faults. Induction method is applicable to metallic ground fault and interphase short circuit fault.
The above five steps are general survey steps, and some of them can be omitted according to the specific situation during the actual side search. For example, if the cable laying path is accurate, it is not necessary to find the path laterally. For high resistance faults, the flashover method can be used directly without burning through. For some flashover faults, it is not necessary to carry out fixed points. The data can be consulted according to the distance data obtained from the side finding, and the indirect head can be directly checked and judged. For cable faults in the wire trench or tunnel, impact discharge can be carried out, Monitor directly to determine the fault point.
