First, the type of cable failure 1. Insulation fault
(1) The insulation level of the cable is low, and leakage occurs; (2) The insulation resistance of the wires between the wires or the ground does not meet the requirements; (3) The leakage current between the wires or ground is too large. 2, ground fault
(1) Fully grounded (also called dead ground), that is, the core of a cable is grounded. If the measurement is made with a rocker (or universal meter), the insulation resistance between the two is zero;
(2) Low-resistance grounding refers to the fact that the insulation of one or more phases of the cable to the ground is less than 500kΩ;
(3) High-resistance grounding means that the insulation resistance value of one or more phases of the core wire to the ground is above 500kΩ and even above 1 MΩ.
3. Short circuit fault
There is a complete short circuit, low resistance or high resistance short circuit; there are two when the same ground short circuit or two-phase direct short circuit; there are three-phase short circuit and ground.
4. Breakage fault
The core of one or more phases of the cable is broken or a part of the core of one phase is broken. 5. Flashover failure
When the voltage of the cable reaches a certain value, a flashover breakdown occurs between the cores or the core to the ground; when the voltage decreases, the breakdown stops. In some cases, the breakdown does not occur even if the voltage value is increased again, and it may occur after some time. This fault has the characteristic of automatically closing the fault point.
Second, the cable fault causes
There are many reasons for the failure of the cable, which are closely related to design selection, installation and construction, use environment, operation status and maintenance management. The specific reasons are as follows:
(1) When the cable is in use, it encounters squeezing, pressing, burying, boring, planing, ramming, pulling, etc., which causes damage to the electrical edge of the cable and leakage, grounding or short circuit.
(2) During the transportation work, the motor vehicle, the mine car off-track or the material vehicle caused a collision and pulled the main cable of the transportation lane; the material vehicle hit the support of the lane and damaged the electric wire.
(3) When laying wires, the bending radius of the armored cable is too small, which causes cracks in the lead package of the cable and causes moisture or moisture and damages the insulation. When the cable is laid, it exceeds the allowable height difference specified by the manufacturer, causing leakage of the cable and damaging the insulation. Damage to the cable during laying damages the insulation performance over a long period of time and causes an accident.
(4) The quality of the junction box does not meet the requirements, or the wire joints have large contact resistance and cause heat, or the quality of the material is poor, or the insulation strength is low due to moisture, or the seal is not good and damp, and the insulation deteriorates after a certain period of operation.
(5) The daily maintenance and repair are poorly managed. Drop the cable on the ground and even soak it in water for a long time; connect the cables into “chicken pawsâ€, “sheep tails†and bright joints, resulting in leakage, grounding or short-circuit faults.
(6) The cable is overloaded and the core heats up, causing insulation aging and damaging the cable. (7) Operating overvoltage, fault overvoltage and atmospheric overvoltage.
Third, the cable fault handling
(1) When the cable is faulty, the type of the accident should be correctly judged based on the phenomenon and status of the accident and it should be handled immediately. If the fault cannot be dealt with immediately, it should immediately report to the competent authority and the mine dispatching office; On-site processing.
(2) When using ordinary type carrying electrical measuring instruments to measure cable faults, the methane content of the place of use must be measured by a gas inspector. Measurements can only be made when the methane concentration is below 1 %.
(3) When the cable catches fire due to a fault, immediately cut off the power supply on both sides of the cable, and then extinguish the fire with sand, fire extinguisher, and other fire extinguishing materials, and report to the dispatching room according to the situation.
(4) For cable faults in coal mines (gas) and gas outburst mines and gas vented roadway areas, it is forbidden to use test transmission methods to determine the fault point of the cable.
(5) When using a cable fault test but with a multimeter in conjunction with manual bending of the cable, etc. to find the point of failure of the cable, it must be done after the power of the faulty cable is cut off.
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