Wire and cable maintenance is out of order
Wire and cable grounding fault can be summed up as, short circuit, break three categories, specific the following categories
(1) the short circuit fault. Two core or three core cable short circuit.
(2) the ground fault. Cable core or multi-fiber grounded.
(3) the break line fault. Cable or more core is a core fault current burn out or external force damage to get off, form a complete or incomplete break line.
(4) the flashover failure. This kind of failure occurs mostly in the preventive test, and most appear on the cable joint. Breakdown when reaches a certain value of the applied voltage, low voltage to a value when the insulation and recovery.
Have two or more at the same time the nature of the fault is called the comprehensive fault, tianjin jin into wire and cable fault comprehensive intuitive is hard to find, need a test instrument to determine the fault location of cable fault.
In general, cable fault can be summarized as grounding, short circuit, break!
Methods for searching the cable fault point:
(1) the sound law: a sound method is according to the fault cable discharge voice search, the method for high voltage cable core insulation flashover discharge is more effective. This method used equipment for the dc withstand voltage tester. Circuit connection as shown in figure 1, which is suitable for high voltage testing transformer SYB, C for high voltage capacitor, ZL for high voltage rectifying silicon stack, R in the limit of flow resistance, Q for the discharge gap, L for the cable core. Discharge, cable conductor at fault on the insulation layer discharge spark discharge of the "zi and zi", for Ming laying cable by hearing can be directly to find, if buried cable, first to determine and indicate the cable to, again at the time of mixed noise minimum, with the aid of deafness audio amplifier devices such as hearing AIDS or stethoscope lookup. Lookup, pickup close to the ground, along the cable to move slowly, when heard "zi and zi" discharge maximum, it is the point of failure. Using this method must pay attention to safety, in the end of the test equipment and cable should be monitored by designated personnel.
(2) the method of bridge: the bridge method is to use double bridge measure the dc resistance of cable core, to accurately measure the cable length, according to the cable length of direct proportion relationship between the resistance, calculate the point of failure. The method for direct short circuit or short circuit point contact resistance between the cable core is less than 1 Ω fault, general judgment error is not more than 3 m, for the failure of point contact resistance is greater than 1 Ω failure, can adopt the method of heightening voltage burn through resistance drop below 1 Ω, then measured by this method.