Nature of power cable fault judgment
the nature of the cable fault judgment, is the first step in cable fault test work program. The nature of the cable fault judgment accurate or not directly affects the correctness of the method of coarse select. Sometimes, due to the nature of the fault judgment, lead to the selection of test method error, caused the entire test until the failure of the work. Therefore, must be familiar with and can accurately judge various
the properties of the cable fault. Below, it is divided two parts to operation failure and trial test failure respectively introduces fault judgment method of the nature of the choice of test methods and fault distance.
1, the running fault
operation fault is refers to the cable in operation, caused by insulation breakdown or wires burn out protector action and suddenly stop power supply failure. Running malfunction can be caused by cable of the single phase or multiphase high resistance, low resistance, linear fault, or their combination of failure. Want to possess the exact nature of cable fault, can make the following two kinds of electrical test.
( 1) Insulation resistance test
insulation resistance testing request to do the three phase fault cables at both ends are open, and then measuring the interphase, insulation resistance to the ground. Is worth questioning when using high resistance testing instrument measuring insulation resistance, if the measured result is zero, the fault resistance comparing different Rx at zero, to determine the fault nature is high resistance also play's resistance.
( 2) Conduction test
conduction test is to identify whether continuous fault cable wire core test. Conduction test requirements will be fault, three phase short circuit and grounding end of the cable and the fault cable head end one by one to test the relative resistor Rx.
conduction test generally are not allowed to use instrument to measure high resistance test. Because, linear fault break fault point insulation may be carbonized carbonized channel and form a low resistance, and hence resistance may be present in the high resistance testing instrument for the appearance of zero, causing false judgment.
2, forecast of fault
the pilot test of the cable fault refers to insulation breakdown or insulation fault in the preventive test and inspection must be conducted after insulation to restore power cable fault. Prophylactic dc withstand voltage test cable connection mode is in a phase of dc withstand voltage, other each ( Except for single core cable) Ground wire along with earth. Due to cable preventive test was conducted by phase, and the energy is small, so the cable pilot test failure could not have caused break line failure, for single phase and more commonly and high resistance, low resistance grounding or short circuit fault. Nature shows, the pilot test of cable fault fault is much simpler than running.
cable is easy to determine the nature of the pilot test failure. According to the result of preventive withstand voltage test and fault phase insulation resistance measurements can make accurate judgment. Cable adopts dc negative high voltage of the preventive test, compression test, requirements, three-phase opening end of the cable under test measured cable insulation resistance testing also requires the three-phase opening at the end.
due to the pilot test failure generally will not result in break linear failure, therefore in the forecast of nature of the fault judgment without conduction test.