Author: Noyafa–CCTV Tester
Question: What is a cable high resistance fault Answer: Leakage high resistance fault: When the leakage current value of the cable increases continuously with the increase of the applied DC voltage, and far exceeds the specification value required by the tested cable itself. That is, the cable insulation medium is damaged and a solid problem is formed: What is a cable high resistance fault Answer: Leakage high resistance fault: When the leakage current value of the cable increases continuously with the increase of the applied DC voltage, and far exceeds the measured cable The normative value required by itself. That is, the insulating medium of the cable is damaged and a fixed resistance channel is formed, but the resistance value is relatively high.
See below. Flashover high resistance fault: within the pre-test voltage range of the cable, when the pre-test voltage of the cable is added to a certain value, the leakage current value of the cable suddenly increases, and its value far exceeds the specifications required by the tested cable value. The faulty insulating medium, although damaged, does not form a fixed resistive path.
The essence of high-resistance fault is shown in the equivalent circuit shown in the figure below.“High resistance leakage resistance”superior,“High resistance leakage resistance”The resistance value directly determines the characteristics of the high resistance fault. ① When R is approximately infinite, the DC voltage at both ends of the fault point J can be increased to a relatively high level without the leakage current exceeding the rated value. ② When R is less than a certain value, a withstand voltage test is performed at this time. Due to the existence of R, a large leakage current will be generated. The leakage current will produce a large voltage drop on the internal resistance of the high-voltage power supply, and the voltage across J Unable to rise, J may not be broken down.
To increase the voltage, the leakage current is bound to increase, so the relay protection may be activated because the leakage current greatly exceeds the allowable value, and the flashover phenomenon will not occur. ③ When R is equal to or less than the characteristic impedance of the cable under test, the nature of the fault becomes a low-resistance fault.
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