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Common Faults and Treatment of Power Cable
Release time:
2020-01-09
To improve the technical level of cable fault testing, different methods should be adopted for different fault properties, and new technologies and new equipment should be introduced continuously. At the same time, experience should be explored in new equipment and new functions should be developed. For example, the test technology of sending audio signals to cables and receiving signals at fault points is now used.
Ground or short circuit fault, disconnection fault, disconnection and ground fault and flashover fault, etc.
The method of determining the type of cable fault is to measure the insulation resistance of each phase at one end of the line with an insulation resistance meter. The fault type is generally determined according to the following conditions:
(1) When the insulation resistance of one or more cores of the shaking cable to ground, or the insulation resistance between cores is less than 100 kilohms, it is a low resistance grounding or short circuit fault.
(2) When the insulation resistance of one or several cores of the shaking cable to ground, or the insulation resistance between cores is much lower than the normal value, but higher than 100 kilohms, it is a high resistance grounding fault.
(3) When the insulation resistance of one or more cores of the shaking cable to ground is high or normal, a conductor continuity test should be carried out to check whether there is a disconnection. If there is, it is a disconnection fault.
(4) When the shaking cable has one or several conductors that are discontinuous and grounded by resistance, it is a broken wire and a ground fault.
(5) Flashover faults mostly occur in preventive withstand voltage tests, and most of them occur in cable terminals and intermediate joints. Flashover sometimes occurs several times in a row, with intervals ranging from a few seconds to several minutes.
Test methods for faults
The instruments and equipment used in the past include QF1-A type cable detector, DLG-1 type flash detector, cable path meter and fault point meter. At present, the most popular test method is the flash test method, which includes flash and straight flash, the most commonly used is the flash method. The flash test has high precision, simple operation, safety and reliability. Its equipment is mainly composed of two parts, namely, high voltage generator and current pulse meter. The high voltage generating device is used to generate DC high voltage or impact high voltage, which is applied to the fault cable to force the fault point to discharge and generate a reflected signal. The current pulse meter is used to pick up the reflected signal to measure the fault distance or directly use the low voltage pulse to measure the open circuit, short circuit or low resistance fault. The following is a brief description of the test method based on the fault point resistance:
(1) When the resistance of the fault point is equal to infinity, it is easy to find the open circuit fault by measuring with low-voltage pulse method. Generally speaking, pure open circuit fault is not often seen. Usually, open circuit fault is relative to ground or interphase high resistance fault, and relative ground or interphase low resistance fault coexists.
(2) When the fault point resistance is equal to zero, it is easy to find the short-circuit fault measured by the low-voltage pulse method, but this kind of fault is rarely encountered in actual work.
(3) When the fault point resistance is greater than zero and less than 100 kilohms, it is easy to find low-resistance faults by low-voltage pulse measurement.
(4) Flashover fault can be measured by direct flash method. This kind of fault generally exists inside the joint. The resistance of the fault point is greater than 100 kilohms, but the value changes greatly, and each measurement is uncertain.
(5) High resistance fault can be measured by flash method. The resistance of fault point is greater than 100 kilohms and the value is determined. Generally, when the test current is greater than 15 mA, the test waveforms are repetitive and can overlap, and one waveform has one emission, three reflections and the pulse amplitude gradually weakens, the measured distance is the distance from the fault point to the cable test end; Otherwise, it is the distance from the fault point to the opposite end of the cable test.
In order to improve the technical level of cable fault testing, different methods should be adopted for different fault properties, and new technologies and equipment should be continuously introduced. At the same time, experience should be explored in new equipment and new functions should be developed. For example, the test technology of sending audio signals to cables and receiving signals at fault points and the accurate positioning of fault points by SDC series high-intelligence cable fault flash tester using T16/910 cable fault tester are adopted. These devices can control the measurement error within tens of centimeters, directly find the fault point for processing, and improve the efficiency of fault detection.
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