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Common faults and treatment of power cable

Common faults and treatment of power cable

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  • Time of issue:2020-01-09
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(Summary description)The method to determine 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. Generally

Common faults and treatment of power cable

(Summary description)The method to determine 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. Generally

  • Categories:Company news
  • Author:
  • Origin:
  • Time of issue:2020-01-09
  • Views:7
Information

Ground or short circuit fault, disconnection fault, disconnection and grounding fault, flashover fault, etc.

The method to determine 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. Generally, the fault type is determined according to the following conditions:

(1) When the insulation resistance of one core or several cores to the ground is measured, or the insulation resistance between cores is less than 100 kiloohm, it is a low resistance grounding or short circuit fault.
(2) When the insulation resistance of one core or several cores to the ground is measured, or the insulation resistance between cores is much lower than the normal value, but higher than 100 kiloohm, it is a high resistance grounding fault.
(3) When the ground insulation resistance of one or more cores of the cable is high or normal, the conductor continuity test shall be carried out to check whether there is a broken line. If there is, it is a broken line fault.
(4) When one or more conductors of the telemetry cable are discontinuous and grounded through resistance, it is a broken line and grounding fault.
(5) Flashover faults often occur in the preventive withstand voltage test, mostly in the cable terminal and intermediate joint. Flashover sometimes occurs several times in a row, with an interval of a few seconds to a few minutes.

Test method of fault

The instruments used in the past include qf1-a cable detector, Dlg-1 flash detector, cable path detector and fault locator. At present, the most popular test method is flash test, which includes flash and direct flash, and the most commonly used method is flash test. It is easy to operate, safe and reliable. The equipment is mainly composed of two parts: high voltage generator and current pulse meter. The high voltage generator is used to generate DC high voltage or impulse high voltage, which is applied to the fault cable to force the fault point to discharge and generate the reflected signal. The current pulse meter is used to pick up the reflected signal to measure the fault distance or directly measure the open circuit, short circuit or low resistance fault with low voltage pulse. 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 infinite, it is easy to find the open circuit fault by using the low-voltage pulse method. Generally speaking, pure open circuit fault is not common. Usually, the open circuit fault is phase to ground or phase to phase high resistance fault, and phase to ground or phase to phase low resistance fault coexists.
(2) When the resistance of the fault point is equal to zero, it is easy to find the short-circuit fault by using the low-voltage pulse method, but it is rarely encountered in practical work.
(3) When the resistance of the fault point is greater than zero and less than 100k Ω, it is easy to find the low resistance fault by using the low voltage pulse method.
(4) Flashover fault can be measured by direct flashover method. This kind of fault generally exists in the joint. The resistance of the fault point is greater than 100 kiloohm, but the value changes greatly, and each measurement is uncertain.
(5) The high resistance fault can be measured by impulse flashover method, and the resistance at fault point is greater than 100 kiloohm 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 decreases, 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 according to different fault properties, and new technologies and equipment should be constantly introduced. At the same time, experience should be explored on new equipment to develop new functions. For example, the test technology of voice frequency signal to the cable and receiving signal at the fault point, and the SDC series high intelligent cable fault flash tester of T16 / 910 cable fault tester are used to accurately locate the fault point. 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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