Cable Troubleshooting

Cable fault refers to the fault that the cable has insulation breakdown during the preventive test or in operation, due to insulation breakdown, wire blown, etc., which forces the cable line to lose power. So, what are the reasons for cable faults? How to deal with cable faults?

1. What is the cause of the cable failure?

1. Mechanical damage

Cable faults caused by mechanical damage account for a large proportion of cable accidents. Some mechanical damage is so minor that it did not cause a failure at the time, but it took months or even years for the damage to develop into a failure.

2. Insulation damp

3. Insulation aging and deterioration

The air gap inside the cable insulation medium is dissociated under the action of the electric field to reduce the insulation. When the insulating medium is ionized, chemical products such as ozone and nitric acid are produced in the air gap, which corrodes the insulation; the moisture in the insulation causes the insulating fiber to hydrolyze, resulting in a decrease in insulation.

Overheating can also cause insulation aging and deterioration. Electric dissociation in the air gap inside the cable causes local overheating and carbonization of the insulation. Cable overloading is a very important factor in cable overheating. Cables installed in cable-intensive areas, cable trenches, cable tunnels and other poorly ventilated places, cables in drying pipes, and parts close to cables and heat pipes will all cause accelerated insulation damage due to their own overheating.

4. Overvoltage

The effect of the atmosphere and the internal overvoltage causes the insulation breakdown of the cable to form a fault, and the breakdown point is generally defective.

5. Poor design and production process

The waterproof design of the intermediate joint and the terminal head, the design of the electric field distribution is not careful, the selection of materials is improper, the workmanship is poor, and the production is not in accordance with the requirements of the regulations, which will cause the failure of the cable head.

6. Material defects

Material defects are mainly manifested in three aspects.

One is the problem of cable manufacturing, defects left by the lead (aluminum) sheath; during the wrapping insulation process, defects such as wrinkles, cracks, breaks and overlapping gaps appear on the paper insulation;

The second is defects in the manufacture of cable accessories, such as sand holes in cast iron parts, insufficient mechanical strength of porcelain parts, other parts do not meet the specifications or are not sealed during assembly, etc.;

The third is poor maintenance and management of insulating materials, resulting in damp, dirty and aging cable insulation.

7. Corrosion of the sheath

Due to the influence of underground acid-base corrosion and stray current, the lead sheath of the cable is corroded and pitted, cracked or perforated, resulting in failure.

8. The insulation of the cable is lost

When the oil-impregnated paper insulated cable is laid, the trench is uneven, or the outdoor head on the pole, due to the ups and downs and the great difference in height, the insulating oil in the high place flows to the low place. The insulation performance of high-altitude cables is reduced, leading to failures.

Second, how to deal with cable faults

For general common cable faults, using a cable fault locator purchased in the market can generally determine the location of the fault point within a few minutes or a few hours. However, when encountering special difficult faults and the detection is not smooth, it may be necessary to call multiple cable fault detectors with different functions to test repeatedly, and take turns to detect, locate, compare and confirm.

The types of these fault detectors mainly include various cable fault detectors designed, manufactured and developed based on the principles of the bridge method and the waveform method. Such positioning may take a few days or even longer. In this way, if you are lucky, you can determine The location of the fault point, if you are unlucky, the location of the fault point cannot be determined.

In the northern part of our country, the ground is frozen in winter, and when the directly buried cable fails, the actual fault finding and processing process is actually a very difficult job. First of all, the cable fault location instrument used must have high precision, and secondly, there must be corresponding personnel who have a clear understanding of the actual laying route of the cable. Although some cable fault detection instruments are equipped with cable path testers, they must also have The accuracy of positioning can only be improved by the cooperation of on-site personnel who know the approximate laying path of the cable. The actual handling process of cable faults is often three-pointed by people and seven-pointed by machines.

Due to the variability of the power cable laying environment, coupled with the application of various new materials for cables and accessories in cable lines, the difficulty of on-site fault location for power cables is increasing day by day.

The difficulty of on-site cable fault location is prominently reflected in the fault location of directly buried power cable lines. For the high-resistance faults that occur in power cable lines at present, although there are relevant classic technical documents and advanced fault detectors available. However, when using a professional cable fault locator to locate on site, sometimes some special difficult faults that cannot be located are encountered.

For example, creepage flashover faults appearing locally on the insulation surface of medium-voltage cross-linked power cable terminals and intermediate heads, and the precise location of metallic short-circuit faults, etc., often appear powerless or powerless to use professional cable fault locators.

About the cause of the cable failure and how to deal with it, I will tell you here today. Of course, there are many other reasons for cable failures. What I have listed today are only common causes of cable failures. I hope they can help you.