1. Insulation aging and deterioration

The wire and cable insulation is subject to the thermal, chemical and mechanical effects brought by the electrical action, so that the physical and chemical changes of the insulating medium occur, and the insulation capacity of the medium is reduced. Insulation is damp, the insulation is damp due to the upper and lower sealing of the structure or poor installation quality of the intermediate joint or terminal head, and defects such as sand holes or cracks are left when manufacturing the cable package lead, which will also make the cable damp.

2. Cable overheating

There are many reasons for cable overheating. The internal cause is the cable insulation internal air gap free caused by local heating, so that the insulation carbonization. External causes are cables installed in dense cable areas, cable tunnels, etc., cables worn in dry pipes and cables close to pipes will accelerate insulation damage due to cable overload or poor heat dissipation.

3. Mechanical damage

Mainly refers to the external force caused by cable damage. This is mainly due to mechanical effects such as vehicle vibration, which deform the cable. The deformation of the cable causes excessive bending, damages the internal insulation or causes air gaps in the insulation.

4. Corrosion of sheath

Due to electrolysis or chemical action, the cable lead package is corroded. Due to the different nature and degree of corrosion, the lead package has red, yellow, orange and light yellow compounds or pores similar to sponge.

5. Breakdown caused by overvoltage

Atmospheric overvoltage and internal overvoltage make the stress of cable insulation exceed the allowable value and cause breakdown. Moreover, the analysis of practical problems shows that many outdoor terminal problems are caused by atmospheric overvoltage.

6. Design and manufacturing process of intermediate joints and terminal heads

When stripping semiconductors, the internal insulation is damaged or the insulation surface is contaminated with particles, dust and other impurities; The cable head is poorly sealed, resulting in moisture inside the insulation, causing the insulation to be damp; The cable joint process is not standard and the sealing is not standard, resulting in grounding; The humidity in the production environment is too high, causing the insulation integrity of the production part (cable head) to be damp; The cable grounding error leads to the formation of circulation or fracture of grounding wire.