Power cable insulation will change in thermal, chemical and mechanical action with the electric effect, so that the medium has the physical and chemical changes in the insulation, the insulation level of medium decrease.
Insulation damp. Inadequate sealing methods for terminal head and installation of poor quality cover heads will cause insulation damp, and holes or cracks and other defects left during manufacturing also make cable damp.
There are many reasons for cable overheating. The internal cause is the internal gas heated up by local heating, this will cause the external insulation charring. Cables installed in drying tube and pipe have accelerated insulation damage due to overload or bad heat dissipation.
Mainly refers to the damage caused by the external force. This is mainly due to the vibration of vehicle and mechanical action. Cable deformation caused excessive bending, damaged inner insulation.
Electrolysis or chemical action make cable sheath corrosion. Due to the nature and extent of corrosion are different, the lead covered with red, yellow or orange and yellow compound pores or sponge like organism.
5,Over voltage breakdown
Atmospheric over voltage and the cable internal stress exceeds the allowable value cause breakdown. Moreover, the actual fault analysis shows that many outdoor terminal faulty, is due to the atmospheric over voltage.
6,The design and manufacturing process and the intermediate connector faulty
Stripping semiconductor, there are dust and other impurities on damaged inner insulation; Cable head sealed badly will cause the internal insulation moisture up; Cable joint sealing process is not standard, resulting in grounding faulty; production environmental humidity is too wet , causing insulation integrity damp; Cable grounding errors lead to ground circulation or break.