(2) The vibration or impact load of the driving vehicle will also cause the lead (aluminum) package of the underground cable to crack. (3) The cable is accidentally bumped during installation, the cable is pulled by excessive mechanical traction, and the cable is damaged by excessive bending. (4) Damage caused by natural phenomena.
For example, the inner insulating glue of the intermediate joint or the terminal head expands and bursts the outer casing or cable sheath; or the cable sheath installed on the nozzle or bracket is scratched; or due to excessive tension caused by land settlement, the intermediate joint or conductor is pulled off. Third, the overvoltage (lightning strike or operating overvoltage) atmosphere and internal overvoltage act, so that the cable insulation is broken down, thereby forming a cable fault. In general, the breakdown point is defective.
Fourth, the insulation is damp. After the insulation is damp, it will cause the cable withstand voltage to drop and cause failure. The main reasons for the cable getting wet are: (1) The metal sheath is perforated or stabbed due to corrosion by foreign objects. (2) Water ingress due to unsealed structure or poor installation of joint box or terminal box.
(3) The cable is poorly manufactured, and the metal sheath has small holes or cracks. Fifth, insulation aging and deterioration Insulation aging will cause the cable withstand voltage to drop and cause failure. The main reasons for cable aging are: (1) Power cables are used over time.
(2) The cable is overloaded or the cable is poorly ventilated, causing local overheating and carbonization of the insulation. Among them, cable overload is an important factor for cable overheating. (3) When the oil-impregnated paper insulated cable is laid, the ground is uneven. Due to the existence of the height difference, the insulating oil that is higher will flow to the lower place, which will reduce the insulation performance of the cable at the higher place, resulting in failure.
(4) There is slag or air gap inside the cable insulation medium, and the insulation is lowered due to dissociation and hydrolysis under the action of the electric field. Cable fault tester manufacturer Shenzhen Noyafa Electronic Technology Co., Ltd.