According to voltage grade, it can be divided into medium and low voltage power cables (35 kV and below), high voltage cables (110 kV and above), ultra-high voltage cables (275~800 kV) and ultra-high voltage cables (1000 kV and above). In addition, it can also be divided into AC cable and DC cable according to the current system. According to the insulation material, 1. Oil impregnated paper insulated power cable. It has the longest application history. It is safe and reliable, with long service life and low price. The main disadvantage is that the laying is limited by the drop. Since the development of drip free impregnated paper insulation, the problem of drop limitation has been solved, so that oil impregnated paper insulated cables can continue to be widely used. 2. The insulation layer of plastic insulated power cable is extruded plastic power cable. Commonly used plastics are polyvinyl chloride, polyethylene and cross-linked polyethylene. The plastic cable has simple structure, convenient manufacturing and processing, light weight, convenient laying and installation, and is not limited by the laying drop. Therefore, it is widely used as medium and low voltage cables, and has the tendency to replace sticky impregnated oil paper cables. Its biggest disadvantage is the existence of dendritic breakdown, which limits its use at higher voltages. 3. The insulation layer of rubber insulated power cable is made of rubber and various additives, which are fully mixed, extruded and wrapped on the conductive core, and then heated and vulcanized. It is soft and elastic, and suitable for occasions with frequent movement and small laying bending radius. The rubber materials commonly used for insulation include natural rubber styrene butadiene rubber mixture, ethylene propylene rubber, butyl rubber, etc. According to the voltage grade, it is divided into 1. Low voltage cable: it is suitable for fixed laying on the transmission and distribution lines with AC 50Hz and rated voltage of 3kv and below for power transmission. 2. Medium and low voltage cables: (generally 35KV and below): PVC insulated cables, polyethylene insulated cables, cross-linked polyethylene insulated cables, etc. 3. High voltage cable: (generally 110KV and above): polyethylene cable and cross-linked polyethylene insulated cable, etc. 4. Ultra high voltage cable: (275~800 kV). 5. UHV cable: (1000 kV and above).