Power cable is the most common type of cable in our daily life. If you look closely at the cable, you will find that the outer layer of the power cable is covered with a layer of insulation. What role does the insulation play in the cable? What are the classifications of insulation materials for power cables?

Power cables are often used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines across rivers and seas. The insulation layer of the power cable is to electrically isolate the wire core from the ground and the wire cores of different phases, so as to ensure that no phase-to-ground or phase-to-phase breakdown short circuit occurs when transmitting electric energy, so the insulation layer is also indispensable in the cable structure component. According to the voltage level, power cables can be divided into medium and low voltage power cables (35 kV and below), high voltage cables (above 110 kV), extra high voltage cables (275-800 kV) and ultra-high voltage cables (1000 kV and above) ).

                                           
一.According to the classification of insulating materials, power cables can be divided into plastic insulated power cables and rubber insulated power cables.
1. Plastic insulated power cables
Power cables with extruded plastic insulation. Commonly used plastics are polyvinyl chloride (PVC), polyethylene, and cross-linked polyethylene (XLPE). Among them, PVC is still widely used in low-voltage cables due to its advantages of convenient process, good comprehensive electromechanical performance, good flame retardant performance, and low cost. Polyethylene has excellent properties such as electrical properties, moisture resistance, sweat resistance and moderate mechanical properties, so it is most widely used in cable insulation and outdoor cable sheathing, and cross-linked polyethylene has excellent electrical properties and mechanical properties. The performance is widely used in the insulation of medium and high voltage cables. Because of its superior electrical properties, good high temperature resistance and oil resistance, polypropylene is often used for insulation of communication cables and oil well cables, and is also the first choice for insulation materials of telephone and computer cords.
Plastic cables have the advantages of simple structure, convenient manufacturing and processing, light weight, convenient laying and installation, and are not limited by laying differences. Therefore, they are widely used as medium and low voltage cables, and tend to replace viscous impregnated oil-paper cables. Its biggest disadvantage is that there is branch breakdown, which limits its use at higher voltages.
2. Rubber insulated power cable

                                                        
The insulating layer of the rubber insulated power cable is made of rubber and various compounding agents. After being fully mixed, the insulating layer is extruded on the conductive wire core and vulcanized by heating. The insulation is soft and flexible for frequent movement and has a small bend radius. Commonly used rubber materials for insulation are natural rubber-styrene-styrene rubber mixture, ethylene-propylene rubber, butyl rubber, etc.
The long-term allowable working temperature of ethylene-propylene rubber material is 90 degrees, and the allowable temperature of short-circuit thermal stability is 250 degrees, which is suitable for large temperature perimeter, cold resistance and high temperature resistance. Because of its strong environmental adaptability, weather resistance, light resistance, oxygen resistance, ozone resistance, and moisture resistance, it is widely used in Europe and the United States.
二.Main features of power cables
1. Smaller footprint
More traditional power cables appear on the ground, forming the form of spider webs, which greatly affects our lives and is not beautiful at the same time. Nowadays, more power cables are buried underground, so the space on the ground is effectively saved, and it is also more beautiful.
2. High power supply reliability
The performance of power cables has continued to break through, especially in terms of reliability. It can be used in different harsh environments, and at the same time it is very stable and reliable in terms of power transmission, so it has won wide demand in the market.
3. The possibility of electric shock is small
The cable line is laid underground. No matter what kind of fault occurs, because the live part is in the ground shielding part, it will only cause tripping and will not harm people and animals, which is relatively safe.
4. Larger distributed capacitance
The materials selected as the conductive core of the power cable are all highly conductive, and there are generally multiple conductive cores inside the cable. Compared with the overhead line of the same cross-section of the power cable per unit length, the power of the power cable is higher. The capacity is also larger.
5. Less maintenance workload
The cable line is underground, and in general (except for oil-filled cable lines), it is only necessary to conduct regular road observations to prevent external damage and to do a preventive test every 2 to 3 years.

                                                            
6. The possibility of electric shock is small
The conductive core of the power cables is wrapped with insulating layer, shielding layer and protective layer. Layer-by-layer protection and its laying method can slow down the aging speed of the line, and the possibility of damage to it is relatively small, and the possibility of electric shock will decrease accordingly.