The basic structure of a power transmission cable mainly consists of four parts: the conductor, insulation layer, shielding layer, and protective layer. These parts work together to ensure the safe and efficient transmission of electrical energy.
Conductor: As the conductive part of the cable, it is responsible for transmitting electrical energy and is usually made of copper or aluminum, which have high conductivity. Depending on the application, it can be divided into single-core, double-core, three-core, or four-core cables, suitable for DC, single-phase AC, three-phase AC, and neutral-grounded systems, respectively.
Insulation Layer: Used to electrically isolate the conductor from the ground and from conductors of different phases, preventing current leakage and short circuits, and ensuring normal power transmission. Commonly used materials include polyvinyl chloride (PVC), polyethylene (PE), and cross-linked polyethylene (XLPE). XLPE is widely used in medium and high voltage cables due to its good heat resistance and high breakdown strength.
Shielding Layer: Generally installed in cables with voltage levels of 15kV and above, it includes a conductor shielding layer and an insulation shielding layer. Its function is to improve the electric field distribution on the conductor surface, eliminate the tip effect caused by the twisting of multiple wires, avoid damage to the insulation layer due to localized electric field concentration, and enhance the contact effect between the insulation layer and the conductor.
The protective layer includes an inner sheath, an armor layer, and an outer sheath, primarily used to prevent the intrusion of external impurities, moisture, and mechanical damage. The inner sheath is often made of aluminum or lead to prevent the impregnating agent from leaking out; the armor layer, such as steel strip or wire armor, provides compressive and tensile strength, suitable for direct burial or subsea laying; the outer sheath is made of materials such as polyvinyl chloride to resist environmental corrosion.
