Since the power cable has relatively large current ,electric current will produce a magnetic field, in order not to affect other components, so the shield can shield this electromagnetic field inside the cable.It can play a certain role in grounding protection. 

If the cable core is damaged, the leaked current can flow along the shielding layer such as the grounding grid to play a role of safety protection.It is commonly used in control cable,medium voltage cable and high voltage cable.

Shielding is the most common countermeasure against noise. Various types of shielding, and have their own characteristics, it is necessary to choose the shield methods as the use of places and the surrounding electrical environment .

The following is the commonly used shield ways:

1. Copper wire braided shield cable: Tinned copper or bare copper wire mesh to cover the shielding cable structure, stretching and bending is not easy to damage its resistance to bending shielding structure. 

2. Copper wire winding shield cable : the number of tinned copper wire or bare copper wire closely arranged like tape and then rewound the cable shielding structure. Although the shielding efficiency than woven high shielding, strong anti-interference, but if used in mobile wiring, it may damage the shielding structure. Therefore, it is usually used for fixing wiring.

3.Aluminum-plastic composite tape shield cable: aluminum foil and polyester tape synthetic tape roll around the wire shielding structure, especially for reducing the high frequency of interference.

Power cables 6KV and above are usually metal shielding outside the insulation, in addition to its function of shielding electric field, there is an important function is to leak short-circuit current. Due to the different grounding of the cable, metal shield structure is also different. Arc suppression coil cable grounding, the metal shield with copper tape around the package. If the cable with a small resistance to ground, the use of more metal shielding copper sparse winding structure or metal sleeve.

In addition, the 10KV and above xlpe power cable insulation both inside and outside the semiconductor shield, its function is not to shield electric field, but the homogenization of the electric field, even if the electric field within the insulation tends to be uniform, so as to improve and provide insulation performance and prolong the service life of the cable. 

Semiconductor shielding materials are mostly added with carbon black polyolefin, a cross-linked and non-cross-linked type, using three-layer coextrusion process closely attached inside and outside the insulation, the thickness of the standard.