Shielding layer In order to uniformly conductive core and insulated electric field, medium and high voltage power cables of 6kV and above generally have a conductor shielding layer and an insulating shielding layer, and some low voltage cables are not provided with a shielding layer.
The shielding layer has two kinds of semi-conductive shielding and metal shielding.
The semi-conductive shielding layer is usually disposed on the outer surface of the conductive core and the outer surface of the insulating layer respectively referred to as an inner semi-conductive shield and an outer semi-conductive shield.
The semiconductive shielding layer is composed of a semiconductive material having a low electrical resistivity and a relatively small thickness.
The inner semi-conductive shielding layer is for a uniform electric field on the outer surface of the core and avoids partial discharge of the conductor and the insulation due to the unsmooth surface of the conductor and the air gap generated by the strand twisting.
The outer semi-conductive shielding layer is in good contact with the outer surface of the insulating layer and is equipotential with the metal sheath to avoid partial discharge with the metal sheath due to defects such as cable insulation surface cracks.
For medium and low voltage power cables without metal sheaths, in addition to the semi-conductive shielding layer, a metal shielding layer is added.
The metal shielding layer is usually wrapped by a copper strip or a copper wire and mainly serves to shield the electric field.
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