The structure design of XLPE insulated cables is based on the relevant technical parameters. Firstly, the appropriate current carrying section, inner semi-conductive shielding and anti-emission shielding of high voltage cables are determined by the maximum allowable operating temperature.
For medium and low voltage XLPE insulated cables, the current-carrying section can be determined and then the structure design can be carried out. For high voltage cables, other related factors, such as core section, economic current density, allowable working temperature of insulating materials and insulation structure form, must be determined. If not taken seriously, cable insulation life and mechanical properties will be affected.
The inner and outer sheaths of medium and low pressure cross-linked polyethylene are usually made of PVC with a thickness of 3 ^ - 4 mm, and PE material is also used in heat shrinkable tubes of inner sheath. This is mainly to reduce water seepage, because the water absorption of PE is less than that of PVC. PVC material is generally used for sheath, because the fire-retardant and flame-retardant properties of PVC material are better than PE, this kind of cable structure has been widely used in Beijing area. For the outer sheath of 110 kV XLPE insulated cable with ultra-high voltage, because of the requirement of withstanding voltage, it is necessary to coat a layer of conductive graphite on the outer layer of PVC sheath for field test. When accepting the cable, it is necessary to check whether the conductive layer is complete or not. Otherwise, the test of the sheath will be meaningless.