Structure Of XLPE Insulated Power Cable

- Aug 06, 2019-

XLPE cable is a plastic cable insulated by XLPE. XLPE is the abbreviation of Cross Linded Polyethyene in English. Domestic XLPE insulated cables are represented by YJLV and YJV, YJ by XLPE, L by aluminium core (copper core can be omitted), V by PVC sheath.

Except for special requirements, all cores used in XLPE cables are compacted cores. Their functions are as follows:

(1) Make the outer surface smooth, prevent the effect of guide wire and avoid electric field concentration;

(2) Prevent the semi-conductive material from entering the core when the semi-conductive shielding layer is extruded.

(3) It can effectively prevent moisture from entering the wiring core.

Therefore, when installing the cable, we should choose the fittings matching the compact core, otherwise the quality of the compaction is not good, which will cause the heating of the connecting parts.

The semi-conductive shielding layer inside and outside the insulation is made of cross-linked polyethylene with carbon black, and some of them are coated with heat shrinkable tubes. The outer semi-conductive shielding layer of the early cross-linked cable is also wrapped with graphite cloth, but the structure performance is not good. With the extrusion of the inner and outer semi-conductive shielding layer and the insulation layer at the same time, the extrusion process is formed. Well-known, now has been eliminated, when electing cables, wrapped shielded structure cables should be avoided as far as possible. The volume resistivity of the semi-conductive shielding layer is generally less than 100 Q cm, and its thickness is generally 1-2 mm. According to the national standard, the outer semi-conductive layer of the cable below 10 kV is peelable layer, and the layer above 35 kV is non-peelable layer. The main reason for this requirement is that the existence of peelable layer reduces the resistance to partial discharge of the cable, when installed. When attachments are made, air gap will be created in small parts.

Cable metal shielding layer, also known as copper strip shielding, will provide a circuit for cable fault current and provide a stable ground potential. The cross-section of copper strip (wire) can be selected according to the magnitude and duration of fault current, and whether grounding is one end or two ends. Single-core and three-core cross-linked cables with voltage levels below 35 kV are equipped with steel strips to provide mechanical protection. The platinum sheath of 110 kV and above voltage grade XLPE cables is made of corrugated aluminium (copper, lead, stainless steel) in Sichuan, which is used as the assembly and inner waterproof sheath. Because the water absorption of PE or PVC sheath is 0.01% and 0.15%-'l% respectively, while the metal is almost impervious, the metal inner sheath of UHV cables is impervious to water, such as Guangzhou. The 10 kV XLPE insulated cables imported from Japan by the Power Supply Bureau are made of corrugated aluminium sheath in Caichuan; the 110 kV XLPE insulated cables imported from Sweden by Shijiazhuang Power Supply Bureau are made of corrugated copper sheath; the Australian I10 kV XLPE insulated cables imported from Jinan Power Supply Bureau are made of corrugated stainless steel sheath; and so on. In addition, in the inner sheath of UHV cables, there are waterproof tapes and other water-proof technologies, which make the water that has entered difficult to diffuse.