In XLPE cable stranded aluminium conductor is first screened in the form of a semiconducting extrusion which provides a smooth conductor surface and prevents formation of cavities at the surface of the conductor when the cable is subjected to bending.
The screened conductor is insulated with extruded XLPE compound. The insulation is further screened with layer of nonmetallic semiconducting material and over that a non magnetic metallic screen in the form of copper or aluminium tape is applied.
In case of multicore cables cores are laid together with suitable filler in the interstices and wrapped with PVC tapes or extruded PVC. For mechanical protection non magnetic aluminium wire/ strip/tape armour for single core cables and steel wire armour for multicore cables are provided over the inner sheath.
A layer of PVC/PE is extruded as outer sheath usually in back colour to prevent ingress of moisture.
Pure polyethylene is a thermoplastic material i.e. it becomes soft and plastic on heating and hard on cooling. Pure polyethylene is converted into thermosetting XLPE i.e. it sets permanently when heated. By cross linking process the polyethylene insulation of the cable is made thermally stable and also the melting point is greatly increased.
This is because PVC has a maximum working temperature of 70°C which is exactly what is needed for standing building cables, whilst XLPE has a maximum working temperature of 90°C.
It also can withstand vibration and has up to 100 times more moisture resistance capacity compared to PVC.
The XLPE insulation will not melt or drip, even at the temperatures of soldering irons, and it has increased flow resistance and improved ageing characteristics.
Improved water-tree resistance is another benefit of XLPE insulation for LV cables and MV cables over PE insulations.
So XLPE insulated cable has better resistivity to thermal deformation for its higher thermal tolerance property. Due to excellent thermal properties the current carrying capacity of XLPE cable is higher than that of conventional cable.
XLPE insulation has higher dielectric strength compared to other conventional dielectrics used for cables resulting low dielectric loss.
XLPE cable is made suitable for high voltage and extra high voltage application puto 132 kV. This cable can be used for long cable routes in high voltage transmission where the dielectric losses play a major role. This cable can easily be hadled due to lighter in weight than any other high voltage cable. As there is no case of oil migration from insulation it can be installed for inclined or vertical runs without any hesitation.
XLPE insulation is highly resistant to moisture for which no special precaution is needed at the time of jointing & termination. The joining of XLPE cable needs less time than that of any other conventional cable of similar grade.
These cables can safely be used on any vibrating layouts like bridges. These cable have the better resistance to salinity of water in the ground, chemicals, oils and corrosive furnes. These are free from fire risk. These cables are not prone to failure due to ageing characteristics and have longer life.
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