XLPE, Cross-linked polyethylene, has stable intermolecular bonds between polyethylene particles created by thermochemical action, due to the presence of organic peroxide.
XLPE has the same electricl properties as the conventional polyethylene and as result of stable intermolecular bonds, has much better thermal and mechanical properties. This provides XLPE insulated cables to be used at maximum continuous conductor temperature of 90 °C while conventional polyethylene insulated cables to be used at that of 75 °C. Maximum overload conductor operating temperature is 130 °C ( operating at the emergency overload temperature shall not exceed 100 hours per year). Maximum conductor short-circuit temperature is 250 °C. This provides an important advantage in cable ratings and is of special significance in countries or situations where the ambient temperature is high and derating factors have to be applied.
The cross-linking tehnology is based on entirely "dry" cross-linking and cooling process. This eliminates micro inclusions of water from the insulation which, unless prevented, lead to so called "water treeing" effect. A triple crosshead extrudes the screen over the conductor and screen over insulation in a single technological operation. All that gives the cable excellent electrical, thermal and mechanical properties.

DESCRIPTION
Three-core XLPE/SWA/PVC cable is being made in accordance with IEC 60502/98.
Copper or aluminium compacted stranded circular conductor, conductor screen of extruded layer of semi-conducting XLPE, XLPE insulation, insulation screen of extruded layer of semi conducting XLPE, semi-conducting bedding tape, metallic screen consisting of copper wires applied helically with a counterspiral of copper tape. Three cores are being laid-up together with suitable fillers, covered with PVC separation sheath, armoured with galvanized steel wires applied helically and covered with PVC outersheath over in black colour.

APPLICATION
XLPE-insulated cables can be used for nearly all installations : in the ground, in cable ducts, indoors, in power stations, in industrial plants , in switching stations. Thanks to their better thermal characteristics they are particularly recommended where :

• high abmient temperatures exict
• cables are exposed to the sun
• cables are laid in ducts in a concrete block
• cables are grouped
• high emergency loads are important
• high short-circuit currents are required
• high earth leakage currents have to be transmitted by the screens

D - outer cable diameter

Current carrying capacity has been calculated according to IEC 287/82 (100 % load factor) and following conditions:

• Depth of laying 0.70 m, and for 20/35 kV cables 1.0 m.
• Soil thermal resistivity 1.0 K m/W.
• Ground temperature 20^oC, ambient air temperature 30^oC, maximum conductor operating temperature 90^oC.

Sheaths bonded at both ends of an electrical section

RATING FACTORS