LT XLPE Power & Control Cables
Standards
IS-7098 (Part-1)
Conductor
The Conductor of power cable is generally made from EC grade aluminium and annealed high conductivity copper is used for control cables. All conductors conform to IS: 8130:1984. Power Cables with copper conductor can also be supplied as per customer requirement. The conductor is solid / stranded/ bunched as per requirements.
Insulation
The conductor is insulated with XLPE (cross –linked Polyethylene) compound by extrusion.
Laying Up
The cores are laid up with suitable lay. The final layer always has a right hand lay i.e. if you look along the cable, the cores move to your right hand or clock wise.
Inner Sheath
The Laid up Cores Shall be Provided with an inner sheath applied either by extrusion or by wrapping. The fillers and inner sheath shall be on the following:
- Unvulcanised rubber
- Thermoplastic materials
Single Core cables do not have inner sheath it shall ensure that it is as circular as possible.
Armouring
Armouring shall be applied over the insulation in case of single core cables and over the inner sheath in case of twin, three and multicore cables. The armour wires/strips shall be applied as closely as practicable. Where the calculated below armouring does not exceed 13mm. the armour shall consist of galvanised round steel wire and where calculated diameter below the armouring greater than 13 mm the armour shall consist of either galvanized round steel wire or galvanised steel strips.
Outer Sheath
The PVC covering over the armouring in case of armoured cables and over the inner sheath in case of un-armoured cables is called outer sheath. IS: 1554 specifies nominal and minimum thickness of outer sheath for unarmoured cables and only minimum thickness of outer sheath for armoured cables. Types of PVC compounds for outer sheath:
- Outer sheath with type ST1 PVC compound as per IS: 5831, which is suitable for 70°C continuous operation.
- Outer sheath with type ST2 PVC compound as per IS: 5831, which is suitable for 85°C continuous operation.
The advantages of XLPE Insulated cables in comparison to PVC insulated cables are asvunder:
A. Technical Advantages
- Higher current rating, higher short circuit rating approx. 1.2 times than that of PVC.
- XLPE is thermosetting in nature therefore it cannot be reprocessed.
- Higher insulation resistance.
- Higher resistance to moisture.
- Better Resistance to surge currents.
- Low Dielectric Losses.
- Better resistance to chemicals.
- Longer service life.
- Allowable continuous operating temperature for XLPE cables is 90°C whereas it is only 70°C for PVC cables.
- Short circuit temperature for XLPE cables is 250°C whereas for PVC it is 160°C.
B. Commercial Advantages
- Lower installation charges as the diameter of cable is comparatively lesser with smaller bending radius, requiring less space requirement for laying of cables.
- Due to low specific gravity XLPE cables are lighter as compared to PVC cables.
- Capable of carrying high current thru the same cross sectional area as compared to PVC insulated cables.
