LT cables use stranded copper or aluminium conductors. Although small conductor of cables may use solid conductors. The overall assembly may be round or flat. Non-conducting filler strands may be added to the assembly to maintain its shape. Special purpose LT cables for overhead or vertical use may have additional elements such as steel structural supports. Some LT cables for outdoor overhead use may have no outer sheath.
Design
Conductor: The conductor of power cables is made from EC grade aluminium or annealed electrolytic copper. All conductors conform to IS: 8130. The conductors are solid / stranded / compact circular / sector shaped.
Insulation: In PVC Power Cables the conductor is insulated with the poly vinyl chloride covering over conductor as insulation by extrusion process and In XLPE Power Cables cross linked polyethylene covering as insulation over conductor by extrusion process.
Colour of Cores: Cores are identified with a colour scheme as per IS:1554 (pt-1):1988 as under
- 1 Core: Red, Yellow, Blue and Black
- 2 Cores: Red and Black
- 3 Cores: Red, Yellow, and Blue
- 5 And 4 cores: Red, Yellow, Blue & Black (Reduced Neutral Core in case of 3½ Core).
Laying Up: In multicore cables, cores are laid up together with a suitable lay, the outer most layer is laid up in right hand and successive layer with opposite lay. The interstices are filled with non-hygroscopic material wherever necessary to make the laid-up cores circular.
Inner Sheath: The laid up cores are provided with the PVC inner sheath by extrusion or by wrapping of PVC Tape. Single core cables do not have inner sheath.
Armouring: Armouring is applied over inner sheath incase the calculated diameter over inner sheath does not exceed 13 mm, the armour consists of galvanized round steel wires. Where the calculated diameter over the inner sheath is greater than 13 mm the armour generally consists of flat steel. If required, the cable can be manufactured with steel wire where calculated diameter of cable exceeds 13 mm. Single core cables are provided with non-magnetic Aluminium Wire/Strip armouring.
Outer Sheath: Outer Sheath is of PVC Compound applied by extrusion over Insulation in case of unarmoured single core cables over inner sheath in case of unarmoured twin, three and multi core cables and over armouring in case of armoured cables.
Features
- LT-XLPE Cables have longer life as compared to conventional PVC Cables.
- LT-XLPE Cables have a higher conductor temperature rating i.e. 90°C under normal operation.
- LT-XLPE Cables have a higher emergency overload capacity 120°C.
- Max. temperature limit under short circuit conditions for LT-XLPE Cables is 250°C
- Hence XLPE Cables have higher short circuit rating.
- Insulation resistance of LT-XLPE Cable is excellent & superior to Identical PVC Cables.
- LT-XLPE Cables have high corrosion resistance in polluted atmosphere.
- LT-XLPE Cables have higher insulation resistance property than PVC
- LT-XLPE Cables have better properties of resistance to chemical and corrosive gases.
- LT-XLPE Cables have low installation cost because of light weight, dimensions and are far more flexible.
- Jointing of LT-XLPE Cables is easier and quicker.