LT Control Cables

CAIS-7098 (Part-1) compliant cables feature EC grade aluminium or copper conductors with XLPE insulation. They offer advantages including higher current and short circuit ratings, better resistance to moisture and chemicals, and longer service life.

ConductorThe Conductor of the power cable is generally made from EC grade aluminum, and annealed high-conductivity copper is used for control cables. All conductors conform to IS: 8130:1984. Power Cables with copper conductors can also be supplied as per customer requirements. The conductor is solid/stranded/bunched as per requirements.InsulationXLPE (Cross-Linked Polyethylene)Laying UpThe cores are laid up with a 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 clockwise.Inner SheathThe 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 an inner sheath; this ensures that it is as circular as possible.ArmouringArmouring 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 armouring below does not exceed 13mm. The armour shall consist of galvanised round steel wire, and where the calculated diameter below the armouring is greater than 13 mm, the armour shall consist of either galvanized round steel wire or galvanised steel strips.Outer SheathThe PVC covering over the armouring in case of armoured cables and over the inner sheath in case of unarmoured cables is called the outer sheath. IS: 1554 specifies the nominal and minimum thickness of outer sheath for unarmoured cables and only the minimum thickness of outer sheath for armoured cables. Types of PVC compounds for outer sheath:

1. Outer sheath with type ST1 PVC compound as per IS: 5831, which is suitable for 70°C continuous operation.
2. 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 as follows:A. Technical Advantages

1. Longer service life
2. Low Dielectric Losses
3. Higher insulation resistance
4. Higher resistance to moisture
5. Better resistance to chemicals
6. Better Resistance to surge currents
7. XLPE is thermosetting in nature; therefore, it cannot be reprocessed
8. Short circuit temperature for XLPE cables is 250°C, whereas for PVC it is 160°C
9. Higher current rating, higher short circuit rating, approx. 1.2 times that of PVC
10. Allowable continuous operating temperature for XLPE cables is 90°C, whereas it is only 70°C for PVC cables

B. Commercial Advantages

1. Due to low specific gravity, XLPE cables are lighter than PVC cables.
2. Capable of carrying high current through the same cross-sectional area as compared to PVC-insulated cables.
3. Lower installation charges as the diameter of the cable is comparatively smaller with a smaller bending radius, requiring less space for laying cables.

LT PVC Power & Control CablesIS-1554 (Part -1) 1988 compliant cables feature copper/aluminium conductors, PVC insulation, and armouring for mechanical protection. Outer sheath options include ST1 and ST2 PVC compounds, suitable for various continuous operations.ConductorThe most acceptable metals for wires & cables are copper and aluminium due to their higher conductivity & ductility. Copper has higher affinity for sulphur it corrodes in the atmosphere where sulphur fumes is present. In these conditions tinned copper should be used as it forms a protective film over it & prevents it from tarnishing. Aluminium oxide film present on the surface of aluminium conductor acts as a barrier to protect it from corrosion. CONDUCTOR CONSTRUCTION The most economical construction for conductor is solid conductor i.e. conductor made of one single wire. As the area of conductor increases, solid conductor becomes stiffer and difficult to handle, therefore stranded construction is adopted. Here the conductor is made of number of strands. The strands are arranged in spiral layers in 1+6+12+18+…… formations. This geometrical progression of strands provides more compactness & flexibility. The stranded construction of conductors is more suitable for crimping of lugs. To economize the weight of insulating material, to optimize overall diameter, conductors are shaped & compacted in higher sized cables. The stranded conductor is shaped in to a segment of a circle so that when all the cores are laid, they form a complete circle. These segments are identified as 2 Core- 180 degrees, 3 Core- 120 degrees, 4 Core- 90 degrees, 3.5 Core- 100/60 degrees. IS 1554 permits solid conductor construction up to 10 sqmm in aluminium and up to 6 sqmm in copper. It permits the use of shaped conductors for size from 16 sqmm onwards.InsulationThe PVC covering over conductor is called insulation and it is provided by extrusion process only. The insulated conductor is called a core.
PVC insulation as per IS: 1554:

1. Insulation with type A PVC Compound as per IS: 5831, suitable for 70°C continuous operation.
2. Insulation with type C PVC Compound as per IS: 5831, suitable for 85°C continuous operation.

IS-1554 (Part -1) 1988 compliant cables feature copper/aluminium conductors, PVC insulation, and armouring for mechanical protection. Outer sheath options include ST1 and ST2 PVC compounds, suitable for various continuous operations.

DescriptionThe most acceptable metals for wires & cables are copper and aluminium due to their higher conductivity & ductility. Copper has a higher affinity for sulphur; it corrodes in the atmosphere where sulphur fumes are present. In these conditions, tinned copper should be used as it forms a protective film over it & prevents it from tarnishing. Aluminium oxide film present on the surface of the aluminium conductor acts as a barrier to protect it from corrosion.Conductor constructionThe most economical construction for a conductor is a solid conductor, i.e., a conductor made of one single wire. As the area of the conductor increases, the solid conductor becomes stiffer and difficult to handle; therefore, stranded construction is adopted. Here, the conductor is made of a number of strands. The strands are arranged in spiral layers in 1+6+12+18+…… formations. This geometrical progression of strands provides more compactness & flexibility. The stranded construction of conductors is more suitable for crimping of lugs. To economize the weight of insulating material, to optimize overall diameter, conductors are shaped & compacted in larger cables. The stranded conductor is shaped into a segment of a circle so that when all the cores are laid, they form a complete circle. These segments are identified as 2 Core- 180 degrees, 3 Core- 120 degrees, 4 Core- 90 degrees, and 3.5 Core- 100/60 degrees. IS 1554 permits solid conductor construction up to 10 sqmm in aluminium and up to 6 sqmm in copper. It permits the use of shaped conductors for sizes from 16 sqmm onwards. The PVC covering over the conductor is called insulation, and it is provided by an extrusion process only. The insulated conductor is called a core.PVC insulation as per IS: 1554

1. Insulation with type A PVC Compound as per IS: 5831, suitable for 70°C continuous operation
2. Insulation with type C PVC Compound as per IS: 5831, suitable for 85°C continuous operation

An inner sheath is provided over the laid-up cores. It is provided to give a circular shape to the cable, and it provides bedding for the armouring. I.S. 1554 permits the following two methods of applying the inner sheath of any thermoplastic material, i.e., PVC.

• Extruded Inner Sheath : It is provided by extrusion of thermoplastic material over the laid-up cores. This type of inner sheath also acts as a water barrier between the cores and outer sheath. In case of a puncture in the outer sheath, water cannot reach the cores, and hence we recommend that cables for outdoor underground use should have an extruded inner sheath
• Taped Inner Sheath : It is provided by wrapping a thermoplastic tape over the laid-up cores. This method saves a process, and hence manufacturers always provide this type of inner sheath unless the purchase specifications ask for an extruded inner sheath.

Armouring

Cable Armouring consists of galvanized steel wire/strip provided over the inner sheath in multi-core cables and aluminium round wire/strip over the insulation in single-core cables. It provides mechanical protection to the cable & carries earth fault current in case of a short circuit of a core with armour.