H.T and L.T Cables Construction Coding:

H.T and L.T Cables Construction:

H.T and L.T cables construction consists of different insulating and conducting materials. Based on the level of voltage and current carrying capacities the construction of the cable differs.

H.T and L.T cables are underground cables used for transmission of power from transformers to distribution Switchgear. We already know that these cables are terminated one end at the transformer and another end in Switchboard busbar conductors via Current Transformers.

H.T and L.T Cables Construction Coding Details:

Each and every cable LT or HT comes with a Construction code that denotes the various types of materials used in it. This coding is according to Indian standards. With the help of H.T and L.T Cables construction coding, we can identify the materials used in it. The below table gives the construction coding details.

L.T Cable A2XWY Construction:

Take an example A2XWY is the code for L.T cable shown in below Fig.

A2XWY is depicted as

A = Aluminium Conductor

2X= Cross-linked Polyethylene

W = Steel Round Wire Armour

Y  = PVC Outer Sheath

H.T Cable A2XCEWY Construction:

Take an example A2XCEWY is the code for H.T cable shown in below Fig.

A2XCEWY is depicted as

A  = Aluminium Conductor

2X= Cross-linked Polyethylene

CE= Copper Metallic Screening over each  individual core

W = Steel Round Wire Armour

Y  = PVC Outer Sheath

H.T-A2XCEWY and L.T-A2XWY Cable Materials:

Any electric cable consists of the following three essential elements.

1. The conductor for transmitting electrical power.
2. The insulation needed to insulate the conductor from direct contact with earth or other objects
3. External protection against mechanical damage, chemical, fire or any other dangerous effects external to the cable.

Conductors: A

Copper or Aluminium are widely used materials for conductors. Aluminium is used to a considerable extent due to its less cost. To obtain flexibility a number of wires are made up into a strand which makes it easier to handle, less likely to break, and also eliminates the risk of the conductor breaking through the dielectric. The wires in a stranded conductor are twisted together to form layers.

XLPE Insulation: 2X

XLPE means cross-linked polyethylene is a thermosetting compound. It merely comprises polyethylene, an antioxidant, and a cross-linking agent.

XLPE has excellent insulating properties and high resistance to moisture and chemicals.

Metallic Screening: CE

Shielding or Screening is of metal tapes or wires.

The metallic shielding over the insulation gives the following advantages:

• To provide uniform radial field lines from conductor which reduce stress concentration.
• To reduce filed strength and surface stress over conductor.
• Electric field is confined to the portion within the shield.
• Outside electric and magnetic field do not cause induced currents in the shielded conductor.

Armour: W

Armour of three core cable can be of Galvanized steel wire as the magnetic fields of three-phase cancel each other and no appreciable magnetic field is induced in the armour.

Bedding:

The insulating material between sheath and armour is called Bedding. Bedding of compounded fibrous material under the armour is used to provide a cushion between the sheath and steel wires.

Sheath: Y

A Sheath over insulation of a cable to form outer protective cover which is resistant to decay, mechanical abrasion, acids, alkalis, and other corrosive material. The sheath provides mechanical protection to the cable.

The sheath shown in the above figure is PVC Sheath.

Polyvinyl Chloride is a thermoplastic compound. PVC is a polymer derived generally from acetylene and it can be produced in different grades depending upon the polymerization process. For use in the cable industry, the polymer must be compounded with a plasticizer which makes it plastic over a wide range of temperatures. PVC is available in various grades depending upon the plasticizer.

PVC is inert to oxygen, oils, alkalis, and acids and so if the environment is such that these things are present in the atmosphere, PVC is more suitable than rubber.