H.T and L.T Cables Construction Coding:

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H.T and L.T Cables Construction Coding:

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 transformer and other end in Switchboard busbar conductors via Current Transformers.

Each and every cable LT or HT comes with a Construction code which 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. Below table gives the construction coding details.

H.T and L.T cables Construction Coding details

Cable Construction Coding

A2XWY Cable:

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

A2XWY-H.T and L.T Cables Construction Coding

1.1 KV L.T CABLE
L.T Cable Cross-sectional with Construction Coding-A2XWY
L.T Cable Cross Sectional View

A2XWY is depicted as

A = Aluminium Conductor

2X= Cross-linked Polyethylene

W = Steel Round Wire Armour

Y  = PVC Outer Sheath

A2XCEWY Cable:

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

A2XCEWY-H.T and L.T Cables Construction Coding

11 KV H.T Cable
H.T Cable Cross-sectional with Construction Coding-A2XCEWY

H.T Cable Cross Sectional View

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

Description of A2XWY and A2XCEWY 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 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. A 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. Sheath provides mechanical protection to the cable.

The sheath shown in 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 cable industry the polymer must be compounded with a plasticizer which makes it plastic over a wide range of temperature. PVC is available in various grades depends upon the plasticizer.

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

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