High Tension Cable and LT Cables Construction | Insulation | Specifications of HT cable

What is Cable (High Tension cable)

• The cable is used to trans­mit pow­er from one place to anoth­er in an elec­tri­cal system
• These cables trans­mit both low and high loads. Dif­fer­ent size cables are used to trans­mit pow­er at dif­fer­ent voltages
• Cables can be divid­ed into two types, low volt­age and high volt­age cable
• The select­ed cable must be able to trans­mit pow­er at the required volt­age with­out dam­ag­ing and the equip­ment con­nect­ed to it 
• The cable must be installed so as not to pose any dan­ger to those who touch it
• The tem­per­a­ture rat­ing of the cable should be com­men­su­rate with the ambi­ent temperature 
• Cables can be divid­ed into pow­er cable and con­trol cable 
• Pow­er cable The con­duc­tor of a cable that trans­mits a large amount of pow­er from one place to anoth­er is made of aluminum 
• Con­trol cables are often low volt­age cables 
• The con­duc­tor of the con­trol cables is made of strand­ed or flex­i­ble copper

How To Select Good Cables 

The fol­low­ing points should be kept in mind while select­ing cable for a par­tic­u­lar application 

• The volt­age of the system 
• Type of sys­tem that is whether the sys­tem is made to be earth or not 
• Max­i­mum load cur­rent to which the cable is to be transmitted 
• Time to with­stand short cir­cuit cur­rent and short cir­cuit current 
• Volt­age drop that occurs when the motor starts in the nor­mal conditon 
• The amount of load required in Future 
• Full load required 
• The cable laid under­ground is either duct or open 
• Ambi­ent temperature 
• Spac­ing of cables 
• How deep should the cables be laid underground 
• Installing cables in acci­dent prone areas 
• Rules and reg­u­la­tions for lay­ing cables
• Eco­nom­ic status

Cable Construction

Typ­i­cal­ly, the con­duc­tor of cables is made of alu­minum or copper 

Alu­minum con­duc­tor is used in pow­er cables. Con­trol cables Cop­per con­duc­tor is used. 

Cop­per is more con­duc­tive than alu­minum. Alu­minum cable requires more sur­face area for connection. 

Bimetal­lic effect if the end of the alu­minum cable is con­nect­ed to the cop­per ter­mi­nal of the machine. Alu­minum oxide also forms on the sur­face of metal. 

A bimetal­lic wash­er or sheet is placed between the two ter­mi­nals to reduce this effect 

Pow­er cables are made of alu­minum con­duc­tor, strand­ed and designed. Some­times, these cables are non-strand­ed sol­id conductors 

In high ten­sion cables, the con­duc­tor is strand­ed and made firm, round in shape 

In high ten­sion cables, it is not good to shape the con­duc­tors as there is too much elec­tric stress on the edge . In con­trol cables, the con­duc­tor is a high-con­duc­tiv­i­ty shield. 

Con­duc­tors are laid on the cbale accord­ing to IS: 8130. Alu­minum con­duc­tors typ­i­cal­ly up to 10 sqmm in size are solid­ly arranged in a cir­cu­lar cross section. 

If the size is more than 10 sqmm, the con­duc­tor will be stranded 

In cables up to 25 sqmm in size, sin­gle or dou­ble core con­duc­tors are arranged in a cir­cle. Cables larg­er than 25 sqmm can have three or four cores 

Insulation

Dif­fer­ent types of insu­la­tors are used in cables. Insu­la­tion mate­ri­als are used depend­ing on the place of use, the com­pa­nies and the sur­round­ing environment. 

For exam­ple flex­i­ble cables are fit­ted with rub­ber insu­la­tion. Insu­lat­ing mate­ri­als such as PVC (polyvinyl chlo­ride), XLPE (Crossed linked Poly Eth­yl­ene), and paper are used 

Pow­er cables com­mon­ly used in com­pa­nies that are sta­ble are made of PVC and XLPE insu­la­tion. In HT cables, XLPE insu­la­tion is set in col­or. To know the core, col­or mark­ing of the insu­la­tion will spoil the elec­tri­cal prop­er­ties of the cables. 

When installing insu­la­tion, make sure there are no gaps or oth­er materials 

Thus, if there is a gap and oth­er mate­r­i­al, the elec­tri­cal stress on the cables will not be uni­form­ly electric 

XLPE insu­la­tion is of bet­ter qual­i­ty than PVC insu­la­tion. So it is bet­ter to use XLPE insu­la­tion than PVC insu­la­tion in da com­pa­nies too. Also the di-elec­tric loss caused by XLPE insu­la­tion is less 

PVC cable with a sin­gle cross-sec­tion area, and XLPE cables with XLPE cables can with­stand more cur­rent than PVC cables. XLPE cables can with­stand high­er tem­per­a­tures than PVC cables. 

If any cable on the side of a cable mal­func­tions, the XLPE cable can be loaded up to an addi­tion­al 60% and used for emergencies. 

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Inner sheath

In LT cables PVC com­pound or plas­tic is cov­ered over the con­duc­tor (core). It sets the bed­ding for the armor. HT cables have a shield made of a semi con­duc­tor com­pound around the insu­la­tion of the core 

XLPE insu­la­tion is weak­ened by tan­gen­tial elec­tric stress. So it is bet­ter to radi­al­ize elec­tric stress. A shield made of a semi-con­duc­tor is main­ly used to radi­al­ize elec­tric stress 

To reduce elec­tric stress, leak­age and earth fault cur­rent, a non-metal­lic tape is placed over the semi con­duc­tor shield as a screen. PVC is com­mon­ly used as the inner sheath in cables 

Cables are filled with non-mois­ture mate­r­i­al to pre­vent gaps. This forms the bed­ding for the cable 

ARMOURING

It is locat­ed at the top of the cable’s bed­ding. Armor is used to pro­tect the cable from mechan­i­cal injury when lay­ing the cable underground 

It is made of gal­va­nized steel in flat or round shape. In the case of a sin­gle core cable the armor is made round or flat by non-mag­net­ic hard drawn aluminum 

Outer Sheath

On the top of the armour­ing is an out­er­sheath made of PVC com­pound. Cables with­out an armor­ing sys­tem have an out­er sheath made of PVC com­pound over the inner­sheath or non-metal­lic part of the insulation 

In FRLS cables, (Flame Retar­dant low smoke) spe­cial mate­ri­als are used for the out­er sheath 

Specifications Of HT Cable

• Spec­i­fy the volt­age of the system

• Spec­i­fy the core size and num­ber of cores

• Whether the cable is required for Ground­ed sys­tem or unground­ed sys­tem­To be mentioned 

• Spec­i­fy what con­duc­tor mate­r­i­al is required 
• Spec­i­fy whether the armor needs to be flat or round 
• Spec­i­fy the type of insu­la­tion required 
• Spec­i­fy the IS num­ber for the cable 
• Spec­i­fy the length of the cable in a drum
• Spec­i­fy the ambi­ent temperature 
• Spec­i­fy addi­tion­al spe­cial requirements

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