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
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
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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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
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
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