- Technical Blog From My Notebook

Friday, February 19, 2016

Electrical power cable

Power cables are mainly used for power transmission & distribution purpose. It is an assembly of one or more individually insulated electrical conductors, usually held together with an overall sheath. Electrical power cables may be installed as permanent wiring within buildings, buried in the ground and run overhead or exposed. Flexible power cables are used for portable devices, mobile tools and machinery.

Construction of Power Cable
There are various parts of a cable to be taken care of during construction. The power cable mainly consists of
1. CONDUCTOR
2. INSULATION
3. LAY for Multicore cables only
4. BEDDING
5. BRAIDING/ARMOURING (IF REQUIRED)
6. OUTER SHEATH 


CONDUCTOR
Conductors are the only power carrying path in a power cable. Conductors are of different materials. Mainly in cable industry we use copper (ATC, ABC) and aluminium conductors for power cables. There are different types of conductor as Class 1: solid, Class 2 stranded, Class 5 flexible, Class 6 Extra flexible (Mostly used for cords & welding) etc. Conductor sizes are identified with conductor resistance.
INSULATIONThe insulation provided on each conductor of a cable by mainly PVC (POLY VINYL CLORIDE ), XLPE (CROSSLINKED POLYETHYELENE), RUBBER (VARIUS TYPES OF RUBBER ). Insulating material is based on operating temperature.
Cores are identified by colour coding by using different colours on insulation or by number printing on cores
BEDDING (INNER SHEATH)This portion of the cable is also known as inner sheath. Mostly it is used in Multi core cables. It works as binder for insulated conductors together in multi-core power cables and provides bedding to armour/braid. This portion of the cable is mainly made of PVC( PVC ST-1, PVC ST-2 ), RUBBER (CSP SE-3, CSP SE-4 & PCP SE-3, PCP SE-4, HOFR SE-3 HOFR SE-4, HD HOFR SE-3 ETC)
ARMOURINGThere are mainly G.I. WIRE ARMOURING, G.I. STEEL STRIP armouring. It is done by placing G.I. WIREs, GI or STEEL STRIPs one by one on inner sheath. Armouring is a process which is done mainly for providing earthing shield to the current carrying conductors as well as it is also used for earthing purpose of the cable for safety. When there is any insulation failure in the conductor, the fault current gets enough paths to flow through the armour if it is properly earthed. Providing extra mechanical protection and strength to cable an important added advantage of armouring. In MINING CABLES it is done for conductance
BRAIDINGANNEALED TINNED COPPER WIRE , NYLON BRAID , COTTON BRAID are mainly used for this purpose. Braiding is the process which gives high mechanical protection to cable and also used for earthing purpose. Significance of braiding is it is more flexible in comparison to armouring.
OUTER SHEATHThis is outermost cover of the cable normally made of PVC (POLYVINYL CLORIDE ), RUBBER (VARIUS TYPES OF RUBBER) and often the same material as the bedding. It is provided over the armour for overall mechanical, weather, chemical and electrical protection. Outer sheath is protection offered to cable not much electrically but more mechanically.


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