Role
of Polymers
in Power
Cables
The
life of a cable is mostly dependant on life of polymers. Modern polymers
have assured trouble-free life of cables for over 25 years.
Introduction
The developed world has compelled Power Distribution Networks
to use insulated conductors for safety, reliability and environmental
reasons. Overhead distribution is being replaced gradually by insulated
cables from 110 Volts to 400 kV transmission and distribution. Thus,
the role of Polymers has become more prominent in recent years. Synthetic
polymers have replaced natural insulation materials such as paper,
mineral oil and natural rubber.
Polymers in Cable Manufacturing
Normally, the polymers used in cables are classified under two
heads.
1. Thermoplastic
Materials which can be re-soften / re-processed such as polyethylene,
poly vinyl chloride (PVC) and thermoplastic rubber.
2. Cross Linked Polyethylene (XLPE)
This includes elastomers such as ethylene propylene rubber, silicone
rubber, Ethylene Vinyl Acetate (EVA) which are thermoset and have
better thermal properties for insulation and sheath. These materials
once cross-bonded cannot be processed again. Improved Polymers with
required characteristics such as flame retardant, low smoke and halogen
free properties are increasingly getting popular.
Processability of Polymers
for Cables
All the above polymers are developed to have good
processability on extruders. The selection of these polymers is based
on the application and environmental conditions. The dielectric strength
required is also important for the selection of cable. PVC compounds
established in early 1960 have shown good performance as insulation
and outer jacket of cables, however due to thermal degradation at
higher operating temperature cross linked polyethylene is preferred.
The advantages of PVC polymer in cables......
....contd.
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