Correct Answer - Option 4 : High permittivity
The satisfactory operation of a cable depends to a great extent upon the characteristics of insulation used. In general, the insulating materials used in cables should have the following properties.
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High insulation resistance to avoid leakage current
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High dielectric strength to avoid electrical breakdown of the cable
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High mechanical strength to withstand the mechanical handling of cables
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Non-hygroscopic i.e., it should not absorb moisture from air or soil; The moisture tends to decrease the insulation resistance and hastens the breakdown of the cable. In case the insulating material is hygroscopic, it must be enclosed in a waterproof covering like a lead sheath
- Non-Inflammable
- Low relative permittivity
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Low cost so as to make the underground system a viable proposition
- Unaffected by acids and alkalies to avoid any chemical action
The various insulating materials used in manufacturing of cables are rubber, VIR, paper, Polyvinyl Chloride (PVC), Varnished Cambric, Polyethylene, Gutta-Percha, Silk, Cotton, enamel etc.
