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4.14 INSULATORS
4.14.1 Provision of adequate insulation in a substation is of primary importance
from the point of view of reliability of power supply system and safety of the working
personnel. However, the substation design should be such that the quantity of insulators
used is a minimum commensurate with the security of supply.
The creepage distance of the insulators to be used in the traction substation depends
on the degree of pollution level. But as the pollution level, vary from place to place,
therefore insulators to be used at the traction sustation have been provided with a creepage
distance of 25 mm/ KV so that these insulators are able to withstand the service conditons
even under heavily polluted condition including coastal areas.
4.14.2 For strung bus, standard 10” disc insulators of 7000 Kgf. strength have
been used for system voltage upto 132 KV and for 220 KV traction substation 11” disc
insulators of higher strength have been specified. But for rigid bus, on the primary side of
the transformer post type stack insulators have been used and for 25 KV side only solid
core type insulators have been adopted for all applications. Due to development of solid
core insulators even for higher system voltage and their added advantages over conventional
post type stack insulators the same are being used now for all applications such as bus bar
support insulators and isolators. Insulators used for the constructions of circuit breakers,
interruptors, PTs, CTs and bushings of power transformer are of hollow porcelain housing.
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