Types of Insulators in Transmission Lines

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Types of Insulators in Transmission Lines
Transmission line insulators separate, contain and suspend transmission line conductors. (transmission line tower image by Sean Gladwell from Fotolia.com)

Transmission line insulators are devices used to contain, separate or support electrical conductors on high voltage electricity supply networks. Transmission insulators come in various shapes and types, including individual or strings of disks, line posts or long rods. They are made of polymers, glass and porcelain--each with different densities, tensile strengths and performing properties in adverse conditions.

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Pin Type Insulators

Pin type insulators are used for the transmission of lower voltages. A single pin type insulator is used to transmit voltages up to 11 kV (kilovolts) and higher voltages require two-, three- or four-piece pin insulators. They are not economically feasible for 33 kV and higher transmission lines. Pin type insulators are secured with steel or lead bolts onto transmission poles. These are typically used for straight-running transmission lines.

Suspension Type Insulators

Suspension type transmission line insulators suspend and support high voltage transmission lines. They are cost effective for higher voltage transmission, typically replacing multiple pin type insulators. Suspension type insulators have a number of interconnected porcelain discs, with each individual unit designed to support a particular voltage. Together, a system of these discs is capable of effectively supporting high voltages. There are three types of suspension insulators: cemented cap suspension insulators; interlinking or Hewlett suspension insulators; and link or core suspension insulators.

Strain Type Insulators

Strain type insulators are horizontally suspended suspension insulators. They are used to handle mechanical stresses and take the pressure off a conductor at the end of a transmission line, at a sharp corner or curve or over long river crossings. Strain insulators are typically used for higher voltage transmissions.

Shackle Type Insulators

Shackle type insulators, similar to strain type insulators, are used on sharp curves, end poles and in section poles. However, unlike strain insulators, shackle insulators are designed to support lower voltages. These insulators are single, round porcelain parts that are mounted horizontally or vertically.

Stay Insulators

Stay insulators, also called egg insulators, are primarily used to prevent stay wires from becoming energised from accidentally broken live wires. They, therefore, function to provide insulation between stay clamps and transmission poles. Stay insulators are mounted at a height of at least 3 meters (118 inches) from ground level.

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