A Summary of Strain Insulators

A strain insulator is an electrical insulator designed to work in mechanical tension or strain to withstand the pull of a suspended electrical wire or cable. Strain insulators provide support to transmission lines, radio antennas, and other types of electrical wiring. They are used between two wires to electrically separate them from one another, or where a wire attaches to a pole or tower to transmit the pull of the wire to the support while keeping it electrically insulated.

Strain insulators are commonly made from glass, porcelain, or fiberglass that is shaped to accommodate two cables and the supporting hardware on the support structure. The insulator’s shape is intended to maximize the distance between the two cables while simultaneously maximizing the load-bearing transfer capacity of the insulator. As stated, in practice, strain insulators are used in conditions of physical tension.

When the voltage requires more insulation than a long insulator can provide, strain insulators are used in a series connected to each other using specialized hardware. A series will provide the same support as a single insulator, but offers much more effective insulation qualities. If a single string is not sufficient to support the tension, a heavy steel plate can effectively bundle several insulator strings mechanically. One plate is on the ‘hot’ end while the other is located at the support structure. This configuration is used on nearly all long-spanning power lines, such as those that cross a river, canyon, lake, or other type of terrain that requires a longer length to cross.

Strain insulators are frequently used outdoors in overhead wiring where they are exposed to rain and, in urban settings, pollution. For practicality, the shape of an insulator becomes critical, as a wetted path from one cable to another can reduce the resistance of the electrical path. Therefore, strain insulators intended for horizontal mounting feature flanges to help shed water, and those intended for vertical mounting are typically bell-shaped.

To ensure their quality, strain insulators must undergo rigorous tests. The three kinds of test are type, performance, and routine tests. Type tests include dry flashover, thirty-second rain, wet flashover, and impulse frequency tests. Performance tests include temperature cycle, electromechanical, puncture, mechanical strength, and porosity. Finally, the routine tests examine the insulator voltage capabilities, proof load, and resistance to corrosion. While there are many advantages of using strain insulators, the most prevalent are their compatibility with use for voltages up to 11kv, their insulation and protection from the ground, their porcelain design, and if they become damaged, stray wires will not drop to the ground.

Finally, to summarize, strain insulators have a wide range of important applications. They are:

  • Use in electrical wiring to support transmission lines and radio antennas.
  • Use in overhead wiring outdoors, where they protect electrical wiring from rainfall, pollution, and other outside factors.
  • Differing designs tailored to differing uses and mountings.
  • Help transmit wires over long distances and across landmarks like rivers, canyons, etc.
  • Reduces extreme tension on transmission lines that could otherwise be damaging.

Whatever type of strain insulator you need, for whatever application, ensure you are getting them from a trusted source.


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