Polymer insulators were first developed in the 1950s to replace conventional ceramic insulators. They were not, however, available until the 1960s because of initial design flaws. These insulators are generally constructed of fiberglass reinforced polymer rods and a polymer housing. The improved insulators provide cost and weight reduction benefits over its predecessor.
Developed in Europe, the first polymer insulators produced flashover, tracking, and general line drop problems due to flaws that developed in the polymers that were used. The high voltage insulators eventually succumbed to cracking or shedding of the polymer housing, known as chalking. These problems frequently caused shorts and abnormal electrical discharges. The basic construction of the insulators usually includes a fiberglass polymer rod housed in silicone polymers, often referred to as the shed. The fittings and grounding components are usually made of metal.
Ceramic insulators can withstand the elements for decades without failing, but polymer versions are better able to resist incidents of vandalism. Ceramic insulators also frequently have housing cracks, bonding failures, or hardware separation. When these situations arise, water often penetrates the housing, producing voltage leakage. Maintenance of these devices often involves applications of protective coating along with occasional washing of the insulators themselves.
In an attempt to recreate the durability of ceramic insulators, a computer operated accelerated aging chamber was developed. The harsh conditions created within the chamber were designed to simulate 30 years of conditions over the span of roughly three years. The lab regularly tests various designs of polymer insulators. Once inside the chamber, the insulators are subjected to a variety of environmental, electrical, and mechanical conditions, similar to those commonly endured, including changing temperatures and ultraviolet radiation. Humidity tests simulating fog and rain, using fresh and salt water are conducted as well.
Proponents believe that polymer insulators are a far more cost effective product than ceramic insulators. As they reportedly weigh 90% less than ceramic models, loading, unloading, and shipping costs are often dramatically reduced. The insulators typically require little to no maintenance and handle electrical loads more competently than their ceramic predecessors. The design of polymer insulators generally allows the devices to be installed or replaced easily. Some believe the polymer insulators provide a more pleasing appearance.
Polymer insulators are available in a number of designs and sizes. They can be used in place of conventional ceramic products in a variety of environments, including utility poles, substations, and electrical transformers. The insulators are frequently used on suspended lines that carry tension loads or on lines having a dead end. They might be used on the tension bending or compression load lines that are commonly found on poles. Polymer insulators are also incorporated into phase to phase lines that join two lines together and might be used to control conductor spacing.