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Outdoor Polymer Insulating Material Competency

More polymer insulating products used electrical systems, such as polymer insulators are popular used in electrical equipment and electrical systems.

polymer insulators

Figure 1

Experience
More Recent History

High performance polymer materials have been in use for about 30 years. During that time, the use of polymer insulation has grown steadily, and polymerics are now becoming the outdoor insulation material of choice. Common applications include cable terminations, surge arresters, insulators, bus bar insulation, and bushings. Figure 1 shows a highly protected creepage insulator installed in a severely contaminated site. This device is a hybrid design utilizing a porcelain core for strength and environmental aging resistance about the terminals. The elastomer housing provides the creepage in a highly protected geometry as well as the weathering resistance.
Insulation enhancement products, such as creepage extenders, are installed over the weathersheds of porcelain insulators to improve the performance of porcelain insulators in contaminated applications. Figure 1 shows how polymer material can enhance porcelain insulator performance. Other retrofit techniques are in use which apply polymer material to enhance the surface properties of existing porcelain insulators to reduce flashover in contaminated locations.
Not only are polymeric products demonstrating their capabilities in diverse environments, but polymeric devices and materials are routinely used today for contamination flashover of a large installed base of porcelain insulation.

polymer insulators

Figure 2

Advantages
Polymeric insulating materials offer numerous advantages over porcelain.
A partial listing includes:
Light Weight
The density of polymer materials is much lower than ceramic, which results in significant product weight reduction. The weight differences increase with voltage class rating. Polymer devices tend not to require cranes or other lifting devices for handling or installation. The reduced weight also permits the use of lighter and less costly structures and mounting arrangements. The smaller size and weight result in lower shipping costs than equivalent porcelain devices. Polymer insulators are advantageous to use in dense urban areas and offer advantages in narrow rights of way. Non-ceramic insulators offer high strength to weight ratio which permit less expensive structures and improved visual aesthetics. Polymer insulators also facilitate new compact transmission line design with reduced electromagnetic field effects. Polymer distribution surge arresters may be hung directly off fuse cutouts, reducing installation costs and improving aesthetics. Porcelain and polymer 66 kV terminations, installed in parallel, are shown in Figure 2, as evidence of the concurrent use of these two technologies. The polymer termination requires cable support since it is not self-supporting.

polymer insulators

Figure 3

66 kV polymer terminations installed in England in parallel with existing porcelain terminations. Polymer terminations require less structural support because of their light weight. Polymer products are becoming more common installed adjacent to existing porcelain devices on existing systems.
24 kV distribution class polymer surge arrester showing polymer material hydrophobicity with water beading on surface. Discontinuous electrolyte increases voltage required for flashover on polymer material surface compared to porcelain.
Complex Geometry
As polymer insulating housings are typically molded, it is not difficult to fabricate parts on a cost effective basis, which have higher creepage distance per unit length than porcelain. Weathershed profiles can be made more complex without production or yield problems. Alternating diameter weathersheds (big-small) are now commonly supplied, which improves the AC wet flashover by avoiding bridging of all sheds simultaneously during heavy wetting conditions.
Pollution Performance
Polymer materials typically used for outdoor insulating applications have low surface free energy. When new and without exposure to the environment, polymer materials resist wetting and are inherently hydrophobic. Retention of hydrophobic properties with exposure is a desirable attribute. Water on the surface of hydrophobic materials form water beads, so the conductive contamination dissolved within the water beads is discontinuous. This condition results in lower leakage current flow and probability of dry band formation, which in turn requires a higher impressed voltage to cause flashover. Figure 3 shows the hydrophobic nature of polymer materials, where water tends to bead rather than form filaments along the surface. In severe conditions, all materials lose their hydrophobicity. However, the reduced diameters and superior shed geometry of polymer products can still give inherently better pollution flashover performance than porcelain.
Hollow Core Housing Failure Mode
Hollow core polymer housings are likely to have a very different failure mode from porcelain. The physical properties of the polymer material means that it will not shatter like porcelain. With the initiation of an internal fault, the expected failure mode is a rupturing or bursting of the hollow structure with venting of the internal pressure, leading to an external flashover and dissipation of the fault energy outside of the housing.
The actual failure mechanisms between hollow core porcelain and polymer housings may differ depending upon the product design and function, and users are cautioned against assuming all polymer products are inherently safe. Depending upon the specific design, function, failure initiation mechanism and available fault current, internal components can be expelled. However, the volume of available dense material, compared to a porcelain housing, is commonly less. Processing
The manufacturing process for polymer products is inherently shorter than for porcelain. Molding times typically are of the order of minutes, so the lead-time can be considerably shorter than for porcelain devices.

 

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