Components of a Reliable Polymer Compound

Components of a Reliable Polymer Compound

Polymer compounds suitable for electrical insulation can consist of 10 or more ingredients which can be broken down to three major categories. These include the base polymer, fillers which can make up nearly 50% of the total compound, and active additives. Compounding of an elastomer with fillers and additives to achieve the desired results for a given application is critical. The components are carefully selected to enhance field performance and ease of manufacture.

Base Polymer

The base polymer that makes up a compound is called an elastomer. The two widely recognized are EPDM and Silicone. Selection of the base compound is only the first step in designing a reliable polymer compound for electrical applications. ESP™ is an EPDM based compound which was formulated over many years of research starting before the transition from porcelain to polymer.


Fillers are used to support the base elastomer of a compound and typically make up 40-60% of a compound. There are two types of fillers which are classified as reinforcing and extending. Reinforcing fillers can improve tensile strength, modulus, tear strength and abrasion resistance of a compound. An extending filler is a loading or non-reinforcing material used to enhance desirable properties such as electrical characteristics and flammability resistance.

Alumina Trihydrate (ATH, or Hydrated Alumina) acts as an extending filler in ESP™ which further improves the compound’s already good electrical characteristics. As an additional benefit when the ATH is overheated it goes through an endothermic reaction in which it rehydrates to release water. This leaves behind the inorganic component but, in the process, cools the surface making it more resistant to damage due to dry band arcing on its surface.


Additives support the manufacturing processes by protecting the chemical bond between fillers and elastomer during vulcanization. These materials make up a small percentage of the overall compound but help manufacturers achieve consistency in the final product.

The combination of these three components results in a well-rounded polymer that can stand up to environmental factors which might otherwise deteriorate most polymers. For more information on the advantages of enhanced silicone polymer for distribution arresters, read our blog Characteristics of the ESP Silicone Polymer. (link to first blog)

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