Why silicone for HV insulators: Silicone compounds explained

Not all silicone is the same. It’s a chemistry thing. Silicone rubber is a mixture of many ingredients, and the actual silicone polymer base may be only about a third of it. Different materials are added for specific purposes or to enhance specific qualities of the material. Selecting the right ingredients is crucial for high-voltage insulators, especially for achieving a product with a long service life in harsh environments.

Polymer and other non-ceramic insulators were introduced to the market in the 1960s and have become preferred for many challenging high-voltage applications across North America.

Hubbell Power Systems offers insulators constructed with proprietary silicone rubber. But have you ever wondered, why silicone rubber?

Why silicone

Silicone rubber is a man-made compound that is both an electrical and thermal insulator. That makes it useful for high voltage insulators, plus it has superior weatherability and the ability to maintain useful properties over a wide range of temperatures. These include:

• resistance to oxidation
• resistance to UV degradation
• low surface energy (the property of repelling water, known as hydrophobicity).

The benefits of a high-quality silicone rubber are related to two factors. First is the polymer structure itself while the second is the compounding technique. Hubbell recently published an updated white paper discussing the relationship between the two.

The properties of the polymer come from the structure of the molecules. The raw material for silicone rubber is sand. It’s converted to elemental silicon by heating it with carbon. Silicone rubber is classified as an organo-silicon compound, neither organic nor inorganic.

This is where the chemical engineering involved gets exciting. The bond between the carbon and silicon is critical. Several specific properties can be achieved by changing the carbon groups attached to the silicone. This allows Hubbell to tailor silicone rubber to specific applications, such as extreme low temperatures, oil or solvent resistance, transparency, etc.

Key properties for high-voltage applications include high-voltage electrical insulation and arc track resistance as well as hydrophobicity. Our compounding expertise makes the difference here.

Choosing your ingredients

The process of compounding polymers is complex. Silicone rubber can be composed of several materials. The proper choice of ingredients results in those application-specific compounds.

These can include:

• Silicone gum, or pure silicone polymer
• Silicone base, the raw material for silicone rubber compounds
• Reinforcing fillers
• Extending fillers
• Vulcanizing agents
• Special purpose additives, such as antifungal agents, colorants, structuring agents, etc.
• Processing aids, to help mold flow and release
• Coupling agents, to improve the chemical bonds between ingredients
• Plasticizers and softeners, to aid mixing or enhance low temperature performance

For high voltage applications, silicone rubber compounds need to be developed through understanding its properties and behaviors in conditions like those encountered in the field. Hubbell has a long history in developing high-voltage insulators, going back to the Ohio Brass company. Ohio Brass porcelain insulators were used in the first high voltage transmission line in North America, at Niagara Falls in 1905. After years of research, Ohio Brass introduced polymer insulators in 1976.

Find out more about compounding in our white paper “Why silicone for HV Insulators: Silicone compounds explained.”

Continue learning for the bigger picture

Today, our insulators use proprietary hydrophobic silicone rubber to provide advanced, market-leading options for customer applications. Additionally, we offer proprietary polymer silicone blend known as ESP™. This is also discussed in our white papers.

To learn more about polymer insulators, be sure to sign up for our six-part educational series. You’ll be notified of our next installments. We’re here to help. To talk to someone, please reach out to your Hubbell sales rep or customer service representative.