Why a Silicone Fluid for Dielectric Applications ?

When selecting a dielectric fluid, there are a number of criteria that must be met contingent upon the application. One of the strongest advantages that a silicone fluid has over a fluid such as mineral oil is its much higher thermal stability, flash points and fire points. This is critical for fluid used in transformers that are located inside or near to a building where flammability is a significant concern. STO-50 Silicone Transformer Oil can be subjected to very high temperatures, well above normal transformer operating temperatures, without creating excessive vapor pressure, breaking down, or creating corrosive by-products.

The Pure Silicone Fluids, including the STO-50, are 100% linear Polydimethylsiloxane Fluids (CAS# 63148-62-9) with viscosities measured @ 25C. They contain no additives such as pour-point depressants or heat-stabilizers. In addition, they contain no chlorine or other halogens. Pure Silicone Fluids with viscosity >5cSt are chemically inert, non volatile, thermally stable, have excellent oxidation resistance, and are compatible with conventional insulating materials. Material compatibility and thermal stability are closely related. A large number of materials have been tested for compatibility with silicone transformer oil. Below is a list of materials tested and found suitable in STO-50 Silicone Transformer Oil.

Transformer Materials that are compatible with STO-50 Silicone Transformer Oil:

Metals Insulation Plastics & Resins Wire enamels
Copper Kraft paper Nylon Amide-imide
Phosphorous bronze Pressboard Polystyrene Polyester
Aluminum Nomex (polyamide paper) Modified acrylics Amide
Stainless steel Asbestos paper Polycarbonates Formvar
Cold-rolled steel Polyester film Phenolics  
Hot-rolled steel Polyimide film PTFE  
Nickel Polypropylene film Silicone resins  
Magnesium Cross-linked polyethylene Diphenyl oxides  
Zinc Wood Epoxies  
Cadmium Mica Polyesters