Silicone Transformer Oil: Properties, Applications and Availability in Australia

Silicone Transformer Oil: Properties, Applications and Availability in Australia

Mineral oil remains by far the most widely used transformer fluid in Australia. There are, however, alternative dielectric fluids that have a genuine role in specific applications, including high molecular weight hydrocarbons, biofluids, natural and synthetic esters, and silicone fluids. Understanding where each fluid excels, and where its limitations lie, is essential for engineers specifying transformer insulation systems.

What Is Silicone Transformer Oil?

Silicone transformer oil is more precisely described as polydimethylsiloxane (PDMS), a fully synthetic fluid that can be formulated for use as a dielectric coolant in high voltage transformers. Pure PDMS is entirely free of additives; there are no pour-point depressants, heat stabilisers, or halogens present. This makes it compatible with the full range of internal materials used in transformer construction, including copper, aluminium, steel, timber, and Kraft paper windings. It is equally compatible with standard oil processing equipment such as filters and drying units.

The production of dimethylsiloxane begins with the manufacture of dimethylchlorosilane from chloromethane and silicon. This then undergoes a series of hydrolysis reactions to produce cyclical siloxane, which is then polymerised to the desired viscosity grade. Established manufacturers include Dow Corning, Wacker, and ClearCo. There are no PDMS manufacturers in Australia, but Benzoil imports and supplies silicone transformer oil through established channel partners, with stock available from local warehouses.

Key Properties of Electrical Grade Silicone Oil

Like any transformer fluid, silicone oil must meet a set of electrical and physical performance criteria. Key properties include:

• High dielectric strength
• High flash point and fire point
• Broad in-service temperature range
• Low vapour pressure
• Low pour point
• Minimal viscosity change across high and low temperature extremes
• Chemical inertness

These characteristics make silicone oil a technically sound choice in situations where the standard properties of mineral oil are not sufficient for the application or location.

Thermal Stability and Fire Safety

The primary advantage of silicone fluid over mineral oil is its superior thermal stability combined with a substantially higher flash and fire point. Silicone transformer oil can be subjected to temperatures considerably above normal transformer operating temperatures while resisting excessive vapour pressure generation, maintaining dielectric integrity, and not producing corrosive by-products. Research also indicates that insulating paper impregnated with silicone oil ages at a slower rate than paper in standard mineral transformer oil, because silicone oil draws moisture away from the paper windings over time.

In practical terms, the fire point of silicone transformer oil is approximately 370 degrees Celsius, with a flash point of around 300 degrees Celsius. Compare those figures with mineral transformer oil, which has a flash point of approximately 160 degrees Celsius and a fire point of around 175 degrees Celsius. This difference is substantial from a fire safety engineering perspective.

Applications Where Silicone Oil Is Specified

While pole-mounted and outdoor substation transformers are the familiar face of the transformer fleet, a significant number of transformers must be installed in constrained or sensitive locations. Building basements, tunnel substations, rooftop installations, rail infrastructure, and underground city substations all present fire risk scenarios that outdoor installations do not. In these settings, a dielectric fluid with a fire point above 300 degrees Celsius directly reduces the risk profile and, as a practical matter, results in lower insurance premiums for the asset owner.

This financial incentive has been driving a steady programme of transformer retrofills in Australian cities and infrastructure projects, where standard mineral oil is decanted and replaced with a synthetic fluid. Silicone oil is one option in this context, alongside synthetic and natural ester fluids, which have also gained significant traction in fire-safe applications in recent years due to their biodegradability credentials.

Silicone Oil Versus Ester Fluids: A Note for Engineers

Both silicone and ester-based transformer fluids (natural and synthetic) are classified as K-class fluids, meaning they have a fire point above 300 degrees Celsius and are considered non-flammable by transformer safety standards. Ester fluids offer the additional advantage of biodegradability, which makes them the preferred choice in environmentally sensitive locations. Silicone oil, by contrast, does not biodegrade readily. For indoor and tunnel installations where fire safety is the primary concern and environmental exposure risk is limited, silicone oil remains a well-proven option. The choice between them should be driven by the specific installation requirements, including location, environmental risk, temperature profile, and compatibility with existing equipment.

Silicone Oil Supply in Australia

Silicone transformer oil is not manufactured in Australia; it is imported and distributed through established supply channels. As a specialist transformer oil supplier, Benzoil maintains local warehouse stock to support Australian projects without extended import lead times. This is particularly important for maintenance and retrofill projects where transformer downtime needs to be minimised. Supply can be arranged in quantities ranging from small pails for top-ups through to bulk deliveries for new transformer commissioning or full oil changes. Technical data sheets and safety documentation are provided with all supply.

Key Takeaways

• Silicone transformer oil (PDMS) is a fully synthetic, additive-free dielectric fluid compatible with all standard transformer construction materials.
• Its fire point of approximately 370 degrees Celsius and flash point of approximately 300 degrees Celsius make it substantially safer than mineral oil in fire-sensitive applications.
• Silicone oil is the appropriate choice for transformers in basements, tunnels, rooftops, and other indoor or constrained locations where fire hazard must be minimised.
• Use of silicone oil in sensitive locations typically results in lower insurance premiums for transformer owners.
• Benzoil imports and supplies silicone transformer oil from Australian warehouse stock through established supply channels.
• Ester-based fluids offer comparable fire safety with the added benefit of biodegradability, and both options should be evaluated for specific project requirements.

Frequently Asked Questions

What is silicone transformer oil made from?

Silicone transformer oil is polydimethylsiloxane (PDMS), a fully synthetic polymer produced from dimethylchlorosilane. It contains no petroleum-derived components, no pour-point depressants, and no halogens. This makes it chemically inert and compatible with all standard transformer construction materials including copper, aluminium, steel, timber, and Kraft paper.

What is the fire point of silicone transformer oil?

Silicone transformer oil has a fire point of approximately 370 degrees Celsius and a flash point of around 300 degrees Celsius. This compares with mineral transformer oil, which has a flash point of approximately 160 degrees Celsius and a fire point of around 175 degrees Celsius. The substantially higher fire point classifies silicone oil as a K-class dielectric fluid under transformer safety standards.

Where is silicone transformer oil typically used in Australia?

Silicone transformer oil is specified for indoor substations, building basements, tunnel installations, rooftop transformers, rail infrastructure, and underground city substations where the fire risk from a mineral-oil event would be unacceptable. Its high fire point reduces fire risk and typically results in lower insurance premiums for the asset owner.

Can silicone oil replace mineral oil in an existing transformer?

Yes, a retrofill from mineral oil to silicone oil is achievable, but it requires proper planning. The transformer must be thoroughly de-oiled and the silicone fluid must be confirmed compatible with the existing seals and construction materials. Benzoil can advise on the retrofill process and supply the correct grade of silicone oil for the specific transformer.

Is silicone transformer oil biodegradable?

Silicone oil does not biodegrade readily. For applications where environmental exposure risk is a concern, such as outdoor installations near waterways or ecologically sensitive areas, natural ester fluids offer a biodegradable alternative with a comparable high fire point. For indoor and tunnel installations where fire safety is the primary requirement and environmental spill risk is limited, silicone oil remains a well-proven option.

Enquire About Silicone Transformer Oil Supply

To discuss your transformer oil requirements, including silicone, ester, and mineral oil options, contact the Benzoil team. Contact us here, call 0497 645 008, or email info@benzoil.com.au.