Insulating oil – also known as transformer oil – performs two central functions simultaneously in oil-type transformers: it electrically insulates conductive components from one another and carries away the heat generated during operation from the windings. Choosing the right oil significantly affects the transformer’s service life, safety, and environmental compatibility. The quality and condition of the insulating oil are decisive factors in the service life and operational safety of every oil-cooled transformer.
What types of insulating oil are there?
Mineral oils, proven for decades, are traditionally used. In addition, synthetic esters and natural vegetable esters such as rapeseed oil are gaining increasing importance. They are biodegradable, flame-retardant (fire class K), and have a higher flash point – ideal for particularly sensitive applications.
Key Characteristics at a Glance
- Excellent electrical insulation properties
- Efficient heat dissipation from the winding area
- Mineral oil, silicone oil, or ester fluids available
- Biodegradable variants for sensitive locations
- Regular oil analysis reveals ageing and defects at an early stage
- Breakdown voltage as a key quality indicator
- Online monitoring systems for continuous oil condition analysis
Frequently Asked Questions
How often must insulating oil be changed?
Under normal operation, high-quality transformer oil can last for decades. Instead of a complete change, regular oil analyses are carried out and the oil is reconditioned as needed (filtration, drying) to preserve its insulating properties.
What advantages do ester fluids offer over mineral oil?
Esters are biodegradable, less toxic, and more flame-retardant. This makes them ideal for environmentally sensitive locations such as water protection areas, city centers, or offshore applications. Esters also often extend the service life of the insulating paper.
What values are typically checked in an oil analysis?
Breakdown voltage, water content, acid number, interfacial tension, dissipation factor, and dissolved gases (DGA). These values provide information about the ageing condition, moisture ingress, and possible internal defects in the transformer.
How is insulating oil disposed of or recycled?
Mineral oils are cleaned in specialized reprocessing plants and can usually be reused. Heavily contaminated or aged oils are thermally recovered. Ester fluids are biodegradable and therefore environmentally uncritical. In all cases, proper disposal in accordance with the relevant environmental regulations is mandatory.
Our experts are available for any questions regarding the selection of the optimal insulating oil and corresponding transformer concepts. Feel free to contact us.