Transformer oil has a crucial role to play in the extended lifespan and effective operation of electrical transformers, performing four critical functions.
It is designed to dissipate heat, making sure that the transformer’s coil and core stay at optimal temperatures by allowing syphoning of thermal energy.
Oils have dielectric capabilities that insulate and work to protect key components of the transformer. They shield the transformer’s solid insulation (usually paper) from incurring damage that weakens the tensile strength of the transformer, reducing longevity.
Transformer oils also facilitate easy monitoring via regular testing in a lab environment, providing invaluable insights into equipment condition.
Here, we work our way through the different varieties of transformer fluids and their colours, and examine the importance of adopting correct maintenance practices that promote safe and efficient electrical transformer operation. Read on for everything you need to know about transformer oils in one place.
What is transformer oil?
Sometimes referred to as insulating oil, transformer oil is a specialist lubricant used both to cool and insulate high-voltage transformers, along with other electrical equipment like circuit breakers, switches and capacitors.
What are the four functions of transformer oil?
As mentioned briefly above, transformer oil has four crucial functions to perform. Here we discuss each in depth.
Heat dispersion
Transformer oil must disperse heat emitted from the transformer’s core and coil; the oil does not stay static in the transformer. As it heats, it rises to the top and exits, entering radiator tube tops.
Here, it starts to cool and begins to work down inside the radiator tubes, before re-entering the transformer located at the cooling tubes’ bottom. This complete process is called “Thermal Syphoning”.
Dielectric capabilities
Transformer oil can protect the solid insulation, typically made from paper, inside the transformer. If the paper experiences damage, its tensile strength weakens, reducing its effectiveness as an insulator and reducing the transformer’s active service life.
Easily testable
Transformer oil allows users to take a representative sample from a transformer for laboratory testing. This give operators detailed insights into how well the transformer is currently operating.
A full battery of tests can be carried out from a single oil sample including moisture content, oil ageing and dissolved gas analysis (DGA).
What are the different types of transformer oils?
Today, leading lubrication manufacturers like Millers Oils, Morris Lubricants and Fuchs produce a vast array of transformer oils. The most common solution remains mineral oil, with an abundance of refineries working to purify products ready for use.
Transformer oils typically fall into one of two categories: Type One transformer oils and Type Two.
While Type One is an uninhibited oil, Type Two includes an oxidation inhibitor. When oxygen enters a transformer, it accelerates the ageing process.
In most cases, oxygen enters via leaks, which can be countered by regular visual inspections and swift repairs when issues are identified. Over time, the oxidation inhibitor included depletes, and the lifespan of the inhibitors is directly related to oxygen levels inside the transformer. The more oxygen present, the quicker the inhibitor runs out.
Transformer oil also has a set breakdown voltage (BDV). The dielectric BDV of an insulating fluid is important, as it is a measure of the transformer oil’s ability to hold up to electric stress without failing.
What colour are transformer fluids?
There are many different types of transformer fluids. While some are natural, others have a synthetic ester base. As a result, different products can vary in colour when new. However, oil colour can still be useful as a visual indicator of fluid health.
Standard insulating fluids like transformer oils are usually completely clear when new, but change in colour as they age, turning from white to a darker brown, and sometimes even black when carbon builds up inside the transformer.
Many of the more recent natural esters have a green tint to them; however, when a transformer is in use for a long time, the fluid inside them may no longer even be produced. If a leak occurs, a suitable substitute must be sourced that is compatible with the transformer.
What is hot oil cleaning?
Decayed products from oxidation are damaging to solid insulation in transformers, shortening their lifespan. Hot oil cleaning, sometimes called oil processing, removes unwanted deposits like sludge from mineral oil transformers. The fouled oil is removed from the transformer using an oil processor, where it is filtered before being re-entering the transformer.
Use this helpful guide as reference whenever you need a refresher on transformer oil and the key role it plays in effective transformer operation.
