The Difference Between Dry-Type and Oil-Filled Transformers

Transformers are very useful devices that allow electricity to be used efficiently by things that can only handle low voltage electricity. Trying to power a small appliance directly from an electric pylon would lead to an unwanted explosion! They take the high voltage electricity from power stations, and transform it into low voltage electricity that can be safely used by industrial and commercial properties like offices, homes, and large factories.

There are two types of transformers that are being used right now: Dry-type transformers and oil-filled transformers (also known as liquid-filled transformers). They serve the same purpose, but have some major differences between them. These differences are important enough that certain types of transformers are better for certain situations.


A cooling medium is important to stop the transformer from overheating and becoming a potential fire or explosion hazard. Overheating is inevitable when transformers are under load, but it must be solved because temperature rises are not acceptable when transformers are being used.

Dry-type transformers use air as the cooling medium, while oil-filled transformers use oil instead of air.

Some public places do not use oil-filled transformers because they are considered to be a big fire hazard and, instead, use dry-type transformers. This is because the liquid being used is flammable. A situation where the oil spills, leaks, or becomes contaminated could easily happen and put the building’s residents at risk. For this reason, they are restricted to outdoor installations.

Dry-type transformers are the safer option, and you will see them in public places such as transportation hubs and company buildings.


Generally, oil-filled transformers require maintenance procedures to be performed more often than with dry-type transformers. The oil also needs to be sampled so that there are no problems with contamination. The dry-type is very resistant to chemical contaminants, which means that it will not have to be taken apart every time a minor accident happens. Consult the OSHA guidelines regarding the safety rules for transformers and other electrical conductors.


Oil-filled transformers are generally cheaper than the dry-type variant, with some exceptions.


Transformers are generally known for being noisy when they are running. With that being said, oil-filled transformers are quieter than the dry-type ones.


Oil-filled transformers are known to be more efficient than dry-type transformers, which are limited in their voltage rating and their size. This makes the dry-type far more prone to overheating if they experience overload, and it’s important to remember that their performance is limited during overload. As a result, it is also more expensive to maintain the dry-type transformers power supply over time.

Those are the main differences that exist between the oil-filled and dry-type transformers. Your choice of transformer will depend on your safety requirements and the budget set aside for the purchase.

Although these differences are accepted as general rules, be on the lookout for exceptions. Many leading manufacturers of transformers are making huge advances in the technology used to create them. There is a big push towards the use of non-flammable, liquid-filled transformers that use naturally degradable fluids like veggie oils and animal fats.  They are safer for the environment and are still more efficient than dry-type transformers. Look out for these changes to take place in the near future.

Whether you are buying an oil-filled transformer or a dry-type transformer, you always want to choose a reliable source that provides the best products on the market for a good price. You will need to look at your installation and safety requirements when making your final decision.