Right Choice of Dry Type or Liquid-Filled Transformer


Transformers are necessary for routine life for the simple reason that they are the most efficient form of power when it comes to devices that can only operate on low-voltage electricity.

The reason, current passing through the mainline is too high for these appliances to handle – this is the reason why power stations distribute power to households using transformers that power down or distribute the high-electricity to low-voltage substations as per voltage requirement.

Dry-Type, or Liquid-Filled: Which Type of Transformer Should You Opt For?

Now, these transformers come in two different variants – the liquid-filled ones, which are insulated and cooled using mineral oil, and the non-liquid insulated variant that uses air/gas – these are also known as the dry-type transformers. Both types of transformers serve the same purpose, however, there do have some major differences, which is why certain types of transformer are best suited for certain conditions.

Liquid-filled transformers

  • Are more efficient than dry-types
  • They have a longer life expectancy (up to 30 years as against an average of 25 for dry-type) as the hot-spot temperatures in the coils are well-maintained by the liquid that functions as a more efficient cooling medium
  • They have a better overload bearing capacity

Dry-type transformers

  • Have limited voltage rating due to the limitations of their size
  • Are more prone to overheating in case of an overload
  • Maintenance costs are higher

Point to note here is that: The coils in liquid-type variants are easy to repair whereas the cast coils in the dry-type ones can only be replaced. This means that the liquid-filled ones can be repaired and used whereas the dry-types are mostly dispose-and-replace designs.


In case of overheating, a liquid-filled transformer has more potential for becoming a fire hazard as an explosion would throw out the oil which may catch fire. This is where dry-type transformer scores – they use air instead of oil and are, therefore, better suited for public spaces.


The other drawback with liquid-filled transformer is that its installation will need a containment trough so that it’s protected from possible oil leaks. Even then, the chances of oil spills and possible contamination are high when it comes to residential areas, which is the reason why dry-type transformers are mostly preferred for public spaces and residences, company buildings as well as transportation hubs.

Companies like Electric Power Inc, Mississauga, ON, Canada, manufacture a full line of standard and custom-engineered dry-type transformers at their facility. They have a wide variety of sizes, voltages, phases, frequencies and ratings up to 500kVA, up to the 600V class; all in accordance with CSA and UL standards. What’s more, their professional engineers, coil winders, electrical assemblers and staff are knowledgeable, capable and committed to providing complete customer satisfaction.


Just because of their set-up, oil-filled transformers require more maintenance, and regular sampling of the oil is a must to keep contamination issues under check. For the dry-type, on the other hand, an annual infrared examination of bolted connections, vacuuming of grills and coils and an overall check to maintain cooling is enough (though, it’s advisable to consult the OSHA guidelines and safety rules once in a while)

Price: Price-wise, dry-type transformers are costlier than their oil-filler counterparts.

Running sound: In many parts of the world, Europe, especially, decibel levels of appliances are a big issue and strictly monitored. And though transformers are a noisy bunch when they are running, liquid-filled ones are quieter than the dry-type ones because, well, they’re inside a huge heavy liquid container.

Even as you’re reading this, leading manufacturers of transformers are taking giant technological strides to create better versions of their model. To get a dry type transformer today contact Electpower.com.