How to make the right choice of dry type or oil-filled transformer?

Blog September 20, 2021

“The transformer is constant structured equipment that serves the unitary purpose of stepping up/down the power of distinct voltages.”

Is that true?

Not really, in fact transformers are highly versatile equipment deployed at any facility fulfilling different purposes of installation. They come in different design, sizes, configuration, and medium filled in it. Depending on your application, location, power requirements, you can get one custom-built.

Considering the generic requirements and conditions, the transformer manufacturers offer multiple options. Out of the versatile range of products, the two most commonly used are – Dry Type and Oil-filled transformers. These transformers serve the common purpose of cooling down the equipment. But use a distinct method of cooling down the heat generated during a transformer’s working.

The oil-filled transformers can use two mediums – conventional mineral oil or high fire point hydrocarbons and silicones. On the other hand, a dry-type transformer uses air or air/gas as the cooling agent.

Are you confused and stuck with the choice? Read the factors stated below to understand the key differences, guiding your decision in the right direction.

  1. Location – The most crucial factor is the location of the transformer’s installation. The dry-type transformers are best for the spaces like – buildings, schools, offices, or near them. They are less flammable and environmentally safer. The oil-filled transformers are apt to use in outdoor spaces. Due to the risks of oil spills/leakages and fire, it serves as a better environment-friendly option.
  2. Operational Life – The life of a oil-filled transformer is 25-35 years, and a dry-type transformer is 15-25 years. The longer life span of the former saves its users the costs of material, labor for replacements, etc.
  3. Footprint – A dry-type transformer is a heavy piece of equipment in terms of its size in comparison to a oil-filled. Hence, increasing your demands for space, lighting, and ventilation.
  4. Efficiency – The oil-filled transformers are highly efficient, smaller in size, and have lower space demands. In contrast, the dry-type transformers are larger. They offer lower voltage capabilities and are more prone to overheating in case of excess loading. They, therefore, incur higher electrical losses, and are costly to maintain.
  5. Voltage – The dry-type transformers can handle low-medium voyage ratings and MVA (up to 35 kV), ideal for smaller applications. And oil-filled transformers can easily handle high voltage requirements (up to 1000KV) and are ideal in the circumstances of heavy power requirements.
  6. Costs – The transformer operates at different levels of efficiency and incurs distinct energy and additional losses. An oil-cooled transformer is bound to generate lower losses in comparison to a dry-type transformer. Due to their high energy efficiency, oil-filled transformers have lower initial and transformer costs and a higher life span.
  7. Serviceability –


Maintenance Requirements

Dry Type Transformer

●     Inspection, infrared analysis, grills, and coil vacuuming.

●     The coil and grill cleaning requires de-energization of the transformer, often resulting in no cleaning requirement.

Oil-filled Transformer

●     Drawing an oil sample to get a detailed analysis of oil and transformer’s operational efficiency.

In the case of a dry-type transformer, overlooking the cleaning requirements can cause fire hazards. Due to improper airflow impacting the transform efficiency, and is a hectic process to undertake. Inversely, the maintenance of a liquid-type transformer seems coherent and less hectic. It does not affect the transformer’s efficiency and is not prone to fire hazards.

         8. Sound and Noise Levels – Heavy equipment like transformers are bound to produce high levels of sound/noise while operating. The oil-filled transformers generate less sound, contributing less to noise pollution.

        9. Reparability – The cast coils used in dry-type transformers are typical to repair. Hence, calling for the consumer to replace it. In contrast, the coils in the oil-filled transformers are easy to repair.
Oil-filled transformers, when fail, offer the scope to repair/replace the damaged component instead of replacing the entire equipment.

      10. Reclamation/Recycling – We witness that companies prefer replacing the old coils in the transformer and continue using the old transformers.

Recycling the components of a oil-filled transformer is simpler than that of a dry-type transformer. One can revitalize the fluid for future use and economically recycle other components (like steel, copper, aluminum). Moreover, it extends a positive cash flow. All of this is hard to achieve at the end of a dry-type transformer’s life cycle.

All the factors considered, the oil-filled transformer seems to be a better option. It offers higher efficiency, recyclability, lower noise levels, lower losses, etc. But you cannot use them everywhere. As said earlier, the location has the most crucial role to play. The suitability of dry-type transformers in commercial and indoor spaces makes it the most preferred option. It poses lower risks of fire hazards and is safe to install at the places surrounding people.

Now based on your requirements and spending capacities you can make your choice in the light of all the factors listed above.