Dry Type Vs Oil Filled Transformer: Which One to Choose?

These issues usually arise when someone designs an electrical system for their project. This can be a residential, commercial, or industrial project and can vary depending on the nature of the project at hand. A key aspect is a question of how we power the system, so after careful consideration of several very important factors that we will discuss in this article, either a dry type transformer or an oil-filled transformer should be selected.

Before we get started, let's quickly try to understand the differences between dry-type and oil-filled transformers.

Transformer Types

What are oil-filled transformers?

As the name suggests, the coils in this type of transformer are immersed in oil (mainly mineral oil), which helps to control the temperature of the transformer. This oil is dissipated by means of a heat sink mounted on the transformer tank, called an ONAN type transformer. To further improve the cooling of the transformer, the heat sink is fitted with a fan that helps to reduce the temperature, known as the ONAF type transformer. This type of transformer can reach high voltage capacities, in some cases up to 1000 kV.

What is a dry type of transformer

In this type of transformer, the air is used as a cooling medium. They are made using vacuum pressure impregnation in polyester or silicone varnish. Some of them are also made with VPI epoxy and cast resin for harsher environmental conditions. Because they are limited in cooling, they are limited to a maximum voltage of 35 kV.

Dry-type Transformer     

Selection Considerations

1.  Maintenance: There is no doubt that oil-cooled transformers require more maintenance procedures than dry-type transformers. As part of preventive maintenance, the oil needs to be sampled and sent for testing, and transformer oil filtration should be performed at least once a year; dry-type transformers, on the other hand, are highly resistant to chemical contaminants.

2.  Operating costs: Compared to oil-cooled transformers, dry-type transformers have higher operating losses. Oil-cooled transformers, on the other hand, have higher efficiency and therefore a longer service life.

3.  Noise: Compared to oil-cooled transformers, dry-type transformers produce more noise

4.  Recyclability: At the end of their service life, dry-type transformers have very limited recycling, as the oil units are more likely to recycle the core/coils. In addition to this, oil-cooled has superior service life and maintainability, generates less waste, and requires less replacement and labor.

5.  Efficiency: Compared to oil-filled transformers, dry-type transformers are larger, have limited voltage ratings, and are more likely to overheat if overloaded, resulting in higher electrical losses and more expensive maintenance costs. On the other hand, oil-filled transformers have little impact on the environment.  

6.  Location: This is probably the most important factor when considering which transformer to use. Dry-type transformers are considered safer for the environment because of the lower risk of fire and are therefore ideal for indoor applications such as shopping malls and hospitals. Whereas oil-cooled transformers are well suited for outdoor installations due to the possibility of oil leaks and spill-causing fire risks.

Conclusion

Considering these factors, oil installations appear to be better alternatives in all respects, with higher energy efficiency, recyclability, lower noise pollution, lower operating costs, and a small environmental footprint. In any case, oil units cannot be used in essentially any situation. Dry types are the best and preferred for commercial and indoor operations because they are safer units for working around individuals and areas where fire risks may exist.

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