Dry-type transformers are safer and more environmentally friendly, while requiring less maintenance. This is why much of the world has moved towards this technology, and away from oil-cooled transformers. While Africa lags considerably in its uptake of dry-type transformers, there is a growing recognition of their benefits.
The key differentiator is that dry-type transformers are cooled by air, not oil. Conventional transformers are oil-cooled, and the presence of oil introduces a number of safety and environmental risks. Among these are the oil’s flammability, making the units unsuitable for inside use – requiring their own solid structures to contain the risk of fire or explosion. Where an oil-filled transformer is in a location where people or facilities might be at risk, there is an added requirement for fire detection and fire suppression systems to be installed.
There is also an environmental risk of oil leaking from a conventional transformer, especially since there are various sensors protruding from the oil-filled tank to measure levels, temperature and other variables. This risk leads to a legal requirement for a containment bund to catch leaking oil, adding to the infrastructural burden of installing these transformers.
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The temperature variations of the oil in the transformer tank – rising with added load and cooling when the load drops – means opportunity for moisture ingress, so regular oil sampling and testing is essential. This makes maintenance more onerous, especially if the transformer is located in a remote area. If such testing and maintenance is not done regularly and competently, there is high potential for transformer failure.
Dry-type transformers, on the other hand, can be installed inside or outside of a building or substation, with no need for a special structure to be built – or for fire protection systems to be provided.
Being cooled only by air, these transformers will be designed so that sufficient air moves around the equipment to remove heat. To protect them from dust and humidity, they can operate in ingress-protected enclosures, which can also be fitted with fans and ventilation accessories as required.
With no need for oil testing, dry-type transformers require very little maintenance and are therefore very cost-effective to operate. All these factors add up to a highly cost-effective solution that reduces the operational burden on owners while reducing any environmental and safety risk.
