What is a Dry Type Transformer ?

A Dry type transformer is a transformer that is naturally cooled with normal and or forced air that flows over and between the windings. Dry type Power and distribution transformers have been developed and used over the last 40 years as an alternative to oil cooled transformers. As with any new technology, the dry types have seen resistance to change but, like the car replaced the horse and carriage and the email replaced “snail mail”, the paradigm shift is inevitable. The perceptions about dry type transformers are definitely changing, mainly as a result of a more educated market and the reliability of the units already in operation.

1. The price of the dry type in comparison to oil cooled transformers 

• Dry type transformers in comparison to oil as far as price is concerned depends on the size and the installation method of the unit.
• Generally the smaller sizes up to 500kVA is more expensive if you compare only the transformer.
• With transformers rated in excess of 500kVA, the prices start from somewhat more to sometimes less and the same as oil cooled units.
• The factor that does influence the price of the unit is the required housing and installation method.
• Due to the fact that it is an air cooled unit, it must be protected from the elements and therefore must be housed in a ventilated substation or a specific enclosure designed for the installation criteria.
• Installing the unit in a “brick & mortar” indoor substation will require an inexpensive housing, or none at all, depending on substation access. In this type of installation the dry type could be a more cost effective option than the traditional oil cooled transformer.

2. The question of reliability in comparison to oil

• Due to the continued development of dry types transformers over the last 20 years, there is no more question regarding the reliability of a dry type in comparison to the oil.
• It is the same if not better than an oil cooled unit for various reasons.
• Dry type transformers can be designed to operate in ambient temperatures of minus 60 to + 60 deg Celsius due to the hi class of insulating materials used in the manufacturing process.

3. Availability of Dry Type transformers:

• The standard manufacturing time of a dry type transformer today is between 8 and 10 weeks from date of order at the factory.
• As the bulk of dry type transformers is manufactured overseas, the shipping time can add an additional 4 to 6 weeks to the delivery period (Total 14 – 16 weeks).
• Generally the availability of an oil type locally is between 12- 18 weeks from date of order which is basically the same.

4. Guarantee :

• Dry type Transformers supplied by Power transformers carries a 2 year factory guarantee included in the price ( Standard terms and  conditions apply )

The advantages of using dry type transformers includes the following:

• Low Maintenance required which refers back to maintenance cost being very low
• Environmentally friendly – No Oil  and possible oil leaks
• No Moving parts and all connections can be inspected when required due to accessibility.
• Fire Proof – Manufactured in F1 class , they are guaranteed to be self-extinguishing and give of very little fumes & toxic substances  
• More compact in design to enable installation trough confined spaces.

Although dry types transformers are not always the least expensive option , the long term benefits  of using dry types is definitely an option to consider when replacing , upgrading or planning of a new substation .