Isolation Transformer

Transformer oils are not readily inflammable so the risk of fire hazard is very low.

In fact normally the most preferable type is ONAN (oil immeresed, natural air cooled).

However your KVA rating is quite small and you may even think about dry type transformers.

Surely you are not buying your 250kva trafo at your family grocers, along with jalapeno peppers and onions or ordering one with your local carpenter, where you must tell him to make it liquid cooled or not.

I assume (perhaps naively) that you are buying it from a known and accredited transformer manufacturer. So what does he recommend?? Besides, liquid cooled transformers are a standard feature and there are zillions of them all over the world.

Some questions are so bizarre it boggles the mind.

Hi Dinesh,

Buying a transformer should be done with the guidance of a competent and experienced electrical Engineer and not the job of a layman. Oil cool transformer has the probability of fire hazard. But the technology is time tested and protective devices are available.Normal working conditions they work safely .

Now with the technical advancement dry type transformers( Cast resin or Resin impregnated) are available at a higher cost and manufactured by reputed transformer manufacturers in India. Choosing a dry type transformer is always dependent on the location and environment where the transformers are to be used. So get the help of a competent Electrical Engineer to decide weather you need to go for Oil cooled transformer or Dry Type transformer.

If you are of old generation buy oil cooled and if new generation go for dry type.

Write down a specification on a sheet.

It should have all your requirements that allows the suppliers to work out what goes in and what comes out. Also specify what the environmental spec is i.e. where is it sited, cooling that you can supply, temperature during the year, its mounting etc. Also if you are worried about fire or even people stealing the oil out of the transformer- put it in.

Let the suppliers give you a quote against your requirements - that will also act as a arbitration if anything goes wrong.

You do not state the voltage, I will assume low voltage (<1000V) since 250KVA is small for medium or high voltage. For a low voltage transformer of this size, oil dielectric is not necessary.

dear dinesh,

250 kva is moderate range of transformer and only oil-cooled tranf. are avilable in the market. oil-cooled tranf. are compact in size and often for out door use.Fire hazards are prevented in tranf. by Buccholz relays and enough indictions are gotten before it really blows up. For sea- going vessels air cooled (dry type, meaning no oil) transformers are used. Of course they bulky.

Vijay saradhi