Transformer Conversion

Possible, but not practical.

If operate transformer at a lower temperature will reduce copper losses slightly.

Why do you wish to convert a dry type transformer to an oil insulated transformer?

Due to the non availability of spares and relative high losses dry type transformers are not very popular in our part of the world. It is our intentenion to convert existing dry type transformers to oil emmersed units. Disregarding the cost of the conversion the question arises: Can one expect adverse affects on winding insulation, live span and electrical performance?.

This is a strange request.Cast resin dry type transformers (CRT) are usually having lower losses than oil immersed ONAN transformers of the same KVA rating and voltage ratio manufactured by the same manufacturer.Transformers complying to IEC76 and 726 have efficiencies between 97 to 99% at 75C @ different load levels.You cannot improve it much more.However you can get more continous KVA capacity out of the original transformer by adding force cooling fans( not ventilation fans) at the bottom of the transformer.The heat will be maximum from the LV coil which is logically the inner coil (to save huge amount of conductor material).CRT from a respectable manufacturer can easily yield 30% increase in KVA capacity with AF cooling.I have used smaller cast resin transformer with guaranteed 50% increase.That is 1000/1500KVA AN/AF.No need of spare as the 2nd and 3rd can takeover the duty of the 1st failed Tx.At lower loadings,below 50% load,the cooling does not contribute to lower losses as AF cooling consume more energy than the lower Cu losses.the core losses which is much smaller than load loss depends on the quality/grade/thickness of silicon steel,stepped,joints,lamination,air gap designs.While you can put the the CRT in a tank (with fins to achieve ONAN cooling) of transformer oil( better electrical insulating and heat conducting medium than humid air)without adverse effects,but this is bad engineering.I can change your CRT for ONAN Tx for free as it cost 50 to 70% more to buy CRT of the same KVA.Only one sensible good that I can think of is that immersing it in oil will prevent surface high voltage tracking/flash-over in enviroment that has carbon/coal dust,sea spray/salt formation,cotton fibre etc.Also if the transformer's HV coils are not true cast resin type such as paper insulated with varnish imprenation method.I have seen such transformers but often fail in tropical area.For extremely low no-load/core loss transformer,armorphous steel is used.As the ribon of this steel is rquired to form the TX core,5 limbs instead of 3 limbs resulted which give rise to problem of bracing it.Thus capacity of 1500KVA is about the biggest available 15 years ago.Such transformers are used in remote stations with low intermitent loadings.They are expensive.

Keep the transformer room well vetilate at <40C,need no air conditioning,clean CRT with dry cloth and vacuum anualy,load upto 95%,it can work for 40 years.No spares required except temperature sensors and thermometers.(CRT is not suitable where daily HV switching is required such as HV supply to HV motors for huge A/C in Mecca.HV coils fail very quickly due to induced high transcient surges when the CB is opened)

Best regards,

Khor

Short answer, no. It's like trying to convert a car into a motorcycle.

What is your application?

Hai,

Its econmically not viable,

First of all conversion is not at all possible.

Second you have to invest another 20 to 30% of amount for procuring oil, outer body with accessories etc for a little improvement in efficiency.

Adding cooling fans would be a whole lot cheaper...

No the insulations are different for dry type and oil filled type.

Probably less expensive to purchase new oil filled units. I never heard of it being done and wonder what the impact is on heat transfer.

What about fire code in your part of the world? Oil filled units will probably require a fire proof vault if installed inside the building. Also, if installed in the upper floors of a multi-story building, can the elevator handle the weight of oil filled units?