Transformer Heating

[rukmal]

Can some one suggest me a method og heating a 10MVA/ 33/415V transformer winding on site. The transformer was manufactured in 1971 & it needs oil filtering also as it is noe been used for last two years. Is it advisable to filter as winding insulations will remove in flakes(as it is old) when filtering.

 

[gordonl]

If the transformer can be energized, you could short the secondary with bus, and apply a relatively low voltage to the primary winding. The voltage you need to apply to the primary will be about the impedance times the voltage rating. Be sure not to exceed the transformer current rating.

 

[prc]

There are several methods of heating depending on site situation . Let me elaborate a few.
1)Simple ,common used is hot oil circulation .But since trf was exposed for along time lot of moisture will be inside and this will not be effective.
2)Hot oil circulate for few hours and drain im mediately,with simmultaneous filling with dry nitrogen. Keep for few hours .Pull vacuum for 6hours .Fill with oil ,continue hot oil circulation for heating ,continue the cycle ,till satisfactory dew point is got for N2 gas .Hot oil circulation will not cause damage to paper insulation of trf and if it does it only shows trf is beyond its useful life.
Other methods used for trf heating are as follows .details can be got from literature or manufacturers like Micafil.

1)Hot oil spray drying
2)Low frequency Ac (2-3 Hz)is passed through winding after shorting secondary winding.
3) Hot Kerosene vapour is sent inside trf and active part is heated there by
4)Wind Cable around trf tank and pass current . Tank wall gets heated by eddy currents and heat is passed inside the trf. This method seems popular in Russia.

 

[BJC]

Westinghouse use to publish a series of books called "Electrical Maintenance Hiints" that gave very detailed instruction for field heating of oil. The section included a flow diagrams and a drawing for building the heater.
I am not sure who publishes the books now ( or if they do at all). The ones I have are a four volume boxed set. I think ABB still publishes some of the good stuff
Circle-Bar-W use to publish.
If you can't find or borrow the book I can send you the info on the heater. The pages in the book are 5x8 and the print is very small.

 

[rukmal]

Dear BJC,

can you pls. send me the diagram. Its difficult to find the book here. My email is

rukmalj@yahoo.com