What is the Transformer Class A Insulation?
Class A insulation in a transformer include.
The Materials of class Y (cotton,silk,paper,wood,cellulose,fibre etc. without impregnation or oil
immersion) impregnated with natural resin,cellulose esters,insulating oils,laminated
wood,varnished paper and cellulose-acetate film etc.
credit: Electrical Machines 3rd edition, B.J Le Roux
The classes of insulation systems (at least on NEMA) are based on temperature.
Class A is not worth talking about because it is so low.
Class B is common – uses a 80 deg C total.
Class F is usually used in large motors – 115 deg C system total.
and Class H is used in dry-type transformers and large utility generators operating up in the 15
–20kV ranges – 220 deg C system total.
Use ambient + winding temp rise + hot spot temperature to get the totals.