Transformer Insulation Classes

The following table summarizes the different insulation systems available.

Insulation Rating Insulation Class Average Winding Temperature Rise Hot Spot Temperature Rise Maximum Winding Temperature
Class 105 A 55 degree C 65 degree C 105 degree C
Class 150 or 130 B 80 degree C 110 degree C 150 degree C
Class 180 F 115 degree C 145 degree C 180 degree C
Class 200 N 130 degree C 160 degree C 200 degree C
Class 220 H 150 degree C 180 degree C 220 degree C

Note: the maximum acceptable temperature rise based on an average ambient of 30 degree C during any 24 hour period and a maximum ambient of 40 degree C at any time.