Transformer insulation

The insulation class of a transformer is not a concept of dielectric strength, but is a permissible temperature rise criterion, ie, insulation class refers to the heat-resistance grade of the insulation material used, which is classified into Classes A, E, B, F, and H. The insulation temperature class is divided into A grade E grade B grade F grade H grade. The specific allowable temperature rise standards for each insulation class are as follows:

The maximum allowable temperature (°C) 105 120 130 155 180

Winding temperature rise limit (K) 60 75 80 100 125

Performance reference temperature (°C) 80 95 100 120 145