The total heat loss of a Liquid Filled (Insulation Class "A") Power Distribution Transformer at various loads is calculated as follows :

At 100% load the total heat loss is the addition of the No Load Loss and the Load Loss

At X% load, the total heat loss is (X/100)² x Load Loss at 100% Load + No Load Loss

i.e. The No Load Loss is a constant loss and does not change with load
The Load Loss varies to the square of the per unit load

e.g. 1000kVA transformer with a No Load Loss of 1340 Watts and a Load Loss of 12500 Watts at 100% load and reference temperature of 75ºC, has the following losses at various loads

• 100% Load