Modest changes in operating voltage, so the loss can be considered as a fixed value

Transformer loss is a load loss (also called fixed losses) and the load loss (also called change loss) of two parts. No-load loss and operating voltage proportional to the square, the modest changes in the operating voltage, so the loss can be  air circuit breaker  as a fixed value, so that the fixed losses; load carried by the transformer loss is proportional to the square of the actual load, due to the general use  power transformers  load is constantly changing, so called variable losses. Comprehensive loss of the transformer may be the capacity of the transformer, voltage transformer load rate, load current, impedance voltage, power factor and the use of time and other parameters, obtained by calculation.