Why core loss is constant in a transformers?
Core loss is constant in a transformer because it depends on the voltage and frequency of the supply, which are fixed, and not on the load current, which varies.
Core loss is caused by two effects: hysteresis and eddy currents.
Hysteresis loss is the energy dissipated when the magnetic domains in the core material are repeatedly aligned and realigned by the alternating magnetic flux. Eddy current loss is the energy dissipated when currents are induced in the core material by the changing magnetic flux.
These currents circulate within the core and produce heat.
Core loss can be reduced by using core materials with low hysteresis, such as silicon steel, and by laminating the core to reduce eddy currents.