Two forms of energy loss in a transformer are:
1. eddy current
2. heat loss (1²R) / Joules heat or copper loses.
3. Magnetic flux leakage.
4. Hysteresis
These energy losses can be reduced by
1. Eddy current can be reduced by laminating the core
2. Heat loss can be reduced by using thick wires, or low resistance wire to form the coils
3. Magnetic flux leakage – by efficient core design.
4. Hysteresis – by soft iron core or special alloy