TRANSFORMER EQUIVALENT MODEL

This is the equivalent model of a transformer, the inductance and capacitance of transformer are separated outside where Ic is the current due to loses where Im is the current flowing in winding to magnetize the core 

REGULATION OF A TRANSFORMER

When a transformer is connected with a load if a load has low power factor so high voltage drop will be their due to it 

The only way to prevent is by  increasing the primary voltage 

lower regulation higher will be efficiency