Energy Efficiency of Power and Distribution Transformers

Power Transformer:- these are used at the sending and receiving end of a long, high voltage transmission line for stepping up or stepping down the voltage,they are manipulated to operate almost at or near their rated capacity (KVA rating). In view of this a power transformer is designed to have maximum efficiency at or near full load.(rated KVA). Hence choice of transformer should be based on full load efficiency.

Distribution Transformers are the one which are installed at consumer premises, where they are use to step down the voltage. The secondary winding of distribution transformers are directly connected to consumer terminals. The load on this transformer varies wide range during 24 hours day due to varying requirement ranging from zero to a maximum of its rated capacity. Note the primary of distribution transformer is constantly energized therefore core losses occur continuously.So  these transformer are designed to have minimum core losses, but for reduced core loss the maximum efficiency may occur at about one-half of its rated capacity. therefore choice of distribution transformer must be calculated as follows
Energy efficiency of a transformer is defined as the ratio of total energy output for a certain period to the total energy input for the same period