Those transformers installed at the ending or receiving end of long high voltage transmission lines are the power transformers. The distribution transformers (generally pole mounted) are those installed in the location of the city to provide utilization voltage at the consumer terminals.
Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.
Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.
A power transformer usually has one primary and one secondary, and one input and output. A distribution transformer may have one primary and one divided or “Tapped” secondary, or two or more secondaries.
Power transformers generally operate at nearly full – load. However, a distribution transformer operates at light loads during major parts of the day.
The performance of the power transformers is generally judged from commercial efficiency whereas the performance of a distribution transformer is judged from all – day – efficiency.
The rating of a high transformer is many times greater than that of distribution transformer.
In Power Transformer the flux density is higher than the distribution transformer.
Power transformer’s primary winding always connected in star and secondary winding in delta while in distribution transformer primary winding connected in delta and secondary in star.
In The Sub station end of the transmission line, The Power Transformer Connection is Star-Delta.( For the purpose of Step down the Voltage Level)
In the star up of the Transmission line (H-T), The Connection of the power Transformer is Delta – Star (For the purpose of Step Up the Voltage Level) But in case of Distribution Transformer, But Generally it is used in there-phase Step down distribution transformer( Delta – Star).