All transformers work on the same principles of electromagnetic induction and are primarily used to change voltages to serve different purposes within the power system. Power and Distribution transformers, however, serve two different purposes and therefore require different classifications.
Power transformers are used in high voltage transmission networks for step-up and step-down applications (400 kV, 200 kV, 110 kV, 66kV, 33kV) and are generally rated above 200MVA. When voltage is generated (e.g., nuclear, hydro, renewables) it is usually stepped up to a very high voltage to minimize I2R losses that occur in transmission lines. Since Power transformers are used in Transmission networks and are not directly connected to end consumers (e.g., commercial, Industrial, residential), load fluctuations are minimal. They are loaded 24 hours a day and designed for maximum efficiency at full load.
Distribution transformers are used in lower voltage distribution networks for end-user connectivity (11kV, 6.6 kV, 3.3 kV, 480V, 208V) and are generally rated less than 200 MVA.
Distribution Transformers are used at the distribution level where the secondary voltage is typically delivered to the end consumer. Because of the voltage drop that occurs when traveling long distances, Distribution transformers are generally located in close proximity to the end user. MGM Transformer Company is the leader in manufacturing distribution transformers up 10MVA in both dry type and liquid substation.
Distribution transformers are connected to end-users who don’t operate at full load all the time, so they are designed for maximum
efficiency at 50% to 70% load. This explains why the DOE (Department of Energy) efficiency regulations define the maximum efficiency at 50% load for medium voltage distribution transformers and 35 % load for low voltage distribution transformers.