Power Transformer Characteristics

The power transformers are design to operate with an almost constant load which is equal to their rating. The maximum efficiency being designed to be at full load. Therefore, the fullload winding copper losses must be equal to the core losses.

Actually, all the transformers are the same that is same design formulae apply for small signal transformers to the power transformers. In case of power transformers, the designer needs to consider both voltage and current, to remember that heat will need to be dissipated and the series resistance is a cause of low efficiency.

Therefore, a power transformer has the following fundamental characteristics −

• The power transformers are heavy due to their iron core and can be of very large size.

• They may have one or more primary and secondary windings.

• They may have one tapped winding like an autotransformer.

• They have laminated core to reduce eddy current losses.

• The power transformers are restricted to low-level frequencies and should not be operated at high frequencies as that would lead to excessive losses.

• They are wound with thick conductors to minimise the series resistance.

• They are built with carefully chosen insulation suited to the applied voltages.

• The power transformers are arranged such that the thermal losses in the core and windings do not cause overheating.

• The flux path should be short as possible as to reduce leakage flux and minimising energy needed.

• The power transformers operate at large amount of current.

• The core of the power transformer is shaped either a shell type or a core type. In shell type design of power transformer, both the primary and secondary windings are placed on the central limb, whereas the core type has windings on separate lags.