What is Power Transformer? Diagram and Rating

A power transformer is one of the types of transformer. The basic function of this transformer is to transfer electrical energy from one voltage level to another voltage level without changing the frequency. These transformers are used at specific locations in power systems. In this article, we will see the basic characteristics of a power transformer.

Power transformer diagram

power transformer

A power transformer is used at generating stations to step up the generated voltage. The electrical energy is transmitted through transmission lines at very high voltage. The transfer of electrical energy at high voltage reduces the transmission line losses and hence there is less drop in voltage. Power transformers provide this very high transmission voltage.

A power transformer is also used at substations to step down the high transmission line voltage. Since this high voltage can’t be utilized by the consumers. Hence power transformers are used at sub-stations to reduce the transmission line voltage suitable for feeders.

It is noted that a power transformer both increases and reduces supply voltage at generating station and sub-stations, respectively.

The size of a power transformer is very large. It is an important point to note is that a power transformer operates only during load periods. During the light load periods, power transformers are disconnected. Hence it is operated for few hours a day.

A power transformer always operates at full load conditions. It is specially designed with higher leakage reactance. It is also noted that load fluctuations are very less in the power transformer. Hence voltage regulation is less important here.

The power transformers have a higher flux density. It is specially designed to have maximum efficiency closer to 100%.

The efficiency of a power transformer can be calculated using the transformer efficiency formula.

Power transformer rating

A power transformer generally has a rating above 200 MVA. The secondary voltage ratings of a power transformer are higher as compared to the distribution transformer. It can have rating as 400kV, 200kV, 66kV, and 33kV.


1. [image reference] https://www.siemens-energy.com/global/en/offerings/power-transmission/portfolio/transformers/power-transformers.html

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