Q. Show Transformer equivalent circuits?

Transformers come in various sizes, from very small, weighing only a few ounces, to very large, weighing hundreds of tons. The ratings of transformers cover a very wide range. Whereas transformers applied with electronic circuits and systems usually have ratings of 300 VA or less, power-system transformers used in transmission and distribution systems have the highest volt- ampere ratings (a few kVA to several MVA) as well as the highest continuous voltage ratings. Instrument transformers (potential transformers and current transformers) with very small volt- ampere ratings are used in instruments for sensing voltages or currents in power systems.

Transformers may be classified by their frequency range: power transformers, which usually operate at a fixed frequency; audio and ultrahigh-frequency transformers; wide-band and narrow- band frequency transformers; and pulse transformers. Transformers employed in supplying power to electronic systems are generally known as power transformers. In power-system applications, however, the term power transformer denotes transformers used to transmit power in ratings larger than those associated with distribution transformers, usually more than 500 kVA at voltage levels of 67 kV and above.