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Although the transformer is not classified as an electric machine, the principles of its operation are fundamental for the induction motor and synchronous machines. Since A.C. electric machines are normally built for low frequencies only the low-frequency power transformer will be considered in this text.

Function. The function of a transformer, as the name implies, is to transform alternating current energy from one voltage into another voltage. The transformer has no rotating parts, hence it is often called a static transformer.

When energy is transformed into a higher voltage the transformer is called a step-up transformer but when the case is otherwise it is called a step-down transformer. Most power transformers operate at constant voltage, i.e. if the power varies the current varies while the voltage remains fairly constant.

Applications. A transformer performs many important functions in prominent areas of electrical engineering.

  • In electrical power engineering the transformer makes it possible to convert electric power from a generated voltage of about 11 kV (as determined by generator design limitations) to higher values of 132 kV, 220 kV” 400 kV, 500 kV and 765 kV thus permitting transmission of huge amounts of power along long distances to appropriate distribution points at tremendous savings in the cost of transmission lines as well as in power losses.
  • At distribution points transformers arc used to reduce these high voltages to a safe level of 400/230 volts for use in homes, offices etc.
  • In electric communication circuits transformers are used for a variety of purposes e.g., as an impedance transformation device to allow maximum transfer of power from the input circuit to the output device.
  • In radio and television circuits input transformers, interstage transformers and output transformers are widely used.
  • Transformers are also used in telephone circuits, instrumentation circuits and control circuits.