Electrical Machine - IES Academy

1. Transformer
Theory at a Glance (For IES, GATE, PSU)
Introduction
The transformer is a static electromagnetic device, which transfers electrical energy from one
electrical circuit to another electrical circuit through the medium of magnetic field (magnetic
coupling) and without a change in the frequency. The two circuits are not connected
electrically, but coupled magnetically and electromagnetic energy conversion takes place.
Since a transformer has no moving part, it has maximum efficiency of all machines. Important
applications of a transformer are:
1. For changing voltage and current levels from one circuit to another.
2. For impedance matching of a source and its load for maximum power transfer in
electronic and control circuits.
3. For isolating DC while permitting flow of AC between two circuits or for isolation.
Main Application
Voltage generation is limited to 11kV due to insulation limits, but transmission of electrical
power is more economical at higher voltage. So the most important application of power
transformer is to step-up & step-down the voltage of the transmission lines.
Transformer Construction
Based on the manner in which the windings are wound around the magnetic core, the
transformers are of two types: (i) core type and (ii) shell type
(a)
(b)
Constructional details of single-phase (a) core-type transformer (b) shell-type transformer
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