Production of AC Voltage Notes

Production of AC Voltage

The machines which are used to generate electrical voltages are called generators. The generators which generate purely sinusoidal a.c. voltages are called alternators.
The basic principle of an alternator is the principle of electromagnetic induction. The sine wave is generated according to Faraday’s law of electromagnetic
induction. It says that whenever there is a relative motion between the conductor and the magnetic field in which it is kept, an e.m.f. gets induced in the conductor.
The relative motion may exist because of movement of conductors with respect to magnetic field or movement of magnetic field with respect to conductor.
Let a single turn coil be free to rotate at constant angular velocity symmetrically between the poles of a magnet system.

An e.m.f. is generated in the coil (from Faraday’s Laws) which varies in magnitude and reverses its direction at regular intervals. The reason for this is shown in
Figure(in next page). In positions (a), (e) and (i) the conductors of the loop are effectively moving along the magnetic field, no flux is cut and hence no e.m.f. is
induced. In position (c) maximum flux is cut and hence maximum e.m.f. is induced. In position (g), maximum flux is cut and hence maximum e.m.f. is again induced.
However, using Fleming’s right- -and rule, the induced e.m.f. is in the opposite direction to that in position (c) and is thus shown as -E. In positions (b), (d), (f) and
(h) some flux is cut and hence some e.m.f. is inuced. If all such positions of the coil are considered, in one revolution of the coil, one rycle of alternating e.m.f. is
produced as shown. This is the principle of operation of the a.c. generator (i.e. the alternator).


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