Methods Of Excitation
Various methods of excitation of the field windings are
series generators, shunt generators, compound generators
With self-excited generators, residual magnetism must be present in the machine iron to get the self-excitation process started.
The relation between the steady-state generated emfEa and the armature terminal voltageVa isVa=Ea−IaRa
Typical steady-state dc-motor speed-torque characteristics are shown in Figure.1.4, in which it is assumed that the motor terminals are supplied from a constant-voltage source.
In a motor the relation between the emf Ea generated in the armature and the armature terminal voltage Va is Va=Ea+IaRa. The application of dc machines lie in the variety of performance characteristics offered by the possibilities of shunt, series, and compound excitation.
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