We shall now derive an expression for the e.m.f. generated in a d.c. generator.

Let

Ø= flux/pole in Wb
Z = total number of armature conductors
P = number of poles
A = number of parallel paths = 2 … for wave winding
= P … for lap winding
N = speed of armature in r.p.m.
Eg= e.m.f. of the generator = e.m.f./parallel path

Armature Resistance (Ra)
The resistance offered by the armature circuit is known as armature resistance (Ra) and includes:
(i) resistance of armature winding
(ii) resistance of brushes
The armature resistance depends upon the construction of machine. Except for small machines, its value is generally less than 1Ω.

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