The per phase DC armature resistance of an atlernator is 1 Ω. The effective AC armature ressitance should be around:
- 1.5 Ω
- 2.5 Ω
- 3.5 Ω
- 4.5 Ω
Correct answer: 1. 1.5 Ω
Since harmonics are generated in individual coils of alternator windings, some high frequencies are present.
Due to skin effect, effect AC resistance of armature windings is greater than DC resistance.
This difference factor varies on the basis of base frequency and winding arrangement. Usually it ranges from 1.2 to 1.8. However in case of 50 Hz machines, it is usual practice to take AC armature resistance as 1.5
In present case Rac = 1.5 Rdc = 1.5 * = 1.5 Ω