Question

No-load voltage observed at two different field resistance values, is V1 < V2. What will be the relation in speed if field resistance is kept same for both cases?

(a) N1 < N2

(b) N1 = N1

(c) N1 > N1

(d) Can’t determine from no-load voltage

The question was posed to me during an interview.

The above asked question is from Characteristics of Self Excited Generator in section DC Generator of DC Machines

Answer 1

Correct answer is (a) N1 < N2

Easiest explanation: For Field resistance kept constant, field resistance line will intersect OCC at different points as speed variation may shift OCC up or down. When speed is increased OCC shifts up indicating that no-load voltage will also rise up.