Question

OCC is drawn at two different speeds both less than rated speed. OCC drawn at speed N1 lies below OCC drawn at speed N2. Which of the following relation is correct?

(a) N2 = N1

(b) N2 < N1

(c) N2 >> N1

(d) Can’t comment

I had been asked this question in an online quiz.

This intriguing question comes from No Load with On Load Characteristics of DC Generator topic in portion DC Generator of DC Machines

Answer 1

Correct choice is (c) N2 >> N1

To elaborate: As a speed on which OCC is taken decreases, the residual voltage appearing on Voc axis also decrease and OCC starts from below, compare to first one. Thus, N1 is less comparatively, as its OCC lies below than the OCC drawn at other speed.