Question

For determining IaRa maximum _____________

(a) Distance between Rf line and v+ IaRa line is taken

(b) Distance between OCC and v+ IaRa line is taken

(c) Maximum Distance between OCC and v+ IaRa line is taken

(d) Can’t calculated graphically

This question was addressed to me during a job interview.

The above asked question is from Graphical Representation of External Characteristics topic in section DC Generator of DC Machines

Answer 1

The correct choice is (c) Maximum Distance between OCC and v+ IaRa line is taken

The best I can explain: OCC when starts from some residual voltage on y axis, goes on increasing till some maximum value and then starts reducing slightly. The bulk is formed where maximum distance between OCC and v+ IaRa line is taken, to get effective frop in armature.