Question

For a DC series generator what is the condition for self-excitation?

(a) (Ra+Rse) > RC

(b) (RSE+Rse+RL) < RC

(c) (RSE+Rse+RL) > RC

(d) (Rse+RL) > RC

This question was posed to me in an international level competition.

My enquiry is from Characteristics of Separately Excited Generators in chapter DC Generator of DC Machines

Answer 1

Correct option is (c) (RSE+Rse+RL) > RC

For explanation I would say: Summation of armature resistance, series field resistance, load resistance must be less than the critical resistance. As seen in self-excited DC generator characteristics if this value is greater than critical resistance, voltage build-up will not be possible.