Question

No-load voltage observed at two different field resistance values, is V1 < V2. What will be the relation in field resistance values?

(a) Rf1 < Rf2

(b) Rf1 = Rf1

(c) Rf1 > Rf1

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

I have been asked this question in a national level competition.

I need to ask this question from Characteristics of Self Excited Generator in chapter DC Generator of DC Machines

Answer 1

Right choice is (c) Rf1 > Rf1

For explanation I would say: When field resistance value increases the line of field resistance shifts towards more +ve slope, proving that field current decreases. This line will now intersect OCC at lower regions indicating lower values of terminal voltage.