Question

When a constant power output is desired to maintain __________

(a) Ef*sinδ and Ia*cosθ are to be maintained constant

(b) Ef*sinδ is be maintained constant

(c) Ia*cosθ is to be maintained constant

(d) Ef*sinδ and Ia*sinθ are to be maintained constant

The question was posed to me by my college director while I was bunking the class.

Origin of the question is Power Factor Control of Synchronous Machines topic in chapter Synchronous Machines of Electrical Machines

Answer 1

Correct choice is (a) Ef*sinδ and Ia*cosθ are to be maintained constant

To explain: For constant real power output the component of the excitation voltage lagging to Vt should remain constant as per the phasor diagram.