Question

Mark the correct expression for alternator working at a lagging power factor.

(a) tanψ = (IaXq – Vtsinθ)/(Vtcosθ – Ia*ra)

(b) tanψ = (IaXq + Vtsinθ)/(Vtcosθ – Ia*ra)

(c) tanψ = (IaXq + Vtsinθ)/(Vtcosθ + Ia*ra)

(d) tanψ = (IaXq – Vtsecθ)/(Vtcosecθ – Ia*ra)

This question was addressed to me at a job interview.

Origin of the question is Two Reaction Theory of Salient Pole Machines topic in portion Synchronous Machines of Electrical Machines

Answer 1

Correct answer is (a) tanψ = (IaXq – Vtsinθ)/(Vtcosθ – Ia*ra)

The explanation is: The internal power factor angle is given as tanψ = (IaXq – Vtsinθ)/(Vtcosθ – Iara) for an alternator.