Question

The operation of a synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ?

(a) exceeds internal angle θ

(b) is less than θ

(c) is more than θ/2

(d) is less than θ/2

The question was asked during an online exam.

Enquiry is from Synchronizing Power and Synchronizing Torque in section Synchronous Machine Stability of Electrical Machines

Answer 1

Correct choice is (a) exceeds internal angle θ

To explain I would say: Power angle should not exceed θ, to operate under normal conditions.