Question

What is the formula for rotor turns per phase?

(a) rotor turns per phase = (winding factor for stator/winding factor for rotor) * (Rotor voltage per phase/Stator voltage per phase) * Number of turns per phase for stator

(b) rotor turns per phase = (winding factor for stator/winding factor for rotor) / (Rotor voltage per phase/Stator voltage per phase) * Number of turns per phase for stator

(c) rotor turns per phase = (winding factor for stator/winding factor for rotor) * (Rotor voltage per phase/Stator voltage per phase) / Number of turns per phase for stator

(d) rotor turns per phase = (winding factor for stator/winding factor for rotor) / (Rotor voltage per phase/Stator voltage per phase) / Number of turns per phase for stator

The question was asked in a job interview.

Origin of the question is Design of Wound Rotor topic in portion Three Phase Induction Motor of Design of Electrical Machines

Answer 1

Correct answer is (a) rotor turns per phase = (winding factor for stator/winding factor for rotor) * (Rotor voltage per phase/Stator voltage per phase) * Number of turns per phase for stator

To elaborate: Firstly, the winding factor for stator is obtained along with the winding factor for stator. Next the ratio of the rotor voltage per phase to the stator voltage per phase. Finally, the number of turns per phase for stator is also calculated to obtain the rotor turns per phase.