Question

In an induction motor slip will be negative when the _________

(a) rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field

(b) stator magnetic field and rotor rotate in opposite direction

(c) rotor rotates at speed less than synchronous speed and in the opposite direction of the rotation of stator field

(d) rotor rotates at speed more than synchronous speed and in the opposite direction of the rotation of stator field

This question was addressed to me in an interview.

This intriguing question originated from Rotor EMF, Current and Power topic in chapter Induction Machines of Electrical Machines

Answer 1

Right option is (a) rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field

Easy explanation: s = (Ns-Nr)/Ns;   Slip is negative when rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field.