Section 15.2: Slip
Given the rotor’s speed n, and the stator’s rotating field (synchronous) speed ns = 120f/P (see Eq. 14.3, text p. 536), the slip is: s = (ns - n)/ns
The numerator (ns - n) is how much faster the stator field is rotating than the rotor (relative motion) and n = (1- s)ns
The relative motion between the stator field and the rotor determines how frequently the rotating stator field cuts the rotating rotor conductors¾so the frequency of the rotor currents is: fR = sf
The frequency of the rotor currents determines the speed of the rotor field with respect to the rotor: nRf = 120 fR /P = 120 (sf)/P = sns
The speed of the rotor field with respect to the stationary stator structure is the rotor speed plus the rotor field’s speed with respect to the rotor which is: n + nRf = (1- s)ns + sns = ns
Ergo, the rotor field and the stator field rotate together at the synchronous speed