Suggestion: Reference:
Gordon R. Slemon "Magnetolectric Devices Transducers, Transformers, and Machines," John Wiley and Sons, Inc., 1966,
page 372:
P= 2 x ws x (1-s)/n
where
P = number of motor poles, in poles
ws = 2 x pi x fs, in rad/sec synchronous angular speed
fs = synchronous frequency in Hz
s = slip, in per unit
n = rotor speed in rad/sec, (p-pole motor rotor speed)