How this calculator works
Mechanical shaft power equals torque times angular speed. Electrical input power should first be multiplied by motor efficiency to obtain shaft power. A rotating stator field completes two electrical cycles per pole pair, so synchronous speed depends on supply frequency and pole count. Slip compares rotor speed with that field speed. Negative slip describes a rotor running above synchronous speed, as in generation.
Formula
Pshaft = tau omega = 2 pi n tau, with n in rev/s. ns = 2 f/poles = 120 f/poles rpm. Slip s = (ns - nloaded)/ns.
Worked example
A shaft delivering 100 pi W at 50 rev/s has torque 1 N m. A four-pole motor on 60 Hz has synchronous speed 30 rev/s or 1800 rpm; a loaded speed of 29 rev/s gives slip 3.3333%.
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Frequently asked questions
Which power belongs in the torque formula?
Use mechanical shaft output. Electrical input includes losses and overstates torque unless efficiency is applied.
Why are poles even?
Magnetic poles form north-south pairs, so the count must be an even positive integer.
Can slip be negative?
Yes. It means the rotor exceeds synchronous speed. The formula also allows slip above one for reverse rotation, although this form accepts nonnegative loaded speed.