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Slip

The rotor of an induction motor runs slightly slower than the magnetic field. The difference is called slip. Without slip no current would be induced in the rotor, and the motor would produce no torque. Typical slip is 2–6 % at full load.

s=ns−nnss = \frac{n_s - n}{n_s}slip
n=ns(1−s)n = n_s(1 - s)rotor speed

Symbols

ssslip
nnrotor speedrpm
nsn_ssynchronous speedrpm

Example

ns=1500n_s = 1500 and 4 % slip:

n=1500⋅0.96=1440n = 1500\cdot 0.96 = 1440 rpm.

Slip increases with load. At no load there is almost no slip.
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Part of Electric Power and Machines: Electric motors.