Slip is the fraction by which an induction motor's rotor turns slower than the rotating magnetic field, (ns minus n) divided by ns. Without slip no current would be induced in the rotor and no torque produced, so a four-pole motor with a synchronous speed of 1500 rpm on 50 Hz runs at about 1455 to 1485 rpm at full load, a slip of 1 to 3 percent. Slip rises with load, so measured speed is a rough guide to how hard a motor is working.
Nameplate says 1475 rpm and the tach reads 1440, the slip tells you that fan is badly overloaded.
Also heard as
- rotor slip
Related terms
Inrush current
Large transient current drawn when a transformer, motor or capacitive load is first switched on.
Bump
To energise a motor for a split second to check its direction of rotation before running it properly.
Per-unit system
Shorthand that states voltages, currents and impedances relative to chosen base values, so 1.0 means nominal.