Induction motor speed and slip
Synchronous speed from the supply frequency and the number of poles, slip from the rated speed, and the speed on a variable frequency drive — for example, of an ESP motor or a pumping unit drive.
n_s = 60 · f / ps = (n_s − n) / n_sn_2 = 60 · f_2 / p − (n_s − n)With constant V/f control and an unchanged load torque, the slip in revolutions (n_s − n) stays the same, so n_2 is slightly below a proportional estimate. With pumps the torque falls with the speed, and the slip at a reduced frequency is even smaller. Above the rated frequency the motor runs with a weakened field and the allowable torque falls.
Source: Induction machine theory: n_s = 60 · f / p
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
ESP motors are two-pole.
From the nameplate.
Without a drive, enter the supply frequency.
Unit converter for this formulaRotational speed · Fraction and percent
- rpm1
- rev/s0.0166667
- rad/s0.10472
- s — Rated slip–
- n_s — Synchronous speed–
More in Motors and transformers
Reactive power of a capacitor bank that raises the power factor from cos φ_1 to cos φ_2, and the resulting reduction of the supply current and line losses.
Design apparent power from the installed load, the demand factor and cos φ, and the transformer rating from the standard series for the allowed loading and the number of transformers in the substation.
Estimate of the voltage dip on the substation busbars during direct-on-line starting of an induction motor, and of its reduced starting torque — to check whether a large pump or compressor can be started from a given transformer.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.