Slip is defined as the percentage difference between which two speeds?

Slip is defined as the percentage difference between which two speeds?

• A. (Ns - Nr)/Ns
• B. (Nr - Ns)/Ns
• C. Nr/Ns
• D. Ns/Nr

Answer: (A)

Slip is the percentage difference between the synchronous speed and the rotor speed. It shows how far the rotor lags behind the rotating magnetic field produced by the stator. The correct expression uses the difference in speeds in the numerator and the synchronous speed in the denominator: slip = (Ns − Nr) / Ns. Multiply by 100 to express it as a percent. Ns is the speed of the rotating magnetic field (synchronous speed), and Nr is the actual rotor speed. For example, with a 60 Hz, 4-pole machine, Ns = 1800 rpm. If Nr = 1750 rpm, slip = (1800 − 1750) / 1800 = 50 / 1800 ≈ 2.78%. At standstill (Nr = 0) slip = 100%; at full speed (Nr = Ns) slip = 0. This is the measure engineers use to characterize induction motors.

Slip is the percentage difference between the synchronous speed and the rotor speed. It shows how far the rotor lags behind the rotating magnetic field produced by the stator.

The correct expression uses the difference in speeds in the numerator and the synchronous speed in the denominator: slip = (Ns − Nr) / Ns. Multiply by 100 to express it as a percent. Ns is the speed of the rotating magnetic field (synchronous speed), and Nr is the actual rotor speed.

For example, with a 60 Hz, 4-pole machine, Ns = 1800 rpm. If Nr = 1750 rpm, slip = (1800 − 1750) / 1800 = 50 / 1800 ≈ 2.78%. At standstill (Nr = 0) slip = 100%; at full speed (Nr = Ns) slip = 0. This is the measure engineers use to characterize induction motors.