Motor Synchronous Speed, Slip, and Rotor Frequency

The synchronous speed Ns = 120 x frequency / poles, the slip relative to the nameplate full-load speed, and the rotor (slip) frequency, for commissioning a motor, reading a VFD parameter set, or diagnosing a wrong-speed complaint. The nameplate full-load speed governs.

Ns = 120 x f / P (the 120 carries the 60 s/min x 2 poles-per-pole-pair bridge); slip = (Ns - rated_rpm) / Ns; slip_pct = slip x 100; rotor (slip) frequency = slip x f.

First-principles AC-machine speed relation; classical induction-machine theory.

First-principles physics; no licensed source required.

Estimate. AHJ and licensed professional govern.

Field names used by the API: line_freq_hz, poles, rated_rpm, sync_rpm, slip_pct, rotor_freq_hz

• Rated speed the nameplate full-load speed governs the slip; a speed near synchronous indicates a lightly loaded machine, rising slip indicates loading or a rotor faultmotor nameplate / manufacturer
• Pole count the stator pole count is an even integer (2, 4, 6, 8, ...)AC-machine construction