Motor Speed / Poles / Slip
Find synchronous speed from supply frequency and pole count, then actual speed from slip; or back-calculate slip and slip frequency from measured speed.
Key points
Motor Speed / Poles / Slip: Find synchronous speed from supply frequency and pole count, then actual speed from slip; or back-calculate slip and slip frequency from measured speed. Formula: n_s = 120f/p ｜ s = (n_s − n)/n_s ｜ f₂ = s·f. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. Synchronous speed depends only on frequency and pole count; an induction motor runs slightly slower, and that fractional difference is slip. Ordinary 50/60 Hz induction motors have about 1–5% rated slip; deep-well / high-slip motors can be higher. A sudden increase often means overload or low voltage.
Inputs
n_s = 120f/p ｜ s = (n_s − n)/n_s ｜ f₂ = s·fCalculation model (updates with parameters)
| Synchronous speed n_s | 1500 r/min | 120f/p = 120×50/4 |
| Rated / actual speed n | 1455 r/min | n_s×(1−s) |
| Slip s | 3.00 % | 普通异步motor额定点常 1~5% |
| Slip frequency f₂ | 1.5 Hz | 转子currentFrequency = s·f |
| Mechanical angular speed ω | 152.37 rad/s | ω = 2πn/60 |
| Time per revolution | 41.24 ms | 60/n |
| Pole pairs at synchronous speed | 2 对 | p 为极数，极对数为 p/2 |
Engineering notes
- Synchronous speed depends only on frequency and pole count; an induction motor runs slightly slower, and that fractional difference is slip.
- Ordinary 50/60 Hz induction motors have about 1–5% rated slip; deep-well / high-slip motors can be higher. A sudden increase often means overload or low voltage.
- With a VFD, n_s changes with f; at low frequency watch motor cooling and torque reduction (constant-torque / constant-power regions).
FAQ
- What is Motor Speed / Poles / Slip for?
- Find synchronous speed from supply frequency and pole count, then actual speed from slip; or back-calculate slip and slip frequency from measured speed.
- What is the formula for Motor Speed / Poles / Slip?
- Core formula: n_s = 120f/p ｜ s = (n_s − n)/n_s ｜ f₂ = s·f. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Motor Speed / Poles / Slip?
- Synchronous speed depends only on frequency and pole count; an induction motor runs slightly slower, and that fractional difference is slip. Ordinary 50/60 Hz induction motors have about 1–5% rated slip; deep-well / high-slip motors can be higher. A sudden increase often means overload or low voltage. With a VFD, n_s changes with f; at low frequency watch motor cooling and torque reduction (constant-torque / constant-power regions).