Motor slip is the difference between the synchronous speed of the magnetic field and the actual rotor speed in an induction motor, expressed as a percentage. It is essential for torque production — without slip, there would be no induced current in the rotor and therefore no torque.

What are typical slip values for induction motors?

Typical full-load slip values range from 1% to 5% for standard induction motors. Small motors (fractional HP) may have slip up to 5-8%. Large motors typically have lower slip around 1-2%. NEMA Design B motors have slip of 1-5%, while Design D motors have slip of 5-13%.

Why does slip exist in induction motors?

Slip exists because the rotor must turn slower than the rotating magnetic field to induce a voltage (and current) in the rotor bars. This relative motion between the field and rotor is what produces torque. At synchronous speed (zero slip), there would be no relative motion, no induced EMF, and no torque.

How does load affect motor slip?

As mechanical load increases, the motor slows down, increasing slip. Higher slip means more relative motion between rotor and stator field, inducing more rotor current and producing more torque to match the load. At no load, slip is very small (0.5-1%). At full load, slip reaches nameplate value (typically 2-5%).

How to measure motor slip?

Motor slip can be measured by: 1) Using a tachometer or stroboscope to measure actual RPM and comparing to synchronous speed. 2) Using a vibration analyzer to detect slip frequency in the spectrum. 3) Reading the nameplate RPM — the difference from synchronous speed gives rated slip at full load.

免費工程工具

馬達轉差率與實際轉速計算機

計算感應馬達的同步轉速、實際 RPM、滑差百分比及滑差頻率。輸入 RPM 以計算滑差，或輸入滑差以計算 RPM。

50 / 60 Hz 2–12 極 Ns = 120f / P

結果

同步轉速

—

實際轉子轉速

—

轉差率

—

轉差頻率

—

轉子電氣頻率

—

同步轉速

感應馬達中旋轉磁場的同步轉速：

f — 電源頻率 (Hz)：50 Hz 或 60 Hz
P — 極數

轉差率

馬達滑差是同步轉速與實際轉子轉速之間的相對差異：

由滑差計算實際轉速

轉差頻率

轉子中感應電流的頻率：

同步轉速參考

極數	50 Hz (RPM)	60 Hz (RPM)
2	3000	3600
4	1500	1800
6	1000	1200
8	750	900
10	600	720
12	500	600

實務範例

範例 — 50 Hz 下的 4 極馬達

已知： f = 50 Hz, P = 4 極, 銘牌 RPM = 1450

N_s = 120 × 50 / 4 = 1500 RPM

s = (1500 − 1450) / 1500 × 100 = 3.33%

f_轉差率 = 3.33/100 × 50 = 1.67 Hz

f_轉子 = s × f = 0.0333 × 50 = 1.67 Hz

提示： 滑差頻率是振動分析中的關鍵指標。在電源頻率周圍出現 2 倍滑差頻率 (2 × f_轉差率) 的邊帶特徵振動，通常表示感應馬達存在轉子導條問題。

⚠️ 注意： 銘牌 RPM 代表滿載轉速。在部分負載下，實際轉速會較高（滑差較低）。在無負載時，滑差通常為 0.5–1%。

馬達滑差與實際 RPM 計算器 | Vibromera

結果

同步轉速

轉差率

由滑差計算實際轉速

轉差頻率

同步轉速參考

實務範例

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