Question

How to calculate slip RPM?

Answer 1

Slip RPM is the difference between the **synchronous speed (Ns)** and the **actual rotor speed (N)** in an induction motor. It represents the relative speed at which the rotor moves compared to the rotating magnetic field.

### **Formula for Slip RPM:**
\[
\text{Slip RPM} = N_s - N
\]

Where:
- **Ns** = Synchronous speed (RPM)  
- **N** = Rotor speed (RPM)

### **How to Calculate Synchronous Speed (Ns)?**
Synchronous speed is given by:

\[
N_s = \frac{120 \times f}{P}
\]

Where:
- **f** = Supply frequency (Hz)  
- **P** = Number of poles of the motor  

### **Example Calculation**
Let’s say:
- **Supply frequency (f) = 50 Hz**
- **Number of poles (P) = 4**
- **Rotor speed (N) = 1440 RPM**

1. **Find synchronous speed (Ns):**
   \[
   N_s = \frac{120 \times 50}{4} = 1500 \text{ RPM}
   \]

2. **Find slip RPM:**
   \[
   \text{Slip RPM} = 1500 - 1440 = 60 \text{ RPM}
   \]

Thus, the slip RPM is **60 RPM**.

Would you like help calculating slip percentage as well?