1. What is the Electric Motor Speed Equation?

The electric motor speed equation calculates the rotational speed (RPM) of an AC induction motor based on the power supply frequency and the number of magnetic poles in the motor. This fundamental relationship helps in motor selection and performance analysis.

2. How Does the Calculator Work?

The calculator uses the motor speed equation:

Where:

• \( RPM \) — Revolutions per minute
• \( f \) — Frequency of power supply (Hz)
• \( p \) — Number of magnetic poles in motor

Explanation: The equation shows that motor speed is inversely proportional to the number of poles and directly proportional to the supply frequency.

3. Importance of RPM Calculation

Details: Knowing a motor's speed is essential for proper application matching, gear ratio selection, and performance prediction in mechanical systems.

4. Using the Calculator

Tips: Enter frequency in Hz (typically 50 or 60 Hz) and number of poles (always an even number, typically 2, 4, 6, etc.). All values must be valid (frequency > 0, poles ≥ 2).

5. Frequently Asked Questions (FAQ)

Q1: Why is the number 120 in the equation?
A: The factor 120 comes from converting seconds to minutes (60) and accounting for the fact that each AC cycle produces two magnetic pole passes (×2).

Q2: What is synchronous speed vs actual speed?
A: This calculates synchronous speed. Actual speed is slightly less due to slip (typically 2-5% less for induction motors).

Q3: How does this apply to variable frequency drives?
A: VFDs work by varying the frequency (f) to control motor speed according to this relationship.

Q4: What about DC motors?
A: This equation doesn't apply to DC motors, whose speed is controlled by voltage, not frequency.

Q5: Why are pole numbers always even?
A: Magnetic poles always come in north-south pairs, so the count must be even.