1. What is the 3-Phase Motor RPM Equation?

The 3-phase motor RPM equation calculates the rotational speed of an AC induction motor based on the electrical 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 3-phase motor RPM equation:

Where:

• \( RPM \) — Revolutions per minute
• \( f \) — Frequency of the power supply (Hz)
• \( p \) — Number of poles in the motor (always an even number)

Explanation: The 120 factor comes from converting cycles per second to minutes (60 seconds) and accounting for the three-phase nature of the power supply (2 poles per phase).

3. Importance of RPM Calculation

Details: Knowing a motor's RPM is essential for proper application matching, speed control, and mechanical system design. It affects torque, power output, and efficiency.

4. Using the Calculator

Tips: Enter the power supply frequency in Hz (typically 50 or 60 Hz) and the number of poles in the motor (common values are 2, 4, 6, or 8 poles). All values must be valid (frequency > 0, poles ≥ 2 and even).

5. Frequently Asked Questions (FAQ)

Q1: Why is the number of poles always even?
A: In 3-phase motors, poles come in pairs (north and south) for each phase, so the total number is always even.

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

Q3: What RPM can I expect from a 4-pole motor at 60Hz?
A: 1800 RPM synchronous speed (about 1750 RPM actual speed accounting for slip).

Q4: How does voltage affect RPM?
A: Voltage doesn't directly affect RPM in induction motors. RPM is primarily determined by frequency and poles.

Q5: Can this be used for single-phase motors?
A: No, single-phase motors have different speed characteristics and often require capacitors to start.