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Electric Motor Speed Formula:
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The electric motor speed formula 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.
The calculator uses the motor speed equation:
Where:
Explanation: The formula shows that motor speed is directly proportional to frequency and inversely proportional to the number of poles. The constant 120 comes from converting seconds to minutes (60) and accounting for the fact that each AC cycle produces two poles (60×2=120).
Details: Knowing a motor's synchronous speed is crucial for proper equipment selection, performance analysis, and troubleshooting. It helps determine if a motor is suitable for a specific application where certain speeds are required.
Tips: Enter frequency in Hz (typically 50 or 60 Hz for mains power) and number of poles (always an even number - common values are 2, 4, 6, or 8 poles). All values must be valid (frequency > 0, poles ≥ 2 and even).
Q1: Why is the number of poles always even?
A: AC induction motors require pairs of magnetic poles (north and south) to function, so the pole count is always an even number.
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: How does this apply to variable frequency drives?
A: VFDs change motor speed by varying the frequency while keeping the voltage/frequency ratio constant.
Q4: What are typical motor speeds?
A: For 60Hz systems: 3600 RPM (2-pole), 1800 RPM (4-pole), 1200 RPM (6-pole). For 50Hz systems: 3000 RPM, 1500 RPM, 1000 RPM respectively.
Q5: Does this formula work for DC motors?
A: No, DC motor speed depends on applied voltage and load torque, not on poles and frequency.