Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

What is the outcome if a four-pole motor operates at a frequency of 50 Hz?

1. 1500 rpm

2. 1800 rpm

3. 1200 rpm

4. 2400 rpm

The correct answer is: 1500 rpm

To determine the speed of a four-pole motor operating at a frequency of 50 Hz, it is essential to use the formula for synchronous speed, which is given by: \[ \text{Synchronous Speed (RPM)} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}} \] In this case, if we input the values: - Frequency = 50 Hz - Number of Poles = 4 Substituting these into the formula results in: \[ \text{Synchronous Speed} = \frac{120 \times 50}{4} = \frac{6000}{4} = 1500 \text{ RPM} \] This calculation shows that a four-pole motor running at a frequency of 50 Hz operates at a synchronous speed of 1500 RPM, which matches the answer selected. Higher speeds such as 1800 RPM and 2400 RPM are achievable but would correspond to motors with different pole counts, where 1800 RPM typically aligns with a 6-pole motor at 60 Hz and 2400 RPM with a 2-pole motor at 60 Hz. The speed of 1200 RPM is associated with