In variable frequency drives, how is motor speed related to frequency drop?

In variable frequency drives (VFDs), the relationship between motor speed and frequency is a fundamental concept in electric motor control. The speed of an electric motor is directly related to the frequency of the electrical supply it receives.

As the frequency increases, the motor speed also increases, following a linear relationship. This is because the motor operates based on the principle that the rotational speed is proportional to the frequency of the alternating current (AC) supplied to it. For most AC induction motors, the synchronous speed can be calculated using the formula:

[ \text{Speed (RPM)} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of poles}} ]

From this formula, it is clear that an increase in frequency results in an increase in speed, while a decrease in frequency results in a decrease in speed. Therefore, when the question refers to how motor speed relates to frequency drop, it correctly identifies that motor speed is directly proportional to the frequency. A reduction in frequency will proportionally reduce the motor's operating speed, which makes option C the right choice.

This understanding is critical in applications that use VFDs to control motor operations, allowing for precise adjustments in speed to match process requirements.