How is motor speed related to frequency in single-phase motors?

How is motor speed related to frequency in single-phase motors?

• A. Speed is independent of frequency
• B. Speed is inversely proportional to frequency
• C. Speed is directly proportional to frequency
• D. Speed depends solely on torque

Answer: (C)

In single-phase motors, the speed of the motor is directly related to the frequency of the supply voltage. This relationship is based on the principle that the synchronous speed of an alternating current motor is determined by the number of poles and the frequency of the electrical supply. The formula used to calculate synchronous speed is: Synchronous Speed (N_s) = (120 × Frequency) / Number of Poles. As you can see, an increase in frequency will result in a proportional increase in synchronous speed, assuming the number of poles remains constant. Therefore, if the frequency increases, the motor speed also increases, making this direct relationship essential for understanding how to control and operate single-phase motors effectively. The other options suggest different types of relationships that do not accurately reflect the behavior of single-phase motors in relation to frequency.

In single-phase motors, the speed of the motor is directly related to the frequency of the supply voltage. This relationship is based on the principle that the synchronous speed of an alternating current motor is determined by the number of poles and the frequency of the electrical supply. The formula used to calculate synchronous speed is:

Synchronous Speed (N_s) = (120 × Frequency) / Number of Poles.

As you can see, an increase in frequency will result in a proportional increase in synchronous speed, assuming the number of poles remains constant. Therefore, if the frequency increases, the motor speed also increases, making this direct relationship essential for understanding how to control and operate single-phase motors effectively.

The other options suggest different types of relationships that do not accurately reflect the behavior of single-phase motors in relation to frequency.