What happens to the speed of a synchronous motor when the frequency of supply changes?

What happens to the speed of a synchronous motor when the frequency of supply changes?

• A. The speed remains constant
• B. The speed decreases
• C. The speed increases
• D. The speed can vary significantly

Answer: (B)

The speed of a synchronous motor is directly linked to the frequency of the AC supply. Synchronous motors operate at a speed that is determined by the number of poles in the motor and the frequency of the supply voltage, as expressed in the formula: Speed (RPM) = (120 × Frequency in Hz) / Number of Poles. When the frequency of the supply changes, the synchronous speed of the motor also changes in a direct relationship. For instance, if the frequency decreases, the synchronous speed will also decrease; if the frequency increases, the synchronous speed will increase accordingly. In this context, if the frequency were to decrease, the speed would indeed decrease as a result. This fundamental characteristic is critical in applications where precise speed control of the motor is necessary, emphasizing the synchronous motor's dependence on the supply frequency for its operational speed.

The speed of a synchronous motor is directly linked to the frequency of the AC supply. Synchronous motors operate at a speed that is determined by the number of poles in the motor and the frequency of the supply voltage, as expressed in the formula:

Speed (RPM) = (120 × Frequency in Hz) / Number of Poles.

When the frequency of the supply changes, the synchronous speed of the motor also changes in a direct relationship. For instance, if the frequency decreases, the synchronous speed will also decrease; if the frequency increases, the synchronous speed will increase accordingly.

In this context, if the frequency were to decrease, the speed would indeed decrease as a result. This fundamental characteristic is critical in applications where precise speed control of the motor is necessary, emphasizing the synchronous motor's dependence on the supply frequency for its operational speed.