When does a synchronous motor experience maximum efficiency?

• A. When it operates below the supply frequency
• B. When it runs at a constant speed in sync with the supply frequency
• C. When it is subjected to periodic maintenance
• D. When it experiences varying speeds

Answer: (B)

A synchronous motor achieves maximum efficiency when it operates at a constant speed that is in sync with the frequency of the supply voltage. This means that the rotor of the motor rotates at the same speed as the stator’s magnetic field, aligning with the frequency of the electrical supply.

At this point, the motor is effectively converting electrical energy into mechanical energy, minimizing losses such as reactance and maximizing power factor. When a synchronous motor is synchronized with the supply frequency, it operates under optimal conditions where it maintains stable performance and reduces energy waste.

In contrast, running below the supply frequency may cause the motor to operate inefficiently, and experiencing varying speeds can introduce instability, leading to increased operational losses. Periodic maintenance is critical for overall performance and longevity but does not directly correlate with the efficiency that is maximized by operating in sync with the supply frequency.