Electrical Engineering MCQ on AC Motors
AC motor while operating on variable frequency supply requires variable voltage in order to
- Avoid effect of saturation
- Shield the insulation
- Improve the capabilities of the inverter
- Protect thyristor from dv/dt
Correct answer: 1. Avoid effect of saturation
Explanation:
Whenever frequency is changed, the induction motor characteristics require the applied voltage to be proportionally adjusted. As an example, if a motor is designed to operate at 440 Volts at 50 Hz, the applied voltage must be reduced to 230 Volts when the frequency is reduced to 25 Hz.
The ratio of volts per hertz must be regulated to keep up to a constant value (440/50 = 8.8 in this case).
If such condition is not achieved, then due to the saturation in the core, the machine can get the magnetized soon if we continued to run the motor, the motor can be damaged.