Engine 2014: Electricity

1. A the motor speed is controlled by varying voltage and frequency and the direction is controlled by reversing the polarity of the motor field
2. B the motor speed is controlled by varying voltage, but keeping the frequency constant and the direction is controlled by phase sequence reversal
3. C the motor speed is controlled by varying frequency, but keeping the voltage constant and the direction is controlled by phase sequence reversal
4. D the motor speed is controlled by varying voltage and frequency and the direction is controlled by phase sequence reversal

Tip: press A-D to answer