Question 247Electricity & Electronics - 1st Asst/Chief

The correct answer is C) reversing any two phase leads to the motor. In an AC diesel-electric propulsion vessel, the direction of the main shaft rotation is controlled by the rotation of the electric motor. To reverse the direction of the main shaft, the phase sequence of the power supplied to the electric motor needs to be reversed. This can be achieved by switching any two of the three phase leads connected to the motor, which will cause the motor to rotate in the opposite direction. The other options are incorrect because: A) reversing the prime mover (diesel engine) rotation does not directly affect the motor rotation, B) increasing the generator frequency would not reverse the motor rotation, and D) decreasing the generator frequency would not reverse the motor rotation.