Question 25 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is C **Why option C is correct:** A DC (Direct Current) motor operates based on the interaction between the magnetic field produced by the field windings and the current flowing through the armature windings. The direction of rotation of a DC motor is determined by the polarity of the magnetic flux (generated by the field windings) relative to the direction of current flow in the armature. To reverse the direction of rotation (reversal of propulsion), you must reverse either the field polarity or the armature current direction, but **not both**. Reversing the direction of current flow in the motor field windings directly reverses the polarity of the magnetic field, thus reversing the torque and the direction of motor rotation. This is the standard method used for reversing large DC motors, such as those used in propulsion systems, often achieved using contactors or power electronics to switch the field current direction. **Why the other options are incorrect:** A) **the use of a shunt field regulator:** A shunt field regulator is used to control the strength of the magnetic field, which in turn controls the motor's speed (above base speed) or torque. It regulates the *magnitude* of the current but does not inherently reverse the *direction* of the current flow necessary for reversal of rotation. B) **reversing the phase sequence of the incoming voltage:** This method is used exclusively for reversing the direction of rotation of AC (Alternating Current) induction or synchronous motors. DC motors are supplied by DC voltage (or through a DC drive system) and do not have a phase sequence in the same sense as an AC supply. D) **the use of a 12-pulse converter:** A converter (such as a 6-pulse, 12-pulse, or multi-pulse converter) is a device used to change AC power into DC power (rectification) or vice versa, often used to supply the necessary DC voltage to the motor armature and field circuits. The number of pulses (12-pulse being a standard for high-power industrial and marine applications) relates to the quality and smoothness of the output DC voltage, but the converter itself does not dictate the mechanism for motor reversal; reversal is handled by switching the field or armature current within the drive system.