Question 116Electricity & Electronics - 1st Asst/Chief

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On an older two-generator, two-motor DC diesel-electric drive system as shown in the illustration, what are the characteristics of the main propulsion generators? Illustration EL-0141

Diagram for USCG Electrical Chief: On an older two-generator, two-motor DC diesel-electric drive system as shown...
AThe generators of are the direct current type whose output voltage is varied by varying the generator rotational speed and whose output polarity is reversed by reversing the generator armature direction of rotation.
BThe generators of are the direct current type whose output voltage is varied by varying the generator field strength and whose output polarity is reversed by reversing the generator field polarity.
CThe generators of are the alternating current type whose output voltage is varied by varying the generator rotational speed and whose output phase sequence is reversed by reversing the generator rotating field direction of rotation.
DThe generators of are the alternating current type whose output voltage is varied by varying the generator field strength and whose output phase sequence is reversed by reversing the generator field polarity.
AI Explanation

The correct answer is B. The generators in a two-generator, two-motor DC diesel-electric drive system are direct current (DC) generators. The output voltage of these DC generators is varied by varying the generator field strength, not the rotational speed. Additionally, the output polarity of the DC generators is reversed by reversing the generator field polarity, not the generator armature direction of rotation. The other options are incorrect because they either describe alternating current (AC) generators instead of DC generators, or they incorrectly state that the output voltage is varied by changing the rotational speed or that the polarity is reversed by changing the armature direction of rotation.

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Official Resources
46 CFR Electrical Engineering 46 CFR Machinery & Electrical USCG National Maritime Center
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