🔍 Key Concepts

• Study the components connected directly to each propulsion motor in the diagram, especially the items labeled Excitation Transformer and Field Controller. • Recall which type of AC motor requires an external DC field excitation to operate at a constant speed synchronized with supply frequency. • Consider which listed motor types are commonly used as large ship propulsion motors in diesel-electric AC systems with synchro‑/cycloconverters.

💭 Think About

• From the illustration, trace the path from the main switchboard, through the propulsion transformers and syncro-converters, to the propulsion motor. What extra power supply goes to the motor besides the main AC power? • Ask yourself: which of the choices needs a separate excitation system for its rotor, and which ones have their rotor current induced without an external DC supply? • Which motor type among the choices is typically used with variable‑frequency converter systems to provide controllable speed and high torque for large propulsion loads?

✅ Before You Answer

• Verify whether the propulsion motor symbol has an associated excitation transformer and field controller providing what appears to be DC power to the rotor/field windings. • Eliminate any motor types that do not require external field excitation (they get all rotor current by induction from the stator). • Confirm that AC/DC universal motors are generally small, high‑speed machines and are not normally used as multi‑megawatt ship propulsion motors.