Which of the following statements is true concerning a large polyphase synchronous main propulsion motor as used in an electric propulsion drive system?
• Synchronous motor starting methods in large ship propulsion systems • Difference between induction motors vs synchronous motors (especially what happens at start vs at synchronous speed) • Behavior of starting current in large AC motors
• Think about how a synchronous motor develops torque when it is at standstill. Does the field winding alone produce starting torque, or is another principle used? • Which type of motor can produce starting torque from slip between rotor speed and stator rotating field? How might a synchronous motor use this property? • For large AC motors, is starting current usually higher or lower than the rated running current if no special starting equipment is used?
• Verify what is done with the field winding during start on a large synchronous propulsion motor (is it energized, de-energized, or handled differently?). • Confirm whether a rotor resistance changing during start is a feature of wound-rotor induction motors, synchronous motors, or something else. • Check typical starting current characteristics of large synchronous and induction motors: does starting current normally exceed or stay below full-load current?
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