While standing an "at sea watch" onboard an AC diesel-electric drive ship with a synchronous propulsion motor, you notice that the kwatt load is at roughly 75% of capacity with a leading power factor less than 1. Ideally what would be the character of the power factor associated with the main power distribution including all motors?
• Power factor on AC shipboard power systems • Difference between leading and lagging power factor for motors and generators • Why generators are usually operated near unity power factor and what happens if they go too far leading or lagging
• Think about whether large propulsion motors and most shipboard loads (lighting, induction motors, transformers) naturally make the system lead or lag if not corrected. • If the power factor is too far from the ideal value, what happens to current in the generator windings and heating losses for the same kW output? • For overall ship power management, what power factor target gives the best efficiency and least strain on the generators and distribution system?
• Identify whether most AC motors on board (induction motors) draw magnetizing current that is naturally leading or lagging. • Recall what a synchronous motor can be used for besides mechanical drive (hint: power factor correction). • Decide what the power management manual or generator manufacturer would typically recommend as the preferred power factor setpoint for normal operation.
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