Under unusual circumstances, it may be required to operate a ship's service generator above its rated kVA. What supplemental casualty control action will be required?
• Relationship between kVA load, voltage, and frequency on an AC generator • How overloading a generator affects current, heating, and insulation life • Which parameters (voltage vs. frequency) are normally held constant on a ship’s power system for motors and sensitive equipment
• If you must supply more kVA than the generator’s nameplate rating, which variable can you adjust to change the apparent power without forcing the machine to carry excessive current? • Think about what happens to motor performance and generator heating when you change voltage vs. when you change frequency. Which change is usually safer/acceptable for short-term emergency operation? • Which option would more likely reduce stator current and heating for a given kVA, and which options might actually make conditions worse or damage equipment?
• Identify which options hold voltage constant and which hold frequency constant. • Consider which change (lowering voltage vs. lowering frequency) will increase current and heating for the same real power demand. • Eliminate any choices that would likely cause condensation or moisture problems inside electrical machinery, since that is rarely acceptable as a casualty control measure.
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