[L7]_ELECTRICITY & GENERATORS Flashcards
ENGY-688
Who observed a magnet move due to an electric current in 1820?
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Hans Christian Oersted.
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ENGY-688
Why is induction in transformers important in electrical systems?
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It’s used to increase or decrease the voltage of alternating current in a system.
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ENGY-688
What determines the rotor’s alignment with the stator in a synchronous generator under zero load?
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The poles of the stator’s magnetic field align radially with the rotor’s poles.
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ENGY-688
Even when no power is delivered to the grid by the generator, what is the grid still supplying to the stator of a synchronous generator?
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Current to energize the magnetic field of the stator.
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ENGY-688
In newer designs of synchronous generators, how is the placement of the magnet and armature changed?
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The magnet is on the stator and is coupled to the hub, while the armature is on the rotor and is stationary.
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ENGY-688
Why are variable speed generators more efficient for capturing wind energy?
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They can operate at peak power for all wind speeds below the rated wind speed.
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ENGY-688
Why do DDSG generators produce more torque than a 1500 rpm induction generator when comparing at the same power?
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The rotation speed of DDSG turbines is much lower.
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ENGY-688
In asynchronous generators, what is the significance of the air gap in the core?
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It allows the magnetic field to travel between the stator and the rotor.
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ENGY-688
What happens in an asynchronous generator when the rotor speed and stator are in sync?
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The slip is zero.
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ENGY-688
Why are soft starters used in induction generators?
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To control the flow of current during startup, reducing cost and damage to the equipment.
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ENGY-688
Why are capacitor banks deployed in asynchronous generators?
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To reduce the need for reactive power from the grid and thus reduce costs.
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ENGY-688
What challenges arise when trying to make traditional induction generators variable speed?
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They operate with a very small range of slip, meaning their rotor speed is almost constant.
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ENGY-688
How do asynchronous generators differ from synchronous ones regarding the source of their magnetic fields?
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Asynchronous generators’ magnetic fields come from the stator connected to the grid, not from an internal DC source.
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ENGY-688
Why are DDSG generators’ rotors large?
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To accommodate the large number of poles.
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ENGY-688
What is the function of a rectifier in a variable speed synchronous generator system?
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Convert variable AC to DC.
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