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32 Cards in this Set
- Front
- Back
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When is voltage generated in the conductor?
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Whenever a conductor is moved within a magnetic field in such a way that the conductor cuts across magnetic lines of flux.
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The amount of voltage depends on what four conditions?
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1. Strength of the magnetic field. 2. The angle at which the conductor cuts the magnetic field. 3. The speed at which the conductor is moved. 4. The length of the conductor within the magnetic field.
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What determines the polarity of the voltage?
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The direction of the magnetic lines of flux and the direction of movement of the conductor.
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What component causes a generator to produce a DC voltage rather than an AC voltage at its output terminals?
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The commutator
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How many commutator segments are required in a two coil generator?
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four
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What are the main advantages of using an electromagnetic pole?
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Increase field strength and a means of controlling the strength of the fields.
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What is commutation?
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The process by which a DC voltage output is taken from an armature that has an AC voltage induced in it.
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What is armature reaction?
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A distortion of the main field causes a shift in the neutral plane which affects commutation.
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What are interpoles?
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A method of eliminating armature reaction.
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What is motor reaction?
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When a generator delivers current to a load, the armature current creates a magnetic force that opposes the rotation of the armature.
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What is the prime mover?
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The device that produces the turning force applied to te armature.
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WHat is copper loss?
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Power lost in the form of heat in the armature winding of the generator.
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What are eddy currents?
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Currents that are induced in the generator armature core.
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How can eddy current be reduced?
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Using armatures with laminated cores.
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What is Hysteresis loss?
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A heat loss caused by the magnetic properties of the armature.
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What is a Gramme-ring armature?
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An armature where each coil is connected to two commutator segments and each coil is in series with every other coil.
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The windings of a Gramme-ring armature are placed on what type of ring?
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An iron ring
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What is a drum-type armature?
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Armature windings are placed in slots cut in a drum shaped iron core. Each winding completely surrounds the core os the entire length of the conductor cuts the magnetic field.
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How are drum-type armatures wound?
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Lap or wave winding
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Lap winding is used for higher current or voltage application?
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High Current
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Wave winding is used for high current or voltage application?
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High voltage
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What is field excitation?
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When a DC voltage is applied to the field windings of a DC generator, current flows through the windings and sets up a steady magnetic field.
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What is a self excited generator?
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A generator that supplies its own field excitation.
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How is self excitation possible?
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When the field poles have retained a slight amount of magnetism called residual magnetism.
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What are the three types of self excited generators?
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Series-Wound, Shunt-Wound, and Compound-Wound
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Of the three Self-excited generators, which provides a constant output under varying load conditions?
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Compound-Wound generators
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What is the simplest method of controlling the terminal voltage of a DC generator?
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Using a field rheostat connected in series with the shunt field circuit.
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What kind of resistors do field rheostats use?
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Alloy wire
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In a field resistor, rotating it in the direction of the lower arrow (counterclockwise) does what to the resistance and output voltage?
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increases resistance and lowers the output voltage.
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How are generators operating when two or more are supplying a common load?
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In parallel
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What are Amplidynes
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Special purpose DC generators that supply large DC currents, precisely controlled, to large DC motors used to drive heavy physical loads.
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What is the equation for Gain?
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Gain=output/input
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