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Test Bank For Electricity 3: Power Generation and Delivery - 10th - 2014 All Chapters - 9781111646738
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Test Bank For Electricity 3: Power Generation and Delivery - 10th - 2014 All Chapters
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Test Bank For Electricity 3: Power Generation and DeliveryUnit 1: Operating Principles of DC Generators
Unit 1: Operating Principles of DC Generators
TRUE/FALSE
1. The member of a DC generator that spins is called the rotor.
ANS: T PTS: 1 REF: DC Generator Components
2. The commutator is used to change the DC voltage induced in the armature windings to AC voltage
at the generator output terminals.
ANS: F PTS: 1 REF: DC Generator Components
3. In all but a few instances, the output voltage is controlled by varying the field current in the field
circuit.
ANS: T PTS: 1 REF: Output Voltage Control
4. A self-excited generator develops voltage for either direction of rotation.
ANS: F PTS: 1 REF: Rotation
5. All generators have the same voltage regulation characteristics.
ANS: F PTS: 1 REF: Regulation
COMPLETION
1. The ____________________ is the component of the generator that has the voltage (EMF)
induced into it.
ANS: armature
PTS: 1 REF: DC Generator Components
2. The armature ____________________ generate voltage by cutting a magnetic field as the armature
rotates.
ANS: windings
PTS: 1 REF: DC Generator Components
3. Brush polarity markings are often omitted, but the electrician can easily determine electrical
polarity by connecting a(n) ____________________ across the output leads of the generator.
1
,Test Bank For Electricity 3: Power Generation and Delivery
Unit 1: Operating Principles of DC Generators
ANS: voltmeter
PTS: 1 REF: DC Generator Components
4. The magnetic field of a generator is established by a set of ____________________.
ANS:
electromagnets
field poles
PTS: 1 REF: DC Generator Components
5. Generator ratings as specified by the manufacturer shall be found on the ____________________
of the machine.
ANS: nameplate
PTS: 1 REF: Generator Ratings
SHORT ANSWER
1. What is the reason that a generator takes more mechanical power to drive a heavy current load than
a light current load?
ANS:
The reason that a generator takes more mechanical power to drive a heavy current load than a light
current load is that the larger the load current through the generator, the larger the counter torque
produced.
PTS: 1 REF: DC Generator Components
2. What is done to counteract armature reaction?
ANS:
To counteract this effect, commutating poles are often inserted between the main field poles.
PTS: 1 REF: DC Generator Components
3. In the case of generators, what is the difference between brush polarity and electrical polarity of
the brushes?
ANS:
In the case of generators, the term brush polarity is used to distinguish between the electrical
polarity of the brushes, either positive or negative, and the magnetic polarity, either north or south,
of the field poles.
PTS: 1 REF: DC Generator Components
2
,Test Bank For Electricity 3: Power Generation and Delivery
Unit 1: Operating Principles of DC Generators
4. Why is it possible to vary the output voltage by controlling either the speed of the prime mover or
the strength of the magnetic field?
ANS:
Because the induced voltage into the armature depends on the rate at which the magnetic lines of
force are cut per second, it is possible to vary the output voltage by controlling either the speed of
the prime mover or the strength of the magnetic field.
PTS: 1 REF: Output Voltage Control
5. What generator ratings are generally specified by the manufacturer?
ANS:
The manufacturer generally specifies the kilowatt output, current, terminal voltage, and speed of
the generator.
PTS: 1 REF: Generator Ratings
3
, Test Bank For Electricity 3: Power Generation and Delivery
Unit 2: Separately Excited DC Generator
Unit 2: Separately Excited DC Generator
TRUE/FALSE
1. The brush polarity in a separately excited generator cannot be changed by reversing the rotation of
the armature or the direction of the field current.
ANS: F PTS: 1 REF: Brush Polarity
2. If both the armature direction and the direction of the field current change, the brush polarity
remains the same.
ANS: T PTS: 1 REF: Brush Polarity
3. The magnitude of the voltage depends on the rate at which the flux is cut.
ANS: T PTS: 1 REF: Output Voltage
4. Field control of the output voltage is accomplished by varying the total resistance of the field
circuit with a field rheostat.
ANS: T PTS: 1 REF: Output Voltage
5. Brush polarity changes when the field current is zero.
ANS: F PTS: 1 REF: Residual Voltage
COMPLETION
1. If the machine is stopped and then driven in the opposite direction, the ____________________ is
cut in the opposite direction and the brush polarity changes.
ANS: field flux
PTS: 1 REF: Brush Polarity
2. In a separately excited generator, an output voltage increase is ____________________ to an
increase in the armature speed.
ANS: proportional
PTS: 1 REF: Output Voltage
3. The output voltage of a separately excited generator can be varied by adjusting the speed of the
____________________ or the field current.
4
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