AC Theory 3: Lesson 6 - Understanding How The DC Generator Works Flashcards
A generator is a device that converts ______ energy into ______ energy.
a. magnetic / electrical
b. magnetic / mechanical
c. mechanical / electrical
d. mechanical / magnetic
c. mechanical / electrical
When a conductor cuts magnetic flux lines, a voltage is induced into the conductor.
True or False
True
DC generators operate on the principle of electromagnetic induction.
True or False
True
According to the left-hand rule for generators, match the correct meaning of the extended digits in the figure.
Center finger: ______
Forefinger: ______
Thumb: ______
Choices:
- Direction of Flux Field
- Direction of Induced Current
- Direction of Motion
Center finger: Direction of Induced Current
Forefinger: Direction of Flux Field
Thumb: Direction of Motion
______ voltage is being produced when the rotating conductor is parallel to the magnetic flux lines.
a. One half the maximum
b. The average voltage
c. The maximum
d. Zero
d. Zero
Maximum voltage is induced into a conductor when it cuts the magnetic field at ______.
a. 0°
b. 60°
c. 90°
d. 120°
c. 90°
______ voltage is induced into the conductor when the loop is at 0°, 180°, and 360° in relation to the field.
a. One half the maximum
b. The average
c. The maximum
d. Zero
d. Zero
When a conductor loop is continuously rotated in a magnetic field, the AC output voltage follows the ______ function.
a. cosecant
b. cosine
c. sine
d. tangent
c. sine
To convert the AC voltage from the armature to DC voltage, DC generators make use of a(n) ______.
a. armature
b. brush
c. commutator
d. pole piece
c. commutator
A ______ causes the AC voltage that is generated to appear as a DC voltage output, because it is a ring constructed of segments separated by insulating material. The connection of the generator loop to these segments is such that the output is always of the same polarity.
a. brush
b. commutator
c. insulator
d. slip ring
b. commutator
When AC voltage is generated and then converted to DC voltage by use of a commutator, the voltage output is constant.
True or False
False
Note: The voltage is a pulsating DC voltage and is more commonly referred to as ripple voltage.
The frequency of the pulsating DC output voltage of a generator is ______ that of an AC generator.
a. half
b. one-fourth
c. same as
d. twice
d. twice
Note: The frequency of output, for the pulsating DC is considered to be twice that of an AC generator because the commutator maintains “+” polarity throughout 360° of rotation, which provides two ripple pulses for one AC cycle.
What is the name of the rotating member of the DC generator?
a. armature
b. brush
c. commutator
d. pole piece
a. armature
The ______ are components that make up the armature.
a. commutator
b. iron core
c. windings
d. all of the above
d. all of the above
______ is/are a type of armature winding found in generators.
a. Frogleg
b. Lap wound
c. Wave wound
d. All of the above
d. All of the above
The wires connected to the brushes of a generator are designated ______ and ______.
a. A1 / A2
b. B1 / B2
c. F1 / F2
d. S1 / S2
a. A1 / A2
Select the winding type that completes each statement.
______ wound armatures are probably the most commonly used because they are designed for moderate voltages and moderate currents.
______ wound armatures are used in machines designed for high voltage and low current.
______ wound armatures are used in machines designed for low voltage and high current.
Choices:
- Lap
- Wave
- Frogleg
FROGLEG wound armatures are probably the most commonly used because they are designed for moderate voltages and moderate currents.
WAVE wound armatures are used in machines designed for high voltage and low current.
LAP wound armatures are used in machines designed for low voltage and high current.
Which of the following statements are/is a reason brushes are usually made of carbon are:
I. Carbon is softer than copper and allows the brushes rather than the commutator to wear (the latter being more difficult to repair).
II. Carbon withstands the high temperatures that may be present because of arcing and friction.
III. Carbon, copper, and moisture form a very thin, conductive film on the commutator that lubricates and reduces wear.
a. I.
b. II.
c. II. and III.
d. I. and II.
e. I., II., and III.
e. I., II., and III.
What is the function of pole pieces installed in the generator housing?
a. To help concentrate the magnetic field
b. To help reduce vibration
c. To help regulate current
d. To help regulate voltage
a. To help concentrate the magnetic field
Once the pole pieces are mounted in the generator, the field windings are ______ the pole pieces to form an electromagnet.
a. mounted on
b. placed in
c. wound around
c. wound around
Permanent magnets are used sometimes as the field poles in small generators.
True or False
True
What are the two types of connections for generator field windings?
a. Frogleg and lap
b. Series and shunt
c. Wave and lap
d. Wye and delta
b. Series and shunt
The series field windings are made up of ______ turns with large wire, and the leads are labeled ______ and ______.
a. few / A1 / A2
b. few / S1 / S2
c. many / A1 / A2
d. many / S1 / S2
b. few / S1 / S2
Shunt field windings are connected in ______ with the armature in a generator, and the leads are tagged ______ and ______.
a. parallel / A1 / A2
b. parallel / F1 / F2
c. parallel / S1 / S2
d. series / F1 / F2
b. parallel / F1 / F2
The shunt field has a ______ resistance because it is made of ______ wire.
a. high / large
b. high / small
c. low / large
d. low / small
b. high / small
When a load is connected to a series generator, the output voltage ______.
a. decreases
b. increases
b. increases
A series generator is self-excited with residual ______.
a. current
b. magnetism
c. power
d. voltage
b. magnetism
As additional loads are connected to a series generator, the output voltage will continue to ______ until the iron in the pole pieces and armature becomes ______.
a. decrease / reluctant
b. decrease / saturated
c. increase / reluctant
d. increase / saturated
d. increase / saturated
Which of the factors listed determine the level of the output voltage of a series generator?
I. Number of turns in the armature
II. The strength of the magnetic field at the pole pieces
III. The speed of the cutting action
IV. The direction of rotation
a. I. and II.
b. I., II., and III.
c. I., II., and IV.
d. II. and III.
e. II., III., and IV.
b. I., II., and III.
Series generators would be best used with a ______ load.
a. constant
b. varying
a. constant
Self-excited shunt generators make use of ______ to start the generation process.
a. residual current
b. residual magnetism
c. residual power
d. residual voltage
b. residual magnetism
The shunt type of generator provides ______ output voltage before the load is applied.
a. maximum
b. minimum
a. maximum
As the load is increased on a shunt type generator, the output voltage will ______.
a. decrease
b. increase
a. decrease
To control the output voltage of a shunt generator, an electronic voltage regulator is installed to sense changes in the output voltage and makes adjustments to the shunt field current.
True or False
True
Compound generators make use of a ______ field winding and a ______ field winding.
a. frogleg / lap
b. frogleg / wave
c. lap / wave
d. series / shunt
d. series / shunt
Compound generators overcome the voltage regulation problems of a series generator, providing good flexibility, voltage regulation, and load control.
True or False
True
Choose the subdivision of compound generator that completes each statement.
A ______ -shunt compound generator has the shunt field in parallel with the series winding and the armature.
The ______ -shunt compound generator has the shunt field connected in parallel with the armature.
Choices:
- long
- short
A LONG -shunt compound generator has the shunt field in parallel with the series winding and the armature.
The SHORT -shunt compound generator has the shunt field connected in parallel with the armature.
Select the appropriate term that completes each statement.
Cumulative - aid
Differential - oppose
Select the appropriate term that completes each statement.
In a flat compound generator, the load voltage is ______ the no-load voltage.
In an over-compound generator, the load voltage is ______ the no-load voltage.
In an under-compound generator, the load voltage is ______ the no-load voltage.
Choices:
- less than
- equal to
- greater than
Flat - EQUAL TO
over-compound - GREATER THAN
Under-compound - LESS THAN
The greatest generator loss is due to the ______ of the windings.
a. eddy current loss
b. hysteresis loss
c. inductance
d. resistance
d. resistance
Power loss due to induced currents in the core material of a generator is called ______ loss.
a. eddy current
b. hysteresis
c. inductance
d. resistance
a. eddy current
______ loss is due to molecular friction.
a. Eddy current
b. Hysteresis
c. Inductance
d. Resistance
b. Hysteresis
Almost all power losses in a generator, with the exception of flux linkage, are manifested in the form of ______.
a. current loss
b. heat
c. reactance
d. voltage drop
b. heat
The two primary magnetic flux fields in a generator are field flux and armature flux.
True or False
True
The magnetic neutral plane will shift in the direction of the ______ rotation.
a. armature
b. field
a. armature
Note: See AC Theory textbook, Chapter 13, page 235, Figure 13-20.
To prevent a shift in the neutral plane, ______ windings are installed in the generator to cancel the effects of self-induction in the armature.
a. compensating
b. interpole
c. Thomson-Ryan
d. all of the above
d. all of the above
When DC generators are connected in parallel, an equalizing connection is used to connect the ______ fields of the two machines in ______ with each other.
a. parallel / series
b. series / parallel
b. series / parallel
If two DC generators are simply connected in parallel without an equalizer connection, one generator will take the load and the second generator will act as a DC motor, drawing current from the first generator.
True or False
True
