DC Machines Flashcards
(18 cards)
Describe the difference between separately excited and self-excited fields.
Separately excited is from an external DC source & self-excited is from the armature of the generator itself.
What are small generators that use permanent magnets for field excitation are called ?
Magnetos
Which field windings are made of a low number of turns of large-gauge wire?
Series Field Windings
What does the buildup of voltage in a self excited generator require?
Residual magnetism.
List 5 factors that influence generated voltage.
- Number of Poles
- Flux per pole
- Rotational speed of the armature
- Number of paths
- Total number of active conductors on the armature.
Which of the factors that influence generated voltage can be varied in an operating generator?
- Rotational speed of the armature.
- Flux per pole.
The value of field resistance that will limit field current to a value insufficient for voltage buildup is called :
Critical Value of Field Resistance.
Define Armature Reaction.
When an armature is delivering current to a load, a magnetic field surrounds the armature conductors.
Interpole coils are connected:
In series with the armature.
Interpole coils consist of a:
Small number of turns of large gauge wire.
List the three types of power loss in a generator.
- Mechanical Losses
- Electrical Losses
- Magnetic (Core) Losses
How is the effect of eddy currents minimized in the construction of DC machines?
By laminating the core materials.
What are the three classifications of COMPOUNDING?
- Under Compound: Efl < Enl
- Flat Compound: Efl = Enl
- Over Compound: Efl > Enl
EMF is actually produced in a generator by:
Conductors cutting flux.
If a generator was equipped with slip rings the load circuit would receive:
AC Voltage.
A separately excited shunt generator has a decrease in terminal voltage with a decrease in load. True or False?
FALSE, decrease in terminal voltage with an INCREASE in load.
Flux distortion due to armature reaction causes the electrical neutral plane in a generator to:
Move in the direction of rotation.
Why are interpoles used in generators?
To reduce sparking at the brushes.
