Chapter 7 Flashcards
Explain how a DC generator produces electricity
In a DC generator, a magnetic field (created by an electromagnet) is placed in the presence of a rotating coil.
The MOVEMENT of the coil through the magnetic field causes current to be generated in the rotating coil.
Draw the output waveform of a DC generator (you can find this on the page that shows the rotation of a DC generator):
2 rainbows next to each other
What is the advantage of a “two-pole” armature in a DC generator?
Also, by using a two-pole armature, the pulsations of voltage are not as great:
What is the purpose of a “voltage regulator” in a generator circuit?
to keep the output voltage of the generator constant despite changes in electrical load.
What is the purpose of the “slip rings” in an AC generator, and why are they used rather than a commutator?
Slip rings allow the current to stay reversed when the rotating coil is upside-down when the rotating coil has rotated 180 degrees.
Draw the output of an AC generator:
SINE
Draw a schematic diagram of a three phase AC generator:
the stater coils are in a wye formation and this is where the output voltage is induced from the rotor coil.
The rotor coil uses the col symbols with the ends of the line attached to circles to show the slip rings and thick little lock where the electrical connection is made to the DC input for the rotor
Explain how the waveforms of three-phase electrical power relate to each other (in phase):
coils are 60 degrees apart from eachother normally and the wave forms are shifted 120 degrees from eachother
Why is it important to maintain an exact speed in an AC generator?
Speed regulation is critical factor, since the alternator needs to create a frequency of exactly 60Hz. This also needs to be exactly “in phase” with the other alternators connected to the power grid.
Explain the relationship between the number of stator poles and the speed in which the AC generator needs to rotate:
as stator poles increase the speed RPM decreases for the necessary 60 hertz
Explain what the “exciter” in an alternator is, and what its purpose is:
An exciter is a separate generator or alternator connected to the shaft of the alternator or actually built into the alternator. It generates the electricity that is used to power the rotor’s magnetic field.
