DC Motors Flashcards
What’s a nested branch?
A parallel circuit within a circuit
If given a confusing diagram, how can you make it easier and draw it out?
Write an A following one line that’s the same; after crossing a load, make it B. And then see where all the letters line up and can see what’s parallel and series and what not.
If a load is down stream of another load, are the positive ends of both loads the same?
No they’re just positive relative to the load itself (ie more positive than the negative side of the load).
If current splits evenly in a parallel circuit, we know the resistance of both branches is.
The same.
Describe the left hand conductor rule
If current flows away from you (x or
Plus sign, rather than dot, which means away) then thumb shows current direction North Pole and fingers wrap the conductor, showing the direction of the magnetic flux field.
Describe the left hand coil rule
Fingers wrap coil in same direction (neg to pos) as current, thumb indicates North Pole
In what polarity does flux flow?
North to south externally. South to North internally.
Where does flux concentrate in a core? Why?
At the ends. Conductors around a coil induce flux, and flux concentrates at poles as it travels externally from one pole to another.
Characteristic of flux. Name 5.
1) travel North to south externally (this is direction; not polarity)
2) lines never cross each other
3) align parallel and repel side by side
4) pass through everything
5) concentrates into highly permeable paths (ie soft steel)
6) has eleasticity
7) always pull and tighten to smallest possible size
What’s the formula for Egenerated ina generator?
E gen is equal to flux of the field, times length of the conductor, times rpm.
What are the components of a generator?
1) field yolk (pathway for flux; houses other components and is big)
2) pole core (flux travels pole to pole via field yolk; eddy currents limited by laminations in pole core)
3) armature (rotates on a shaft and contains conductors)
4) rotor shaft
5) conductors
6) commutator (rotates with armature and shaft. Conductors laterally spun around armature go back to the commutator where a brush (1-2 pounds per sq inch pressure) attaches to soldered on pig tails a1 a2)
7) bearing
8) end bells (hold bearing and support armature).
If brushes are too loose, then what? What if they’re too tight?
1) arcing and pitting damages commutator
2) brushes break.
What’s the left hand gen rule?
1)index finger is direction of field flux
2) thumb is direction of conductor with respect to flux
3)middle fingers direction of current
What’s neutral plane?
Space where no voltage (and thus no current) is developed.
Where is ac converted into dc ina genarator?
At the commutator.
A generator creates ac before the commutator. T or f.
T.
Permanent magnet generator is called a
Magneto.
A magneto has fixed flux and field conductor length on the windings.
True.
The l in blv refers to armature or windings?
Windings.
What does the l refer to in blv?
The length of the conductor in the armature being cut by flux.
In a separately excited generator, what terminals are there that are not present in a magneto?
The f1 and f2 shunt windings; magneto only has a1 and a2 windings.
What can be changed in a separately excited generator in the blv formula?
The b aka the windings with a dc source that is separate applies to them (changed via the fixed rheostat in series with the dc windings).
Is there flux in a seperately excited generator?
Yea, but it’s current in the separate windings causing magnetization.
What is easy to vary in a self excitedbgenerator?
The field windings.