Generators Flashcards
Why do DC machines have a DC output even though they have AC currents?
Because they Have commutators attached that convert AC current to DC current that is why they’re called commutating machinery.
What is the function of the brushes for DC machines?
They connect the rotor to an external circuit and they provide sliding contact between the commutator and power supply.
Explain the design of the commutator?
- It is mounted on the same shaft as the motor
- Its copper segments are insulated by mica material
- The end of each segment has a flag attached the coil endings are welded to these flags
What is the eqn of the number of conductors of the armature winding?(Z)
Z=2C*NC
- C is the number of coils
- NC is the number of turns
What is the number of parallel paths for the lap and for the wave windings?
Lap: 2a=2p
Wave: 2a=2
What is the general rule of the induced emf?
e=l*(v*ß)
ß=flux density
v=velocity of the wire
l=length
Describe the theory of operation of DC generators?
- An external source is connected to the field widing and this produces a magnetic flux
- An external prime mover is used to rotate the rotor which then cuts the magnetic field to produce a volt which is AC
- The volt is converted to DC by the commutator
- The brushes transfer the power to the load
- The commutator and brushes rotate in a way to act as a short circuit to keep the current DC
What are the Eqns of the Voltage(EA) for the DC generator?
- EA=KØn
- EA=KnIA
K=(2p/2a)*(Z/60)
Z= No. of conductors
Draw the power flow diagram of the Generator?
Draw the seperately excited generator and explain how we can control VT and how it works?
Draw the shunt generator and explain how we can control VT and how it works?
Draw the series generator and explain how we can control VT and how it works?
Draw the long Shunt compound generator?
Draw the short Shunt compound generator?
