DC generators Flashcards
Explain how a commutator enables a single loop generator to produce current
The commutator works by always connecting the conductor next to the north pole to brush A and the conductor next to the south pole to brush B. The resulting output is a pulsating DC voltage
Explain how armature reaction causes an increase in sparking at the commutator of a DC machine. State 2 ways of overcoming sparking.
The main field is distorted by the field created in the armature, which moves the MNA. This can be corrected by moving the brushes or using interpoles.
Show with the aid of 2 simple graphs, how the output voltages of a shunt and series DC generator change as load increases.
The graphs should have Vt on the y axis and IL on the X.
The output of a shunt falls while that of a series increases until saturation occurs.
Show with the aid of a graph the 3 different types of compounding possible in a compound DC generator.
The y axis should have Vt and the x should have IL.
Using a simple sketch describe the construction of a DC generator, labelling the main component parts.
Needs to include:
- Pole pieces
- Field coils
- Commutator
- Brushes
- Rotor
- Armature windings
- Yoke
- Base
What effect does increasing the armature speed have on the output of a generator?
Increasing the speed will increase the generated EMF
Explain how back torque is produced in a DC generator. And state the 2 factors that affect it’s magnitude.
The current produced by the generator creates it’s own magnetic field. This field interacts with the main field to produce a retarding force, this is called back torque. Back is dependent mainly on the speed of rotation and field strength (E = K N Φ )
What are the 2 main types of windings used in a DC generator armature? Which type is used for higher current output?
Lap and wave windings.
Lap is used for higher currents.
