Its about electrical power and machines

1. Lecture 08
Ms. Hinduja Durairaj
EEE2306 - Electrical Power and Machines
DC MACHINES

2. Introduction

3. Introduction

4. Basic Structure of DC Machines

5. Armature Winding Of A DC Machine
• Basically armature winding of a DC machine is wound by one of the two methods:
• The difference between these two is merely due to the end connections and
commutator connections of the conductor.

6. Armature Winding Of A DC Machine
To know how armature winding is done, the following terminologies are essential:
➢ Pole pitch: It is defined as number of armature slots per pole.
For example, if there are 36 conductors and 4 poles, then the pole pitch is 36/4=9.
➢ Coil span or coil pitch (Yc):
It is the distance between
the two sides of a coil measured
in terms of armature slots.

7. Armature Winding Of A DC Machine
➢ Front pitch (Yf):
It is the distance, in terms of armature conductors, between the
second conductor of one coil and the first conductor of the next
coil. OR it is the distance between two coil sides that are
connected to the same commutator segment.
➢ Back pitch (Yb):
The distance by which a coil advances on the back of the armature
is called as back pitch of the coil. It is measured in terms of
armature conductors.
➢ Resultant pitch (Yr):
The distance, in terms of armature conductor, between the
beginning of one coil and the beginning of the next coil is called as
resultant pitch of the coil.

8. Lap Winding
• This is called a lap winding, because as the winding progresses, the coil laps back on
itself. It progresses in a continuous loop fashion.
• In a simplex lap winding, the two ends of a coil are connected to adjacent commutator
segments.
• It is useful for low voltage and high current machines.
• All the conductors in a group are connected
in series and all such groups are connected in parallel.
Number of parallel paths (A) = Number of Poles(P)

9. Lap Winding
• In a four-pole machine, there are four parallel paths between the positive and negative
terminals of the armature.
• In a lap winding, the number of parallel paths (A) is always equal to the number of
poles (p), and also to the number of brushes.

10. Lap Winding
• The winding may be progressive or retrogressive.

11. Lap Winding
• The winding may be progressive or retrogressive.
• A progressive winding progresses in the direction in which the coil is wound.
• The opposite way is retrogressive.

12. Wave Winding
• A conductor under one pole is connected at the back to a conductor which occupies an
almost corresponding position under the next pole which is of opposite polarity.
• This winding will create only two parallel paths independent of the number of poles.
• Wave winding is useful for high voltage low current capacity machines
• The number of parallel paths for
wave winding will be
less than that for lap winding.
Number of parallel paths (A) = 2

13. Wave Winding
• In a four-pole machine, there are only two parallel paths between the positive and
negative terminals of the armature.
• In a wave winding, the number of parallel paths (A) is always two.

14. Difference between Lap and Wave Winding

15. Armature Winding Of A DC Machine
• Armature winding can be done as single layer or double layer.
• It may be simplex, duplex or multiplex, and this multiplicity increases the number of
parallel paths.

17. Armature Voltage
• As the armature rotates in the magnetic field produced by the stator poles, voltage is
induced in the armature winding.
• Lets considering the induced voltage in the coils due to change of flux linkage
(Faraday’s law) or by using the concept of “conductor cutting flux.”
• A turn is made of two conductors, the induced voltage in a turn is:

18. Armature Voltage

19. Armature Voltage

20. Armature Voltage
The voltages induced in all the turns connected in series for one parallel path across the
positive and negative brushes will contribute to the average terminal voltage.

21. Armature Voltage
• Z is the total number of conductors in the armature winding.
• This expression for induced voltage in the armature winding is independent of whether
the machine operates as a generator or a motor.
• In the case of generator operation, it is known as a generated voltage, and in motor
operation it is known as back emf (electromotive force).