Basically a D.C. machine is an alternating current machine. The e.m.f. generated in the conductor is alternating in nature. With the help of the commutator segments this alternating e.m.f. is converted into a direct one. The working of a DC generator is based on the principle that, when a conductor cuts a magnetic field, an e.m.f. is induced in the conductor. A dynamically induced e.m.f. will be produced in the conductor when it will cut the magnetic flux as per the laws of electromagnetic induction

1. DC GENERATOR & DC
MOTORS
By
Dr. M. Ajay Kumar
Associate Professor, EEE.
1
Basic Electrical Engineering

2. A DC generator converts mechanical energy
into electrical energy (DC).
The working of a DC generator is based on
the principle that, when a conductor cuts a
magnetic field, an e.m.f. is induced in the
conductor.
A dynamically induced e.m.f. will be
produced in the conductor when it will cut
the magnetic flux as per the laws of
electromagnetic induction
2
Basic Electrical Engineering

3.  If the circuit is closed this induced e.m.f.
will cause a current to flow through
circuit.
 Basically a D.C. machine is an alternating
current machine. The e.m.f. generated in
the conductor is alternating in nature.
With the help of the commutator
segments this alternating e.m.f. is
converted into a direct one.
3
Basic Electrical Engineering

4. 4
Basic Electrical Engineering

5. 1. Pole
2.Armature
3.Yoke
4.Commutator
5.Brushes
6.Interpole
5
Basic Electrical Engineering

6. 6
Basic Electrical Engineering

7. 7
Basic Electrical Engineering

8. There are two types of windings
Lap winding
• A = P
• The armature
windings are
divided into
no. of sections
equal to the no
of poles
Wave winding
• A = 2
• Used in high
voltage low
current output.
• Requires 2
brushes
8
Basic Electrical Engineering

9. 9
Basic Electrical Engineering

10. 10
Basic Electrical Engineering

11. Let, Ø= flux per pole in weber
Z = Total number of conductor
P = Number of poles
A = Number of parallel paths
N =armature speed in rpm
Eg = emf generated in any on of the
parallel path
11
Basic Electrical Engineering

12. Flux cut by 1 conductor
in 1 revolution = P * φ
Flux cut by 1 conductor in
60 sec = P φ N /60
Avg emf generated in 1
conductor = PφN/60
Number of conductors in
each parallel path = Z /A
Eg = PφNZ/60A
12
Basic Electrical Engineering

13. •Separately excited DC machine
•Self excited DC machine
 Shunt wound DC generator
 Series wound DC generator
 Compound wound
13
Basic Electrical Engineering

14. In this type of machine, the field of
the machine is excited by an
independent external source. This
source can be a battery, rectifier
circuit or a D.C. generator
14
Basic Electrical Engineering

15. Basic Electrical Engineering 15

16. V be the field excitation voltage
Rf be the field resistance.
If be the field current
Eg be the generated e.m.f.
in the armature
Ra be the armature resistance
Ia be the armature current
IL be the load current
VL be the load voltage
16
Basic Electrical Engineering

17. In this type of
machine the
field winding is
connected in
series with the
armature
winding of a DC
generator
17
Basic Electrical Engineering

18. In this type of machine, since the
field winding carry the full
armature current, the field winding
has less number of turns of wire of
large cross sectional area. From the
machine circuit shown,
18
Basic Electrical Engineering

19. In this type of
machine, the
field winding is
connected in
parallel with the
armature
winding.
19
Basic Electrical Engineering

20. 20
Basic Electrical Engineering

21. In this type of DC machine the poles
are having two separate windings.
That is for a compound wound DC
machine there are two field windings,
namely, the shunt field winding and
the series field winding.
21
Basic Electrical Engineering

22. Depending upon how these two
windings are connected with the
armature of the DC machine, they are
classified as,
•Long shunt compound DC machine.
•Short shunt compound DC machine.
22
Basic Electrical Engineering

23. Long shunt Short shunt
23
Basic Electrical Engineering

24. This characteristic is called the
magnetic characteristic or the Open
Circuit Characteristic (O.C.C.) of a
separately excited D.C. generator.
24
Basic Electrical Engineering

25. • Open Circuit Characteristic
• Internal characteristic
• The external characteristic
25
Basic Electrical Engineering

26. The voltage buildup in a DC generator
depends on the presence of a residual flux in
the poles of the generator.
26
Basic Electrical Engineering

27. • Internal characteristic
• External characteristic
27
Basic Electrical Engineering

28. • Line OA represent the field resistance
• Line OB is called the critical field
resistance.
28
Basic Electrical Engineering

29. •DC shunt generator is used for such
applications where constant voltage is
required.
•DC series generators are used as Boosters
and also as a supply for arc lamps.
•Differential Compound generators are used
to supply dc welding machines.
•Level compound generators are used to
supply power for offices, hostels and Lodges
etc.
29
Basic Electrical Engineering

30. •Over compound generators are used to
compensate the voltage drop in Feeders.
• Separately excited generator are used
as a supply for DC Motors ,it is also used
for such applications where a wide range
of voltage is required for the testing
purposes.
30
Basic Electrical Engineering