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2. GROUP MEMBERS

4. CHARACTERISTICS OF DC
GENERATOR

5. • Field coils excited by permanent magnets – Permanent
magnet DC generators
• Field coils excited by some external source – Separately
excited DC generators
• Field coils excited by the generator itself – Self excited DC
generators
CHARACTERISTICS OF DC GENERATOR

7. • According to the position of the field coils the Self-excited DC generators may be
classified as…
• A. Series wound generators
• B. Shunt wound generators
• C. Compound wound generators
Compound wound generators also of 2 types:
a. commutatively compound wound
b. differentially compound wound.

9. Compound wound:

11. LOSSES IN A DC GENERATOR

12.  Windings having resistance consumes certain losses,
these are termed as copper losses because mostly
windings are made of copper.
--Armature copper loss ia²ra ( ia is armature current)
shunt field copper loss ish² rsh.
--copper loss in the series field i se² rse.
ELECTRICAL OR COPPER LOSSES

13.  Copper loss in the interpole winding which are in
series with armature Ia²Ri
 Compound machines both series field and shunt
field copper losses are also there
 Copper losses are there in the compensating
winding
ELECTRICAL OR COPPER LOSSES

14. CORE LOSES OR IRON LOSSES
 The core losses are the hysteresis losses and
Eddy current losses. Since the machine
usually operates at constant flux density and
speed, these losses are almost constant. These
losses are about 20% of Full load losses.

15. BRUSH LOSSES
 There is a power loss at the brush contact
with commutator and the carbon brushes. This
loss can me measured by the voltage drop at
the brush contact and armature current.
Pbd = Vbd Ia.
 The voltage drop is more or less remains
constant over a wide range of Ia and it is
assumed 2V ( approx)

16. MECHANICAL LOSSES
The losses associated with mechanical effect are
called mechanical losses. These consists of
friction losses at bearing and windage losses
( fan losses) . the fans are used to take away the
heat produced due to I²R losses and iron losses
inside the machine.

17. STRAY LOAD LOSSES
 These are miscellaneous losses which are due
to the following reasons:-
-- Distortion of flux due to armature reaction
-- Short circuit currents in the coils due to
commutation.
--These losses are difficult to find out, However
they are taken as 1 % of full load power output.

18. EMF EQUATION OF DC
GENERATOR

19. •The EMF Equation For DC Generator Has
Two Parts:
• Induced EMF of one conductor
• Induced EMF of the DC generator

20. For one revolution of the conductor,
Let,
Φ = Flux produced by each pole in weber (Wb)
and
P = number of poles in the DC generator.
therefore,
Total flux produced by all the poles
And,
Time taken to complete one revolution
Where,
N = speed of the armature conductor in rpm.
Now, according to Faraday’s law of induction, the induced Emf of the armature conductor
is denoted by “e” which is equal to rate of cutting the flux.
Therefore,
Induced Emf of one conductor is

21. Derivation for Induced EMF for DC Generator
Let us suppose there are Z total numbers of conductor in a generator,
and arranged in such a manner that
all parallel paths are always in series.
Here,
Z = total numbers of conductor
A = number of parallel paths
Then,
Z/A = number of conductors connected in series
We know that induced Emf in each path is same across the line
Therefore,
Induced Emf of DC generator
E = Emf of one conductor × number of conductor connected in series.
Induced Emf of DC generator is

22. Numbers of parallel paths are only 2 = A
Therefore,
Induced Emf for wave type of winding generator is
Simple lap-wound generator
Here, number of parallel paths is equal to number of conductors in one path
i.e. P = A
Therefore,
Induced Emf for lap-wound generator is