SERIES, SHUNT AND COMPOUND GENERATORS

DONE BY MY COLLEAGUES IN COLLEGE BSEE-5

1. Series
Generator,Shunt
generators and
compound
generators

2. Series Generator- the armature coils and the series
field coils are connected in series.
In this generator, because field windings are in
series with the armature, they carry full
armature current Ia. As Ia is increased, flux and
hence generated e.m.f. is also increased.

3. Curve Oa - is the O.C.C
ab -the extra exciting current necessary to neutralize the
weakening effect of armature reaction at full load.
ordinate bc = gh = armature voltage drop, then point c lies on the
external characteristic
point c- lies on the external characteristic

4. It will be noticed that a series generator has rising
voltage characteristic i.e. with increase in load, its
voltage is also increased. But it is seen that at
high loads, the voltage starts decreasing due to
excessive demagnetising effects of armature
reaction. In fact, terminal voltage starts
decreasing as load current is increased as shown
by the dotted curve. For a load current OC¢, the
terminal voltage is reduced to zero as shown.

5. Example 1. In a 220 V supply system, a series generator,
working on a linear portion of its magnetisation
characteristic is employed as a booster. The generator
characteristic is such that induced e.m.f. increases by 1 volt
for every increase of 6 amperes of load current through the
generator. The total armature resistance of the generator is
0.02 OHM. If supply voltage remains constant, find the
voltage supplied to the consumer at a load current of 96 A.
Calculate also the power supplied by the booster itself.
Solution.
Voltage increase for 6 amperes = 1 V
Voltage increase for 96 A = 96/6 = 16 V
Voltage drop in series coils = 96
(0.02) = 1.9 V Net Voltage
rise due to booster = 16 -1.9 = 14.1V
Voltage at consumer end = 220 +
14.1 = 234.1 V
Power supplied by booster itself = 14.1(96) = 1354W =
1.354 kW

6. Compound-wound Generator

7. Compound-wound Generator
is unsuitable where constancy of terminal voltage is
essential, because its terminal voltage decreases as the load
on it increases. This decrease in V is particularly
objectionable for lighting circuit where even slight change
in the voltage makes an appreciable change in the candle
power of the incandescent lamps.
may be made to supply substantially
constant voltage (or even a rise in voltage
as the load increases) by adding to it a few
turns joined in series with either the
armature or the load.
shunt generator
These turns are so connected as to aid to
shunt turns when the generator supplies
load.

8. Types of Compound-wound Generator
long shunt compound generator
the series field coils are connected in series with the armature
coils while the shunt field coils are connected across the series
combination.

9. the the series field coils are connected in series with the load while the
shunt field coils are connected across armature coils
short shunt compound generator

10. As the load current increases, the current through the series
windings also increase thereby increasing the flux. Due to the
increase in flux, induced e.m.f. is also increased. By adjusting the
number of series turns (or series amp-turns), this increase in e.m.f.
can be made to balance the combined voltage drop in the generator
due to armature reaction and the armature drop. Hence, V remains
practically constant which means that field current is also almost
unchanged
three causes which decrease the
terminal voltage of a shunt
generator
1. flat-compounded – if the series field amp-turns are such
as to produce the same voltage at rated load as at no-load.
2. Over-compounded – if the series field amp-turns are such that
the rated-load voltage is greater than the no load voltage.
3. under-compounded – if the rated-lad voltage is less than the
no- load.This generators are seldom used.

11. For short distances such as in hotels and office
buildings, flat-compound generators are used because
the loss of voltage over small lengths of the feeder is
negligible. But when it is necessary to maintain a
constant voltage then an over-compounded generator,
which combines the functions of a generator and a
booster, is invariably used.

12. are used for ordinary lighting and
power supply purposes. They are
also used for charging batteries
because their terminal voltages
are almost constant or can be
kept constant.
Shunt generators with field regulators
Uses of D.C. Generators

13. Series generators
are not used for
power supply because of their rising
characteristics. However, their rising
characteristic makes them suitable for being used
as boosters in certain types of
distribution systems particularly in railway
service.

14. Compound generators – is a machine having both
shunt and series excitation where the series field is wound
directly over the shunt field
is the most widely used d.c. generator because
its external characteristic can be adjusted for
compensating the voltage drop in the line
resistance.
cumulatively-compound generator
differential-compound generator
has an external characteristic similar to that of a
shunt generator but with large demagnetization
armature reaction. Hence, it is widely used in arc
welding where larger voltage drop is desirable
with increase in current.

15. THANK YOU!