DONE BY MY COLLEAGUES IN COLLEGE BSEE-5

1. Chapter 5Chapter 5
SYNCHRONOUSSYNCHRONOUS
GENERATOR EXCITATIONGENERATOR EXCITATION
Reporter: CRISELLE O. LLEVAReporter: CRISELLE O. LLEVA
BSEE-5BBSEE-5B

2. EXCITER CAPACITY AND VOLTAGE
A. CAPACITY
-The induced voltage of an alternator is
proportional to the product of the
number of conductors in series upon the
armature, the speed of rotation of the
field, the number of the field poles, and
the magnetic flux per field pole

3. GENERAL CONCLUSIONS
- The excitation required varies
considerably for different machines,
depending upon the size, the number of
poles, the speed, and the regulation desired.
- For alternators of different capacities but
otherwise similar, the relative excitation
naturally decreases as the size of the
alternator increases.

4. - In general, it may be said that small-capacity
machines with many poles require a proportionally
large excitation, and large-capacity machines with
a few poles a proportionally small excitation.
- A small alternator of many poles may require as
much as 3 to 5 percent exciter capacity, while a
large machine of a few poles may require only as
much as 0.3 percent exciter capacity.

5. B.
VOLTAGE
-Exciters are built for either 125 or 250 volts, these two values
being found best suited for all the exciter demands.
-In case of very large alternators it is desirable to use 250-volt
exciters in order to decrease the current, and thereby use small
copper sections in the entire field windings, in both the exciter
armature and alternator field, as well as in the connecting
circuits.
- For the exciters of the same capacity and speed, the 250-volt
machine would require a commutator of only one-half the
length, which is of exceeding importance in the case of high
peripheral velocities.

6. SYSTEM OF EXCITATION
The most common and simplest
system of excitation used in general
practice involves a self-excited direct-
current shunt generator.The alternator
field current is controlled by varying
the exciter voltage by means of a
regulating rheostat in the shunt field
of the exciter

7. For the larger machines it is desirable to
use a separately-excited direct-current
generator as the source of alternator
excitation, the power supply for the field
of the main exciter being supplied by a
pilot exciter.
As before, the alternator field current is
varied by rheostatic control of the main
exciter

8. EXCITER CHARACTERISTICS
A. PILOT EXCITERS
- normally designed to operate at
constant voltage independent of load,
they are compound-wound direct-
current machines with practically flat
load voltage characteristics.

9. B. SEPARATELY EXCITED MAIN EXCITERS
The main advantage of a separately excited
dc generator, over the standard self-excited
type, is the better voltage stability of the
former.Any voltage may be obtained over any
range,depending on the degree of excitation.It
is the feature which makes the separately
excited exciter particularly desirable for large
alternators.
The field circuit should be design with low
inductance in order that the changes in
excitation may take place quickly.

10. METHODS OF DRIVING EXCITERS
1. For high speeds and low speeds it may,
therefore, become economical to use
separate prime-mover drives for exciters.
2. In the case of steam plant the prime-
mover may be a steam turbine.As a
general rule, however, a steam turbine
has too high a speed in the small sizes
that are required for exciter drive;hence it
is not used very widely except as a spare
which may operate as an emergency.

11. 3. In a hydraulic plant, the hydraulic
design is generally too complicated
and the cost too high to consider
water-wheel-driven exciters; hence in
such plants motor drive is generally
used except for those plants using
the direct-connected system.

12. AUTOMATIC VOLTAGE REGULATION
Good voltage regulation of power
networks is probably the most
important element in the normal
process of delivering good service
to the costumer.

13. Voltage Regulators may classified as;
1.Vibrating type regulator
- is one of the older types and
still found in use, but it no longer holds
first place.
- there seems be a definite trend
away from it toward the rheostatic type.
2. Rheostatic Type Regulator
-may be classified as “direct
acting” or “indirect acting”

14. Vibrating-type regulatorVibrating-type regulator
-the alternating voltage regulated indirectly by rapidlythe alternating voltage regulated indirectly by rapidly
opening and closing a shunt circuit across the exciteropening and closing a shunt circuit across the exciter
rheostat, thus varying the exciter voltage in order torheostat, thus varying the exciter voltage in order to
the desired alternating voltage.the desired alternating voltage.
2 main parts:2 main parts:
1. Direct-current control system1. Direct-current control system
-- simple and having a main control magnet andsimple and having a main control magnet and
a relay magnet connected across the exciter mains.a relay magnet connected across the exciter mains.
2. Alternating-current control system2. Alternating-current control system
--has a magnet of ordinary solenoid type,having ahas a magnet of ordinary solenoid type,having a
laminated iron core which is attracted upward by thelaminated iron core which is attracted upward by the
magnetizing force.magnetizing force.

15. General Electric DiactorGeneral Electric Diactor
Three main parts:Three main parts:
1. Resistance plates – has a silver-button1. Resistance plates – has a silver-button
insert passing through the plate near theinsert passing through the plate near the
front end.front end.
2. Metal contact plates– separates the2. Metal contact plates– separates the
individual resistance plates at the rear of theindividual resistance plates at the rear of the
stack.stack.
3. Insulating spacers – located at the center3. Insulating spacers – located at the center
and act as a fulcrums on which theand act as a fulcrums on which the
resistance plates may be tilted.resistance plates may be tilted.

16. INDIRECT RHEOSTATIC-TYPEINDIRECT RHEOSTATIC-TYPE
REGULATORREGULATOR
The heart of this regulator is in the mainThe heart of this regulator is in the main
control unit.This control unit is composed ofcontrol unit.This control unit is composed of
a three-phase torque motor with the movablea three-phase torque motor with the movable
contact arm rigidly coupled to its shaft.Thecontact arm rigidly coupled to its shaft.The
torque of this motor is proportional to thetorque of this motor is proportional to the
average of the three-phase voltage.average of the three-phase voltage.
Air dashpot or magnetic dumping deviceAir dashpot or magnetic dumping device
-- device used to prevent the regulator from-- device used to prevent the regulator from
acting during a momentary change in voltageacting during a momentary change in voltage
not requiring a change in excitation.not requiring a change in excitation.

17. PARALLEL OPERATIONPARALLEL OPERATION
------ The division of load among alternating-currentThe division of load among alternating-current
generators operating in parallel in dependent on thegenerators operating in parallel in dependent on the
power supply to each generator as controlled by thepower supply to each generator as controlled by the
governor of its prime mover and is practicallygovernor of its prime mover and is practically
independent of excitation.independent of excitation.
Two main functions of the regulator to obtainTwo main functions of the regulator to obtain
successful parallel operation of 2 or more generatorssuccessful parallel operation of 2 or more generators
with individual voltage-regulator control:with individual voltage-regulator control:
1. they must hold the voltage constant1. they must hold the voltage constant
2. They must provide proper division of reactive2. They must provide proper division of reactive
kilovolt-ampere load among the generators.kilovolt-ampere load among the generators.

18. LINE-DROP COMPENSATORLINE-DROP COMPENSATOR
--- is used to reproduce in miniature, at the--- is used to reproduce in miniature, at the
regulator, the resistance and reactance dropsregulator, the resistance and reactance drops
to a predetermined point in line.to a predetermined point in line.
FUNCTION:FUNCTION:
-- is to lower the impressed voltage on the-- is to lower the impressed voltage on the
torque motor or solenoid unit as load comestorque motor or solenoid unit as load comes
on, thereby causing the regulator to maintainon, thereby causing the regulator to maintain
normal voltage at some predetermined pointnormal voltage at some predetermined point
on the system regardless of the power factoron the system regardless of the power factor
of the load.of the load.

19. THANKTHANK
YOUYOU!!!!