Marine Online
This section will familiarize you with
voltage regulation the one phase
generator the three phase generator as
we've seen so far in a section the
induced voltage and therefore the
terminal voltage is dependent on the
type of load connected to the generator
terminals to maintain the terminal
voltage within acceptable limits due to
load change on the generator we need to
vary the strength the main field the
curves show the relationship between
terminal voltage and current at constant
magnetism it is evident that an
inductive load demands the largest
voltage regulation however the different
consumers onboard a typical ship consist
of both ohmic inductive and capacitive
loads in which the total power factor on
the generators is normally between 0.8
and 0.9 there are many voltage
regulators on the market and the way in
which an automatic voltage control or
AVR for short controls the excitation
varies from model to model in this
section we will have a look the
principles for the following two types
the brush slip ring generator even
though it is not found on board modern
vessels today all voltage regulators are
based upon the same principle and can
therefore be considered an introduction
to the modern brushless automatic
excitation systems the brushless
generator with current compounding
transformers and electronic control unit
when the road
starts turning low voltage will be
induced because magnetic remanence in
the rotor this small voltage passes the
current limiter and the primary winding
P to the magnitude around p 2 with
induced current in s the current limiter
and the condensate a battery is turned
to resonance at nominal frequency and a
current through the circuit in resonance
is tuned to the nominal terminal voltage
as you can read from the formulas and
the illustrations the impedance will
decrease and the current will increase
until 60 Hertz achieved the circuit is
tuned to give a sufficient excitation
current to maintain 440 volts at nominal
frequency as we remember a reactive load
will weaken the main field in a
generator the regulator has to
compensate for this by strengthening the
magnetization this will automatically be
taken care of by means of the primary
winding p1 as soon as a generator is
loaded a current will flow in the
primary windings which we induce voltage
the magnetic field in p1 induces an
extra current in the secondary winding s
therefore the magnetism current is load
dependent although the above principle
is ingenious due to its simplicity it
does have disadvantages brushes and slip
rings cause attentiveness due to wear
and dirt it is difficult to adjust
nominal voltage the voltage is to a
certain degree dependent on the power
factor on
loads and the prime movers rotational
speed the modern voltage regulator
systems have the excitation equipment
mounted directly on the generator shaft
let us have a closer look at a typical
voltage regulator system found on board
a ship today we have removed the
capacitor bank from this system some
manufacturers do this to prevent the
variation of feel resistance and thereby
affect the component current caused by
temperature variations the brushless
generator has its own excitation
generator mounted directly on the
generator shaft the rectifier and the
excitation machines armature windings a
part of the generators rotating parts
the excitation winding of the excitation
machine represent the stator the
response time is a little slower than
the brush slip ring generator without
AVR because it is more component in a
system which delay the response but does
not have the disadvantages mentioned
under the brush slip ring system voltage
between in the terminals caused by the
remanent in the rotor the star connected
reactor coil l2 can be viewed upon at a
small internal load in the generator the
inductive current which appears in the
reactor coil will flow through the
primary windings t1 this current induces
a current in the secondary windings s
the alternate
is then directed in a three phase diode
bridge v2 a directed excitation current
will flow from v2 through the excitation
winding l1 by strengthening the
magnetization field we will induce
voltage in a stator of the excitation
machine this voltage is then directed
through the diode bridge v3 and fed into
the synchronous generators excitation
winding me all the voltage regulator
system found on board are designed in
such a way that the regulators control
the voltage down in proportion to the n
regulated voltage unregulated voltage
would arise to approximately hundred
twenty percent of nominal voltage if the
regulator or Sai rishta were removed
this over compensation is damned to
achieve as quick a regulation as
possible during connection to large
consumers let's see what happens when we
start the generator as we can see the
actual value equals the setpoint what
happens on the actual value is greater
than the set point when the actual
it is grated moset point the comparator
in the regulator gives an output to the
thyristor gate which opens by rishta the
positive half of the phase in the middle
will be shunted by the open PI rishta
and reduce the output from the rectifier
bridge the firing angle of the fire
rishta is determined by the setpoint
actual value deviation after to the main
breaker applying a load to the generator
the primary winding will come into
action as well as a static voltage
regulator connect the breaker through
the push-button because of the old
impound station ug will be greater than
UN and the thyristor will open to limit
the excitation the regulator is
necessary to ensure equal excitation
current to the generators which will
ensure equal load sharing this was not
necessary for the brush slip ring
generators as the magnetization windings
were accessible but we could parallel
the excitation current wires to avoid an
equal load sharing our
r 2 and the electronic circuit arielle
can be viewed upon a 30 make resistances
with individual voltage drops UT 1
represents the actual voltage at
increasing load the UT one voltage will
drop and the voltage over the resistors
will change proportionally as you
arielle changes in proportion with a
terminal voltage this value is used of
the actual value for the comparator the
actual value is compared to the setpoint
the result of the comparison is
amplified the output from the amplifier
is divided into pulses which switches a
thyristor on and off the size of the
Purser's depends on the deviation note
that the tire wrister works against the
magnetism which means that when you g is
less than un the limitation of
excitation current stops this means that
the thyristor is blocked note that the
resistance r1 is adjusted to a lower
value the voltage will decrease over r1
and respectively increase over arielle
this will cause the actual value in the
set point to be equal at a lower
terminal voltage to achieve equal
excitation current at all loads at
parallel operation we have to provide
the regulator with a current transformer
as we will see in the following pages
the current transformer is a crucial
component required to achieve the
voltage droop this is necessary for a
stable reactive load sharing the
regulator
earlier show is only for single
generator installations when the
generator runs diagonal or not connected
no current is present for the p2 are two
circuit when the generators canna taking
load a current will flow in the t2 are
two circuit which will have another
direction depending on the power factor
for an increasing load the voltage over
r2 will decrease shown as a resulting
you are too in the pop-up the voltage
drop over arielle will increase slightly
due to this let us start the generator
the generator is now running at idle as
we can see there is no current present
in the UT to our to circuit let us
connect the generator as we can see from
the bow
droop pop up the actual voltage is four
percent lower and the set point voltage
the comparator compares the actual
voltage with the set point voltage the
result of the comparison gives an output
to the thigh rishta which will parallel
shift the droop until you g equals um if
the power factor increases the voltage
over r2 decreases and the output from
arielle increases ug exceeds UN and the
comparator will give an output to fire
rishta which would open it to limit the
excitation current until you g equals um
let's see what happens when we reduce
the load to eighty percent the
comparator reads that you g is greater
than un and will give an output which
will parallel shift the droop until you
g equals un note for a single generator
the current transformer is not necessary
because the generator takes the entire
load anyway and therefore the
manufacturers have a switch which
disconnects the current transformer wide
and single operation the regulator then
regulates in relation to voltage alone
let us add another generator to the best
spa in order to share the load press the
start dg2 button
press the contagion a two-button note as
soon as dg2 takes load the load on DG 1
will be reduced ug will therefore be
greater than UN and the fire is still
open the regulators on DG 1 and dg2 will
then decrease and increase the load on
the generators until they are balanced
to ensure equal load sharing at all
loads fiddling with a regulator
components is not recommended we will
now take a closer look at possible
effects of such tampering if we increase
our one on DG 1 during parallel
operation the output from arielle will
then decrease the regulator believes for
the you g is greater than un the
comparator output will cause an
increased excitation current the
generator will then take a large part of
the reactive load as you can see
characteristic dg2 would take a larger
part of the load if we change the
voltage droop on DG one to eight percent
during parallel operation the complete
AVR circuitry is very complex and
includes a few preset variable resistors
for the control of sensitivity offset
error and stability these are adjusted
and set during the generator trials to
achieve an optimum and stable
performance it is strongly recommended
that you do not tamper with such preset
resistors r1 which is found in the main
switchboard should only be adjusted as
an exception in order to define
adjustments to the generator voltage
when it is idle in the following pages