Sure, this is pretty easy.
Is single phase or three phase?
I ask this first because with three-phase, you must first check the
phase-rotation of the alternator versus the infinite bus. This is a
one-time thing that needs to be checked, then it doesn't need re-checking
unless maintenance is performed and the wiring affected.
But to parallel the alternator to the bus, you first match the voltages by
adjustment of the alternator output voltage. This is important to avoid
excessive VAR load changes once the breaker is closed (sometimes referred to
Then, match the frequency of the alternator output to the bus. You don't
have to get this exact because the next step will 'fine-tune' the frequency.
But get within about 1/2 Hz.
Finally, you need a device/method of detecting the phase angle between the
alternator and the bus. The most common such meter is a 'synchcro-scope'.
And this device has to be hooked up correctly. If hooked up improperly,
then you could actually close the breaker at the *worst* possible time and
destroy the alternator. Some older installations have 'syncrhonizing
lights' in addition/instead of the synchro-scope. (they are ordinary lights
connected between the bus and the alternator output in a special way).
Once you have a syncrhoscope hooked up properly, you adjust the alternator
speed in tiny amounts until you can make the synchro-scope rotate slowly in
the clockwise direction (if connected properly, this means the alternator is
going very slightly *faster* than the bus frequency). As the 'scope rotates
around, it indicates the phase angle between the alternator output and the
bus. So just as the needle reaches straight up (12 o'clock, 0 degrees phase
difference), close the breaker tieing the alternator to the bus.
As soon as the breaker is closed, it is important to go to 'raise' for a
moment on the alternator's governor. This will increase power on the
prime-mover and cause the generator to begin supplying power to the bus.
Failure to do this and a small drop in prime-mover power will cause power to
flow from the bus to the alternator ('reverse-powering' the alternator).
Depending on the installation, this can damage the prime-mover and may be
detected/prevented by a 'reverse power trip' circuit that will re-open the
breaker. Immediately picking up a slight amount of load prevents this.
Now that it's actually tied to the bus, VAR and W control comes into play.
But unless you ask, I'll skip that part.
Hope that answered your question...
If you want to do it automatically, then you will need a 'synch-check'
relay. This is a specially designed relay that is wired to the alternator
and the bus to detect the phase angle between the two. In large utility
installations they are commonly wired into the breaker permissives as a
backup protection to prevent shutting the breaker when the alternator is out
of phase with the bus. The 'original' version of these is strictly
electro-mechanical and has been around since the '20s or '30s. I'm sure
that newer, solid-state types exist as well.
These relays can have two sets of contacts. One set will close when the
voltage and frequency are very closely matched. The other will close when
the phase difference is on the order of -15 degrees to 0 degrees. If the
frequency difference is such that a 'syncrho-scope' would be rotating very
fast, the phase difference relay contact won't close at all. Using these
two contacts as input to a controller would be one way to achieve your goal.
After starting the unit, controller outputs could adjust the
voltage/frequency until the first contact closed, then 'pulse' the frequency
in very small increments until the second contact closed/opened. After
monitoring the second contact close/open for a couple of passes to verify
stability of the adjustment, command breaker closer. As soon as breaker
close status is confirmed, begin to load the unit with commands to the
For what it's worth, something like what you're talking about has been done.
In many urban areas, 'peaking units' are installed. These are stand-alone
alternators (usually diesel or gas-turbine driven) that can be remotely
started. When the area electric load control office sees a need for
additional power, they can start these units remotely. The units will
start, come up to speed/voltage, automatically parallel onto the local
distribution and then assume load up to their capacity. When no longer
needed, they are remotely shut down and they unload, disconnect shut down
their engine and resume standby status.
These units have been able to do this for some time using just a small
variety of electro-mechanical relays such as the 'synch-check' relay I
mentioned earlier. Newer ones use programmable logic controllers (PLC).
I'm not sure what part of such a system would need 'fuzzy' logic except the
initial decision to start the unit and the decision to shut the unit down.
Anyway, hope this helped.
In addition to the application that you indicate - there is a utility
(originally Calgary Power but now under the Atco banner) that runs its hydro
plants on automatic control- and has been doing this since the late '40's
and early 50's. At that time these plants were more than peaking units but,
since then they are mainly peaking with the largest units being about 150MW
but others in the 2-60MW range( 2MW units date from about 1918 (horizontal
Francis wheels) but as they were paid for a long time ago, and are almost
run of the river, are gravy makers. Most are Francis wheels but there are a
couple of variable pitch propeller wheels and Pelton wheel units (60MW 900
ft head- not much water) in use (being beside the gate control on these is
quite an interesting experience on start up- sort of a whump to come up to
speed then a delay as the synchronisation takes place somewhat slower than a
good operator would do it).
Initially the control (and it still may be) was through tones on telephone
lines. Automatic startup, synchronization, load pickup, adjustment, shut
down- all the necessary operations- were and are done from a central
location which is now in Calgary, Alberta. Initially a proprietary load
"time" controller system was used to regulate the frequency making
adjustments every second if needed and tied to a master clock which was
adjusted according to WWV. Extremely good time and frequency control. This
latter system was replaced by conventional load frequency control (for
compatibility) when interconnection to the Northwest power pool was made.
As to fuzzy logic-not used but frodo would best be served by studying and
understanding the synchronisation process and rationale before attempting to
apply any control technique. You have given some good direction in this
Don Kelly email@example.com
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actualy i am a student of b-tech final year(electrical engineering).
we have to do project on SYNCHRONIZATION OF AN ALTERNATOR WITH
BUS BAR USING FUZZY LOGIC CONTROL.
i have never done this before (even not the synchronization using
so i am a little bit confused and just dont know how can i implement
FLC in this case.
so i am seeking help.but now i know the operation cannot be done with
FLC, it can be used to initiate or terminate the process.but still is
there any way....?
The first thing is to find out what is required for synchronization and the
second is to determine what tolerances or combined factors that will allow
successful synchronism. Know the problem before applying a solution. Deal
with this first.
If possible talk to operators who have routinely synchronized machines.
You are looking at an infinite bus which will not be disturbed by your
incoming machine so the incoming machine will either pull in or all hell
will break loose (as seen by the incoming machine).
There are a number of factors-speed difference +/-, prime mover (can it turn
electricity to coal, for example), voltage differences. etc.
The fuzzy logic as I see it will look at a rather nebulous frequency
difference /voltage difference space and decide go or no go. Present
automatic synchronisers deal with quite tight limits on this and work well,
if slowly. Human operators can do it faster in most cases because they can,
from experience, do some prediction-(example incoming machine fast, close in
past "phase match" is not generally desirable where prior closing can be OK
as the machine then picks up load rather than adding a load to the system
and trying to produce coal).Depends on how much of a bump you can tolerate
and which way the bump acts.
Fuzzy logic is, as I see it, an attempt to replicate what humans can do with
a bit of experience.
Is it a reasonable application of fuzzy logic?- that is another story but
that is not your problem.
Don Kelly firstname.lastname@example.org
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(well, it has been a while, but I used to 'routinely' do it :-)
Amen to that. Had a fellow that was 'under instruction' close in a small
motor-generator (45 kW) to a large system about 170 degrees out of phase.
It *literally* tore the MG off of its mounts and rolled it up against a
cinder-block wall and managed to break several blocks in the wall. Of
course, it also tore out all the power leads and 'wrapped' them around
itself as it rolled over. Can laugh about it now, but at the time it scared
the s___ out of us.
I don't think so myself. Don't see what it gets you.
You *could* try some rule about 'adjust the closing point based on the
relative frequency difference', somewhat like some operators. Some like the
synch-scope going 'fast' and close in early so it picks up more load right
away, while others take it really slow and wait until almost exactly
Of course, going really slow means less of a disturbance (and with several
hundred MVA machines, there is a lot to be said for that), but it means
almost no load is picked up until the operator starts to raise on the
governor. So reverse-powering is more of a possibility.
As a former operator I can say that we often had to judge things based on
how stable the sync-scope was. If its a small machine (DG set) where the
governor wasn't exactly rock-solid, we'd go a bit 'fast' just to be sure the
synch-scope didn't suddenly decide to 'reverse' because the governor
'hiccups' just as we were about to close-in. But if it's a big 'ole steam
turbine with a *lot* of inertia we could adjust things down nice and slow.
But then, a big 'ole steam turbine has so *much* inertia, if you make one
last 'tweak' on the governor/steam valve, it might take over a minute settle
down. Close in while it's still coasting down an RPM or two and you might
reverse back off (unless you're quick to rise up on the governor after
for what? i think i have missunderstood our project and trouble you
two(you and kelly)
actualy we have to control the oscilation of the rotor in case of a
sudden load change.
this as you know done by damper bars but the small oscilations cannot
be damp out by
damper bars.so we have to introduce FLC to damp out the small
and you are right -i quit finding out what something gets me.
Ah, well that *is* a different sort of problem.
As you said, rotor oscillations (also known as 'hunting') are often dampened
with a second winding on the rotor known as an 'Amortisseur' winding. These
windings are very much like the rotor of induction motors (a large 'cage' of
heavy bars). I've seen them used mostly on salient pole machines, not so
much on 'turbo-rotor' style. And as you imply, yes their dampening force is
a function of the rate of oscillation so their ability to correct
oscillations drops with small or very slow oscillations.
Usually the very slow oscillations is corrected in the governor system of
the prime mover. With a machine that is connected to an 'infinite bus', the
governor isn't used so much for frequency control (an 'infinite bus' has a
fixed frequency) as it is set up for 'load control'. Adjustments to the
governor are used to control the precise amount of load the alternator
When on an 'infinite bus', I'm not sure how you *get* 'sudden load changes'
on the alternator unless they are induced by the prime-mover/governor. By
definition, any load changes on the bus will have no affect on bus frequency
or voltage, so the alternator shouldn't react at all.
But I'll assume your alternator has some sort of disturbance so that its
load momentarily changes and the rotor begins hunting at the new load point.
How are you sensing this oscillation? It's usually too fast to register on
tachometers or watt-meters. Any sustained oscillations would have to be
because the power of the prime mover is oscillating. That's either a
governor problem, or the prime mover has a steep torque vs. speed curve so
that a small change in speed causes such a large torque shift that speed
swings back and forth.
I think this is still not quite right. Perhaps your project is to use FLC
to control the frequency of an isolated alternator to keep frequency in a
narrow band? I could see some use there. Use 'fuzzy logic' to control near
the high end of the allowable band when lightly loaded, and control near the
low end of the band when heavily loaded. This would help reduce the time to
recover to within the frequency band when a large load starts/stops. But
this is just a guess at what you're really after, but its the only FLC
application I can think of.
Well, despite my electrical background, I have spent a few years in front of
a keyboard as well. The first thing one should always do with any software
project, is know what the problem is that you're trying to solve (I guess
that's probably good advice regardless of the area you work in).
Now, it could be that the instructor doesn't have a huge background in power
generation either, and so he/she may be a bit confused too. But since
he/she is the 'customer', take from him/her just exactly what problem they
want you to solve. If his facts aren't quite right, that probably isn't
important towards completing the project and passing the class. So ask him
exactly what it is he wants your FLC to do. If he thinks various load
changes cause the voltage to oscillate back and forth, let's just assume
he's right and you need to find a solution to the problem.
AVR (Automatic Voltage Regulator) are used to control the voltage output and
VAR load on a machine. If the problem statement is something like, "The
alternator output voltage varies too much with load changes," then you will
need to know in what manner the voltage changes. Up/down with load change?
Up/down all the time with no load changes? What?
AVR's are really just simple control circuits that 'sense' a parameter to be
controlled, and 'effect' a change on the machine in an attempt to control
the 'sensed' parameter. With simple, isolated machines, they just sense the
terminal voltage. With machines designed for parallel operation with other
machines or an infinite bus, they 'sense' both the terminal voltage and the
VAR load (actually, the sensing circuit combines a signal from both and
sends the combined signal to the AVR).
Some AVR's will have additional circuitry for protection against various
problems. For example, if the total output of the AVR (generator field
current) exceeds some setting, the AVR will not increase field current any
further, regardless of the 'sensed' parameter (this is commonly called an
over-excitation limit). Conversely, some have a 'floor' that prevents the
output from dropping too low for a given condition, even if the operator
lowers the set-point trying to lower the terminal voltage (one such circuit
is called URAL, for Under-Reactive Ampere Limiting). Most of these circuits
probably wouldn't come into play in your project (they are rather advanced
features of large commercial units).
communicating with u two i got this idea that i have to clear my basics
so this days i am engaged on doing that.
i go through many books but i found only theories.i read them again but
unless i get schemetic diagram of synchronization of an alternator
with infinite busbar in parallel i cannot visualize or understand the
procedure.i tried get that in net also but i failed.
can u help me to have the schemetic diagram of the procedure.
You don't need a schematic. Consider an incoming machine separated from a
system (i.e infinite bus) which has a given frequency and voltage at the
system side of the switch. The incoming machine can have any frequency,
voltage magnitude, phase and phase rotation with respect to the system--
PROVIDED THAT the switch is open. A voltmeter is also very useful.
The object is to match frequency, voltage and phase so that ideally the
voltage across the switch is 0 for each phase. Phase rotation is taken care
of in the wiring so what is left is to try to have the same frequency and no
difference in voltage magnitude or phase. You could put lamps across each
blade of the switch as shown below for one phase.
If there is a speed difference, the lamps will go bright and dark. adjust
incoming speed to get a slow variation. If the lamps don't go completely
dark, adjust voltage to make this so. (this is where a voltmeter helps)Then,
when the lamps are dark or near dark (going dark) close the switch and you
will be close enough. A voltmeter will help as "dark" may occur with some
voltage difference. There are variations on this involving a cross
connection of 2 lamps between phases- this is a bit sexier.
Now to do this electronically requires sensing of the voltage difference
(phase and magnitude) and frequency difference and adjusting to bring these
within acceptable limits before closing the switch. If you have lab
facilities available- see if you can play with it to get a feel for it.
Don Kelly email@example.com
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