Generator synchronization

[**THE-RFI-EMI-GUY**]

I am interested in hearing about simple methods of synchronizing two
consumer grade standby generators under varying loads.

Thanks

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

 

[John Gilmer]

I am interested in hearing about simple methods of synchronizing two
consumer grade standby generators under varying loads.

My first advice would be: FORGET IT.

You can sync them by just starting them both and placing them in parallel.
The one will slow and the other will speed. (I suspect that you may have to
try to do this more than one. If you close when they are far out of sync
you will pop the breakers on both machines.


But without an adjustable governor and some way of monitoring how much power
each machine is delivering, it will be difficult to share the load.

The "classic" way of syncing two machines was to place a lamp across the
contacts of the switch that, when closed, will put the machines in parallel.
You put a 3/4 load on the first running machine and bright the second
machine up to speed but slight slow. You "inch up the speed" of the new
machine and when it is SLIGHTLY faster you thown the switch when the bulb is
out.

 

[SQLit]

I am interested in hearing about simple methods of synchronizing two
consumer grade standby generators under varying loads.

Thanks

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

Small gennys below ~12.5kw are engine speed governed. Above that line there
are usually controls that are speed independent. So if you below the magic
number, buy a bigger gen or split your loads.

 

[**THE-RFI-EMI-GUY**]

Assuming both had an electronic speed control, with constant RPM =
constant frequency, and a zero crossover switch. would both generators
share the load, all things being equal?

My first advice would be: FORGET IT.

You can sync them by just starting them both and placing them in parallel.
The one will slow and the other will speed. (I suspect that you may have to
try to do this more than one. If you close when they are far out of sync
you will pop the breakers on both machines.


But without an adjustable governor and some way of monitoring how much power
each machine is delivering, it will be difficult to share the load.

The "classic" way of syncing two machines was to place a lamp across the
contacts of the switch that, when closed, will put the machines in parallel.
You put a 3/4 load on the first running machine and bright the second
machine up to speed but slight slow. You "inch up the speed" of the new
machine and when it is SLIGHTLY faster you thown the switch when the bulb is
out.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

 

[specific databases]

Assuming both had an electronic speed control, with constant RPM =
constant frequency, and a zero crossover switch. would both generators
share the load, all things being equal?

No. You have no control of phase. One will feed the other if out of phase,
and blow it out. Even if the are EXACTLY on frequency, which they will not
be, they float.

DC is a little different you still get one will try to pull all the load,
and you can get surging which will blow one of them out. .
But You can add series resistance, I used welding rods one time, (as a
series resistor) and got the mismatch in current to within 20%(14 volts at
200 amps)

 

[Don Kelly]

Assuming both had an electronic speed control, with constant RPM =
constant frequency, and a zero crossover switch. would both generators
share the load, all things being equal?

---------
Ideally-yes- in practice- no- there always will be small but real
differences in the speed regulation of the two machines- the net result is
that the "faster" machine will try to grab all the load--trouble. In
particular, for constant speed settings on both machines, even if the load
was equally shared, any change in load would result in one trying to run the
other as a motor as well as carry the useful load. In utilities, the
governors (and yes, there have been and still are, very good mechanical
governors) are set to provide a set speed droop as load increases which
helps control sharing by providing a definite intersection between the two
speed- torque curves (or frequency-power). Attempts to raise or lower speed
on a unit will modify this sharing. With no droop, there is no control of
sharing of load.

If you were to try to run two small units in parallel, then it would be best
to set one to constant speed and adjust the no load speed of the other
(which would have a speed droop) to determine its share of the load. Any
load changes would be handled by the "fixed" speed unit. Mechanical
governors would be adequate but capability to adjust the "no-load" speed and
the droops would be needed. Is it worth the hassle for small machines?- not
likely.

 

[Don Kelly]

No. You have no control of phase. One will feed the other if out of phase,
and blow it out. Even if the are EXACTLY on frequency, which they will not
be, they float.

--------
Utilities have two main controls on the machines- speed and voltage.
They do not have direct control of phase.
They survive.

Adjust the speed of the incoming machine to match the on-line machine as try
to get the differential voltage as low as possible- there will always be
some small phase and voltage magnitude difference but, done properly there
will be no more than a slight "bump' Of course if you try to synch when 90
or 180 degrees out of phase- then there will be major problems. It's not a
problem to synchronise but it may be a problem with load sharing due to
different speed-torque characteristics.

 

[Don Kelly]

not

You are Fucking Nuts. Utilities ALWAYS Sync Phase, that is what Sync means.

You do not know what you are talking about at all. Moron.

Two different generators will ALWAYS be out of phase, you have to sync the
phase up.

Google it yourself, anyone dumb enough to plug one generator into another
without syncing phase up will and should get fried.

That is like plugging phase A into phase B. What happens??

-----------
Note what I said- get the differential voltage as low as possible which
implies matching voltage and phase as well.
This doesn't have to be exact. In fact there may even be a small speed
difference between machines and often is when they are connected. Provided
that the machines are "close enough" the incoming machine will be pulled
into synchronisation. If a bit slow, it will be pulled ahead, If fast, it
will be pulled back.
As I said- the controls are the speed setting of the turbine and the voltage
setting of the generator.

Sure it is ideal to match voltage exactly and match speed exactly and match
phase exactly. If you can get the voltages between machines =0 and
unchanging you are there. In practice there will be some error as I
indicated if you had read rather than jump to invective.

As to two machines - once synched- how do you think that one changes the
load balance- it is by trying to speed up one with respect to the other-
that wont happen but there will be a resulting phase difference between
internal voltages and, depending on the system, between the terminal
voltages.

Also note that I did not say "tie two machines together when they are not
close enough in phase and magnitude " If you could read, rather than simply
jump off the deep end, it would help. Certainly I should have said something
like 30 degrees is too far apart but generally a small phase difference -
while leading to a bump, should not be a problem.

Do I know what I am talking about- Yes - on the basis of theory and practice
as
I have synchronised machines many times. Sometimes using a synchroscope and
sometimes using a set of lights.
And, yes, I have made sure that the phase rotation is right. By the way, if
this is so, it doesn't matter which you call phase A on one machine and B on
the other -think about it.

By the way "synch comes from synchronous which implies the same speed- not
necessarily the same phase.

 

[Tom Grayson]

not

You are Fucking Nuts. Utilities ALWAYS Sync Phase, that is what Sync means.

You do not know what you are talking about at all. Moron.

Two different generators will ALWAYS be out of phase, you have to sync the
phase up.

Google it yourself, anyone dumb enough to plug one generator into another
without syncing phase up will and should get fried.

That is like plugging phase A into phase B. What happens??

WE do this all the time with 3 or 4000 Hp Motors. we found the best way to
do it is
have the speed of the incoming motor or generator slightly faster then that
of the existing system. With this setup the synchronous points come past as
a steady predictible rate enabling the syncrhonising to be easily performed
when the phasing is right. Naturally the voltages must match in amplitude.

a few degrees in error usually do not result in any catastrophic bang and in
fact, the best results are usually when the closing is done a few degrees
before the synchronous point, allowing the slowdown of the incoming set to
be done in these few degrees leading to the synchronous point rather then
after it.

There is no need to synchronise phase. in fact, synchronizing phase is
extremely difficult to do in a dynamic situation because that would require
your incoming generator to follow all of the small shifts in speed and phase
that are forever present in a power system.

I have actually tried to do this in the dim dark ages until we got smart and
let the system work with a small amount of slip and hit the synchronous
point as it comes past.
I can imagine the smaller the generators, the more difficult it would be to
do the synchronising.

Tom

 

[daestrom]

Assuming both had an electronic speed control, with constant RPM =
constant frequency, and a zero crossover switch. would both generators
share the load, all things being equal?

Only in a perfect world, and as we all know, our world isn't perfect.

For two or more AC machines to share the load well, the governors on the
machines (either electronic or mechanical) *must* have a characteristic
called 'droop'. This is the phenomenon where the governor output (fuel
control/throttle) only rises if the speed is below a setpoint. And in order
to get more fuel, the speed further below setpoint. Speed droop is often
measured as a percentage. If the unit is run isolated from all other
generaters and has its load varied from no-load to full-load, the amount of
speed reduction needed to have the governor go from cut-off to full throttle
is measured. This speed reduction (in RPM) is divided by the no-load speed
(also in RPM) and expressed as a percentage. Speed droops of small to
medium sized machines often runs 3 to 7 % (i.e. @5%, the speed of an 1800
RPM, unloaded generator will drop to 1710 when fully loaded)

If you take two AC machines with the same droop characteristic (let us
assume 5%), they will share the load quite nicely, even if one is much
larger than the other and running at a different speed (with different
number of poles in their respective generators). For example, say you have
a 10kW, 1800 RPM machine carrying 2kW operating in parallel with a 100kW,
3600 RPM machine carrying 20kW. Now suddenly switch on a 55kW load. Both
machines will begin to slow down and their governors will increase their
fuel flow. But look closely at what happens. The small machine slows down
about 2.5% to about 1755 RPM. The governor of that machine will increase
fuel flow by 50% of rating and the generator is now carrying 7kW.
Similarly, the large machine slows down about 2.5% to about 3510 RPM. The
governor of *that* machine will increase fuel flow by 50% of rating and the
generator is now carrying 70kW.

So, with the same droop characteristic, these two machines were originally
loaded to 20% of their capacity, and after switching on a large load they
are both loaded to 70% of their capacity. And it all came about because the
two governors have similar characteristics. These machines do *not* need
any cross-connections for this to work. Similarly, a sudden reduction in
load will come off the two machines nicely and neither will reverse power
the other unit.

The only problem is that frequency went from 60hz original, to 58.5hz. This
can be corrected by adjusting *both* governor setpoints upward at the same
time. If you adjust just one of the governor setpoints upward, it will
sense that engine speed is further away from the setpoint and increase fuel
flow to the engine. This will increase the load on the generator. As the
load is 'picked up' by this machine, the opposite machine will see a
reduction in load and start to speed up slightly. So the second machine's
governor will sense speed closer to the setpoint and decrease the fuel to
its engine and its generator load will decrease.

I've paralleled hundreds of generators over the years using both
synchroscope and lights (three phase lights can be fun as they can be wired
to 'rotate' . Almost universally, the 'incoming' machine is run slightly
faster than the system it is being connected to. This helps to ensure that
the moment it connects, its governor will see a slight drop in speed and
increase fuel flow. This is important as most generators intended for
parallel operation have reverse-power protection and in order to avoid false
tripping of the unit, it is best to pick up some load immediately. Even
extremely *large* units (1200MVA), when first connecting in are run slightly
fast (after all, if the speed is exactly matched, the synrchoscope doesn't
rotate at all).

Now, that all said, there is yet a different situation with some of the
small portable units available. Some of the small portable units are
actually DC generators with electronic inverters. Since the machine is
actually DC, all this previous talk about governors and droop is not
applicable. What is important when connecting inverters together is how the
inverter electronics are designed. Some manufacturers (Honda I believe is
one) have a special cable to connect between the units. This cable actually
connects between the *inverters* so the two *inverters* that are inside the
units can communicate and share load between them.

daestrom
P.S. DC generators can be made to share their loads in a similar manner by
designing the voltage regulators to have a 'droop'. Or just the machine's
inherent voltage regulation, if properly designed, will do it as well.

 

[**THE-RFI-EMI-GUY**]

Thanks for the explanation. I didn't know about Honda having a cross
connect. I will look into that feature.

Only in a perfect world, and as we all know, our world isn't perfect.

For two or more AC machines to share the load well, the governors on the
machines (either electronic or mechanical) *must* have a characteristic
called 'droop'. This is the phenomenon where the governor output (fuel
control/throttle) only rises if the speed is below a setpoint. And in order
to get more fuel, the speed further below setpoint. Speed droop is often
measured as a percentage. If the unit is run isolated from all other
generaters and has its load varied from no-load to full-load, the amount of
speed reduction needed to have the governor go from cut-off to full throttle
is measured. This speed reduction (in RPM) is divided by the no-load speed
(also in RPM) and expressed as a percentage. Speed droops of small to
medium sized machines often runs 3 to 7 % (i.e. @5%, the speed of an 1800
RPM, unloaded generator will drop to 1710 when fully loaded)

If you take two AC machines with the same droop characteristic (let us
assume 5%), they will share the load quite nicely, even if one is much
larger than the other and running at a different speed (with different
number of poles in their respective generators). For example, say you have
a 10kW, 1800 RPM machine carrying 2kW operating in parallel with a 100kW,
3600 RPM machine carrying 20kW. Now suddenly switch on a 55kW load. Both
machines will begin to slow down and their governors will increase their
fuel flow. But look closely at what happens. The small machine slows down
about 2.5% to about 1755 RPM. The governor of that machine will increase
fuel flow by 50% of rating and the generator is now carrying 7kW.
Similarly, the large machine slows down about 2.5% to about 3510 RPM. The
governor of *that* machine will increase fuel flow by 50% of rating and the
generator is now carrying 70kW.

So, with the same droop characteristic, these two machines were originally
loaded to 20% of their capacity, and after switching on a large load they
are both loaded to 70% of their capacity. And it all came about because the
two governors have similar characteristics. These machines do *not* need
any cross-connections for this to work. Similarly, a sudden reduction in
load will come off the two machines nicely and neither will reverse power
the other unit.

The only problem is that frequency went from 60hz original, to 58.5hz. This
can be corrected by adjusting *both* governor setpoints upward at the same
time. If you adjust just one of the governor setpoints upward, it will
sense that engine speed is further away from the setpoint and increase fuel
flow to the engine. This will increase the load on the generator. As the
load is 'picked up' by this machine, the opposite machine will see a
reduction in load and start to speed up slightly. So the second machine's
governor will sense speed closer to the setpoint and decrease the fuel to
its engine and its generator load will decrease.

I've paralleled hundreds of generators over the years using both
synchroscope and lights (three phase lights can be fun as they can be wired
to 'rotate' . Almost universally, the 'incoming' machine is run slightly
faster than the system it is being connected to. This helps to ensure that
the moment it connects, its governor will see a slight drop in speed and
increase fuel flow. This is important as most generators intended for
parallel operation have reverse-power protection and in order to avoid false
tripping of the unit, it is best to pick up some load immediately. Even
extremely *large* units (1200MVA), when first connecting in are run slightly
fast (after all, if the speed is exactly matched, the synrchoscope doesn't
rotate at all).

Now, that all said, there is yet a different situation with some of the
small portable units available. Some of the small portable units are
actually DC generators with electronic inverters. Since the machine is
actually DC, all this previous talk about governors and droop is not
applicable. What is important when connecting inverters together is how the
inverter electronics are designed. Some manufacturers (Honda I believe is
one) have a special cable to connect between the units. This cable actually
connects between the *inverters* so the two *inverters* that are inside the
units can communicate and share load between them.

daestrom
P.S. DC generators can be made to share their loads in a similar manner by
designing the voltage regulators to have a 'droop'. Or just the machine's
inherent voltage regulation, if properly designed, will do it as well.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.

 

[torresD]

when

WE do this all the time with 3 or 4000 Hp Motors. we found the best way to
do it is
have the speed of the incoming motor or generator slightly faster then that
of the existing system. With this setup the synchronous points come past as
a steady predictible rate enabling the syncrhonising to be easily performed
when the phasing is right. Naturally the voltages must match in amplitude.

a few degrees in error usually do not result in any catastrophic bang and in
fact, the best results are usually when the closing is done a few degrees
before the synchronous point, allowing the slowdown of the incoming set to
be done in these few degrees leading to the synchronous point rather then
after it.

There is no need to synchronise phase. in fact, synchronizing phase is
extremely difficult to do in a dynamic situation because that would require
your incoming generator to follow all of the small shifts in speed and phase
that are forever present in a power system.

Sorry, you are wrong, Synchronise mean "phase locking".
If not phase locked, then how much current flows from one machine into the
other??
I do it all the time with two 500KW generators at work, you get them close,
then use a phase lock to keep them together.
(the arcing that occures gives on a healthy respect of electricity)
He needs to something else with his little generators, run seperate
circuits.

 

[torresD]

| Utilities have two main controls on the machines- speed and voltage.
| They do not have direct control of phase.
| They survive.

Why not? It can be done.

The phase locking is automatic, very difficult to do by hand anyway.
http://ka9wgn.ham.org/ |

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[Bill Shymanski]

I believe that what everyone is saying is that it isn't necessary to
drive the prime mover to specifically be in phase sync, but rather,
if you switch in the added generator at just about phase sync where
the slight speed difference was slowly taking things in and out of
phase sync, that the load variations due to circulating currents when
the phase varies just a bit will drag them together within a certain
degree of sync.

I've always wondered how they do that with hydroelectric. You can't
just change the water flow levels that fast.

Wicket gates control the water flow to the turbine, driven by a large
hydraulic cylinder. I don't have exact numbers but at Manitoba Hydro's
"Limestone" generating station the units are about 130 MW each, and the
hydraulic cylinder looked to be about a 14 or 15 inch bore - governor
oil systems run about 1000 to 2000 PSI.

Bill

 

[Don Kelly]

--
Don Kelly
[email protected]
remove the urine to answer

 

[Don Kelly]

The phase locking is automatic, very difficult to do by hand anyway.

------------
Synchronism is not "Phase locking" which implies a set phase angle
difference - preferrably 0 on the initial connection. This is the objective.
However the synchronising process involves more than phase
ocking -relative speed and differential voltage. Certainly, if conditions
are not exact- 0 phase difference, 0 speed difference and 0 voltage
difference at the time of connection- there will be a bump - The machines
are more forgiving than you imply.
A utility would have no load control on its generators in a phase lock
situation but I assume that you are referring only to the instant of
connection.
As far as synchronising by hand, this is not a difficult process. It is
easier to do it with a synchroscope than with a set of lights but in either
case it is not difficult. In fact a good operator can synchronise an
incoming machine to the system faster than an automatic control because he
can anticipate and allow for reaction time etc. The automatic synchronisers
dither around to try to get things "just right"
This was touched on by others where the incoming machine is a bit "fast".

As for Phil's comment- yes, a synchroscope does indicate phase (not exactly
a precision instrument) as well as relative speed. It does not indicate
voltage differences. Is a precision circuit needed- no. Is common sense
needed- Yes.

 

[Don Kelly]

r

|
| |>
|> | Utilities have two main controls on the machines- speed and voltage.
|> | They do not have direct control of phase.
|> | They survive.
|>
|> Why not? It can be done.
|>
|
| The phase locking is automatic, very difficult to do by hand anyway.

I believe that what everyone is saying is that it isn't necessary to
drive the prime mover to specifically be in phase sync, but rather,
if you switch in the added generator at just about phase sync where
the slight speed difference was slowly taking things in and out of
phase sync, that the load variations due to circulating currents when
the phase varies just a bit will drag them together within a certain
degree of sync. I just worry that with 3 or more generators, this
can be a chaotic system without a lot of dampened control of the prime
mover power source.

I've always wondered how they do that with hydroelectric. You can't
just change the water flow levels that fast.

----------
Having 2 or more generators on line with one incoming machine (and you are
synchronising one at a time) will make things easier. The incoming machine
is then relatively smaller and has less impact on the system.
Hydor machines are not a problem- yes it can take time to adjust speed but
the process of nearly matching speed and switching as it approaches the best
point works well. Still I have seen a 60MW machine come up from start, on
remote, automatic, control and pick up load within 1-2 minutes (most of
which were due to the synchroniser dithering).
--
Don Kelly
[email protected]
remove the urine to answehttp://ka9wgn.ham.org/ |

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[Don Kelly]

|> I believe that what everyone is saying is that it isn't necessary to
|> drive the prime mover to specifically be in phase sync, but rather,
|> if you switch in the added generator at just about phase sync where
|> the slight speed difference was slowly taking things in and out of
|> phase sync, that the load variations due to circulating currents when
|> the phase varies just a bit will drag them together within a certain
|> degree of sync.
|
|> I've always wondered how they do that with hydroelectric. You can't
|> just change the water flow levels that fast.
|>
|
| Wicket gates control the water flow to the turbine, driven by a large
| hydraulic cylinder. I don't have exact numbers but at Manitoba Hydro's
| "Limestone" generating station the units are about 130 MW each, and the
| hydraulic cylinder looked to be about a 14 or 15 inch bore - governor
| oil systems run about 1000 to 2000 PSI.

But how fast can it react?

---------------
On starting the machine and governor are set to come up to a "speed no load"
setting. This will be quite close to the final speed and only small speed
"twitches" are needed to bring the speed and phase close enough. Fast
reaction is not necessary.
Certainly, for large changes in power output, once synchronised, large gate
changes are needed. No-load to full load may take 0.5 seconds for a steam
turbine and several seconds to a couple of minutes depending on the machine
and its turbine/penstock system for a hydro unit.
I know of a 300ft head plant where the first unit had its gate speed limited
(2 minutes to fully open or close) as faster operation could lead to
problems with the penstock (collapse possible on sudden load increase) while
an older unit of the same size could operate much faster because of a surge
tower.
On the other hand, Alcan's Kemano (Pelton wheel- high head ) plant (160MVA
units) supplying an aluminum pot line is required to, almost
instantaneously, pick up a 100MW pot line (all or nothing). Here the gates
were opened fully and deflector vanes were used for control. Load on,
deflectors moved aside so full blast on the wheel. Not efficient for normal
control so conventional- governors and gates used for that.

Whether the machine is hydro or not- sometimes the slowest synchronising is
when the speed is almost bang on but the phase is out - then the phase may
change in the order of a couple of degrees a second, or seem to dither
around as the system or incoming frequency wobble a bit

--
Don Kelly
[email protected]
remove the urine to answer
http://ka9wgn.ham.org/ |

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