Synchronisation Rules

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electrics

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hi ! İs there any limitation except the capacity of the controller to synchronize the gensets in way of numbers to be synchronized? For example can I sync. 50 genset at the same time?
 
The synchronizer can only close one breaker at a time, after matching voltage, frequency and phase angle on both sides of the breaker.

If there are 50 generators already operating in parallel on one side of the breaker, then you could synch 50 at a time, if you had a means to adjust their frequency and voltage as a group.

From a practical standpoint, one generator at a time is the best way to do it. The auto-synchronizer, or the operator if it is being done manually, has to raise/lower the generator voltage and adjust the frequency and then close the breaker when everything is matched. Doing that for mulitple units simultaneously can be difficult.
 
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so what is the rule to synch. the gensets in terms of powers? Which proportion of powers are dictated if you try to synch. different power gensets? Can you synch. sets like 1000 KVA ,300 KVA ,2000 KVA together? any code or standarts as to this issue? if there is I think it imposes that you can use only 2 gensets of different powers and not more than 2. is it true or I am wrong? I also wonder the proportions if there are. I want rules:)
 
No rules or regulations.

Except if you are trying to tie into the local utility there will be plenty of regulations on the required protection and control equipment. Synchronism check relays, auto-synchronizers and generator controls will be specified.

The size of generator doesn't matter. The utility system can be considered like one large multi-giga-watt generator. It doesn't matter whether you are synchronizing a 500 MW or a 5 kW unit to the utility, the same procedures apply.

Remember, when we synchronizing we are just matching the voltage, frequency and phase angle to minimize any disturbance or excessive torques when the breaker closes. If you get a perfect match there will be no power flow or var flow at closing. Once the units are paralleled, adjusting the throttle settings controls the power transfer and changing the voltage setpoint affects the vars.

Since no power flows on a perfect synch, size of generator doesn't matter.

A specific installation or equipment may only be set up for one size of generator or range of sizes. That may be the rules you are asking about.
 
Never tried anything like this big. But... you could sync 50 gensets if each has a syncroniser, and there is a bus to connect them too that has a stable reference frequency. So 50 gensets, each with its own syncroniser, onto the utility should be OK, they'll come on in sync. And syncing to the utility is realtivey easy, as its big and the genset typically isn't. If you connect a genset to the utility and the phase is wrong, the genset will cme into sync, if the breakers hold. The genset may be literally thown halfway across town in the process, though.

50 gensets cold-start is harder, as there isn't a stable reference, and not a big daddy reference either. You would need one to take the bus, and be stable, and then the rest could follow.

This relies on the syncronisers being perfect, of course, as modern electronic syncronisers are. The electro-mechanical syncronisers from my youth wouldn't work in this scenario, as they were not accurate, and so there was a pulling or pushing as the genset came online. With 50 of those in quick sucession I suspect it would end quite badly.
 
Say we have three very different power gensets. One is 2000 KVA one is 200 kVA and one is 20 kVA , we want to synch these guys between themselves. first question is there any obstacle to synch them with each other due to construction or any other electrical reasons ?
second question. if it is xformers we talk, is it same what we will talk about paralleling? Can we parallel many different power xformers as we want_?

I am asking these questions since I doubt internal impedances may create different circulating currents . if it is not question it seems there is no obstacle for what I ask. Thank you all.
 
I think it's not exactly accurate to talkof syncing multiple generators with each other. You're syncing each one to the bus. Doesn't matter how many are already feeding the bus, the incoming one only has to match the aggragate of all online units, which, being bussed, are all together.

In terms of size, if they're an error, the bigger source wins. So when bringing a 2mw unit onto a bus that only has a 50kw source, you'd better be smack on.
 
"so what is the rule to synch. "
What are the rules is more like it. There is more than one.
The primary rule is the voltage on both sides of the generator breaker is the same. If so close the breaker.
IF you have a dozen generators the first one can close on a dead bus. The rest have to be in synch to close. You can do it manually with phasing light and/or a synchroscope. In that case it will take a while as you do them one at a time.
So generator # 1 closes on a dead bus, Generators 2-11 can close allmost right away depending on your control system.
You can put a dozen 2,500 KVA generators on a bus and delivering load in less than 10 seconds (BTDT).
There a lot of experienced knowledgabel people on this forum but your not going to lean how to build that control system here.
Some good source for learning on this subject is the application notes from relay vendors, Basler, Schwitzer, GE Multilin, Beckwidth, ABB and Siemens etc. and Generator manufactures Cat, Cumins etc.
 
Motorizing

Motorizing

Interesting topic. I have paralleled many generators of varying sizes and drivers. I would hate be be out of synch with more than two. Could be really loud and you might need to be pretty quick to find out which ones are motorizing. ;)
Regards,
Mark
 
mbeatty said:
I would hate be be out of synch with more than two. Could be really loud and you might need to be pretty quick to find out which ones are motorizing. ;)
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There's a big difference between coming in on sync and getting the load sharing wrong (ie one of more gensets are "motorizing"), and joining the bus "out of sync". The latter never ends well.
 
electrics said:
Say we have three very different power gensets. One is 2000 KVA one is 200 kVA and one is 20 kVA , we want to synch these guys between themselves. first question is there any obstacle to synch them with each other due to construction or any other electrical reasons ?
second question. if it is xformers we talk, is it same what we will talk about paralleling? Can we parallel many different power xformers as we want_?

I am asking these questions since I doubt internal impedances may create different circulating currents . if it is not question it seems there is no obstacle for what I ask. Thank you all.
Click to expand...

If you're just operating in Island mode, where these 3 gen-sets are the only power sources, you can share load between them as long as the droop settings for your load sharing circuits are the same for each machine. that way the machine will take on a percentage of the total load on the buss that is equivalent to its "share" for its total rated output, and then, (theoretically at least), you'll be able to reach a total buss load of 2220 KVA where the individual gen-sets are each loaded to their nameplate rating.
from a practicality standpoint, the closer the machines are matched ratings wise, the easier it is to control them in a load sharing arrangement.
if you're paralleled w/the grid in an automatic control mode, there are frequency standards your generator has to maintain along w/whatever protective devices the utility requires you to have on your controls/output breaker.
 
just an add on here:

if you're paralleling AC voltage sources,
1) the voltage levels must match (ex: 460Vac and 460 Vac)
2) the phases must be rotating in the same direction if multi-phase
3) frequencies of machines must match, (w/an unloaded machine being slightly faster than the loaded machine if manually controlling so you'll pick up load when breaker shuts on the unloaded machine)
4) shut tie/output breaker when both machines are in phase using lamp or synchroscope.

if paralleling DC sources,
1) match voltages initially
2) raise voltage slightly on the more lightly or unloaded source if you want to shift load to that machine.
3) shut tie/output breaker.
 
millelec said:
... if you're paralleled w/the grid in an automatic control mode, there are frequency standards your generator has to maintain...
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If you are paralleled with the grid then your genset will stay in absolute synchronization with the grid, of that there can be no doubt. It may not be feeding power to the grid, but it will be in sync!
 
dbuckley said:
There's a big difference between coming in on sync and getting the load sharing wrong (ie one of more gensets are "motorizing"), and joining the bus "out of sync". The latter never ends well.
Click to expand...

I absolutely agree. I was thinking about the possible difficulty in controlling the initial load sharing when bringing so many generators in parallel at the same time. :)
Regards,
Mark
 
for isochronous mode is it true to talk about droop modes? I mean the load will be shared by the sharing circuit to gensets according to their "powers" not their droop modes. Am I wrong?
 
Not that I doubt that it's happened, but are there any documented cases of mechanical damage from bringing a generator online while out of sync? We hear dire warnings of broken mounting bolts and armatures rolling across the floor, but at least the latter seems a bit fanciful.
 
Consumers Power Company, Jackson, MI busted not one but two gas turbine power plants in 1977, there a paper on it: Shaft torques during out-of-phase synchronization

Authors: Krause, P.C. ; Hollopeter, W.C. ; Triezenberg, D.M. ; Rusche, P.A. ;

Briefly; the shaft torque can be as much as three times greater than that exhibited under short circuit conditions, without exceeding the current rating of the stator, ie the breakers dont trip. So the metalwork gives way.

Other papers induicate that even if your genset is well out of sync when brought online, it'll be in sync and stable within 150 milliseconds!
 
electrics said:
for isochronous mode is it true to talk about droop modes? I mean the load will be shared by the sharing circuit to gensets according to their "powers" not their droop modes. Am I wrong?
Click to expand...

We run isochronous at plant where I'm currently employed, and the loading is controlled by the sensed power of the gens KW transducers feeding back to a master control load sharing circuit. in isochronous mode the engines are maintaining a set frequency as load changes, and then have load sharing circuits to allow for load control of the individual units. Droop mode allows for load sharing between units w/out frequency being the overriding setpoint, you have an increasing 'droop' in frequency as the gens are further loaded, and operating machines in parallel w/droop means they'll acquire and shed load proportionately w/a percentage of speed change. I'd google Isochronous vs. droop load sharing as well, because there's lots of guys out there that put it much better than I do ;)
 
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