synchronize generators

[hockeyoligist2]

I am dumb on synchronizing generators. We have a problem. Two generators, one Onan 2500 volt, one Cat 480 volt with a transformer to step up to 2500 volt. Sorry, I don't have exact info on all of it, its in my work truck and I am home now.

The company tried to save money by keeping the old Cat, about ten years old. They are trying to synchronize them. The tech people that sold us the transfer switch can come out fiddle around and they work, the next week, they don't. I can take the one or the other off line and they will synchronize with the utility or transfer with a simulated power outage, but they will not transfer if both are online.

Can they ever work together? Anyone know where I can find hard info that I can show the boss? I am getting sick of standing around watching people work, I'm too hyper!

 

[brian john]

look paralleling gen sets is no easy deal, I am not all that adept at working on paralleling gear but my business partners knows his stuff. We were a service rep for a MAJOR paralleling gear manufacture for years.

There are many aspects to this, pitch of the windings, type of governors, what is going to control the 2 engines speeds and close them on line. Newer generators have controls (if ordered that way) that permit paralleling with a lot less gear, older gen-sets need specialized control gear.

Not as simple as buying two generators, watching the waveforms or paralleling lights and slamming them on line, though that can be done.

 

[hockeyoligist2]

I have noticed something, kind of disturbing to me, maybe not a big deal. After the factory tech's get it to work, the meter on the Cat is saying about 61Hz and the Onan is about 59.9hz. Since I don't know a lot about synching, is there a down side of that? The Cat is running about 150 more rpm than it normally does when it is carrying the load by itself, and it runs dead on 60hz by itself. The voltage seems to stay pretty close.

 

[iwire]

I don't know a lot but if your getting these readings while they are paralleled I would suspect you have at least one bad meter.

 

[mdshunk]

Word on the street is that you can just sync them pretty close, slam them on the line, and they'll straighten each other out in a minute or so...

 

[jrannis]

Word on the street is that you can just sync them pretty close, slam them on the line, and they'll straighten each other out in a minute or so...

I concur doctor

 

[frenchelectrican]

you can get them to parallel them but one warning here make sure you get the correct phase roation line up first before you throw the switch otherwise you will destory the perfectally good generator.

I did see aftermath with wrong phase roation on the generator the damage will varies from stalling the primemover to complety fuber unit [ both primemover and generator part ] the last one i did see few months ago it actally broke the flex plate in half.

Merci, Marc

 

[Rewire]

back in 79 I was stationed at a USAF radar site and I was assigned to the power house we had worthington deisel motors one was governed and was set at 0 droop it controled hertz the other picked up load we had a dial that had an arrow that turned and you had to get it rotating slowly in the fast direction until it was almost at 12 oclock then you closed the switch that was all I remember about that.

 

[dbuckley]

One or other (or maybe both!) of the frequency meters is wrong, as when the sets are paralleled, if you are not surrounded by flying heavy metal and diesel, then they are running at the same frequency.

Other than that, you don't note the power ratings for the two units. If you can get the two phase syncronised and paralleled, then the sharing of the load is the next hardest bit, and they need to share so that neither set is overloaded.

Coulter once wrote a fine piece on fun with paralleled gensets, here.

 

[e57]

Are these precise freq sets? They have fuel control for both? Meaning they have an actuator controling the fuel rates to maintain PRECISE hz....

On top of Hz being correct. You may have some other problems getting them to completely share a load equally. You are using a transformer for one since they are not the same voltage, is the transformer and 2500v generator rated for near the same kw? The kw, voltage and Hz are sensed on one unit before the transformer? If so there will be some lag after the transformer....

If there is a difference in size, slight difference in Hz, or voltage output it may be difficult to get them to share a load EQUALY. The transfer switch may sense this slight variance in voltage and correctly not transfer over. It should only do so when there is ZERO voltage between them through complete cycles. With both generators on, one leading or lagging there will be current between them, and thus not a clean wave form to match the utility - you might not ever get ZERO through a complete cycle. On less complicated low and med voltage gen sets there would be a set of lights between them - when the lights were off - it would be safe to connect them - those lights kind of have a mesmerizing effect as they cycle in and out of phase from each other. If the lights are on - there is a voltage difference. More modern gen sets made to be paralleled, and transfer switches do the same thing waiting for there to be no voltage - they just do it without the fancy old fashioned light bulbs......

And the idea that if they are parallel then the Hz is a dead on match match is a little off base, one may lead or lag, and still be able to function, but never be precise. There will be current and therefore a voltage difference between them at certain points of the cycle. If one is a few degrees off from the other you'll just get some current between them, if off 20-120 or 180 then you have a problem with the OCP tripping - hopefully.... If already linked they will hold each other to a certain degree, but not precisely. As a combined output it will be a broader sine wave than normal. Since you transfer switch is looking for ZERO at peak, and quite possibly between cycles it may never find it....

I suggest finding a safe method of sensing voltage, current, current direction +/or kw, and Hz after the transformer of the 480 set - and you may have a chance????? Since you are really paralleling a generator, and a transformer IMO - base operation of the 480 set on the output of the transformer itself.

FYI - I would not be so worried about standing next to the gen sets - assuming there is good OCP, stay away from that transformer though - there is an electrical arm wrestling match going on inside it that you want no part of.... Most transformers are not designed to parallel two sources through - check with the manufacturer and do thermal testing to see if it is getting too hot IMO.

Also see my responce to coulters well versed post (and I mean that...) in the other thread on post #26

 

[coulter]

... I can take the one or the other off line and they will synchronize with the utility or transfer with a simulated power outage, but they will not transfer if both are online. ...

h2 -

Everyone is telling you that it is near impossible to parallel the two gensets. I think you can. There are issues with generator winding pitch, but that mostly will just lower the available output - they may not put out nameplate rating. Other than getting the synchronizing equipment connected correctly, there are no issues with having a transformer on one of the units.

The fact that the "transfer switch" vendor can come out and fool with the equipment and get it to work tells me the generators will sync, close, load-up. So the electric connections, rotation, sync equipment connections are good.

So, let me see if I can understand the issues:

1. With one gen (either one) (on-line/loaded), you can sync and close on the utility CB.

2. With both gens running and synced together, (on-line/loaded?), you can not sync and close with the utility.

In 1 and 2 above, I can't tell if the utility is loaded or the gens are loaded - which is it.

3. Condition: Utility is on-line, loaded. Two gens running, synced together, not on-line. Utility fails.

Response: Transfer equipment will not put the two gens on-line.

4. Condition: Utility is on-line, loaded. One gen running, not on-line. Utility fails.

Response: Transfer equipment will put the gen on-line.

Let us know if these are infact the issues. Cause if they are, maybe we can narrow down the conversation.

carl

 

[hockeyoligist2]

h2 -

Everyone is telling you that it is near impossible to parallel the two gen-sets. I think you can. There are issues with generator winding pitch, but that mostly will just lower the available output - they may not put out nameplate rating. Other than getting the synchronizing equipment connected correctly, there are no issues with having a transformer on one of the units.

The fact that the "transfer switch" vendor can come out and fool with the equipment and get it to work tells me the generators will sync, close, load-up. So the electric connections, rotation, sync equipment connections are good.

So, let me see if I can understand the issues:

1. With one gen (either one) (on-line/loaded), you can sync and close on the utility CB.

2. With both gens running and synced together, (on-line/loaded?), you can not sync and close with the utility.

In 1 and 2 above, I can't tell if the utility is loaded or the gens are loaded - which is it.

3. Condition: Utility is on-line, loaded. Two gens running, synced together, not on-line. Utility fails.

Response: Transfer equipment will not put the two gens on-line.

4. Condition: Utility is on-line, loaded. One gen running, not on-line. Utility fails.

Response: Transfer equipment will put the gen on-line.

Let us know if these are infact the issues. Cause if they are, maybe we can narrow down the conversation.

carl

In 1 and 2 above, I can't tell if the utility is loaded or the gens are loaded - which is it.

Either way, if the utility is loaded and power goes out (simulated by pulling the fuse on the utility) the gens. will shut down before transferring, if only one or the other is on-line it will transfer. If it transfers to the gens (occasionally) then tries to transfer back to utility when the power is restored, it won't transfer back. Unless only one gen is online. We have to do it manually.

PS. It is always done under a load, it is a sewer plant running 24/7/365. We also have an option of transferring without losing power, load-sharing for the utility. They send a signal and we transfer. With both gen-sets online it usually fails. The newer one (Onan) is the only one capable of handling the whole plant by itself, so we can take the Cat offline, and the Onan will sync, loadshead and transfer. With the Cat online they will not go back to the utility. We have also tried shutting down part of the plant so the Cat can handle it and if it is the only one online it will sync with the utility and transfer back.


I hope my description makes sense?

 

[frenchelectrican]

Let me add one more commnet on this matter senice the OP mention one generator with 480 volts output and boosted up to 2500 volt via the transformer.

But my main condersastion is i know some of you may overlook is phase shift because if one generator is running at 2500 volts and other generator at 480v output and use the transformer to get up to match other generator because if both generator have simuair pitch but the tricky part is phase shift some transformer i know they will shift it somehow.,, i just cant point it excatally but some do shift phase much as 30? or more.

the most impoart is get the HZ dail in first then deal with voltage next and phase roatation.

but once you paralleled as other person mention the control system you have to choise which unit you want to lead first and second unit next [ this part you will see that on the paralleling control gear ]

Merci, Marc

addtional tibbit here becarefull if one generator is wired for delta and other on wye it get more tricky if not carefull if both wye -wye set up or delta- delta kinda stright foward task on it.

 

[coulter]

e57 -
I do disagree with the way you have worded a few of you statements.

Are these precise freq sets? They have fuel control for both? Meaning they have an actuator controling the fuel rates to maintain PRECISE hz....

They will have a governor controlling the throttle and a voltage regulator controlling field drive. If the sets are 1945 flyball governor type it may be necessary to run both in droop. If they have a modern (that would include a 10 year old Cat) electronic governor, with loadshare and varshare lines, one will be in Isoc and one in Droop. They will parallel fine.

... You are using a transformer for one since they are not the same voltage, is the transformer and 2500v generator rated for near the same kw? The kw, voltage and Hz are sensed on one unit before the transformer? If so there will be some lag after the transformer....

Just not an issue. The sync equipment has to be connected to show correct phase relationships when the two gens are indeed in sync at the bus. Makes no difference if there is a 30deg phase difference accross a transformer. There are methods available to check sync equipment connections.

...If there is a difference in size, slight difference in Hz, or voltage output it may be difficult to get them to share a load EQUALY. The transfer switch may sense this slight variance in voltage and correctly not transfer over. It should only do so when there is ZERO voltage between them through complete cycles. ...

While the gens are syncing, before the CB closes there is always a difference in frequency, voltage, phase angle between the two gensets. usually the allowable differences are programmable in the syncing equipment. if the syncing equipment is three lightbulbs and two voltmeters, then your eyeball sets the allowable differences. An example of acceptable limits is
dF = 0.2hz
dV=5%
d(phase angle) = 6 deg

The sync scope is making one rev per 5secs, the sync scope is between 11:00 and 1:00, one voltmeter is 2400V, the other is 2280V. You hit the close button (or the sync equipment initiates "CB Close") and the CB will close, the two gens will lock togethere and be just fine.

...And the idea that if they are parallel then the Hz is a dead on match match is a little off base, one may lead or lag, and still be able to function, but never be precise. ...

The voltage output of the two gens are exactly the same frequency and exactly the same phase. They have to be. The bus is essentially zero ohms impedance. The connections fron the generator terminals to the bus is essentially zero ohms. Zero Ohms is defined as Zero Voltage difference.

Different issue: There may be a phase angle difference in the rotor positions - generally refered to as "power angle". This has to do with the physics/mechanics of a generator developing power - the rotor phase has to lead the stator phase. Think of it as the rotor magnetic field is pulling the stator field around.

...I suggest finding a safe method of sensing voltage, current, current direction +/or kw, and Hz after the transformer of the 480 set ...

This one is a really is a good idea. However, since the vendor can get the equipment to work is likely available.

None of this is rocket science. The basic principles for paralleling gens have been around for 150+ years. As I read the OP, the problem is one of relaibility. There may also be issues of understanding the equipment and its limitations.

... and you may have a chance????? ...

I have faith that h2 will get it. He's sharp, and he is headed the right direction - understanding the equipment.

carl

 

[coulter]

... I hope my description makes sense?

yes -- thinking

carl

 

[coulter]

... We also have an option of transferring without losing power, load-sharing for the utility. They send a signal and we transfer. With both gen-sets online it usually fails. The newer one (Onan) is the only one capable of handling the whole plant by itself, so we can take the Cat offline, and the Onan will sync, loadshead and transfer. With the Cat online they will not go back to the utility. We have also tried shutting down part of the plant so the Cat can handle it and if it is the only one online it will sync with the utility and transfer back. ...

h2 -
Tough to see the setup from my side of your monitor. So, wild guess time:

The system has three synchronizers:

One for each gen:
1. syncs the gen to the bus
2. closes the gen CB to the bus

These two are working fine. Synchronizer raises or lowers gen freq until the dF and d(phase angle) in spec, raisers or lowers gen voltage until in spec, issues CB Close command. Each works as per plan

One for closing utility CB to a hot bus:
1. syncs both gens to utility syncing across the utility CB when a gen (or gens) is on-line/loaded.
2. closes utility CB to bus.

Works in single gen mode, but not with both gens on line.

Alert, Alert - wild guess mode. The synchronizer can't move the utility. So, when the utility CB is open, the synchronizer has to look at the voltages on each side of the utility CB. It then issues signals to each gen synchronizer to raise/lower the frequency and to raise/lower the voltage. Each gen synchronizer then issues commands to it's gen governor and VR until the bus matches the utility. The master synchro then issues a utility CB Close command. And it doesn't.

My experience has been that this is usually caused by gen stability. The loads are crawling around, the gens are crawling around following. The synchros are chasing the utility around trying to catch up. And ithey don't with in the allowed time. I've had luck programming in an automatic sync failure reset, followed by sync retry. Let the synchros try a 6 or 8 times. Another method is to open the sync window as far as the gens will stand. You won't get anybody to go out on a limb and make a decision as to what is a reasonable max sync window. Call the gen mfg and get their take on what is reasonable.


carl

 

[coulter]

... if the utility is loaded and power goes out (simulated by pulling the fuse on the utility) the gens. will shut down before transferring, if only one or the other is on-line it will transfer. If it transfers to the gens (occasionally) then tries to transfer back to utility when the power is restored, it won't transfer back. Unless only one gen is online. We have to do it manually. ...

Here I am a little unclear. Your OP maybe said the vendors could get it to work then it would stop working. If that is the case, you are likely looking for drifting analog equipment.

Or, the system is not programmed/setup correctly for your application.

The system is non-trivial. There is likely a programmable controller, multiple synchronizers, two different generators with different goverenor and VR characteristics, and you have about 12 operating modes, plus kw share and var share.

I have rarely had vendors bother to put together a system that fully/completely works as per design. Unfortunutly it's against the law to fix the vendors. You are likely going to have to send someone to school to learn the intricacies of the system and do it your self.

Or, hire an engineering firm to ride herd on the vendors.

Let us know what you find. This one is interesting.

Oh, yeah - give me some feed back on my wild guess. I'm curious on how close i am to the actual installed equipment

carl

 

[hockeyoligist2]

Yes, The system has three synchronizers, the gens start, sync with each other, look at the utility, sync, transfer.

Thanks Carl, that makes sense, if I'm understanding correctly! Like in my OP I'm kinda dumb on this!

Another thought...The load can go up or down during the transfer, everything is automated. Several 150+ HP motors (and other lower hp motors) can stop and/or start during the transition (if load sharing, not an outage). In a simulated/real outage those motors will shut down, restart on a time delay. Could that sudden drop/rise in demand have an effect? Most of the big motors (blowers) are on a 20 minute delay, so I don't think they factor in with an outage, some are on a one minute delay (pumps).

 

[hockeyoligist2]

Here I am a little unclear. Your OP maybe said the vendors could get it to work then it would stop working. If that is the case, you are likely looking for drifting analog equipment.

Or, the system is not programmed/setup correctly for your application.

The system is non-trivial. There is likely a programmable controller, multiple synchronizers, two different generators with different goverenor and VR characteristics, and you have about 12 operating modes, plus kw share and var share.

I have rarely had vendors bother to put together a system that fully/completely works as per design. Unfortunutly it's against the law to fix the vendors. You are likely going to have to send someone to school to learn the intricacies of the system and do it your self.

Or, hire an engineering firm to ride herd on the vendors.

Let us know what you find. This one is interesting.

Oh, yeah - give me some feed back on my wild guess. I'm curious on how close i am to the actual installed equipment

carl

Yes to above. I was typing real slow (two fingers) and you posted again.

"There is likely a programmable controller, multiple synchronizers, two different generators with different Governor and VR characteristics, and you have about 12 operating modes, plus kw share and var share."

Yes Redundant PLC"s controlling, two different generators with different Governor and VR characteristics. ( and you have about 12 operating modes, plus kw share and var share.) lost me there. It is a Square D transfer switch if that matters?

My feelings: The factory guys tweak, it works, they leave, minor changes in load, utility, etc. it is out of the parameters. The PLC programs are, ummmm, what is that word? Anyway, we can't access the program.

 

[e57]

e57 -
I do disagree with the way you have worded a few of you statements.
Same here....

They will have a governor controlling the throttle and a voltage regulator controlling field drive. ~ If they have a modern (that would include a 10 year old Cat) electronic governor, with loadshare and varshare lines,~
Something we don't know.... The older Cat could not, and yes they still make sets out there with manual throttles... Only asked because it was not stated.... And even then the Cat would be built to be contralled by its output, not the output of a transformer...

~ and the CB will close, the two gens will lock togethere and be just fine.
This is where I think we may disagree - in congress with the statement below...

The voltage output of the two gens are exactly the same frequency and exactly the same phase. They have to be. The bus is essentially zero ohms impedance. The connections fron the generator terminals to the bus is essentially zero ohms. Zero Ohms is defined as Zero Voltage difference.
While the buss may be zero ohm, and any where along it there will be only one voltage, and only one measurable Hz it does not necessarily mean they are in sync perfectly. As the OP has noted before one drops in Hz and the other rises, and also rises in engine RPM. If under load - they will not share it equally, and if not under load in a simular situation there will be a measurable current from one to the other

Different issue: There may be a phase angle difference in the rotor positions - generally refered to as "power angle". This has to do with the physics/mechanics of a generator developing power - the rotor phase has to lead the stator phase. Think of it as the rotor magnetic field is pulling the stator field around. Exactly.... If it is doing this it is not sharing the load, and technicly not really paralleled.

None of this is rocket science. True
carl

Carl you seem really well versed and knowledgable on the subject (I respect that!) so do not take my very simple anaolgy to follow the wrong way....

Normally in a perfect world you would want to paralell apples to apples ect. This is an apple to an orange through a tomato then to a pomagranet. It's practically fruit salad - the problem seems to be the dressing to hold it all together.

From my personal experiance of taking non-govener controlled utility GP sets and govener controlled and ship-to-shore through transformers and swapping those back and forth the fruit salad deal can be a little bit of a pain. Much like the OP. We're talking really low tech - watch the lights wait for them to get as low as possible and connect. And to disconnect what we would do is dial back the throttle one set and completely move the load to the other generator(s) - no longer sharing equally at all, no current on the set to be removed, then disconnect, and since some had no disconnect at all, on a few occassions live - phyically removing conductors off the buss. If you went a little bit more on the throttle one would become a load to the other - which had benifits in certain situations.... And in those situations the phase angle, Hz, the voltage and the RPM's of the engines themselves are fairly far apart from each other.

Anyway, I'm sure the OP is dealing with much more high tech equipment for paralleling and transfer. And for this reason it may be more difficult to get what some of the equipment is looking for - which is quite possibly zero crossing at the switch. (Because it is having a hard time recognizing the combination of tomato and orange juice. :wink: ) Just a slightly broader sine wave.

Anyway I agree it will eventually work itself out with the pro's in charge, but IMO they may have to give up on the orange and tomato if they want to keep the dressing the same.....:wink: