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Thread: synchronize generators

  1. #1
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    synchronize generators

    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!
    Military wives deserve the Purple Heart Medal. They are wounded every time their Soldier goes off to protect our freedom!

  2. #2
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    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.
    Brian John
    Leesburg, VA

  3. #3
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    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.
    Military wives deserve the Purple Heart Medal. They are wounded every time their Soldier goes off to protect our freedom!

  4. #4
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    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.

  5. #5
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    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...

  6. #6
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    Quote Originally Posted by 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...
    I concur doctor

  7. #7
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    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
    Marc
    master electrician
    Wisconsin and Paris France

    "Pas de problème, il marche n'est-ce pas?" (No problem, it works doesn't it?)

  8. #8
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    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.

  9. #9
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    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.

  10. #10
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    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
    Last edited by e57; 01-28-08 at 01:17 AM.
    Electric heretic
    It's always gonna be in the last place you look....

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