Syncing multiple generators

[cschuerm]

Before anyone jumps on me about how I'm going to kill myself and blow up stuff, I want to say that I am a grizzled electrical engineer and I'm doing this for the fun of it.... If I blow stuff up - it's okay.

So, I was working at a facility a few weeks ago that had a very old power plant next door.  Clearly I couldn't stay away and had to go drool over the 1930's vintage Fairbanks and Nordburg 1200-1400 kw generators and the beautiful antique switchgear.  It has given me the bug to want to sync two listeroid generators together (for no particular reason other than to do it).  I have a 20/2 with a 15k ST head and a 24/2 with a 30k ST head already.  Have a good supply of NEMA 3/4/5 contactors that I can use to tie as well as probably everything else I'd need.
Has anyone ever tied multiple ST heads in sync?  Just wondering what issues have been run into by others.  Sounds like a really fun science experiment to me!   Wouldn't it be cool to have two (or more) generators in my "power house" that could be run independently or in parallel depending on load needs?
:-)
Chris

[trigzy]

Hi,
   You're going to kill yourself and blow stuff up!  Make sure someone posts the video on You Tube please.  HAHAHA  Now all joking aside.  Did you take pictures of this old plant, if so, please post a link so we can all see!

Having a syncroscope would be nice.... but you can rig up lamps, voltmeters etc. to measure the in/out of sync condition before closing.  I dont know of any documented cases of people running ST's in sync.  I think this could be quite inefficent, as you dont have any droop control to balance the KVAs.  Maybe if you tied the field windings together you could get a little bit better system balance. 

As you may know, I sell some AVR's, and they happen to have a droop controller built in. I haven't heard of anyone using it, thinking about using it, or even acknowledging it's existance, so your experiment would likely be unique.

And yes it would be cool!

Steve

[cschuerm]

Steve, I did take some pix - I'll try to find some time to post them in the near future.
They had some really cool syncroscopes on the panels.  Lots of engraved brass stuff everywhere.  It's a shame that most hardware has become totally focused on functionality and has lost the aesthetic aspects.
I absolutely agree that without some means of balancing that the system would be very inefficient - probably just turn one of the ST heads into a heater :-)  Interesting idea about tying the fields together - hadn't considered that.  Could something that simple be the solution???
I was thinking of designing a circuit somewhat like an AVR but with the ability to load balance two heads.  Might be a little tricky but not insanely complex.  I think you could do it with feedback from CT's on each generator.  Maybe do primary control on voltage and a secondary logic circuit to offset the two field outputs to balance current.  Thoughts?

Chris (just call me sparky)

[compig]

Hope you can get back to that plant to take some foto's to post up here !!  I love to see old plant and equipment !!

[mike90045]

I think the catch will be getting the engines goveners to lock up.  I don't know if you can "PULL" an ST head into sync like a induction motor, or if one would be a "load" for the other. 
Best, I think the engine RPM's will hunt back and forth between each other.

[Tom]

I think the potential issue here is that when connecting to the grid, it is a stable source whose frequency can not (by our small generators anyway) be moved. In the situation you are planning one generator can have a HUGE affect on the other.

[cschuerm]

Just uploaded a batch of pictures of the giant old generators to the listerenginegallery.  Not exactly sure how to link them here though.  Sadly, even though this powerplant has been maintained in fully operational condition, it sounds like they are going to scrap the whole thing out before long.  Just too expensive to maintain and not used enough to justify.  I could probably have them all in trade for my company executing a couple of projects for the city, but I don't have anywhere to put them even if I could figure out how to move them



Chris

[cschuerm]

Cool - that apparently worked!
I suppose this should probably be re-located to the "other engines" section, but I think if you'll click on the following link you should be able to see the other pix:
http://listerenginegallery.com/main.php?g2_itemId=1550

[trigzy]

Chris,
      Nice photos.

       You never know about the balancing, since generators of the same design, but different sizes, tend to load out evenly on a percentage basis.  Maybe even tying the fields together might not be necessary.  I think you'd have to try it first to be sure, unless you had really accurate impedance numbers for the generators, as well as the loads you intended on using.
      As far as the commercial AVR's go, apparently the CT is only for balancing the reactive power, I think they rely on the relative size of the generators to balance out the kW's themselves.  So I don't know if it's needed, but your idea for the logic circuit sounds neat.  As for synchronization, if you KNEW you wanted all that power on a semi permanent basis, link the two engines/gen heads together with ???chain/drive shaft coupling???  Just a thought.  Then you could also balance the power pulses out, and have one piston firing every 180 degrees.  If you set it up right, you might be able to do that during the electrical linking of the genheads.

Steve

[mobile_bob]

replace the smaller head with an induction motor/generator?

once locked in the squirrel cage would track with the st head
two st heads might get to hunting back and forth, until they start to resonate and blow a fuse.

looking at some of my old text books on syncronous generators and parallel operation
it was common to add a squirrel cage over the rotor, so that both gensets would lock together
and stay in phase.

that was for multicylinder engines as well, so it would seem that if they needed that
for a mulitcylinder, maybe single/twins might even be worse to hold in sync without the squirrel cage?

just a thought

bob g

[1958steveflying]

I wish i could understand all this electrical stuff..... it goes straight over my head ! ! !   And i don't like not understanding things at all. 


 Steve

[rl71459]

Chris
I am fasinated with you question.... I also have contemplated this. Now Ive read that you can use light bulbs to sync to the grid.
and if you properly protect the system with breakers... You should not have to let the smoke out of your gen heads. My understanding is if the units go out of sync the breaker will trip b4 damage occurs.

Please pass along your results.

Rob

P.S. That is one sweet generator.... WOW!

[trigzy]

... properly protect the system with breakers... You should not have to let the smoke out of your gen heads. My understanding is if the units go out of sync the breaker will trip b4 damage occurs.

I've discussed this numerous times before, but I'll mention it again, because I feel it's the most overlooked thing in breaker circuit protection selection.  Make sure the protection is properly sized for the GENERATOR and PRIME MOVER.  Cant emphasize that enough if syncing.  Extra protection on the field windings might not be a bad idea, even more so if locking them together.  I'd really prefer fuses for syncing, usually much faster to react in a fault scenario.  Faster = better when we are talking about the protection of a system that is the electrical equivalent of two trains racing toward each other at full speed.

Steve

[WGB]

Just read Bill Rogers book, he went into some detail on the subject.

[rl71459]

What book is it?  Who is Bill Rogers?