Linking two gens together?

[BioHazard]

The post about induction motors got me thinking about this. What if I have two small generators, say like those cheap little 2 strokes from harbor freight. Is there any way to connect them together at some point when the frequency is in line with eachother? Seems like I remember reading a "trick" for this a long time ago, but can't remember anything about it. I mean without some multi-hundred dollar switching apparatus. And I'm not talking about hooking to the grid.

Alternatively, could you hook up say a 400 watt grid tie inverter with battery directly to a small generator, call it 1000 watts, and have 1.4kw on demand?

[mobile_bob]

the short answer is no

generators made to be sync's together are driven by something other than a single cylinder engine, and the genheads
have what is called an "amotasiur" (sp) winding overlaid on the rotor periphery that effectively locks the two generators together.

without either the two will fight and hunt with each other.

bob g

[BioHazard]

Damn. I'm sure I was reading about bigger generators in the past.

What about plugging a grid tie inverter into a generator? Any way to do that?

[Tom T]

Bob what do you mean by driven by other than a cylinder engine ? Tom T

[Ronmar]

Of course you can do it Bob.  There are no special windings that I am aware of.  The larger plants that I have operated onboard ship did however have some governor and regulator cross link circuitry to help keep the load sharing equal.  They also have some reverse current circuitry to drop an excessivly weak generator off the line before it starts to motor.  The force that keeps the generators synced is the EMF generated by the two AC sine waves interacting with each other.  If the two are not in line with each other, they will VERY quickly do so all on their own.  Now whether the couplings, mountings and interconnecting wiring and switch gear survives this energy transfer is another story.  The trick is to make sure they are very close in phase when the second generator is brought onto the buss.  This is also not expecially difficult to do, and only really requires a couple of light bulbs or a syncroscope.  The syncroscope has the advantage of telling you which engine is faster or slower than the other, but they are expensive.  If in the case of single cylinder gensets, the single cylinders are firing out of phase, they will of course exchange energy back and forth as they alternately accelerate and decelerate, but their electrical "couping" should allow this as neither one is grosely accelerating or decelerating compared to the other 

It would probably be a little less stable with two belt drive generators, as the firing of the single cylinder would be at different phase relationships, and the possibility of belt slippage may allow this relationship to shift.  Single cylinder direct drive gensets should parallel and operate just fine.  Because their firings are fixed to the rotor angle, it would even be possible to alter their relationship till both engines are firing at the same time, then parallel them.  Once parallel the issue then becomes load sharing, both electrically and mechanically.  The governors may interact with each other and alternately hunt back and forth as the governors interact with each other.  Some way to dampen governor response would probably fix this.  The next possible issue is electrical load sharing.  If one generator is putting out more voltage than the other, that generator will try to carry more of the load than the other.  Some way to manually adjust the voltage output of each generator and current meters in line to monitor the electrical load on each generator would be needed.

The same would be needed if you were going to tie a regular syncronous generator to the grid.  You would have to match frequency,  phase and voltage before you connect, otherwise the grid WILL align all these for you in a VERY rapid fashion.  To start sending power to the grid, you would increase the generators output voltage slightly above that of the grid voltage to feed power to the grid.  The higher the voltage, the greater the difference in potential and the greater the energy transfer, up to the power available out of your engine...

[veggie]

Here's one.....

[mobile_bob]

getting two single cylinder engine's such as two lister/oids, is going to be an exercise in futility
the two engines with their related flicker serve to fight one another, so you get one surging
and the other lagging, then visa versa, the end result is two governors working against one another.

it might be possible if both units are driven by cog belts so that the pulses can also be linked, however
everything i have read lead me to the conclusion that it is probably pretty hard to link to generators.

the big gens with their amortisseur windings and their electronic governors along with much smoother prime movers
can easily sync and stay sync'd,

i just don't think that any of the typical single cylinder engine's with their rather simple governors, no provision for the
amortisseur winding can be sync'd successfully, however it might well be possible to sync an induction generator to
a common generator like an st head and have it work out ok.

i could be way off on this and it might be possible, i just have not seen it done yet.

bob g

[mobile_bob]

sync'ing to the grid a small generator is likely much easier than syncing two small generators

the grid is infinite compared to one of our units and as such nothing we can do will affect a governor at
the power plant, it will remain stable so our little gen will only have to work against the grid generator
and see as a stable load.

you tie two little generators together and they will hunt like hell and start to oscillate, unless there is some sort
of provision to tie the two governors together and some sort provision to time the combustion events relative to the
phase angle of the gensets.

i don't see this happening between two 6/1's and definitely not between two harbor freight 2 stroke minigennie's

bob g

[mobile_bob]

for those that are interested

along about page 5

http://140.194.76.129/publications/eng-manuals/em1110-2-3006/c-3.pdf

an explanation of how the amortisseur winding works,

doing a google on the amortisseur winding will return why they are used particularly for generators for parallel operation

you can parallel without the winding, but there is nothing to keep the two in sync reliably without the amortisseur windings.

i suspect all generators that are built to be used in parallel operation have this feature.

bob g

[Ronmar]

I think the two harbor freight gens would sync easier than the listeroids for the same reasons you mentioned.  Because the crank is fixed to the rotor, the two firing events could be brought together which would eliminate them trying to hunt due to alternate firing.  Some drag/delay added to their governors could also do this.  The listeroid governor might also do OK in this regard as it is a little slow to respond, so transients of the other engine firing might pass before the governor has time to react.  That coupled with all the stored inertia might allow it to work OK.  The big issue then would be which one is making the most voltage, and how do you balance the output(equalize the voltage generated). You need some whay to influence the voltage output, and amp meters in each generator output to make sure each generator is holding up it's end of the log.

Once in phase, and the cross tie connection is made, the two rotors are locked in phase, just like the motor on your drill press is locked in phase with the incomming grid.  Once the two generators are "locked" together, you could turn off one of the engines, and it would continue to turn/motor as long as it's generators field is maintained.  They don't like to do it, but they can:).

Thanks for the link.  Now I am tracking what you are refering to.  The reason I am not familliar with it is I believe those are for really big high inertia powerplants, such as large hydroelectric turbines.  The reason they are used is because the large inertia turbine is slow to react.  If for some reason the grid power it is connected to shifts, the rotor inertia slows any reaction, so they add these additional windings to help the rotor catch up before damage is done in the windings or structure.

[mobile_bob]

as used on ship generators for parallel use

http://www.sweethaven02.com/techPDFs/509les14.pdf

pg 14-3 of the document

a bit more on the winding and its use

bob g

edit, there is more at 14-18 and 14-19 of this linked document

[LowGear]

Hey Veggie,

I guess pretending that the grid was one of the generators and only syncing the real generator with the "Heres One" wouldn't work huh?

Casey

[mobile_bob]

i think this is what makes an induction generator so interesting, the squirrel cage winding doubles as the amortisseur
winding, or serves that function as well, acting like one, keeping the generator sync'd to the big generator at the power company.

does anyone have a reference to parallel operation of a motor/induction generator with a generator like an st head?

i wonder how well the would play together?

bob g

[Startomatic]

40 odd years ago when my dad was a engine driver, i see him doing this things;

he has 2 unit JP4 and 1 unit 61/6 under his care. the 61/6 is the main generator set but occassionally, the standby JP4 need to be started to back up the main when there is additional demand.

the JP4 is started with the main switch shut off, but in the circuitry, there is  a incandescent light bulb he relied on. this bulb will blink at a rate depending on the JP4 speed. he will slow down or speed up the JP4 until the blink get slower and slower and once he see the bulb goes off completely, he will leave the engine at that speed throw the main switch to on and the 2 gen set is now syncs.   

how it work i cant understand and i cant trace back as these installations are long gone.

but i do know the system is part of the original Lister set up.

one thing for sure, there isnt any electronic, be it semicon or valve type involve.

[BioHazard]

So...THEORETICALLY SPEAKING....

If you flipped the switch at the right time, you actually could backfeed the grid with an $89 harbor freight generator? Not that I would, just curious...

The lightbulb trick is what I have read about before, don't remember how it works, except that it's supposed to blink, and then when it doesn't blink anymore you can link the generators. I would imagine a governor fight would be the biggest issue.

How about the idea of adding a "grid tie" inverter to an off grid generator. Would that work?