Syncronous motors and the grid

[veggie]

I read this on another thread but didn't want to hijack the topic so I am starting a new one here...

Can an engine driven electric motor be wired to backfeed the grid and lower ones power consumption from the Utility?
If so, what is the method of setting this up and what is the safest way to syncronize the sine waves before engaging power (Other than the flickering light bulb trick).
Lets assume for this discussion that the objective is to lower the utility usage and not to totally offset it or turn the meter backwards.

veggie

[LowGear]

Hi veggie,

I'll look for my book.  It's all about this concept.  I'm always looking at synchronous motors of 5 HP but they're rare on the used market for some reason.  And then all motors are not created equal.  An efficiency rating near 90% is pretty darn good and that's a matter of looking it up on the manufactures spec sheet.  They're are not cheap either with $350 being rather standard.  I'm in Hawaii so shipping will also kick my backside on a near 100 pound anything too.

http://www.microcogen.info/index.php?topic=640.0  Is that google a marvelous thing or what?

Casey

[veggie]

Glort,

Very thorough and understandable. Thanks for that.

cheers !

[BruceM]

+1  That was an excellent write up, Glort.  Very clear and well presented.  Bravo. 

[mobile_bob]

at the risk of being the sissy here

in some instances, there is or can be enough capacitance on the utility line to keep your induction generator generating even with the mains down.

one possibility

your neighbor has a homeshop and is working or has some piece of equipment running on a static converter when a tree falls down in a storm, cutting off the grid between him and the next neighbor, under this atypical condition it is possible for your generator to continue to generate using his capacitance to excite your induction generator.

now this might not be applicable, but then again it is possible that there are other appliances that have enough capacitance to keep you generating.

if under such conditions the power company finds a backfeed, while they generally will always check the down side for power, consider the possibility that after a big storm some poor lineman that has been
in the wires for several days with little sleep might not think and get a buzz...

you might not kill him, however if he gets zapped on the other side of a transformer it is more likely he will be injured or killed...

in any event he is going to be looking for why there is power on the line, and you will likely get a nasty knock on the door.

while this is not likely, bad things can and do happen

it is just something to consider before using the grid for excitation of an induction generator without some form of sophisticated switchgear to make damn sure you are disconnected from the grid should the grid lose power.

odds are probably 1 in a million that you could have a problem, but the odds are 1 in 1 if the conditions are right! 

just something to consider.

another thought

it is also possible if you live in an area with industry, or commercial using on the same line, that they might well have some power factor correction capacitance online in their operation, depending on where these capacitors are setup, you might find significant amounts of capacitance available to you to excite your induction generators...

depending on where you live, just about anything is possible.

just something to think about

Bill Roger's book, available from utterpower.com does a very good job of explaining induction generators, Bill is a retired power company EE and knows his chit when it comes to this sort of thing... among many other subjects.

it would be a book i would strongly suggest investing in if one is wanting to do the induction generator thing and most especially if he is wanting to grid tie.

while there is probably many area's on this rock that one could get buy with grid tie'ing just about anything,  there are also area's where they will pull your meter and charge hefty inspection and reconnect fee's if they find you doing something they don't like... and many power companies take a real dim view of connecting any sort of power to their grid... most especially diy stuff that is not certified stuff installed by a licensed and bonded company, with an EE on staff, with prior notice, and prior approvals.. blah blah blah.

just sayin' 

bob g

[Tom Reed]

I've had that knock on the door, and my generator was running, and the utility super visor was hopping mad. When I insisted it wasn't me he got even madder! So I got him to pull the meter and ..... it wasn't me. The dope grower neighbor had 2 meters and when they disconnected him for stealing power he ran a bypass through the woods to the other meter. The lineman had switched the line off after the bypass, so the line was still hot. The supervisor reminded him to check for power and was he surprised to find the line was still hot!

[vdubnut62]

I have had the lineman ask a bunch of questions when I was the only house on the line with the lights on.
Seriously, he grilled me long and hard about my possibly back feeding the grid while he was working on the lines, but he was a regular guy and saw that I wasn't an idiot ( fooled him good!) and he was fine
with my setup.
Ron.

[mobile_bob]

Glort

you must understand the following

as the admin of this forum, i among others have some responsibility for the content of the forum

as such we (i) am very careful to vet all possible failure points to those who ask, for the following reasons

while you may get by without issues, there is likely someone somewhere at sometime that will underestimate or not fully appreciate all possible outcomes, get hurt themselves or hurt someone else...

i don't want it on my conscience!

maybe you can sleep well leaving loose ends, but i can't.

if for whatever reason your induction generator does not cut out in a power failure, and backfeeds the grid,  and somebodies daddy gets hurt, or maybe worse kid playing in a mud puddle out behind your house when the line drops in the water with him? then what?

you don't think momma bear is going to snag you up by the short hairs?

sure they will try to sue the power company, but when it is found the power that killed their kid was from your setup, you better bet you will be sitting somewhere with lots of time on your hands to think about the err of your thinking.

personally i don't care if it is one chance in 10 billion, the odds are still too high for my liking

no i cannot win the lottery, but i can see me winning (losing) this lottery.

there is a reason for UL listing and the UL1741 and NEC codes,  it keeps everyone safer in the long run.

anyone here can go forth and do whatever they like, but i will state this for the record

ANYONE WISHING TO CONNECT ANYTHING TO BACKFEED THE GRID HAD BEST FOLLOW ALL APPLICABLE LAWS, REGULATIONS, CODES ETC. AS LAID OUT BY THE UL TEST LABS, NEC, LOCAL, STATE, FEDERAL LAWS, AND ALL RULES AS DICTATED BY THEIR POWER COMPANY... FAILURE TO DO SO MEANS,  ALL RISK IS ON YOU, AND DO NOT COME BACK HERE WHINING ABOUT SOMETHING YOU READ HERE AND DECIDED TO GO WITH OR WITHOUT.

THIS FORUM, ITS OWNERS, MANAGEMENT, MEMBERSHIP, AND VISITORS ACCEPT NO RESPONSIBILITY FOR THINGS SOMEONE MIGHT CHOOSE TO DO CONTRARY TO ALL APPLICABLE LAWS, REGULATIONS, CODES AND RULES.

FWIW

now having said all that

i have tried to clearly outline a couple of the possible ways that an induction generator might not de-energize should the excitation current of the grid cease.  i am not the sharpest tool in the shed and the
ways i described are by no means all inclusive, i am sure there are countless other ways such a fault could occur, to deny the possibility seems a bit more than naive to me, it borders on something far worse in my mind.

to say something cannot happen is an open invitation for it to happen.

bob g

[mobile_bob]

i would also like to add the following

power factor correction can be done two ways

at the load or in bulk

at the load means if the machine is not running the capacitance is also offline

in bulk means there is capacitance in larger banks that are connected to the line before the load and its relay/contactors

yes bulk power factor is supposed to disconnect with a power outage, but who can guarantee that? you?

i have worked on electrical systems of enough old plants to tell you that there are all sorts of cobbed together stuff that would never pass a modern inspection... with all sorts of stuff connected here and there in unmarked panels etc.

then there is this

i realize it takes x amount of capacitance to get an induction generator to generate, however how much capacitance does it take to continue to generate once it is excited?  and for how long?  at what voltage drop?  maybe not enough capacitance and the voltage drops but not to zero? then what?  what if it drops to even 30vac and back feeds the transformer in the alley?  even a quarter of a 9600v/240v is going to cause a nasty surprise for someone?

i don't know the answers to all these questions, and i bet you won't find anyone that can tell you definitively either!

don't believe me?  go find an EE and ask him these questions, and be sure to bring along my list of concerns and see if he will sign off on such a scheme! 

it ain't gonna happen my friend. you will not find a single EE to sign off once he reads this thread in total.

bob g

[BruceM]

There is a good chance your neighbor might have 100 uF or more on each split phase.   

There is a former electrician selling "Stetzer Filters" which he alleges will clean up "dirty power".  The filters are 20uF motor run capacitors in a plastic box that plug in.  You neighbor may have 10 of these throughout his or her house.  They are in fact pathetic filters, and have no effect whatsoever on the common mode noise which is so common from switching supplies and power line arcing (arcing on loose hardware from induced voltage).  They do show improvement in the readings by the "Stetzer Meter", since it only measures line to neutral differential interference.  So the capacitor increases common mode noise, while decreasing differential, so wow, things look better with the meter.  A simple AM radio test will show that it does in fact NOT reduce radiated emissions in a meaningful manner. 

There is likely an non-isolating transformer (WYE grounding practice connects the primary neutral to the secondary neutral) between the proposed synchronous generator and neighbor.  That MAY save you.

Does anyone know how the approved gear actually detects grid power?

[glort]

OK, sorry.

I have removed my comments so as no one gets led astray or does the wrong thing or gets hurt.

My apologies again.

[uber39]

Sorry all, but I saw nothing wrong with anything that was writen.
Instructions where clear and safe IMO option
I did do it here after consulting a EE, the main problem I did have was that the gen seemed to upset the solar inverters enough to take them offline, that was the only reason I stopped going in that direction
Now setting up useing a 50 amp DC gen to charge batts, when they get to 54v then a couple GTI's kick in and feeds back to grid safely and almost legal 


       Ian

[BruceM]

A good technical article on grid islanding:

www.icrepq.com/icrepq'12/542-etxegarai.pdf‎

It looks like most smaller scale islanding systems monitor voltage, frequency, waveform, PF to determine that the grid has failed. 
The likelyhood of a very local grid fail such that the load presented will allow the synchronous generator to continue to run at all is unlikely, but those odds would be improved with an islanding system to automatically disconnect and shut down if at least voltage and frequency were part of the shutdown parameters. 

[mobile_bob]

Bruce

thanks for the pdf, very interesting indeed

a few thoughts if i might


because many will be running an induction generator with a single or maybe a twin cylinder engine
and considering the grid frequency is generally very stable at either 50 or 60hz

the induction generator while grid connected is locked in at either 50 or 60 hz of the grid, it cannot shift
one way of the other, so...

could one simply monitor (electronically) the frequency at the generator, and if it is found to shift off frequency even by as much as maybe 0.1 hz the switchgear would be directed to disconnect the induction generator?

so basically you have a bit of electronics, that monitor the hz,  that allows for maybe a tenth of a hz fluctuation, it controls the contactor that has the induction generator connected to the grid... if the little black box ever sees the frequency shift it opens the control circuit relay which opens the control coil on the induction motor/generator contactor.

if that makes sense?

seems to me that might be something that could be pretty simple to put together, have it use positive logic in that if the black box ever fails there would be a disconnect?  maybe some sort of watchdog system that does a concurrent check every second and if it does not get a return signal telling it all things are fine, a disconnect is the result.. sort of a failsafe to disconnect?

would that be a hard thing to come up with?

these GE watt/hr digital meter heads i have been using in testing have an available option card, that card can be programmed to trip a set of contacts based on high/low volts, hz, and heaven knows what else.. also because the meterhead is able to tell and indicate which direction the current is flowing (either from the grid or to the grid) it might be the option card could be setup to control the switchgear for the grid tied induction generator?  i think maybe it could be setup to do so, although it is unlikely that it would be an approved use of the technology, and it might be that GE would not want the thing used in this manner?

i don't want to be the guy that pee's on folks idea's, i just think maybe there are ways to implement them in as safe a manner as is possible.

if that makes sense?

bob g

[LowGear]

so basically you have a bit of electronics, that monitor the hz,  that allows for maybe a tenth of a hz fluctuation, it controls the contactor that has the induction generator connected to the grid... if the little black box ever sees the frequency shift it opens the control circuit relay which opens the control coil on the induction motor/generator contactor.

In Hawaii the SMA inverters are adjusted to accept +- 1.5 before signing off.  And it happens a couple of times a year.

Casey