Has anyone solved the induction gen grid tie problem yet?

[(unknown)]

http://www.fieldlines.com/story/2005/3/16/183628/827

Hi.  I'm Pete Stanaitis from western Wisconsin.  I was trying to ask a quesstion of "Friendly Texas" related to the above thread, but his email is apparently not working.  And, I couldn;t figure out how to get back to the thread above to try to add to it.

Here's our situation, and my question:

Did you ever get your grid-tied induction generator going?  If so, do you have any words of wisfdom to add?  Are you still working on it?

If you are, here's on info source you may not have seen:

http://findarticles.com/p/articles/mi_qa3726/is_200010/ai_n8909370

It's called "Induction Generators, what can go wrong", but it's a pretty good read, and NOT negative.

 My son and I want to build separate 25kw to 45 kw single phase grid tied power generation systems that will be driven by spark ignition engines fed with wood sources producer gas.

    I saw the  infromative thread on an otherpower discussion group this morning and wanted to know  if you guys had gotten further than we have.

We know we can produced the mechanical power, but, of course, the grid-tie thing is the issue.   We got (we thought) a long way on the path to success, working with our local utility, on using the induction motor technique that you guys discussed.    We had found a source company to rewind 3 phase induction motors to output single phase, becuase we couldn't find single phase induction motors big enough.  We found a source of  (we thought) the electrical.electronics package that would do the job.

  We were about ready to start spending money when we had a sorta "final" meeting with the line supervisor.   At that point they said, simply  "nice idea, but no thanks."

They told us that we shouldn't have any problems getting conventional generator systems that came with all the controls, since folks used to sell them power for demand situations back when diesel fuel was cheap.   Yah, but those systems probably started at 10KW or higher.

Just yesterday, I thought that I'd give up and go get a big enough inverter, complete with controls, like the solar and wind guys use.  Yup,  think $50,000 to $80,000 or more!

So, we are sorta back to square one.  25KW to 50 or 75KW seems to be the unreachable range.

Pete Stanaitis

[dnix71]

The issue may be environmental. If you are generating power commercially by burning wood and selling it, then you may be required to get permits from the state and feds to do it legally. If you just make it for your own use and nobody hears about it, then fine.

25kw of wood gas is no small amount of wood either. Nor is the legal, safe disposal of the waste. If you are fined by the EPA or similar for improper disposal, the power company would be financially liable if you couldn't pay, because they knew what you were doing and benefited from it and they have "deeper pockets" than you do. Lawyers go after the money.

Grid tied solar or wind is fine. The tree huggers can't complain too much about that.

In Florida, the power company can't get anyone to sign off on new or existing additions that involve coal or diesel. Everything has to be natural gas or nuke. Even the cleaner coal that is gassified first isn't acceptable.

You are also competeing with the power company, too. Why should they buy from you? They have equipment and full control over it. Why risk buying from someone who may not be there when they really need it.

The best use of self generation is for your own benefit in shaving peak use. Here they charge about $8.30 a watt for every kw over 10 for the highest 15 minute peak during the month. A large church in Fort Lauderdale installed 40KW of generators that just run the a/c on Sunday. They probably have a manual transfer switch for when the generator fails, but it isn't grid-tied.

It was actually cheaper to buy and run a generator than to pay the extra 40kw peak charge each month.

[scottsAI]

Nice write up dnix71.

Peak demand charge does not apply to big customers.

I suggested co-generation to my company. They said don't need it, they had started putting them in and the electric company renegotiated 25yr better deal if they did not. We have our own gas wells to power the generators. We wanted the generators for backup, did not like shutting down due to power failures. Electric company brought in second power line from another grid. Then 4 years ago they lost power for couple days, Now a third grid power is being brought in. Spending Millions on this project. Triple power lines to insure their power. Wow.

Have fun,

Scott.

[(unknown)]

Thank you guys for your input, but maybe I wasn't clear:

   I already know that I can sell the power back at retail.  5 other people in our community are already doing it, with solar and wind.

  And, I don't have any legal problems, the contract with the power company is in hand and hundred of people around here alread have biomass furnaces.

   What I need is information  on exact sources for the controls I need to connect.  There's plenty of it available for wind and for solar, up to about 7 or 8 KW, but that's with DC as the input.

   OTOH, if I want to set up a 1 megawatt system, generating 3 phase AC, again, no problem.  

   If I give up and generate DC in my range (25 KW to 75KW), then the GRID TIE inverters are about $80,000!

   So, I need a practical anti-islanding, line-man safe, under and over voltage controller to manage the hook up in my case.

Pete Stanaitis

---------------

[scottsAI]

Pete,

Your problem is 25kw is outside hobbyist range, few will have any experience. Yet not big enough for a low cost commercial system.

Induction motor used as a generator should not require any voltage control. Grid will control voltage. Generator output (should) fail if grid fails. Provides decently safe grid connection. Some motors have residual magnetism, generator continues outputting with a down grid. Yet the grid should present an overload wiping magnetism. Motor output requires no load protection (loss of grid), over load protection (breaker). Controller should be simple. Basically a reverse power detector and no load detector.

Motor single phase

25kw is 33hp motor, all will be 3 phase.

With a Delta wound motor, in single phase can load it 59%.

56Hp 3 phase motor delta can meet your needs.

Check eBay, not a costly motor.

25kw is pushing what is possible on a residential power feed, to be able to sell at retail.

Check netmetering rules, most do not pay for any power back feed if you don't use it later.

The few that do, will only pay fuel avoidance cost, less then 2 cent kwhr.

NOT retail.

Have fun,

Scott Beversdorf.

[oztules]

Perhaps talk to the fellas at http://www.prairieturbines.com/ . They do micro's for 5kw, and the same controller should be fine for 25kw. They seem to have been through all the problems and solved them.

............oztules

[alcul8r]

A lot of the grid-tied wind gennies from the 70s and 80s solved this by monitoring the frequency output(actually the rpm of generator)

Too low and they were not putting anything into the grid, possibly motoring.

Too high and they were no longer connected to and controlled by the grid.

Other than contactor or electronic switching size, no scaling needed.

[RogerS]

Hi,  If you have your generator controls with a governor that will hold hold your rpm levels where thay need to be I assume all you are needing is anti-islanding protection to make the utility happy and keep everyone safe.  As I understand it,  it would take a very rare alingment of local load matching your exact output and several other factors before islanding could occur with an asynchronous induction machine.  There is also a theoretical chance of something called ferro-resonance which can cause extreme spikes in voltage in just a few cycles.

    Two intertie protections relays I have looked at should work for you if I understand your problem with the utility. Beckwith Electric markets a model M-3410A intertie/gernator proection relay.  Schweitzer Engineering has a model SEL-547 distributed interconnection relay.  I believe the Beckwith is for 10KW to 2MW.   They can both be programmed to meet most any criteria that the utility would require. I think both have options for single-phase.  

Good luck,

RogerS

[Madscientist267]

Additional question for anyone answering the original:

Seems newbish, and is for me, so I'll ask it. I understand the concept of islanding, and have looked at several documents on the subject, but it still doesn't exactly make sense how this condition can be accurately detected.

It would seem to me that a KW range inverter (or generator) would see a significant overload condition under these circumstances (due to surrounding houses, etc), causing some sort of protection trip, but apparently not always (ie middle of the night when loads are minimal).

I have been wondering about this increasingly lately because I am gathering my data now to do a future PV installation that I intend to grid tie, rather than just dump the surplus when the batteries are full. Just something else to apparently watch out for... does it ever end?

Steve

[DamonHD]

You might look at the mechanisms to detect grid failure specified in such engineering standards as the UK's "G83/1" that defines how small UK grid-tie inverters up to 16A per phase must work.  Might be dull reading, but should be definitive.

Rgds

Damon

[RogerS]

Steve,

    When there is a power failure in an area that is caused by lightning, a tree branch over a line or whatever, a portion of the grid is cut off from the working portion of the electrial network.  If the area that is cut off were to have someone living on it that had a grid-tied generator operating,  it might be possible for their generator to produce and "island" of power that was not under the control of the utility company.  This could result in a lineman getting ahold of a "live" line that was presumed to be dead.  This is a very valid concern of the power company and is why they require protection against such an occurrence.  It is very hard for a small generator to keep the power up in even a small area, but gets more likely as the size is increased.  An asyn

chronous induction generator gets it excitation current from the grid and should rapidly fail when the grid goes down.  

   I believe most of the island detecting methods rely of the fact that in a grid failure the voltage and frequency will begin to waiver from the norm.  They also measure how fast it is changing (time-over frequency).  If it gets to far from the utility's parameters  the protection relays will disconnect the generator from the grid.  Others here could explain it much better than myself(also pretty much of a newbie).  There is a document called IEEE 1547 that is going to be the future blueprint for most co-generation.  It looks pretty daunting at first,  but after several reads & sleeping of it a few times it all make more sense.  It why most all small at home systems use inverters  type systems (the companys that make tham have paid big bucks to get them approved).

Good luck with your projects,

RogerS

[(unknown)]

Thank you all for your comments.   Sorry that it took so long to get back to you.  We have bought and set up a Chinese JXQ-10A (wood)gas producer and have tested it.  We are in the final throws of setting up an old 12 hp Briggs and Stratton engine running a 5hp 2 phase induction motor as a generator. It will be connected to the woodgas shortly.  This is all a test setup to help us understand all the relationships better.  

   If anyone is interested, you can see our progrese, slow though it may be, at:

http://www.spaco.org/JXQ10A.htm

I have connected the 5hp motor in Wye, so I can get some 120 volt power and I can't quite get the C-2C connected phase currents right.  Things are close enough for our tests, though.  I will probably ask for help on that issue soon.  

P.S.  I did buy a copy of "motors as generators" by Nigel Smith.

Thanks again. I now have some digging to do to see about this switchgear.

Pete Stanaitis