Prairie Breezy Turbines again?

[CoolBreeze]

My understanding is that Prairie Turbines Breezy 5.5kw and 10kw  use passive blade stalling (aka blade flutter?) as a way of limiting current in the motor. According to Paul Gipe "most wind turbine designers do everything they can to avoid blade flutter, because flutter can destroy both the blades and the wind turbine".

According to Hugh Piggot "flutter is like driving downhill with badly balanced wheels". 

This seems to be the main possible issue with the Breezy...its ability to handle the large forces from higher winds.

Supposedy these turbines can handle high winds up to 70mph but what kind of stresses does this cause?

Is there anyone still lurking  out there who has long term experience with their Breezy. What are the maintenance/repair issues and costs? What about frequency
of bearing replacement? Blade replacement? Any incidences of tower strikes especially with the longer rotors of the 10k Breezy? All input appreciated


Also I wonder if Prairie Turbines have considered using larger blades to extract more power and some sort of current sense feedback to brake the machine at a certain max current.

[Perry S]

The breezy does use passive stalling to limit their rotor speed. This is a common method. But do not confuse stalling with flutter. Flutter entails the blades deforming, changing shape, and returning. This happens quickly and is usually a feature of very small turbines with flexible plastic blades like Southwest works with. Aerodynamic braking is merely using a specific airfoil (usually low perf) at a specific angle of attack such that the drag limits their top speed.

Perry

[12AX7]

I've never seen specs that mention "flutter" without "wow".

yes,   Wow and Flutter should be expressed in a percentage.

Guess I'm remembering the 'good old days' of analog.

ax7
Mark

[Flux]

I don't know much about this machine but as far as i know it is a grid tied induction generator. It therefore works at constant speed and the blade tsr will fall with wind speed. At some point the blades go into hard stall and the power drops off rapidly enough for the alternator not to pull out of its torque curve.

if this is balanced correctly it will be perfectly ok in high winds as long as it remains tied to the grid. If it comes off grid it will go out of control and it must have some safety feature such as a powerful brake or tip spoilers. These have been around a while so they must have this essential feature.

You are confusing normal blade stall at excessive angle of attacks with  the so called aeroelastic stall uses in certain small turbines to limit speed. This is the blade flutter that you refer to and apart from the stress on the blades you can't live with the noise so it's a no go process as far as I am concerned.

The Prairie certainly doesn't use this, it would not work beyond small machines.

Induction grid tie is a proven method and has been around a long time. As long as it incorporates the back up I mentioned for grid loss then it should be fine.

Flux

[CoolBreeze]

Thanks for clearing up the differences between flutter and stall.

From reading the Prairie turbines website, and having purchased the book and talked to Tim the owner it appears the Breezy 5.5 begins producing partial power (connecting and then disconnecting to grid intermittently as it is spinning up to speed) at around 11mph (4.9 m/s)  or 12 mph, reaches 1.5kw at 14mph (6.39 m/s) , 2.2kw at 15mph (6.7 m/s) and doesn't reach full power until about 37mph (16.5 m/s) at which point the output is flat at 5.5kw even with increasing wind speeds.

I am looking at a few wind sites for this turbine(s). One has cheap easy to purchase land but marginal wind speeds. I'm thinking that the Breezy and its  power curve is more suitable to a higher wind class.


Currently this turbine has an electromechnical brake that stops the turbine if motor shaft rpms exceeds a certain limit. It also brakes when utility power is lost or disconnects .

Would it make sense to   change the power curve and increase  energy production  by increasing blade size? So that max power is reached closer to say 30mph? I assume dangerous  overcurrent might  be reached but could be prevented by triggering the microcontroller to energize the same brake relay to shut down the turbine.   I don't know if that microcontroller takes digital or analog input(s)? Is it worth the trouble?

 

[Flux]

As you say this is a high wind machine.

The first thought is that the blade size and profile has been chosen to maintain stall control in all wind speeds. if you fit larger blades or change the profile you will most likely pull it out of stall and it will have to activate the brake. There is no certainty that this brake is designed to stop bigger blades and it is probably designed for fault only use. if you start activating it regularly as you pull the generator out during gusts then you may be taxing it beyond its design factors.

Induction machines are not the best suited to low wind production anyway as you have to supply the magnetising current before you get useful power.

It may be possible to extend the low wind performance with bigger blades if you rarely see the high winds and you make sure the brake can cope. You will almost certainly not burn the alternator out but it will pull out of its torque curve and shed 90% of the load and let your blades run away.

More advanced induction machines have 2 alternators with different speeds ( pole number or gearbox) and change speed in the higher winds. That way you get a better compromise in low winds without spoiling the top end power.

Flux

[CoolBreeze]

This motor is an off the shelf Nord brand induction gearmotor used in overhead crane operations. According to Paul Gipe in Windpower generally you want the
brake on the main (low speed) shaft not on the high speed generator in case the gear box fails the brake can still stop the rotor. Not sure where the brake is on this
particular motor. Gipe also says wind turbine manufacturers have learned over the years that an aerodynamic brake is good to have as well in case
the electromechanical or hydraulic one fails in a no electric load condition. He says the most  succesful aerodynamic brakes have been centrifugal tip brakes and spoilers.

[Perry S]

A parking brake is good to have on the low speed side but an operational brake is best left to the high speed side. Much less braking torque and associated wear presented there. Those forces are translated through the gearbox which is not great but that is the least of the two evils. I have no idea where Breezy 's brakes are.
Aero braking is actually the primary braking method for larger turbines, accomplished via pitch control. Redundancy is required via IEC turbine codes so each pitch axis has its own independent system with battery backup in case of a grid loss. Larger turbines will have a secondary brake that kooks like a 4-5 ft dia disk brake right between the gen and gearbox.

Perry

[Tom Sullivan]

I've monitored this site on and off for a few years, but finally joined, since I may have some knowledge useful for posting once in a while too.  I have extensive experience with the Breezy 5.5.  I dropped my 140' tilt tower down yesterday and removed it for the final time.  It's very noisy, and production numbers were well below my expectations (some of which is my wind zone).  Feel free to ask me any questions about experiences with the design. Some detail of the original construction is here; http://www.builditsolar.com/Projects/Wind/TomTurbine/Main.htm

Looking at possibly building a large axial flow (non-grid tie) to supplement my solar hot water heat.  Seems a shame to have such a nice wind tower and no turbine on it.  I befriended a retired electrical engineer just recently while looking at his recently comleted 500w axial flow turbine.  His review and assessment of the Breezy was enough to push me to the inevitable decision to remove it.  He's offered me free use (for unlimited time) of an 1800 watt Jacobs that he's reconditioned, but needs a bit more work (blades, tail, bearing assy and slip-ring).  But that's another decision.

Tom Sullivan

[Perry1]

Hi Tom and welcome aboard! Glad you joined.
I'm interested in your opinions on why the Breezy wasn't a good turbine. You mention noise and power performance. Have you been around other similar sized turbines to have a feel as to the relative sound levels between different makes? Also with the power. Can you elaborate? How much was your site and how much was the turbine? Did it perform to their power curve?
Thanks,
Perry

[Tom Sullivan]

Perry,
  I had looked at a lot of turbines, wanting something big enough to make a significant dent in my electric bill.  Numbers posted on their site showed I should generate $50 to $60 a month, based on my wind zone in the U.P. of Michigan.  I generated 600 KWh of juice in a bit over 1 1/2 years, clearly rendering this investment a hobby.  During a good wind event, the unit would produce 20 or 30 KWh's in a day or two, and in the spring of 2009 I saw a 25 day period with almost 100 KWh's generated, still no where near enough juice for me to recommend this unit to builders in a zone 2 or 3 area.  I spoke with a builder in Saskatchewan that wanted info on my tower for his 10K Breezy he was building, and his production numbers on his 5.5KW unit were very good; $80 a month in generation.  This unit will work when erected in the wind belt.
   My opinion, and now substantiated by Larry, the electrical engineer I'm working with now, is that the design will not work in lower wind zones.  I've had emails from a bunch of Breezy owners in "like wind zones" with "like results".  The Breezy designers promised us over the last couple of years they were going to develop improvements so these units would work in lower wind zones, but their time has been spent on the 10K unit instead.  I can't blame them, selling new units makes them more money than supporting ones already sold.  They talked about different blade designs, a different controller that would lock in one phase until generation reached enough to support 2 phases, and also a motorized furling tail that would allow a better blade for lower winds but still protect the unit during higher winds.
As far as noise, the blade noise is substantially louder than units of comparable blades size.  I was near every turbine at the Midwest Renewable Energy Fair and none were even close to the noise level of mine.  Then when the unit locks in, having reached generation speed, a load "doyng" is heard everytime it locks in.  In marginal winds, the unit can lock in every 10-15 seconds, since it disengages within a second or two of when the amperage drops below generation.  I live in the middle of a 30 acre lot and have had neighbors from every side of me "comment" that they can "really hear" my wind turbine, kind of a friendly reminder their not real impressed with the noise level. 
   I haven't even touched on the experimental blades and hubs I've gone through to attempt to improve the production.  That's for another posting.

Tom Sullivan

[clintonbriley]

Hey Tom,
Thanks for the information on the performance of your breezy here in michigan. 
I decided early on that the only way the breezy 5.5 is likely to work well here in a
part of michigan with a similar wind zone to yours, is with a considerably larger
swept area  (conclusions which your assessments support, thanks very much
for sharing by the way).   
In my opinion switching to a 3 blade efficient profile prop (with the largest diameter
that the gear ratio of the gearbox will allow....perhaps as much as 25 feet) would
be what is needed to generate suitable amounts of electricity in my wind zone rated
at between 2 and 3.
Of course the issue of regulating the prop in higher winds requires further modification.
The motorized tail sounds interesting and is probably the simplest method to limit
power input.  I've been looking at some different designs for blade pitch control as
well (both active and passive).  To prevent damage to the prop from overspeeding
in a no load condition (failed brake system) a Jacobs style passive pitch control would
work.... http://www.fieldlines.com/board/index.php/topic,128283.html
but would do no good in regulating torque input while an asynchronous generator is
connected to the grid. 
One passive design from the 1920's I found that will regulate torque within a narrow
rpm range is here... http://www.freepatentsonline.com/1533467.pdf
I've been considering an active pitch control design with a passive overspeed
protection built in.  This would require more slip rings on the nacelle and on the
prop shaft to control the blade pitch though as well as programming a logic
circuit to handle this extra responsibility.  So more complexity and cost in
the long run.  It's all a lot of work to go through for what is likely to be a very modest
return though, especially since my power company in Michigan does not offer a
favorable net metering plan. 
Thanks again for sharing, I'm very interested to see how your future projects
work out, please keep posting!
Clint

[Tom Sullivan]

I built a beautiful set of 11' blades for the machine within a month of going live.  I used a variety of sources for designing my final blade profile (mostly OtherPower.com info).  They had 4 degrees at the root, and a gradual decrease down to 0 at the tips.  Since the hub already has 4 degrees built into it, the profile was pretty agressive.  I re-used the 4 blade hub and the thing went into overspeed in the very first wind.  The following spring a built a new 3 blade hub, with little if any built in pitch on the hub (can't remember now, it's been well over a year ago, but I think it was 2 degrees).  The turbine actually did decent for a couple weeks, and the blade noise was significantly better.  Production went up maybe 20%, but 20% of almost nothing is still almost nothing.  I feared high winds with those blades without a furling tail, or all the safisticated controls like the Endurance Wind Turbine uses for an A/C induction motor wind turbine (a beautiful machine, but way out of my price range).  The 3-blade hub was an "experiment" and as such, was not built up to be used more than a few days.  Since it was working OK, I forgot about the temporary nature of the hub.  We had a pretty good wind one night and I remember hearing the thing running most of the night.  Really early, before daylight, I noticed the turbine was quiet, and figured it went into overspeed.  Looked at it as soon as I got up that AM and there were no blades on it.  I suspected a shaft failure, but found the hub had "oil canned" since it hadn't been beefed up in the "temporary design" to deal with that problem (like my original hub).  With 2 blades pretty much destroyed, one damaged but usable, and one left over from the 4 blade hub, it was evident I could go back to the original system or start laminating and carving again.  The original design was reinstalled, I settled for my 50 KWh's a month and started working on my solar prrojects, which actually give me a pretty decent ROI.

I too looked at the Jacobs feathering prop design (I'm a pilot flying with that same concept on my airplane), as well as possible tail furling systems.  The real issue is minumum wind for generation.  I'm not as educated in wind theory, or have the overall wind generation experience of the guru's on this site, but I can explain in simple layman terms what the issue is for me.  Minimum generation for the turbine is 2200 watts, any less and the motor "uses juice" instead of generating it.  The generation band for the unit is very narrow.  Prairie Turbines gets away with this limitation when the unit is working in wind zones where they can "afford" to waste off some of the wind energy.  The narrow generation band and poor efficiency blades work decent in those good wind zones, but do not in marginal ones.  I've had days, even weeks I could have produced a 1 KWh, every hour, for that long,with a better matched turbine for my winds, but the unit had not met the "2200 watt minumum" kick in power (well, actually 120 RPM's, but one in the same; not enough wind to support generation with this turbine).
 
   I'm presently about half way through the new book from Dan & Dan, and the first several chapters pretty much explains a lot of the problems I've seen with this design.  I need a turbine that will make much less than the 2.2 KW threshold of the Breezy 5.5.  I will be much more satisfied with 600-1200 watts all day, for days, than the ocassional 2300 KW's for a few hours.

   Finally, my posting about this is not to knock the product, but to make others aware of what to watch for based on their unique wind resources and any close proximity of neighbors.  A series of posts like mine, found by me a few years ago, could have saved me a lot of work, heart ache, and money.  And I have a bunch of emails and past phone calls from other builders in the Midwest that have experienced the same results.

Tom Sullivan

[clintonbriley]

I didn't know that the breezy's motor was a "2200 watt or nothing" generator.
I do agree that it is a good turbine for high wind areas, and I think it could be
modified to work well in fair wind areas too, but to do it would require making
it a more complex and higher maintenance machine.
Clint

[RogerS]

Tom,

I read your diary at builditsolar sometime ago with great interest because I have been pursuing a Breezy build for sometime now.  Lately I've been trying to understand and educate myself on stall regulation and how it pertains to the breezy.  The rotor on the breezy turns at about a constant 124 RPM when it is generating.  At 18 foot diameter, this gives a tip speed of about 77MPH.   If I'm figuring correctly, this woud give an angle of attack of the apparent wind over the blade tip of 16 degrees (wind speed 23/blade tip speed 77= tan AOA)   From this you must subtract the 5 degree incidence (setting angle) that is build into the hub and we get an AOA of 11 dregrees at 23MPH windspeed.  Now we don't have stall data for the airfoil profile that the breezy uses on the outer 1/3 of its blade, but most flattish bottom airfoils that I have found data on (www.worldofkrauss.com) stall at about 15 degrees or have a maximum coefficient of lift at about 15 degrees.  What I think this means is that the breezy if no where close to aerodynamic stall at 23MPH.  At that windspeed you have to move back to the 7 foot mark (14 ft diamter) to get a AOA that would be at stall.

    I've almost concluded that the breezy is a "drag regulated" machine.  The 4 blades and high drag inner blade profiles matched with a rotor size that keeps it in check at higher wind speeds.  I have no idea what percentage of the blade needs to be in  aerodynamic stall to "stall regulate", but since most of the power is generated by the outer 1/3 of the blade I would think  most all of it would need to be.  (if anyone has an idea on this please respond).

   The breezy was developed in a pretty high wind area (probably zone 3 or 4) and I believe their production numbers  are correct at that location.

   I am considering using a twisted blade (maybe just the outer 1/3) along with a different airfoil at the tip that stalls at about 10 degrees AOA, and maybe with a lower max lift coefficient.  This might allow for a slightly larger rotor.   I think a torque regulating hub would be a great answer.  We know the max torque that we can allow by what motor we are using.

   By the way, the 10K version which I understand uses the same ratio gear box but with a 5 foot larger diameter rotor and a tip speed of about 100MPH is even further from stall at 23MPH wind speed.

  Again, I maybe way off base with my ideas.  I'm just trying to figure out "stall regulation"  and I thin the breezy could be made to work better.

RogerS

[Tom Sullivan]

Roger,

I too think the unit could work in lower winds, but it will take a pretty sharp turbine guy to get there without a lot of experimenting and frustration (re; time, energy, patience and money).  The real challenge is the "narrow band" of blade speed the unit will work in, especially the minimum start up threshold of 2200 watts.  In winds between 10 and 15 MPH, it will not stay locked in, and the blade speed drops at every "lock-in" , creating this in and out cycling.  More aggressive blades helped some, but not as much as I expected.  With the better blades, I was seeing more situations with the unit on the edge of "overspeed shut down".  This unit has no auto reset feature, so every time it shuts itself down it requires a manual reset.  A furling tail may be the answer for more aggressive blades, but that will entail a complete rework of the bearing, mount, and tail attach point.  We're going into severe experimental land with that too.  No telling how many versions / modifications it would take to get it right.  I'm just not sure I've got enough desire to work through all that and still have a good chance the effort does nothing to increase production.
   Having studied the "Endurance Wind Turbine", which uses an induction motor much like the Breezy, I see they have dedicated a lot of resources to get where they are at.  I'll bet they spent 10's of thousands, if not 6 figures, to get the quality unit they have today.  They rely on full electronic controls, and have used those controls to get a much lower "lock-in" speed.  I think their minimum generation is at least half that of the Breezy, which I think puts it a lot closer to that of a comparably sized DC turbine.  Unfortunately, I can't drop $35k-$40K for one.

Tom

[RogerS]

Tom,

I can only imagine your frustration.  Did the 3 bladed rotor that you made also use the 11 foot blades that you made or were they different?  I'm know that the Breezy is now using an electronic soft starter in place of older mechanical relay that they used originally.  This was to help the the noise or shock to the turbine when it kicked on.  Do you know which you had?

I am familiar with the Endurance turbine.  I actually spoke on the phone with the designer several years ago  when it was still listed as a prototype.  A really nice guy who spent about 45 minutes talking to me about wind turbines.   He said they were selling them as prototypes, but since my area did not have net metering  there was no way it would work out for me.  I  looked at their web site this morning and I see they now have two 5kw models.  One uses a larger rotor & larger ratio gear box.  Both  appear to have about the same tip speed.  The larger unit lists itself as being a split phase generator.  I wonder if this somehow allows for the dual voltage generation.  A 7.5 to 10HP split phase motor would be pretty rare I think.

I see that the nation renewable energy lab (NREL) is now testing an 11KW turbine from Gaia-Wind (www.gaia-wind.com) that uses a huge 13 meter rotor that is designed for low wind areas.  Interesting stuff.

Thanks for your helpful posts.

 RogerS

[Tom Sullivan]

Roger,

I used the 11 foot "custom built blades" on both the 4 blade and 3 blade hubs.  I had the best success of the turbine during the 3-blade test (wasn't significantly better though).  I wasn't aware of the soft start feature, suspect I have the mechanical relay.  With all the discussion here on this unit, and reviewing the total cost to get the old Jacobs going on my tower, I'm at least "thinking" about building another 11' blade to match the two I have left and re-construct the bearing/mount/and tail system to a furling tail concept.  That minimum threshold of power at 2200 watts is still a nagging issue though.  In my wind zone I still think the DC units will win the tortoise and hare contest, in relation to net production.

Tom

[clintonbriley]

The Gaia turbine that RogerS points out has a 42 foot dia blade matched up to an asynchronous generator rated at 11 kw.
Like the breezy, it employs a passive stall blade design, a disc brake located behind the gearbox, and what appears to be
an industrial 3 phase motor for the generator.  It also has centrifugally activated tip flaps for redundant over speed control
in case the brake fails to stop the rotor, and has a two blade rotor with a "teater" hub.  Cut in speed is listed at 7.8 mph
with full rated output at 21 mph.  For such a large swept area in proportion to a comparably small generator, I'm impressed
that they were able to design a blade which uses passive stall to regulate input to the generator.  Perhaps there is hope
that a better low wind blade can be designed for the breezy after all. 
Clint

[Tom Sullivan]

Clint,

Found some pictures of my 10 foot turbine blades I made for the Breezy that were too much for the machine (at least too much without other major changes like a furling tail and who knows what else).  The blades are 16" wide at the root, and 8" at the tip.  The two I have left are in very good shape after 18 months in the weather.  No sign of warpage or deterioration.  I really like the way laminating stabilizes the wood.

Hope someone finds this interesting.  I filled twelve 45 gallon trash bags with shavings after this project.

Tom Sullivan

[clintonbriley]

The blades look great Tom.  Are these straight pitch blades or is there a taper? 
Clint

[Tom Sullivan]

The blades were set with a 4 degrees washout on the actual blades, and the hub had 5 degrees twist designed into it.  So the effective blade angle of attack was 9 degrees at the root and 5 degrees at the tip.

Tom

[clintonbriley]

Very nice, I intended to write twist, not taper.  Thanks for reading
between the lines.  I recall you said these weren't on your
breezy for very long, but did they run much quieter than
the clubby breezy blades?
Clint

[clintonbriley]

Sorry Tom, I didn't recall you said you used the same blades on the 4 blade hub as you did on the 3 blade hub.
You called them "custom built blades".  Where did you get the specs to build them?
Clint

[Tom Sullivan]

   The blades were installed on the original 4-blade hub in early December of 2008.  The turbine went into "overspeed shutdown" right after turning it on (pretty good winds that day).  Since I was scheduled for rotator cuff surgery two days later, I immediately resigned to the fact they were not going to work without more changes, and pulled those blades off and lived with the original ones until spring.  In May of 2009 I built a 3-blade hub with only 2 degrees of washout.  I installed that combination and it was quieter, and production was a bit higher (see earlier post for demise of that test).

  I designed them myself, using information from a variety of sources, including Other Power.  I knew I was pretty much in "extreme experimental land" with these blades, as no one else had every put a true "airfoil" blade on this turbine.  With a "soft start" to possibly get rid of the "lock in bang", and a furling tail so the unit can handle more blade for low wind speed generation, the unit might have promise.  I am just too impatient at this point to put a bunch more time into it, not knowing at what point I'll actually get a productive machine.

Tom

[clintonbriley]

I've had days, even weeks I could have produced a 1 KWh, every hour, for that long,with a better matched turbine for my winds, but the unit had not met the "2200 watt minumum" kick in power (well, actually 120 RPM's, but one in the same; not enough wind to support generation with this turbine).

Hey Tom, I've still been going over different possibilities concerning the breezy design limitations.  What can I say, I find the subject interesting.

Looking for a practical modification that will fit the existing breezy 5.5 platform, the basic options I see are to increase the blade diameter and/or
decrease generator size.  Both of these would require either pitch control or furling as have been previously disscussed.
My preference is to go with the torque governing pitch control hub option.
By going with a smaller generator, the 2200 watt minumum kick in could be reduced to better match lower wind potential, though it would
reduce the high end output.

With longer blades, tower strike due to blade flex is one concern that the breezy guys have mentioned.  Beyond that, the gearbox step-up
ratio becomes an issue if going very much larger.
How large do you think you can go with a three blade prop on your machine?
Clint

[Warrior]

Hello fellas,

Interesting post! I've been following this one. I have no experience with the Prairie turbine, but from what I can tell, the controller is based on rpm only to lock in the machine to the grid. RMP only is not a valid indication of actual windpower as the machine is free-wheeling and suddenly locks in and slows down, then cut out..etc

The old Enertech machines had a both windspeed & rpm based controller. The machine would cut it only if the wind was strong enough, i.e. enough power in the wind for the blades to overcome all loses and still have enough juice to pump into the grid. It has an anemometer on the tower. IMHO, it needs both parameters to controll the machine and avoid the cut in-cut out cycling.

Keep us posted on any progress.

[clintonbriley]

Hey Warrior,
No argument here about the value of an anemometer's input in the control circuit.  I'm guessing it's not included in the design due to
the extra cost it would add to the system since it does work without it.
Clint

[Tom Sullivan]

Clint,

Warrior hits the nail on the head, exactly what my EE said;  The TSR goes to heck on this thing because of the minimum generation level of the AC Inductive motor.  Once kicking in, unless the wind is pretty substantial, it will constantly kick back out because the tip speed drops below generation (the unit will actually use power if not dropped off line by the controls).  The blades I built would work with the original pitch I tried of 9 degrees; I really didn't need any additional length.  The issue was over-speed.  I am almost done on the Jacobs; presently rebuilding the variable pitch hub.  This hub design would probably work well on the Breezy, but the hub is way to small for a mill with 10' or larger blades (think my custom ones were 11').  A furling tail would work too, but would require a complete rework of my existing mill.

I'll run the Jacobs for a while, and then decide if I want to build a large PM Machine, or rework the Breezy.  I have a guy about 80 miles south of me (Abrams, WI. about 20 north of Green Bay, WI) that has two Endurance Turbines up on 128' towers.  He started with one, and added the second one a year later.  I have to believe he's happy with the production if he bought a second one.  I've studied that turbine on the company web site and it uses the same principal as the Breezy, but with far more sophisticated controls.  One feature that helps this unit is they energize one of the 3 windings in the induction motor rather than two in lower winds.  This drops the "cut-in" generation point in half from where the Breezy is at.  He was featured on the local radio station when installing the first unit, and quoted his installed price at $40,000.  Kind of puts that out of the reach of most of us with that price point.

Tom

[clintonbriley]

 

This hub design would probably work well on the Breezy, but the hub is way to small for a mill with 10' or larger blades (think my custom ones were 11').

Hey Tom,  I'm sorry if I misunderstood what you meant in the above quote, but the Jacobs hub is centrifugal (rpm-sensing-rpm-regulating) and is
designed for use in a variable speed wind turbine such as the Jacobs and the permanent-magnet axial flux generators that are the most common
subject matter on this site.  For those designs the centrifugal type hub works to prevent the turbine from overpowering the generator and also
protects from unloaded overspeeding.
For a "fixed speed" turbine such as the breezy, it would be completely useless for preventing the turbine from overpowering 
the generator, triggering the overspeed shutdown.  (ok, technically the fixed speed turbines are actually variable speed turbines, but as you
have pointed out, the rpm range for generating electricity is extremely narrow and so they are reffered to as fixed speed turbines).

The centrifugal type hub would protect a breezy turbine from self destruction in the event of brake failure, gearbox failure, or torque limiting
clutch failure (free wheeling turbine) though, so I'm not saying it wouldn't be useful.
If you look at this youtube video of the wes turbine, you will see a demonstration of a passive (spring controlled) torque
sensing- torque regulating hub of the type that would work on the breezy (I'd adapt it to a 3 bladed bevel gear type hub though).
http://www.youtube.com/watch?v=UC6TKcjNvyk
There is also this link to a fieldlines thread of which someone has posted pictures of a homemade looking hub which
works on similar principles though it pitches to stall instead of feather (opposite of the wes).
http://fieldlines.com/board/index.php/topic,140114.0.html

[jondecker76]

Hello

I have a lot of experience with Asynchronous Induction wind turbines, so I thought I would chime in.
About 2 years ago, I built a PLC controller to run some older 40KW and 60KW Enertech wind turbines (the old analogue controls were getting to be too much to maintain).  Since then, I have produced over a dozen controllers which run over 20 wind turbines (each controller can run up to 2 units).  I have also picked up a contract with a fairly large wind company to begin retrofitting some of their installations (they have over 7o installations around the US). I am currently also making a microcontroller based system for another client.

Here is what I can tell you from my experience:
- Tip brakes ("flippers") or other mechanical means to slow a runaway down is absolutely necessary with an induction turbine. I can't even begin to tell you how many I've seen self destruct from a runaway (either from failed controls or "slipping out" - going past the slip rating of the motor/alternator)
- Breezy's controller is overly simplified and not up to the task, IMO. I have seen them in person and I have the plans package. Using a simple hall-effect pickup on a slow rotating prop simply does not supply enough resolution to determine accurately enough when the turbine is crossing synchronous speed. (for comparison, I use a 500 pulse per revolution optical encoder on the 1800 RPM side, and polling this over 40 times per second BARELY gives me enough resolution to determine the difference of a 1 RPM change) The end result is a lot of harmonics when it cuts to the line, as well as un-needed cycling back and forth as described earlier in this thread.  It also lacks important interlocks and safety features that every induction machine should have.
- On our Enertech units, a good anemometer is part of the control equation. These turbines have no active blade pitch controls nor do they have any kind of furling or limiting system.  We simply have the turbines shut down automatically if the windspeed is higher than a setpoint (40MPH is what we normally have it set for).... Who would want their machine getting slammed around in 60 MPH winds anyways? Its a small price to pay to protect the machines.
- Brakes, brakes, brakes!  You must have a suitable braking system - we use pneumatically operated tractor trailer brakes (not cheap at over $3000 per set up). I've even seen these get burnt up before when people want to get too aggressive when they set the pitch of their blades.
- I personally love induction turbines for several reasons, but we have had to butt heads with utility companies many times. Be prepared to fight over power factor and harmonics (on freewheeling designs anyways). We've won all of our fights so far, but it isn't always easy!
- I haven't seen an induction machine yet that is as efficient as a correctly matched perm. magnet alternator. Almost all induction generators will have gearing at minimum to deal with, and they normally don't produce very well in low wind zones.

[Tom Sullivan]

   First off, thanks for the feedback.  You obviously know your induction motor turbines.  To make a couple points about the Breezy though; 1) the hall device reads the motor speed, not the blade speed, 2) the original motor has a brake, and is used for over-speed protection.  I can't say how long it will last being used for this function, but it did a nice job shutting down mine in over-speed wind events.

   Now to comment on your points about features for a successful inductive machine.  The Endurance Wind Turbine seems to be a very nice machine.  I've studied their website, and found many of the features you elude to on this machine.  They use a high quality caliper and rotor brake for stopping the unit.  They use an anemometer for control function, and tie this to what appears to be a pretty sophisticated electronic control unit, controlling engagement point, generation level, overspeed, and reactivation after overspeed protection (sensing winds over a period of time before allowing it to go live again).  They use no blade pitch, nor do they use any tail furling; exactly as you noted is typical for induction motors.  Lastly, my retired friend Larry is a PE and an EE, was the lead Engineer for one of the largest transmission line companies in the US, and has built a pile of wind turbines and Hydro generators as a hobby.  Only after completely reading the Breezy book, listening to my comments on the problems experienced with this unit, and studying the operation of this machine, his comment was; "for lower wind zones, it's a piece of s@#t".  He did love my 140' tilt tower though.  I think he felt bad for me enough to give me the 1800 watt Jacobs I'm almost done with, which will grace the tower in a few weeks.

Tom

[jondecker76]

Tom

Thanks for the correction on the location of the hall effect sensor - but still, even on the motor side, 1 PPR (or even 100 PPR) is just too low resolution
(1800 RPM / 60 seconds = 30 revolutions per second... 1000 milliseconds/30 = 33.333ms between pulses @ 1800RPM.. Now look at the math for 1801 RPM... 1801/30 = 30.016666 revs per sec. 1000/30.01666=33.314ms- esentially the same amount of time.  Even microcontrollers that operate comfortably in the microseconds accuracy and using interrupts won't be able to compute the difference accurately and often enough - aside from the fact that microsecond timing is normally only accurate in 4-8us increments - adding another 20%-40% margin of error. Besides that, delta timing is just a terrible way to determine RPM...)

Another point to bring up, is that adding swept area to an induction turbine to increase output at lower wind speeds is not nearly as trivial as with perm. magnet designs.  The extra torque generated tends to cause the turbine to "slip out" even in moderate windspeeds. You can change shutdowns and interlocks to match the new max windspeed, but in the end all you end up doing narrowing the already narrow windspeed band that the turbine can run in. This is why you either have:
A) An induction turbine that is inefficient in lower winds
B) An overly-expensive and overly-complicated hub design with pitch control. This gets around the problem of being inefficient in lower winds, but puts it out of the realm of most hobbiests.
C) I haven't seen it personally, but a passive yawing system could work here - but keep in mind that even smaller induction turbines easily weigh into the thousands of pounds - so engineering such a system could be a bit difficult as well

Aside from all of the problems mentioned in this thread, I still love induction turbines for their simplicity and pure/clean sine wave they produce. They do have a place in alternative energy, but low wind speed areas and the hobby market haven't had a whole lot of experimentation and there is a pretty big lack of information in this area.