| Post Info | TOPIC: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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keithturtle
Senior Member
Posts: 174
Date: Feb 23, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| Online calculator for magnet strength at distance, various arrangements http://www.magnetsales.com/Design/Tools1.htmThanks, aussepom Turtle
Soli Deo Gloria |
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keithturtle
Senior Member
Posts: 174
Date: Feb 19, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| Windone, for the 480 VAC grid intertie, you will find yourself committed to a DC conversion, thru an inverter to the desired output voltage and frequency. The variable nature of the speed and power output means that without some sophistcated variable speed drive and control, you'll never get suitable frequency parallel. Just like an AFD running a large variable speed AC pump, you must needs convert the rotor's output to DC, then reconvert to AC with an appropriate inverter http://www.sma-america.com/en_US/products/grid-tied-inverters.htmlThe losses really add up. If you're into hydrogen, you'd be money ahead to go DC straight to the electrolyser. Turtle
Soli Deo Gloria |
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Caleb
Senior Member
Posts: 473
Date: Feb 18, 2010
| Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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I learned a lot from making a small turbine. I shudder to think of the mistakes I would have made jumping into a project that size without that experience. Is this going to be a product or a one-off? If it is a product, then I'd get a quarter or half scale version up and running asap, put some instruments on it and see what happens. I don't think drag theory is developed enough to make a good loading estimate. You will probably end up with something that is over-designed or you might get some surprise vibrations as others have found.
Do your electronics offer you the option of varying the load on the generator so you can optimize turbine RPM or is your generator going to run at a nearly constant speed? It would be nice if you could play around with the electronics to get the generator to match the turbine; something Steve was looking into. Otherwise, a gearbox or chain drive would be nice so you can make adjustments; at least until the design gets settled.
-- Edited by Caleb on Thursday 18th of February 2010 01:46:29 AM
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- Bryan
Mechanical Engineer turned stay-at-home dad. |
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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Its Direct Drive!
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| danthe72man@gmail.com is best for your Phone number, if you would like. |
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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MOI is Moment of Inertia, the Torque Required to start the Gen. About 200 lb. ft. at center shaft for this generator.
We are using a rectifier and Inverter and directly interconnecting into a 480 Volt Zone on a commercial building.
What State are you oated in Steve? What is you phone number I'd be happy to fill you in on what we are doing. Best, Windone
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sjh7132
Guru
Posts: 1252
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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Is that a 425v permanent magnet motor?
How do you plan to use the output? Charge batteries? Run a line inverter? Just go directly to some load? (I'm asking the question because we need to know what voltage range you can tolerate.)
You said the average wind is 6m/s, but what range of winds do you want to make power in?
What is MOI?
This project is on a scale that I don't normally deal with, even in my job.
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Steve
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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We are finding that it is very difficult to make the attached Generator function optimaly. How do you feel our RPMs would effected and could we overcome our MOI needs in relation to 5 m/s wind for starting a strong cut in? Thanks for the advice!
Overcoming the proper RPM requirments and MOI requirment whether we utilize a gearbox or not is what we are focused on overcoming. 6 m/s average wind should yeild a 20% or so annual cap rate or 100,000 kWh's per annum!
PLease see attached, I'd love to get some outsiders feedback on their thought for making this 50kW gen function.
Thanks for the initial mechanical overview Steve, great stuff here and thanks for taking the time to put it together.
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sjh7132
Guru
Posts: 1252
Date: Feb 17, 2010
| Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| Windone wrote:
Steve, Could one of my colleages and I give you a call? We really appreciate your help, our engineers are all over the map right now!
I'm an Electrical Engineer so I don't know how much help I could be on mechanical questions. Plus if you watch my videos, you'll see most of my turbines don't work as well as I'd like. Why not just post your ideas here and let people weigh in with their expertise? (or opinions) The first thing I'd say is if you are worried about max torque, then you should probably assume the turbine is locked in place, and the wind is coming from the worst direction to put max force on the blade. The blade is 5ft x 47ft or 235 square feet. force in pounds would be .00492 x area x windspeed^2. (sq ft and mph) So for forces I get: 5 mph - 29 lbs 10 mph - 115 lbs 15 mph - 260 lbs 20 mph - 462 lbs 25 mph - 722 lbs 30 mph - 1040 lbs 50 mph (storm) - 2890 lbs Multiply by arm length to get torque. It's true that the force and torque will be less if you let it spin, but you don't want your turbine breaking apart just because you have it stopped for repairs and a wind comes up. Just for kicks, lets say the turbine is spinning so well it appears as a solid object to the wind and has a total cross section of 1551 sq ft. The forces on the pole would be: 5 mph - 191 lbs 10 mph - 763 lbs 15 mph - 1716 lbs 20 mph - 3052 lbs 25 mph - 4769 lbs 30 mph - 6867 lbs 50 mph (storm) - 19077 lbs (9 tons!) Are you sure you wouldn't rather make 5 or 6 smaller turbines? -- Edited by sjh7132 on Wednesday 17th of February 2010 05:22:07 PM
Steve
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sjh7132
Guru
Posts: 1252
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| Caleb wrote:
I was using the figure of 5ft that was given in the original post. But you make a good point that it would no longer be a Savonius with those dimensions.
I noticed that line after I posted. Its more like a big scoop type of turbine. Maybe they could add a tail and have the worlds largest Lenz2. :-)
Steve
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Caleb
Senior Member
Posts: 473
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| sjh7132 wrote:
If you are calculating power of the turbine to divide by speed and get torque, then don't include the generator and gear box inefficiencies. The turbine still produces the power that's lost in the generator and gear box.
It also looks like you assumed a TSR of 1.3? That might be true for unloaded, but I think at the peak power point it will be less, like 0.6 or so.
For a turbine of this size, you can't afford to use an alternator with low efficiency. If you waste 8KW of power, that's a LOT of heat to manage. Either your coils will melt or you'll start something on fire.
Caleb, where did you come up with 5ft? I see the turbine is 47ft x 33ft, so at a minimum a blade is 16ft wide. That's bigger than the sail on a lot of sail boats.
I was using the figure of 5ft that was given in the original post. But you make a good point that it would no longer be a Savonius with those dimensions.
- Bryan
Mechanical Engineer turned stay-at-home dad. |
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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Steve, Could one of my colleages and I give you a call? We really appreciate your help, our engineers are all over the map right now!
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sjh7132
Guru
Posts: 1252
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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If you are calculating power of the turbine to divide by speed and get torque, then don't include the generator and gear box inefficiencies. The turbine still produces the power that's lost in the generator and gear box.
It also looks like you assumed a TSR of 1.3? That might be true for unloaded, but I think at the peak power point it will be less, like 0.6 or so.
For a turbine of this size, you can't afford to use an alternator with low efficiency. If you waste 8KW of power, that's a LOT of heat to manage. Either your coils will melt or you'll start something on fire.
Caleb, where did you come up with 5ft? I see the turbine is 47ft x 33ft, so at a minimum a blade is 16ft wide. That's bigger than the sail on a lot of sail boats.
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Steve
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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Being that you may have some time, you seem to really knowVAWTs, could one of my colleages and I give you a call? We really appreciate your help, our engineers are all over the map!
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Caleb
Senior Member
Posts: 473
Date: Feb 17, 2010
| RE: Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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I haven't found any problems with the calcs yet, but I think your Cp is a bit high. I'd use about .15 for a good Savonius design which drops the torque to 3180 lb-ft. You've got some pretty large blades there. The force on a blade turns out to be about 3180 lb-ft / 14 ft (mid blade radius) = 227 lbs. I could believe that on a blade 5 ft wide by 48 ft long in a 13 mph wind.
__________________
- Bryan
Mechanical Engineer turned stay-at-home dad. |
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Windone
Veteran Member
Posts: 32
Date: Feb 17, 2010
| Some help regarding some calculations I have been making? DO THESE NUMBERS HOLD UP?? |
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| Calcs done on a Large Savonius with 5 foot wide cupped blades.
6 Meter per second wind.
Swept area is 14.63 m * 10.06 m = 147.18 m2
P =.5 x 1.225 * 147.18 X (V3) 6 * 6 * 6 P = 19,472 Watts P = 0.5 x rho x A x Cp x V3 x Ng x Nb
P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
rho = air density (about 1.225 kg/m3 at sea level, less higher up)
A = rotor swept area, exposed to the wind (m2)
Cp = Coefficient of performance (.59 {Betz limit} is the maximum theoretically possible, .35 for a good design)
V = wind speed in meters/sec (20 mph = 9 m/s)
Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)
Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)
P =.5 x 1.225 * 147.18 X .35 w/WAT X (V3) 6 * 6 * 6 X .93 (Generator Efficiency) X .95 (Direct Drive Gen)
P = 19,472 Watts 19,472 Watts = 19.5kW V=6 m/s
Vinlet = 1.3* 6 = 7.80 m/s with a 33 foot diameter this translates to 18.5 RPMs or so!
T = HP X 5252 (which is the constant) Divided by the RPM
T= 26.10 HP X 5252 = 137,086 divided by 18.5 RPM = 7,410 lb ft. torque out of a 48 X 33 {5 foot wide Blade VAWT @ 6 m/s (13.44 mph)} |
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