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Anonymous Poster

Windspeed Questions Related to a Windmill Generator

02/18/2007 9:55 AM

I am interested to install a windmill generator on my property, but I have difficulty in some terminology the seller used. Can anybody help?

1/ What is 5 m/s cut in = ? mile/hr windspeed.

2/ what is 56 m/s cut out = ? mile/hr windspeed.

3/ how windmill cut out when the wind is too strong?

Thanks

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Guru

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#1

Re: Windspeed Questions Related to a Windmill Generator

02/18/2007 11:18 PM

1m/s=2.237 mi/hr (1mi=1,609.344m, 3600s/hr), so 5m/s=5*2.237=11mi/hr, and 56m/s=125 mi/hr (WOW-that seems high for cut out).

Large windmills feather the blades (rotate them so they point into the wind, parallel to the axis), so they stop rotating. If they did not do this, in high winds the blades would spin so fast that 'centrifugal' force would pull them off - a disaster!!!

Since the mechanism to feather the blades is expensive, cheap windmills have fixed blades that can't rotate (around the blade axis). I have no Idea what they do for safety in high winds - one posibility would be a centrifugal brake (weighted brake shoes that are spring mounted, so above a given RPM they will make contact with a brake drum). Such brakes would get very hot in continued high winds!

The fact that the manufacturer specifies a cut-out speed at least indicates that they have made some provision...

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Guru
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#10
In reply to #1

Re: Wind speed Questions Related to a Windmill Generator

02/21/2007 3:54 AM

All is OK for now.

Typical small and medium windmill braking is done through a mechanical brake and shorting the generator.

First the generator is shorted to use as much of the rotational energy as possible, a normal generator can do this without problem but you need to do this at a certain wind speed, else the energy stored in the propeller is to high and the braking time could become to long. The mechanical brake is used to get the speed to 0 and keep the rotor to a standstill.

Don't try to do this on you own, without knowing which current your generator can have for which time. Also you need to calculate very precisely the energy stored in your propeller/gearbox.

These are the things that you pay for when you buy a windmill.

Gwen

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Commentator

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#2

Re: Windspeed Questions Related to a Windmill Generator

02/18/2007 11:28 PM

Doing the unit conversions: m/s * 2.23 = mph

5 m/s approx 11 mph

56 m/s appros125 mph

The cutout procedure depends on the windmill design.

Some advice: If you need help at this level, you are pretty much at the mercy of the salesman. It would be wise to get some technical advice from someone who will not be selling the equipment. Expect to pay for the advice. That is cheaper than buying something that does not fit your application.

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Anonymous Poster
#3

Re: Windspeed Questions Related to a Windmill Generator

02/18/2007 11:32 PM

Dear Guest,

The cut-in wind speed is the minimum speed required to rotate the rotor of the windmill generator.

The cut-out wind speed is the speed at which the rotor is cut-out from the wind direction,i.e. as said in other reply the direction of rotor surface is changed and made parallel to the wind direction.

regards

Mahendra P. Gade

Pune

India.

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Anonymous Poster
#4

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 12:05 AM

The cut-in (when the prop is rotating fast enough to generate the minimum power) and the cut-out (when it is too fast to be safe) is listed in meters per second in your spec (just do the math to convert).

Windmills perform cut-out in several ways including turning 90 degrees to the wind, rotating blades among others. Much of it depends on the size and design.

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#5

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 3:17 AM

1. 11.85 miles/hr ( Statute miles; 5280 ft.)

2. 125.268 miles/hr.

3 Depends on design; swing tail 90 deg (windmills with tails); Set blades at zero lift (rotating blades)

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Guru

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#6

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 8:07 AM

You are asking all of us, when you need to ask the supplier. His answer is the one you are paying for. Showing this thread during a warranty will not impress him. Showing his answers will.

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Participant

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#7

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 8:14 AM

http://www.jne.ca/

I think would be a good ideea to contact the company listed above to get a professional opinion

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Active Contributor

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#8

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 9:01 AM

You might try www.massmegawatts.com

Good Luck

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Power-User

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#9

Re: Windspeed Questions Related to a Windmill Generator

02/19/2007 3:09 PM

You have got already answers to Your questions. But First of all You have to answer for the economics: what will be return rate, if any. If it is a small installation just for fun then have a nice time. But if it is for money, then You have to have in mind that:

1. Produced energy depends wery much on wind , is proportional to V^3, what means:two times bigger wind velocity V= eight times more energy.You can have wind distribution data from national or local Meteorological Institute.

2. Localisation: best is open area. Forest , trees, even bushes lower wind velocity. If height of Your tower will be lets say 10m , then around, especially from the most frequent direction of blowing, You should not have obstacles in 15 x height = 15 x 10m = 150m distance. And upside down : Forest, trees of height 30m should be far 30m x 15 = 450m at least.

3. If nominal power plant is 10kW, You should be expected to have 1kW..2kW in average, due to variation of wind velocity.

4. the higher the tower the higher wind velocity proportional to V^0.5= 4 times higher = 2 times bigger Velocity = 8 times more energy. But also more high , more costly! Putting on the top of flat hill greatly helps. However hills increase turbulention - speed is less constant - lower efficiency of blades.

5. Usually installation pays back money in 30years! Only best locations pay back in 10years. Most of installations in the world appeared, because were supported by governments (by tax reductions for example, or special low rate loans).

6. Visit few people having done this kind installations and talk with them. Then make decisions.

7. Install reliable cutting off system to aviod disaster. Wind speed of 60miles/hour will apply to 5m long rotating blades a force in the range of 1000kG! Many times more than if they are stopped! (braked and cannot rotate or turned parallel to wind direction) . Force is proportional to V^2: two times bigger velocity = four times bigger force!

8. But costs of fuel are rising, so Your chances too.

Good luck

czgut

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