What RPM is the wind turbine blade most efficient?

[Warrior]

Hi all,

I've been investigating this also, and thought it was a good future project to decrease the energy bill at home (which has grid supply).

The idea is to run a three phase induction motor above synchronous speed, either with a geared wind turbine or with batteries and a DC motor as was suggested above.

I have seen dc motor / ac generator approach called "rotary inverters" that supply 120/220 volts ac from a low voltage battery bank (it uses a dc motor to drive an ac alternator). Similar technology can be used to get the induction generator up to speed.

Here's a few links to the awea-wind-home yahoo message board where a homemade system is described:

http://groups.yahoo.com/group/awea-wind-home/message/4146

http://groups.yahoo.com/group/awea-wind-home/message/4149

You might have to sign up to read it.

There was also a wind turbine manufacture called Enertech that built grid tied turbines. I know they used the gear-box/induction generator approach but have no idea how the sytem was controlled.

I think it's worth a try...

Warrior

[Nando]

Warrior:

Indeed, this could be a cheaper way to go, many years ago, I used to suggest a 3 motor system.

A Wind mill generator feeding a DC motor that was driving an AC induction motor, a good RPM detector and GRID switching to GRID tied generation.

Efficiencies : AC induction 85 %, DC motor 85 to 90 %, wind mill generator 85 % for a gran total of 0.85 *0.85 *0.85 = 61.4 % input to output and even if the efficiency drops to 50 %, the investment is financially lower and most important long life.

One scheme: a geared up 3 phase AC induction motor as generator, power 3 phase rectified feeding a DC motor that is coupled to an AC induction motor to be coupled to the GRID.

No need to have any component to control levels because the set up will maintain constant power out and the phase angle may stay within ia good wind regime angle.

Furling to limit power and the current and as well the RPM of the mill generator to vary the furling point.

Pitch control ideal for this set up.

The GRID in this set up forces MPPT conditions in a wide wind velocities ranges. from low to high winds.

In addition, with a simple switching one can have local power in cases of of electrical power emergencies.

Nando

[MartyM]

Would this make a good generator?  You mentioned beform that fewer poles may work better. Why?

[MartyM]

Hello,

How will this adjustment in power factor affect my desire to turn the meter backwards.

A)  Makes my electric meter register less power then I actually provided to the utility company (bad for me).

B)  Makes my electric meter register more power then I actually provided to the utility company (good for me).

C) No change, the meter registers exactly the same amount of KWH transfer in both directions.

I thought the utility company handled the power factor correction by adding Cap. banks on poles and at substations.  Comments please?

[oztules]

Hi MartyM

I'm guessing that this question pertains to what Flux mentioned about the power factor correction caps causing problems if the grid goes down, and Nando's reference to it elsewhere.

I'm guessing this post did not appear where you expected. If these guesses are correct then

"How will this adjustment in power factor affect my desire to turn the meter backwards.

A)  Makes my electric meter register less power then I actually provided to the utility company (bad for me).

B)  Makes my electric meter register more power then I actually provided to the utility company (good for me).

C) No change, the meter registers exactly the same amount of KWH transfer in both directions."

Answer A

As power factor moves away from unity, the current you have managed to generate out of phase with the voltage will not register at the meter. This out of phase current still needs to be generated. A vector of the current at the phase angle will show the new in phase current

The watthour meter only sees the inphase amps x Voltage. The further the Power Factor moves away from unity, the more the difference between power into the generator, to useable in phase power out will be.

We can use Caps on the output to correct for this, but the anti-payoff comes when the grid goes down. Then the caps will provide the exciter field  and the induction motor will continue to generate. At this point without load, it can (depending on capacitance and load) generate quite high voltages and currents, which if still hooked up to anything in the house, could be detremental to their health.

Why the phase variance with increased power? Flux or Nando may be best for this. I think it has to do with reactance through restive inductors. This gets worse as current goes up, slippage goes up, and resistance drops voltage through the inductor, and so things get a little out of whack..... but I could well be wrong here.

..........oztules