I have a turbine that will not stop

[makenzie71]

I’ve got a turbine made from a samsung washing machine motor, setup for 48v, five iSta Breeze blades cut down to 75cm.  When wind gets too strong i shut my turbines down by shorting the phases.  This turbine, though, when you short the phases it just speeds up.  The only way to stop it is to drag it out of the wind or wait for the wind to die.  If it’s calm for half a second rpm drops fast and it’ll stop but so long as it’s got wind it screams.  It’s almost like shorting the phases completely unloads the turbine.

Why would it do this?

[Mary B]

Are you shorting all 3 phases to ground or just each other?

[makenzie71]

Shorting phases to one another

[TerraSolis]

What kind of phase to phase resistance do you see across it?

[makenzie71]

never measured, can't check right now because the wind's blowing about 35mph lol.

[SparWeb]

Shorting phases is not a sure thing, especially with iron-core generators.  It can work, but it's a balance between power put into the shaft by the blades and power pulled out by the generator.
The torque is really high when you short the leads, but if the combination of phase resistance PLUS the tower wires is high enough, then the current doesn't actually get high enough above the wind power to slow the thing down.  Other problem is the electric brake may work at moderate wind speeds, but the cube-power law of wind power can bring the wind power over the braking if the wind is strong enough.

Do you have a furling tail on this turbine?

If not, I suggest you don't keep the leads shorted because it's 100% heat and you could melt something.  Better to use a resistance load at the ground level that can dissipate several kilowatts as a diversion load.

[Adriaan Kragten]

The Q-n curve of a PM-generator for short-circuit depends on the way how the generator is short-circuited. It can be short-circuited in star or in delta. The highest peak torque is obtained for short-circuit in delta as higher harmonic currents can circulate in the winding for short-circuit in delta (see my public report KD 78 for measurements). Short-circuit in star is the same as short-circuit in delta if the star point is short-circuited too. However, for most PM-generators, the winding is connected in star and the star point is lying inside the generator. So if only three wires are coming out of the generator, only short-circuit in star is possible.

Short-circuit must be made as close as possible to the generator. It must be made before the rectifier. The best place for the short-circuit switch is at the tower foot. If short-circuit is made in the DC line near the batteries, there can be a rather high voltage drop over the lines at high currents and this results in shifting of the Q-n curve to the right.

The Q-n curve for short-circuit has a peak value at a rather low rotational speed. So at high rotational speeds the torque can be much lower than the peak torque. So if you make short-circuit at a high rotational speed belonging to a high wind speed, the torque may be too low to slow down the rotor. If the windmill has no safety system which limits the maximum power and so the maximum torque, there will always be a wind speed for which the generator torque is too low to slow down a fast rotating rotor if short-circuit is made. There is even a wind speed for which the rotor will start from stand still position if the winding is short-circuited.

[makenzie71]

The Q-n curve of a PM-generator for short-circuit depends on the way how the generator is short-circuited. It can be short-circuited in star or in delta. The highest peak torque is obtained for short-circuit in delta as higher harmonic currents can circulate in the winding for short-circuit in delta (see my public report KD 78 for measurements). Short-circuit in star is the same as short-circuit in delta if the star point is short-circuited too. However, for most PM-generators, the winding is connected in star and the star point is lying inside the generator. So if only three wires are coming out of the generator, only short-circuit in star is possible.

Short-circuit must be made as close as possible to the generator. It must be made before the rectifier. The best place for the short-circuit switch is at the tower foot. If short-circuit is made in the DC line near the batteries, there can be a rather high voltage drop over the lines at high currents and this results in shifting of the Q-n curve to the right.

The Q-n curve for short-circuit has a peak value at a rather low rotational speed. So at high rotational speeds the torque can be much lower than the peak torque. So if you make short-circuit at a high rotational speed belonging to a high wind speed, the torque may be too low to slow down the rotor. If the windmill has no safety system which limits the maximum power and so the maximum torque, there will always be a wind speed for which the generator torque is too low to slow down a fast rotating rotor if short-circuit is made. There is even a wind speed for which the rotor will start from stand still position if the winding is short-circuited.

I think this is the first comment I've read from you that I've read that didn't require me to look up other things to know what you were telling me

What I've had a few others explain to me is that essentially I'm running the turbine so far outside of its ideal efficiency range that it more or less floats on the flux when the leads are shorted.  It doesn't seem to hurt the turbine, but there's no stopping it outside of a physical brake once it's spinning faster than about 100rpm.  I've had a dozen other fellows running these fischer and paykel/samsung style motors with similar problems...also got a lot of hits from people running Delco-style alternators like missouri wind sells with lots of blades, but I think that's probably a "lots of blades" problem more than an issue with the style of turbine.

I think it's going to be something I'll have to build a furl for.  Also considering trying some smaller blades.

[SparWeb]

I think this is the first comment I've read from you that I've read that didn't require me to look up other things to know what you were telling me

Actually, it's you, learning.  <thumbs-up>

[makenzie71]

Well I mean certainly it is, you can't try to understand what he's saying without picking up a thing or two but I still think that's the simplest explanation he's ever given me on anything, I usually have to open a new browser window to make it through one of his comments, and then often another browser window to understand what I was reading to try and understand what he was explaining to me lol

[makenzie71]

which is not a complaint, Adriaan's information is invaluable and I'm honored he shares it with me and others!