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Forum Index : Windmills : Physical/Hydraulic/Electromechanical Braking of Turbines?

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Kamak
Senior Member

Joined: 13/04/2021
Location: Canada
Posts: 150
Posted: 07:24pm 05 May 2021
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The Neotard Retarder
 
kitestrings
Senior Member

Joined: 23/04/2014
Location: United States
Posts: 102
Posted: 08:44pm 05 May 2021
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Yes, isn't this similar to what they use on those mag-lev trains?  It is an interesting approach.

I recall the company I worked for, Enertech it was called, had a dynamic brake design on a fairly large turbine... ~40 kW IIRC.  They used water immersion elements in free air, but they were only good for the one, fail-safe attempt and then had to cool.

We use a combination of strategies for speed-control and self-protection.  Initially, keep the thing electrically loaded, right, so charge the batteries in our case.  Then we load-divert to a pre-heat tank for hot water.  We also have a resistive load-bank on the 3-ph source that is triggered off a PWM relay setting on the CC.  It is a user-adjustable V-hi setting.  So when the batteries are charged and the water is hot, this provides load.

On the mechanical side, there is the furling.  A big gust and the turbine folds presenting a smaller and smaller ellipse to the wind.  You give up some of the high-wind potential, but in the end it is very soft, passive and forgiving.  This operates independent of the actuator, solely based on thrust on the rotor versus restoring moment.

Lastly, on another non-PW relay setting, we have a (NC) contact that will open when a bit higher voltage is reached and furl the turbine with the actuator.

My admitted bias is to have things as simple as possible up on the tower, and keep the electronic wizardry on the ground; inside if possible.
 
Kamak
Senior Member

Joined: 13/04/2021
Location: Canada
Posts: 150
Posted: 04:17am 06 May 2021
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I agree with you on simple, and robust, and as little electronics up on the tower, as possible. But if a permanent Neo magnet eddy current disc could be used, that's dead simple. The cool thing about eddy current brakes is that they are self-adjusting, to a certain degree, without a single external control added. The faster the disc moves through the magnetic flux, the more drag is created. So that gives a certain inherent degree of proportional applied torque resistance. Only as the torque surpasses the applied flux field's ability to maintain a steady rotational speed, would a magnetic proximity adjustment need to be made. But that's also very simple to implement. The electromagnet makes this even simpler, but it's bulkier and with less magnetic flux density per volume. But it might be the best way.
 
Kamak
Senior Member

Joined: 13/04/2021
Location: Canada
Posts: 150
Posted: 02:56pm 08 May 2021
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Understandably, the other method of speed control is load control, using torque. This is how some of the big boys do it. It's called a doubly-fed induction generator converter (DFIG). This demo of a modeler called Plexim describes how it works, and allows a free trial for a month, with access to the files that model this wind turbine system. I might check it out just for educational fun.

https://www.plexim.com/sites/default/files/plecs_dfig.pdf
https://www.plexim.com/support/application-examples/282
 
pollenface

Regular Member

Joined: 01/09/2020
Location: Australia
Posts: 41
Posted: 11:46pm 10 May 2021
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I have a 24v system and a cheap 3-phase 24v turbine.

I rigged up a brake using 2x automotive relays which short the 3-phases on the AC side of the rectifier using a voltage sensing relay from a dual battery system.

At 27.4v the VSR supplies signal to the 2x automotive relays and it brakes the turbine. At 25.6v it recovers.

My 1kw solar array virtually makes this system redundant during good sunlight hours as my mppts float @ 27.6v, thus my turbine is only functional during non-sunlight hours or rainy days and under wind power alone it doesn't get anywhere near the braking voltage.

My system works well with the small turbine, but I am unsure as to how well it would work with a larger turbine with more (spinning) inertia.

On another note...

I hypothesized building a turbine with a centrifugal clutch from a whippersnipper and adjusting the throw of the clutch pads to engage at high rpm (eg hurricane wind).
Edited 2021-05-11 09:50 by pollenface
Off grid man caver
 
Kamak
Senior Member

Joined: 13/04/2021
Location: Canada
Posts: 150
Posted: 04:08am 11 May 2021
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  pollenface said  I have a 24v system and a cheap 3-phase 24v turbine.

I rigged up a brake using 2x automotive relays which short the 3-phases on the AC side of the rectifier using a voltage sensing relay from a dual battery system.

At 27.4v the VSR supplies signal to the 2x automotive relays and it brakes the turbine. At 25.6v it recovers.

My 1kw solar array virtually makes this system redundant during good sunlight hours as my mppts float @ 27.6v, thus my turbine is only functional during non-sunlight hours or rainy days and under wind power alone it doesn't get anywhere near the braking voltage.

My system works well with the small turbine, but I am unsure as to how well it would work with a larger turbine with more (spinning) inertia.

On another note...

I hypothesized building a turbine with a centrifugal clutch from a whippersnipper and adjusting the throw of the clutch pads to engage at high rpm (eg hurricane wind).


Yup. those are all really great ideas, I hope you can demo the weedwhacker idea, here someday. I am also itching for an approach that will allow charging and speed control simultaneously and something that is frictionless, in doing so. Something like a simplified DFIG idea (if that is even possibly simplifiable) or a truly simple frictionless eddy current brake/torque reactor. Also something along the lines of a "parking brake". Something manual, that once the rotor is slowed down to a stop, then locks it in place. A smallish motorcycle brake could possibly do, without adding too much mass, I suppose.
 
Kamak
Senior Member

Joined: 13/04/2021
Location: Canada
Posts: 150
Posted: 04:11am 11 May 2021
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This is how some of the big boys do it. It's called a doubly-fed induction generator converter (DFIG).
 
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