Furling Assist Device for Stator Thermal Protection

[snowcrow]

The "Furling Assist Device" just in the idea and design stage at present.

The purpose of this device is to add furling action for stator thermal protection.

The Plan is to use a sensor embedded in the stator to energize a solenoid on a tail flap to aid the furling action. I'm still at present looking at what to use as the energizing circuitry. G's little gem of a circuit may work for this application as well.

Note the tail flap is cut at a slight diagonal, with the top being bigger than the bottom, this will also aid in lighting the tail as well as aid in furling.

All comments and \ or ideas are welcome!!

Blessings, Snow Crow

[richhagen]

I had a vent damper that was made of bi-metal material, when the temperature changed sufficiently the metal would bend opening the vent.  It was similar in theory to the coils in common thermostats for temperature control, except that the material was larger.  Just an idea, but I wonder if you could use the force from a bimetal strip in some way for a mechanical thermal control.  Just an idea, but I thought I would throw that in.  Rich

[Drives]

I think it is a good idea.  

My twist on this was to use a DC linear actuator in the tail that took power direct from the wind turbine to activate it.  High temp closes electrical contact (look up KLIXON) connects turbine output to rectifier, from rectifier to actuator, tail is forced to furl.  All of this could be located up on the turbine.

If this did not work, then same circuit but use a DC cable winch at the tower base to activate a cable furling setup instead of linear actuator.  A number of commercial wind turbines have the cable furling arrangement, but it requires slip rings....should still work.

The neat part about this safety feature is the fact that you could put a high voltage latching relay connected direct from the turbine.  Once a overspeed was created the voltage would be high enough to trip the relay, the contacts would be in parallel with the KLIXON contacts, and "force furl" your turbine.

Essentially you could have both an overtemperature, and overspeed fault protection that would cause a furled condition for protection, and would not require an external power source.  The gravity furling tail would still be needed for regulation, this would just be an extra measure of protection, in case of an abnormal condition.

[Flux]

I tend to agree with Dean, using a manual furling scheme. Most people seem to be inclined to avoid mechanical shut down devices at all cost.

I can't see any hope of the tail flap thing working but I don't want to pour cold water on something that has been given some thought. I have tried several things that ought to have worked and don't and I tend to spot the ones likely not to work.

I have never been in the position of needing to worry about stator temperature but I have used a motor operating a manual furling scheme as a protection against overspeed from loss of load and also as a convenient way to shut down during violent storms when things are better not thrashing themselves to bits. The addition of over temperature would be perfectly easy and could be simulated from a resistor in a pot of oil at ground level with the same thermal time constant as the stator.

Flux

[wooferhound]

If you put a Temperature Sensor inside of the stator, then the spinning magnets will generate voltage in your sensor wires and throw off the reading or destroy the sensor & electronics. I think you can use shielded wire to avoid that, but I'm not sure the sensor itself will be immune to the spinning magnetic fields.

[snowcrow]

Thanks for idea Rich, but the Bi-metal won't work with spinning magnets. I think I'll be using a NTC thermistor in the stator.

Blessings, Snow Crow

[snowcrow]

Hi Dean, I did think about using a DC linear actuator but, I only really need 1.5" of travel at most and the DC linear actuator is too long for moving a tail flap. The DC linear actuator would also need to be powered to reset the flap position, but the spring loaded solenoid would not, and if the solenoid should fail it will be in the normal position, not so with a linear actuator!

As far as the Circuitry goes, I'll be using the a NTC thermistor in the stator (as stated above) connected to the voltage divider in Ghurd's LVD Circuit. If I do it right I will have both thermal and over-speed protection!

Blessings, Snow Crow

[snowcrow]

Hi Flux, I agree with the manual furling too, but I live 3 hours away from camp and need my mill to fly solo. Last winter my solar panels got buried under 2 feet of snow and the batteries were almost frozen solid. Having my mill running autonomously is a most!!!

Well... If it doesn't work, than it doesn't work but if there is nothing ventured than there is nothing gained!! I did a search but find nothing about using tail flap to aid in furling.  I should have a good idea if it's going to work before I even put it on the tower. Just wish me luck!

Blessings, Snow Crow

[Flux]

Leaving a mill running alone for months is a tall order but at least you will be out of harms way if anything goes wrong.

Rather than worry about protecting from burnout I would be inclined to make sure it furls safely so that there is no danger of burn out. I don't know what you can do about about things freezing up and causing problems such as a frozen furling hinge.

Protecting against overspeed is worthwhile if you can devise something.

I don't see what the flap is going to do to help you, it's not going to significantly reduce the weight of the tail and that is the only way it could work.

I certainly wish you luck and I really can't see it doing any harm.

Nearly all complex protection devices fail and create as much of a problem as the thing they are supposed to protect and unless they are constantly tested and maintained they tend to defeat the intention.

With an air gap alternator you may be lucky that a freeze up would occur at a time of no wind and if the alternator froze it would be fail safe.

Flux

[Ungrounded Lightning Rod]

I don't see what the flap is going to do to help you, it's not going to significantly reduce the weight of the tail and that is the only way it could work.

(I don't see the post I thought I made earlier.  Now Flux has covered part of it but I'll fill in the rest.)

The flap, directing the air sideways, won't do anything to assist the furling.  It will just change the apparent direction of the wind at the tail vane, which will make the mill fly at a somewhat different angle up to essentially the same furling windspeed.  In fact it will make the mill turn the wrong way.

To assist furling the flap must direct the air DOWNward when activated.  Then it will effectively reduce the weight on the tail and cause the hinge to start folding at a lower wind speed - which is what you want.