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DaveP68
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Posted: 06 May 2017 at 5:31am | IP Logged Quote DaveP68

Have been doing some research into the possibility of have a form of automatic electronic braking in high winds.

There has been a lot of previous discussion of F&P stators operating above 500 RPM the core becomes saturated with the torque curve dropping off. With furling set up correctly this can keep things under reasonable control. In very stormy conditions this may not all work out so well so some form of braking should be considered.

F&P washing machines made between 1993 and 1998 had a 300 W peak rated dynamic brake function. A safety feature used if a lid was opened at max spin of 1000 RPM it could bring a load of bowl + clothes 20 kg's max to a stop in less than 4 seconds. They type of stator used was the 80s on all those machines.

For a day job I repair these boards and need to activate this function as part testing the motor control module.

Here is a photo of a modified module used as a load at 900 RPM 1000 W of energy being extracted from the stator.



The proposal I have is to use a capacitor doubler to extract maximum current out of the stator before the core becomes saturated. The trick is to extract maximum power from say 2 stators on the same shaft when a peak RPM is reached. If more power is taken from the shaft than the blades can deliver we go into a lower TSR range. That way a controlled shut down can be done before the wind gets too strong.

This requires some fine tuning in terms of a workable system, but from some testing I've done with one stator it should be possible.

With this separate cap doubler (one for each stator) is used for braking only when running in over drive mode on a 36 pole 4x 3p Delta I get 72 VDC 16.4 Amps 1.18 kW @ 550 RPM. Thing is the shaft power required to drive the stator is >2 kW. That is from just 1 stator! This same stator when not used in braking mode would normally be charging a 48 VDC battery system. The same system can be set up for a 6x 2p Delta, with the brake operating at 48 VDC 24.6 Amps peak at brake application.

Taking more power from the shaft than it can deliver will push the blades into stall region slowing them down by dropping the TSR to below 5. The maximum current and voltages of course would reduce and have to be carefully controlled to slow the blades down.

This way the blades can brought to almost stopped state (tuning slowly if wind is strong enough) if set up correctly. The brake would release when the stormy conditions have passed so to speak. Yes you would not be making power while storm passes but wind turbine stays safe

This is only in a concept form at present so no working system yet.

Cheers

David

Edited by DaveP68 on 06 May 2017 at 8:39am



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Hatman
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Posted: 07 May 2017 at 3:56am | IP Logged Quote Hatman

Hi, David I'm looking at dynamic braking for my system as well, (8xf/p) I was thinking that maybe for me a way to do this is to use the dump load or a voltage from the DC side of the rectifiers at a point before saturation to trigger a short on the AC side of individual stators and using different DC voltage to trigger different stators increasing braking but still producing charge from the un triggered stators do you think this is a viable thing?
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DaveP68
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Posted: 07 May 2017 at 7:17am | IP Logged Quote DaveP68

Hi Hatman

You can't apply a short circuit to an F&P stator as it just puts them directly in saturation. From tests I've done on any version of F&P stator, saturation happens below 60 RPM on a short circuit condition (AC or after rectifier DC side).

What is outlined above, is that 'Electronic Dynamic braking' must happen under controlled conditions. By diverting the maximum amount of energy into a load that takes more power out than what it can deliver efficiently is the key. It causes the stator to take 'as you would say' the maximum Nm of torque from the drive shaft. This puts turbine to a stalled sate to slow it down in a controlled way.

From what I've seen on this website, no one has been able to do Electronic Dynamic braking on an F&P wind turbine to date. Anyone is welcome to correct me if I'm wrong on this one, but it requires a complete understanding of the F&P stator operating perimeters to do so. I have that understanding, as deal with them every working day.

Cheers

David

Edited by DaveP68 on 07 May 2017 at 10:48am
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Warpspeed
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Posted: 12 May 2017 at 1:58am | IP Logged Quote Warpspeed

I think its going to be extremely difficult to achieve sufficient braking in a nice simple way using just a standard bare F&P motor and no microprocessor.

A very effective electromagnetic eddy current brake can be made with just a plain aluminium disc and a dc electromagnet. The faster it spins, the more braking torque it can produce (for a given applied electromagnet strength).

https://en.wikipedia.org/wiki/Eddy_current_brake

Couple that up to the dc output of your F@P rectifier.


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govertical
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Posted: 12 May 2017 at 3:15am | IP Logged Quote govertical

http://www.circuitstoday.com/wp-content/uploads/2009/09/Over-Voltage-Circuit-Protection.jpg

https://youtu.be/Eg3mL_NJSkM

Hi, I found and manually tested the above circuit. D5 brake down voltage triggers the SCR. When the AC goes to zero the SCR turns off and the circuit resets. I am not sure if this is dynamic braking, if you need a parts list I can provide a list of the parts I used.

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DaveP68
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Posted: 13 May 2017 at 5:30am | IP Logged Quote DaveP68

Hi to you both and thanks for the feedback.

Warpspeed wrote:
I think its going to be extremely difficult to achieve sufficient braking in a nice simple way using just a standard bare F&P motor and no microprocessor.


Think you're mostly correct in what's stated above.

govertical wrote:
Hi, I found and manually tested the above circuit. D5 brake down voltage triggers the SCR. When the AC goes to zero the SCR turns off and the circuit resets. I am not sure if this is dynamic braking, if you need a parts list I can provide a list of the parts I used.


I also like your idea govertical, but being AC needs to be a 3 phase input for the F&P stator operation. Let me know some component values anyway as got lots of bit lying around the workshop may able to try it out.

Understanding these F&P stators, especially them wanting to give a max current regardless of RPM/Volts range gives me a clue for a simple control circuit. It could be built without the need for a microprocessor.

How this breaking function coukd still work on a stator(s) output is by having a trigger point from a anemometers wind speed output. Once this threshold is reached (say 12-14 m/s) the braking circuit would take maximum current from the stator(s). This max current draw would be kept constant (just below saturation point) with the voltage dropping down. The RPM would decrease due to the blades being pushed into low TSR range.

The stator(s) can give maximum current at less than 60 RPM. The brake still taking maximum current could stay on due to the anemometer output showing a trending high wind speed over say a timed period. Once the winds reduce below a set threshold for certain time period the electronic break would be released.

Warpspeed wrote:

A very effective electromagnetic eddy current brake can be made with just a plain aluminium disc and a dc electromagnet. The faster it spins, the more braking torque it can produce (for a given applied electromagnet strength).

https://en.wikipedia.org/wiki/Eddy_current_brake

Couple that up to the dc output of your F@P rectifier.


Tony I do think your above idea has far more merit, as it's very simple to build and can be electrically activated from the F&P stator(s) rectifier output.

One extra thing to consider though. The wind still putting lots of force on the blades when the RPM drops to a low level "with brake on" the power feed from the stator(s) would drop off. This would need to managed properly as the blades RPM would start hunting. This is due to brake starting to release in low RPM, blades speed up a bit, brake on again etc etc. Probably a simple thing to overcome though as an equilibrium point should be reached at some point.

Reason I bring this point up is on train which this system is used on, the power from traction motors is shut off. Then the braking system only needs to act on the inertia of the train cars still moving to bring them to a stop.

I just like the concept of having the brake function as part of the stator(s), but this could prove wishful thinking on my part

Cheers

David

Edited by DaveP68 on 13 May 2017 at 5:32am
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Warpspeed
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Posted: 13 May 2017 at 6:13am | IP Logged Quote Warpspeed

All the excess power has to go somewhere.....
Burning up the small coils in the F&P is not going to be very productive.

Rapidly stopping a spin dry load only produces a short once only heat spike which may be tolerable.
But like the terrifying brake fade in your vehicle on a very long steep hill, using dynamic braking continuously is a very different thing to a one time panic stop.

This is where an eddy current brake really shines. It has a significant exposed surface area that will easily dissipate kilowatts of power continuously if it has a sufficient amount of cooling airflow. Not too much of a problem for us in a storm.

I have at home a 400 Hp continuously rated eddy current dynamometer that has a pair of 330mm brake discs.
Larger units are used to brake fully loaded semi trailers and buses, and even bullet trains.

Its just like a disc brake, but without the pads or a friction surface. The "caliper" is an electromagnet that puts braking heat into the disc electrically through circulating eddy currents that may be hundreds or thousands of amps.
The difference is that a friction brake has almost constant braking torque at any speed, including fully stationary.
An eddy current brake produces more braking torque the higher the rpm.

So even without a proportinal control system, an eddy current brake would significantly reduce turbine rpm by working much harder at higher turbine rpm when switched in.



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Posted: 13 May 2017 at 6:15am | IP Logged Quote govertical

R1 any high wattage load
SCR1 and SCR2 MCR8SNG
D1, D2, D3, D4 HFA 08TB60
D5 select a zener with a high brake down voltage, you can connect a few in series to get a higher brake down voltage.

Hi, you can make 3 circuits, one for each phase. Once the circuit triggers there is a combined load from R1 and the (I squared R) loss at the stator.

Edited by govertical on 13 May 2017 at 6:23am


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DaveP68
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Posted: 13 May 2017 at 10:22am | IP Logged Quote DaveP68

Warpspeed wrote:
All the excess power has to go somewhere.....
Burning up the small coils in the F&P is not going to be very productive.

Rapidly stopping a spin dry load only produces a short once only heat spike which may be tolerable.
But like the terrifying brake fade in your vehicle on a very long steep hill, using dynamic braking continuously is a very different thing to a one time panic stop.


Have you ever heard of an F&P stator burning out? To my knowledge of how they work it will never happen if run in it's designed operating envelope. This is exactly the point I was trying to get across with the train slowing down, it's the same as rapidly stopping a spin dry load. We are talking cross purposes again I'm more ahead in my thinking than perhaps you think I am. Not trying to be critical here Tony but just a bit of deja vu coming back to from another recent topic.

When going into controlled shut down, this is done over a period of 5 to 10 seconds with the blade RPM taken from 600 RPM down to below 100 RPM. This is achieved by initially putting the blade into a "Tip Speed Ratio" (TSR) of lower than 5 effectively putting them into partial stall condition. When the blades are in this stalled operating region the amount of torque on the shaft drops off a cliff. Please refer to the power coefficient curve below relating to "TSR" with formula relating to RPM.



So the initial braking application will take a lot of energy to bring the blades under control and down into that partial stalled region.

I hold a pilots licence which means I understand stall condition very well, if I didn't could have killed myself and my passengers. I formally worked in aviation sector which gives me a bit of understanding of this stuff.

There is practically no difference between the amount of lift that a wing "generates" and the amount of power blades can feed into a shaft. This is shown at the top of "that nice curve" above. Stall condition once it's reached (not desirable in an aircraft) is exactly what we want to use to bring the blades electrically under control.

When the RPM is under control (below 100 RPM in stalled condition) the current in the stators will be at a manageable level, so no excessive heating of those small coils!

Like I said above your idea does have lots of merit and I like it Please also consider I have put good amount thought put into a concept before it is published.

govertical wrote:
R1 any high wattage load
SCR1 and SCR2 MCR8SNG
D1, D2, D3, D4 HFA 08TB60
D5 select a zener with a high brake down voltage, you can connect a few in series to get a higher brake down voltage.

Hi, you can make 3 circuits, one for each phase. Once the circuit triggers there is a combined load from R1 and the (I squared R) loss at the stator.


Thanks govertical will check what bits I have on hand and try out your circuit just for the fun of it to check what it does.

Edited by DaveP68 on 13 May 2017 at 10:30am
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Posted: 13 May 2017 at 10:49am | IP Logged Quote Warpspeed

I was a student pilot once myself, passed my BAC (basic aeronautical knowledge) logged quite a few hours solo too, then decided I really could not afford to do it as well as buy a house. The house won, and I have not flown since. Still have my pilots log book around here somewhere.

Anyhow, you are quite right about putting the blades into a completely stalled condition.

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DaveP68
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Posted: 13 May 2017 at 11:26pm | IP Logged Quote DaveP68

Got my Private Pilots Licence just over 20 years ago while I was working at Air Traffic Control known as Airways here in NZ. So didn't flying for a living, but did clock up quite a few hours.

Here's a picture of me on the job taken in the late 90's.


Do miss working in aviation, as it's very structured in the way it operates at the sharp end. But in Feb 2000 the domestic operations were centralized in Christchurch and I didn't want to move there so took redundancy.

They have earth quakes in Christchurch, so putting all their eggs in one basket with only ONE centralized control center can shut the whole domestic operation down. Planes stay on the ground when this happens for up to 4 hours. While this is happening nothing moves from Auckland to Wellington and other cities (International airspace control is still in Auckland). In the last 6 years they've had at least 3 major shut downs of our domestic airspace for a few hours at a time. Airlines and Airport companies put pressure on Airways NZ to improve the system. They have now made the wise decision to bring the upper North Island airspace control back to Auckland. Back to how it was when I worked there.

I probably wont go back as get more time off with what I do now and lots less stress.

Have a similar story to you with the flying being an expensive hobby. I brought a house with the help of a large redundancy payment mentioned above 17 years ago and haven't done much flying since. The house always wins so to speak

Edited by DaveP68 on 13 May 2017 at 11:42pm
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Posted: 13 May 2017 at 11:44pm | IP Logged Quote Warpspeed

Quote:
I brought a house with the help of a large redundancy payment

That is definitely the best way to do it.
For me it was my savings from two year long expeditions to Antarctica. Nothing to spend money on down there, and the pay was good.
By that time I had not flown for three years, so would have had to begin my training all over again.

I could not fly now because of medical problems. I always had trouble clearing my ears of pressure during descent, and I have gradually lost my hearing to the point where I am completely deaf in one ear and have lost 80% hearing in the other.
So flying and Amateur radio are no longer hobbies I can really pursue.

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