axial generator with lamination core

[Adriaan Kragten]

(Attachment Link)

9 coils / 12 magnets.
According to the Bavaria Winding Diagram Table, 9 coils / 10 magnets would be a better combination.

If nine coils and ten magnets is better a better choice than nine coils and twelve magnets depends on, if the coils have an iron core in the coils or not. I will explain this for four different options A, B, C and D.

A) Assume we have nine coils and twelve magnets (so a ratio 3/4) and no iron in the coils. This means that the coil sequence must be U1, V1, W1, U2, V2, W2, U3, V3, W3. This means that if the north pole N1 is opposite to U1, the north pole N3 will be opposite to U2 and the north pole N5 will be opposite to U3. So the voiltage generated in the three coils of one phase are exactly in phase to each other and this gives the maximum total voltage. It can be proven that the phase angle in between coils of phase U and coils of phase V is 120° and that the phase angle in between coils of phase V and coils of phase W is also 120° and so a 3-phase current is generated. As there is no iron in the coils, the armature will have no preference positions and so the generator will not suffer from cogging. So this is a good choice

B) Assume we have nine coils and twelve magnets and iron cores in the coils. Now four of the twelve magnets are just opposite to four iron cores at the same time and this gives a strong preference position. The armature pole angle is 360 / 12 = 30°. The stator pole angle is 360 / 9 = 40°. So the difference is 10°. This means that the armature will have a preference position every 10° and so it will have 36 preference positions per revolution. This results and a very strong fluctuation of the cogging torque. So this is a bad choice.

C) Assume we have nine coils and ten magnets (so a ratio 9/10) and no iron in the coils. This means that the coil sequence must be U1, U2, U3, V1, V2, V3, W1, W2, W3. This means that if the north pole N1 is opposite to coil U2, the south pole S6 will be almost opposite to U1 and the south pole S1 will be almost opposite to U3. So the voiltage generated in the three coils of one phase are not exactly in phase to each other and if coil U2 is wound right hand, coils U1 and U3 must be wound left hand. It can be proven that the difference in phase angle is 20° and this results in some reduction of the total voltage if the three coils U1, U2 and U3 are connected in series. As there is no iron in the coils, the armature will have no preference positions. So this option works but is not as good as option A because using ten in stead of 12 magnets results in a frequency which is a factor 10/12 lower. The total voltage will therefore also be lower than for option A if the same magnets are used.

D) Assume we have nine coils and ten magnets and iron cores in the coils. This means that the coil sequence must be U1, U2, U3, V1, V2, V3, W1, W2, W3. This means that if the north pole N1 is opposite to coil U2, the south pole S6 will be almost opposite to U1 and the south pole S1 will be almost opposite to U3. So the voiltage generated in the three coils of one phase are not exactly in phase to each other and if coil U2 is wound right hand, coils U1 and U3 must be wound left hand. It can be proven that the difference in phase angle is 20° and this results in some reduction of the total voltage if the three coils U1, U2 and U3 are connected in series. However, as now the coils contain iron cores, the armature will have a preference position if a magnet is just opposite to a core. But for a ratio 9/10 this happens only for one magnet and one core at the same time. The armature pole angle is 360 / 10 = 36°. The stator pole angle is 360 / 9 = 40°. So the difference is 4°. This means that the armature will have a preference position every 4° and so it will have 90 preference positions per revolution. This is much more than for option B and the peak on the cogging torque will therefore much lower than for option B but it wiil be bigger than for option A and C. The advantage of using iron core in the coils is that the air gap is much smaller which results in a much larger flux density in the coils and therefore in a much higher voltage at a certain rotational speed. Option D is a good choice if iron cores are used. But compared to option A and C, it will suffer from cogging and so one needs a windmill rotor with a rather high starting torque coefficient to get a sufficiently low starting wind speed.

[mbouwer]

@ Adriaan Kragten,

Lots of nice information. My previous test setup had iron in the coils and I will do that again for my next axial generator.

[Adriaan Kragten]

What I have explained in my previous post for ratios 3/4 and 9/10 in between the number of coils and the number of armature poles is also valid for higher numbers. But the number of coils must be divisible by three and the number of poles must be even. So for a PM-generator with no iron in the coils one can use 12 coils and 16 magnets or 15 coils and 20 magnets or 18 coils and 24 magnets and so on. For a PM-generator with iron cores in the coils one can use 18 coils and 20 magnets or 27 coils and 30 magnets and so on.

For a PM-generator with iron cores in the coils there are better options than 9/10 like for instance 15/16 or 21/22 or 27/28. Lets take 15/16. Now the coil sequence is U1, U2, U3, U4, U5, V1, V2, V3, V4, V5, W1, W2, W3, W4, W5. So there are three bundles of each five coils. The coils in one bundel must be wound alternately left and right hand. The angle in between the coils is 360 / 15 = 24°. The angle in between the poles is 360 / 16 = 22.5°. So the difference is 1.5°. This means that there are 360 / 1.5 = 240 preference positions per revolution. This is much higher than for the ratio 9/10 and the peak on the cogging torque will threfore be much lower. A simular calculation will show that the ratio 21/22 is better than 15/16 and that the ratio 27/28 is better than 21/22.

[brandnewb]

I think only skilled people can use create coil enhanced coils.

I for one am not one of them yet.

I know that having the cores enhanced will result in more ability to exact power from the wind via the the PMA.

Yet it will also introduce facts like;

"Ok boy, can you build something strong enough?"

hahah I still can not

So I focus on the DIY aspects.. is it at al conceivable that one can build this? That is DIY!!

Truth be told though that I am starting to0 lean towards outsourcing to machining shops.

I do not want to do it. and doing so will mean the biggest fail in history.
Yet I am considering!!

[brandnewb]

Dear Adriaan,

You know I have you in the highest of regards!!

I realize I am still not hibernating even thouh I said I would and I should yes agreed.

Please make sense of it all. what is wrong, other than build ability, with my current setup of the PMA?

[brandnewb]

@ Brandnewb,

Our government is increasingly positive about wind energy.

Wicked!

I had never understood that any government was able to influence the power potential of a given wing span.!

But I am always humble.

[mbouwer]

Back to the blade adjustment in the spinner of the Nordex model.

[brandnewb]

are we sure that a 2m rotor diam is going to be useful?

Adriaan do you concur?

If so then I think we should all be updated on a new way of calculating as then it seems that this omincalcularor I refereed to is useless.

[Adriaan Kragten]

are we sure that a 2m rotor diam is going to be useful?

Adriaan do you concur?

If so then I think we should all be updated on a new way of calculating as then it seems that this omincalcularor I refereed to is useless.

It all depends on the Cp of the rotor and on how much mechanical power P you want at which wind speed, what rotor diameter is required (see KD 35 formula 4.1 and 7.10). It depends on the efficiency of the generator and the efficiency of the transmission which electrical power you get (see KD 35 formula 4.2). So it is possible to design an effective wind turbine with a rotor diameter of 2 m but you must know what you are doing and realise an good matching in between rotor and generator (see KD 35 chapter8) and use a proper safety system (see KD 485). If you don't understand all the theory, you can build one of my small VIRYA designs specified at the menu VIRYA folders on my website. Report KD 35 is available in English and in Dutch at the menu KD-reports on my website: www.kdwindturbines.nl.

[Adriaan Kragten]

Something more about ways to prevent a large peak on the cogging torque. If the housing of an asynchronous motor is used for a radial flux PM-generator, there are several ways to prevent cogging. One way is to use two less or two more armature poles than stator poles and to use a 1-layer winding with coils around only one stator pole. This methode is described in my reports KD 560, KD 624 and KD 648. Another way, for which the standard winding of a 4-pole motor, a 6-pole motor or an 8-pole motor can be used, is described in reports KD 730, KD 747 and KD 760.

[mbouwer]

This is the Nordex that I want to make a working model of.

[mbouwer]

The shape of the blades is not optimal, but for the model I only want them to rotate about 20 revolutions.

[mbouwer]

This small generator with planetary gearbox fits well in the model.

[brandnewb]

Please allow me to potentially ask about something I could have already known would I have studied the whole thread.

Please tell us your expectations. what is the goal.

One thing for sure is that you have mad skills! far beyond mine. no question.

But what is the intend?

If I look at your latest image. Unless the scale if unclear it looks like a small dc motor of some kind.

Anyway. If your intend is small scale then sure keep at it as I think you know full well how to craftsmen stuff. I still look up to you regarding that!.

If your intend is aimed a little higher, like where my crosshairs are, than we should seriously have a sit down together to compare plans. I want to warn you for possible disappointments ahead in that case.

[mbouwer]

The intention is that I make a working model of a Nordex.
A windmill friend is going to add the controls.

[JW]

Brandnewb



Notice the mention of a planetary gearset.

The trick is to getting the desired output in watts.

This is where Thermodynamics comes into play. The amount of heat in the conductors is acceptable for the expected power output.

Small alternators are also useful.

You have to understand the balance of all components on any gen-system.

I see your thinking outside the box, and that's fine. You need to understand the harmony of your intended system goals.

I am a Process Engineer people ask me what's that? Its a type of "systems technology" for example front the base of your structure, branches it to other types of systems that are interacting with each other.

JW

 

[Adriaan Kragten]

Brandnewb



Notice the mention of a planetary gearset.

The trick is to getting the desired output in watts.

This is where Thermodynamics comes into play. The amount of heat in the conductors is acceptable for the expected power output.

Small alternators are also useful.

JW

 

I doubt if this conclusion is true without having made detailed calculations for both options.
 
The main advantage of an increasing gear ratio in between rotor and generator is that the generator runs at a much higher rotational speed and therefore a much lower torque level is needed to get the same mechanical power level. So the generator is much lighter and much cheaper. However, the costs of the transmission have to be added. The main advantage of a direct drive generator is that it has no gear box which needs lubrication, will wear or can even break down, makes noice and has its own efficiency and its own friction torque. However, a direct drive generator is heavier and more expensive.

If the efficiency of both generators are the same, the dissipation of the heat is much easier for a direct drive generator than for a geared generator as a direct drive generator has a much larger area. In the beginning of the development of big wind turbines, all of them used an accellerating gearing in between rotor and generator. But starting with Enercon, direct drive generators are now also used for big wind turbines of other manufacture. The disadvantage that the generator is more expensive is compensated by the fact that no transmission means no maintenance, no noice, no extra friction torque because of gear wheels and more bearings and seals and no risk of failure.