Generator winding using diametrically opposed magnet.

[Ripcrow]

TL;DR Summary

I’m wanting to build a high speed generator to run above 30,000 rpm and perhaps as high as 100,000 rpm.

I’d like to build a high speed generator using a diametrically opposed magnet. I’m asking if when using a diametrically opposed magnet rotating on a shaft if the generator coils can simply be a continuous wound loop around the magnet like a electro magnet is wound therefore only requiring one coil or will the generator still require at least two coils placed opposite sides of the magnet.

 

[Baluncore]

Summary:: I’m wanting to build a high speed generator to run above 30,000 rpm and perhaps as high as 100,000 rpm.

I’d like to build a high speed generator using a diametrically opposed magnet.

Why?
What is the source of 100,000 RPM.
If you want to generate high frequency you should use a multi-pole generator, at a more sensible RPM.

 

[Ripcrow]

Why?
What is the source of 100,000 RPM.
If you want to generate high frequency you should use a multi-pole generator, at a more sensible RPM.

For direct drive off a turbine. I could use multiple coils but thought one continuous coil would be easier to make. Turbine is experimental so looking to incorporate a generator to measure output.

 

[berkeman]

For direct drive off a turbine. I could use multiple coils but thought one continuous coil would be easier to make. Turbine is experimental so looking to incorporate a generator to measure output.

What power level is your prototype targeting? Is 100,000 RPM typical for gas turbine power generators?

https://www.siemens-energy.com/glob...QEfrmElUVeIS4UvNrDpBTvWjKnLD9iphoCKyEQAvD_BwE

 

[Ripcrow]

the maths says about 6 hp at 30,000 rpm which is my benchmark for calling it successful. Using diametrically opposed permanent magnet rotating on the shaft increases the safety as it should not want to fail at high rpm due to centrifugal force. I’m just asking if one coil can be wound around the rotating magnet or is two coils still required. Being homemade and with lots of engineers saying that it can’t be made anything I can do to improve the efficiency is worthwhile. Setting the distance with two coils increases the chances of errors where as one coil wound around a mould and tightly fitted into a machined housing limits the possibility of errors in output. Using one coil I can achieve a 1mm gap between coil and magnet. I don’t think I can achieve that tight of gap fitting two coils.

 

[Baluncore]

A single peripheral coil will not work since the wire will not be cut by the rotating magnetic field.
You will be generating AC, so it will be described as an alternator. You will need a multi-pole stator. The stator will need an iron powder or ferrite core to operate at that frequency.
You should consider generating three phase to minimise torque vibration, which may become a synchronous problem with the number of blades in the turbine.

 

[Ripcrow]

What power level is your prototype targeting? Is 100,000 RPM typical for gas turbine power generators?

View attachment 293963
https://www.siemens-energy.com/glob...QEfrmElUVeIS4UvNrDpBTvWjKnLD9iphoCKyEQAvD_BwE

Large gas turbines don’t run near as fast and have professional gearing available to access shaft power. I have built a turbo based jet engine and even using a freepower turbine to turn thrust into shaft hp it is still 30,000. My prototype is small But the higher the rpm the higher the output. Limited by materials I’m setting the design around 30,000 and 6 hp. There is potential to increase rpm after proof of concept.

 

[Ripcrow]

A single peripheral coil will not work since the wire will not be cut by the rotating magnetic field.
You will be generating AC, so it will be described as an alternator. You will need a multi-pole stator. The stator will need an iron powder or ferrite core to operate at that frequency.
You should consider generating three phase to minimise torque vibration, which may become a synchronous problem with the number of blades in the turbine.

Thanks. If I were to go to three phase is it possible to run 3 coils or will I need 6. I haven’t researched 3 phase so I’m sorry if it’s stupid question. Is there a way to break the field with a peripheral coil. I have seen peripheral coils used in microwave turntable motors but they use standard poled magnets and steel tabs to guide the flux lines.

 

[Baluncore]

If I were to go to three phase is it possible to run 3 coils or will I need 6. I haven’t researched 3 phase so I’m sorry if it’s stupid question.

You will need a stator with a minimum of three coils. That stator provides the external magnetic path needed to complete the rotor magnet field.

If you consider a single phase alternator, there are times when there is zero voltage, when no torque is present, hence the vibration problem. That does not need to happen with 3PH as it can continuously convert energy. You need to study the subject before proceding.

Before designing your 6HP, 4.5 kW alternator, take a look at what is available for vehicles, typically 1.2 kW. You will be building something for about 4 times that power, but it will be running at 8 times the speed. Because you use permanent magnets it will have no field control, so the output voltage will be unregulated, proportional to RPM. You might be able to use the stator and windings from a heavy-duty automotive alternator, but you will need to remove the voltage regulator and replace the rectifiers with an external 4.5 kW load. Then there is the frequency and pole count to consider.

 

[Ripcrow]

The 6hp is the energy input so at 100% efficiency it could produce 6 hp output. The generator is a dynometer. Vary the load and test how the turbine performs to find efficiency.
what are your thoughts of using coils wound along the length of the diametrically opposed magnet. Like tubes running parallel with the shaft. If this is a viable plan then the housing can be machined to position the coils as close as possible to the magnet and be fixed in place.
I had planned on making my coil without a core. I thought that a core held the flux longer and therefore at high rpm the change in flux change is delayed. What are your thoughts.

 

[Baluncore]

what are your thoughts of using coils wound along the length of the diametrically opposed magnet. Like tubes running parallel with the shaft.

You will need to produce a 3D sketch, or a link to a picture on a website.
If you can't find an image, that is probably because it is impractical, or cannot work.

I had planned on making my coil without a core. I thought that a core held the flux longer and therefore at high rpm the change in flux change is delayed.

True, but it is more important to close the magnetic circuit. You can use iron powder or ferrite for high frequency magnetic components. The two pole frequency will be about 1.8 kHz.

Perhaps you might consider using an eddy current brake with forced cooling.
https://en.wikipedia.org/wiki/Eddy_current_brake

 

[anorlunda]

Wow. I wouldn't want to be within 100 m of your device. It sounds very dangerous to me.

I assume you're talking about a permanent magnet synchronous generator. If it is three phase, then you must have three phase loads to consume the power. DO NOT attempt to connect this device to the power grid.

Don't forget to calculate the forces on the coils at maximum output and in short circuit conditions.

What contains the debris if a component breaks making the whole thing unbalanced?

Are you working under supervision of a mentor or an experienced engineer? Are you qualified to analyze the mechanical/electrical/contingency hazard risks?

 

[berkeman]

The 6hp is the energy input so at 100% efficiency it could produce 6 hp output.

What does this mean? How are you putting 6hp of power into your turbine?

 

[Ripcrow]

Wow. I wouldn't want to be within 100 m of your device. It sounds very dangerous to me.

I assume you're talking about a permanent magnet synchronous generator. If it is three phase, then you must have three phase loads to consume the power. DO NOT attempt to connect this device to the power grid.

Don't forget to calculate the forces on the coils at maximum output and in short circuit conditions.

What contains the debris if a component breaks making the whole thing unbalanced?

Are you working under supervision of a mentor or an experienced engineer? Are you qualified to analyze the mechanical/electrical/contingency hazard risks?

30,000 rpm is not that fast. Not qualified but the unit is contained by heavy wall steel construction. The actual mass that is rotating is light.

 

[Ripcrow]

What does this mean? How are you putting 6hp of power into your turbine?

The 6 hp is the kinetic energy available in the working fluid at full throttle according to my maths. the efficiency of the turbine can be determined by the amount of electrical output that can be obtained at full fluid flow rate

 

[anorlunda]

30,000 rpm is not that fast. Not qualified but the unit is contained by heavy wall steel construction. The actual mass that is rotating is light.

So what are you thinking for the rotating mass and the diameter of the generator rotor?

Edit: I recall doing overspeed tests on a turbine. We used railroad ties to catch flying debris. Wood is much better than metal at absorbing energy without fracture.

 

[Ripcrow]

So what are you thinking for the rotating mass and the diameter of the generator rotor?

Edit: I recall doing overspeed tests on a turbine. We used railroad ties to catch flying debris. Wood is much better than metal at absorbing energy without fracture.

Rough calculation of .7 kg plus the magnet And shaft. Encased in mild steel housing with 10 mm thickness. Individual turbine stage weight of about 70 grams

 

[Ripcrow]

You will need to produce a 3D sketch, or a link to a picture on a website.
If you can't find an image, that is probably because it is impractical, or cannot work.True, but it is more important to close the magnetic circuit. You can use iron powder or ferrite for high frequency magnetic components. The two pole frequency will be about 1.8 kHz.

Perhaps you might consider using an eddy current brake with forced cooling.
https://en.wikipedia.org/wiki/Eddy_current_brake

This actually brings up something I had thought about but had dismissed but I’m starting to think I need to revisit it. The turbine working fluid enters at 40 degrees celcius. As it passes through the first stages it will lose temperature and the second stages should decrease the temperature to below 0 degrees celcius depending on its efficiency.

My design was to pass the working fluid through the generator to the second stage. The generator being mounted on the shaft between stages. How much heat is produced by the generator itself. Is there a calculation for determining heat produced in generating 4.5 kw. Passing the working fluid through or around the generator will keep the generator cooled but also heat up the working fluid again. Depending on the heat available the turbine may need to go to 3 stages to decrease the temperature enough or it may require mounting the generator in another position on the shaft.

Being a low temperature turbine the greater the difference in temperature that can be achieved the greater the efficiency will be. Heating the working fluid a second time using the generator heat could be beneficial But I may need to add a third stage.