Steam turbine generator

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dusty
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Re: Steam turbine generator

Post by dusty »

RET wrote: Sat Jun 26, 2021 10:16 pm
This picture shows the stator with windings. Note that the windings are protected from the sharp corners of the stator with an insulating sleeve the same way Wolfgang mentions in his post. Also note that the completed stator is protected by a laquer coating.

Richard Trounce.
Did you consider using Litz wire for your windings instead of solid wire? https://www.newenglandwire.com/why-pref ... c-devices/

At the high frequency of your generator, using Litz wire should provide noticeable increased power.

Have you run your turbine generator yet?
Wolfgang
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Re: Steam turbine generator

Post by Wolfgang »

At 60,000 rpm the frequency is 1000 Hertz. This is not such a high frequency to warrant stranded wire in the windings which, in any case, is quite thin at 26 or 28 gauge (I forgot which).

My turbo-generators, at least 2 of them, have run, perhaps, 100 hours or so once I resolved the rusting and bearing wear issues.

Performance-wise let me put this in perspective: A typical bicycle generator produced 3 watts I seem to recall. My turbo-generators produces the same power output, in a size of 7/8" outside diameter and about 2" long including the prime mover (turbine).

And this with a single steam jet powering the turbine wheel.

The 5/8" diameter turbine is capable of MUCH more power with full admission nozzles. But then the generator would have to be larger than scale to absorb that power.

As it is, the turbine output and generator output are in nice balance, powering the 3 Watt LED at full brightness as determined by Voltage and Amperage measurements, all while maintaining the 1/16 scale requirements.
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dusty
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Re: Steam turbine generator

Post by dusty »

Wolfgang wrote: Wed Sep 01, 2021 11:30 am
The 5/8" diameter turbine is capable of MUCH more power with full admission nozzles. But then the generator would have to be larger than scale to absorb that power.

As it is, the turbine output and generator output are in nice balance, powering the 3 Watt LED at full brightness as determined by Voltage and Amperage measurements, all while maintaining the 1/16 scale requirements.
I agree that you already have a nicely balanced turbo-generator that you're justifiably happy with. So I will introduce the topic of "ironless" motors and "ironless" generators only as a possible solution to the cogging problem discussed earlier in this thread. The ironless design will also eliminate the need to acquire special mu metal laminations and fabricate an iron stator. I grabbed a pic from the internet of an ironless stator:
Ironless Stator.jpg
Because there is no iron in the stator, the rotor does not cog, making this design ideal for turbines.

This YouTube video I found shows how simple it is to wind the stator coils and assemble the finished stator: https://www.youtube.com/watch?v=K4xfHgw-m8I
When used as a generator (actually it's an Alternator), coil placement is not terribly important as the AC output will be rectified into DC. After the stator is fully constructed the assembly should be saturated with a low viscosity epoxy to give the finished stator more rigidity. In small assemblies the epoxy-wire stator can be used as the outer shell of the finished alternator.

Just another option to consider.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

There is an article "Machining a Turbine Wheel on a Manual Mill" by David Brush on machining the wheel for a 2.5" scale Pyle E-2 in Live Steam & Outdoor Railroading, Sep/Oct 2021.
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Re: Steam turbine generator

Post by dusty »

1) Perhaps this isn't the right thread to post these pics, but perhaps there will be some interest, so here they are.
2) I'm not a "model steam" or "steam model" person. My interest in steam turbines is to build a high power output, small, light weight engine.

About 10 years back I built a small CNC mill from scratch. One of the primary reasons I did this was to have the ability to machine turbine blades. Below are pics of some of the Blisks (Bladed Disk) I've recently machined. The largest blisk is 3.5" diameter at the exit, while the nozzle has a 2" diameter:
Turbine Parts.png
Blisks & Stator.png
The steel bearing in the pic has been replaced with a Silicon Nitride all ceramic bearing. The outer case is machined from a single round of 6061 aluminum. The 8 threaded holes are for steam input lines from the boiler and feed High Pressure steam into the steam chest.

This final drawing shows the nozzle, blades, and stator shapes at their roots. As was mentioned earlier in this thread, forcing the steam to make large turns as it passes through a set of blades extracts the most energy from the steam; notice the large turning angles the steam makes as it passes thru blades and stators. Also notice the nozzle is convergent-divergent which increases the velocity of the steam as it encounters the first set of blades, which are the impulse-reaction design. Purple circles on the drawing show end mill diameters at the root
Steam path thru blades.png
This turbine has only been tested using my completely inadequate, under-powered shop air compressor, which can only get the rotor turning rather slowly. More thorough testing will have to wait until my boiler is operational, or until I can find a shop that has a much larger compressed air system that doesn't mind humoring an old retired tinkerer. :)
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Re: Steam turbine generator

Post by Wolfgang »

Dusty:
The lamination stack shown in the pics by Richard Trounce eliminates all cogging with a 2 pole permanent magnet rotor. With this design the turbo-generator is self-starting, ie. no push is required with a wire in the exhaust port:-)) My laminations are practically identical with the ones shown in Richard's pics.

Wish I could claim inventing it but, alas, "There is nothing new under the sun...". I found this field lamination design in an ancient electrical text dated from the very early 1900's.

Initially I picked this design because it is so very easy to manufacture, and requiring very few turns of wire in each coil. The draw-back is that the coils need to be wound in-situ, making the protective sleeve in each winding hole most important.

Each of the 4 coils in the field consists of 13 turns, not too difficult to wind by hand.

Viewed the youtube vid you recommended. What are the advantages, from the electrical/efficiency point of view? I can see that the rotational inertia is minimized, this being desirable for fast-acting servos. Also a lower overall weight?
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Re: Steam turbine generator

Post by dusty »

Wolfgang:
Besides ease of fabrication, zero cogging, and lower weight, when used as an alternator I'm not sure if the coreless design is more or less efficient compared to a cored design. For me, from a DIY perspective, the ease of winding the coils and not needing to make an iron core from stacked laminations, is more than enough reason for me to choose an ironless design, even if I have to give up a little efficiency.

From a theoretical viewpoint I see two more advantages for ironless: fabricating a core from laminations instead of a solid chunk of metal reduces eddy currents, but it does not eliminate them completely, eddy currents still flow in laminations, they're just much, much smaller. Ironless design has zero eddy currents. Finally, lines of magnetic flux prefer to flow through the iron core rather then jump through the holes where the windings are located, and since you want the flux lines passing through the copper windings, having the flux go around the wire is not good. With no iron, all flux lines from the PMs pass through the the copper windings. Of course this is all just over simplified theory where I haven't addressed issues of core saturation, flux density in iron vs air, and how the PM flux will change once current flows through the windings and they begin generating their own magnetic fields.

So which design has better power output? I don't know. For greatest efficiency and simplicity, I prefer a three disc axial flux design. But I doubt it scales down to a size you might like for modeling.
Axial Flux.JPG
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

Here is a text book from the turn of the last century that describes these very well.

http://icsarchive.org/asc/asc_steam_turbines_2_1917.pdf

Scroll down to page 13 and further for descriptions and illustrations.
In a May 1, 2017 post Wolfgang gave the above reference. I wasn't able to open it but found a copy at Archive.org at https://archive.org/details/steamturbin ... ew=theater
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dusty
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Re: Steam turbine generator

Post by dusty »

Dick_Morris wrote: Sun Sep 05, 2021 5:47 pm
found a copy at Archive.org at https://archive.org/details/steamturbin ... ew=theater
Thanks for posting the steam turbine link,...looks like a good read with a lot of info that's still relevant today.
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Re: Steam turbine generator

Post by RET »

Hi Dusty,

"Have you run your turbine generator yet?" If you read everything I posted about Bill's turbogenerators, you will see that I didn't make them, Bill Huxhold did and they work well in all 3 sizes. The output on the 1/16th size is not very high, but it works and will power several led's. On the other hand, the 1/8th scale unit has a very impressive output that will actually run a small motor.

Bill routinely makes things that the rest of us can only dream about and at our meetings, when he explains how he does it, he makes it sound SO simple that even a novice should be able to do it while standing on their head!

The only real advantage the "coreless" design has is that it can respond quickly to high angular acceleration which isn't a requirement for a generator and by the way, if you look at the assembly, it still has a core, the core just doesn't rotate and that is what gives the high acceleration capability.

In a commercial steam turbine, I'm sure the design of the stator and rotor blades take into account the requirement for laminar flow wherever possible, because turbulent flow over the blades wastes energy. The calculations and formulae required to achieve this are way beyond my simple knowledge and capabilities, I just know that in today's commercial units the calculations will be done to make the efficiency as high as possible. Curvature, shape and angle of attack will all vary as the blade radius changes, so blade design becomes very complex and all of this is only efficient at the design rpm., temperature and pressure for the turbine.

I have to give you kudos for the concept and machining, but in your pictures, the stator and rotors don't look right, the blades have to twist as the radius changes to keep the angle of attack the same. I also think the blades have to be closer together (more blades on the disk) and narrower at the root than at the outer end. To machine this using CNC would require a 4 or 5 axis machine. Like you, I also built my own CNC and it can handle 4 axes at once, but doing blades properly is beyond its capabilities. The programming also gets quite complex. I'm sure Bill Shields can tell you more than you would want to know on this.

You say a regular air compressor doesn't have the airflow required to spin the turbine up. What you might try is to only use two nozzles on opposite sides, that will give you higher pressure on the vanes and perhaps the rpm will be higher. Obviously, more nozzles will be required for more power, but if you just want to spin it up, fewer nozzles might work better.

I'm sorry to "rain on your parade" a bit and I'm far from being an expert, I'm just trying to tell you what I see. There are a lot of very knowledgeable people on chaski (Harold, Bill Shields, etc.) and in most cases, someone is going to know what you need.

Hope this helps a bit.

Richard Trounce.
Last edited by RET on Mon Sep 06, 2021 2:17 pm, edited 1 time in total.
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Re: Steam turbine generator

Post by Dick_Morris »

Can you get much insight into how well a steam turbine generator turbine and construction functions using compressed air, versus steam?
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Re: Steam turbine generator

Post by dusty »

Dick_Morris wrote: Mon Sep 06, 2021 2:08 pm Can you get much insight into how well a steam turbine generator turbine and construction functions using compressed air, versus steam?
Using compressed air for initial spin-up is an easy way to test for dynamic balance of the rotating parts as well as turbulent air flow through the blades, without heating up all the parts so hot that you need to wait for hours for everything to cool down so you can attempt to fix any problems you may have found.
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