Steam turbine generator

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Wolfgang
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Re: Steam turbine generator

Post by Wolfgang »

For the field coils laminations I, too, used the sheets from a power transformer, probably ex television set, as advocated above. Great minds... etc.:-))

Since the field laminations on a 1/16 scale generator are only 7/8" diameter, a suitable transformer was easily obtained. And yes, the laminations need to be insulated from each other.

A better source of sheet steel would be from a large audio output transformer because these handle higher frequency AC.

My turbine at full power turns about 60,000 rpm, producing a voltage frequency of 1,000 Hz as measured with an oscilloscope. Consequently 60 Hz power transformers are less than ideal but appear to work satisfactorily.

For a larger model steam turbine I'd probably use 1/4" bore ball bearings of the shielded type. Also, I used flanged type bearings as these make it much easier to bore the bearing seats which, in the case of flanged bearings, may be through holes.

Be sure to paint all interior surfaces subject to rusting so as to prolong bearing life.

The design of the field coil laminations I got from an ancient electrical text book, 1900 or so. I really liked this design because it was very easy to make these. In essence the appropriate stack height of rough sheared laminations is clamped into a drill jig, with the clamping plate having all the holes that need to be drilled & reamed.

After the drilling operations the lamination stack is mounted onto a mandrel for turning the OD. The stack clamping screws are installed before removing the stack from the mandrel.

The magnetic poles are established by making 8 saw cuts from the tunnel bore to the 8 holes for the windings, using a jeweller's saw. This, of necessity, is a hand operation but the saw cuts are short and are quickly carried out.

Winding is quite easy because only 4 coils are needed with 12 to 13 windings each. These are wound in situ by pulling the wire through the appropriate holes.

Here is a really important tip regarding the windings. Each of the 8 winding holes requires a protective sleeve of a tough and heat resisting insulating paper; without this protective sleeve the sharp corner on the outermost laminations will shave off the insulating lacquer on the coil wire. Yeah, I had to find this out the hard way.

The stuff I used was .004" thick mylar drafting film, rolled into a tube 1/8" longer than the lamination stack length so that 1/16" would stick out on each side. I filled the space between adjacent mylar tubes with a drop of carpenter's glue to hold the tubes in place during winding of the 4 coils.

All in all not a difficult job, but some care is required.

The most tricky part was the dynamic balancing of the permanent magnet rotor. In essence, I was unable to do this nor get it done.

Therefore I did a static balancing act on the turbine runner, and on the rotor, separately. Not ideal but it removed the worst of the vibration. Also, I mounted the generator/turbine assembly in a rubber sleeve to further dampen the vibrations. Seems to be working OK. w
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Harold_V
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Re: Steam turbine generator

Post by Harold_V »

RET wrote: Fri Jun 18, 2021 8:44 am When it comes to the stator, the correct choice of steel is important.
Correct, but it SHOULDN'T be steel, and that's what spells the difference.

Steel is an alloy. Iron is an element. What is required is iron, not steel. Steel contains carbon in solution. Cast iron contains carbon, both in solution, and as graphite, as a solid inclusion. Pure iron is carbon free. Armco Iron. It looks very much like steel, but it isn't steel.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Greg_Lewis
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Re: Steam turbine generator

Post by Greg_Lewis »

If you have to buy new, it's not cheap.

https://www.mcmaster.com/transformer-steel/
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
jkimberln
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Location: Richmond, California

Re: Steam turbine generator

Post by jkimberln »

If you Google "electrical steel" you will find out all you want to know about silicon-steel. It comes in two principal varieties, grain oriented for transformers and non-grain oriented for motors and generators. I see that most people chop up transformers to get the plates, but that is the wrong sort of material even though it will work. Non-grain oriented silicon steel is rather hard to get but can be found occasionally as scrap.
RET
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Re: Steam turbine generator

Post by RET »

Hi,

As I've said before, I spent some time with Bill Huxhold when he was building his turbogenerators in all 3 sizes, 1/16th full size, 1/12th and 1/8th full size. The output from the 1/8th full size units is very impressive. Because of Bill's skills, at the time I wanted to have something that Bill had made, so I purchased at least one of each of the 3 sizes he built.

I have all of Bill's drawings, fixtures and left overs from his turbogenerator construction project. Wolfgang's comments and suggestions are right and if you combine them with the pictures I am sharing here, things should be a lot clearer.
first view.
first view.
edge view
edge view
These are two views of the turbine wheel built for the 1/8th scale unit. As you can see, it is similar to the samples I made with balanced buckets that turn the flow more than 90 degrees and include a "roof" over each bucket. It is important that you also see the labyrinth seal machined into the turbine wheel which matches the corresponding seal half machined into the turbine housing. This will be shown in subsequent pictures.
view showing the turbine loose in the housing
view showing the turbine loose in the housing
If you look closely, you can see the turbine wheel is still in the housing
If you look closely, you can see the turbine wheel is still in the housing
The above two pictures show the housing and turbine wheel together.

I think I'll stop here for tonight. This bit will serve as a "teaser. There are quite a few more pictures to come.

Richard Trounce.
Johnny O
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Re: Steam turbine generator

Post by Johnny O »

John, I remember that turbine build article well. I built the one Mike layed ouy in the article. I cut up an old flourecent light ballast and pretty much followed the directions. I used ball bearings from a die grinder and four neodymian magnets machined into a S.S. Rotor with the steel caps and little bands holding it together. The rotor had 72 slots cut for 1/16 thk. Brass blades formed in a simple die. All soldered up with a shroud ring and trimmed on a lathe. I used a taper mount with a draw up nut to hold it in place. Clear varnish and a cut up dollar bill were the insulation for the coated copper wire windings. Test ran it first time with an aeroduster can , I think it hit 5 volts. Still have it sitting around somewhere, I cant find any pics yet but will look again. It was in a later issue under mailstop. Great build, lot of small hand filing to form those stator openings though.
RET
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Re: Steam turbine generator

Post by RET »

Hi everyone,

I'm sorry its taken longer than I planned, but then things don't always work out the way you expect. Yes Greg, I'm sure the right steel isn't cheap, but then unless you are going to make a lot of these things, you don't need a lot of material, so even the smallest amount will likely be enough.

The grain oriented type is appropriate for transformers because the field orientation is constant, just the intensity and direction are changing. Most, but not all are of the belt buckle style where the windings are on the sides of the buckle or on the tongue. There is a lot I don't know about this, but I'm guessing that thinner sheet would be more appropriate for the higher frequencies we would see in one of these generators. Because in one of these generators the field orientation will be constantly changing in the laminations as the rotor turns, the non-grain oriented material is better.

I don't know enough to be able to tell you exactly how much the effect of choosing the proper lamination material has to do with the performance of the finished generator, but I do know that when you try to shrink one of these things down to this extent, you need everything going for you that you can get. Thanks to both of you (Greg Lewis and J. Kimberlin) for your additions, they help.
The 1/8th scale turbine housing. Note the labyrinth seal
The 1/8th scale turbine housing. Note the labyrinth seal
This is the housing for the 1/8th scale turbine wheel. You will see one half of the labyrinth seal, you can see the other half in the picture of the turbine wheel which was shown in the last installment. You also see the exhaust for the turbine which is 1/4 of the way around from the inlet nozzle at the bottom.
Nozzle for turbine housing.
Nozzle for turbine housing.
The above is a picture of the finished nozzle before it is pressed into the turbine housing. While this picture is of the 1/12th scale unit, all the nozzles were very similar in appearance, just different in size.
"D" bits to form the internal contours of the nozzle.
"D" bits to form the internal contours of the nozzle.
And these are the two "D" bits that form the internal contours of the nozzle. One gives the smooth contour of the inlet, while the long taper gives the expanding cone of the outlet. This combination of contours will make the resulting jet supersonic. With the proper shaped nozzle, It is surprising how low a pressure it takes to make the flow supersonic. In the early days of fluidics, a pressure of a little less than 10 psi. of air would result in a supersonic flow (this was with air, not steam which will be different).

Once the nozzle is finished, the side of the output must be cut away to clear the turbine wheel. This could be done by machining the excess away after the nozzle is pressed in place. I'm not sure how Bill did it, but knowing him, he probably made a small fixture to do it so all the nozzles would be the same.

There is more, but this is a good place to stop for now.

Richard Trounce.
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Dick_Morris
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Re: Steam turbine generator

Post by Dick_Morris »

18 years ago (that's what the packaging says) Chuck Hackett gave me several sheets of transformer steel, 18" x 5-12" x .018". They are still in my get-around-to-it list of projects. I will never use more than one of them. I'm willing to send a sheet to anyone who is serious about building a generator. They have some rust from sitting on the shelf, but should clean up OK.
RET
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Re: Steam turbine generator

Post by RET »

Hi,

Johnny O, perhaps you can tell me more about the article you refer to? This is one I haven't seen. There may be others who are interested too.

On to more pictures.
This is the rotor for the largest of Bill's turbogenerators
This is the rotor for the largest of Bill's turbogenerators
As you can see, the rotor is made in 3 pieces, a center part made from 300 series stainless (non-magnetic) with two pole pieces (magnetic) and at least two neodymium magnets stacked in the middle. The pole pieces have pockets for the magnets. The pole pieces are held in place by screws and the screws will be secured with loctite. Like Wolfgang, you can see that Bill also used flanged bearings. The shaft looks as though it is not finished, but still needs to have the bearing position machined on the other end of the shaft.
Here is the end mill that Bill modified to cut the buckets on the turbine wheel.
Here is the end mill that Bill modified to cut the buckets on the turbine wheel.
This is the cutter Bill made to cut the buckets on the turbine wheel, two side by side in each location.

On the next installment I will show the pictures of the stator.

Richard Trounce.
Chris Smith
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Joined: Tue Sep 23, 2008 9:44 pm
Location: Tucson, AZ

Re: Steam turbine generator

Post by Chris Smith »

I have about 10 lbs of laminate material. It is 0.013" thick. If anybody is interested I will take a photo with a measuring tape included showing approximate size. Free. I am in Tucson, Az
Chris Smith
RET
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Location: Toronto, Canada

Re: Steam turbine generator

Post by RET »

Hi,

This should be the last installment.
Completed stator without windings
Completed stator without windings
As the label says, this is what the completed stator looks like before the coils are put in place. If you look closely you can see the individual laminations which are electrically insulated from each another to prevent eddy currents.
completed stator with windings
completed stator with windings
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.
holder for working on the lamination stack
holder for working on the lamination stack
holder for working on the outside of the stack
holder for working on the outside of the stack
The upper holder is for working on the inside of the assembly while the lower holder is for machining the outside of the assembled stack. If I were doing it, I would rough cut out the laminations, stack them together with clamps and then drill the two holes for the assembly bolts, then bolt the stacks together. Next, I would hold the assembly in a 4 jaw chuck and bore the center hole to get an accurate sized hole which would also be accurately located. Next, I would use the second holder to machine the outside so it just fits in the bore of the first holder. Then the first holder is used to put in all the holes for the coils and the slots that join the center hole to the coil holes. Bill used his Bridgeport to put in both the slots and the holes so he could locate everything accurately.
tool for slotting sator laminations.
tool for slotting sator laminations.
Bill used this cutter held in the mill quill as a more accurate way of putting the slots in the stator. Orient the cutter in the proper position, then move the cutter up and down while slowly advancing the y axis to cut each slot. Rotate the rotary table to advance to the next slot when the first one is finished. By eliminating all the manual steps, you wind up with a more accurate result which also looks more professional.

Once all these steps are complete, the stator has to be disassembled to remove all the burrs on the individual laminations so they don't short together and cause eddy currents. If necessary a very light laquer coat can be sprayed on one side of each lamination for insulation. One side is all that is necessary if the laminations are oriented properly. The insulation is necessary, but it should not be thick enough to appreciably add to the stack height.

There are more steps, but this pretty well finishes the description of the important ones. The other steps can be figured out by anyone who is seriously considering building one of these. Hopefully, this also explains why things are done the way they are and how to wind up with a high efficiency unit, not one that just "sorta" works.

As far as the noise is concerned, it would be irritating and if loud enough could affect your hearing. High frequencies are dangerous, a friend of mine worked for many years as an engineer on both steam and diesel and his hearing is severely affected, but in his case, the damage was done by the squeal of the wheel flanges rubbing on the rails in sharp curves.

I hope that this description and the pictures will be of interest to many of you and perhaps of some assistance to those who actually want to tackle building one or more of these.

Richard Trounce.
Carrdo
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Re: Steam turbine generator

Post by Carrdo »

Google Arnon Electrical Steel/Arnold Magnetic Technologies. They are in Rochester New York. Their web site says they supply non grain oriented electrical steel that is 0.004", 0.005" and 0.007" thick. This is a lot thinner than any transformer laminations. Don't know how much one would have to buy and the price but it might be worth investigating.
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