36 pole induction motor 1

[andymel]

Hi There,

I'm in the process of trying to design a 36 pole induction motor for one of our test beds in the factory. It'll be used to test a range of winches that we manufacture and by controlling this motor through a VSD we can perform certain tests without the primary gear box that gets fitted to the completed unit.

I've looked on the web at the various motor manufacturers - a motor of this size (55kW)does not exist as far as I can see, hence my efforts to design a fit for purpose motor.

Despite my best efforts, all I can achieve is a 25kW design, that runs, but with a terrible power factor (copper losses and a huge differential reaction are killing the machine).

My question (eventually) is this: is this a viable proposition in motor design? Should I be looking at a different type of motor (such as a brushless DC or similar)?

Has anybody had any experience with a motor of this size?

Best Regards

 

[Skogsgurra]

This is an impressive undertaking. But next to futile.

I have seen 18-pole motors once upon a time. Must have been 30+ years ago. If this is for a test bench, I would try and find an old low-speed DC motor - or get one rewound. It should be possible to wind an armature with many turns and thin wire so that you get the desired speed.

ABB has a new range of DC motors and they have no standard. "Everything special" so I guess they would be prepared to make one that fits your needs.

Do not fear brushes and commutator. It is a mature technology and I still see lots of DC machines around. They are even being installed in new applications.

Another way to get a low speed is to use a hydraulic drive. Although 55 kW seems to be rather low for such a drive.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

What's wrong with a standard 4 pole machine and a gearbox, using a VFD if necessary? The shaft speed and torque at the geabox output shaft can be designed to match the 36 pole machine. It will likely be smaller and definitely be cheaper than a 36 pole machine. The only machines I have seen with such a high pole count have been big low speed synchronous machines.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

I agree with ScottyUK.
When you drop the speed of a motor, the torque often stays the same and the horsepower drops. A simple evaluation indicates that a 36 pole machine will have about 1/9th the HP of a 4 pole machine in the same frame. A rigorous solution will probably yield similar results.
You can probably find an off the shelf motor with an integral gearbox to serve your purpose for much less than the cost of a 36 pole machine. If you have to design and build it yourself, the savings will be even greater. The higher speed motor with a gear box will also be lighter and easier to handle than a 36 pole monster.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Gunner and Scotty are giving about the best solutions. You could probably even find a good used DC motor if you search for it.

I have seen induction motors around 24 poles or so. They were used for low speed pumps and ran somewhere around 300rpm. FYI, any induction motor with that many poles will have a low power factor and efficiency. Those motors drew about 50% more current at full load compared to a 1800rpm motor of the same hp.

No manufacturer will list such a motor on their website. You are talking about a custom design. If you were looking at a larger motor I'd suggest using a brush-type synchronous or possibly using a brush type synchronous design with a squirrel cage rotor.

 

[dpc]

Probably not practical in the size you are looking for. I have seen motors this slow, but only much larger horsepower.

 

[itsmoked]

A gear box is so obvious I wonder why andymel, working in a gearbox laden factory(winches), has gone to such herculean effort?

andymel; Maybe you could better describe your ultimate use/rational?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Why not accept that a guy needs low speed and some torque?

He says that "It'll be used to test a range of winches that we manufacture and by controlling this motor through a VSD we can perform certain tests without the primary gear box that gets fitted to the completed unit"

That is a perfectly valid reason to me. And it would surprise me a lot if he hadn't given use of a gearbox some consideration. Especially since he mentions them in his OP. What is really difficult to understand is that andymel actually seems to have tried a 36 homebrew pole motor. That's amazing.


Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sreid]

If you want to look at brushless motors, ETEL makes some whopper sized frameless, brushless DC torque motors.

http://www.etel.ch/Torque_Motors

 

[stardelta]

Is physical size a factor? lets hope not.... .a 36-pole 55kw induction motor is going to be quite a substantial and very heavy item. As a guide here in IEC land a 55kw 8-pole requires a 315 frame.

 

[edison123]

About two months back, my shop did convert a 440 V, 75 HP, 350 RPM, 20 pole, 60 Hz GE motor to a two speed motor (415 V, 37.5/75 HP, 150/300 RPM, 40/20 Poles, 50 Hz).

It was a custom-built, vertical motor by GE made some 40 years back. The core size of the motor was 250 mm long x 675 mm dia. Your size could be around 500 mm x 700 mm. Not that big.



* I would go green if only I were not yellow *

 

[andymel]

The whole premise of this design is to be able to test our planetary gearboxes/drum assemblies without connecting the clutch gear / primary gearbox assembly. Mechanically I can design the motor/shaft interface to fit where the clutch gear would normally be and the rest of the motor is not that challenging. By using a VSD we hope to easily simulate the duty cycle. Keeping it simple is our rationale for using one motor.

Edison123, I used an IEC 355 frame as the basis for lamination design as this also ties in nicely with my space factor (700mm od x 500mm lg is in my current design). A copper barred rotor with laser cut stator/ rotor lams makes for a very simple manufacturing process.

A gearbox arrangement may be my only out at this stage. Thanks guys,for all the comments on this post, it confirms my earlier fears that I might be flogging a dead horse with this project. However, the fact that somebody has seen one (cheers Edison123) gives me some hope. Back to the drawing board!

Best Regards

 

[oftenlost]

I know of at least 6 horizontal pump motors in the New York area running at 177 RPM so the design is there and as these motors are old units being converted to VFD, I would say that the design is proven. I,too, would expect a high line current.

 

[waross]

You may reduce the reactive portion of the high line current with capacitors. This is a common remedy for motors running at low power factors.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Andymel

Thanks. As you know, the pf will be poor due to the high poles. In my case, the no-load current was 50% / 80% for 20 / 40 poles. And you cannot use capacitors with VFD's.

The rotor was aluminum die-cast.

If you are doing the 36 pole design from scratch, avoid stator/rotor slot combination where the difference between slots is equal to 1, 2, 34, 35, 36, 37, 38, 72, 108 & 180.

Best wishes for your interesting & courageous (!!!) project. Keep us posted with the results.

* I would go green if only I were not yellow *

 

[richs]

Along the lines of oftenlost, might I also suggest looking
for low speed water driven AC dynamos? Horizontal Pelton
water wheel generators.

There might be quite a market in small stream hydro power
plants with multipole generators and indeed, with the VFD
driving it, might prove an alternative to rolling your own?

Hey, bear with me. I'm just a computer (confuser) guy. Just
a thought.

Cheers,

Rich S.

 

[automatic2]

here's a motor that we use as singles, or stack them in doubles/triples.

not in your requirements, but check the size/wieght to horsepower ratio.