Optimizing Electric Motor Core Materials for High Frequency Performance

[Jdo300]

Hello Everyone,

I'm interested in designing my own custom electric motor for some experiments and I am trying to do some research on some of the various laminated steel materials available. I have a decent working knowledge of general magnetic material properties, saturation characteristics, etc. but I'm not sure what kind of Silicon steel is best to use (or what is typical in motor designs)

In particular, I'm looking for a metal that has good high frequency characteristics (up to 10k perhaps), though from what I understand, most motors use the same kind of steel used in the 60Hz transformers which top out at about 1kHz or so before the frequency response drops off. I want to find a material with a higher frequency response because the design I'm working with is very similar to a switched reluctance stepper motor.

Some questions I'm asking are how to determine what thickness the laminations should be, and what grade of metal to choose? If anyone could offer any insights to point me in the right direction, that would be most helpful.

Thank you,
Jason O

 

[Carl Pugh]

By 10k do you mean 10kHz or 10 kilogauss?

If 10kHz and it was a transformer, would use nickel iron material.

If 10 kilogauss and it was a transformer, would use silicon iron material. Maybe M27 or something similar.

Whatever you use, getting a custom punching is going to be expensive.

 

[Jdo300]

By 10k do you mean 10kHz or 10 kilogauss?

If 10kHz and it was a transformer, would use nickel iron material.

If 10 kilogauss and it was a transformer, would use silicon iron material. Maybe M27 or something similar.

Whatever you use, getting a custom punching is going to be expensive.

Hi Carl, thank you for your input. Actually, the 10k was referring to the max frequency through the core material (for high frequency pulsing). As for the magnetic field, the motor will be using Ceramic 8 magnets but the flux density at the teeth can get as high as 2 Tesla in strength. is there a material out there that would be a good compromise between the two extremes? Also, how do you determine how thick the laminations should be?

Thank you,
Jason O

P.S. As for getting the steel punched, I have access to a CNC router table that can cut out very thin steels.

 

[Jdo300]

Ok, I was just doing some reading around and found some good information on the subject from this website:

http://www.protolam.com/page7.html

They say that M19 seems to be the most common silicon steel alloy to use for motor laminations. (Not sure where to look for information on Nickel Alloys?).

And for the lamination thickness, they said:

The most common thicknesses are .014 in., .0185 in., and .025 in. (29 Gauge, 26 Gauge, and 24 Gauge, respectively.) These thicknesses are supplemented by thin electrical steels, available in .002, .004, and .007 in. thick. Thin electrical steels are available in one grade (Equivalent to M19) and are made by re-rolling standard silicon steel. Due to substantially higher material cost, thin electrical steel is used primarily for high performance and high frequency applications.

So apparently, the thinner the laminations the lower the losses (makes sense), but how does one determine how the lamination thickness affects the frequency performance of the material?

- Jason O

 

[Carl Pugh]

The core materials that are good for 10 kHz aren't good for high flux density.

Motors aren't my specialty, but if you have turns of wire around a core, aren't you going to have high inductance? This means you will be unable to obtain high current, which means the motor will be low power.
You may be able to have a low frequency modulated by 10 kHz. (This would allow use of a core material similar to that used in audio transformers)

The lamination thickness depends on the resistance of the core material. (Ferrite cores don't use laminations because of the high resistance of the ferrite)

 

[Jdo300]

Hi Carl,

Great point about the inductance. Yes it is true that the number of turns around the core would have to be minimal to keep the inductance low enough to get a higher frequency response. I will need to do some more simulations to determine exactly what the inductance values of the drive coils are to get an idea of the upper end frequency for the setup.

Thanks,
Jason O

 

[m.s.j]

I adopt you face to high frequency problems in stepping motor, however the amorphous metals are high frequency magnetic material alternative for rotating electrical machines. They have the advantage of being very thin, e.g. 25 microns, while having a high resistivity, e.g. 100 + Ωm × 10 ^8. This leads to very low eddy current losses. However the high alloy content limits high-field operation and magnetostriction noise is quite high. Amorphous metal is awkward to handle and requires protection from stress. Microcrystalline and nanocrystalline (not amorphous) versions of spin cast metal are coming into wider use. Operation at frequencies up to 20 kHz seems practicable. These materials offer only a limited maximum width, e.g. 30 cm, hence applications tend to be limited to low-power devices. These materials have excellent properties, such as high saturation induction, up to 2.4 T and Curie points up to 900+ ◦C, and dominate niche markets where high Jsat and high Curie points are essential. Their high cost, however, makes them unattractive for widespread industrial use. Applications range from aircraft generators to submarine drives.



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[stator rotor]

In US, M19 is common type material for motor lamination stamping, but in China, we use B50A1300 stpe silicion steel to stamping for customer.

For more information, please check it there : http://www.stator-rotor.com/

 

[syntax]

Some questions I'm asking are how to determine what thickness the lamination's should be?

smaller plates are, less eddy currents there is and it will not heat up as if you would use a hole peace.

Do you still building that motor?