Steel laminations in an induction motor in the stator

Thread Starter

Heaviside

Joined May 26, 2021
9
Hello, sorry if this is a stupid question but I'm curious and haven't been able to find a decent answer to it. Are the steel laminations that hold the copper conductors necessary to be magnetically permeable and electrically conductive? (Note I understand that they are not electrically conductive between each separate steel lamination) Could they be made from some other type of material that is not electrically conductive in order to eliminate eddy currents? Is their only purpose to just hold the wires in place? Are they increasing the strength of the magnetic field because they are magnetically permeable? I am looking for a rather in depth type of answer, also please don't lecture me. I am simply here to learn, Thanks!
 

LowQCab

Joined Nov 6, 2012
517
An "in-depth" answer ???
That's a MASSIVE Subject that You want summed-up in a few paragraphs !!!

Start simple with a DIY Electric Motor Project on YouTube.

An Eddy-"Current" is an extremely low-Voltage/high-Current, Electrical-Circuit.

Any Electrical-Current will always cause a Magnetic-Field to be generated.

Any moving Magnetic-Field will cause Electrical-Current to flow in any near-by Conductor.

Poor-Conductors make weak Magnetic-Fields.

Copper is a great Conductor of Electricity, but makes a very poor "Permanent-Magnet",
because it is not a "Ferrous-Metal".
.
.
.
 

Yaakov

Joined Jan 27, 2019
3,153
Welcome to AAC.

The rotor's steel laminations are there for magnetic properties. They are needed for the magnetic field that induces current in the windings. Eddy currents are parasitic and so steps are taken to reduce them as much as possible, but removing the steel core, which is a highly optimized silicon steel constructed like a transformer core, would not just eliminate eddy currents, it would eliminate the part of the rotor that interacts with the magnetic field.
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
An example of various degree's of steel in the stator of a AC induction motor and their effects is where the typical 50hz/60hz motor is used with a VFD application, the general maximum frequency for these motors is around 70Hz - 80Hz
But there are HS 24krpm 400Hz versions made, these have a much smaller mass of steel material in the stator, therefore due to the much less inductive reactance at low frequency they cannot be ran below 6khz without destruction occurring.
 

Thread Starter

Heaviside

Joined May 26, 2021
9
An "in-depth" answer ???
That's a MASSIVE Subject that You want summed-up in a few paragraphs !!!

Start simple with a DIY Electric Motor Project on YouTube.

An Eddy-"Current" is an extremely low-Voltage/high-Current, Electrical-Circuit.

Any Electrical-Current will always cause a Magnetic-Field to be generated.

Any moving Magnetic-Field will cause Electrical-Current to flow in any near-by Conductor.

Poor-Conductors make weak Magnetic-Fields.

Copper is a great Conductor of Electricity, but makes a very poor "Permanent-Magnet",
because it is not a "Ferrous-Metal".
.
.
.
Thanks for telling me to go to youtube....lol, what a joke of an answer. Listen if you don't wish to spend time to elaborate then don't answer, which you really didn't answer any of my questions at all. I didn't ask for a definition of an eddy current, nor did I ask for an introduction to electromagnetic induction. I asked are the steel laminations necessary. Then explain why exactly they are necessary. Is it to balance the dielectric and magnetic field as to maintain some type of balance between the two? Is it to increase the magnetic field strength?

Note in some of nikola tesla's original induction motors he had wound the coils in a toroid, instead of the standard way we see it done today. I am trying to think outside the box in this way. Why don't we do wind the coils in a toroid anymore? (Note unnecessary to answer this, but if you do know. I would love an explanation)
 

Thread Starter

Heaviside

Joined May 26, 2021
9
Welcome to AAC.

The rotor's steel laminations are there for magnetic properties. They are needed for the magnetic field that induces current in the windings. Eddy currents are parasitic and so steps are taken to reduce them as much as possible, but removing the steel core, which is a highly optimized silicon steel constructed like a transformer core, would not just eliminate eddy currents, it would eliminate the part of the rotor that interacts with the magnetic field.

Can you elaborate on what exactly might happen if the steel laminations were to be removed? Would the motor not spin? If it does spin then would it constantly slip? Would the current spike? How much torque of the motor could be lost? Could it be possible that a different geometry of the magnetically permeable material wouldn't suffer from eddy currents? Could the laminations be coated in bismuth to help deal with the eddy currents? Thanks I really do appreciate the answers!
 

Thread Starter

Heaviside

Joined May 26, 2021
9
An example of various degree's of steel in the stator of a AC induction motor and their effects is where the typical 50hz/60hz motor is used with a VFD application, the general maximum frequency for these motors is around 70Hz - 80Hz
But there are HS 24krpm 400Hz versions made, these have a much smaller mass of steel material in the stator, therefore due to the much less inductive reactance at low frequency they cannot be ran below 6khz without destruction occurring.
Do these high speed motors have very low torque? Is the low torque due to not having a high amount of a magnetically permeable material?
 

Yaakov

Joined Jan 27, 2019
3,153
Can you elaborate on what exactly might happen if the steel laminations were to be removed? Would the motor not spin? If it does spin then would it constantly slip? Would the current spike?
Without the laminated core, the squirrel cage would rotate in the rotating magnetic field as it does with the core. The purpose of the core is to increase motor efficiency. The core increases the magnetic field while being carefully designed to have minimal eddy current in itself. The core has a very high resistivity because of the silicon in the steel. This means the steel itself resists the formation of eddy currents but it enhances the magnetic field which is being used to induce the eddy current in the copper loop.

How much torque of the motor could be lost? Could it be possible that a different geometry of the magnetically permeable material wouldn't suffer from eddy currents? Could the laminations be coated in bismuth to help deal with the eddy currents?
Almost all of the torque will be lost for any given magnetic flux. It is not a practical motor.

Any proposed enhancements to modern induction motors would have to be extremely non-obvious. Consider the role of the induction motor in industry, the sheer number of motors in operation, and the crucial element of efficiency.

With all the engineers and all the economic incentive to make induction motors more efficient, if something is obvious to a neophyte it is either mistaken or has been tried and rejected.

Thanks I really do appreciate the answers!
Sure. You might want to watch the MIT E Mag lectures of Walter Lewin on YouTube. They are very good and if you stick with them you can get a solid foundation in Maxwell and Faraday.
 

shortbus

Joined Sep 30, 2009
8,568
The core has a very high resistivity because of the silicon in the steel. This means the steel itself resists the formation of eddy currents
Only partly true. Like Max said different steels for different motors, some are not even a silicon steel. The biggest thing that stops eddy currents in motor or transformer lamination's is the heat treatment done after they are stamped out and before assembly. Not treat treatment in the normal hardening way but in and atmosphere furnace to coat the surfaces with an oxide layer. The oxide isn't very conductive, more like a dielectric than what the normal steel surface is. https://www.researchgate.net/figure...-non-oriented-electrical-steel_fig1_298956376

depending on the application there are two different type of silicon steel too, oriented and non oriented.
 

Yaakov

Joined Jan 27, 2019
3,153
Only partly true. Like Max said different steels for different motors, some are not even a silicon steel. The biggest thing that stops eddy currents in motor or transformer lamination's is the heat treatment done after they are stamped out and before assembly. Not treat treatment in the normal hardening way but in and atmosphere furnace to coat the surfaces with an oxide layer. The oxide isn't very conductive, more like a dielectric than what the normal steel surface is. https://www.researchgate.net/figure...-non-oriented-electrical-steel_fig1_298956376

depending on the application there are two different type of silicon steel too, oriented and non oriented.
Yes, I mentioned the transformer-like property of the laminations, I was contrasting the resistivity of the steel to the copper or aluminum. Thanks for clearing up the omission.
 

Thread Starter

Heaviside

Joined May 26, 2021
9
Without the laminated core, the squirrel cage would rotate in the rotating magnetic field as it does with the core. The purpose of the core is to increase motor efficiency. The core increases the magnetic field while being carefully designed to have minimal eddy current in itself. The core has a very high resistivity because of the silicon in the steel. This means the steel itself resists the formation of eddy currents but it enhances the magnetic field which is being used to induce the eddy current in the copper loop.



Almost all of the torque will be lost for any given magnetic flux. It is not a practical motor.

Any proposed enhancements to modern induction motors would have to be extremely non-obvious. Consider the role of the induction motor in industry, the sheer number of motors in operation, and the crucial element of efficiency.

With all the engineers and all the economic incentive to make induction motors more efficient, if something is obvious to a neophyte it is either mistaken or has been tried and rejected.



Sure. You might want to watch the MIT E Mag lectures of Walter Lewin on YouTube. They are very good and if you stick with them you can get a solid foundation in Maxwell and Faraday.
Hmm....interesting way to answer part of my question with an insult. Instead of simply stating that you have no idea how the motor would behave if the laminations were coated in bismuth, you call me a neophyte and say that if something was that obvious then it must have already been tried and rejected. Maybe this "neophyte" just likes to question things that other "experts" blindly accept. Yeah, ive watched the E Mag lectures on Walter Lewin already, again thanks for pointing me towards youtube. Is that automatically what everyone does on this site? Pretend like you have such an in depth understanding and when questioned on it say go to youtube, LOL.
 

Thread Starter

Heaviside

Joined May 26, 2021
9
I believe because a motor with a toroid wound field winding would not be as efficient (magnetically or electrically) as the way it is done now.

Can you specifically tell me why that might be the case? I am unaware of any real reasoning for switching the way motors were wound from toroid to the normal way they are done today. I would really be fascinated to see if there has been any research done on this. Thanks!
 

Thread Starter

Heaviside

Joined May 26, 2021
9
It also takes up a lot more space, and smaller is almost always more desirable.
yeah......thanks for pointing out the obvious, I really gained a lot of insight from that. I'm surprised you didn't just say well go to youtube and see how a toroid winding is larger, or tell me to go watch a video on how motors are wound.
 

Thread Starter

Heaviside

Joined May 26, 2021
9
And yes for the motor to be of any real use it needs the steel/iron. Most all induction motors are wound in a distributed way. Where the windings for each pole cover a large part of the stator. without the steel there wouldn't be a good magnetic path.

https://ceme.ece.illinois.edu/files/2019/07/9-16-16-induction-motor-seminar-handout.pdf
Thanks! Will definitely take a look over this handout. I was looking for something exactly like this to better understand induction motor design! Truly thank you.
 

LowQCab

Joined Nov 6, 2012
517
yeah......thanks for pointing out the obvious, I really gained a lot of insight from that. I'm surprised you didn't just say well go to youtube and see how a toroid winding is larger, or tell me to go watch a video on how motors are wound.
May you lead an interesting Life.
 
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