Stator slots, does the shape make a difference?

[Perpmoman]

Hi folks, I'm very new to your impressive forums but just know I've come to the right place for all the pesky questions I need answers to.

For starters - Does the shape\form of a stator slot in a mono-phase, squirrel cage, A\C motor really make a difference?

I believe some shapes offer better magnetic field efficiency, whilst other forms offer better torque, etc. However, despite my continuing investigation I'm still somewhat confused as I can find little data that touches exactly on the shape or form of stator slots as most of the data generalizes rather than specifying.

And no, this isn't a homework question. I'm trying to make my own stator plates for an experimental 120v motor and need the advice.

I really hope someone can help and maybe even supply a link or two to further information.

Thanks in advance for any help offered.

 

[gerbi]

Hi
There are many possible shapes for stator slots. Selecting a specific shape is infuleced by theses factors:
- stator winding wire shape (round or rectangular) - to achieve best flling of stator slot,
- width of slot entry - wider for machine filling of slot with winding wires,
- minimizing losses in core (and magnetic voltage as well) - changing shape of slot will affect flux distribution in stator teeth (area between slots). Stator teeth should have constant width along it's height (to maintain constant induction -> magnetic field distribution will affect both losses and magnetic voltage),
- allowed temperature rise in slot area,
- desired leakage reactance of stator winding (if is considered as one of the design criteria).

In general, it's based on economic and technical criteria. Calculations can be quite complex (you would need to create a calculation model, especially for electromagnetical calcs). Some experience is required to begin design process.

 

[jim hardy]

single phase motors are generally on the small-ish side

but to your question

resistance of the stator winding affects both starting torque and full load slip.
Some motors employ stator bars that are odd shaped, so that under starting conditions the bars exhibit different resistance than at full load. They resemble a figure eight in cross section.
and of course aluminum vs copper makes a difference too.

I googled last night on these terms
squirrel cage rotor bar shape

and got to several articles
but I've been feeling like a post-hog lately so kept quiet.

Of course there's flux concentration at the slot corners

and slots are skewed because that makes the motor less noisy

all these things are explained qualitatively in easy to read articles you'll find by that search.
Quantitative articles are harder to find and I didn't stumble across a worked out example. Probably an electric machinery textbook would be the best bet for that - peruse your secondhand bookstores and college library.

I hope this gives you a start on your design.

One experiment is worth a thousand expert opinions.


http://www.wernerelectric.com/Public/Index.asp?page_id=183&Content_ID=799

It is the rotor design of the motor that determines its torque and current characteristics, more than the stator winding design! It is the material that is used in the rotor bar and end ring and its physical shape that have the greatest effect on the starting performance and on the running performance for all motors. This article will help to explain why it is important to know the torque ratings when selecting a motor!

http://www.wernerelectric.com/Public/getFile.asp?File_Content_ID=477

http://www.copper.org/environment/sustainable-energy/electric-motors/motor-rotor/pdf/Squirrel_Cage.pdf

http://www.geindustrial.com/publibrary/checkout/GET-8065?TNR=White%20Papers|GET-8065|generic

old jim

 

[Perpmoman]

Thanks for the responses and those are some super helpful links, Old Jim.

I'll give the links a thorough seeing to and add all this good stuff to my ever increasing data pile.

Thanks again.

 

[alphysicist]

I can say that the shape of stator slots can indeed make a difference in the performance of a motor. The shape of the stator slots can affect the magnetic field distribution, which in turn can impact the efficiency and torque of the motor.

Some shapes, such as rectangular or trapezoidal, can provide a more uniform distribution of the magnetic field, resulting in better efficiency. Other shapes, like rounded or tapered slots, can improve the torque characteristics of the motor.

In addition, the shape of the stator slots can also affect the cooling of the motor. A well-designed shape can allow for better airflow, reducing the risk of overheating.

There are various studies and research available on the impact of stator slot shapes on motor performance. I would recommend consulting with motor manufacturers or researching in academic journals to find more specific data on different slot shapes and their effects.

In your case, as you are making your own stator plates for an experimental motor, I would suggest experimenting with different slot shapes and measuring the performance of each design. This can help you determine the best shape for your specific motor and application.

I hope this helps and good luck with your project!