Motor Theory Education

Im looking for some opinions and perspectives - I'm a mechatronic instructor at a community college. I'm not a motor expert but I'm starting to learn more about it.

Can I ask the group a question - is power factor, corrective capacitors to minimize reactive power, apparent power - is this stuff critical for a mechatronic technician? Its kind of blowing the heads of my students unfortunately.

Also - do they need to understand how every single type of AC motor works in detail?
I could be very wrong but it seems like capacitor start induction motor and 3 phase motors are the main ones out there?
Thank you for any advice. Hope everyone is keeping safe....
Tim

tim_callinan said:

Im looking for some opinions and perspectives - I'm a mechatronic instructor at a community college. I'm not a motor expert but I'm starting to learn more about it.

Can I ask the group a question - is power factor, corrective capacitors to minimize reactive power, apparent power - is this stuff critical for a mechatronic technician? Its kind of blowing the heads of my students unfortunately.

Click to expand...

From a mechatronic standpoint, Power factor is irrelevant. They can ignore it, unless they get into a discussion of how much it COSTS to operate a machine. Then it's a good idea to understand the basics of PF.

Also - do they need to understand how every single type of AC motor works in detail?
I could be very wrong but it seems like capacitor start induction motor and 3 phase motors are the main ones out there?
Thank you for any advice. Hope everyone is keeping safe....
Tim

Click to expand...

In my opinion if they don't understand the different types of AC motors, they can get caught in a trap or scam from someone trying to peddle the wrong type to them for an application.

For single phase, they will likely never need a Shaded Pole motor except for a cooling fan for something, and most machines now don't use Split Phase motors any more. Power Tools and especially high speed ones use Universal motors. So I would just gloss over them and focus on Capacitor Start and Permanent Split Capacitor (PSC) type.

Three phase is easy for mechatronic, but there are also now 3 phase Permanent Magnet AC (PMAC) motors, and Synchronous Reluctance motors that are becoming more popular because of energy efficiency and precision speed control. If mechatronics means under 10HP for the most part, the rest are pretty much irrelevant.

jraef said:

In my opinion if they don't understand the different types of AC motors, they can get caught in a trap or scam from someone trying to peddle the wrong type to them for an application.

Click to expand...

To piggy back off this, I think they should understand at a high level and not the details. Like, calculating magnetic fields wouldn't add a lot of value.

Also, a mechanical engineer in my experience usually specs the motors and gearing. Then they work with electrical engineer/electricians on fitting it into their site.

Quick search this website looked about right on a nice to know about motors. https://www.elprocus.com/different-types-of-electric-motors/

Mechatronics is the AUTOMATION side of machinery having an all round understanding of machine control and sensing is crucial. knowing why a motor trips out while it starts is a must know situation. A basic motor is considered to having a 0.8 PF the only other info you need is on the motor name plates ( teach the newbies to always read and record that information, test them on this

ive been in the trade for 44 years
My apprenticeship was relay logic Mechatronics
lol im 62

I think a brief overview of DC motors would be worth its time.

I've always been amazed at how little motor theory/control (3ph squirrel cage) was included in the curriculum of the automation education in my days (2001-2004) compared to how common they are in the industry.
Though we learned the hard parts with the electrical calculations and equations but the more hands on parts were not on par with work life.


To OP:
Maybe take the basics of the engineering part with them and teach them where they can find more information about it. You never know who will persue a more theoretical path when you have sparked their interest.

Having taught students the motor theory. I can say that Electrical teaching covered all DC and AC motors.

The thanks is to Tesla.

tim_callinan said:

Also - do they need to understand how every single type of AC motor works in detail?

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It depends. Do your students want to be designers or users?
We are all users in that we use other people's tools to get something done but if one needs to design AC motors then they must trained to design AC motors.
The ratio of designers to users is small but being a designer pays more.

Whether they are users or designers they will encounter the terms power factor, capacitor, synchronous motor, etc. in the course of their activities. It is my opinion that they should be given basic coverage of these topics in their training so they at least know the terms and have a rudimentary understanding of their significance.

The OP did qualify this query as AC motors... I would also imagine that DC, Servo and Stepper motors are already a deep part of the curriculum for mechatronics.

Given that "mechatronics" is a portmanteau of mechanics and electronics, I considered that most machinery they will be working on will not need big Synchronous or Wound Rotor motors, nor will they be dealing with simple machines like pumps and fans except as accessories to more complex machines, hence not wasting a lot of time on motors that are for the most part only good for those applications. But a simple review of them would not hurt in helping them to understand the difference if they come across one.

Thank you for all of the information. Id say over ten years Ive been teaching Ive gotten so much good advice from this site on PLC, motors, automation, etc. The motors and motor control course is the most recent course we added at our community college. I always felt that in our whole curriculum - motors was a hole that needed to be filled. Im teaching it online right now and it is far too theoretical for my liking. It doesnt help that Im really not a motors expert. My feeling is for a good course I want to provide my students with skills that they will use when they leave our place. A lot our students work for amazon now and they work on conveyor systems in a big way. Im hearing that they run into a lot of VFDs, powerflex 525s and DC servo motors. My students are definitely not going to be designers - they are troubleshooters and technicians.
Talking about power factor - if i do a search on www.mcmaster.com on AC induction motors I cant find a single thing on power factor?? That seems strange to me if its so important?
Anyhow I defo appreciate all the advice Ive gotten from this site. Thank you for your time and very useful info.
Tim

This being a mechatronics class (controls, basically) I would focus on what is required for controlling an AC motor; such as overload protection for the motor, protection for the wires feeding the motor, appropriate fuse sizes & circuit breakers and basic circuits such as start/stop, reversing, HOA control, VFDs, etc.

The motor class I had focused entirely too much on torque curves, magnetic fields, etc. If you have mechanical designers in the class as well, I suppose that is important, but in a real-world application, the mechanical designer will specify the motor, and the controls guy needs to know how to control it and how it should be protected/etc electrically.

From a mechatronics standpoint, I would make a good part of the class focus on start/stop circuits and ladder logic – since single motor starters are one of the few electro-mechanical control devices still commonly in service. I’m not saying to avoid teaching the torque curves (or especially the concept of the inrush current) but don’t make it the sole focus.

If you want to find more info on power factor, try someone like Myron Zucker who makes power factor correction capacitors. They have some decent literature, if I recall correctly.

Enlightenment

According to different theories capacitors are miraculous devices which lead the reactive current to certain angle and blah blah blah, but for a motor instructor point of it would just a type of switch thingee which is added to single Phase induction type motor to make a start or power back throw type of thing and nothing else , all those old motors which requires which are used as generators needed them but not now in these days...

Power factor is not important to how a motor functions, it is a consequence of it. So its importance is to the SYSTEM that is feeding power to the motor. That’s why you won’t find a lot of info on power factor as it relates to how motors function. But when you start designing the POWER DISTRIBUTION system for the entire facility, then you need to understand the EFFECTS of power factor on that system. Lastly when you get the BILL from the power company, the importance of power factor will be most evident.

The utility must supply kVA to make sure everyone gets enough. But users are billed for kWh, and the difference between kVA and kW is power factor (W = V X A x PF). So the lower your PF is, the less KWh you pay for. But the UTILITY still has to deliver you the full kVA, so if your PF is low, they penalize you with a multiplier on your power bill. You can correct PF at the loads by adding PFC capacitors. But also understand that VFDs also correct the PF as seen by the distribution system, so PF of the motor becomes irrelevant if it is being run by a VFD.