We are re-starting this topic.

The purpose of this string in this forum is based upon a discussion outside of this forum with Terry O'Hanlon. We are going to try to perform an interactive discussion on electric motor design.

The purpose is to discuss motor design (a learning portion of the string) with interactive questions and comments. We are looking for constructive comments on the topic (agree or disagree with concepts and statements is fine).

Sincerely,
Howard

This message has been edited. Last edited by: MotorDoc,

Howard,

It's very generous of you to share your knowledge with us. I'm listening and taking notes.

Probably not the foremost of your accomplishments was the time you spent at Dunkum's Electric. While you were there, I was in the Engineering Dept. at Transmission Products which was a friendly competitor in motor sales.

Small world indeed.

Thanks again,

Dear Howard ( Motor Doc )

Wow, that is some extensive road map, my friend. I've read all 8 pages of your C.V.
Your knowledge will surely complement the content of this site and, for sure, shed a lot of light on Induction Motor problems and solutions thereoff.

Nice of you to devote some of your precious time on this forum.

Thanks for sharing,

MarkoLeo

Doc,
One of tests we perform on overhauled motors is the stator core loss test.
The overhaulers use the acceptance criteria of less than 6 watts/lb. I recently attended a motor course where they recommended less than 4 watts /lb.
What is the accpetance criteria do you use and what is the source of the information?
Regards,
James

Doc,
I understand that the 6watts /lb is not an absolute limit but allows some sort of criteria to be applied.
One paper that I read suggested that it was more reasonable to consider infomation on a population of motors when considering core loss as the quality of the steel in the laminations will affect the core loss value.
Recently, one of our 1200HP verticals undergoing a core loss test indicated a core loss of 7 watts/lb and no indication of hot spots, that is no area greater than 20C over the general stator during test. I accepted it as the previous operating history did not indicate operating excessively hot.
Thanks for this post as I am one of the " mechanicals" who appreciate the opportunity to gain more knowledge on the motors that comprise most of our drivers.
I will ask more questions as you keep the post alive.
Regards,
James

Just for info EPRI Medium voltage motor repair spec 1000897 lists a limit of 4 watts per pound. But I agree it is not practical to establish a general absolute limit on this parameter. There are differences in design of motors and differences in the flux pattern during operation as compared to the flux pattern during the test.

At least these things are repeatable so we should expect repeatable tests - as Doc says no change. The EPRI spec allows no more than 5% increase in core loss from before winding removal to after winding removal. The high temperatures used for baking out the winding, if not controlled properly, can damage the core and increase the core loss.

We have exceeded the 4 pounds limit on the as-found test and accepted it using similar reason as yours (satisfactory winding temperatures under load, no hot spots). Our limit for hotspots is 10C rise, not 20C.

This message has been edited. Last edited by: electricpete,

One must be commended for getting a Ph.D. in 3 years after the BS and 2 years after the masters. This takes much work even going full time, but to accomplish this while holding serious positions like director of field service, vice president, Senior Research Engineer, and General Manager is laudable.

My background has not always been in engineering, so I am not very familiar with General Engineering or with Kennedy-Western University. After looking up Kennedy-Western University on the internet I see how it is physically possible to get the degrees, but still this must entail much late night effort to obtain these lofty accomplishments. Not to mention the practical experience!

Howard,

This is very impressive. Could you please share what the title/research field of your PhD dissertation?
Thanks.

Doc,
Thanks for sharing your motor knowledge! How old is the end bell bearing seal design that isolates lubrication from the windings? Allot is being said about lubrication procedures and issues of the grease, over a time, getting into the windings.

I trust that you have contacted the authorities. This sounds serious. How could they get your number?

Howard
The way it looks form here if you (Father of
electric motors) and Sam (Father of Vibration
Analsis) were to merge the rest of us would be
out of work.

You may also want to persue a MD as well. Sooner or later you wil need Medical attention on your shoulders from frequent patting of your on back.

For me most of your post are more about trying to impress us than help.

Barry, I am new to the forum but have read through a number of the threads which the MotorDoc has contributed to and I am sure most will agree to have invaluable experience, knowledge paticipating is to the benifit of all! If you dont value such expertise then as the Doc says "do not read".

Paul

Hey Doc,
I see that you have edited this thread. Sure appreciate all the information you have and are willing to share. Thanks for the brief insight about motor construction and maintenance. The presentation is very informative. The question I posted earlier was intended to review the way the bearing seal is designed and how grease does penetrate to the windings during greasing, even if just a little. It would seem that motor manufactures could do some improving on the seal design since grease is so important to the bearings but so destructive to the windings. Some are trying to make better purge vents but I think that a better seal is not to far in the future. Seals for the external have been improved over the past 15 years but have not seen much for the inner seal (between bearing cavity and windings). Thanks again for sharing your experiences and knowledge!

Don:

Yes, I have edited out information from this string and one other, that initiated this string. It appears that the answers and information I was providing effected some people enough to call my phone with threats and to post insults. I felt the best way to handle the issue was to eliminate the problem, but I was unable to delete this string.

I am also going to take a break from this forum.

However, yes, you asked a very interesting question and I will take a quick stab at it (I am at a stop on my drive to Chicago for my class next week).

Yes, there have been changes to seals, shields, greases and insulation systems in electric motors. These changes have accelerated from the 1970's on.

The problem with grease seepage and motor design is that the manufacturers (if there are any exceptions I have not found them, yet) recommend, in their manuals, to de-energize the motor for greasing. An operating motor generates several issues including pressure and couette flow. The flow issue involves a physical property where if you have a stationary outer cylinder and a rotating inner cylinder an incompressible fluid such as oil or grease shears and starts to circulate between the cylinders. The result is a pumping action into the winding.

When the motor is greased stationary, then there is less movement of grease into the winding.

As a result, some manufacturers will install grease automatic grease relief plugs. In most other cases, the motor manufacturer will not necessarily design for what they would term, improper greasing.

If you are interested, I will re-post the presentation when I arrive at my hotel tonight.

Grease and oil themselves actually do not, in most cases, react with the motor insulation system. It is normally either the contaminants that are absorbed into the grease, such as moisture, that increases the surface leakage of the windings. This will begin to cause a reaction within the insulation system. Also, if too much grease gets into the winding, other than lubricating the spaces between the rotor and stator, it can generate a thermal blanket which will cause the winding temperature to increase.

The best approach is actually to implement proper greasing procedures and processes in order to avoid over or under-greasing.

Sincerely,
Howard

Howard,
Only re-post if you feel comfortable doing so. Some never learn good manners. The saying is if you don't have something nice to say don't say anything. In other words they do not have to read what is wrote. No one is holding them hostage.

Knowledge is beneficial. If you do not agree with the comments then you don't have to use them. It is good to know someone's background when knowledge is presented so you can decide if the person is talking out their hat or really has dealt with the issues.

I will be in a meeting week after next and would like to use some of the information on greasing motors. Do you know where simular information can be found?

You could have picked a warmer time to travel to Chicago!

Thanks,
Don

Howard - I am glad you are still posting. I have learned a lot from some of your comments and hope to continue doing so.

I'm not sure if this would be the presentation Howard mentioned, but you can see his articles on greasing electric motors Parts 1 and 2 here:
http://www.reliabilityweb.com/fa/motor_testing.htm

Don:

The pdf below is from my IMC presentation last year. It works along with the articles that ElectricPete just linked to.

ElectricPete: Thanks. I think I see where things went out of control and it all primarily relates to simple communication. Your comments did bring a few things to light that I am going to try out with the PdMA instruments that some of my class are bringing along. It may help bring a link between some of the ATPro and PdMA test results that result from the differences in applied frequencies.

Don, to finish the thought. If any of the presentation is useful and you would like the slides, let me know and I will upload them then post a link (the slides are too large to upload here, so I have converted the slides to pdf).

Sincerely,
Howard

Bearing_Greasing.pdf (823 Kb, 27 downloads)

DOc,

I hope you come up with something on the applied frequency. I would like to understand better the differences obtained when using 300 Hz. vs. 1200Hz.

Dave

Barry, have you ever heard the expression "There are more horse's asses than there are horses."?

Dave and ElectricPete (Dave's question):

Yes, and I am going to restart this string on a different footing, including reposting the information on motor design, from where we are now.

There is something that you alluded(sp?) in the other string, Pete, that I am going to explore using the ATPro 4 (auto-selects 100, 200, 400 and 800Hz) and 31 (25, 30, 50, 60, 100, 200, 400 and 800Hz, selectable), and PdMA (300 and 1200Hz). Combining the motor design information and the instrument findings should be interesting.

I am also looking to see (may have to wait until I return home) if I can find a spreadsheet that the motor guru from Vermont Yankee (Pete Longo) developed for low voltage (<600V) motors using the ATPro impedance measurements. He developed a rather lengthy set of formulae to determine the full load current based upon knowing the applied test frequency. Part of the trick, in addition to knowing the applied frequency and resulting phase angles, was also that all of these test technologies operate in the 6-10 Vac range, and the type of output voltage also plays a part.

Having access to my old electronics lab at Dreisilker should provide some additional insight, there.

I will update at the end of the week.

Howard