pete

I have seen a few rotors where the rotor core was loose on the shaft creating vibrations. Reshafting with proper core-to-shaft fit stopped the vibrations completely.

Muthu
www.edison.co.in

Probably best to have the question be the first sentence of the post. Sadly, I don't know of anyone.

Dave - In my defense I did have the question in the title and in caps below.

But based on your suggestion, I added clarification in caps at the very beginning so nobody wastes their time reading through everything if they don't have an expert in mind.

=====================================
(2B)+(2B)' ?

Pete,

This guy is around a lot:

https://motordoc.com/

I have had no personal contact. I just remembered that you may have had some online "discussions" with him in the past!

Another place to search:
https://easa.com/

Walt

> motordoc

oh no you didn't!?! I think you were around maintenanceforums.com when he and I had just a tiny bit of disagreement about torque producing force on conductors in slots (remember?). Suffice it to say, I personally do not value his expertise in motors very much.

But I appreciate the input.

Now that you mentioned EASA, I'm thinking that's a very good place to check. I'm very familiar with them, but for some reason the possibility of contacting them for help on this never occurred to me until you mentioned it. LPS for that.

=====================================
(2B)+(2B)' ?

Pete - A "tiny" bit of disagreement is an understatement.

Maybe try Isidor "Izzy" Kerszenbaum, I know that his expertise is in generators and transformers, but he may be able to help you or direct you to someone else.

http://izzytech.com/blog/staff/
949-230-5986

One of the obstacles in solving certain motor problems is... the knowledge pool of "experts" are getting old, retiring, or dead.
It takes years of experience(s) working on numerous pieces of equipment over a long time to grasp all the potential
possibilities that may/can exist in a problematic apparatus.

To drop some names...
Here in the United States, the grand daddy for mechanical repair for a couple of decades was Charlie Koffler in California.
Is he still around? I have no idea. Another outfit that comes to mind that advertised for years in Electrical Apparatus magazine
is Darby Electric in South Carolina. Their advertising thrust for years was that they knew how to rebuild rotors.
Do they still employ their noted experts or have they retired by now as well? Who knows.

As mentioned, The Electrical Apparatus Service Association is a problem solving source for repair shops IF... (IF) one is a member.
Without full active membership however, it's not possible to access their staff of engineers and library of technical information.
There's a limit to what EASA can provide in certain instances as well because it can become another opinion exchange based on phone calls,
email photo sharing and so on. (Similar to this whole on-line Internet experience.)

Back to the rotor subject, a disheartening observation that remains is the trek of evidence pointing to the OEM regarding the rotor issue.
This does not solve Pete's problem, it somewhat makes it worse because as he mentions... the OEM is not particularly helpful or cooperative.

Pete writes,

"The short story is 4 different rotors among a family of motors have developed increasing (over time) and thermally-sensitive (higher at high temperature) 1x vibration. Each has their own story but in all cases the vibration was resolved by replacing the rotor."

Four rotors? That's a very good sampling rate of a manufacturer's troubled design or a discrepancy in a manufacturing process.

I dread asking this question because it opens up a kind of finger pointing... "but",
are these motors of Toshiba heritage by chance? (Acknowledging, you don't have to answer the curiosity... I understand this.)

Why pick on Toshiba and not GE, Reliance, Siemens, Baldor and a host of other long time dwellers?
Well, experience(s) with their products, that's all.

Pete's quote above also aligns with my original hunch in the 2019 discussion thread that the manufactured rotors were suspect from the beginning.

I've come to understand manufacturers are proud of their products... and for the most part... items made for industry are top notch.

In this circumstance... Never mind using one finger. I'll point my entire hand at the maker of the rotors.

John

Post Script to last post:

Another name Drop.

Tom Bishop gave a Squirrel Cage Rotor Testing presentation at the 2003 EASA convention.

In the very first sentence of his presentation he states,
"Determining whether or not a squirrel cage rotor is defective is an issue that is a challenge to every service center as there is often no simple
way to determine the integrity of a rotor."

His 26 page presentation covers nearly every single test one can perform on a rotor.
Visual Inspection
Tap Test
Dye Penetrant Test
Temperature Indicating Paints
Ultrasonic Testing
Electrical Tests (such as a Growler Test)
High Current Excitation

And a host of other tests that can be performed with the motor assembled.

The above are mentioned because if after exploring every kind of test, and the results reveal nothing to act on...
one has to think in terms of the product itself being suspect.

(And don't let anyone tell you it was the rain on the insulators that day ; )

John

Hi Pete

It is getting increasingly difficult to find the real Gurus these days. Most seem to have retired or passed on, so sorry, I do not have a name for you, but an observation.
I have been seeing increasing rotor problems that are associated with harmonic voltages applied by the network. These can cause increased bar heating - expansion and in some cases, transient vibrations during start.
Cracked welds seem to be on the up, possibly because of reduced tolerances, but often due to supply quality issues.

Mark Empson
Advanced Motor Control Ltd

A couple of the best motor people I have run across were twin brothers, Wally and Don Brithinee, who owned Brithinee Electric, a huge motor shop in Colton CA (SoCal) that did a lot of large motors from all over the west because they were one of the few who had the equipment and expertise to handle them. Their company is now owned by Sulzer (2018) and I heard that Don and Walley retired, but I didn't see any obits for them...

Wally has a LinkedIn page where he lists himself as a consultant now.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden