Hello Thermal Land!
I have a 300 hp drive motor that appears to be running at a higher temperature than normal. This is the third motor in three years. Myself and another Mtech installed it about a month ago. During installation we did the soft foot check, alignment, etc. It went in well. In the last couple of days babysitting it, I've watched the temperature go up. The gearbox has been doing the same. We have about twelve gearboxes around so a baseline was easy. I'm thinking that the problem is in the gearbox but I'm waiting on data from vibration.Yesterday the air temp was 79f and humidity was at 18%. The motor was pulling a normal 320amps.
All of my other drive motors run around 65c and gearboxes about 108f. This motor is about 100c and the gearbox about 167f.
I shot the motor today and noticed the warmest signature is around the eyebolt at the top of the motor. Same spot as yesterday but warmer. We have another Mtech (doesn't like new technology) that said that the eyebolt is shorting out inside the motor! What? Honestly, I have never heard that before. So I metered it and saw no voltage to ground. I always shoot these at the site of the eyebolt due to being a great cavity radiator.
Does anyone have any information that I could use. Are your eyebolts shorting out?
Cary Weaver IR L III, UE LI, MCA
Is there a possibility that the threaded bolt end of the eye-bolt may have pierced some insulation in the windings?
After analizing the image, I did a voltage check and didn't get a reading. Then I strapped on the PPE and removed the eyebolt. I did another voltage check with the probe inside the cavity, still no reading.
I measured the length of the eyebolt threads versus the cavity depth and found out that the eyebolt is shorter than the cavity.
I'm not sure what size the rebuild shop used when they had the motor. I wish I would of seen a readind on the meter. I did check the meter for correct operation.
Have you seen this issue before?
I can't tell for certain, but this looks like and ODP motor and not a TEFC. Are all of your other similar motors of the same design? I'm also curious as to how the motor is loaded to a "normal 320 amps." I'm assuming the other motors are running similar processes at the same current reading on all phases.
How is the process controlled to these machines? I've seen where a screw press which had it's feed controlled by variable drives, these drives would slow down or speed up to keep the press motor near full amp load as measured on one phase. During an electrical scan I noticed the press was single phasing. The electricans couldn't believe it was running singled phased, but the way the feed was controlled allowed it to continue with a very low feed rate compared to normal.
That the gearbox is running warmer suggests that it might have an issue, is the oil being checked for wear also? I can't see this causing that much of temperature rise on the motor.
Another issue could be if the motor bearing grease has been mixed and is turning to clay. I've seen motor repair reports that have shown this to be the reason a motor was running hot.
These drive motors are used for extrusion. They are all very similar in hp,amp load and design. This one is always running at the 320 amp set point at the drive panel. We set up the drive panel to drop out at 356 amps. This one is on a primary screw. (AC)
We do conduct oil analysis regularly and this gearbox had gotten good grades.This motor is like the rest, they are connected with a Faulk coupling. Grease is another strange issue with this motor and the ones I've replaced in the past. For some reason this coupling cannot handle the Faulk grease that is recomended because it turns to clay. We use a high pressure grease that seems to last between Pm's. Once a month they are taken apart and inspected.
I took a vacation day today because it's my wife's b-day, so any helping hints that I get, I'm callin the boss with.
Thank you for the help.
After reviewing your discussion I would like to make the following observations:
This is the third motor installed in this application in 3 years.
That fact alone should focus your attention in four areas:
1. The circuit powering the motor.
2. The load driven by the motor.
3. The location where the motor is installed
4. Quality of work you are getting from the motor repair shop
Motors should last substantially longer than 1 year, 5-7 years is an industrial norm and that number should be much higher.
The first and easiest thing to check is the circuit powering the motor.
Use of Motor Circuit Analysis (MCA), Electrical Signal Analysis (ESA), and Motor Current Signature Analysis (MCSA) would be best utilized for this testing, however if you do not have this equipment or access to a contractor to provide the service, you can perform the following:
Check current in all three phases, simultaneously, if possible. If you cannot check all three phases at the same time, try to ensure hat you have a steady load and that the load is greater than 70% of full load rating for the motor. The balance of the phase currents should be less than 5%. Using the formula 1.2 x HP yields a full load of around 360 amps. With the unit drawing 320 amps you are within the proper range.
Next check voltage phase to phase and to ground. Your phase to phase voltage should be <3% unbalance and <1% to neutral.
Any unbalance in voltage and or current is indicative of problems in the power circuit. Use IR on all accessible portions of the power circuit, looking for connection problems. If none are found, de-energize the motor and check all connections for proper torque, crimp connections, look for signs of corrosion, burnt or embrittled insulation, broken or frayed conductor strands, discolored terminations. Also check local disconnects, if utilized. They are notorious for developing high resistance connections.
With the circuit de-energized, check the circuit protection devices, breaker trip points, fusing and overload sizing. It is possible that binding in the load may be occurring with possible overloading of the circuit causing thermal damage to the motor windings. Improper circuit protection will allow this to occur without tripping and lead to subsequent failure.
The next thing to check would be the gearbox:
If a new or refurbished gearbox is available, change it out and monitor temperature and current for a change in magnitude.
It may have worn or defective components causing excessive loading or intermittent binding which will cause the motor to run hotter and lead to subsequent failure.
The installation location should be rechecked for Softfoot or any anomalies that would prevent proper alignment. Since you have already checked this it is doubtful that this is the problem, however, it doesn’t hurt to be sure. After checking the above, perform vibration analysis on the complete drive train, at load, compare all acquired data to comparable equipment at comparable load.
Lastly, check the motor history:
Is it a used motor?
If rewound, how many times? Multiple rewinds may have caused serious damage to the core, resulting in excessive heating and premature failure.
Motor acceptance testing should be done when the motor is returned to you after rewind, this data will give you some idea of the quality of the rewind.
We are still waiting on vibration to get his information together. The load is around the 70%. I did a phase to phase and found a floating ground! This issue is going to be taken care of at the end of the month. I have to schedule it in.
Now I have to pray it lasts till then. That is the part of the job I do'nt like!
I can't help but to keep digging until I find out what the issue is.
I think next is to get scheduled in a good MCA class. I bet you know where!
Anyway, Thanks everyone and I'll post what I find.
Hello Thermal Land!!
Finally getting hot around here! I just wanted to post an update on my 300hp problem child. I am happy to report that I have tracked down the issue and put that kid to bed. I was doing a route on our switchgear and found this door concerning me. This bucket controls the drive panel to my problem child. I had the plant leader and other chief's over my shoulder (at a distance) and carefully opened the door. BLAMMO!!
I'm glad to see the bosses with their new found respect for switchgear! At a closer inspection, the root cause was the two bolts that connect the bussbar to the bucket were installed improperly. The two contact surfaces were not exact and the installer pulled the threads which made a loose connection. We know what happens with something when it appears to have a loose connection!
Thanks for all the replies. It helped putting fire under the boss to give me time to get this solved.
Cary do you have the IR Pics from the bucket when you opened it up so we can see. Did you see the problem from indirect heat or could you get a look at the exact problem. Here is a pic of a problem where I caught it from indirect heat. Thanks for the good work.
Good to hear you found the problem. When I first read your post I mistook your "Blammo"-- I was thinking Kaboom! Glad that was not the case, I too would like to see the image from inside if you have one as Jeremy said.
Well, it was a Blammo! When I saw the signature on the front of the door, It instantly hightened my awareness and caution. As I carefully started to open the door, that's when it happened. You could hear the arching and the snapping. Quickly and carefully, I closed the door like it had a bomb tied to it! Then turned to the plant leader and told him to shut it down!
I hope the digital is clear enough to see the two screws. There is clearly some stuff happening around them.
Again, Thanx for the tips!
See ya in June
Yes sir. Off of a 2500K transformer and an isolation transformer.
Gonna be lookin at the isolation transformer next. Looking at vibration analysis on the motor since the new switch was installed, the imbalance is alot better, but still some there. The motor is running so much better. Did an analysis on the motor and got lucky. No damage done. Is that preventive maintenance or what! We also didn't get dinged for the shut down due to it being a controlled one.
That alone saved over 35K!