MV Motor maintenance 1

[vennivivi]

Hi,

We have on site one 4,0 MW 11 k V wound motor which has been operating well since installation two years ago.The insurance company is now pushing us to overhaul the motor for bearing and winding inspections.We have contacted the motor manufacturer and they said that this decison should be taken by the client!!
We are planning to effect a non-destructive analysis of the winding of the motor by a third company. The test will evaluate the insulation condition for winding contamination. This test will also determine early winding defects ( for a new installed motor ). In addition, we are also planning to contract a third party to effect an analysis of the bearings on the motor notwithstanding the fact that we have on-line vibration measurements on both drive and non-drive ends.
I am afraid the insurance company would still stick to the stupid idea of overhauling. I am looking for IEC or NEMA maintenance recommendations for a motor of this size. Thanks for any input.

Grundig

 

[edison123]

The motor manufacturer was right. Overhaul schedule is entirely up to the client. Reasons for overhaul

1. Contaminated environment inside the motor.
2. Abnormal winding and bearing temps.
3. Abnormal noise
4. Abnormal vibration
5. Low IR values (Trending)
6. Abnormal currents

As a motor repair man, I am not aware of any standards about scheduling of motor overhauls.

And insurance company is definitely not the reason to do it especially if the motor has been running well. There is always a possibility that you screw up during the "overhaul" and spoil a well-running motor.

My 0.02 $

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[electricpete]

The most aggressive interval for large motor refurbishment recommended by EPRI is every 10 years. Less often if motor has mild duty and mild environment.

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[vennivivi]

Thanks Edison123.Agree that overhauling could have detrimental consequences instead if improperly done.I am of opinion that insurance people need engineering people instead of accountants to advise them on such particular matters. I hope I would not have to overhaul this motor to please the accountants.

Grundig

 

[vennivivi]

Thanks electricpete for your comments. I perused through EPRI docs and have come across a document about maintenance scheduling for large motors and they quote physical inspection of the stator winding and core every one and a half year. Could we inspect stator winding and core without overhauling it ? I presume by removing the heat exchanger where the stator winding could be inspected but definitely not thoroughly.What about the stator core ?

Grundig

 

[edison123]

Grundig

You can kick the ball back at them by asking them if they can show any standard for their claim and if they are willing to foot the bill for the "overhaul" and any consequential damages.

I too hate the bean counters.

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[electricpete]

I haven't seen the 1.5 year in the EPRI documents. I'll try to find the document number with the 10 years (don't have it handy at the moment).

Here is something else with a discussion of intefval (seems very agressive to me).

IEEE Guide for Induction Machinery Maintenance Testing and Failure Analysis (IEEE 1415-2006)
The original equipment manufacturer’s (OEM) instruction book is a good source of information and precautions on
required maintenance, inspections, and testing. If an instruction book is not available, contact the local OEM sales
person. Typically critical machines are opened (may include rotor removal) for inspection, cleaning, and general
maintenance every three to seven years. More or less frequent inspections are needed as dictated by contamination
and fouling, load cycle, or operating temperatures. For example, boiler feed pump machines may require a seven
year cycle while most large fans (induced draft, forced draft, gas recirculation) may demand a five year cycle or
less. Not all machines need time-based maintenance, but the service life of all machines will be increased if prudent
repair and testing programs are followed. Annual inspection and cleaning may be required where abrasive
contamination or coal dust buildup is significant, as with pulverizers and coal handling equipment. Annex B
contains several checklists to consider for providing inspection support.

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[electricpete]

Here is one EPRI reference mentioning 10 year interval or less frequent:

EPRI 1003095 - Electric Motor Tiered Maintenance Program

In addition, it is suggested that some motors be disassembled and tested at 10-year to 15-year intervals. The disassembly recommendations should be adjusted by either motor run-time and/or materiel condition assessment of the motor, which should be part of an inspection and routine testing.

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[electricpete]

One more thing. I work at a large 2-unit nuke plant. Our motor program is subject to the requirements of Nuclear Electric Insurance Limited.

Our most agressive interval for motor refurbishment is 10 years. We have some motors 15 years, some 20 years, and many not at all.

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[Laplacian]

What is this motor used for, and what are the consequences for its failure? The answer will help drive what type of maintenance to do.

Also, is this a batch process or continuous operation?

You can install a partial discharge monitoring system at this voltage to get a decent indicator of insualtion health online. This, coupled with your vibration monitoring system and temperature monitoring would tell almost everything you need to determine what maintenance is required and when.

 

[edison123]

pete

What are the works you would cover under refurbishment ?

Would motor refurbishment also include rewind ?


* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[electricpete]

edison - For us, refurbishment does not include rewind. It is something like: disassemble, inspect, check bearing clearances, steam clean and bake stator, balance rotor, reassemble, test.

Grundig - If this is a horizontal motor, you can usually do half of this scope in-place with only 10% of the effort: pull the end-covers, inspect end-windings, clean them with dry ice, support rotor, roll out bearings for inspection, reassemble, test. If you get to negotiating with your insurance carrier, this may be something they would accept instead.

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[edison123]

Thanks Pete. That's my idea of refurbishment too.

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *