Refurbishment/replacement schedule for dockside electric motors

[mt88]

Hello,

I am currently conducting research on service life for some electric motors my company uses. The goal of the research is to develope a 40 yr schedule of what needs to be done to keep this equipment running. My question now is how long can electric motors be expectied to run without any intervention? What is a good ball park value? I would appreciate any first hand experience as to how long it took for motors to fail and how they failed, as well as any references.

Here are the operating conditions:

-motors run at high rpm and low load
-the equipment is used dock side and then stored in a shed, so they are sheltered from rain but not temperature or humidity fluctuations
-over the entire scheduled life (55yr) of the equipment, it will be used for approximately 4000 yr.
-the equipment is use about once a month.

Thanks

 

[mt88]

Correction:

-over the entire scheduled life (55yr) of the equipment, it will be used for approximately 4000 HOURS.

 

[jbartos]

Suggestion: Visit

http://www.efficiencymaine.com/smallbusiness/pdfs/LifeCycleCosting.pdf

http://www.powderbulk.com/ag_19991201.110223.htm

http://www.mech.uwa.edu.au/DANotes/motors/unsteady/unsteady.html

http://www.manufacturingtalk.com/indexes/browsestories.html

http://www.reliance.com/prodserv/motgen/c7090/

etc. for more info

 

[busbar]

You might try an advanced search of this site on "motor reliability" for reference material.

Large-motor reliability is also discussed in IEEE Std 493-1997 Appendix H.

 

[jbartos]

Suggestion: Please notice that nuclear power plants have 40 years plus 1 year for decommissioning, total 41 years, life-expectancy placed on many electrical items including motors. If not in the nuclear power generation business, it may be a good idea to check their resources on this topic.

 

[electricpete]

It is a tough question. Similar topic has been discussed several times before.

Here is one thread (there are more):
thread237-56166 factors to think about:


Possible areas of degradation:
- greased bearings - If sealed they have a finite lube life. Even if relub'd after awhile the grease may accumulate and harden.

- bearing sealing method - adequate for outdoor application.

- Open ventilated motor? If yes then debris dirt is sucked into the motor when running. Filters can help but not perfect.

- Winding type. If not a sealed winding, I think you will get improved reliability in an outdoor application using sealed winding system.

- I'm guessing thermal aging of insulation will not be a factor because of low accumulated run time and "low load".

- Do the motors have space heaters energized when not running. If not moisture can invade the winding and also corrode bearings and other metal parts.

How many motors do you have? How many years experience.
What is the cost of a failure of motor in-service?

If you have many (20+?) motors with many (10+?) years of experience and no failures yet, you have some idea the motor is standing up well. Maybe if the cost of failure is maybe 10% of cost of replacing motor, I would say you might consider doing nothing other than routine maintenance.

At some point when you take a motor out, that may be a good opportunity to dissect it and try to judge how the various components are standing up. Maybe take 10% out and inspect them and refurbish and possibly rewind.

Large motor manufacturers typically recommend a fairly aggressive interval for motor maintenance 5-10 years. Even the most critical motors in nuc plants are generally refurbished only at intervals 10-20 years.

Not knowing any details yet I say 20 years is a good number for critical motors with reasonably preventive maintenance and monitoring. There simply is no standard so one persons opinion means as much as the next.

 

[jbartos]

Suggestion: A commanding factor is the content of "Scheduled Maintenance." Even a mere periodic visual inspection of the motor is better than nothing to achieve a high motor life-cycle.