Motors sitting for 4 years.

[Riggspsk]

I'm currently working at a site that was inactive for the last 4 years. In their great wisdom, the last contractor to leave site left all the electric motors out in a shed out back.

The site owner wants to test the motors intergrity before coupling. His question to me was, "Is there any rule of thumb on this?" and goes on to explain that he wants to know if there are any HP ranges that should be tested and for how long. Such as 50-100 hp motors need to be tested for 2 hours.

Motors are all 3-phase, some are 480, some are 4160V.

Does anyone have any expereince with this, so at least I can go in the right direction?
The warrentys on these motors have long since expired and they want to do all the work on site. We have motors from 1-300 HP, the site is a power plant.

Thanks in advance to anyone who can help out!!!

 

[Skogsgurra]

I would start drying them out with a reduced voltage - or DC - for several days.

Then megger them or do Baker test.

The bearings may have false brinelling, but probably not in this size range. Grease doesn't age much at low temperature. And four years is not such a long time after all. Turn the rotor by hand and see if all seems to be OK, smooth turning, no binding.

Start them on reduced voltage (so you do not have to screw them down) and listen for noise from the bearings. A vibration analyzer may be used but does often produce too high values if motors are run standing on the floor.

Cleaning and visual inspection is of course also something that shouldn't be forgotten.

Gunnar Englund

http://www.gke.org

 

[electricpete]

I agree with skogsgurra’s good advice as usual.

One thing I would clarify is that any surge testing (Baker test equipment) should not be done until the megger and PI indicate drying is complete. Surge test on damp winding can damage the winding (similar to hi-pot testing in that respect).


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[electricpete]

There may be some additional issues with bearings from long storage without any maintenance. I don't think practices are well-established in this area and it varies depending on user preference.

If grease lubricated bearing, you might consider disassembling the motor to repack the grease (unfortunately usually dictates replacing bearings as well).

If oil-lubricated bearings, you might sample, flush, sample at some point (of course motor has to be drained for movement), and preferably inspect bearings if easily accessible.

Depending on the plant situation, in some cases a shop unloaded run would be a good idea prior to installing in the plant. In other cases when there is anticipated enough time to address any problems after plant uncoupled run, it would be a waste of time to perform shop uncoupled run.

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[Zogzog]

Hire a testing firm that specilizes in this type of testing. You can find one near you at

http://www.netaworld.org

 

[waross]

I agree with Skogsgurra.
Dry and megger, or megger, dry, and megger.
Don't forget to check for nests of small animals before starting.
respectfully

 

[machmech]

Our better good quality motors come with excellent maintenance manuals and covers details of everything mentioned above, here is a link for one, there are many more available w/Google.

http://www.reliance.com/prodserv/motgen/h7000.htm

Chuck

 

[moira]

Hi,Riggspkk: 4 years is NOT that long a period of time for well made and previously maintained motors. Your biggest problem may be with the bearings of the larger size motors. I don't know your budget! Its own weight has tended to impose "flat" spots on the big ones. How much; I don't really know! I would suggest suggest trying the motor and bearing manufacturers for starters in this issue. One place I like is ELECTRICAL APPARATUS magazine.

http://www.eamagazine.com

They might even give your questions some consideration in their features. At least, point you to some of their best articles . For a small fee you ,hopefully, will get much info. Make standard MEGGA tests for insuluation resistance and proper continuity. You want approaching infinity resistance and normal continuity inside. With all else to do, you probably will have to warm-up these motors to dissipate any moisture problems that may well show up. If you get at least a 2M reading; I would run them to get rid of the moisture. Open all the "dog houses" and make sure moisture problem isn't in them. Run the motors with their own dead weight and held in place, if needed, with large "c" clamps on their feet. Each will be its own case. Tied down with cables, rope, etc. When motor Meg. dry; make uncoupled running load test: you want no more than aprox. 35% of the motor's FLA! When you Meg. low and pass the running load test; you are good to go! You will need a 5000 volt MEGGA for the higher voltage motors. Many operations keep their spare motor supply in wharehouse supply for longer than 4 years. Many are nothing but "Butler" types (corrogated steel, can't knock them); with the ony heating to preven fire line freeze! Check out the big bearing issue with the experts. My opinion is that you are OK, Right Now!! But check with others!!! Dry out; IF NEEDED and UNCOUPLED LOAD test ( bearing worth) should be your normal proving test. Rule of thumb, if choosed to be called!!! Never have heard of any time cycle testing! Electricity costs alot of $$$$$. Just get (make sure) them DRY and that they are LOADABLE. Hope this is help, MOIRA

 

[aolalde]

Hi Riggspsk

I disagree with most of the opinions above. Four years inactive is a lot of time for electric motors. One of the main problems is moisture condensation which will produce deep contamination into the insulation and will develop bearings corrosion.
Make a detailed disassembled test and inspection to define the required recondition for each motor. At least bearings must be changed and winding reconditioned.
The other option is; expensive random premature failures out of control.

 

[moira]

Riggspsk: I'm in aggreament with SKOGSGURRA and WAROSS base testing (insulation test and bearing conditions must be done) before any extensive and expensive break downs become necessary. If you don't want to or can't run motors; then banks of heat lamps and small blowers/fans can be set up to dry motors. You will have to disasemble the bell housing ends, pulling out the armature and exposing the windings to the drying heat. Remember many times by just exposing the "dog house" wiring to normal room air and the use of electrical grade cleaners/moisture displacers ( a good one is CRC's 2-26) you will most probably see an increse in resistance. Always use a MEGGA when measuring insulation resistance. Just a reminder: make sure your MEGGA is set on MEG OHMS scale. 2-26 can be used in the bell housing break down method. DON"T USE 2-26 AND HEAT LAMPS TOGETHER, IT IS FLAMMABLE!!!!! Make sure that any excess cleaner is wiped off before heaters are used! Should have no problems with normal warm air warfing thru the stators. Again, you hopefully won't have to do any of this; if you meg out high enough! If you meg out at about 3/4 of the way upscale, I would hook up and run even in place and make futher look at it. These are my first steps from what I know. Do what you can yourself inhouse with the insulation testing and if necessary different forms of drying. I think you will have good luck, right off the bat! With the number of motors involved, you don't want to send too much out of house. The 20th century induction motor is a pretty tough animal. Its developement has come a long way. It is made to take a lot of not the best conditions. Motors are in storage all over the world, in many different climates and protected differently. I've taken many different motors out of storage places; many over 4 years in storage. Some I certainly didn't like the way they looked; but they worked! Again, only my educated 40 years in the trade opinion, four years of storage; even not the best, has'nt so badly affected your motors. Four years in high school; went all too FAST! MOIRA

 

[panelman]

I had a site problem recently…motor resistance was down to 250k due to moisture. I wired a fan heater in series with the windings and plugged it into the mains. Use the fan heater controls to adjust the current to about 4 amps and eight hours later the resistance was back where it should be (>999 meg). Add some new grease to the bearings and you are good to go

 

[oftenlost]

I would think that a simple megger and PI, if successful, followed by an unloaded test run to determine bearing condition should suffice. Many of my customers have spare motors sitting for this amount of time and have few problems. The problem, as I see it, after these preliminary checks, do you know what type of lubricant is in the machines now. The most popular grease bases, lithium and urea do not play well together.

 

[powerjunx]

Hi Riggspsk,

Just as above, it is better to make it sequential.

I've been in field services, and i did this manner:

1. Visual Inspection
2. Insulation resistance test
3. P.I Test
4. Surge Comp. Test
5. Check Bearing
6. Check Grease/Lube oil
7. No load test
While running at no - load add small amount of grease like
Calcium 12-hydroxy Grease where evidently have almost comptible to all grease type except Polyurea.
8. Load test
9. Condition monitoring
9.1. Temp. stabilize at least 1 hour
9.2. Vibration
9.3. Load currents

Any failure of subsequent test or inspection is subject to rectification or repair at your own discretion with an aid of published standard procedure. Else, suggestions posted as above would greatly help you out.