Motor Storage - space heaters? 7

[electricpete]

For spare large motors which are in long-term storage (20+ years) in an air-conditioned warehouse (except when ac periodically goes down), should the space heaters be energized?

We do periodic maintenance on the spares which includes insulation resistance tests (no problems seen) and motor rotation. Even with no insulation problems seen I wonder whether rust might form over long time due to the semi-confined air within motor and less-than perfect air conditioning system which still allows some daily temperature swings.

I'm thinking in particular of an 800hp 4kv vertical induction motor with oil bath bearings (almost full with oil).

 

[BJC]

I think your going to want to do more that just turn on the heaters for 20 years of storage.
First that long a period would justify a monitoring and alarm system to assure the heaters were always on. When a motor is heated and the heat is removed the insulation absorbes moisture. Over 20 years your going to loose powere a few times and the on - off cycle will not help the insulation.
I would look at a inert gas purge over the windings and bearings. They can be sealed to keep leakage to an acceptable rate.
Viberaton of the storage area can brindle or deformed bearings. We had some motors on a construction site that had to have the bearing changed because they were in a warehouse next to an area that was being compacted. A large viberating compactor over a couple weeks hammered the bearings flat. Twenty years stored near a train track might not be good. If you have oil reservious sample and have the oil analyzed periodically.
General Electric had some proceedures for storing motors over long term. These were to cover storage at nuke sites where construction was long and/or delayed. There was one for Core Spray and RHR pumps that were vertical pumps like yours. You may be abel to get a copy at a BWR plant. There are also people out at the Hanford Washington site that have nuke parts for sale. I'm sure they are storing them to some manufactures specification. Look in the surplus equipment ads in Power or Electrical World.
I remember GE had a proceedure for long term storage of some motors that involved disassembly and cocooning. GE also coated unpainted parts with "Tectol", a blact substance similar to cosmoline except tha it dried hard.
Lastly the motors may make it 20 years but statistically you probably won't. Write a good proceedure with references etc for the next guy.

 

[THooper]

Greetings electricpete!

We have developed a storage program at our facility with information from several mfg recommendations. I will research this info, In the mean time the storage facility must provide protection from contact with rain, hail, snow, blowing sand and dirt, accumulation of ground water, corrosive fumes and infestation by vermin or insects. Outdoor storage is not recommended for any motor components, including complete spare motors. Environmental conditions can affect idle parts or machines, variations in temperature and humidity can cause condensation throughout the parts or machine, producing rust and corrosion in metal parts as well as deterioration of electrical insulation. Avoid storage in an atmosphere containing corrosive gases, particularly chlorine, sulfur dioxide, and nitrous oxides. There should be fire detection and a fire fighting plan in all storage areas. Allow adequate space around stored motors for test and inspection. Avoid storage of motors in areas with intermittent or continuous floor vibration from moving equipment. Ensure that all machined surfaces such as shaft extensions, mounting feet, c-faces or mounting face, have rust preventative in place. Coat all exposed machined parts with solid film corrosion inhibitor (Rust-Ban 326 or equivalent) Motors in storage, equipped with brushes, should have the brushes lifted in the brush holder so they are not in contact with the collector rings or comm. Otherwise, ensure that there is a strip of protective strip such as mylar between the brushes and rings. Ensure that there is a moisture barrier between the machined feet or if on a skid. Ensure that temperature is controlled and that motor components or motor temperatures are above ambient temperature by at least five degrees F or three degrees C. (at temperature equal or below room temperature and relative humidity above 60%, water vapor can condense and promote rapid deterioration). Always keep component or motor temperature above the freezing point. To prevent condensation, energize the space heaters of large motors in storage. During periods of extreme cold or rapid temperature drops the space heaters may not adequate to maintain the temp differential and supplementary space heating may be required. It is a good practice to seal any shaft openings with silicone, rubber caulking, or tape. During storage of large motors, fill the bearing housing with oil containing 5% rust preventive concentrate. Ensure to drain the concentrate and refill with applicable lubricant prio to operation. (Note that the normal oxidation and rust inhibitors in oil are usually sufficient to protect the internal parts for 30 days without operation). Rotate the motor shafts monthly 1 and 1/4 turn. Mark the front of the shaft with a metal marker for reference. While the shaft is rotated it should be pushed to both extremes of endplay to allow for oil flow, over entire length og journal. Ensure that during transportation of motors that the shaft/rotor is prevented from moving by applying a shaft lock bar. We install this loc-bar on all motors in storage and loosen monthly when performing rotation.

The above information is our storage program taken from years of storing motors and input from various mfg. I hope this helps. Good input BJC!

Kind Regards,
motorhead1

 

[kjb]

Excellent tips motorhead1 and BJC!
When storing large motors for prolonged periods of time, it is a good idea to diassamble the motor. Also, your storage programme should include scheduled peroidical (annual or biannual?)visual and insulation checks. Visual checks shall be done to see any signs of rusting and excessive dust accumulation. Insulation resistance should be measured and recorded for comparison with later readings. Progressively lower values of insulation resistance will indicate ingress of moisture. Corrective action should be taken to avoid further lowering of the insulation resistance.
The programme should also include procedure for reassembly of the motor for operation. This includes heating of the motor stator and rotor in the oven to dispel any moisture thus improving the insulation resistance. Temperature and duration of heating should be established in consultation with the manufacturer.

Regards
KJB

 

[THooper]

I found some more storage information for reference:

General Electric has some basic storage instructions in the custom 8000 Horizontal Induction Motors manual.
REF: GEH-3170B Page (4).

WEG Installation and Maintenance manual for Electric Motors,
REF: Catalog 651.15/0393 PE Page (1). 2.3-storage.

Reliance has started a storage program, but I have not seen all of the details.

KJB, Thanks, I did fail to mention in the 08-22. post that a Polarization Index needs to be perform on storage motors with the results recorded. Knowing the P/I of the motor or generators can be useful in appraising the fitness of the motor for service. The index is calculated from measurements of the winding insulation resistance.

The recommended minimum value of P/I for an ac and dc motor or generators is 2.0 Motors having windings with lower index are less likely to be suited for operation.

The procedure for determining the polarization index is covered in detail by IEEE standard No.43

Kind Regards,
motorhead1

 

[jbartos]

Suggestion: Normally, any long term storage may require to store equipment within certain temperature range, dust particle range, and humidity range. The humidity control may require heaters during air-conditioning. Namely, the heaters elevate the temperature (superheat) of the moist air, which is drying, and then the dry air is air-conditioned to avoid humidity and condensation at specified temperature. Typical places that use this process are: Libraries, archives, train cars (e.g. Amtrak), some buses, etc.