TEFC Motors 4

[ARAMCAWEE]

Greetings,

In our plants there are a lot of TEFC motors. Whenever one of those motors get shorted, we used to send over to a local shop for re-windings. The re-windings are OK but I was thinking would the motor be as it was before the re-windings as TFEC??? Is there any test or procedures to check that?? How can we ensure the enclosure level of the motor after any windings repairing process??

 

[motorsdirect]

Hi
TEFV is not a level of enclosure..It is actually an abbreviation fo 'totally enclosed fan cooled' and the enclosure rating is the IP number...usually IP56 or better on a totally enclosed motor..
We also rewind motors, and if a motor comes to us with a high enclosure rating, we make sure the parts are resealed on reassembly!
hope this helps
jeff

http://www.motors-direct.co.uk

 

[ARAMCAWEE]

Hi Motorsdirect,

Thanks for your inputs. What I meant is that, in case you have to re-winde a Totally Enclosed Fan Cooled motor, then after the repair, how could you make sure that the motor is still TEFC???

 

[motorsdirect]

All that totally enclosed fan cooled means, is that the motor is not ventilated or have openings in the casings, and is cooled by a shaft driven fan at one end of the motor, so, yes all rewound motors will still be TEFC.

Jeff

http://www.motors-direct.co.uk

 

[weh3]

TEFC means that none of the windings are exposed to the environment. It is the manner of construction and not a manner of winding.

I don't know what your application is, but these motors are used in hazardous locations to make sure that an open-circuited winding does not produce an arc that can ignite the atmosphere. It also means that the winding thermal cutout is completely potted for the same reason. You have to make sure that the Class, Division, Group, and Surface Temperature rating are compatible with the environment.

They are also useful in environments where dust or liquid is likely to get on equipment.

William

 

[ARAMCAWEE]

Thank you all,

The reason I asked the question is that I'm working in an Oil Refinery and all of our motors are TEFC. Yet, we've noticed that during heavey rain water passed into the motor. This is was happened mostly to the motors that have re-winded motors or motors that their casings were opened for any reasons. So, if the motor was opened for -let say- rewindings, would that effect effect the TEFC feature?? if

 

[stardelta]

You need to ensure your rewind company is re building the motor after the rewind to the same specification as the makers to ensure the IP integrety. Items often missed are terminal box/lid gaskets and lip seals,gamma seals or v ring seals on both DE and NDE shafts. Hylomar or a similar sealant on the endplate spiggots can also help prevent water ingress, ask your rewind co if they are doing this. Some motors employ removable plastic drain plugs at the lowest point to drain condensation, check they are fitted and have not melted during the rewind process. I would suggest you conduct a detailed inspection of any returned motor and if your not happy throw it back at the rewind co but first ensure its not condensation in the motor or the water is entering through the cable gland.

 

[bigbillnky]

ARAMCAWEE
My experience has been that usually the problem is in the motor connection enclosure and/or the manner the feeder is brought into it. I have worked in refineries, so I know the battle you are fighting. The absolute best rewound motor is worthless if the conduit and enclosure are not sealed properly. If you are in a refinery, you will have 2 different types of connection enclosures for a hazardous location( maybe 3, but I have never seen a labrynth path enclosure installed on a motor). One is a machined flat surface, and the other is a threaded cover. Both prevent heated gases and vapors from an internal explosion from escaping while hot enough to ignite the hazardous enviroment. This is where the problem starts. The most important aspect of the design is to prevent igniting the atmosphere, not preventing water from entering. If any type of sealant is used, it could possibly cause an explosion by creating a seal for moisture and not for the heat and pressure of the escaping gases and vapors. Make sure the manufacturers recommendations for installing the enclosure and assembling the cover are followed. Also check to make sure the XP flex and seal off are installed in the best possible manner to prevent rain from entering the enclosure. It is always best practice to enter below rather than above. Also, most enclosed motor designs have a drain plug installed at the bottom. Most manufacturers recommend as part of the PM's to drain trapped moisture from the housing. MAKE SURE you follow the manufacturers instructions concerning draining each particular motor and make sure to remove the plug only when the motor is locked out and verified. As a last ditch effort, I have seen covers built to shield the motor. If the motors are located under pipe racks, catwalks, or other stuctures, check and make sure they are not exposed to considerable runoff. Best of luck

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[weh3]

True, big bill, I wonder whether a rewind shop is ever tempted to "improve the design" and put a gasket on the machined mating surfaces--this would negate the explosionproof label.

William

 

[itsmoked]

bigbill: Nicely put.

 

[aolalde]

ARAMCAWEE:

I assume now that you are meaning Explosion Proof Motors. Not all TEFC motors are XP.

In USA the repair shop must be certified for UL (Underwriters Laboratories). Specific repair process are issued and tests are monitored by UL (inspectors verify compliance).A UL Listed label is issued with each repaired motor, to certify the XP Class, Group and Division.

 

[macmckim]

You mentioned in earlier comment that all your motors in the refinery are TEFC. Then in your latest comment, you mention not all TEFC motors are XP.

For majority of Nema T-frame explosion proof motors (frame 1802T and larger) are "fan cooled motors" Depending on the brand of motors used in your refinery, some motor manufacture's TEFC and Explosion Proof motors look very similar (similar castings). Of course the motor's nameplate will indicate if its an explosion proof motor, but also by the number of endbell bolts and the shaft end slinger (XP have brass slingers vs varioius rubber types for TEFC)

XP motors will not have a gasket between the conduit box and motor frame. TEFC motor will have gasket. XP motors motor leads coming out of frame are typical sealed with Chico (grouting material) and TEFC do not.
XP motors have a special breather/drains to keep any explosion internal to the motor, but still allow condensation to drain out of the motor, while TEFC motors goes from a plain hole, plastic plugs and small T-drains.

 

[ARAMCAWEE]

Thank you all for your valuble inputs.