Hot bearing 3

[IRL]

Hi Guys,

We have installed a 250Kw 4pl motor on a pump application, the motor is running at 47hz and drawing 350 amps, the nameplate details are as follows: 250Kw 4pl 400-690 D/Y 50Hz Class F, B temp rise, IP55, VSD rated with 3 x PTC's. This motor is working in a large machine room with an ambient of 13 deg C at present outside temp at the moment between -5 to + 2. The bearing on the drive end is a cylindrical roller, the NDE is a insulated ball. The roller at the DE is measuring 78 deg at the bearing cap and the NDE bearing is 23 deg C, around the top of the fins behind the terminal box (roughly in the middle) the temp is 67 deg. The motor is cooled by its own fan, the vsd has not gone out on over temperature or over current and it is working away fine but we are concerned by the temp of this NDE bearing, i checked the grease plate and it is not over full, when we stopped it for a few hours the temp dropped and it gradually creeped back up to 78 deg over the coarse of a few hours as the motor warmed up. Any comments would be welcome.

 

[edison123]

Vertical or horizonatl motor ? If horizontal, I would suspect skewed bearing.

 

[electricpete]

If it is a TEFC motor, it is not unusual for the DE bearing cap to be the hottest point since that is the only location that is not cooled by the external fan.

If it really is a higher than normal temeprature as compared to historical or sister units, then some possible causes can include:
overgreasing (housing full)
recent greasing (temperature tends to spike up
other lubrication problems - incompatible or aged lubriants
excess load - from misalignment of direct coupled machine or from excess belt tension of belted machine.
skidding - use of cylindrical roller bearings in direct coupled application.

In addition to question above, if you provide the machine speed, bearing part number, and connection to driven load (belted or coupled), we can provide some more discusion. For example the SKF website lists minimum load for cylindrical roller bearings to prevent skidding at various speed. If you provide the requested info we have enough info to determine whether this is a misapplication of a cylindrical roller bearing.


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[waross]

What electricpete said!!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[IRL]

The Motor is a Dutchi, DM355- 4 250Kw 1488 rpm TEFC, i checked the grease by removing the outer grease plate and sliding in back as the motor is still in place i could only slide it back about 70mm. The grease looks good and it does not look too full, the bearing is a NU319. The motor is directly coupled with a Flender N-Eupex Flexible H style spacer coupling and is aligned properly. I was thinking of putting in some misalingment to see if this would help but it is hard to know if this would be a good idea long term. There is another 2 motors that look to be a different brand they are the same spec and the pump is the same but the motor is badged with the pump makers name and it gives no bearing data it is drawing the same current and the same speed but the bearing cap is 10 deg C cooler. This motor has only been working 4 weeks now, as this part of the plant has just come on line the older ones were supplied around the same time but have been running now for 6 months. They are horizontaly mounted.

 

[electricpete]

Roller bearing in a direct drive application is a red flag... sometimes it's ok but sometimes not. Here it appears not to meet the beairng manfuacturer guidelines or at best marginal if we have underestimated the rotor weight. . It could certainly be that skidding is contributing to your heating. Here are my calculations to show this does not appear to meet minimum load requirements for this beairng.

The attached spreadsheet is a calculation for NU319 bearing showing the minimum load is 2.5kN. I used the per SKF guidelines shown here

http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_4_12

If you look here you will see a motor somewhat similar to yours... weight is 2650 pounds

http://www.baldor.com/products/deta...00&rpm=1400-1800&winding=18WGW287&rating=CONT

If you look here, the rotor weight is typically somewhere around 1/3 of motor weight.

http://books.google.com/books?id=4-...+rotor+weight+motor&ei=pvCIScKVEZWYkwSJ8rmFBg

So let's round up to 2700 pounds motor weight and take 1/3 to estimate your rotor weight as 900 pounds. Half of rotor weight per bearing would be 450 pounds. That is around 2 kN load per bearing. It falls short of the 2.5kN minimum load to prevent skidding specified in the SKF catalogue.


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[electricpete]

Sorry, the file attached last was incorrect. Attached is the correct file for your case to calculate the 2.5 kN minimum load.

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[itsmoked]

Nice analysis Pete!
I learned something here.
Thanks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRL]

Thanks Pete,this gives me something to work on.Thanks again for a detailed reply.