Folks,
I have a customer that has replaced the bearings in a 6000hp 4000 volt 2 pole motor. The vibration levels are all below 0.11 inch/second. After approx. 1 hour of operation, the NDE motor bearing has reached the shut down temp of 179 F. The motor is driving a boiler feed pump and a forced lube system feeds all four bearings, including the thrust bearing in the pump.
The DE bearing operates in the low 160's.
The lube system feeds the pump bearings first, the motor inboard bearing next and the motor outboard bearing last. There is a sight glass for flow below the motor bearings and flow can be seen. My problem is there is no indication of how much flow and I have suggested measuring the flow.
We have opened the sides of the bearings several times, assuming the oil is not getting down into the bottom. We have mic'd the bearing and the journal and all readings are within the ballpark.
Also, there is only one pressure guage on the oil system, NDE motor bearing, so there is no comparison to know if there is a restriction.
Has anyone out there worked on one of these large Elliot 2 poles and had these issues?

Ron,

No direct experience, but I would also be looking at the oil flow, but I might suspect too much.

Either way, it would seem you need some way to know the flow.

Ron,

These beasts typically have a shell-tube lube oil cooler that can get clogged and reduce cooling. The oil flow rate is unaffected. Measure 4-temperatures: water in, water out, oil in, oil out. Also measure water flow rate or delta-P across water connections. Even city water can foul heat exhangers in less than 1 year.

Walt

A few questions? Is it oil ring lubrication? If it is so, there is normally one plug at bearing housing top . Remove it and see flow of oil and movement of ring.Normally there is a flow control valve to maintain flow of lub oil into each bearings. Is it there?There must be a oil HX to cool oil and maintain its temperature. Pl. check cooling water flow. Also in stopped condition , you can check for flow of oil into each bearing by collecting it in a measuring beaker. MI manual must contain information about oil flow rate through each bearing . Normally, it is highest for thrust bearing , then motor bearings, and then pump bearings.

folks,
A few more tidbits. The oil lube system is common for all bearings. The piping parallels off a common header to each bearing. There are no water cooling jackets, the oil is cooled in a common sump.
The only bearing that is running warm is the NDE motor bearing. It is also the last bearing fed by the header.
Another issue that we are investigating is the bearing RTD. It is a thermocouple type and sits in a bore in the bronze bearing, touching the back of the babbit.
We are scheduled back tomorrow and we are formulating a work scope now which includes trouble shooting the RTD's to confirm the temps are real. Also, checking oil flow rates at the two motor bearings.
We have requested historical motor bearing temps, but have not received them as of yet.

I've done some work on a Elliot Company (Ridgeway Works; Ridgeway PA) frame 3645 2000 HP 4-pole induction motor (vintage 1924 as I recall). The bearings were very strange in that machine; several vendors had actually put them in backwards. I was fortunate in getting some info on these motors from a rebuild shop in Connecticut that normally did the rebuilds.

The bearings had an adjustment bolt through the casing at the 12 o'clock position. It was not uncommon to have this too tight causing excessive temperatures and wiped bearings. The rebuild shop suggested they be only finger tight until the motors had been run for about an hour or so and then tightened very slightly and locked in place.

Rather interesting, if you slacked this bolt off you could easily put the shaft into whirl but just as easily get rid of the whirl with slight tightening. The trick was to get a thermally stable motor and then adjust for a happy compromise.

John form PA

John,
Thanks for the info. These bearings have an access port at 12 o'clock, but no bolt, like a sleeveoil bearing.
At this point, we believe the RTD may be in further than the previous probe. I have a system where all the vibration readings are stable, the oil lube system is common to all bearings, including the pump thrust bearing and every other bearing tempurature is good, the motor is sitting on mechancal center (couldn't even find mag center it was so weak).
So, anytime I have an issue that is so localized, I dig into that area to sort everything out. We have mic'd the bearing and the clearances are right there, and the sides have been relieved to allow the oil into the wedge.

Your comment about Elliot motors caused me to put the blinders on and only think about motors. Reading the last post about the depth of RTD's or thermocouples brought to mind a situation I ran into a few years back. We had just performed a routine inspection of a large turbine driven boiler feed pump. After restart the outboard bearing was running at and above the alarm point. We rode this out for about a month before we had the opportunity to inspect it. What we found was the thermocouple had been inserted too far. This happened by the way the thermocouple was inserted into a pipe thread to tubing swedgelock fitting. When the technician reinstalled the thermocouple into the fitting it screwed the fitting about a 1/8 turn farther into the bearing housing and pushed the thermocouple into the babbit. This actually raised a dimple on the inside of the bearing creating a very localized hot spot. You could barely feel the raised dimple but you could see a shiny spot about a 1/8 inch in diameter.

The thought of the RTD being in too far is something we are investigating, but as with almost all work we get involved with these days, someone finally spoke up (an old timer), and it was then we learned for the first time that the oil supply lines to the motor bearings had orifices in them and they pulled them out!!!
So, with 10 lbs of pressure on a 1/2 inch oil line, calculate out that amount of oil and you find it will be way too much. We are currently investigating with the customer his pressures and flows to all bearings.
The only reason the last bearing ran cooler is because the clearance was huge (the vibration levels were double what they are now, with multiple harmonics of running speed.
I'll keep you posted.
By the way, my old timer technical guy told me that users hated the orifices because a very small piece of debris would severly restrict oil flow.

Folks,
As with most jobs, it was something easy in the end. Someone filled the oil sump with the wrong oil. Use the correct oil and watch all of the bearing temps drop 20 degrees F!