Oil seepage from bearing into motor 5

[sabap]

Last year we opened up a 6.6 KV 2600 HP motor as the winding temperatures were nearing 150 C. Upon inspection we found that bearing oil from sleeve bearing had seeped into motor. Combined with small dirt particles, the sticky material was all over the windings and ari paths. Subsequently the motor was cleaned. The temperatures came down to less than 95 C.

As a preventive measure, we also repalced the labyrinth seals on both bearings.

We kept on monitoring the oil level in the bearing through the gauge glass. It remained within 40-50 % filled.

But when we opened it up this year, it has the same condition. We contacted the vendor TECO-Westinghouse but they only advised to replace the seals and keep the oil levels within range.

Kindly advise what can be done to rectify this situation. Please note that bearing lubricating oil is being supplied by pumps, aux pump and then a shaft driven pump. Bearing clearances were within limits. Vibrations are also well within limits. Bearings seals do not have any air pressurization for sealing against leakage.

Thanks in advance.

 

[aolalde]

It seems to me that the motor internal fans for cooling are creating a negative pressure that sucks the oil. Put pressure equalizer hoses to feed back the discharge pressure of the fans to the internal lubrication chamber, you need to drill properly the inboard seals and attach and run the pressure lines.

 

[BobPE]

what is the motor driving?

BobPE

 

[electricpete]

I agree with aolalde the pressure distribution is important.

All of the difficulties in avoiding sucking air accross the bearing compartment are compounded if the inlet air filters are clogged. The more clogged, the more negative pressure at the end of the rotor, the more d/p.

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[macmckim]

TECO-West typically use RENK sleeve bearings Renk usually supply air differential or air equalizing tube (hoses) that go inside from the Renk mounting flange to the air deflector inside the motor. You may not have to drill any holes in the Renk housing, but only in the air deflector. Check with RENK - there should be some sort of bearing number IE EM type, so that you can buy the hoses from RENK.
If motor still in warranty, get TECO to do it.

 

[motorman]

I am basically just reiterating what has already been said. From what I have seen, the most frequent causes for oil being pulled from Renk bearings into the motor are:

1. The air vent holes are plugged. There are two holes in the mounting flange on the Renk bearing approximately on the same elevation as the sight glass. These holes are the air inlets for the inboard air buffeted, shaft seal. They are connected to the seal by hoses. Warning, these holes are threaded. Renk does this so that temporary threaded plugs can be screwed in them to protect the equipment during shipping. Too many times, the motor user either does not remove these plugs OR someone at the site will see the threaded holes with nothing in them, notices a suction at the holes, then plugs them thinking that this opening into the motor shouldn’t be there.
2. Next, make sure the motor air filters – if they were ordered- are kept clean. When the motor can not breath through the filters, it will breath through the bearings. The air seal design mentioned above should prevent this but especially on 2 pole motors, oil laden vapor still gets pulled onto the windings.
3. If filters were not supplied by the motor manufacture, make sure someone didn’t install disposable paper filters as the will only allow about half the air through that the motor will need. Too many times I have seen these paper filters sucked all the way into the machine.

 

[sabap]

The motor is driving boiler feed water pump which is centrifugal.

Important thing to mention here is that the air filters were being fabricated locally instead of buying from TECO. Maybe you guys have helped identifying the true cause.

We will inspect for the equalization holes next week and i will post the results.

Thanks for good ideas.