Successive Bearing Failure in Cooling Water Motors in a Combined Cycle Plant

Clearly your bearings show electric arcing, you need to provide a proper grounding system and replace the bearings with either coated aluminum oxide or silicon nitride type bearings...

https://www.emerson.com/documents/automation/brochure-electric-motor-problems-diagnostic-techniques-ams-en-6652274.pdf

https://www.pumpsandsystems.com/how-prevent-electrical-erosion-bearings

<...These motors have just completed their commissioning phase...> means that they may well be within their commercial warranty period.

How did the telephone calls with the vendor go?

Have arrangements been made to get the vendor in to examine them?

Are there any other variable frequency drives on the same side of the power transformer?VFD's can cause trouble with motors that are not connected to them.

The regularly spaced bars on the photo are a sigh of arcing,but false brinelling can cause a similar pattern.This is caused by vibration while the bearing is not in motion and the rollers rotate in one spot on the race.Electrical arcing usually goes all the way around the bearing ,these seem to be localized.

Is there high vibration in the area?

SE's suggestion is also good advice in my opinion.You can never have too much good grounding.

Also,a consultation with the vendor may shed some light on the matter.

I'm with SE on this. That looks like arcing. Are your motors driven by frequency converters or variable speed drives? If so, your motors are probably not grounded properly. Also, it wouldn't hurt to check your motor-pump alignment. If the motor and pump aren't alighed properly, it can also cause bearing failure...among other things. regards, Vulcan

Lots of good comments, except asking about whether there are inverter drives supplying the motors, as you already state in your list. While I haven't seen insulated bearings on similar voltage motors, that is a big motor. Perhaps the sea water you handle is compromising the insulation, allowing bearing currents to circulate through the rotor shaft. Also, shaft grounding brushes are also applied, to keep a low potential at the bearings by holding the shaft at the same potential as the motor frame.

A bit of more detail would be usefull. Like the orientation of motor shaft (vertical vs horizontal). If vertical, pump on top, is damage on pump side bearing? Because the pitting I see on the rollers away from the contact surface does look like salt effect. And salty water is known to deteriorate seals faster depending on its contamination with sea water solids. And on a non continous use, effect gets worse. It doesn't take much leak to damage. It may just take a rubber disk to centrifuge leak drops away from bearing itself, depending on the specific design, available space etc. If this is not the case, an AC reactor between motor and inverter (assuming inverter drive) combined with better grounding like SE said, does help. S.M.

I don't see anything that looks like proper lubrication has been maintained. I know one may need to clean bearings of grease and oil to show bearing damage but sometimes the condition of residual lubricant can tell what is the root of the problem.

Since multiple premature failures have happened I also wonder about alignment problems. Alignment errors can happen in assembling a motor and setting that motor into a machine.

Thanks to all for very valuable inputs. I am adding more information and observations as they come in. It's been observed that the motor has been operating on 376 A which is far greater than the Full Load Amperes (356.8 A). Could this indicate designed capacity issue? Pump Nameplate Data: Type SEZ 2000-1670/1310 Capacity 33228 M3/Hour Head 26 m Power 3100 KW Speed 370 r/min Weight 31420 kg Also, in response to queries, I would like to mention that the pump arrangement is vertical. On the same end of transformer, i.e. Plant's MV System, we have the starting frequency converter for our Generator (584 MVA), and we also have the Generator's excitation system installed.

The bearing dragging could elevate the amps....That is one big heavy honkin' motor, rotating at a rather leisurely rate...It seems the mounting would be quite an ordeal to get it exactly straight and at the correct height and angle and all...I wonder if you could provide some photos of the pump motor assembly in operation, and please tell us the mounting and alignment procedure, if you could....and what is the resting weight on the bearing?

https://www.processingmagazine.com/pumps-motors-drives/article/15587470/the-ins-and-outs-of-vertical-pumps

https://www.sulzer.com/-/media/files/products/pumps/vertical-pumps/presentations/sjt_sjm_sjp_sales_presentation.pdf?la=en

Hi,

I am sharing the photo and the Pump's data below.

Maybe you need to restrict the volume the pump is moving? It is not uncommon that the actual total discharge head is significantly lower than the figure used at design. Close down your discharge valve until the load falls into normal range, and see if that helps. It could be that the higher axial load on the impeller & shaft may stabilize the load on the thrust bearing, smoothing the load on the radial bearings.(?)

It seems like your motor and pump are matched. What I'd like to know is what is the actual flow rate? And have you checked the alignment? Vibration?

Bearing failure, aside from the earlier suggestion of arcing, can be caused by overheating bearings (speed too fast, no lubrication), vibration due to misalignment, loose mountings, poor foundation.

regards,

Vulcan

There is also the possibility that the motors were stored in a high vibration area which may have led to bearing damage of fretting or brinelling. Were the shafts locked with a retaining device to stop slow rotation of the bearings under local vibration. Just recently wind generator bearings, installed for only a small time ago, sat on a dock for many months and the bearings were damaged by this exposure to vibration. We stored motors of such large size disassembled and only assembled prior to installation with inspected or new bearings.

I find your first photo of a roller with vertical symmetric/regular "lines" fascinating - why is it so different from the rest? Are those lines on the entire circumference of that roller or just in the area shown. From the photographs and the irregular discolouration (or damage) to the rollers I do not see any of the pitting or fluting that would indicate arcing (electrical discharge). Are the dark areas on the rollers damage or merely discolouration? Have you had single failure on all 4 pumps or have you had multiple failures of one or more pump.

There is evidence of brinelling on the rollers. This could be due to vibration in the structure as has been said. It could also have occurred in transit. Were the motors delivered assembled? If so, was there a locking bar between the stator and rotor to stop the rotor moving in transit? You could have a warranty claim if this was not done.

Hence #2⇑.

GA

No, the motors were assembled on site.

Assuming that the two pieces of damage indicated by the two fingers in the third picture are spaced the same distance apart as the rollers, then this indicates that the damage was caused by a huge shock when the bearing was rotating, or, a lot of vibration when it was not.

I would recommend looking at the following issues: 1) Pump misalignment 2) Coupling manufacturing defect 3) Misalignment 4) Disbonding 5) Resonant frequency 6) Are couplings appropriately sized for the application?

Disbonding is the failure of a coating to adhere to the substrate to which it was applied. It is a loss of adhesion between a cathodic coating and its metal substrate due to a cathodic reduction reaction (corrosion reaction) taking place.

Have much information from your input. Still, please confirm whether the following are existing in your case: Yours is a vertical pump with bottom bearing grease-lubricated and the top bearing oil lubricated. Oil lubrication in a vertical pump is tricky (oil seal, bearing isolator, etc.), towards maintaining oil level. But your pics don't reveal thermal marks due to loss of oil. So, shall we confirm that, "inadequate lubrication is not existing"? Are your pumps take water from a hot well? I have witnessed pumps at such installations with shallow wells exhibiting water whirls, despite having vertex-breakers at the entry of the pumps. Such whirls take air through spinning spews. Consequently, a false cavitation (and true cavitation are possible if the NPSH is low) can happen. Such cavitations could make the flow entry turbulent and rattle the pump. If the pump is huge, cavitation noise may be subtle due to mass of equipment. Then the failure continuum could be: Cavitation (true/false) > Jog the rotor train assembly, up and down > Brinelling and then spalling failure. Note: When the defective story happens at the pump end, it is quite possible to show up in the motor end as well, subject to the following prevailing condition at the site. A brainstorm could help: Is the subject equipment a mono-block pump? If yes, is it a unishaft? If not, what is the coupling type? Is the lube oil system working good? NPSHR and NPSHA? What are the possibilities of false/true cavitation? A picture worth's thousand words, can you attach a drawing?

Wouldn’t the load tend to be be less with two phase flow in the pump? Otherwise good insight! He is seeing higher than rated load....

Here is a link to the most common bearing failures. https://jadanalysis.co.uk/bearing-failure-faqs--- with pics and causes.

Check to see if you have the proper preload on the bearing,and that proper installation procedures are followed precisely,including pre-heating the bearing,and pressing,not driving it onto the shaft.Looks like load concentrated in small area,due to warping of race,with improper preload.

Many here have provided plausible motor assembly errors as the root cause of your repeated failures. Few have addressed why repeated failures keep occurring. If all of these assemblies have been done by the same crew or contractor, hire somebody else to assemble this motor and pump. If different installation teams all produce premature failures then somehow your operations are burning up these bearings.