new motor getting overheating

[Al-Wazeery]

Hi expert engineer,, could you please help me for my issue below :
We commissioned a new pump with new electric motor (315 kw, 546 A, 2985 RPM, 50 Hz), but we have get rising in temperature (overheating) in the MTR DE bearing crazily during first four hours reach to 107 °C, so we stop the motor immediately and the problem still come after run the motor (for two days), so we have decided for opening its shield bearing housing cover (single type) to inspect bearing greasing (proper initial quantity , proper distributed, over greasing or lack of greasing), but we found the bearing greasing well also the initial quantity of grease good also,, for satisfying we have greased the bearing by hand in the some gaps between the balls, after that we run the motor again ,, but the rising of temperature problem @ bearing still (same as before). We have check motor vibration and bearing shock pulse by spatial device we found the motor in perfect condition (max vibration reading reached to 1.8 mm/s and Carpet value -5 & max value 4)

So your help required plz to solve this issue and my questions:
1. Is this rising in the temperature normal for new motor? (Bearing type TKN 6317 C3).
2. Are there other reasons than those related to greasing?
3. Are there any related to motor Hz in bearing overheating ( max. Hz reached 46 Hz )?
4. Practical solution for solving the problem

 

[Tmoose]

How are you monitoring bearing temperature?
I'd calibrate the sensors by some method.

Then I'd run the motor solo ( uncoupled) and monitor the bearing temperature.

What is the installed axial gap of the coupling ? Are the coupling hubs installed flush with the ends of the motor and pump shafts, or however the coupling manufacturer specifies ?
If the gap is insufficient, then the motor can become the thrust bearing for the pump, or the pump and motor thrust bearings can fight each other, to the death.

Is your vibration analysis gear capable of taking spectra to 600 kcpm and beyond, or "demodulated" measurements, like Spike Energy ? Spike energy is pretty good at detecting the crazy high frequency screeches and other cries for help that an axially loaded bearing emits. Sensor mounting becomes much more demanding for those type measurements.

 

[electricpete]

1. Is this rising in the temperature normal for new motor? (Bearing type TKN 6317 C3).

It doesn't seem normal to me, especially if you have verified there is not excess grease, and you have run the motor for two days.

2. Are there other reasons than those related to greasing?

Some possibilities that come to mind: Wrong grease. Too much axial or radial load imposed by driven equipment (due to belt drive, gear drive, or misalignment of coupled machine). Lack of loading causes skidding. ODE and DE bearings are not coordinated properly to accomodate thermal growth. Loss of internal clearance of ode bearing as a result of differential thermal expansion of shaft above housing and/or excessive interfence at shaft fits and low clearance of housing fit.

Less likely possibilities but included for brainstorming: inner ring spinning on shaft or outer ring creeping in shaft (usually would show up on vibration, but you never know). Severe contamination of the lubricant is causing increased friction (again typically should show on vib). Something is causing rotor to heat and that heat is being transmitted by bearing to the housing.

3. Are there any related to motor Hz in bearing overheating ( max. Hz reached 46 Hz )?

In general as you increase speed, the bearing gets hotter. However there may be an exception for VSD motor driven very slow, let's say 25% speed. In this case as you decrease speed you are decreasing cooling flow from the attached fans but you are not necesssarily decreasing generated heat by the same proportion. In this case I would expect the entire motor frame to run hot (you don't tell us the temperature in the middle of the motor frame).

4. Practical solution for solving the problem

I don't know. Is the motor TEFC? Is motor vertical or horizontal? If vertical, is there a wavey washer. Is it a coupling or belt drive? Was the driving equipment connected during the run? What is the loading level? Do you know what type of grease? Do you have a thermal image?... image would give an idea of the rest of the motor and the shaft and may provide some clues.

=====================================
(2B)+(2B)' ?

 

[Al-Wazeery]

Dear Tmoose.

Many thanks for your kind replied,,
1- we monitored the temp. by temp. gun, unfortunately no sensor has been installed yet..
2- First we will check axial gap of the coupling ( if insufficient we will correct as per manufacturer specifies)
3- Then we will run the motor solo ( uncoupled) and monitor the bearing temperature.

Yes I agree with you For (If the gap is insufficient, then the motor can become the thrust bearing for the pump, or the pump and motor thrust bearings can fight each other, to the death ).

4- Unfortunately currently we have vibration tool/pen for taking the reading, I can't do analyzing or check high frequencies by this device.

Many thanks again

 

[Al-Wazeery]

Dear electricpete,

I appreciate your kind replied ,,

1- Regarding to motor arrangement is Horizontal (multi stage pump) & Type of grease Mobilux EP3
2- The winding temp. very normal ,,, NO thermal imager we have ,but the hotter zone is the MTR DE bearing housing Zone especially upper place..

thank you

 

[Al-Wazeery]

Here I have question to you ( Mr. Tmoose & Mr. electricpete)

IF there is too much axial load imposed by driven equipment or insufficient gap of the coupling , usually would show up on vibration (external), but our readings are very perfect For : V = 0.47 H = 0.48 A = 0.54


waiting your reply Please

 

[Al-Wazeery]

vibration unit mm/s for above readings

 

[Al-Wazeery]

Vibration readings for pump DE
V = 1.16 mm/s H = 0.73 mm/s A = NA

 

[electricpete]

In theory, incorrect coupling gap can in theory give a static force (no time variation), which can give a static response (no vibration). What type of coupling?



=====================================
(2B)+(2B)' ?

 

[rob768]

Slipping caused by an UNLOADED bearing can be an issue to. Make sure the bearing carries sufficient load.

 

[desertfox]

hi

My question is the motor loaded when it over heats? If so is the motor capable of handling the pump load?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Al-Wazeery]

Dear Expert,,

Today I have run our motor solo (uncoupled) as your recommended to me with full Hz & RPM (50, 2999),
The temperature in the DE bearing & NDE was 59 °C & 48 °C (Because still hot from the last running before shutdown),,
The test run was one hour only (readings taken every 10 min.)
Time DE NDE
00:00 59 48
00:10 64 44
00:20 70.9 43.6
00:30 77.4 43
00:40 80.6 42.5
00:50 82.8 40.4
01:00 83.4 40.3

We observed the temp. of motor shaft near to seal reached to 95 °C.
Total rising in one hour = 24.4,, but when the motor coupled motor temperature rising from 37 °C to 75 °C (38 diff).

** Coupling gap reduced to 198.8 mm (200 mm as per design), because thermal expansion .. type Flexible Disc Coupling**

NOW ,,
- Is this rising in the temp. with solo test normal?
- Are there any effect with the shaft expansion (1.2 mm) on the this coupling type (the flexibility good in this type)
- If do solo test morning @ 37 °C the diff. in one our will be 24.4 i.e. the temp. will become 61.4°C or will be 75 °C as every day.
- Any problem with motor bearing or Not?
- Are there any direct related if the motor designing NOT capable of handling the pump load (Motor big than pump or Not fully loaded )

@ rob768 & desertfox
Regarding to motor loaded when the bearing overheated ,, today morning we have observed our pump reached to 170% than its capacity while the motor still not reached to full load in Hz & Amperage??!
Also we have old backup pump (still operating) its motor capacity 200KW, but the new pump motor 315KW while the two pumps same in designing capacity

 

[Al-Wazeery]

Hi guys,,

Any reply

 

[Al-Wazeery]

Are there any related between bearing spacer & shield bearing housing ,,, we have observed this zone hotter than other and some scratching/polishing @ top surface which it touch with each other
it is possible to be the heating source due to friction ???!!

 

[BrianE22]

Are you using an infrared measuring device? I'd confirm its accuracy by getting an RTD or thermocouple or something else in there. Maybe you've already done that and have faith in your measurements.

 

[JJPellin]

I have seen two instances where the motor repair shop accidentally installed both drive-end and non-drive-end bearings in the fixed configuration. Normally the DE bearing would be fixed and the NDE would be floating. As the rotor heats up and grows, the bearings are overloaded.

Johnny Pellin

 

[JJPellin]

That seems like an unusual bearing and grease combination for a horizontal motor. I would expect a heavy duty thrust bearing with extreme pressure grease in a vertical motor direct coupled to a pump with very high thrust load. For a horizontal motor coupled with a flexible coupling to a pump that has its own thrust bearing, this seems a poor choice. I would expect a radial bearing (6200 series) and a polyurea based grease like Polyrex EM.

Johnny Pellin

 

[Al-Wazeery]

Today I have do these activities :

1- Run the motor solo w/out shield bearing housing (after see some polishing on the spacer rim) --- Result temp. constant @ 57
2- Grind bearing spacer rim by using sand paper & motor running
3- Run our motor solo (uncoupled)& bearing covered with full Hz & RPM (50, 2999) for 3.5 Hrs --- Result Temp. rising from 31 C to 80 C then decreasing from 80 C to 66 (coutenouse decreasing), but we stop the motor.
4- after that we run the motor coupled with full pump load --- Result temp. rising from 60 C to 117 C , then we stop the motor..

--Please your suggestion required after these observations--

 

[desertfox]

Hi

The pump load to great for the motor?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[JJPellin]

What are you referring to as "shield bearing housing" and "spacer rim?" What parts are these? Can you provide a drawing?

Johnny Pellin