3 Phase LV motor failure 2

[raj2488]

Hi,

I have a situation. We recently installed two brand new motors(name plate details are attached) to pump units and both failed. They are identical to previous old units which were sent for servicing. One of the new units tripped and the rotor found in jammed state. the second one has one of the phases in open loop(burnt). trying to find root cause of the failure as they were both brand new. the operating current is 5.6amps and rated current is 5 for 415V supply. What is the service factor for 3hp motor or allowed over current percentage? Appreciate expert advise.

Best regards,
Raj

 

[RedSnake]

@edison thanks. since its a brand new motor and manufacturer strongly arguing it could not be bearing failure

If the motor name plate attached are from the "new" motor it says it is manufactured in 2013.
There is a strong possibility that if the motor has been stored and the rotor not turned during that time.
That the grease has ended up in the lower part of the bearing and that the topp part has rusted, so when you start it the bearing brakes in no time.
Especially if it has been stored in a hot and humid environment.

ALTERNATIVE DESIGNATIONS:
These designations mean the same as that the bearing is open.
6206 ZZ
6206-ZZ
6206-2Z

This 6206 2Z SKF ball bearing with the dimensions 30x62x16 is a single-row groove ball bearing with protective plates on both sides.
Advantages of sheet metal sealing are that you get low friction and that the bearing can handle higher speeds.
It protects against shocks and larger particles from eg metal shavings, stones etc.
But less good at excluding dust and retaining grease in the bearing compared to a rubber-tight bearing.

The same goes for 6304ZZ.

Ones we got a motor back from renovation and they hade forgotten to fill the bearings with grease or they forgot to tell us they didn't.
It didn't work for long. :-(

Best Regards A

 

[edison123]

@redsnake

The grease is not a liquid to settle down. If anything, the grease becomes more solid if the motor was idle for a long time. Caking of grease can result in loss of its lubrication properties and lead to premature bearing failure.

Muthu

http://www.edison.co.in

 

[RedSnake]

No if it hade been a liquid it hade been oil.
Caking meaning.

The shoulders should be rotated regularly (once a quarter) for hand so that the grease film in the bearings does not penetrate.
Stationary heating, if installed, recommended to avoid condensation in the engine.
The motor must not be exposed to external vibrations stationary, as this can damage the bearings.

1 Greased layer
We recommend that you rotate the motor shaft at least once a month (by hand, at least five turns, and stop
the shaft in a different position from the original).
If the engine is equipped with a shaft locking device, you must remove it before rotating the shaft and reinstalling it before performing any handling procedures.
Vertical motors can be stored in vertical or horizontal position.
If engines with open bearings are stored longer than six months, the bearings must be lubricated before the engine is used.
If the engine is stored for more than 2 years, bearings must be replaced or removed, washed, inspected and lubricated

It might be the opposite if you leave the motor in store without turning it all the weight from the rotor will be on the balls at the lower point of the bearing so eventually the grease will be pushed aside and it will only be iron against iron.

"the grease film in the bearings does not penetrate"

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

My mechanic later became a tribolog, at one time he was greasing some bearings through a nipple and since he didn't clean up properly on the outside afterwards the end result was grease dollops on my electrical drawings, that was lying beneath the nipples, so he got the evil eye.
The conclusion is that Newton certainly can have a attraction on grease. ;-)
At least to me it is a proven fact.

Putting to much grease in a bearing can also break it, everything needs place to expand when getting hot.
In this case I would not consider it being a problem since it wasn't a tightly sealed bearing.

What I would like to know is what kind of pump it is?
And what is it pumping?
A displacement / screw pump, water / oil / dirt.
I think someone asked what kind of motor protection device it hade too?

Best Reagards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[TFinstad]

Great tips on motor failure analysis. Have you considered the load. What has changed with the pumps. Do we have impeller restrictions, material buildup causing blockages, pump bearing wear or failure, viscosity changes in fluids being discharged from the pumps. What kind of liquids or materials are going through these pumps. If your pumping molasses and the environment changed to cold temps you can be in overload. Good motors usually have a SF or service factor of 1.2 with some additional unpublished safety factor which has been exceeded. Is there a controller driving a VFD at half speed minimizing torque causing overload.

I'd start with the pump as two sets of motors have failed. Put on a clamp on ammeter and check the current draw when you reinstall the refurbished motors out for service and that should tell you what you are up against. If your underpowered upgrade the motors to a non-Chinese name brand. Down time is too expensive to screw around with cheap motors or pumps.

 

[waross]

Welcome to Eng-Tips TFinstad.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Kiribanda]

raj2488,
You have mentioned that the first motor was taking 5.2A while running in contrast to the name plate FLA=5A.
1) The O/L relay in the starter should be either Class 10 or 20. In that case, if the O/L is set to FLA=5A,
then it will trip only after 2Hrs of operation for 1.2xFLA.
2) In IEC motors there is no service factor given like in NEMA motors. IEC motors should show the range of rated output.
3) Your motor has no other rated outputs given for the rated voltage 415V. Therefore, your motor has to be
overload protected by Class 10 or 20 setting its setting as 5A.
4) Even though it is new, looks like it has got some jamming and continued to run and tripped by O/L relay in the starter.

 

[LittleInch]

Oddball question here, but I notice that the 220V supply is supposed to be Delta and the 380/415 as star. Would it make a difference if they got that the wrong way around?. i.e. wire 415V to the delta connections?

Or are these just sh1te motors?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[RRaghunath]

Raj seems to have vanished.
May be, he is not happy with the advice he got in this forum!!

 

[LittleInch]

Well he was trying to get the OK to run a motor at 112% of its rated max value and when we said don't think so clearly hasn't logged in since....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.