Damaged motor

[bob]

Hi,

 

We just overhauled a submersible pump and noted that two windings were burnt . Moreover, the thrust pads were found broken and the carbon seals severely weared. The motor is a 200 k W one. This was installed one year back and had hardly run.

Any clue.

 

Bob

[jraef]

How are you starting / controlling the pump?

[bob]

The motor is started through an auto-transformer starter. Besides all our submersible pumps are started this way.

 

Regards.

 

Bob

[jraef]

Lots of possibilities, the best answer would come from someone analyzing the type of winding damage. Here is a simple guide:

 

EASA winding damage link

 

Could be that your auto-transformer is taking too long to transition into run, could be that your taps are too high so you have too much starting torque and therefore too much upthrust, could even have been hit by lightning!

[GGOSS]

Most submersibles are designed for DOL starting, so I would find it difficult to believe that this could be the cause of damage.

 

Wear to the thrust pads tends to suggest not enough upthrust ie insufficient upthrust can result in insufficient lubrication of the thrust pad leading to wear. This would indicate that the AT tapping selected is too low.

 

Bob, it's been a while since you first raised this. Have you been able to identify the fault cause? What action has been taken to ensure it does not occur again?

 

Regards,

GGOSS

[bob]

Hi GGoss,

 

Thanks for your concern. We sent the motor and pump assembly back to Italy and although they did not claim that it was a design problem, they agreed to send us back a new one. We have not yet completed the installation. You are right , we have got plenty of submersible pumps which are D.O.L started and which are still in operation since years.

 

Bob

[GGOSS]

Hi Bob,

 

Your very welcome.

 

It does sound like they are aware of a design/manufacturing problem.

 

Submersible motors are a wonderfull thing, particularly those fitted with thrust bearings. When applying a reduced voltage starter, be it electronic or otherwise there is always some compromise required. Start the pump slowly to minimise fluid hammer and there's a chance that the thrust bearings will fail prematurely. Start it more quickly to minimise damage to the thrust bearings and introduce water hammer.

 

I'm not sure if there's a single answer for every application. In my experience each needs to be handled/addressed on a case by case basis.

 

Hope this installation goes well for you.

 

Regards,

GGOSS

[mariomaggi]

Dear bob,

We sent the motor and pump assembly back to Italy and although they did not claim that it was a design problem, they agreed to send us back a new one.

 

Free substitution? I've found some cases in which the manufacturer is not able to explain what happened, and prefer to lose some money substituting the unit. Not all manufacturers have enough statistics on their motors to be in position to give a sure report on damages.

 

Regards

Mario