Failure of Well Electrical Submersible Pump

[sowhatso]

I have a problem with one of the submersible pump in my water priject. the pump operating point is 100m3 at 315m , the normal operating current reading is 32 Amp . the well pump is connected with soft start . In the last two month we have seneral power outages and interruption in the power supply line. Yesterday we tried to run the pump but it ran for few seconds and then it tripped due to OVER CURRENT ,the water reached the wellhead during this trial, during the trial to run the pumps the current rise up to starting current through the ramp time and then it went down to the normal current value (32 amp ) , and then in few seconde the vaule of current started to rise up gradually from 32 amp to , 34 , 35 , 36 ,37, .. and then it tripped due to overcurrent.

We checked the ohm readings for the motor windings and they were within the accepted range .

Befor I pullout the pump ,is there are any other check I need to do , and what is the expected cause for this curent gradual riseup during starting ?????

Thanks in advance ,

 

[Artisi]

Assume this is a 3 phase motor - have you checked each phase?

 

[sowhatso]

Yes Artisi , It is 3 phase motos and we did acheck for each phase . In addition ,the three phases during startup we giving the same values of currents.

 

[chief]

It would appear that something is seizing mechanically in the pump.
May have been a build up of sand or other debris in your suction while the pump was idle.
If there is not a downhole check valve it may be possible to backwash the pump by means of a temporary water hose.

Offshore Engineering&Design

 

[ScottyUK]

Off chance - is the supply voltage ok? A lower voltage will result in a higher current being drawn, until the motor stalls. Sounds more like a mechanical problem with the pump or motor as Chief suggests.


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If we learn from our mistakes I'm getting a great education!

 

[sowhatso]

We checked the supply voltage , it is OK . Also we checked the resistance for the three phases and they were the same.

 

[Artisi]

something funny with your info- 100m3h @ 315 m should be round 100kW this would be something like 180 amp. Where is your 32 amp figure from?

 

[ScottyUK]

Artisi,

He hasn't quoted the supply voltage so we can't say what the current should be but yes, if this is an LV motor I agree those currents are wrong for a 100kW load.


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If we learn from our mistakes I'm getting a great education!

 

[sowhatso]

Artisi ,

The motor is running with medium voltage 3300 VOLT

 

[Artisi]

ok - 3300v solves that question - as for overloading looks like you will have to pull the pump that's assuming all the electrics have been checked and cleared of any problems.

 

[EdStainless]

Is there a check valve? It sounds like an obstruction in the line, maybe a broken or jammed check.
What is the thrust bearing configuration? It could be a shot TB that as the pump thrust load increases the friction does also.
Back flushing first would be a the easiest thing to try.

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Plymouth Tube

 

[thewellguy]

You stated that it was a submersible well pump, I'm going to assume that you have a standard sub motor like Byron Jackson, Gould, Hitachi, or Franklin. The brand doesn't matter, they all work on the same principle. They all have a fluid lubed thrust bearing in the bottom of the motor. This bearing has minimum speeds that must be maintained. The reason being that (in most cases) if the bearing doesn't get to min. speed there is no speration between bearing faces and then just grind the bearing into mush. Then min. speed isn't reached the fluid isn't present to prevent wear.

The problem that you discribed to me is a clasic description of this. As the load increases the bearing creates more drag and spikes the amps. I would check the ramp time on the soft start and see what that is. In most cases the manufactuer requires that a motor get to min. speed in 2-3 sec. This is why I'm not a fan of soft starts on well pumps. You have not way to tell at what speed the motor is turning and when during the ramp time.

Please tell us what brand of motor it is an I may be able to help more. Also as the amps climbed, did the operating pressure also climb?

 

[sowhatso]

thewellguy,

The motor brand is CENTRILIFT ,50 Hz , 3000 rpm.

Two days after I sent this thread , we have afailure with the pump. we pulled out the pump and we found the shaft is broken at the coupling connection between the motor and the seal ( See attached photo) and we found other problems with the seal.

After contacing some experts in this type of pump, and after looking through the sent pictures for the broken shaft , they confirmed that the shaft failure in the picture is indicitave of the improper soft start settings.


The ramp time was 10 seconds , they recommended to modify the ramp time settings to be very short for 2 seconds , and to raise the current limit to 500% and start voltage to 90%.

We are now in the process of installing the new pump , we will run the pump after 2 days, If you have any recommendations before we run it , I appreciate if you can send them to me ...

Thewellguy , you wrote "Thewellguy , you wrote " They all have a fluid lubed thrust bearing in the bottom of the motor. This bearing has minimum speeds that must be maintained. The reason being that (in most cases) if the bearing doesn't get to min. speed there is no speration between bearing faces and then just grind the bearing into mush. Then min. speed isn't reached the fluid isn't present to prevent wear.The problem that you discribed to me is a clasic description of this. As the load increases the bearing creates more drag and spikes the amps. I would check the ramp time on the soft start and see what that is. In most cases the manufactuer requires that a motor get to min. speed in 2-3 sec."

I think what you described above is very close to the type of failure that we had , can you please provide me with more technical details of how the ramp time affect on the bearings and how it can cause the shaft break ????

Again , I appreciate all your efforts to help , but realy we are in urgent need.

 

[thewellguy]

I only have a basic understanding of centrilift pumps. In the Chicago area we don't see this brand of motor. From what I understand they have a strong presence in the oil field.

I think that you can order that motor with different thrust bearings, so I would suggest that you re-check to make sure that the motor hp, thrust bearing, and pump end all match.

As far as the soft start setting, follow the manufactuer's recommendation. From my experience what you stated about sound right.

 

[sowhatso]

I sent the broken shaft to a lab to detect if we have any manufacturer defect with the shaft , the result is that the material of the shaft match exactly the specified construction material which is Alloy Steel (ASTM No. A519,GR 4130).

The important thing is that the lab expects that we had a galling ( Cold welding phenomenon ) between the shaft and the coupling that likely caused the shaft braek.

My question is : If we had a hard starting for the pump that may cause a high temperatue and overheat for the shaft, can we have this galling between the threaded male side of the shaft and the coupling , while both the shaft and the coupling are from diffrenet material as shown below:

Shaft Material : Alloy Steel(ASTM No. A519,GR 4130).
Coupling Material: Nickel Chrome Steel(ASTM No.582,Type 303)

 

[Artisi]

Can not see how galling can cause a shaft failure or how direct start could cause high temp of the shaft and subsequent failure.

You or the lab need to identify the mode of failure as your photo shows catastrophic mechanical failure of some type.