ESP underload question.

[ahendawy85]

Dear Experts;

I have a question concerning ESP. I was told that operating the pump against a closed valve would cause the system to trip on underload. Is there any truth to this? If so, can you offer an explanation as to why this happens? It does make more sense that it trips on overload to me.

Thank you.

 

[zdas04]

An ESP is a dynamic device. If it has no flow it is doing no work. No work means minimal power draw or underload.

David

 

[DubMac]

If it were to trip on anything it would be overheating, due to fluid not moving through the pump, which is used to cool the motor.

There could be a trip point set for power dropping below a certain point, say at anything below some percentage of rated power, but it is protecting against heat buildup, not "underload".

 

[zdas04]

I'm not sure I buy the concept that windage losses will cause over heating before the underload trip. As I understand it, the underload trip is there to guard against the over heating.

David

 

[Pumpsonly]

It is true and a pro-active protection for ESP and also canned motor pumps to trip the motor when dry running or loss prime occurs in the pump.It has been around for some time.In the a case of ESP, to prevent the motor from over heating when insufficient or no liquid flowing across the motor for cooling.

It is an electronic devise wired into the motor control circuit and by measuring the motor current drawn.
When a centrifugal pump encounters shut valve or dry run situation, the power will decrease and hence the motor current. The device will trip the motor starter contactors when it sensed the motor line current is below the set value.

Below are some links to such devices.

http://www.benderrelay.com/datasheets_US/CSD25_new_LV.pdf

http://www.rototech.com.au/pdf/eucr_2c.pdf

 

[OilHunter]

Base in my experience on ESP if is operating againts closed valve it might trip on overload.. if low production it will trip on underload

 

[Pumpsonly]

OilHunter,

I agree with you if the pump is progressive cavity type.

 

[zdas04]

Pumpsonly,
That is an odd statement. A PCP is a positive displacement pump and if you dead end it you'll get really high pressure until something breaks or goes down of overcurrent.

The whole underload discusison is about dynamic pumps.

David

 

[Pumpsonly]

David,
My response was in reply to oilhunter's statement.

"Base in my experience on ESP if is operating againts closed valve it might trip on overload."

And is correct for PCP. Dynmaic pump will not over load with shut valve except for axial flow pump.

 

[d23]

ahendawy85

In general the statement is true for ESP’s. This statement assumes the underlaod has been properly set. At 0 flow (Closed Valve) the power required will be minimal. The motor seal assembly, intake, pump and induction motor all have losses when operating at very low flows and loads. The typical ESP induction motor will not go below 40% of its nameplate current when operating against a closed valve.

Our industry also has axial flow charge pumps used in gassy wells. Axial flow stages require more power at low rates. The combined load of an axial flow charge pump and the mixed or radial flow primary pump could prevent an underload device working as we would want.

If you would supply an equipment list of the installed equipment I could tell you the actual no flow motor current.

I did make a quick search on the internet and found an explanation by Irrigation Craft on their site. This shows three typical impellers, radial flow, Frances and Axial flow pump curves. I am not aware of any Frances impellers in our industry, but the Frances does behave similar to the mixed flow designs we use.

http://www.irrigationcraft.com/power_1.htm

D23