Vertical pumps tripping

[Ekow123]

We run a 2*100 pump skid in our circulating water system for the cooling of our steam turbine.

One of the pumps tripped on high motor current with equivalent high discharge pressure and high vibration,the other pump on auto-standby also tripped within a minute on high electric current,high discharge pressure and high vibration.

I am wondering what might lead to such pump behaviors.We attributed these to the system conditions since the problem was common to both pumps,but after a thorough inspection of our pipelines and condenser tubes,they were found to be okay.

I really need ideas to help resolve this problem.

 

[LittleInch]

We might need a bit more info to really help, such as a sketch of your system, the pump curves and some idea of how pressure and flow control works. The high current and high vibration sound like excess flow through the pump, but the high pressure is a bit strange unless the inlet pressure also went up.

If your pumps have a high head at low/no flow then you could get the same result. The pump curve would be very useful to provide more response. If you don't have it look it up on google and normally you can get a generic one from the vendors website.

If the system was running fine before then you needs to see what changed, even if it looks unrelated and post the results. Pumped systems don't normally just stop working unless some aspect of the system changed.

At the moment it sounds like too much flow or too little flow, but why? - I don't have enough information to guess at the moment.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Scipio]

Any chance these are high head/low flow type pumpslike regenerative turbine or side-channel pumps? High pressure and vibration sounds to me like the pumps were dead-headed, but the simultaneous high current only makes sense with pumps like those that have peak power requirements at shutoff. That could either be unusually high pressure on the discharge or (less common) low pressure on the suction.

Also, new installation or an existin installation that was running fine for awhile and this just showed up? Like LittleInch mentioned, more details are necessary to come up with some ideas why it's happening.

 

[electricpete]

Are these by any chance low speed, high flow, low dp pumps? Axial flow? (that's what our large steam power plant circulating water pumps are)

Those tend to have decreasing BHP with increasing flow as shown in fig 7 here:

http://locator.gouldspumps.com/cpf_0009.html

Then high discharge pressure (low flow) would be consistent with high motor current. System blockage is suspected.

If system didn't change, let me think about increased fluid density due to decreased temperature. That would cause increasing discharge pressure and increasing BHP for a given system.

All above assumes fixed speed pumps.

If you have variable speed pumps, of course increasing speed results in both increased dp and increased bhp... look into the control system for speed and what it's sensing.




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(2B)+(2B)' ?

 

[Tmoose]

current, pressure and vibration levels all were high enough to trigger a trip?

 

[LittleInch]

Ekow123, I can see this is your first post under this name, so the way it works best is that you post a question, get some responses normally asking for more information, you supply it and the replies get more specific to your problem. We are now waiting for you.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Ekow123]

The pump is a low head high flow centrifugal pump.The design TDH is 17 m and the design flow is 7.5m3/s.These pumps take a suction from our cooling tower basin of about 8m deep.The inlet temperatures of the circulating seawater at the discharge of the pump ranges between 32 deg C TO 35 deg C.This circulating seawater exits the steam turbine condenser at about 40 deg C to 45 deg C.

I appreciate your inputs so far.I hope these additional information can help.

will do my beat to send the pump curve.

 

[Artisi]

Lets establish what pump configuration you have to start with. Your post heading say's vertical pumps and then you change to skid high flow centrifugal - a bit confusing.
However, for the flow and head advised probably axial or very mixed flow impeller, this being the case - if axial, power will rise as head increases and flow reduces, if mixed flow depending on design, they too can perform in a similar fashion with power rising and head increase.
You need to give more detail on pump configuration / manufacturer / model etc.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Ekow123,

Everyone is of much the same opinion here that for this type of pump, the symptoms you describe (high current + high vibration + high pressure) are all symtomatic of very low or no flow occurring. Therefore you need to look at or post your system and try and see how this could have occurred. Usual things to look at at blocked filters, closed valves, low inlet water level, control valves closed - that sort of thing.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Ekow123]

Thank you for your inputs so far..
I have been out of town for sometime now that is why I have not replied.

These pumps are vertical axial flow centrifugal pumps.

Presently,the problem has stopped after we performed the following;

1. cleaned the steam turbine condenser outlet to the cooling tower of scale deposits build-up.You know,its a circulating system which works as follows;

cooling tower basin seawater(lower temp) pumped by the pumps described earlier to the condenser,then the higher temp(after heat exchange with the exhaust steam) water moves to the cooling tower for heat extraction and the process continues.

2.Cleaned the condenser tubes which were found to be very clean and void of dirt build up and scales.Only little traits of Calcium deposits.

3.Emptied the basin and refilled with fresh seawater.

The pumps were started successfully and the current reading is presently 190 Amp,which is the normal running current.Its has been stable for a week now and we are still monitoring to see any change.

Can't specifically point on the actual cause but we still open to your inputs and ideas as we continue to troubleshoot and monitor.

 

[Artisi]

The before and after discharge pressure would have been useful data. If head reduced then it follows that power would also reduce.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)