high Amps on newly replaced pump 4

[somacast]

hello,

I just had a non-seal centrifugal pump replaced with newer one as the old pump was obsolete after almost 20 years of service, its used in a high temperature application and the new pump is almost 100% exactly the same specs of the old pump, just the new model from the manufacturer with newer bearing monitor (digital), tested with ambient temp glycol instead of 205, however that is not the issue because if you calculate the head at the density at this temperature it will not still lead to this number in power and hence to current of 6 amps...

the pump sound is quite, nothing looks abnormal, however its drawing 6 Amps of current instead of its stated in datasheet of full load of 5.2 Amps, which causes the breaker to trip as the set point is 6.2 amps, I know that we can increase the set of the breaker but that is not the case, why would it take higher current?

direction of rotation is correct (shown in digital monitor panel of the pump), both radial and axial bearings indicates very well condition.

any clues?

pump info: suction 2 inch , discharge 1 1/2 inch
suction pressure = 0
discharge pressure 2.94 barg
rated BHP (KW) = 1.34
Max BHP (KW) = 1.79
pumping temp = 205 C
sp gravity @temp = 0.98

 

[QualityTime]

If you look at the equation, if your voltage is low, to get the same watts the amps have to be higher.

Again you should do a shut in head test to see if your impellor has been overcut

 

[LittleInch]

"I'd be very surprised if this was a single phase motor"

Why - its 1.7kW. My circular saw motor draws more power than that and it's single phase 240V.

I agree 400V sounds like 3 phase, but then the amps don't work so something isn't correct in the description. a picture of the name plate would probably solve a lot if wheel spinning....

With no flow measurement I don't think we'll ever know, but the pump is doing what it is supposed to do. The issue is with a system which allows more flow and an inefficient motor compared to what has gone before.

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

 

[QualityTime]

I doubt it is single phase. Single phase is a two wire system + ground. A three phase system can be a 3 wire system + ground (sometimes it can be 4 wires, where the 4th wire is the neutral). It would be kind of tough for an electrician to screw this up.

"With no flow measurement I don't think we'll ever know, but the pump is doing what it is supposed to do. The issue is with a system which allows more flow and an inefficient motor compared to what has gone before."


I think doing a simple shut in head test will help in determining if the pump curve that has been supplied is as what is shown. If the impeller is overcut then this will explain the increase in power consumption. BUT you have to reconcile the reported elecrical numbers by supplyimg the information everyone has asked for. Everything is so fuzzy right now

 

[somacast]

At first I would like to really express my deepest gratitude to all of you, your efforts are really appreciated, thank you all .

and good news is that I finally got it, OPS people insisted on testing it with cold glycol @ 20 , while I had density effect on head checked and checked with pump curve and found it minimal I did miss the viscosity effect, it might sound stupid from me but believe it or not I had many senior people with me and non even though about it, and not even the vendor helpdesk !!, visc @ 205 C is about 39 Cp while at 20 its about 0.8 Cp !!! that's a HUGE difference.

and when I came back to office and topic here it seems like Artisi had it right

the motor is now drawing about 5 Amps, and regarding the discussion above , its really 3 phase @Littleinch , but as you said its low HP pumps, but special type (canned motor), old pump used to draw about 5.2 Amps when operated too @ 205 C ..

Thank you all really

 

[ScottyUK]

QualityTime,

"Remember that for a 3 phase motor POWER (WATTS)= 1.73 * VOLTS * AMPS"

That calculation gives you the apparent power delivered to the motor.

You also need to know the power factor to calculate the active power input from the apparent power, and you additionally need to know the motor efficiency if you want to calculate the power output rather than input. IEC motors are rated based on output power at the shaft, so the relationship between voltage, current and power is a little more complicated than you wrote.

 

[LittleInch]

At 5 amps though it still means you're operating at a different duty point - 5A is very close to your max rated current and shaft power (1.78kW) compared to what the pump should need at your duty point (1.34kW).

Hence I suspect you're still pumping more like 9 m3/hr instead of 6.8...

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

 

[somacast]

@Littleinch , noted thank you, however there was a big debate on this regard with the vendor when they supplied the pump as their acceptance criteria is just the current, anyway I expect to go to the optimum point when the boiler goes on full duty as our test might have just heated the gycol to a point near 190 C or so , hence there is a chance for improvement when the boiler is on normal operation .

 

[LittleInch]

I'm surprised they accepted that as the power consumption is dependent on the system curve, flowrate, density and viscosity, all of which is outside their control.

You also need to ask them for the phase current next time - I still don't know what the amps you quote relate to...

See if you can get a clamp on flow meter or some other way of working out what the flow is.

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

 

[Artisi]

If the pump is now operating under the max setting for overload and the system is delivering somewhere near to what is required and management and operator's are happy - why worry about splitting hairs - sign it off as successful and go tackle the next problem.

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]

Because it's still pretty close to the limit and who knows whether some aspect of the plant is working incorrectly because they think 6.8 m3/hr is coming at them instead of 9 or more??

As I know you are aware, far too many people think of centrifugal units as simply "blocks" of flow - "I've bought a pump that says it does 6.8m3/hr so why is it doing 5 or 9? The pump is at fault". I would say 90% of posts that appear here saying the pump isn't working properly turn out to be a system or motor issue instead. If you don't match the pump to the system or provide some sort of flow control or measurement, it won't do what you think it's going to do.

Anyway somacast has the information so he can do what he likes.

It looks like the old pump was operating well beyond its duty point if it was also operating at 5 Amps so maybe that's actually what everyone wants....

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

 

[Artisi]

LittleInch: after a few years in the pump game, I would say that it is more like 99% of "the pump isn't working properly" isn't the pump - but poor selection, installation, system, or not knowing what the hell they are doing. Some of the stories I could relate are unbelievable - wrong direction, closed valves / blank flanges, no coupling between pump / motor, inlet pipework connected to outlet flange, no product available, no power connected / wrong connections - this isn't even talking about completely wrong selection / specification, or wrong pump for the application 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.)

 

[somacast]

Thanks again Artisi & Littleinch , in fact there is a pressure there is a pressure control valve on the discharge, but it was fully open at testing, and over here not really many helpful seniors, I mean I was in this trying to figure it out as it might have caused loss production but thanks God it was solved eventually, but now they are about to do a stupid thing, but it wont be my under my scope as Artisi said, that's it sign it completed..

they are about to about to raise the set current of tripping in the power breaker, justification is : when station is cold started current will jump high... ok go ahead, I am not the one to pay for repairs when the motor is roasted

thnx again

 

[Artisi]

Why not start against a restricted discharge until product gets up in temp. and viscosity lowers - this will reduce running current and motor overload.

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.)

 

[somacast]

artisi : the problem with operation people is that they are stubborn, so it is not easy to suggest a change in a written procedure, and likely they will go ahead with current set point variation.

Thanks again

 

[Artisi]

Well that's a management problem and it's managements problem to address it. Make your point clear in a written report on the problems of start-up with a cold products and set out the consequences and recommendations to overcome failure - this covers your arse.

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.)

 

[somacast]

Thanks I will keep it in mind

 

[pumpking]

Have you taken into account Eddy Current losses through a canned motor ? With seal less pumps you loose quite a lot through this (passing magnetic fields through the shroud/isolation shell) I read that the motor power is 2.2kw - if you were to look at a similar magnetic drive pump that we manufacture, the eddy current losses on this size of coupling are 0.31kw so the pump will pull more power and will result in high current drawing...

The manufacturer will be able to tell you the eddy currentl losses specific to the pump you have purchased.

Ash Fenn

http://www.cdrpumps.co.uk