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

 

[Artisi]

Non-seal means what?
Almost 100% - so what is not 100% - slightly higher flow, slightly less efficient?


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]

non-seal is another way of writing seal-less pumps, its canned type centrifugal pump, I hope this answers this part

in fact its almost 100% because the new pump has got higher efficiency 41% compared to 34% of the old one.

 

[JohnGP]

You need a copy of the pump curves to check where the previous pump was operating and compare to the new pump. It could be this pump is operating further out on the curve, as Artisi suggests, thereby consuming slightly more power. Bit hard to tell without all the facts.

 

[somacast]

I did that already, and I can assure you that nothing has changed in operating parameters and the new pump ordered in accordance with that, the effect of slight change in density due to lower temp had almost minimum effect when checked on pump curve and corresponding power (no amps in their curve so I just converted via V*I*cos@ ) , its almost an identical replacement, so what is the reason for high amps?

thnx

 

[Artisi]

We need a copy of both curves and full operating conditions, flow, head,pump speed etc- otherwise it's all guess work.

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]

OK, to try and make sense of this what we need is

Please humour us and post the curves and copy of the test results for the pump (you stated it had been tested) and also test results for the motor (if available/).
What does 6 amps represent in shaft power?? Need to know running voltage at the motor and efficiency of the motor

Flowrate

Also are those values you quote measured or from the data sheet?

Options for excess amps include many of what you have apparently checked but also:
Your motor voltage measured across the terminal isn't what it says it should be - needs electrician to check when running
There is something extra rubbing on the pump shaft

This is a small pump and motor so often the variances in either pump or motor from the data sheet / brochure can be significant. As can be any small mechanical issue.

Await further info.



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

 

[somacast]

ok first of all many thanks for the replies
@Littleinch , as for running the motor solo, I have mentioned that its canned motor type, there is no chance for dis-coupling this, and there does not seem to be any indication of abnormality during operation, its quite, both radial and axial bearings are giving healthy lights, and for current it was checked by electricians and confirmed to read 6 instead of 5 or below. the rating of the motor is 1.7 KW.

the curves are attached as requested,

regards,

 

[somacast]

and for the new pump this is the curve

 

[Artisi]

Mystery, the new pump should be drawing less current than the older unit assuming the thru'put in terms of flow and head are the same.
Can you verify the output of the old unit compared to the new unit in real terms -not hearsay or wishful thinking,

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]

OK, so the pumps at their duty point are quite similar.

SO what about the other things?

Have you actually measured flow?

Strikes me the new pump has a larger capacity so it may be that whereas the old pump might have been working at the end of its curve and the head dropped off, this new pump will maintain a higher head resulting in more flow and hence use more power?

Also you mention glycol - have you allowed for the difference in viscosity in the pump curves? might be very low, but you have only a fine margin here.

Also is that new pump curve just what the vendor supplied or was it actually tested?? before being installed? Can you alter discharge pressure / flow to do your own test and check the actual pump curve versus the one supplied by the vendor?

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

 

[bimr]

The newer pump should have a higher efficiency motor which runs at a different rpm than the old motor. Because of this, the flow will be greater than the old pump and require more amps.

Do you measure the actual flow?

 

[Artisi]

bimr makes a good point, a 20 year old motor of this power could run at speed a fair bit less than a current motor - it needs checking - but I would have thought the supplier would have picked this up and sized the impeller to suit the supplied motor. However speed and diameter are not shown on the curves.

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.)

 

[QualityTime]

[ol 1]
[li]Is this a 3 phase motor?[/li]
[li]What is the voltage rating of the motor?[/li]
[li]What is the actual voltage? Check voltage phase to phase and phase to ground?[/li]
[li]Are you sure the impellor is cut to what the curve says? Easiest way to check it is to do a shut in head test or you can open the pump and measure the impellor diameter (this is a small pump). Is it the same as what the curve says?[/li]
[li]What is the efficiency of the motor?[/li]
[li]Your electricians can only measure shaft power. Therefore your actual bhp will be (shaft power * motor efficiency). Convert this into WATTS[/li]
[li]Remember that for a 3 phase motor POWER (WATTS)= 1.73 * VOLTS * AMPS[/li]
[li]Plug in the numbers to see if it makes sense and use the information you gathered from all of the above to come to a conclusion. By using this method you can actually determine where you are running on the pump curve ;-)[/li]
[/ol]

 

[Artisi]

are we talking about a 2kW or 2000kW, just get real and have a good look at what is what - check flow and head against what you think it should be -you have given Q and H for the pump requirements but have not given any actual operating figures - you are just running around in circles spinning wheels without any chance of a meaningful answer.
Come back with something that's actual and measured if you want answers.

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]

Thank you all for your replies, I will try to answer all the question to help you help me

@Artisi : yes you are right and both datasheets agrees with you , old pump motor is 2.2KW (2200 watts) Synchronous speed is 3000 rpm , volts = 400 , phases = 3, hertz = 50 , full load amps 5.5 Amps,,,, for new pump motor is 1.7KW (1700 watts), full load amps = 5.2 Amps , speed volts phases hertz are the same, this data is from both pumps data sheets.

@Littleinch : the pumped fluid is the same since the old pump as this is an existing unit, however we are currently running the glycol @ 20 C instead of 200 C, although its a huge difference in temperature the impact on density is minimal when checking by pressure = density x G x head and applying on pump curve (testing result curve & rated curve which I uploaded earlier) you are not going to go higher than 5.2 Amps anyways, and so did the old pump.

We do not have any flow device at this line, there is one orifice further but not sure about it if its restriction orifice or delta P for flow testing.

when we ran the pump, pump is quite, no any visible abnormality, and dismateling the pump is not an option its a new item and we have procedures over here, I am trying to get help as the vendor is faaaar away.

efficiency of old pump is 34% and 41% for the new pump ...

 

[Artisi]

What is the viscosity difference if any between 20c and 200c?

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]

somacast,

Thanks for info

1) Your motor details don't make sense I'm afraid. 5.2 A only makes sense when looking at a single phase motor when power = V X amps ( and that's electric power, not shaft power). Are you sure it's a 3 phase motor?? Looks to me like someone is giving your single phase motor two phases from a 3 phase supply.
2) Even allowing for that, the new motor is less efficient. Old motor 400W/Amp, New motor 325 W/amp
3) I still think you're actually operating on the RHS of your curves. Because the old pump head dropped off quite rapidly this limited the max flow and max power. New pump head curve is longer and flatter so can flow more at a higher head hence more power. Allied to less efficient motor = more amps. Pump is quite happy because it's still operating inside its head curve, but motor is undersized.

You need to be able to measure flow to sort this out. Either that or somehow throttle a valve somewhere in the line to bring the power / current down.

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

 

[QualityTime]

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

 

[bimr]

Regarding: however its drawing 6 Amps of current instead of its stated in datasheet of full load of 5.2 Amps

The nameplate current may be different than the actual full-load current and should not be considered an accurate indication of motor load. Nameplate full-load current value applies only at the rated motor voltage. The root mean square current measurements should always be corrected for voltage.

Did you measure the amps on the old motor?