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Thread: Why does higher voltage results in higher current drawn?

  1. #21
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    Quote Originally Posted by retirede View Post
    Correct about the effects of pressure on loading. But he also reported that the flow increased by 10% post installation. The only thing that can cause a PD pump to do that is to proportionately increase the speed.

    I think we are presuming a standard AC induction motor and constant speed transmission (direct coupled, belted, etc.).
    I still think something is wrong with the data collection.
    Maybe or maybe not.
    The clear idea I get is that the speed of the drive motor increased to effect an increase in flow! Since Flow = k x Speed in a PD pump, there is no other variable on the right side that will compensate for an increase of flow (left side) except the Speed.

  2. #22
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    Quote Originally Posted by topgone View Post
    Maybe or maybe not.
    The clear idea I get is that the speed of the drive motor increased to effect an increase in flow! Since Flow = k x Speed in a PD pump, there is no other variable on the right side that will compensate for an increase of flow (left side) except the Speed.
    They only way I can fathom a speed change is if the frequencies are different between the test stand and the final installation. Maybe the factory uses a gen set for test power? Unless we get more from the OP, it's all speculation.
    I'll just stick with bad data for now.

  3. #23
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    A speed change of 10% is not plausible



  4. #24
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    An IDEAL pd pump is linear with (only) speed
    a real one also is affected by the system curve, net positive suction head/inlet pressure, viscosity, etc
    a 10% variation caused by these factors is a possibility

    btw, flow measurements are typically 3-5% error depending on method, venturi location, etc
    it sounds like he did not use a flow element
    or just a pitot, not an array
    only dp across the pump
    guessing he used this pressure to get flow from the pump curve



  5. #25
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    Back calculating head
    assume eff 65%
    gpm 84 (avg 300-330 l/min)
    hp 93 (~ 460, 105 A, pf 0.825)
    head is 3000 ft (head) 1300 psi
    sounds high for a single stage pump?



  6. #26
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    Jul 2013
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    Quote Originally Posted by Crowbar View Post
    ...

    also checked the medium used in factory and on site, I was told they are generally the same. ..

    same flow meter was used (despite some months later) .....

    removed the connecting hard pipes and attached the flow meter with a 1 meter hose that goes from supply to return outlet directly.

    The pressure was kept about the same (~1.5% different from factory) and I supposed the head remains the same?

    they claim they use 460V ...... on site, the power supply is about 480V before 1-2% voltage drop.
    A'int the internet wonderfull? An assumption wonderland! No wonder the amperage was different. OP presented lots of assumptions as 'fact', when the fact is that Crowbar has no clue what the test conditions were, or does not understand all the variables possible and assumes a whole set of constants.

    Re-reading the OP and the quoted later added data, this is a wide open, uncontrolled, set of test data , so who knows:
    e.g PD pump ; how about more detail, gear, radial, piston, ???? type of drive? direct, gear, chain, multiple belt, ????

    e.g. "medium used" ?? oil, gasoline, water, what? - temperature and viscosity variables, etc. etc.....

    e.g. missed this registering on my brain first time read: MONTHS LATER - who knows what changes in the interim or differences in the 'medium'

    e.g. from supply to return outlet directly --- so, apparently a valve or other orifice to control 'about the same' pressure, wide open data point is a variable that is unknown

    e..g. claim they use -- ? means no direct knowledge of what the voltage was

    etc.

    Crowbar be chasing his tail or seeing who is gullible ?

  7. #27
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    I'm sorry that the whole case was presented badly with piece-meal information. I was pulled into the picture of finding the root cause of the high current on site (compared to factory) based on the recent test results and a factory test report that was done many months ago. I am equally frustrated facing such a situation.

    This is a direct driven piston pump that can pump up to 207 bar and the skid that it sits on has the relevant pipes where it draws hydraulic oil from a built-in tank, goes to an pressure outlet flange on the skid. Since this pump is supplied for a closed loop system, there is a return line with the return flange on the skid so that the hydraulic oil is pumped back to the tank. Additional pressure (beyond 207bar) is relieved back to the tank. I saw in the photo during factory that they hook up a flow meter at the pressure outlet, followed by a 1m hose that goes back to the return flange. This same setup was repeated on site after they disconnected the system pipe to hook up the flowmeter and the hose between the supply and return flange. Pardon me when I did not explain clearly previously.

    We are quite puzzled by the readings because prima facie, there seems not much major difference in the set-up between factory and on site. The differences seems to be power supply and the hydraulic oil (we don't re-use the same hydraulic oil in factory) But we measured a higher flow (when measured rpm is the same?!) and a 10% higher current. I am not a pump expert so I thought I seek the experts' views here in guiding what are the parameters that I should watch out for and I tried to answer whatever points that are being discussed. This pump is new and no parts have been replaced. I wanted to rule it as bad measurement but the flowmeter used should be within the same year of calibration as the gap between the factory and on site tests is not more than a year.

    "In factory, they claim they use 460V" - I guess the statement reveals my skepticism. I am trying to find out more about the characteristics of the generator they used during factory test.

    Will the characteristics of the medium affect the current?

    Once again, thank you for your expert views and do let me know what other information I need to furnish.

  8. #28
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    Quote Originally Posted by Crowbar View Post
    I'm sorry that the whole case was presented badly with piece-meal information. I was pulled into the picture of finding the root cause of the high current on site (compared to factory) based on the recent test results and a factory test report that was done many months ago. I am equally frustrated facing such a situation.

    This is a direct driven piston pump that can pump up to 207 bar and the skid that it sits on has the relevant pipes where it draws hydraulic oil from a built-in tank, goes to an pressure outlet flange on the skid. Since this pump is supplied for a closed loop system, there is a return line with the return flange on the skid so that the hydraulic oil is pumped back to the tank. Additional pressure (beyond 207bar) is relieved back to the tank. I saw in the photo during factory that they hook up a flow meter at the pressure outlet, followed by a 1m hose that goes back to the return flange. This same setup was repeated on site after they disconnected the system pipe to hook up the flowmeter and the hose between the supply and return flange. Pardon me when I did not explain clearly previously.

    We are quite puzzled by the readings because prima facie, there seems not much major difference in the set-up between factory and on site. The differences seems to be power supply and the hydraulic oil (we don't re-use the same hydraulic oil in factory) But we measured a higher flow (when measured rpm is the same?!) and a 10% higher current. I am not a pump expert so I thought I seek the experts' views here in guiding what are the parameters that I should watch out for and I tried to answer whatever points that are being discussed. This pump is new and no parts have been replaced. I wanted to rule it as bad measurement but the flowmeter used should be within the same year of calibration as the gap between the factory and on site tests is not more than a year.

    "In factory, they claim they use 460V" - I guess the statement reveals my skepticism. I am trying to find out more about the characteristics of the generator they used during factory test.

    Will the characteristics of the medium affect the current?

    Once again, thank you for your expert views and do let me know what other information I need to furnish.
    Given all this, something in the pump has changed.

    I'm just a lowly EE but I did spend part of my career at a pump manufacturer.

    How do the 2 sets of readings compare to the specs of the pump? Could you have had a leaking suction valve at the factory that is now seating better? I just grasping at straws

  9. #29
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    So it is a hydraulic pump
    the difference in fluid type alone could do it
    that fluid is going to get very hot: atm to 1300 psi
    this and all the nebulous data could account for any difference
    10% delta is really nothing
    what is the pump hp?
    100?
    fla?
    sf? Usually high for a hydraulic pump



  10. #30
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    Will the characteristics of the medium affect the current?
    ABSOLUTELY!

    If I want to pump 1 liter/minute of water, and 1 liter/minute of peanut butter, the PB is going to require a LOT more energy.
    So the amount of difference in viscosity of your oil may not result in MUCH change, but 10%, sure, easily.

    https://blog.craneengineering.net/th...pump-selection

    So just to be clear, I'd bet a dollar that your test oil at the factory has a LOWER viscosity than the oil at the site, and in fact the temperature difference between sites likely had an effect as well.
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