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Thread: Vertical 300hp Well Pump Motor

  1. #1
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    Vertical 300hp Well Pump Motor

    All,

    I'm working on installing a 300hp VFD for one of our vertical Well Pump motors...is this a constant torque or variable torque application? Please advise, thanks

  2. #2
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    Quote Originally Posted by adamscb View Post
    All,

    I'm working on installing a 300hp VFD for one of our vertical Well Pump motors...is this a constant torque or variable torque application? Please advise, thanks
    If it would be a positive displacement pump it could be constant torque, centrifugal pump would be variable torque.

  3. #3
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    Quote Originally Posted by adamscb View Post
    All,

    I'm working on installing a 300hp VFD for one of our vertical Well Pump motors...is this a constant torque or variable torque application? Please advise, thanks
    Most likely variable. All the ones I've done have been. But note what kwired posted.
    Si hoc legere scis nimium eruditionis habes.

  4. #4
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    is the pumping rate constant? head and gpm?
    is the drive modulated or running at a constant speed once started?
    The difference between genius and stupidity is that genius has its limits.

  5. #5
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    Quote Originally Posted by Ingenieur View Post
    is the drive modulated or running at a constant speed once started?
    300hp VFD
    Si hoc legere scis nimium eruditionis habes.

  6. #6
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    Quote Originally Posted by Besoeker View Post
    300hp VFD
    we used vfd's, to limit inrush current, but the sewage pumps always ran at full speed
    they were not much more expensive than a SS, but offered more flexibility
    our utility REQUIRED anything over 25 HP to have a vfd (or SS), even for constant speed application

    best to include the whole post rather than selectively edit and highlight to demean someone
    Ingenieur
    is the pumping rate constant? head and gpm?
    is the drive modulated or running at a constant speed once started?




    The difference between genius and stupidity is that genius has its limits.

  7. #7
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    If it is a centrifugal, as some of suspect, wouldn’t it still be a VT application steady state speed or not?
    Tom
    TBLO

  8. #8
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    Quote Originally Posted by Ingenieur View Post
    we used vfd's, to limit inrush current, but the sewage pumps always ran at full speed
    they were not much more expensive than a SS, but offered more flexibility
    our utility REQUIRED anything over 25 HP to have a vfd (or SS), even for constant speed application

    best to include the whole post rather than selectively edit and highlight to demean someone
    Ingenieur
    is the pumping rate constant? head and gpm?
    is the drive modulated or running at a constant speed once started?

    We are planning on varying the frequency on this drive, in the past we started it across-the-line and ran it at a full 60 Hz all the time. I'm in an industrial plant, if we used a VFD for everything above 25hp we'd be broke haha. I believe we're trying to change the pumping rate with this VFD.

  9. #9
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    constant torque at a fixed speed
    variable if speed varies, I guess true for both centrifugal and PD pumps

    T = Torque
    P = Power
    n = speed
    subscript 1 and 2 denote speed change
    affinity laws P1/P2 = (n1/n2)^3

    T1 = P1 5252/n1 and T2 = P2 5252/n2 or 5252 = T2/P2 n2
    substitute
    T1 = P1/n1 T2/P2 n2 or T1/T2 = P1/P2 n2/n1
    substitute
    T1/T2 = (n1/n2)^3 n2/n1 = (n1/n2)^2
    so torque changes with the square of the speed
    if speed does not change torque is constant
    let n1 = 1200, n2 = 1800, T1 = 100
    T2 = T1 (n2/n1)^2 = 100 (1800/1200)^ = 225
    The difference between genius and stupidity is that genius has its limits.

  10. #10
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    Quote Originally Posted by adamscb View Post
    [/INDENT]We are planning on varying the frequency on this drive, in the past we started it across-the-line and ran it at a full 60 Hz all the time. I'm in an industrial plant, if we used a VFD for everything above 25hp we'd be broke haha. I believe we're trying to change the pumping rate with this VFD.
    the requirement applied if you took service at 480 vac or less (which we always did for remote pumping sites)
    you probably take it much higher

    you app is variable torque then
    but honestly, iffy, say if you change the speed once a year, then fixed for long periods, versus a controller constant varying speed under changing head conditions
    either way, safe with variable torque
    Last edited by Ingenieur; 12-18-17 at 01:21 PM.
    The difference between genius and stupidity is that genius has its limits.

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