Page 3 of 12 FirstFirst 12345 ... LastLast
Results 21 to 30 of 113

Thread: Vertical 300hp Well Pump Motor

  1. #21
    Join Date
    Jan 2016
    Location
    PA
    Posts
    4,530
    Quote Originally Posted by adamscb View Post
    One thing I do want to point out, is that the PID loop isn't set up inside the VFD, but rather in our PLC.
    doesn't matter as long as tuned well
    a plc gives alot more flexibility



  2. #22
    Join Date
    Apr 2015
    Location
    IL
    Posts
    156
    just got word this is a centrifugal pump (so variable torque), is V/Hz still recommended?
    Last edited by adamscb; 12-18-17 at 07:40 PM.

  3. #23
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
    Posts
    7,167
    Quote Originally Posted by adamscb View Post
    just got word this is a centrifugal pump, is V/Hz still recommended?
    Might as well. V/Hz control is just the basics of what a VFD can do. From there you get into various forms of "Vector Control" that improve torque control and response to changes in loads, but on a centrifugal pump that does little to nothing to enhance your experience. The down side however is that for Vector Control to function, it must be "tuned" to the motor. That's not too difficult either now days, but if you ever someday have to replace the motor, that means the drive must be tuned again to the new motor. If there is nobody available who knows how to do that when it happens (because Murphy's Law says it will happen at 3:00AM on Christmas Eve), then your pump is down until that person is available. Using V/Hz means that issue is not there, so any time the motor is swapped, the drive doesn't care. I always recommend using V/Hz on centrifugal loads for that reason alone.

    Just for the record, not ALL pumps that are not positive displacement are necessarily centrifugal. Axial flow (propeller) and "mixed flow" pumps started into a filled system can display a mixture of CT and VT characteristics depending on the speed and head conditions, so the drives should often be sized as CT to be safe. But yours is a vertical turbine pump, so VT sizing should be fine.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  4. #24
    Join Date
    Jan 2016
    Location
    PA
    Posts
    4,530
    Quote Originally Posted by adamscb View Post
    just got word this is a centrifugal pump (so variable torque), is V/Hz still recommended?
    doesn't matter much

    2 basic equations, learn these

    pump HP = (gpm x 8.34 x ft head)/(60 x 550 x pump eff)
    = (gpm x ft hd)/(3957 x eff)

    T = HP x 5252/rpm
    8.34 lb per gal
    60 sec/min
    550 ft-lb/sec
    5252 = 60 x 550/(2Pi)
    typ eff 55-65%

    positive displacement
    flow proportional to speed x displacement ie, constant for a fixed speed
    flow ~ constant with head, pumps the same at low or high head
    what changes is torque, ie, variable, more force to lift the same mass higher

    centrifugal
    flow increases as head decreases
    the curve is raised/lowered based on speed
    if head decreases, flow increases, HP/torque increase
    variable torque

    the result is similar for both
    by varying speed you are 'sliding' the pump curve up/down the system head curve (static + friction)
    Last edited by Ingenieur; 12-18-17 at 08:29 PM.



  5. #25
    Join Date
    Apr 2015
    Location
    IL
    Posts
    156
    Quote Originally Posted by Jraef View Post
    Just for the record, not ALL pumps that are not positive displacement are necessarily centrifugal. Axial flow (propeller) and "mixed flow" pumps started into a filled system can display a mixture of CT and VT characteristics depending on the speed and head conditions, so the drives should often be sized as CT to be safe. But yours is a vertical turbine pump, so VT sizing should be fine.
    Since this was my first foray into VFD's larger than 30hp, I went ahead and sized it for a Heavy Duty rating of 300 hp, Normal Duty rating of 350 hp, just to err on the side of caution.

    Is it generally safe to say that if the load is constant torque, then size VFD according to Heavy Duty rating, and if the load is variable torque, then sizing according to Normal Duty rating is acceptable?

  6. #26
    Join Date
    Jan 2016
    Location
    PA
    Posts
    4,530
    you want to size it for fla of the motor, not hp
    hd basically derates power but allows greater overload
    std duty is fine for most properly sized pumps
    if starting stopping under load hd may be prudent

    keep in mind many pumps have a sf >1.15 so you may want to set ol's higher, ie, heavy duty



  7. #27
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
    Posts
    7,167
    Quote Originally Posted by Ingenieur View Post

    keep in mind many pumps have a sf >1.15 so you may want to set ol's higher, ie, heavy duty
    You will find that most (if not all) motor mfrs will tell you that if a motor is run from a VFD, the SF becomes 1.0.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  8. #28
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    34,323
    Quote Originally Posted by Jraef View Post
    You will find that most (if not all) motor mfrs will tell you that if a motor is run from a VFD, the SF becomes 1.0.
    Makes sense. Many just throw a drive on an existing application for various reasons and never consider if the motor might already been running into any service factor load levels.

  9. #29
    Join Date
    Jul 2006
    Location
    San Francisco Bay Area, CA, USA
    Posts
    7,167
    Quote Originally Posted by adamscb View Post
    Since this was my first foray into VFD's larger than 30hp, I went ahead and sized it for a Heavy Duty rating of 300 hp, Normal Duty rating of 350 hp, just to err on the side of caution.

    Is it generally safe to say that if the load is constant torque, then size VFD according to Heavy Duty rating, and if the load is variable torque, then sizing according to Normal Duty rating is acceptable?
    At 300HP, the cost difference is significant, I likely would have gone ahead with ND, but there is nothing wrong with HD if you can afford it.

    The difference is, as Ingineur said, in the Overload Capability of the power components inside the drive. In a VT load profile, the slower the motor runs, the LESS load there is on the motor, so the current requirement drops, meaning the components inside of the drive have LESS thermal stress. Even at full speed, a properly sized motor cannot be overloaded when matched to the flow requirements. Flow = load, so the only way to "overload" a centrifugal pump is to have more flow, and if properly sized, the only way for that to happen is if a pipe breaks and you go 'open channel flow". That's not something you WANT to have happen, so there is no need to have the VFD capable of it. So then if you have a properly sized VFD (meaning sized per the MOTOR NAMEPLATE amps), it cannot be overloaded when running a centrifugal pump even at full speed, so there is no need to build-in the capability for that in the transistor selection.

    Sizing it for HD on a centrifugal load therefor becomes overkill, but not harmful to anything other than budgets. So to your question, if it is NOT specifically a Variable Torque load like a centrifugal pump or centrifugal fan, it is always going to need HD sizing. However according to the last US Census (which if you didn't know, tracks this sort of stuff), 70% of all AC induction motors used are used on centrifugal PUMPS alone, so I'd hazard a guess what when you add in centrifugal fans, it's close to 90%. That then becomes the definition of "Normal" duty.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  10. #30
    Join Date
    Apr 2015
    Location
    IL
    Posts
    156
    Good deal, thanks everyone for all the replies, this is really good stuff.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •