×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pump motor size

Pump motor size

Pump motor size

(OP)
I have a situation that requires a vertical turbine pump. The pump will need a motor to provide 67-70 horsepower, depending on head. However, the available motor sizes jump from 60 hp to 75 hp, and the cable supplying electricity to the building can't be made any bigger, so 70 hp is the limit. Is it OK to install a 75 hp motor but only supply it with enough electricity to run at 70 hp? Is there a special controller that will allow this?
 

RE: Pump motor size

The steady state power drawn by the motor depends primarily on the pump/fluid system, not on the motor.

The larger motor will likely have higher starting current and may have different power factor and efficiency.  

=====================================
(2B)+(2B)'  ?

RE: Pump motor size

Guess you can limit the current to the motor by setting the overloads to below maximum available from the supply but the problem with this is if the pump demand exceeds this setting it will force a shut-down.
As electricpete has pointed out, the system hydraulics dictates the power requirements and to reduce power demand you need to reduce the pump duty which will lower the power requirement, this can be achieved by 1. reducing impeller diameter or 2. imposing more head on the pump.

Remember, power reduce by the cube of the diameter change.    

RE: Pump motor size

To me your statement "67-70 HP depending on head" raises a red warning flag.
The motor size should be evaluated at "end of curve".
You want the pump to operate throughout its entire dynamic range.
Consider pump start and flowing into an empty pipeline.
The pump starts at "end-of-curve" and backs up the curve as pipe friction is encountered.  

RE: Pump motor size

You can control your power requirement by either throttling you discharge valve or fitting an orifice in the discharge. This of course affect your flowrate.

Offshore Engineering&Design

RE: Pump motor size

Another method (more expensive) is to use a small VFD to limit your amp draw.  For a 460V installation, there are NEMA cabinet sized VFDs that can be used to give you exactly the limit of what your utility or lines can handle.

We've used this method in a couple installations where the total draw from a system could be no more than X amps.  The amp limit on the VFD prevents the pump from ever hitting overload.  Another bonus is improved control and starting characteristics.

Get a good system curve and a good pump curve and see if a variable speed drive could work in your situation.   

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources