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 larger motor will likely have higher starting current and may have different power factor and efficiency.
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(2B)+(2B)' ?
RE: Pump motor size
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
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
Offshore Engineering&Design
RE: Pump motor size
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.