VFD Pump Control 1

[alanElec]

I am using a VFD to control a constant pressure water pump.In the technical specifications of the pump,it says 90% load at 50 hz.
1.Is it possible for me to load the pump above 90% by using VFD?(by increasing/decreasing frequency?)
2.If I were to operate the pump at 45 hz,what would the motor current be?Please provide me formula for relation between current and frequency...

Thanks & Regards,

Alan

 

[waross]

No simple answers. If you speed the pump up, the capacity increases. The flow will be greater than the flow at rated speed, but you must apply the pump laws to the pump curve and consider the dynamic resistance to flow of the piping system for an exact answer. It may work and it may overload the motor.
The relation between the current and frequency may be fixed for a linear load, but for a pump the pump laws predominate, possibly modified by the system dynamic characteristics.
Post a question in a pumping forum asking the effect of changing speed on pump capacity, and motor loading.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

And you will need to describe exactly what type of pump it is. We can ASSume it is centrifugal, but that is poor engineering practice.


"Will work for salami"

 

[hooverdale]

1.Is it possible for me to load the pump above 90% by using VFD?(by increasing/decreasing frequency?)

For the sake of possibility, yes its possible. But why would you manually change it? If it is a constant pressure, the VFD should automatically adjust according to your system requirements.

2.If I were to operate the pump at 45 hz,what would the motor current be?Please provide me formula for relation between current and frequency...

Forget about the formula since it will not going to be that simple. If you already had the VFD, measure it.

 

[alanElec]

Im sorry the pump is not constant pressure.The application is for a chilled water pump and that means variable flow/variable pressure.The HVAC enginner asked me whether it is possible to load the pump above 90% and we finalising the pump and vfd ,so just wanted to confirm.


Yes,the pump is centrifugal.