Ross Mackay Forum Moderator 94 Posts
Re: What is the power factor of VFD systems?28 September 2009 at 1:29pm
Regardless of the driver, centrifugal pump load will theoretically increase as the cube of the speed increases. The VFD motor typically is rated constant horsepower (or kW) above its line frequency speed. The VFD and motor combination must have the power capability to drive the pump at the highest speed.
If the example 100kW pump load was at say, 2000 rpm, and the motor base speed at line frequency was 1750 rpm, the motor power rating would need to be at least 100kW at 1750 rpm.
I am planning to replace a Variable Frequency Drive (VFD) electric motor instead of existing steam turbine to increase the pump speed by using a lower speed standard electric motor. I want to know whether I consider a separate additional horsepower in excess of pump brake horsepower due to using VFD motor or not. Suppose the pumping required power is a 100kw with the ordinary electric motor. If I decide to apply a VFD one for higher rpm, would the required power be the same as ordinary motor for VFD motor as well? If not, what is the power factor or efficiency of VFD systems?
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