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VFD Operating Efficiency

VFD Operating Efficiency

VFD Operating Efficiency

(OP)
I have a standard motor with a standard full load efficiency powered and controlled through a VFD system.

For calculating power demand on the motor, can I combine both motor and VFD efficiencies (i.e. motor Eff=0.93, VFD Eff=0.97, equivalent load efficiency = 0.90) using the motor power as load power

OR

Using, the same motor power, I will use VFD efficiency?

RE: VFD Operating Efficiency

If you are trying to determine the electrical power required to the VFD, use the VFD input current at rated output and the VFD efficiency and power factor if you can get that information.  

If this is for design, just use 1 kVA per hp and you'll be fine.

If this is for energy efficiency or power measurements of an existing system, you can probably read the power data from the VFD.  

If you are trying to determine the power used by the motor, it's more complicated since the motor efficiency data provided with the motor is based on operating on a sine wave at rated frequency, not a PWM waveform at some random frequency.  The VFD waveform creates some additional losses in the motor compared with operation on a sine wave.  

 

David Castor
www.cvoes.com

RE: VFD Operating Efficiency

(OP)
Thanks david.

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