Dear Automation Experts, I am wondering why an inverter specification features something like this: "Output Ratings - 3Phase Motor Rating"=2.2kW and "Input Ratings - Input kVA"=5.7kVA.

What's the reason why they are so different? When I size the trafo supplying the inverter, what kind of data shall I consider?

Thank you in advance

 

The ratio does seem too high ( I compared to a 230V/2kVA pwm drive spec I have) even after taking into account the motor's rated phase angle and efficiency; drive efficiency and power factor. I would ask the manufacturer to verify the spec values and explain any high ratio. A high ratio input kVA (kW) to output kVA (kW) may indicate a low cost/crude drive design (power conversion) as a typical 2.2kW motor should not be the cause of high ratio.

 

Hi,
The inverter input stages are normally diode bridges. Even though the power factor (fundamental) is unity, the harmonic power factor is poor. So it is more relevant to rate the input in kVA which only gives the current information which is really required for the capacity calculations. The output is for standard motors. Hence it is normally refered with motor rating. The best way is to rate the output also with current rating. This is because the switching devices and the resulting power loss depend on the current carried by them.

Thanks.



> Dear Automation Experts, I am wondering why an inverter specification features something like this: "Output Ratings - 3Phase Motor Rating"=2.2kW and "Input Ratings - Input kVA"=5.7kVA.
>
> What's the reason why they are so different? When I size the trafo supplying the inverter, what kind of data shall I consider?
>
> Thank you in advance