Current readings in VFD to motor

[freecrowder]

We have a high HP VFD 3Phase@480vac input. It also has a LC LPF inline with the motor. When measuring current at the input of the filter and comparing to current output of the filter the current output is higher than input. Is this explainable?? I am wondering if it is an anomaly of trying to measure a PWM signal @2kHZ at the input and a 60HZ signal at the output of the filter. The 2kHZ PWM might need to be filtered at the meter leads and also to see if it is in the bandwidth of the meter.
Any opinions?

 

[Jraef]

LC means it has capacitors. The capacitors are providing some of the reactive current for the motor side so that is not having to come from the line side of the filter. It’s the same effect as having Power Factir Correction Capacitors, but in this case the caps are not sized for the full kVAR because their purpose is in just being part of the filter. They still function in a similar manner however.

 

[ron]

We have a high HP VFD 3Phase@480vac input. It also has a LC LPF inline with the motor. When measuring current at the input of the filter and comparing to current output of the filter the current output is higher than input. Is this explainable?? I am wondering if it is an anomaly of trying to measure a PWM signal @2kHZ at the input and a 60HZ signal at the output of the filter. The 2kHZ PWM might need to be filtered at the meter leads and also to see if it is in the bandwidth of the meter.
Any opinions?

If you measure kW on the input to the filter and on the output, you should essentially get the same number. The LC filter has relatively low losses.

The current changes because the the other variables are changing too, like the power factor.