Sinewave filters 5

[Designmen90]

Hello everyone,
Sometimes when we use VFD for controling motor speed, we use sinewave filters on the output of VFD. But, how to know is this filters neccessary or not?

 

[mparenteau]

Harmonic analysis...

Mike

 

[electricuwe]

The topic is much more complex as it looks like on the first view. As the majority of VFD applications can be operated without sinewave filters and sinewave filters have a negative impact on cost, size and overall efficiency, several aspects need to be considered. See list below for conditions that might require sinewave filters:

- unusal low motor stray inductance

- high speed drives

- long cables at low power

To cope with other aspects og VFD operation, there are other types of filter (e.g. dV/dt filter) that can cope with the specific challenge at much lower cost.

 

[jraef]

I usually make recommendations as follows:

1) Motor is designed for operation by inverter:
<10m, no filter
>10m to 2000m, dV/dt filter
>2000m, sine wave filter

2) Motor NOT designed for inverter duty;
<10m, 230V and under, no filter necessary in most cases.
>230V, up to 1000m, dV/dt filter
>1000m or any motor that is custom made and difficult to replace, sine wave filter.

But as electricuwe said, adding a filter can reduce performance so doing it without needing it is something to be avoided.



" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[edison123]

Great tips, guys. Thanks.

Muthu

http://www.edison.co.in

 

[mparenteau]

For inverter duty motors, I usually just specify VFD rated cable as I haven't run into any situations where harmonics have been a problem using this method.

Thoughts?

Mike