filter inductor and DC
filter inductor and DC
(OP)
Hi,
I have a 3phase 8.8mH inductor rated for 4A and switching appications (3 columns regular laminated iron core), used for output filter in a VFD.
In some motor configuration VFD fails starting in about 10s and trips by overload.
I took some measurements, and it happens that in the initial freq. ramp-up, it stucks at almost zero freq.,
phase current is then being about a triangular wave at switching freq. of 0,2A DC level, 5A peak to peak, until it trips.
I did a very simple simulation of an equivalent circuit, and got a similar current wave, but using 1mH inductor instead of 8mH.
The question is, ¿could that small DC level seen saturate the inductor rated for 4A AC?
Regards
I have a 3phase 8.8mH inductor rated for 4A and switching appications (3 columns regular laminated iron core), used for output filter in a VFD.
In some motor configuration VFD fails starting in about 10s and trips by overload.
I took some measurements, and it happens that in the initial freq. ramp-up, it stucks at almost zero freq.,
phase current is then being about a triangular wave at switching freq. of 0,2A DC level, 5A peak to peak, until it trips.
I did a very simple simulation of an equivalent circuit, and got a similar current wave, but using 1mH inductor instead of 8mH.
The question is, ¿could that small DC level seen saturate the inductor rated for 4A AC?
Regards





RE: filter inductor and DC
Neil
RE: filter inductor and DC
I passed the question to the inductor manufacturer, lets see what they say...
One thing that I do not fully understand is that if inductor is rated for 4A AC, then it will move each cyle in the magnetizing B-H curve up to a B1 field level, but certainly a non saturated level.
Why a small level of DC could cause so much effect if I<<4A?.
In this case, H field will be much less than with 4A (independently of the freq.), so my understanding (probably wrong) is that B value should be also in non saturation zone.
Please let me know what I am missing.
Regards
RE: filter inductor and DC
Neil
RE: filter inductor and DC
So for DC, change in Volts*seconds is actually zero as dv/dt is zero, so you get the DC flux level corresponding to the DC current level (independently of the freq.)
it remains however the DC bias and cumulative residual flux phenomenon,
that remanent flux, is it really so significative in % of the saturation flux?
(sorry fo the open question, but just want to have an idea about how much could affect)
Regards
RE: filter inductor and DC
Neil