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Re: Ferrite chokes & saturation




From: 	Gary Lau  19-Nov-1997 1728[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: 	Wednesday, November 19, 1997 3:39 PM
To: 	tesla-at-pupman-dot-com
Cc: 	lau-at-hdecad.ENET.dec-dot-com
Subject: 	Ferrite chokes & saturation

Many of us employ ferrite core chokes in our xfmr protection networks.
While the effectiveness (HF attenuation factor) of an L-C low pass filter
can be fairly easily calculated, I haven't seen any quantitative
discussion on whether core saturation is occuring.  If it is, that pretty
much wipes out the benefit of an inductor.

I've looked over the Amidon web site for info on saturating ferrite core
chokes, but the graphs, beyond being illegable, I just didn't know how to
apply them.

Does anyone actually know how to determine, either through specs or
measurement, if a ferrite core choke is likely to saturate in a Tesla xfmr
protection network?  Is it the 60 Hz current or the HF current that is
significant, or both?  How would either of these be calculated?

If it is the HF current that causes saturation, could one then assume
that if a primary strike occurs, saturation current may then be reached
and choke effectiveness lost, at the time it is most needed?

And on the topic of xfmr protection networks, assuming safety gaps are
employed at the xfmr outputs, are series chokes and/or R's integral to
the safety gap's effectiveness?  I'm trying to rationalize why many on
this list use chokes but no bypass caps, or R's but no chokes.  Could
these series components be viewed as ballast devices, significant only
if and when the safety gap fires?

Gary Lau
Waltham, MA