On Wed, 22 Aug 2007 23:51:10 +1000, Peter Dettmann
wrote:
On Wed, 22 Aug 2007 06:49:47 GMT, Ross Herbert
wrote:
You are right that the 3000 style as an AC type is rare, as there
are
much better designs used for AC, but still using the same principle
of the divided magnetic path as Ron described.
Actually, I haven't found any description on AC relays which refers
to
a "divided magnetic path", or anything remotely resembling this
term,
so I doubt that it means anything at all. What I did find is a
description of the various types of shading ring (as refered to by
Ron
and others) which might be found on AC relays and/or contactors
meant
for 50/60 Hz operation. See page 36.
http://books.google.com/books?id=gES...sKmenpcNVhKamU
Ross page 36 does not seem to be relevant, however, your comment that
you find no reference to a divided path would indicate that you have
no idea what I have been talking about. You need to understand that
on an AC relay, the pole face is divided, and one section has the
shading ring around it, and the other section has no shading ring (so
that unshaded section it is just like you find on a DC relay). The
armature is therefore is attracted by the sum of the fluxes from each
of the two pole faces. The idea is that while the the coil is
energised, then even when the un-shaded pole flux is zero (twice per
cycle), there is still flux from the shaded (lagging or delayed)
pole, and so that there is no time during the AC cycle when there is
zero flux pull on the armature.
Peter Dettmann
I certainly understand the principle of operation as described on
pages 36 and 37, and you seem to be saying very much the same thing as
depicted in fig.a(3) along with the accompanying description. As I
understand it the total flux in the core is divided where it passes
through the pole face and the electromagnetic force on the armature
will be the sum of the two forces produced by the two flux paths
through the shaded and unshaded parts of the pole face. The
electromagnetic force resulting from both flux paths never actually
drops to zero throughout a full cycle of current so the armature
remains held in.
I thank you for your patience and your comments have been helpful.