On Mon, 20 Aug 2007 12:04:01 GMT, Ross Herbert
wrote:

On Sun, 19 Aug 2007 16:27:02 +1000, Peter Dettmann
wrote:

On Sun, 19 Aug 2007 14:39:50 +1000, Peter Dettmann
wrote:

In the telephony industry these are known as "slugged" relays. Such
relays have a solid copper slug of a specific length - eg. 1/2" or
1"
depending on delay period required - the same diameter as the coil
itself. The slug could either be at the armature end or the heel
end
of the coil depending upon whether a predominantly slow operate or
slow release was required. For ac operation it hardly matters which
end is slugged and if pushed for a part you could use a relay with
a
spare winding on it and simply short circuit this winding to
produce a
"slugging" effect.

No there is a difference here Ross, in the AC relay, the "slug" does
not cover the whole of the magnetic iron path,

I didn't say it did.

Here we have a communications problem.
You referred to the normal slugs which do in fact enclose the magnetic
path (not the magnetic loop or circuit) While there is some leakage
flux outside the iron circuit. the major operating flux is through the
iron core for the coil, which is path to which I referred. With the
exception of Ron(UK) all the posts are still centered on DC relays
whether slugged or not. Ron said "some did have a D shaped shading
pole set into the armature end of the pole".

There is a slot cut into the pole face (to which the armature is
attracted). The slot divides the pole face into two sections with a
ratio of about 1/3. In this slot is usually just a solid D shaped
copper piece which forms a shorted turn on the smaller pole face
section. What happens is that the flux attracting the armature is the
sum of the fluxes from the two sections of the pole face. With an AC
energised coil, the smaller pole face flux actually lags the flux in
the un-shorted larger pole face section, so that even when either pole
face section has zero flux (and zero pull) there is still flux in the
other section. Therefore the armature always has some pull from the
pole face while the coil is energised. For larger relays, the
magnetic circuit is made up of laminations, but the same style of
having two distinct sections of pole face, with one having a shorting
coil around one section.

I hope this is clear, and I would rather have shown a diagram, but
with the painters in I have rather limited access to my library to get
at the old basic theory books. I should add that I have had many
years working directly with relay, protection and control equipment

Peter Dettmann