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Re: Potato Chips (fwd)
---------- Forwarded message ----------
Date: Tue, 28 Apr 1998 01:46:02 -0500
From: Chuck Curran <ccurran-at-execpc-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Potato Chips (fwd)
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Monday, April 27, 1998 10:24 PM
Subject: Re: Potato Chips (fwd)
>
>
>---------- Forwarded message ----------
>Date: Mon, 27 Apr 1998 16:32:31 -0500
>From: Michael Smith <md.smith-at-earthling-dot-net>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Re: Potato Chips (fwd)
SNIP
>
>----------
>As for the placement of the weld, I can only surmise that it is welded in
>a spot that is going to have the minimal effect, because there will be
>eddie currents there. I would like to know how they decide where to weld
>it. I might get in touch with an engineer from Signal or someplace and
>get the scoop.
>
Michael & All:
I've worked in the electric motor industry for 20 years now and I hope I can
offer some additional bits of information relative to this topic. One point
that hasn't been made yet is that the primary purpose of the varnish, is for
the winding insulation system, that must be UL recognized in order to stay
in the industry. This is an especially critical point now a days with the
inverter drives being used on many motor installations--the resulting
stresses created by the spikes from the drive create havoc with insulation
systems. An observation that many have already made is that the varnish
does quiet down the "hum" in the laminations. This is activity/movement
will occur in a loose wire in a motor or transformer winding--it will
vibrate back and forth, with the wire fatiguing and finally breaking.
Another good reason for the varnish in the winding.
The real reason for this note is the point relative to the weld.
Laminations are welded, bolted, riveted, cleated, and left loose, with most
manufacturers of motors now leaving the stacks loose on motors under 3 HP
which is 80% of the volume. The welding system of choice is TIG welding
which is set up for minimum penetration. The location is of little
importance since it adds only a small loss to the total motor or transformer
efficiency picture. Well, up until October of 1997 anyway, when government
mandated efficiency levels made a 15-20 watt loss a big deal. An
interesting point is that on some larger motors you may have noticed
external through bolts, or the four bolts that hold the endbells in place.
Eliminating these 1/4" diameter bolts from a hole in the lams and keeping
them out of the magnetic circuit is also a big plus for motor/ transformer
efficiency. Oh, another comment too on the lams themselves. All
transformer and motor laminations are stamped and then run through an
annealing furnace. The blue/grey coating mentioned earlier is the result of
this annealing operation and yup, you better leave that alone or you are
going to make a significant increase in your losses. Hope this adds some
more information to the discussion.
Chuck Curran