Thanks all for the replies.
The one point of contention seems to be in what ways varnish impregnation is
helpful. I think there are three aspects to this question:
1. Varnish as electrical insulation: Rich gives good reasons why varnish
is not suitable as electrical insulation for safety purposes, and I agree so
lets drop that one.
2. Varnish as a sealant per cl. 2.9.6 - As Mike Rains argues, a layer of
varnish surrounding the transformer windings creates a microenvironment that
is Pollution Degree 1, greatly reducing the creepages and in some cases
clearances as well. I note Mike said "vacuum impregnation", which is not
what we do at this time (we dip). I would think, though, that all we would
have to accomplish is an envelope, not the complete filling of internal
voids that vacuum impregnation is intended to achieve. Has anyone had
acceptance of this idea from an agency?
3. Varnish as an encapsulant per cl. 2.9.7 - This clause mentions
impregnation specifically but not varnish, and gives inspection criteria in
addition to the test for sealed parts in 2.9.6. Again, I think this should
be valid, but I wonder how hard it is to eliminate all "significant" voids
in the sample, and what "significant" really means. Has anyone used this
idea and had an agency accept it? How did they judge the significant voids?
Thanks again for your input,
Regards,
Jim Eichner
Statpower Technologies Corporation
jeich...@statpower.com
The opinions expressed are those of my invisible friend
----------
From: richn@anetMHS (Rich Nute){MHS:ri...@sdd.hp.com}
To: JEichner
....4. Does our varnish impregnation help us in any way?
No. For the purposes of safety, varnish is not considered an
insulation. This is because (a) its thickness is not controlled,
(b) its coverage is not necessarily 100%, and (c) it is considered
fragile and subject to damage from handling.
_____
It would seem reasonable to consider that the vacuum impregnation reduces
the
microenvironment surrounding the transformer windings from a pollution
degree 2 to a pollution degree 1 when the equipment is located in a
pollution degree 2 environment. This can help a little with
primary-secondary end turn creepage distance issues.
- Mike Rains
_____
>jeich...@statpower.com wrote:
>.....
>
>
> 2. Does our varnish impregnation help us in any way? It covers the
complete
> core and windings, but obviously not the coil terminations.
>
>If your impregnation is according to 2.9.7 then there are no clearances and
>creepage distances in the transformer. The construction can then be treated
as
>solid insulation according to 2.9.4, except the coil terminations, as you
correctly >state.
>
>
>Kind regards,
>Horst Dierich, Convenor IEC TC74/WG6
>Germany
>EMAIL: dier...@ibm.net
>
