🚀 go-pugleaf

I am experiencing a breakdown of the insulating properties of a high
voltage wire which seems to be related to several possible causes.  I
am having difficulties determining the exact cause of the breakdown.
The following is a description of the materials, the application and
the failure mode:

This is a high voltage anode wire which connects the high voltage power 
supply (29KV) to a CRT in a color monitor.  The wire is constructed from
a single strand copper wire (.01" diam.) and wrapped with a braided copper
which has been tinned (solder dipped) resulting in a .031" diameter
conductor.  This is surrounded by a PVC insulation which has markings
such as "XLPVC   TV-40   VW-1 OR CSA   40KV DC STYLE 3239".  The high
voltage power supply is self contained in a metal box and the anode wire
exits the box through a rubber grommet.  The wire makes an "S" bend
inside the box and exits the box at a slight angle which causes some
compression of the insulation by the grommet.  I forgot to mention that
the wire insulation is .185" diameter with a wall thickness of .154".
The anode wire insulation is breaking down either under the grommet or
right at the edge of it resulting in high voltage arcing to the metal
box.  The arcing leaves a hole in the insulation and can occur either
inside the box or outside but is always associated with the grommet.

Has anyone had any experience with this kind of problem?  Our theories
so far include the possibility of a plasticizer in the grommet causing
a breakdown of the insulation but we have other designs which use the 
same materials but are oriented differently and these do not experience
the problem.  This leads us to believe that a combination of bends in
the wire, compression by the grommet and residual plasticizers within
the grommet could all contribute to the failures we are experiencing.
I am looking for a source of information or first hand knowledge from
anyone who is familiar with high voltage phenomenon.  Any info or 
direction to a source of information would be greatly appreciated.

      ******************************************************************
      *   Dwight Brantley    *   Failure Analysis & Reliability Dept.  *
      *  Intergraph, Corp.   *  Reply To: brantley@falab1.b21.ingr.com *
      *   Huntsville, AL     *           Voice: 205-730-4456           *
      ******************************************************************