To examine the electrical tree behavior in XLPE, special sheets
(thin layers) of such material were prepared. These sheets need
special treatment under heat and pressure. Preparation of these
sheets was a very sensitive stage due to the difficulties of
grooving and fixing the needle inside the XLPE piece.
Therefore, special drilling machine was used with 0.3 mm
radius. The distance between the needle tip to ground is 2-3
mm. tip radius is 15 to 25 μm, this arrangement needs accurate
control during the drilling process. Immersing of samples into
insulating oil to prevent any surface discharge was a must.