Impact of Contact Pressure on Breakdown Strength of Solid-Solid Interfaces

Abstract

Solid-solid interfaces are considered as weak points of
the insulation since combination of two solid dielectrics
increases the risk of cavities and moisture at the interface
against the tangential component of the applied electrical
stress. The main objective of this paper is to investigate
the impact of the applied contact pressure on shrinkage
of the size of cavities on the interface that leads to
enhancement in the breakdown strength. Experimental
measurements of AC 50 Hz breakdown voltage of solidsolid
interfaces assembled under standard laboratory
conditions were conducted using two different
specimens, namely XLPE and silicon rubber. For the
same applied contact pressure, breakdown strength of
XLPE-XLPE and silicon rubber-silicon rubber interfaces
were also analyzed to yield the influence of elasticity
modulus (softness) of the solid material on the
effectiveness of the applied pressure. Two different
levels of contact pressures were applied for each type of
interface and higher interfacial pressure (8.02→11.59
bar) led to improved breakdown strength about 50% for
XLPE-XLPE interface whereas the enhancement for the
much softer interface (i.e. silicon rubber) was about 7%
under increasing pressure (1.34→2.67 bar).
Additionally, breakdown strength of silicon rubber
interface was found to be higher than that of XLPE
interface around 53% at the same applied pressure.