Abstract
Partial discharge (PD) and breakdown (BD) characteristics of various initial defects of 66_??_77kV or more XLPE cable joints (EMJ, TMJ, PMJ, and TJ) were investigated by empoying model electrodes, It is possible to classify various defects into following 4 types depending on each distinctive PD (including φ-q-n pattern) and BD features.
Type I: Interface (rubber/epoxy & rubber/XLPE) filled with silicone oil (no cavity)
Type II: Interface (rubber/XLPE) without silicone oil (cavity-void discharge)
Type III: Defect led to treeing breakdown (protrusion & XLPE with fiber)
Type IV: Interface with conductive path (wet fiber along interface)
To give one example for the feature depending on each type, PDIV (partial discharge inception voltage)/ BDV (breakdown voltage) ratio which can be regarded, as the tolerance time from the inception of PD to breakdown tend to be type III> I>>IV> II.
As for the effect of interface silicone oil (the difference between type I and II), the values of PDIV and BDV in type I (interface with silicone oil) are remarkably higher than these of type II (interface without silicone oil) and PD attenuation shortly after PD inception is recognized in Type I. The above effect on interface silicone oil may be thought to be similar phenomena against discharge in oil impregnated insulation systems.
