Microscopy techniques for the analysis of EPR cable insulation

Routine microscopic examination of EPR insulated cables and cable accessories has been hampered by a lack of adequate sample preparation methods and established microscopic inspection techniques. During the course of our analyses of failures in EPR insulated cables and accessories, we have developed routine methods for the preparation of continuous ribbons or “slinkies” of EPR insulation as thin as 2 mils. Methods for the examination of these materials in transmitted illumination with the polarizing microscope have been developed. Techniques for the identification of contaminants and filler agglomerates with the Scanning Electron Microscope and X-ray Emission Spectroscopy have also been perfected. The measurement of void and filler particle size distributions in EPR insulation has been facilitated through the use of computerized image analysis. Development of macroscopic observation techniques to allow the inspection of insulation for homogeneity of filler distribution has been completed. In addition, these novel techniques allow for the inspection of the insulation/shield interfaces for protrusions, voids, and contaminants. Preliminary techniques have been devised for staining of water and electrical trees within EPR insulation.