Measurement of Dielectric Breakdown Strength of Engineering Plastics Considering Materials Structure and Ion Migration

This publication compares two different methods for measuring the dielectric breakdown strength on three different engineering plastics (poly butylene terephthalate- glass composites). The current standard procedure DIN EN 60243-1 is compared to a new insulation fluid free method based on a novel test specimen design. Material-specific differences between the materials are only detected in the new test design. These results are compared to material characteristics, such as glass fiber orientation, microstructure and ion content. It is shown that the glass fiber orientation in the new test design is much more random in the electrode area compared to the ideal orientation of the DIN EN 60243-1 method. This allows a more realistic estimation of the dielectric breakdown strength taking a unfavorable fiber orientation in real housing materials into account. In addition, differences in the glass fiber adhesion and thus the microstructure are found in nominally identical materials from different manufacturers. In this context ion accumulations in breakdown paths are detected. To verify ion migration, contrast ions are introduced and their movement can be detected, allowing initial assumptions about the migration mechanism.