Test methods for polymeric insulating materials for outdoor HV insulation

The paper describes an analysis of standardized and non-standardized test methods for polymeric insulating materials, either suitable or applied for, outdoor HV insulation. The analysis particularly considers the increasing use of silicone elastomers for composite insulators. In the first part, test methods covering erosion/tracking performance and hydrolysis phenomena are discussed. These are inclined plane test (IPT) and arc test (AT) for the evaluation of the tracking and erosion behavior as well as boiling water test (BWT) for the evaluation of the HV diffusion-breakdown-strength. These tests have a long tradition in the field of material research. Secondly, the resistance of hydrophobicity under accelerating aging conditions using simultaneous moisture and voltage stress is considered. Results from the rotating wheel dip test (RWDT) are presented and related to results from an equivalent salt-fog test. The third part of the paper deals with the regeneration of hydrophobicity after sample exposure to moisture and corona discharges. Recovery includes also the transfer of hydrophobicity into pollution layers, which is quantified by measurement of dynamic contact angle