Study of DC Breakdown in Multilayered Insulation Systems

摘要

Multilayer insulation systems have been widely used in both high voltage alternating current (HVAC) and high voltage direct current (HVDC) power systems. A well designed multilayer insulation structure could benefit the performances and reliability of the overall insulation system and as well as costs reduction. In this present work, DC breakdown strengths of various combinations of multilayer polyethylene terephthalate (PET) films (from one to four layers) with a same total thickness were investigated. It has been found that multilayer symmetrical structures can enhance the breakdown strength of the insulation system. Space charge characteristics of these various configurations have been initially studied, in order to understand the results of the DC breakdown tests. The space charge results indicate that large amount of fast moving charges presences immediately after the voltage application, which can be partially blocked and trapped by the interfaces between film layers. The trapped charges could further distort the electric field distributions in the insulation system, and resulting field enhancement in thin layers, particularly in unsymmetrical configurations. However, more evidences and investigations are required for better understanding the mechanisms of breakdown in multilayer insulation system.