Characterization of cavities in polyetherimide and the influence on insulation performance of ultra-high voltage pulse

Cavities are widely spread inside the polyetherimide which is a super engineering plastic. As the main source of partial discharge, they may lead to the tree-like breakdown and insulation failure of material. With the 30 MHz ultrasonic scanning microscope, the cavities of single sample and batch samples are identified and characterized. Small cavities (1-5 pixels) occupy more than 95% of all cavities for a typical sample. The mean area, total area and cavity number of each batch are closer to normal distribution. By the improved experimental system, the breakdown characteristic and insulation life of samples are tested. The cavities scanning from the front and back sides increased by 31% and 41% respectively after breakdown. The normalized insulation life is reduced by nearly 36 times as the mean cavity area increased by only 2 times. (C) 2019 Elsevier B.V. All rights reserved.