The Effect of DC Electrothermal Aging on Breakdown Strength of Poly (ethylene terephthalate) Used in Laminated Busbar

Abstract

The effect of DC electrothermal aging on breakdown strength (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> ) of polyethylene terephthalate (PET) used in laminated busbar is studied. It is found that a maximum E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> of 837 kV/mm was found for 96 hours' aged sample. The dependence of activation energy of dc conductivity on aging time is investigated. It is shown that the activation energy rise from 1.87 eV to 2.01 eV and then decline with increased aging time. The molecular chain is studied by FTIR to lucubrate the variation of activation energy, and the aggregation structure is studied by DSC. The results reveals that, for 96 hours' sample, crystallinity of PET increases from 33.05% to 36.12%, while the results of FTIR show no significant distinction. Decreased crystallinity and increased absorbance at the crest of carbonyl and hydroxyl groups are found with aging, indicating destroyed aggregation structure as well as broken molecular chains. Thus, the degradation of microstructure results in the reduction of activation energy of dc conduction, which finally leading to a decrease of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> .