Experimental study on the lifetime of the all-film pulse capacitor in LTD systems

摘要

Linear transformer driver (LTD) is a promising pulsed power technology to construct high voltage high current pulse for building the next generation of fast z-pinch drivers. The repetitive output specification and reliability of LTD are severely limited by the lifetime of all-film pulse capacitors. The lifetime of capacitors are determined by the aging characteristics of internal polymer film and the performance of whole structure under repetitive pulses. In this paper, aging characteristics of two types of polymer film under pulse voltage and the lifetime of all-film capacitors used in LTD systems were studied with emphasis on the breakdown appearance and failure mechanism. The surface conditions of polyester and polypropylene films after electrical breakdown as well as the frequency domain dielectric loss spectrum were obtained and found changing significantly during the aging process. The tree tracking and dense convex region were obvious in the film surface after successive pulses. There would be decomposition of polymer film from long chain molecule to micro molecule during the film aging process. The lifetime of capacitor decreased rapidly with charging voltage from 90 kV to 110 kV. The most important failure reason was the internal discharge happening between the capacitor terminal and one sub unit and at the edge of two capacitor units. The pre-discharge process would benefit the lifetime of capacitor through the burning effect of unsmooth electrode foil. The lifetime of capacitors could be prolonged through internal electric field improvement and pre-discharge process.