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The characteristics, breakdown probability, and statistical distribution of breakdown time delay under different du/dt in hundreds of nanoseconds pulse for millimeter gaps have been investigated by employing the statistical experimental method in this paper. The experimental results indicate that both the breakdown time delay and jitter are essentially decreased as the slope of the pulse voltage- du/dt is increased for 1-, 2-, and 4-mm gaps; in particular, increasing the value of du/dt is useful to obtain the smaller relative deviation of breakdown time delay under the same breakdown electric field. The breakdown probabilities for different gaps have been analyzed and a method of utilizing the Gaussian distribution function has been proposed which can be used for evaluating the statistical distribution of breakdown time delay. When the experimental condition is 100% breakdown probability, the breakdown time delay follows a Gaussian distribution. However, it is unsuitable for the fitting of breakdown time delay utilizing a Gaussian function for 2- and 4-mm gaps from the cumulative probability distributions of breakdown time delay because of the lower du/dt values and breakdown probabilities. [ABSTRACT FROM AUTHOR]

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon. [ABSTRACT FROM AUTHOR]