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Charge accumulation on an insulator surface under AC electric field is uncertain and is different from DC. In this paper, a method of extracting the phase of voltage truncation time is proposed. The characteristics of charge distribution on an insulator surface under AC voltage is obtained, and the relationship between the voltage phase and the surface charge distribution is investigated. The measurement results of charge distribution and the microscopic discharge process are compared and analyzed which can overcome the deficiency of the traditional off-line measuring method. In addition, the effect of voltage amplitude and insulator material characteristics on the surface charge are studied. It is shown that the charge distribution on an insulator surface shows a three-tier concentric circular structure, and the distribution characteristic of the charge is closely related to the phase of the AC voltage truncation time and the insulation material. The charge density is also affected by the voltage amplitude. [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]

In this paper, power frequency breakdown tests as well as positive and negative lightning impulse breakdown tests have been performed. The breakdown voltages of CF3I/CO2/N2, c-C4F8/CO2/N2, CF3I/c-C4F8/CO2 gas mixtures have been measured in different gas pressures, mixing ratios and electrodes distances in slightly non-uniform electric fields. In addition, the breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures have been comparatively analyzed with SF6/CO2, CF3I/CO2, c-C4F8/CO2 gas mixtures. The results show that CO2 is excellent buffer gas to CF3I and c-C4F8 as it has synergistic effect. The power frequency breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures are basically the same as that of c-C4F8/CO2 gas mixtures, which are higher than that of CF3I/CO2 gas mixtures. Besides, the 50% breakdown voltage of c- C4F8/CF3I/CO2 gas mixtures under lightning impulse are higher than that of CF3I/CO2. Compared with SF6/CO2 gas mixtures, CF3I/c-C4F8/CO2 gas mixtures have the same insulating performance in short electrode distance, and show more excellent insulating ability at an electrode distance more than 20mm. [ABSTRACT FROM AUTHOR]

The uneven distribution of voltage along the composite insulator strings harmed their electrical and mechanical properties heavily, which threatened the safety of power system. Inserting metal electrodes in the silicone rubber sheds of composite insulator helps increase their self-capacitance, thereby ameliorating the voltage distribution along the string. In this paper, a new structure of weather sheds with metal electrodes inserted has been designed. Tests on composite insulators with different metal electrodes setup were conducted to examine their voltage distribution performance. Corona inception voltage of the mentioned composite insulators was obtained by a remote monitoring system as a criterion of the voltage distribution performance. Simulation model of the insulators were set up and calculation of their voltage and electric field distribution were carried out by finite element method (FEM). The calculation result was in good compliance with the experiment result. The applied voltage at the live end of composite insulator decreased by 4% when inserting electrodes in the weather sheds, which was verified by both experiment and simulation results. [ABSTRACT FROM AUTHOR]

This paper considers the possibility of numerical generation of pulse breakdown voltage random variable in SF6 gas. A theoretically constructed model was tested at low, medium, and high values of \(pd\) product (pressure \(\times \) interelectrode distance), ranging from 0.1 mbar mm to 50 bar mm. Numerical generation of the statistic sample of the pulse breakdown voltage random variable was performed in homogenous and nonhomogenous fields. Variable experiment parameters were the pulse rise rates (from 1 to 400 kV/ \(\mu \) s). Obtained results indicate that the proposed theoretical–numerical model is absolutely satisfactory at high values of \(pd\) product (10–50 bar mm), which is the very region of SF6 gas application. At lower values of \(pd\) product (less than 10 bar mm), there are certain deviations between a numerically generated statistic sample of the pulse breakdown voltage random variable and the one obtained experimentally. However, this deviation is not relevant from the aspect of engineering practice. [ABSTRACT FROM PUBLISHER]