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Highlights • Using the experimental tests, the effects of longitudinal and fan-shaped non-uniform pollutions on the ac flashover voltage of SiR insulators are investigated and analyzed. • The experimental results indicate that the flashover voltage increases under longitudinal non-uniform pollution and decreases under fan-shaped non-uniform pollution, compared to uniform pollution. • A new flashover voltage correction factor under combined longitudinal and fan-shaped non-uniform pollutions is proposed based on the test results. Abstract The pollution non-uniformity in the axial and circumferential directions of insulator surface has a great impact on the ac flashover voltage. So far, few studies have been conducted about the flashover voltage performance of Silicone Rubber (SiR) insulators under fan-shaped and longitudinal non-uniform pollutions. Therefore, this paper aimed to investigate the effects of longitudinal non-uniform, fan-shaped non-uniform, and combined longitudinal and fan-shaped non-uniform pollutions on the ac flashover voltage of four different types of SiR insulators. The analysis of experimental results indicated that longitudinal and fan-shaped non-uniform pollutions compared to uniform pollution contributed to an increase and a decrease in the ac flashover voltage, respectively. The ac flashover voltage increases with the increment of longitudinal non-uniformity degree and decreases with the increment of fan-shaped non-uniformity degree. Furthermore, a new correction factor of flashover voltage under combined longitudinal and fan-shaped non-uniform pollutions has been proposed. For all types of insulators, the correction factor under different non-uniform pollution conditions ranges from 0.85 to 1.13. [ABSTRACT FROM AUTHOR]

• Artificial pollution flashover tests have been utilized under ac voltage to investigate the impact of uniform and FSNU pollution on flashover voltage of composite insulators. • Morphological effects of multi-stress aging have been carried out by the SEM analysis. • The effects of contamination roughness and extension on flashover voltage of the polymeric insulators have been conducted. • Simultaneous presence effect of non-uniform pollution and multi-stress aging on the flashover voltage of polymeric insulators has been analyzed. Pollution deposition along with ultraviolet (UV) radiation and electro-thermal stress cause the composite insulators to face with critical conditions. The type of pollution which settles on insulators is not only uniform but also it can be non-uniform and uneven. In this study, the results of the uniform and fan-shaped non-uniform (FSNU) pollution tests on four various types of virgin and aged polymeric insulators under AC voltage are presented. To find the effects of accelerated aging on polymer chains of composite insulators, scanning electron microscopy (SEM) is carried out. Based on IEC 60507, the solid layer method is applied to settle pollution on the insulator surface. The results demonstrate that the flashover voltage of virgin and also aged samples decreased when pollution non-uniformity degree (J) increases from 1 to 13. The flashover voltage of studied insulators is reduced by increasing the occupation ratio (K). However, the impact of K was lesser than J on flashover voltage of the polymeric insulators. Investigated polymeric insulators have been aged up to six weeks (1000 h). Although the influence of two weeks (333 h) accelerated aging on flashover voltage and morphology of the composite insulators was not tangible, therefore flashover strength of the samples is decreased while the aging period time increases. Statistical analysis has been done to estimate the flashover voltage of accelerated aged composite insulators under uniform and FSNU pollution based on virgin insulators. The research aimed to select insulators in windy and sunny areas. [ABSTRACT FROM AUTHOR]

• Evaluate the effect of different insulator profiles on Flashover Voltage (FOV). • Analyze the risk of the insulators utilization under different ambient conditions. • Effect of different pollutions and humidities variations on the reliability of the aged Silicone Rubber (SiR) insulators. • Reliability of the aged Silicone Rubber (SiR) insulators has been calculated. In this paper, the effect of different pollution and humidity variations on the reliability of aged Silicone Rubber (SiR) insulators are investigated. Firstly, four different types of 20 kV SiR insulators have been selected to evaluate the effect of different insulator profiles on Flashover Voltage (FOV). Then artificially accelerated aging tests with 1000 h duration have been conducted for the aging of insulators. Numerous FOV tests have been carried out on the aged SiR insulators under different humidity and pollutions. Next, the risk of insulators utilization under different ambient conditions have been calculated by using the experimental test's data. Finally, the reliability of insulators under different conditions have been calculated and a new mathematical model for the reliability in different humidity has been proposed. The effect of SiR insulator profiles on FOV has been studied and the results have been shown that lower FOV is related to insulators with thicker profiles as well. [ABSTRACT FROM AUTHOR]

• A dynamic theoretical model is proposed for AC flashover under pollution condition. • It calculates flashover parameters for the fan-shaped non-uniformly degrees. • The experimental tests are performed on the sample insulator to validate model. • With increasing non-uniformly degrees, the critical flashover voltage decreases. • Using experimental results, the propoer insulation level is selected for a sample system. The geometry of fan-shaped pollution on the surface of an insulator accounts for two different values of Salt Deposit Density (SDD), conductivity, and resistance on the leeward and windward sides of the insulator. This paper proposes a novel dynamic theory model of AC flashover based on equivalent resistance in the presence of a fan-shaped pollution layer. The proposed model can calculate flashover parameters for different values of the fan-shaped pollution density degree (T) and extension degree (J) considering instantaneous variables in arc progression. In this model, the arc current is formulated using the arc equivalent circuit for a constant arc voltage in terms of arc length propagation. Also, the Form Factor (F) is defined as a function of the arc length by sampling from the desired insulator and curve fitting. To validate the analytical model, some experiments are performed on an insulator unit of suspension porcelain by applying artificial pollution at three levels: light, medium, and heavy. Test results show that the critical flashover voltage (CFO) is reduced by 19% by varying J from 1 (uniform pollution) to 1/15. Moreover, by varying T from 10% to 30%, the CFO decreases by 9%. As the non-uniformity degree increases, the correction factor varies in the range of 0.798 ~ 0.938. The proposed modeling of flashover provided by the paper could be used to perform a dimensioning method on insulators under fan-shaped pollution conditions. Also, the proposed model can be included in the EMTP-type platforms to determine the minimum insulator flashover characteristic that will provide an adequate flashover performance under pollution conditions. [ABSTRACT FROM AUTHOR]