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In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (SiR) insulators under pollution and aging conditions in the presence of surface charges have been presented. For this purpose, four different types of standard HTV-SiR insulators were selected, and then, DC flashover performance was carried out on the studied insulators in the three states including non-aged, aged, and contaminated conditions in the presence surface charges. The surfaces of the insulators were charged by an external corona source in the experimental tests, and then, the surface electric charges were measured. The experimental results of DC flashover voltage showed that the positive and negative surface charges affected flashover performance in all the states. Based on obtained empirical models of the DC flashover performance, it can be concluded that the increased aging time, positive electric charges, pollution, and average diameter reduced DC flashover performance, while the ratio of shed spacing to shed depth and negative charges enhanced the flashover voltage level. [ABSTRACT FROM AUTHOR]

This study aims to predict the flashover voltage (FOV) of silicone rubber (SiR) insulators. Accordingly, it benefits from two methods, including an artificial neural network (ANN) model and a FOV gradient fitting model. The FOV and leakage current (LC) tests are carried out on one un‐aged and three aged specimens under uniform and longitudinal non‐uniform pollution circumstances. The proposed ANN model is designed based on equivalent salt deposit density (ESDD), pollution non‐uniformity degree, aging time, LC first harmonic magnitude I1, and total harmonic distortion. Furthermore, a FOV gradient model is proposed based on ESDD, I1, and creepage distance. To validate the proposed models, the FOV and LC tests are conducted on two different types of SiR insulators. Then, the predicted FOV from the ANN model and calculated FOV from the voltage gradient model are obtained. The results indicate that the relative errors of the ANN model and FOV gradient fitting model are <6.4 and 7.3%, respectively. [ABSTRACT FROM AUTHOR]

This paper proposes an Artificial Neural Network (ANN) model for AC flash-over voltage prediction of Silicone Rubber (SiR) insulators based on the experimental tests. In flash-over tests, the flash-over voltages of four different types of SiR insulators are measured under the uniform, longitudinal non-uniform, fan-shaped non-uniform and combined longitudinal, and fan-shaped non-uniform pollution conditions. The proposed ANN model is designed with six inputs data (insulator geometry and pollution parameters) and one output data (flash-over voltage). In order to validate the model, three different types of SiR insulators are tested under different pollution conditions. Then, their flash-over voltages are predicted using the proposed ANN model. The validation of the model shows that the absolute values of relative errors between flash-over voltages of test and prediction are less than 6%. This indicates a high efficiency of ANN technique in the flash-over voltage prediction of SiR insulators. [ABSTRACT FROM AUTHOR]

In this study, the results of measurement for DC flashover characteristics of silicon rubber insulators in the presence of surface charges and in terms of geometric characteristics have been examined and analysed. In the carried out experimental tests, the surface of different insulators was charged by an external corona source and both the metal end fittings were kept grounded while the needles have been connected to a certain applied negative and positive DC voltages and then surface electric charge measured. A series of flashover tests have been carried out on the charged insulators under positive DC voltages to investigate the effects of surface charges. The experimental results revealed that positive electric charges reduced flashover performance while negative charges increased the flashover voltage level. Also, the experimental modelling of DC flashover of charged insulators regarding the ratio of shed spacing to shed depth and specific leakage distance in terms of surface electric charges, revealed that flashover voltage gradient of the charged insulator is most affected by specific leakage. [ABSTRACT FROM AUTHOR]

This article presents an online diagnostics method to predict critical conditions in ceramic insulators. For this purpose, a variety of experimental tests have been conducted on different kinds of ceramic insulators under different environmental conditions in order to analyze their leakage current. Fast Fourier transform analysis of leakage currents shows a strong correlation between the ratio of the third to fifth harmonic amplitude regarding occurrence of critical conditions and degree of insulator ageing. Therefore, the index of the third to fifth harmonic amplitude is utilized as the detection indicator of critical conditions in ceramic insulators. An increase in the index of the third to fifth harmonic amplitude to more than one represents a critical condition in the insulators and estimates a high probability of flashover occurrence. The obtained results have also shown the viability of the index in insulators monitoring procedures. Training the proposed index to a microprocessor powered device gives ability to the system for online diagnosis of ceramic insulator qualifications, detecting critical conditions, and predicting flashover occurrence. [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]

• Proposing comprehensive equivalent electric circuit of polluted insulator. • Considering dynamic behavior for arc parameters instead of static one. • Evaluating proposed mathematical model with experimental results for real insulators. • Comparing the proposed mathematical model with static models for the same frame of real insulators. • Analyzing leakage current behavior under various pollution and humidity. This paper presents an improved dynamic mathematical model of critical parameters for ceramic insulators based on an extended equivalent electric circuit model of a polluted insulator. The extended equivalent electric circuit model introduces a capacitance in dry band. The model proposes that the electric arc constants (n, N) of critical parameters (voltage and current) in the mathematical model are not static. These factors depend on insulator's profile, pollution intensity and thermal characteristic of insulator discharge. The dynamic values of electric arc parameters are suggested based on the analysis of the experimental data and mathematical calculation of critical voltage of the polluted insulators. The calculated critical voltage of the proposed mathematical model is compared against the experimentally measured values of the critical voltage under different operating conditions. The experimental test results validate the competency of the proposed dynamic model in an accurate performance prediction of the polluted insulators. [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]