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Due to wind and uneven distribution of the field along the insulator, a kind of non‐uniform contamination is deposited on the insulator surface as fan‐shaped and longitudinal pollution. This paper investigates such non‐uniform pollution from theoretical and experimental points of view. For this aim, the residual resistance of the pollution layer is formulated based on the geometry of fan‐shaped and longitudinal non‐uniform pollution. Also, the arc current is formulated using the arc Obenaus's equivalent circuit for a constant arc voltage in terms of arc length propagation. Finally, the AC dynamic theoretical model of pollution flashover is proposed that can estimate flashover parameters for different values of the fan‐shaped density degree (J), extension degree (K) and longitudinal non‐uniform pollution density degree (Z) considering instantaneous variables in arc progression. It results that with increasing Z, the flashover voltage increases, while by increasing the J and K, the flashover voltage decreases. To validate this model, the experimental tests are performed on the sample silicone rubber (SiR) insulator that show acceptable accuracy of theoretical model. Furthermore, based on experimental results, a new correction coefficient is proposed under fan‐shaped and longitudinal pollution that varies in the range of 0.85–1.62. [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]

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]

Highlight • Under DC voltage, surface charge indicates polarity effect. • Increasing the voltage amplitudes led to an increase of the surface charge density. • Corona voltage and the charging time for both polarities rise, the amount of charges increases linearly. • Relationship between amount of surface charges and number of photons have been carried out using corona camera. Abstract The objective of the present study is to investigate the surface charge measurement on the surface of polymeric insulator under AC and DC voltages experimentally. According to the test results, increasing the voltage amplitudes led to an increase of the surface charge density, the voltage application duration was also extended. During the tests, it was observed that as the corona voltage and the charging time for both polarities rise, the amount of charges increases linearly. The results show that more surface charge was deposited by negative corona charging when compared with positive corona charging. Also in this paper, the effect of the corona variations on the amount of surface charge have been investigated. For this purpose, relationship between amount of surface charges and number of photons have been carried out using corona camera. Moreover, attempt was made to investigate the effects of surface charges on potential and electric field distribution along polymeric insulator under AC and DC voltages using computer simulations based on finite element method (FEM). The present paper was conducted to study the effects of magnitude, polarity, and location of surface charges on surface potential distribution along the insulator. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of the surface charges and charge decay measurement on the surface of polymeric insulator. In this research, the effect of surface charges on electric field and potential distribution has been investigated. Therefore, using measured electric charge and charge decay, the electric field and surface potential on insulator are studied by computer simulations. The accumulation of electric charge under DC electric field makes a significant difference compared to AC electric field, and this increases the rate of electrical failure and corrosion in HVDC insulators. So, a thorough understanding of the surface charge effect on insulation performance is necessary under various stresses. The experimental results revealed that the amount of charges increases linearly with the rising corona voltage and the charging time for both polarities. It was also observed that the amount of surface charges deposited by positive corona charging is less than negative corona charging. The simulation results illustrate that surface charges are important in potential and electric field variations. [ABSTRACT FROM AUTHOR]

In this paper, an improved method to diagnose the critical conditions in the porcelain and glass insulators has been proposed through investigating leakage current (LC) and applied voltage signals. Hence, Fast Fourier Transform (FFT) analysis has been used to calculate the phase angle values of the applied voltage and LC signals. Analyzing phase angle difference of LC and applied voltage waveforms demonstrate a strong correlation of the phase difference between the applied voltage and LC waveforms with the insulators conditions. So, the phase difference cosine (P.D%) has been offered as a diagnostic index of porcelain and glass insulators conditions. In this case, when the P.D% value is lower than 30%, the insulators are in clean and normal conditions. On the other hand, if the P.D% is more than 30%, the insulators are in extreme conditions. Moreover, by increasing %P.D value more than 85%, the probability of the flashover occurrence in porcelain and glass insulators will be very high. The obtained experimental results validate the veracity of considering P.D% as a criterion for prediction of flashover in porcelain and glass insulators. [ABSTRACT FROM PUBLISHER]

• 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]