To perfect the wetting mechanism of hydrophobic insulators, it is urgent to explore the impact of hydrophobicity on wetting characteristics of the pollution layer of composite insulators. In this paper, the wetting test of the hydrophobic pollution layer was carried out in artificial hot fog. The local surface conductivity of the pollution layer with different hydrophobicity were measured. The test results show that the local surface conductivities of different hydrophobic pollution layers are obviously different at the same wetting time. For researching the regularity of wetting process in greater detail, three characteristic quantities were proposed to represent the wetting characteristics. They are the duration of local surface conductivity close to zero (DLSCCZ), the saturated wetting time (SWT) and the maximum value of local surface conductivity (MVLSC). With the enhancement of hydrophobicity of the pollution layer, DLSCCZ and SWT increase, while MVLSC and the growth velocity of local surface conductivity both decrease.

Arc discharges of moist polluted composite insulators pose a serious threat to the stable operation of transmission line. However, there is no effective detection technology for arc discharges. The evolution mechanism of interface temperature accompanied by arc discharges is not clear. In this paper, a 10 kV composite insulator with quasi‐distributed fibre Bragg gratings (FBGs) embedded at the insulator core‐housing interface was developed. The temperature calibration experiment of interface FBGs, and the arc discharges experiment of the uniform moist polluted composite insulator were conducted. Applied voltage was controlled to get the continuous arc with an arc time of 46 s and the intermittent arc with an arc time of 8 s. Exposed to the two types of surface arcs, the interface temperature evolution was explored. A new phenomenon of the sharp drop of the interface temperature was observed: the interface temperature first drops sharply and then rises rapidly during the continuous arc. Test results show that quasi‐distributed FBGs are valid for detecting the two types of surface arcs by interface temperature rise. This paper provides a technical means to evaluate the state of surface discharges and insulating properties of composite insulators.

The hydrophobicity of composite insulators is a great significance to the safe and stable operation of transmission lines. In this paper, a recognition method of the hydrophobicity class (HC) of composite insulators based on features optimization was proposed. Through the spray method, many hydrophobic images of water droplets on the insulator surface at various hydrophobicity classes (HCs) were taken. After processing of the hydrophobic images, seven features were extracted: the number n, mean eccentricity E_av and coverage rate k₁ of the water droplets, and the coverage rate k₂, perimeter L_max, shape factor f_c, and eccentricity E_max of the maximum water droplet. Then, the maximum value Δx_max, the minimum value Δx_min, and the average value Δx_av of the change rate of each feature value between adjacent HCs, and the volatility Δs of each feature value, were used as the evaluation indexes for features optimization. After this features optimization, the five features that are most closely related to the HC were obtained. Lastly, a recognition model of the HC with the five features as input and the seven HCs as output was established. When compared with the spray method and the contact angle method, the correct rate of the proposed recognition method was 98.1% and 95.2%, respectively. The influence of subjective factors on the spray method was effectively overcome.

Umbrella‐type structure, the material of insulators and surface positions influence the wetting process of polluted insulator surfaces tremendously. Using a custom‐made phase‐angle‐difference (PAD) detection device, the PAD of the different positions of different polluted insulators is measured, and the PAD curves and partial pollution surface electrical conductivity γ ₂₀ varying with time are plotted. The results show that there is a certain difference in the wetting characteristics of different positions. The saturated wetting time of different positions of LXAY‐70 insulators is 12.5–15 min; that for LXHY5‐70 insulators is 12–25 min; that for XWP2‐70 insulators is 8–14 min; and that for FXBW‐10/70 insulators is 18–26.5 min. The umbrella‐type structure is shown to have a direct effect on the wetting process of polluted insulators. The complicated umbrella‐type structure, especially the existence of umbrella ribs, causes an uneven degree of wetting between the upper and lower surfaces, and leads to the increase of the difference in wetting state between the different positions. Furthermore, there is a certain difference in the wetting speed of insulators comprised of different materials. Hydrophilic porcelain and glass insulators are more easily wetted than composite insulators, even though the hydrophobicity class of composite insulators is 7.