Pollution accumulation and the wetting of the contamination layer subsequently formed on the insulator surface are two important factors influencing the pollution flashover of the insulators. To investigate the wetting of contamination layer on the insulator surface, the saturated water absorption of contamination layer on glass specimens was measured in a fog room and the experimental results were analyzed. Under saturated moisture condition, there is a fixed ratio of conductive particles to water molecules in the salt fog that is generated by an ultrasonic humidifier. When the salt fog particles were deposited on the specimens, the surface conductivity of the contamination layer will increase linearly with the salt fog mass deposited. In this paper, a new method was proposed to measure the saturated water absorption of the contamination layer based on the surface conductivity. Based on this method, the influence of non-soluble deposit density (NSDD) and the inclination angle of specimen on the saturated water absorption of the contamination layers were analyzed. The experimental results showed that the saturated water absorption of contamination layer gradually decreased with the increase of inclination angle. With the same NSDD, the saturated water absorption of the contamination layer at the bottom surface of the specimen was less than that of the top surface. The increase of NSDD would lead to an increase of saturated water absorption of the contamination layer under vertical arrangement.

High-temperature-resistant epoxy composites play a crucial role in enhancing the operational reliability and service life of devices such as DC bushings, which is of great significance for the long-term stable operation of ultra-high voltage and flexible power transmission and distribution systems. In this study, the epoxy composite was prepared, and long-term thermal aging tests were conducted at 250 °C and 270 °C. The changes in physical properties, electrical characteristics, and bending strength of epoxy composite were systematically investigated, and the thermal aging mechanism of these materials was elucidated. The experimental results revealed that with the progression of thermal aging, the epoxy composites exhibited volume shrinkage due to the breaking of chemical bonds. After 10 thermal aging cycles at 270 °C, the mass loss rate of the epoxy composite reached 20.52%. At 250 °C, the breakdown strength decreased by 9.9% compared to the unaged state. After aging at 250 °C and 270 °C, the volume resistivity decreased by a maximum of 53.75% and 76.94%, respectively, while the dielectric constant decreased by a maximum of 50.34% and 41.94%, respectively. After 10 aging cycles at 250 °C and 270 °C, the bending strength of the cured epoxy composite decreased by 39.79% and 53.91%, respectively. These findings provide valuable insights into the thermal aging characteristics of epoxy composites used in DC bushings and other electrical devices, offering a scientific basis for material selection and reliability assessment in high-voltage insulation applications.

Due to their hydrophobic properties, composite insulators have excellent anti-pollution flashover performance and have been widely used in power systems. For a better understanding of the flashover characteristics of a hydrophobic surface at wet conditions, the hydrophobic surface is covered with water droplets and water film, respectively, in this paper. The initiation and development of partial arc are observed by an ultrahigh-speed camera and the leakage current is also recorded. It is found that there exists a critical water proportion for a given dry band length and water volume conductivity. Beyond this water proportion, the partial arc does not necessarily lead to the flashover. On the contrary, flashover will take place right after the occurrence of partial arc. Furthermore, it is also found that when the water proportion is below the critical water proportion, the flashover voltage is barely related to the volume conductivity and the flashover voltage generally decreases with the increase of water volume and water droplet number. The results obtained are of great significance to understand the flashover process of hydrophobic surfaces.

Under rain conditions, the sliding water droplets on the insulator’s surface shorten the air insulation distance between the sheds and even cause a flashover. In order to study the mechanism of air gap breakdown with rain droplets, the breakdown process was recorded by a high-speed camera and the influences of rain water droplets (conductivity, volume, and position) were studied. The experimental results show that the impact of the water droplets on the direct current (dc) breakdown voltage is related to the air gap length. The shorter the air gap, the greater the drop of the flashover voltage. Although water conductivity does not affect the breakdown voltages, the arc development path is related to it. This research has significance for revealing the rain flashover mechanism of insulators.