The composite crossarm insulator differs greatly from the suspension insulator in structure and arrangement. This study aims to determine the pollution flashover characteristics of composite crossarm insulators under different voltage grades. Four types of AC composite crossarm insulators with diameters ranging from 100 mm to 450 mm are subjected to artificial pollution test, and then the effects of the surface hydrophobicity state of silicone rubber, core diameter, umbrella structure, arrangement, and insulation distance on the pollution flashover voltage of the composite crossarm insulators are analyzed. Under the pollution grade 0.2/1.0 mg/cm² and voltage grade from 66 kV to 1000 kV, if the silicone rubber surface changes from HC5 to HC6, the pollution flashover voltage of the composite crossarm insulator will increase by 13.5% to 21.0% compared with the hydrophilic surface. If the core diameter changes from 100 mm to 300 mm, the pollution flashover voltage gradient decreases with the increase in core diameter; if the core diameter changes from 300 mm to 450 mm, the pollution flashover voltage gradient increases with core diameter. Under the same insulation height and core diameter, the umbrella structure will have a certain impact on pollution flashover voltage by up to 1.7% to 5.4%. Under the horizontal arrangement, the pollution flashover voltage can increase by 10.5% to 12.1% compared with that under the vertical arrangement. Under the hydrophilic surface and weak hydrophobicity state, the pollution flashover voltage has a linear relationship with the insulation distance. The above results can provide a reference for the structural design and optimization of the composite crossarm insulator.

Artificial simulation of rapid insulator contamination can obtain the contamination characteristics of suspension insulators in a short time, providing important reference for the electrical design, operation and maintenance of external insulation. To obtain the contamination characteristics of insulators closer to those under the natural environment, this paper proposed a test method for artificial simulation of rapid natural contamination of insulators using the characteristic parameters of straight-flow wind tunnel, and carried out the artificial rapid natural contamination test of cap and pin insulators under different wind speeds, wind directions, contamination duration and contaminant concentrations. The test results showed that with the wind speed increasing from 2.2 m/s to 7.5 m/s, the contamination degree of insulator surface gradually increased firstly and then decreased, and reached the maximum near 4.5 m/s. With the increase in contaminant concentration, the contamination degree of insulator surface increased, and tended to be saturated when the dust spreading speed was 54 g/min. With the extension of contamination duration, the contaminant accumulation on insulator surface was slow in the initial stage, accelerated in the middle stage, and then slowed down and gradually saturated in the later stage. Under the same contamination conditions, standard, double-shed and triple-shed insulators presented high-to-low equivalent salt deposit density (ESDD) successively on their top and bottom surfaces, and the ratios of ESDD on the top and bottom surfaces were 1:1.20:0.9 and 1:0.63:0.53, respectively.

Composite insulators that have been in service for over 10 years account for more than half of the total number of composite insulators in China. Due to the aging of materials, some composite insulators have to be phased out of the power grid when they approach their service deadline. As the running time increases, the number of waste composite insulators grows year by year. If not disposed properly, the waste composite insulators will cause serious damage to ecological environment. The disposal of waste composite insulators has become an issue that needs to be addressed urgently, so as to ensure the safe, economical and efficient operation of the grid and maintain the healthy and sustainable development of the composite insulator industry. This paper summarizes the status quo of disposing waste composite insulators through a large number of investigations and statistics, and explores the recycling methods of waste composite insulators based on the existing problems. Finally, solutions are provided to recycle waste composite insulators from four perspectives, namely pretreatment before recycling, advanced treatment of silicon rubber, development and verification of recycling products, and recycling and disposal strategy. The recycling and disposal strategy of waste composite insulators is further improved by providing policy guidance, strengthening management and establishing a sound recycling mechanism. The findings can promote the "recycle, decrease and decontamination" of waste from the power grid, and help China build a new green and eco-friendly grid.

The ±500 kV valve halls of wind farm offshore platforms are integrated through a high-voltage direct current (HVDC) transmission system and constructed in deep-sea conditions, making the design of net air clearance distances particularly critical. This paper investigates key factors influencing air clearance distances associated with the impulse overvoltage characteristics of the main equipment in the valve hall. Based on the preliminary design of a ±500 kV offshore converter valve hall, critical air gaps were determined. The full-scale samples were employed to conduct standard switching impulse overvoltage tests. In this way, the overvoltage discharge characteristics of air gaps in the offshore converter valve hall were obtained. Finally, based on the air gap configuration method and the obtained discharge characteristic data, a recommended net air clearance distance range is proposed for the ±500 kV valve hall of the offshore platform, providing a vital reference for the compact design of offshore wind farm valve halls.