Investigation of the Discharge Characteristics Induced by Free Metallic Particles on Insulation Surfaces Under Low-Pressure Conditions

Metallic particles attached to epoxy resin surfaces can severely distort the local electric field, degrade surface-insulation reliability, and reduce the partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), and flashover voltage (FOV). These adverse effects become more pronounced under low-pressure conditions. To investigate the discharge mechanism of metallic particles on epoxy resin surfaces in high-altitude, low-pressure environments and to assess the effectiveness of conventional online partial discharge (PD) monitoring methods for detecting metallic-particle defects, a low-pressure surface discharge test platform was developed. The motion and discharge behaviors of metallic particles subjected to an electric field were recorded under both atmospheric and reduced-pressure conditions. The PDIV, PDEV, and FOV were systematically measured for epoxy resin specimens with and without metallic particles. In addition, the responses of ultrasonic, transient earth voltage (TEV), and ultra-high-frequency (UHF) sensors to metallic-particle-induced discharges were evaluated. The results showed that, under low-pressure conditions, metallic particles substantially reduced the PDIV, PDEV, and FOV of epoxy resin surface insulation. They also altered the dominant flashover behavior. All three sensing methods can effectively detect discharges caused by free metallic particles, whereas the ultrasonic signal is attenuated as the air pressure decreases.