Excessive humidity is not simply a sealing issue; its essence is moisture penetration driven by partial pressure differences. Even if the total pressure of SF₆ inside the equipment is high, the water vapor partial pressure may still be much lower than that of the outside atmosphere (with a pressure difference up to 111 times).
Due to their V-shaped structure and an equivalent diameter of only 0.7 times that of SF₆, water molecules can penetrate microscopic gaps in sealing materials, leading to gradual moisture accumulation.
Chemical Corrosion: When the temperature exceeds 200 °C and moisture is present, SF₆ hydrolyzes to form hydrofluoric acid, corroding key components such as arc extinguishing chambers.
Insulation Failure: Moisture condenses at low temperatures, forming conductive paths on the surface of insulation parts, reducing flashover voltage and causing breakdown accidents.
- Gravimetric Method: A reference method that measures weight after moisture absorption by desiccants. It features high accuracy but cumbersome operation.
- Cooled-Mirror Dew-Point Method: A high-precision mainstream technique that measures temperature via mirror condensation (dew point down to -60 °C, accuracy ±0.2 °C).
- Electrolytic Method: Specialized for trace moisture analysis using P₂O₅ to electrolyze water. It has fast response and is suitable for on-line monitoring.
- Alumina Resistance-Capacitance Method: The sensor is small in size and fast in response, but requires regular calibration.
Excessive humidity is a comprehensive problem involving gas physics, material penetration, chemical corrosion, and electrical insulation technology.
Fundamental safety of power equipment can be ensured only by understanding the penetration mechanism, identifying the nature of hazards, and implementing long-term monitoring with precise detection instruments (e.g., cooled-mirror dew-point meters).