Application NoteTrace Moisture Measurement in SF6 Gas Sulfur hexafluoride (SF6) is a critical insulating and arc-quenching gas widely used in high-voltage electrical equipment. Ensuring the purity of SF6, especially controlling trace moisture levels, is essential for safe and reliable operation. This application note highlights the significance of trace moisture measurement in SF6 gas, common moisture-related issues, effective solutions, and references to key standards. What is SF6 Gas? SF6 is a colourless, odourless, non-flammable gas with exceptional dielectric properties. Its high electro negativity and thermal stability make it ideal for use in: • Circuit breakers The ability of SF6 to withstand high voltages and suppress electrical arcs has made it indispensable in modern power transmission and distribution systems. SF6 gas is used in cables and busbars as a high-performance electrical insulator and arc quencher in gas-insulated switchgear (GIS). It allows for more compact equipment designs compared to air-insulated systems because its superior dielectric strength enables conductors to be placed closer together. In circuit breakers, SF6 gas is also used to instantly extinguish the arc that forms when a circuit is opened. • High dielectric strength: SF6 has a much higher dielectric strength than air, meaning it can withstand higher voltages before an arc forms, allowing for smaller clearances between live parts and grounded components. • Protection: This insulation is crucial in medium and high-voltage switchgear, protecting the live parts and preventing electrical arcing in normal operation. • Arc interruption: When a circuit breaker opens to interrupt a fault, an electrical arc is created. • Quenching process: A blast of pressurized SF6 gas is directed overthe arc, which rapidly cools it and absorbs free electrons, increasing the gas’s dielectric strength to extinguish the arc. • Self-healing property: After quenching the arc, the SF6 gas molecules can “self-heal” by recombining, which is a key feature for its repeated use in switchgear.

Application Note Trace Moisture Measurement in SF6 Gas Benefits in Cables and Busbars • Compact designs: The superior insulating properties allow for gas-insulated substations that are significantly smaller (about one-tenth the size) than conventional air-insulated ones, which is especially beneficial in areas with limited space. • Reliability: The dry, inert gas environment protects internal components from moisture, dust, and UV radiation, leading to a longer equipment life and less frequent maintenance requirements for internal components. Despite its stability, moisture contamination in SF6...