Why Test SF₆ Gas in Switchgear?

The Gas Can Tell You About the Condition Inside the Equipment.

Pure SF₆ is used in gas-insulated switchgear, but over time the gas compartment can accumulate water vapor through permeation and desorption from internal materials. Under high-energy electrical discharge conditions, reactions involving SF₆ and water-related constituents can form decomposition products, including SO₂ and HF, which can be corrosive to internal components.  Monitoring gas condition therefore provides valuable information for preventive maintenance and equipment condition assessment.

SF₆ Humidity & Dew Point Measurement

Know How Much Moisture Is in the Gas.

Moisture is a critical SF₆ gas-quality parameter.  The 973-SF₆ uses chilled mirror technology to determine frost/dew point. A polished mirror is cooled until condensation forms, and the mirror temperature at that condition is precisely measured. Unlike a replaceable humidity sensor, the chilled mirror determines moisture from the physical condensation point.

Measurement Range

• Frost/Dew Point: −50 to +20°C
• Humidity by Volume: 40–20,000 ppmv
• Humidity by Weight: 5–2,500 ppmw
• Frost/Dew Point Accuracy: ≤ ±0.5°C
• ppmv / ppmw Accuracy: ≤ ±1 ppm + 6% of reading

Water Vapor Can Affect SF₆ Gas Quality and Equipment Condition.

Water vapor can enter gas compartments through permeation and desorption from internal materials. While SF₆ and water vapor do not normally react directly, high-energy electrical discharge can create conditions that produce decomposition compounds, including SO₂ and HF.

For that reason, accurate and repeatable humidity measurement is an important part of SF₆ gas-quality assessment and GIS preventive-maintenance programs.

Customer Challenges

Moisture Is Increasing – “Is water vapor accumulating inside the gas compartment?”

Measure dew/frost point and moisture concentration using direct chilled mirror technology.

Gas Purity Has Changed – “Is the SF₆ concentration still where we expect it to be?”

Measure SF₆ concentration from 80–100% in the same instrument used for humidity measurement.

Electrical Decomposition May Be Occurring – “Are decomposition by-products beginning to appear?”

Optional SO₂ measurement provides another parameter for assessing SF₆ condition.

Every Test Uses SF₆ – “How do we test gas quality without unnecessarily releasing SF₆?”

The integrated containment and recovery system captures the sample and allows it to be returned to the equipment.

SF₆ COUPLINGS