Gas leakage in SF6 circuit breaker equipment exhibits the following characteristics:
Stealthiness: Leaks cannot be directly observed and require scientific methods for detection.
Impact on Performance: A decrease in gas pressure directly affects the circuit breaker's interruption capability.
Degradation Risks: Repeated refilling of gas, especially under uncontrolled conditions, may lead to excessive moisture content and overall performance deterioration of the circuit breaker.
Diverse Leak Sources: Leaks are not solely caused by seal failures. Other common causes include pinholes in casting ports or welds, improper sealing groove dimensions, and leaks in pressure gauges.
High Maintenance Complexity: Replacing leaking components during a power outage involves significant effort and requires advanced technical skills. Disassembling gas-insulated switchgear (GIS) entails additional safety risks, and decisions must be made between disassembly repairs and pressurized sealing while the equipment remains operational.
Primary Leak Locations and Causes
Leakage primarily occurs at pipe joints, flanges, valves, and welded joints with pinholes, which should be key focus areas during inspection. A small percentage of leaks occur along pipelines or tank bodies and are harder to detect. Main causes include insufficient tightening torque of joints and flanges, thermal expansion and contraction, aging seals, scratches or impurities on sealing surfaces, manufacturing defects, and installation errors.
SF6 Gas Leak Detectors
Detection Methods for SF6 Gas Decomposition Products
Common methods for detecting SF6 gas decomposition products include gas chromatography, mass spectrometry, infrared absorption spectroscopy, detector tubes, chemical analysis, and electrochemical sensors. These methods vary in detection principles, technical requirements, and applications. Gas chromatography, detector tubes, and electrochemical sensors are widely used, with electrochemical sensors being particularly prevalent in field applications due to their practicality. This article focuses on electrochemical sensor technology.
Detection Principle
Electrochemical sensors operate by inducing chemical reactions in the target gas under high-temperature catalytic conditions, altering the sensor's electrical signal output to determine gas composition and concentration. These sensors offer high selectivity and sensitivity, making them suitable for on-site detection of SF6 gas decomposition products.
Detection Instruments
SF6 decomposition analyzers based on electrochemical sensors are widely used for live detection in operational equipment. Key technical requirements include:
Effective and simultaneous detection of SO₂, H₂S, and CO concentrations.
Detection range of at least 100 μL/L for SO₂ and H₂S, and 500 μL/L for CO.
Gas flow rate during detection should not exceed 300 mL/min.
The instrument interface must meet equipment requirements and withstand internal pressure.
Detection Precautions
Results should be expressed in volume ratio and rounded to one decimal place.
Inspect gas pipelines and instrument connections carefully before detection to prevent leakage. Operators should wear protective gear if necessary.
Open gas valves slowly and adjust pressure and flow rate to maintain stability. Monitor equipment pressure throughout the process to prevent pressure drops.
SF6 gas decomposition product detection should be performed on energized equipment only when reliable safety measures are in place.
Emitted gas from the detector must be collected and properly disposed of.