1、 Characteristics of sulfur hexafluoride (SF ₆)

Sulfur hexafluoride is a colorless, odorless, non-toxic, and non flammable synthetic gas that is stable at room temperature and pressure. Its characteristics can be summarized as "duality": on the one hand, it has extremely excellent electrical performance, and on the other hand, it has potential huge environmental risks.

1. Excellent performance

• insulation performanceThe dielectric strength (insulation ability) of SF ₆ is very high, about 2.5-3 times that of air under a uniform electric field. This means that under the same voltage, devices using SF ₆ can be made smaller in size.

• Powerful arc extinguishing abilityThis is one of the core values of SF ₆. As an arc extinguishing medium in circuit breakers, its arc extinguishing capacity is more than 100 times that of air. It can quickly absorb arc energy, making it difficult for the arc to reignite after the current crosses zero, thus safely cutting off high voltage and high current.

• Excellent thermal and chemical stabilityAt room temperature, SF ₆ is very stable and does not react with metals, insulation materials, etc., ensuring long service life and reliability inside electrical equipment.

• Good thermal conductivityThe thermal conductivity of SF ₆ is better than that of air, which can more effectively dissipate the heat generated during the operation of electrical equipment and facilitate equipment heat dissipation.

Main application areasBased on the above characteristics, SF ₆ is widely used inHigh voltage and ultra-high voltage power systemsChinese

• Gas insulated composite apparatus

• high-voltage circuit breaker

• Transformers, bushings, etc. for high-voltage transmission lines

• Some special scientific research and equipment (such as electron accelerators, tracer gases, etc.)
  

  2. Potential risks and environmental issues

  Strong greenhouse effectThis is the most serious environmental problem in SF. It is explicitly regulated under the Kyoto ProtocolOne of the six major greenhouse gases.

• Global warming potentialThe impact of 1 kilogram of SF ₆ on global warming is equivalent to22.8 tons of carbon dioxideIt is CO ₂22800 times.

• Extremely long atmospheric lifespanThe lifespan of SF ₆ in the atmosphere can reach3200 yearsOnce leaked, its contribution to the greenhouse effect is long-term and irreversible.

• Toxicity of decomposition productsPure SF ₆ is non-toxic, but when electric arcs, corona discharges, or spark discharges occur inside electrical equipment, it will decompose and produce various toxic and corrosive substances (such as sulfuryl fluoride SOF ₂, disulfide decafluoride S ₂ F ₁ ₀, HF, etc.). These substances are harmful to the human body and corrosive to equipment.

• suffocation riskAlthough non-toxic, SF ₆ is about 5 times heavier than air and can easily accumulate in enclosed and poorly ventilated spaces such as cable trenches and equipment room bottoms

2、 Application conditions of SF gas detector

Due to the strong greenhouse effect, potential decomposition toxicity, and suffocation risk of SF ₆, accurate and reliable detection is crucial. The SF gas detector is mainly used in the following working conditions:

1. Leakage detection and localization

This is the most common application scenario. The purpose is to ensure the sealing of power equipment, prevent SF ₆ gas leakage into the atmosphere, and ensure that the gas pressure inside the equipment is within the normal working range.

• Application scenarios：

• Equipment installation and debuggingNewly installed GIS, circuit breakers, and other equipment need to undergo comprehensive leak detection after inflation.

• Regular inspection and maintenanceConduct periodic leakage surveys on SF ₆ electrical equipment in operation.

• troubleshootingWhen the device emits a "low pressure alarm" or "abnormal pressure" signal, it is used to accurately locate the leakage point.

• Type of detector：

• portable leak detector: Usually usedInfrared absorption methodHigh sensitivity, equipped with sound and light alarms, the probe can move flexibly and is used to scan various connection parts, welds, and sealing surfaces of the equipment.

2. Environmental safety monitoring (indoor/enclosed space)

To prevent SF ₆ from accumulating in the equipment room and posing a risk of hypoxia or poisoning from decomposition products, continuous environmental monitoring is required in specific areas.

• Application scenarios：

• GIS room/switch stationInstall a fixed SF gas concentration monitoring and alarm system.

• Cable layer, underground channelThese low-lying areas are the easiest places for SF to accumulate.

• Type of detector：

• Fixed online monitoring systemInstall multiple detection probes at different heights in the room (especially near the ground, as SF ₆ is heavier) to monitor SF ₆ concentration in real-time.

• function：

1. Hypoxia alarmWhen the SF ₆ concentration (or oxygen content) reaches a preset threshold (usually oxygen below 19.0% or SF ₆ concentration reaching 1000ppm), an audible and visual alarm is activated.

2. Automatic linkage ventilationThe alarm signal can automatically activate the exhaust system and force ventilation.

3. remote monitoringUpload the alarm signal to the main control room to remind the operators.

3. Gas purity and decomposition product analysis

Used to evaluate the quality of SF ₆ gas inside the equipment and determine whether there are latent faults (such as partial discharge, overheating, etc.) inside the equipment.

• Application scenarios：

• Acceptance before equipment operationEnsure that the purity of the SF ₆ gas filled is qualified.

• Regular supervision testAccording to regulations, regularly take samples from the equipment to analyze gas purity and decomposition product content.

• fault diagnosisWhen there is suspicion of abnormal discharge or overheating inside the equipment, the type and severity of the fault can be determined by analyzing the type and concentration of decomposition products.

• summary

• Detection Type	main purpose	application conditions	Common detection techniques
  leak detection	Locate the leakage point to prevent gas leakage	Equipment installation, inspection, and troubleshooting	infrared absorption
  environmental monitoring	Prevent suffocation and poisoning, ensure personnel safety	GIS room, cable trench and other enclosed spaces	Fixed sensor (often using infrared principle)