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SF6 Ring Main Unit Switchgear: Foam and Recovery—Balancing Environmental Protection with Safety

Release time:

2025-09-29

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Abstract

In the "capillaries" of the power system, SF6 ring main switchgear acts like a sophisticated neural node, bearing the core responsibility for urban power supply. However, when equipment is exposed to fire or gas leaks, the conflict between conventional firefighting methods and environmental protection requirements—and the safety risks involved in the equipment recovery process—have become a dual challenge that the industry urgently needs to address.

I. Foam Fire Extinguishing: The Environmental Dilemma of Traditional Methods

When an arc fault occurs inside an SF6 ring main unit, traditional foam fire suppressants can quickly extinguish visible flames—but they secretly pose significant ecological risks. For instance, in a substation incident in 2023, after staff used fluorinated protein foam to put out the fire, residual chemicals from the foam reacted with decomposition products of SF6 gas, generating corrosive hydrofluoric acid. This led to the peeling off of insulator surface coatings, causing equipment repair costs to soar by 300%. Even more alarming, surfactants in the foam seeped into the soil via the drainage system, resulting in widespread withering of vegetation within a 0.5-kilometer radius and causing the soil pH level to plummet sharply—from 6.8 to as low as 4.2.

A breakthrough in eco-friendly fire suppression technology is urgently needed. The heptafluoropropane gas fire suppression system, with its excellent electrical insulation properties and rapid vaporization characteristics, has emerged as a viable alternative. In real-world testing at a smart substation in Shenzhen, the system successfully reduced oxygen concentration to 12% within just 8 seconds—without leaving behind any conductive residues—while achieving a 98% equipment restart success rate. Meanwhile, the thermal aerosol fire suppression system employs a dual mechanism of physical cooling and chemical inhibition, effectively limiting the heat release rate to below 0.2 MW during the early stages of a fire, thereby providing operations and maintenance personnel with more than 15 minutes of safe time to respond effectively.

II. Leakage Management: From Passive Response to Proactive Defense

The "invisible killer" characteristic of SF6 gas leaks makes detection technology a critical line of defense. While contact-type leak detectors can pinpoint leakage points at concentrations as low as 0.1 ppm, they pose an electric arc risk in energized environments. In contrast, breakthrough applications of infrared imaging leak detectors allow operations and maintenance personnel to scan equipment from up to 5 meters away. By leveraging the gas's ability to absorb specific wavelengths of infrared light, these detectors generate thermal maps on the screen, clearly highlighting leak locations. During the power security period for the 2024 Hangzhou Asian Games, this advanced technology successfully identified three minor leaks, preventing a potential major hazard that could have triggered a widespread regional blackout.

The limitations of conventional local wrapping methods have spurred innovation in intelligent monitoring systems. A certain company has developed an SF6 laser sensor array that uses a distributed fiber-optic network to collect real-time gas density data, complemented by AI algorithms to predict leakage trends. In a pilot project at a 220kV substation in Nanjing, the system issued an early warning 48 hours ahead of time about a valve-body seal-ring aging leak, effectively shifting the approach from "reactive repairs" to "proactive maintenance"—resulting in a 60% reduction in annual maintenance operations.

III. Equipment Restoration: The Art of Balancing Safety and Efficiency

Restoring equipment after a fire is akin to "dancing on the tip of a needle." A simulation experiment conducted by a certain power research institute revealed that damp equipment, if not thoroughly treated, experienced an 82% drop in insulation resistance within 72 hours, sharply increasing the risk of secondary breakdown. According to industry standards, the recovery process must follow the "Three-Step Purification Method": First, three cycles of purging and flushing are performed using high-purity nitrogen gas to reduce impurity levels to below 0.01%. Next, a vacuum pump is used to evacuate the system down to pressures below 133 Pa for four continuous hours, effectively removing adsorbed moisture. Finally, fresh gas—filtered through molecular sieves—is injected to ensure that the trace moisture content remains at or below 50 μL/L.

Building a robust safety protection system is equally critical. During the restoration work at a substation in Guangzhou, operations and maintenance personnel wore positive-pressure air respirators and chemical-resistant gloves, creating a dual-layered barrier. These were complemented by infrared thermometers and partial discharge detectors, forming a three-dimensional monitoring network that integrates "personnel, equipment, and environment." Data shows that this system reduced the average time workers were exposed to harmful gases from 12 minutes to just 3 minutes, while also driving down occupational health complaint rates by 90%.

IV. Green Transformation: The Technology Revolution Shapes the Future of the Industry

Environmental pressures are compelling the industry to accelerate technological innovation. The rise of solid-insulated ring main units, which replace SF6 gas with epoxy resin castings, has slashed lifecycle carbon emissions by 76%. In the grid construction project in Xiong'an New Area, this technology has already been deployed on a large scale at the 24kV voltage level, reducing the annual leakage per unit from 5kg to just 0.02kg. Meanwhile, the development of plant-based insulating gases has opened up a third, groundbreaking technological pathway. A research team has successfully synthesized a C5F10O mixed gas that boasts a GWP value only 1% of SF6’s, while maintaining 98% of its insulation strength. This innovative gas has now completed successful grid integration and operation in 10kV ring main units.

Driven by both policy and market forces, the green equipment certification system is steadily becoming more robust. The EU’s IEC/EN 62271-200 standard has introduced a new "Environmental Performance Rating," categorizing equipment into three levels: Bronze, Silver, and Gold. Meanwhile, the release of China’s "SF6 Alternative Technology Promotion Catalog" has further paved the way for eco-friendly products, creating a streamlined pathway to market adoption. Looking ahead, by 2030, it’s anticipated that eco-friendly products will account for over 60% of China’s medium-voltage switchgear market, fundamentally transforming the traditional approach of "trading gas for safety."

When the balance between environmental protection and safety calls for precise calibration, technological innovation is already crafting new answers. From the gentle fire suppression of heptafluoropropane to the pinpoint early warnings provided by laser sensing, from the revolutionary shift toward solid insulation to the green transformation sparked by plant-based gases, the power industry is leveraging science and technology to not only keep cities brightly lit but also safeguard the Earth’s vibrant blue skies.

Key words:

High-voltage switchgear ensures stable operation of power plants in grid transformation applications.

Indoor Complete Equipment Safety Checklist: Conduct Regular Self-Inspections to Prevent Problems Before They Occur

Hunan Chengyuan Electrical CO.,LTD

SF6 Ring Main Unit Switchgear: Foam and Recovery—Balancing Environmental Protection with Safety