SISとガス絶縁の比較：環境の視点

はじめに

The global push toward sustainable infrastructure is reshaping how engineers and procurement managers evaluate medium voltage switchgear. For decades, SF6 gas-insulated switchgear dominated compact substation design — but SF6 carries a global warming potential of 23,500 times that of CO₂¹, and regulatory pressure to phase it out is accelerating across the EU, North America, and Asia-Pacific. Solid-insulated switchgear (SIS) has emerged as the definitive SF6-free alternative for medium voltage power distribution, delivering equivalent dielectric performance without the environmental liability of gas insulation across its entire lifecycle. For EPC contractors specifying new substations, utility engineers managing long-term asset portfolios, and procurement managers navigating tightening ESG compliance requirements, this comparison is no longer academic — it directly determines which technology earns project approval in 2025 and beyond. This guide delivers a rigorous, engineering-grounded environmental comparison between SIS and gas-insulated switchgear.

目次

• What Is SIS Switchgear and How Does Its Insulation System Work?
• How Do SIS and Gas-Insulated Switchgear Compare Across Environmental Metrics?
• In Which Power Distribution Applications Does SIS Switchgear Deliver the Greatest Environmental Advantage?
• What Lifecycle and Maintenance Factors Determine the True Environmental Cost of SIS vs GIS?
• FAQs About SIS Switchgear vs Gas-Insulated Switchgear

What Is SIS Switchgear and How Does Its Insulation System Work?

Solid-insulated switchgear (SIS) is a medium voltage switching technology in which all live components — busbars, vacuum interrupters, current-carrying contacts, and connection terminals — are fully encapsulated in solid dielectric material, typically cast epoxy resin or cross-linked polyethylene (XLPE). This eliminates the need for any insulating gas medium, including SF6, to maintain dielectric isolation between phases and between live parts and the grounded enclosure.

The insulation architecture operates on a fundamentally different principle from gas-insulated switchgear. Rather than relying on pressurized gas to suppress ionization and maintain dielectric strength, SIS uses the molecular structure of solid polymer materials to provide permanent, maintenance-free electrical isolation. The vacuum interrupter handles arc interruption during switching operations, while the solid encapsulation manages steady-state insulation.

Key Technical Specifications of SIS Switchgear

• 定格電圧： 12 kV / 24 kV / 40.5 kV (medium voltage range)
• Insulation Material: Cast epoxy resin (dielectric strength: 20–25 kV/mm) or XLPE
• Insulation Standard: IEC 62271-200, IEC 62271-1
• サーマルクラス： Class F (155°C) or Class H (180°C) depending on epoxy formulation
• Protection Rating: IP67 standard — fully sealed against moisture and particulate ingress
• Arc Interruption: Vacuum interrupter (VI) technology — zero SF6, zero oil
• 沿面距離： ≥125 mm per kV for outdoor-rated solid insulation (IEC 60815)
• **Mechanical Endurance: ≥10,000 operating cycles per IEC 62271-100²

Core Insulation Properties of Solid Dielectric Systems

• Zero gas pressure dependency: Dielectric performance is independent of ambient pressure or altitude
• No moisture sensitivity: Solid encapsulation eliminates the dew point management required in SF6 systems
• Self-contained insulation: No external monitoring equipment (gas density relays, pressure gauges) required
• Pollution immunity: Fully encapsulated conductors are unaffected by salt fog, industrial pollution, or condensation

How Do SIS and Gas-Insulated Switchgear Compare Across Environmental Metrics?

The environmental case for SIS switchgear over gas-insulated alternatives rests on four quantifiable dimensions: greenhouse gas emissions, end-of-life disposal, manufacturing footprint, and operational environmental risk. Each dimension reveals a structural advantage for solid insulation that compounds over the equipment lifecycle.

SF6 gas does not degrade naturally in the atmosphere. Its atmospheric lifetime exceeds 3,200 years³, meaning every kilogram released during manufacturing, maintenance, or end-of-life disposal remains climatically active for millennia. A single 12 kV GIS panel contains approximately 1.5–3 kg of SF6. At a GWP of 23,500, this represents a CO₂-equivalent burden of 35–70 tonnes per panel — before accounting for any operational leakage over a 30-year service life.

SIS vs Gas-Insulated Switchgear: Environmental Comparison

環境パラメータ	SISスイッチギア	SF6 Gas-Insulated Switchgear
Insulation Medium GWP	Zero (solid epoxy)	23,500× CO₂ (SF6 gas)
Operational Gas Leakage Risk	なし	0.1–0.5% annual leakage per IEC 62271-2034
End-of-Life Gas Recovery Required	いいえ	Yes — mandatory certified recovery
Disposal Complexity	Epoxy recycling / landfill (regulated)	Hazardous gas handling + enclosure disposal
Manufacturing Carbon Footprint	Low–Medium (epoxy casting)	Medium–High (SF6 production + filling)
Regulatory Compliance Risk	最小限	High — EU F-Gas Regulation, EPA SNAP
Lifecycle Environmental Cost	低い	ミディアム-ハイ

Real-World Case: ESG-Driven Specification Switch in a European Utility Project

A procurement manager at a Northern European utility contacted us during the specification phase of a 24 kV urban distribution substation project. Their internal ESG committee had flagged SF6-containing equipment as incompatible with the company’s 2030 net-zero commitment, and local environmental regulators required a written SF6 mitigation plan for any new installation. We supplied a twelve-panel SIS switchgear lineup rated at 24 kV / 630 A, eliminating approximately 420 kg of SF6 equivalent — or 9,870 tonnes CO₂-equivalent — from the project’s environmental liability register. The procurement manager noted that the SIS specification also simplified the project’s environmental impact assessment by removing the gas handling and monitoring requirements entirely.

In Which Power Distribution Applications Does SIS Switchgear Deliver the Greatest Environmental Advantage?

The environmental advantage of SIS switchgear is not uniform across all applications — it is most pronounced in scenarios where SF6 leakage risk is elevated, regulatory scrutiny is highest, or end-of-life gas recovery is logistically difficult.

Step 1: Define Voltage and Load Requirements

• Confirm system voltage: 12 kV, 24 kV, or 40.5 kV
• Specify rated normal current: 400 A / 630 A / 1250 A per feeder
• Verify short-circuit withstand: typically 20 kA or 25 kA for 3 seconds

Step 2: Evaluate Environmental Sensitivity of the Installation Site

• Indoor urban substations: High regulatory visibility — SIS eliminates SF6 monitoring obligations
• Altitude above 1,000 m: SF6 gas density drops with altitude; SIS performance is altitude-independent
• High ambient temperature zones: Solid insulation thermal class F/H outperforms gas systems in sustained high-temperature environments

Step 3: Align with Applicable Environmental Standards and Certifications

• EU F-Gas Regulation (EU) 2024/573 — restricts SF6 use in new switchgear from 2030⁵
• IEC 62271-200 — covers both SIS and GIS; SIS units carry no gas-related annexes
• ISO 14001 Environmental Management — SIS installations simplify environmental compliance documentation

Application Scenarios Where SIS Environmental Advantage Is Maximum

• Renewable Energy Substations: Solar and wind collection substations increasingly specify SF6-free equipment under green financing covenants — SIS is the primary beneficiary
• Urban Underground Power Distribution: Confined spaces amplify SF6 leakage risk to personnel; SIS eliminates this hazard entirely
• Industrial Campus Microgrids: Manufacturing facilities with ISO 14001 certification require documented SF6-free equipment lists — SIS simplifies compliance
• Coastal and Marine Environments: Salt fog accelerates SF6 enclosure corrosion, increasing leakage probability; SIS solid encapsulation is inherently corrosion-resistant
• Developing Market Grid Expansion: Regions without certified SF6 recovery infrastructure benefit from SIS technology, which requires no gas handling at any lifecycle stage

What Lifecycle and Maintenance Factors Determine the True Environmental Cost of SIS vs GIS?

Lifecycle Maintenance Best Practices for SIS Switchgear

1. Inspect epoxy encapsulation surfaces annually — check for tracking marks, surface cracks, or contamination deposits that indicate insulation stress
2. Verify vacuum interrupter integrity every 5 years using contact resistance measurement (should be <100 µΩ per IEC 62271-100)
3. Test operating mechanism — confirm spring charge time and closing/opening force within manufacturer tolerance
4. Check earthing continuity on all enclosure panels — solid insulation does not self-heal; earthing integrity is the primary safety barrier
5. Record thermal imaging data annually — hot spots in solid-insulated busbars indicate connection degradation before insulation failure occurs

Common Lifecycle Mistakes That Increase Environmental and Safety Risk

• Ignoring surface tracking on epoxy: Early-stage tracking on solid insulation is reversible with cleaning and re-coating — neglecting it leads to irreversible insulation breakdown and forced replacement, generating unnecessary waste
• Skipping vacuum interrupter end-of-life assessment: VI units have a defined mechanical and electrical endurance limit; operating beyond rated cycles increases arc interruption failure risk without any visible warning
• Incorrect disposal of epoxy components: Cast epoxy resin is classified as non-hazardous solid waste in most jurisdictions but requires segregated disposal — mixing with metal scrap streams contaminates recycling processes
• Assuming zero-maintenance due to SF6 absence: SIS requires less maintenance than GIS but is not maintenance-free — the absence of gas monitoring creates a false perception of complete passivity that leads to deferred inspections

結論

Solid-insulated switchgear represents a genuine structural shift in how medium voltage power distribution equipment is evaluated — not just on electrical performance, but on lifecycle environmental accountability. By eliminating SF6 gas entirely, SIS switchgear removes the most significant environmental liability in conventional switchgear design, while delivering equivalent dielectric performance, superior pollution immunity, and dramatically simplified end-of-life handling. The key takeaway: for any power distribution project where environmental compliance, ESG commitments, or long-term lifecycle cost transparency are decision criteria, SIS switchgear is not merely the greener choice — it is the strategically correct one.

FAQs About SIS Switchgear vs Gas-Insulated Switchgear

1. “Fluorinated Gas Emissions”, https://www.epa.gov/ghgemissions/fluorinated-gas-emissions. [The EPA identifies SF6 as having a 100-year global warming potential of 23,500, supporting the article’s climate-impact comparison against CO₂.] Evidence role: statistic; Source type: government. Supports: The claim that SF6 has an extremely high global warming potential compared with carbon dioxide. ↩

2. “Basic Function Vacuum Circuit Breaker 0-12kV 75kVp 31.5kA 3s 1250A 210 IEC”, https://www.se.com/id/en/product/EXE123112L1B/basic-function-vacuum-circuit-breaker-012kv-75kvp-31-5ka-3s-1250a-210-iec/. [Schneider Electric’s IEC-rated vacuum circuit breaker data lists 10,000 mechanical operating cycles, supporting the endurance benchmark used for medium voltage switching equipment.] Evidence role: statistic; Source type: industry. Supports: The mechanical endurance value stated for vacuum interrupter-based switchgear. Scope note: This supports the cited operating-cycle benchmark as an industry product example, not a universal rating for every SIS design. ↩

3. “Free Alternative Medium and High Voltage Circuit Breakers”, https://www.epa.gov/sites/default/files/2020-10/documents/sf6_alternatives_webinar_091420.pdf. [EPA training material states that SF6 has environmental persistence of 3,200 years, supporting the article’s long-term atmospheric-impact claim.] Evidence role: statistic; Source type: government. Supports: The claim that released SF6 remains climatically relevant for millennia. Scope note: Some recent assessments report revised atmospheric lifetimes, but this source supports the 3,200-year value used in the article. ↩

4. “SF6 Leak Rates from High Voltage Circuit Breakers”, https://www.epa.gov/system/files/documents/2022-05/leakrates_circuitbreakers.pdf. [The EPA paper notes that the IEC standard for new SF6 equipment leakage is 0.5 percent per year, supporting the upper bound of the leakage range in the environmental comparison table.] Evidence role: statistic; Source type: government. Supports: The stated annual leakage benchmark for SF6 gas-insulated equipment. Scope note: The source directly supports the 0.5% IEC upper-bound figure; lower real-world rates may vary by equipment age, design, and maintenance quality. ↩

5. “F-Gas Regulation (Regulation (EU) 2024/573)”, https://www.esbnetworks.ie/services/get-connected/renewable-connection/f-gas-regulation. [ESB Networks summarizes Regulation (EU) 2024/573 phase-out dates, including the 2030 prohibition for medium voltage switchgear above 24 kV up to and including 52 kV.] Evidence role: general_support; Source type: government. Supports: The claim that EU F-Gas rules restrict SF6 use in new medium voltage switchgear from 2030. Scope note: The same regulation also introduces earlier 2026 restrictions for switchgear up to and including 24 kV. ↩