SF6-Free Solution for Air-Insulated/Eco-friendly Gas Ring Main Units

Ⅰ. Technical Bottlenecks of SF₆ Substitution

1. Insulation Medium Performance Gap
   o Dried Air/N₂ insulation strength is only 1/3 of SF₆, requiring expansion of contact gap from 60mm to ≥150mm.
   o Conventional spring mechanisms lack energy to drive rapid closure of large gaps, easily causing contact ablation due to pre-strike.
   o Synthetic gases (e.g., C4+CO₂) decompose under arcing, leading to irreversible insulation degradation.

2. Mechanical Structural Limitations
   o National Grid standardization fixes cabinet width at 420mm, restricting longitudinal space.
   o Large gaps necessitate longer moving blades in three-position disconnectors, increasing insulation design difficulty.

II. Core Solutions and Technological Innovations (I) Insulation System Enhancement Design

Technical Direction

Implementation

Effect

Composite Insulation

Moving blade + high-strength insulation cover + PTFE partition

Blocks discharge path; withstands lightning impulse voltage (≥125kV)

Medium Synergy Optimization

Dried Air/N₂ fill + vacuum interrupter core

Vacuum interrupter ensures breaking; gas insulation maintains isolation

Zero-Gauge Reliability

Cabinet passes power frequency/lightning impulse tests (ambient pressure)

No leakage risk; maintenance safety equals sealed cabinets

Key Breakthrough: Achieves SF₆-grade insulation at 150mm gap, overcoming medium limitations.

(II) Three-Position Disconnector Dynamic Optimization

• Rotational Inertia Reduction:Extended nylon main shaft → Improved angular velocity conversion → Closing speed >4m/s (enables 20kA short-circuit making while suppressing pre-strike <1ms).
• Moving Blade Design: Insulation-clad extended blade ensures earth/phase clearance ≥180mm at open position.
• Earthing Capability: Lower disconnector equipped with E2-class contacts (withstands 5 short-circuit making operations).

III. Key Technical Parameter Comparison

Parameter

SF₆ Ring Main Unit

Air/Eco-friendly Gas Solution

Contact Gap

60mm

≥150mm (incl. insulation cover)

Closing Speed

Adequate for springs

Optimized shaft + lightweight blade

Breaking Medium

SF₆ gas

Vacuum interrupter + dried air

Zero-Gauge Withstand

Fails

Passes 42kV power freq./75kV LI

Environmental Impact

GWP=23,900

GWP=0 (dried air)

IV. Engineering Implementation Assurance

1. Insulation Verification Process
   o Phase 1: 3D electric field simulation (gap field strength <3kV/mm)
   o Phase 2: Full/cutoff lightning impulse tests (±200kV)
   o Phase 3: Repeated insulation tests post E2-class short-circuit making

2. Mechanism Reliability Strategy
   o Hexagonal nylon shaft: Deformation-resistant lifespan >10,000 ops
   o Three-position mechanical interlock: Mandatory anti-misoperation locking
   o Making characteristic monitoring: Displacement sensors provide real-time closing speed curves

V. Solution Advantages Summary

• Leakage-Free Safety: Ambient pressure operation eliminates gas dependency; insulation failure risk approaches zero
• Full Compatibility: Dimensions/interfaces fully comply with National Grid 420mm standard
• Maintenance-Free Design: Vacuum interrupter lifespan >20 years; no gas replenishment needed
• 100% Eco-Friendly Path: Dried air enables carbon neutrality; zero F-gas management cost