Ⅰ. Technical Bottlenecks of SF₆ Substitution (I) Insulation Medium Performance Gap
Dried Air/N₂ insulation strength is only 1/3 of SF₆, requiring expansion of contact gap from 60mm to ≥150mm.
Conventional spring mechanisms lack energy to drive rapid closure of large gaps, easily causing contact ablation due to pre-strike.
Synthetic gases (e.g., C4+CO₂) decompose under arcing, leading to irreversible insulation degradation.
(II)Mechanical Structural Limitations
National Grid standardization fixes cabinet width at 420mm, restricting longitudinal space.
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
(I)Insulation Verification Process
Phase 1: 3D electric field simulation (gap field strength <3kV/mm)
Phase 2: Full/cutoff lightning impulse tests (±200kV)
Phase 3: Repeated insulation tests post E2-class short-circuit making
(II)Mechanism Reliability Strategy
Hexagonal nylon shaft: Deformation-resistant lifespan >10,000 ops
Three-position mechanical interlock: Mandatory anti-misoperation locking
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
