SF₆-Free Solution for Air-Insulated/Eco-friendly Gas Ring Main Units
Ⅰ. Technical Bottlenecks of SF₆ Substitution
- 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. - 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
- 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 - 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
