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Technical Proposal: CT Reliability Enhancement Solution Based on Hybrid Gas Insulation

Rockwill 07/10/2025

Application Scenario: Extreme cold regions (-40°C environment), environmentally stringent projects (e.g., Nordic wind power grid connection stations)

Core Goal: Enhance long-term reliability of Current Transformers (CTs) within Gas-Insulated Switchgear (GIS) while meeting low-carbon environmental requirements.

I. Insulation Medium Optimization: SF₆/N₂ Hybrid Gas Technology

Parameter - Solution Design

Gas Ratio: SF₆ (80%) + N₂ (20%) mixture
Insulation Strength: At 20°C & 0.5MPa, insulation strength >85% of pure SF₆
Environmental Performance: GWP (Global Warming Potential) reduced by 70%, significantly lowering greenhouse gas impact
Low-Temperature Suitability: Hybrid gas liquefaction point ≤ -60°C, ensuring no liquefaction risk at -40°C in extreme cold environments

II. Anti-Partial Discharge Shielding Design

Structural Innovation:

Epoxy Resin Casting:

CT coils manufactured using vacuum casting process, epoxy resin filling rate >99.9%, eliminating internal voids.

Equipotential Metal Shielding Mesh:

Zinc-plated copper mesh added to the outer layer of the casting body, maintained at equipotential to the CT primary conductor.
Eliminates surface electric field distortion and suppresses partial discharge.

Performance Validation:

PD (Partial Discharge) level <5 pC (per IEC 60270 standard)
Passed -40°C thermal cycling test, with no risk of insulation cracking.

III. Dynamic Temperature Rise Control System

Intelligent Control Architecture:
Sensor Layer → Control Layer → Execution Layer
PT100 Temp Sensors → GIS Monitoring System → Fan Speed Control Module
Function Implementation:

Real-time Monitoring: Built-in PT100 probes (±1°C accuracy) locate CT hotspot temperatures.
Active Cooling: Automatically activates GIS fan arrays when temperature rise exceeds threshold (e.g., ΔT >40K).
Energy Efficiency Optimization: Fan power dynamically adjusted based on demand, reducing wasted energy.

IV. Key Technical Advantage Comparison

Indicator	Traditional SF₆ CT	This Solution: Hybrid Gas CT
Insulation Lifetime	25~30 years	>40 years
GWP Value	100% (SF₆=23,900)	Reduced by 70%
Low-Temp Reliability	Prone to liquefaction at -30°C	Stable operation at -40°C
Partial Discharge Control	10~20 pC	<5 pC

V. Scenario Adaptability Validation

Extreme Cold Wind Power Scenario (Nordic):

Passed -40°C /72h cold start test; CT ratio error ≤ ±0.2%.
Optimized Pressure-Temperature curve for hybrid gas prevents excessive pressure drop at low temperatures.