Liquid Silicone Rubber Overmolded Insulation Protective Fitting for Vacuum Interrupter

# Liquid Silicone Rubber Overmolded Insulation Protective Fitting for Vacuum Interrupter

Product Overview

The Liquid Silicone Rubber (LSR) Overmolded Insulation Protective Fitting for Vacuum Interrupter is a high-performance electrical insulation component designed to enhance the operational reliability and extend the service life of medium and high-voltage vacuum interrupters. Custom-engineered for precision overmolding directly onto vacuum interrupter ceramic or metal housings, this fitting eliminates air gaps between the interrupter surface and insulation layer, effectively suppressing partial discharge, preventing surface creepage, and resisting environmental degradation in harsh operating conditions.

Unlike traditional assembled epoxy or heat-shrink insulation sleeves, this LSR overmolded fitting forms a permanent, molecular-level bond with the interrupter substrate via a controlled injection molding process, delivering 360° seamless protection. It meets the strict insulation requirements of 10kV to 110kV power distribution and transmission systems, with core selling points including ultra-low partial discharge levels (<10pC at rated voltage), excellent high and low temperature resistance, and a 30-year expected service life under continuous electrical load. The product is tailored to fit standard and custom vacuum interrupter sizes for circuit breakers, reclosers, contactors, and load break switches.

Technical Specifications

Material Properties

The fitting is manufactured from high-purity, electrical-grade liquid silicone rubber formulated specifically for high-voltage insulation applications, with the following material characteristics:

Physical Performance

The cured LSR insulation layer delivers consistent mechanical and environmental resistance across extreme operating conditions:

Process Parameters

The overmolding process is optimized to ensure zero defects and strong adhesion to the vacuum interrupter substrate:

Product Advantages

1. Ultra-Low Partial Discharge Performance for Long-Term Electrical Reliability

The seamless overmolding process eliminates micro-air gaps between the insulation layer and vacuum interrupter surface, a common cause of partial discharge in traditional assembled sleeves. With PD levels consistently below 10pC under rated operating voltage, the fitting avoids long-term insulation degradation caused by corona discharge, reducing the risk of interrupter failure by 85% compared to non-overmolded insulation solutions. This performance meets the strictest requirements of IEC 62271-100 for high-voltage switchgear.

2. Extreme Environmental Adaptability for Harsh Operating Scenarios

Unlike epoxy resin insulation, which becomes brittle at temperatures below -20°C and softens above 120°C, the LSR fitting maintains stable mechanical and electrical properties across a -60°C to +200°C temperature range. It resists salt spray corrosion, UV radiation, acid rain, and fungal growth, making it suitable for outdoor installations in coastal, high-altitude, desert, and cold-climate regions. The material’s inherent hydrophobicity ensures that surface water forms discrete droplets rather than continuous films, preventing flashover even in heavy rain or high-humidity environments.

3. Integrated Structure Reduces Assembly Workload and Failure Points

The overmolded fitting integrates creepage extension sheds, mounting positioning slots, and sealing interfaces into a single component, eliminating the need for separate gaskets, adhesive bonding, or sleeve assembly during switchgear production. The integrated structure reduces assembly time by 70% compared to traditional multi-part insulation solutions, while eliminating potential failure points caused by misaligned sleeves or degraded adhesive bonds over time.

4. Excellent Mechanical Shock and Vibration Resistance

The high elasticity of LSR (300% minimum elongation at break) allows the fitting to absorb mechanical stress caused by short-circuit current impact, switch operation vibration, and thermal expansion mismatch between the vacuum interrupter’s ceramic housing and metal switchgear frame. It will not crack or delaminate after 10,000 mechanical switching operations or 10g random vibration testing per IEC 60068-2-6, making it ideal for applications in high-vibration environments such as wind turbine switchgear and railway traction systems.

Applications

This LSR overmolded insulation protective fitting is widely used in medium and high-voltage electrical equipment where vacuum interrupters are deployed, including:

• Power Distribution Systems: 10kV~35kV indoor and outdoor vacuum circuit breakers, pole-mounted reclosers, and load break switches for urban and rural power grids, where it provides reliable insulation against pollution flashover in heavy smog or industrial dust areas.
• Renewable Energy Facilities: Wind turbine step-up transformers and photovoltaic inverter grid-connected switchgear, where it withstands extreme temperature fluctuations, high vibration, and high-altitude low-pressure conditions.
• Railway Traction Systems: 27.5kV vacuum circuit breakers for high-speed rail and subway traction power supply systems, where its low partial discharge performance avoids interference with railway signal systems.
• **Industrial Electrical Equipment: Medium-voltage vacuum contactors for mining, steel mill, and chemical plant motor control centers, where it resists corrosion from corrosive gases and dust in industrial environments.
• **Smart Grid Equipment: Digital switchgear and solid-insulated ring main units, where its stable dielectric properties support precise online partial discharge monitoring systems.

Selection Guide

Hardness Selection

• 30~40 Shore A: Recommended for vacuum interrupters used in high-vibration applications (e.g., wind turbines, railway equipment) or for interrupters with complex outer profiles, as the softer LSR provides better stress relief and adhesion to irregular surfaces.
• 50~60 Shore A: Standard for most 10kV~35kV power distribution circuit breakers and reclosers, balancing mechanical rigidity, insulation performance, and cost-effectiveness.
• 65~70 Shore A: Recommended for 110kV high-voltage vacuum interrupters and applications requiring high creepage distance, as the harder material maintains structural stability for larger shed profiles and avoids deformation under long-term electrical load.

Size Specifications

The fitting is custom-molded to match the specific dimensions of your vacuum interrupter, with standard models available for all mainstream interrupter sizes from 10kV to 110kV. When placing an order, provide the interrupter’s ceramic housing outer diameter, end flange dimensions, required creepage distance (minimum 20mm/kV for pollution level III areas, 25mm/kV for pollution level IV), and switchgear mounting interface dimensions to ensure a perfect fit.

Material Grade

• Standard Electrical Grade: Suitable for most indoor and general outdoor applications, meeting IEC 60455-2 requirements for high-voltage insulation.
• High-Tracking Grade: Formulated with enhanced CTI (>600V) and pollution resistance, recommended for heavily polluted industrial areas, coastal regions with high salt spray, and high-altitude installations above 3000m.
• RoHS-Compliant Low-Toxicity Grade: Meets EU RoHS 2.0 and REACH requirements for low heavy metal and volatile organic compound content, suitable for indoor switchgear installed in public areas such as residential buildings and hospitals.

Quality Assurance

All LSR overmolded insulation protective fittings undergo a strict multi-stage quality control process to ensure compliance with international and industry standards:

1. Incoming Material Inspection: Each batch of LSR raw material is tested for viscosity, curing time, and dielectric properties before production, with traceability codes maintained for all batches.
2. In-Process Control: The overmolding process is monitored via real-time pressure and temperature sensors to ensure consistent material flow and curing, with dimensional checks performed on every 20th unit during production.
3. Final Performance Testing: 100% of finished products undergo partial discharge testing, power frequency withstand voltage testing, and X-ray internal void inspection before shipment. A 5% random sample from each batch is subjected to tensile strength, thermal aging, and water immersion testing to verify long-term performance.
4. Certifications: The product is certified to IEC 62271-100, GB/T 11022, and UL 94 V-0 standards, with RoHS 2.0 and REACH compliance available for export markets.

We offer a 5-year warranty against material defects and manufacturing faults, with long-term performance guarantees available for custom projects, supported by 15 years of LSR overmolding expertise in the electrical insulation industry. Our engineering team provides custom design support to optimize the fitting’s profile and material formulation for your specific application requirements.