Epoxy Electrical Encapsulation System (Transformer and Power Electronics Grade)
Key Features
- High dielectric strength (>18 kV/mm) for HV electrical insulation
- Low dissipation factor (<0.01) minimizes dielectric heating losses
- CTI >600 V for outdoor and tracking-resistant applications
- Anhydride cure for low exotherm — safe for large winding encapsulation
- Mineral filler reduces CTE to match copper/aluminum windings
Epoxy Electrical Encapsulation System is a precision-formulated two-part epoxy system designed for vacuum casting and potting of dry-type transformers, high-voltage bushings, current transformers, power inductors, and power electronic modules. The system provides the combination of high dielectric strength (>18 kV/mm), low dissipation factor (<0.01 at 50 Hz), high tracking resistance (CTI >600 V), and thermal class F/H service (UL thermal class 155-180°C) required for high-reliability electrical insulation applications.
The resin is based on BPA or cycloaliphatic epoxy (cycloaliphatic grades provide better UV/tracking resistance for outdoor service) with anhydride (MTHPA or HHPA) cure system, enabling low exotherm casting of large components without thermally damaging the windings. Mineral filler (aluminum trihydrate, quartz) at 40-60% loading reduces CTE to match the embedded copper/aluminum windings, minimizing thermal fatigue stress during thermal cycling.
The system is designed for vacuum pressure impregnation (VPI) and vacuum casting processes to eliminate voids, corona discharge initiation sites, and partial discharge in the insulation. Degassing before casting at <5 mbar removes dissolved air. Gel time at 100°C is 4-8 hours; cure at 120-150°C/6-8h achieves full conversion and Tg >120°C for Class F service. For Class H (180°C), DDS cure or anhydride cure with 180°C post-cure is required.
Specifications
| Parameter | Value |
|---|---|
| Filler Content | 40-60% (ATH or quartz) |
| Thermal Class (UL) | Class F (155°C) or H (180°C) per grade |
| Dielectric Strength | >18 kV/mm |
| Tg (120°C/8h cure) | >120°C |
| Dissipation Factor (50 Hz) | <0.01 |
| Volume Resistivity (23°C) | >10^14 Ω·cm |
| CTI (Comparative Tracking Index) | >600 V |
Applications
FAQ
Anhydride cure (MTHPA/HHPA with imidazole catalyst) is preferred over amine cure for transformer casting for three reasons: (1) Lower exotherm — large transformer windings (10-100 kg resin cast) require <50°C exotherm rise to protect copper enamel insulation (rated 130-200°C) and prevent thermal stress cracking; amine cure produces 60-100°C exotherm peak in large masses; anhydride cure produces only 20-40°C exotherm due to slower reaction kinetics; (2) Better electrical properties — amine cure products retain ionic amine residues in the cured network, increasing conductivity and dissipation factor; anhydride cure produces ester network with ionic residues only from catalyst (0.5-1% 2-methylimidazole); (3) Lower viscosity at processing temperature — MTHPA is a low-viscosity liquid (50-100 mPa·s at 25°C) that maintains system viscosity <1,000 mPa·s at processing temperature (40-60°C), enabling complete void-free impregnation.
Direct Contact
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