Corner Stays for Dry-type Transformers & Reactors
1. Product Introduction
Pultruded spacer bars (commonly known in the industry as ventilation strips or dog-bone strips) are high-strength structural insulation components specifically designed for high-voltage dry-type transformers and reactors.
Manufactured using continuous E-glass fiber roving and glass fiber tape as reinforcing materials, combined with a high-temperature-resistant epoxy resin system, the product is produced through a vacuum impregnation + continuous pultrusion integrated automated process: the fibers are first fully impregnated under vacuum degassing, then cured at high temperature through a shaping die, and continuously pulled and cut to length. The resulting product features straight and aligned fiber distribution, 100% resin impregnation, and virtually no voids or delamination defects internally.
Heat resistance classes are available in Class F (155°C) and Class H (180°C), with a standard UL94 V-0 flame retardancy rating. A full range of cross-sectional profiles is available (rectangular, I-beam, dog-bone, trapezoidal, L-shaped strips, etc.). Compared to FR4 board cut parts and conventional rolled insulation strips, it offers significantly improved mechanical strength, partial discharge performance, and dimensional consistency, making it the core insulating profile for dry-type transformer winding support and ventilation isolation.
2. Product Core Features
(1) Ultra-low Porosity, Low Partial Discharge, Stable High-Voltage Insulation
The vacuum degassing impregnation process eliminates internal air bubbles, resulting in a dense and homogeneous structure with high dielectric strength and extremely low partial discharge levels. Long-term operation under high electrical fields poses no risk of flashover or tracking, making it suitable for the stringent insulation demands of 10kV–35kV dry-type transformers.
(2) Superior Longitudinal Mechanical Strength vs. Standard Epoxy Sheets
With continuous fiber alignment along the length direction, the product exhibits excellent tensile, compressive, flexural, and creep resistance. Under high-temperature loads and long-term compression, it does not deform or crack. Its load-bearing capacity per unit cross-sectional area is more than 1.5 times that of FR4 cut spacer bars, making it ideal for winding support structures.
(3) High Dimensional Accuracy, Excellent Straightness, and Consistent Batch Quality
Molded and integrally pultruded, the bars feature tight tolerances on wall thickness and width, with no bending or twisting over long lengths. The smooth, burr-free surface requires no secondary sanding, ensuring high assembly fit. Large-volume production maintains uniform specifications, suitable for automated transformer assembly lines.
(4) Heat and Aging Resistance, Stable Over a Wide Temperature Range
Class F ensures continuous operation at 155°C, and Class H at 180°C. Thermal cycling from -40°C to 180°C causes no embrittlement or delamination. Resistance to electrical and thermal aging ensures that insulation performance does not degrade under long-term heat exposure in dry-type transformers, significantly extending equipment service life.
(5) Extremely Low Water Absorption, Moisture and Condensation Resistant
The resin fully encapsulates the fiber skeleton, with water absorption ≤0.03%—far lower than conventional laminates. In humid, condensing, or coastal high-salt-fog environments, the insulation does not degrade due to moisture ingress, eliminating leakage hazards.
(6) Flame Retardant, Environmentally Friendly, and Chemically Resistant
UL94 V-0 self-extinguishing rating; flames automatically extinguish when the ignition source is removed. Resistant to transformer oil, weak acids, weak alkalis, and SF6 gas corrosion. No emission of hazardous substances, meeting environmental and safety standards for electrical equipment.
(7) Easy Machining and Customizable Special Profiles
Can be cut to length, end-chamfered, and drilled. Supports custom non-standard cross-sections such as rectangular, dog-bone ventilation strips, L-shaped angle bars, I-beams, etc., with lengths tailored to requirements, accommodating various dry-type transformer winding structure designs.
(8) Lightweight and High-Strength, Enabling Lightweight Construction
With a density of only 1.85–1.95 g/cm³, the material is significantly lighter than metal support components, reducing overall transformer weight and easing transportation and installation loads.
3. Primary Applications
(1) Dry-Type Transformers (Core Application)
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High/low voltage winding ventilation spacer bars and dog-bone spacing strips, forming cooling ducts between windings.
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Interlayer support pads for coils and positioning insulation strips at winding ends.
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Core clamp insulation isolation strips and lead wire fixing insulation supports.
(2) Reactors and Special Transformers
Internal winding supports, heat dissipation, and isolation insulation profiles for filter reactors, smoothing reactors, and furnace transformers.
(3) High and Low Voltage Switchgear
Busbar insulation support strips in switchgear cabinets, internal isolation insulation components for instrument transformers, and load-bearing insulating beams for high-voltage test equipment.
(4) Rail Transit and Renewable Energy Power Systems
Insulation spacer bars for wind power, photovoltaic energy storage step-up dry-type transformers, and traction transformer insulation supports in rolling stock, capable of withstanding equipment vibration and frequent temperature cycling.
(5) Industrial Special High-Voltage Equipment
High-strength load-bearing insulation structural components for rectifier transformers, medium-frequency power supplies, and high-voltage test devices.
4. Basic Technical Parameters
| Parameter | Value |
|---|---|
| Heat Resistance Class | Class F 155°C / Class H 180°C |
| Flame Retardancy Rating | UL94 V-0 |
| Density | 1.85–1.95 g/cm³ |
| Water Absorption | ≤0.03% |
| Dielectric Strength (perpendicular) | ≥20 kV/mm |
| Volume Resistivity | ≥1.0×10¹⁴ Ω·cm |
| Flexural Strength (longitudinal) | ≥500 MPa |
| Arc Resistance | ≥180 s |
| Operating Temperature Range | -40°C ~ +180°C |
| Standard Cross-Sections | 4×6, 6×6, 8×10, 10×12, 12×16, 16×20 mm, dog-bone ventilation strips, L-shaped strips, etc. |
| Standard Colors | Off-white, light cream yellow (custom red and black available) |
5. Machining and Usage Instructions
(1) For cutting, carbide-tipped saw blades are recommended. Use low cutting speeds to avoid fiber fuzzing at the cut ends or resin burning due to high temperatures.
(2) Avoid forceful impact during assembly to prevent localized stress cracking. For long strips, ensure multi-point uniform load support to prevent bending creep under long-term compression.
(3) Designed solely for dry-type equipment internal insulation support. Do not immerse in strong acids or strong alkalis for extended periods.
(4) Surface dust and oil contamination may be cleaned with a dry cloth or anhydrous alcohol.
6. Storage Guidelines
(1) Store in a dry, well-ventilated, temperature-controlled warehouse, away from rain, ground moisture, and direct sunlight.
(2) Stack profiles flat and level; avoid unsupported overhanging edges or heavy point loads to prevent long-term bending deformation.
(3) Keep away from acids, alkalis, and corrosive chemicals. Recommended storage temperature: 0–40°C.
(4) Do not stack too high to avoid crushing and damaging profiles at the bottom of the pile.
