Description
F/H Class Fiberglass FRP Dog Bone Insulation for Dry-Type Transformers
The F/H class fiberglass FRP dog bone is a dumbbell- (dog-bone-) shaped fiberglass-reinforced plastic (FRP / GRP) spacer used inside dry-type transformer windings to separate conductor layers, support the coil, and form uniform cooling ducts. The distinctive waisted "dog bone" profile interlocks with the winding structure while keeping the conductor turns at a precise, constant distance - combining mechanical support with dielectric insulation in one component.
Molded from high-strength glass-fiber reinforcement, our dog bone spacers are available in Class F (155°C) and Class H (180°C) thermal ratings, making them suitable for cast-resin, vacuum-cast, and open-wound dry-type transformers, reactors, and similar dry insulation systems. They are lightweight, non-magnetic, dimensionally stable, and cut to length on request.
Thermal class: Class F (155°C) / Class H (180°C) per IEC 60085 Material: Fiberglass reinforced plastic (FRP/GRP) Shape: Dog bone (dumbbell / waisted profile) Application: Dry-type transformer winding spacers & cooling ducts Sizes: Standard and custom thickness / width / length
Key Features of the FRP Dog Bone Spacer
Class F (155°C) and Class H (180°C) thermal endurance - matched to the temperature rise of dry-type transformer windings.
High mechanical strength - fiberglass reinforcement gives excellent compression and creep resistance under sustained winding loads.
Excellent dielectric strength - reliable electrical insulation between winding layers and conductor turns.
Low moisture absorption - stable electrical properties in humid and tropical operating conditions.
Dog-bone (waisted) profile - creates evenly spaced vertical cooling ducts that improve heat dissipation from the coil.
Dimensional stability - holds conductor spacing during winding and resin casting, reducing winding deformation.
Non-magnetic and lightweight - eddy-current free, easy to handle on the winding table.
Machinable & cut-to-length - supplied in standard lengths or cut to your winding dimensions.
Custom profiles available - thickness, width, dog-bone geometry, and color to your specification.
Display
Material & Thermal Class
| Item | Detail |
|---|---|
| Material | Fiberglass reinforced plastic (FRP / GRP) |
| Reinforcement | Continuous / chopped glass fiber (confirm) |
| Resin system | Epoxy / vinyl ester / polyester - specify by temperature class (confirm) |
| Thermal class - Class F | 155 °C (IEC 60085) |
| Thermal class - Class H | 180 °C (IEC 60085) |
| Color | Light yellow / green / white / custom (confirm) |
| Flammability | Self-extinguishing (UL94 V-0 optional) (confirm) |
Technical Specifications
| Parameter | Typical / Available | Unit |
|---|---|---|
| Profile | Dog bone (dumbbell / waisted) | - |
| Standard thickness (T) | 3 / 5 / 6 / 8 / 10 | mm |
| Standard width (W) | On request | mm |
| Length | Cut to length / standard stock lengths | mm |
| Density | ≈ 1.8 – 2.0 | g/cm³ |
| Dielectric strength | ≥ 10 | kV/mm |
| Tensile strength | ≥ 300 | MPa |
| Flexural strength | On request | MPa |
| Water absorption | ≤ 0.5 | % |
| Thermal class | F (155°C) / H (180°C) | °C |
| Operating temperature | Up to the rated thermal class | °C |
| Color | Custom | - |
| Tolerance | Per drawing | mm |
Shapes & Custom Sizes
Standard dog bone profile - symmetrical waisted section for uniform conductor spacing and cooling-duct formation.
Cut-to-length service - supplied to your coil height and winding dimensions.
Custom geometry - thickness, waist width, end width, and length manufactured to your drawing or sample.
Matched sets - multiple thicknesses per drawing for multi-layer windings.
application
Cast-resin dry-type transformers - inter-layer spacers and cooling-duct formers within the cast coil.
Vacuum-cast and open-wound dry-type transformers - winding support and layer separation.
Dry-type distribution transformers in 10kV / 20kV / 35kV networks.
Reactors and inductors - coil spacers and duct formers.
Packing
Rod Bakelite Insulating Material packaged in wooden crates, wooden framed cases or other strong enough materials covered with moisture-proof materialoutside.Gross weight of each package not exceeds 3000kgs.
Factory Display
Installation & Selection Notes
Select the correct thermal class - the dog bone class (F or H) must meet or exceed the transformer's winding hot-spot temperature.
Position circumferentially - place spacers at even intervals around the coil to form straight, uniform cooling ducts.
Match spacer thickness to the required conductor spacing and cooling-duct width.
Secure during winding and casting - hold spacers in place so winding geometry is maintained through resin casting and curing.
Verify after build - confirm duct alignment and conductor spacing before the insulation/electrical routine tests.
fAQ
Q1. What is a fiberglass FRP dog bone used for in a dry-type transformer? It is a dumbbell-shaped fiberglass-reinforced plastic spacer placed inside the winding to separate conductor layers, support the coil, and form uniform cooling ducts. It provides both mechanical support and electrical insulation.
Q2. What is the difference between Class F and Class H dog bone insulation? Class F is rated for a maximum continuous temperature of 155°C and Class H for 180°C (IEC 60085). The correct class depends on your transformer's winding hot-spot temperature.
Q3. Is the dog bone suitable for cast-resin dry-type transformers? Yes. The spacers hold conductor spacing during winding and resin casting and are designed for dry insulation systems.
Q4. Can you supply custom sizes and profiles? Yes. Thickness, width, dog-bone geometry, length, color, and resin system can all be produced to your drawing or sample.
Q5. What materials are used? High-strength fiberglass reinforcement in an epoxy, vinyl ester, or polyester resin system (confirm per grade), in Class F or Class H formulation.
Q6. Do you offer both F class and H class in the same profile? Yes - the same dog-bone profile can be supplied in either thermal class; select based on your winding temperature class.
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