I. What Is a Fiberglass Filament Wound Tube End Ring?

Fiberglass filament wound tube end ring is an insulating structural component manufactured from alkali-free glass fiber and epoxy resin using a filament winding process, then cut into ring or semi-ring shapes according to design requirements. It is widely used at the end sections of windings in dry-type transformers.

Common names include:
Fiberglass filament wound end ring
Insulating end ring
Winding end support ring
GFRP End Ring / Filament Wound Tube Ring

II. Installation Position in Dry-Type Transformers

Location:

• Installed at the upper and lower ends of high-voltage or low-voltage windings
• Positioned between the winding ends and metal clamping plates as part of the end support system

Typical structural arrangement:

Clamping plate
Fiberglass filament wound end ring
Winding end
Spacer / air duct structure

III. Main Functions and Roles

1. End Insulation and Electrical Isolation

• Provides high dielectric strength to isolate winding ends from metal clamping components
• Prevents creepage, partial discharge, and flashover
• Suitable for 10 kV, 20 kV, and 35 kV dry-type transformers

2. Mechanical Support and Structural Stability

• Bears axial compressive forces at winding ends
• Prevents deformation and axial displacement under short-circuit conditions
• Improves short-circuit withstand capability

3. Electric Field Optimization and Partial Discharge Reduction

• Smooths electric field distribution at winding ends
• Reduces electric field concentration points
• Lowers partial discharge (PD) levels

4. Thermal Resistance and Service Life Improvement

• Suitable for Class F (155°C) and Class H (180°C) insulation systems
• Maintains stable performance without softening or carbonization

IV. Why Dry-Type Transformers Rely on Fiberglass End Rings

Advantages of fiberglass filament wound end rings:

• Low moisture absorption and excellent dimensional stability
• High mechanical strength compared to paper-based insulation
• No oil compatibility limitations, ideal for dry-type transformers

V. Key Performance Requirements

VI. Selection Guidelines and Considerations

1. Selection by Voltage Class

• 10 kV: Standard fiberglass filament wound end rings
• 20–35 kV: Increased wall thickness and high-density filament wound tubes recommended

2. Selection by Mechanical Strength

• For dry-type transformers ≥ 2500 kVA, axial compressive strength is critical
• Ordinary FR4 laminated boards assembled into rings are not recommended

3. Surface Quality and Machining

• Smooth inner and outer surfaces without burrs
• Flat cut edges to avoid local electric field concentration
• Chamfered or rounded edges when required

VII. Summary

Fiberglass filament wound tube end rings are essential insulating and structural components in dry-type transformers, providing high dielectric strength, excellent mechanical support, thermal resistance,and superior short-circuit performance, helping reduce partial discharge and extend transformer service life.