Epoxy Dog Bone Profiles for Dry-Type Transformers

Epoxy Dog Bone Profiles are advanced fiberglass-reinforced insulating components designed for dry-type transformers, reactors, and high-voltage electrical equipment.

The Epoxy Dog Bone Profile（Epoxy Glass Fiber Pultrusions） is a special fiberglass-reinforced insulating component with a dumbbell-shaped or double-T cross-section. Its core function is to provide precise ventilation and cooling gaps as well as mechanical support for high-voltage electrical equipment.

I. Introduction and Applications of Epoxy Dog Bone Profiles

What’s an Epoxy Dog Bone Profile?

It is manufactured using high-strength E-glass fibers as reinforcement materials, impregnated with high-performance epoxy resin, and continuously pultruded at high temperatures in specialized molds. Due to its larger ends and narrower middle section, resembling a dog bone or dovetail structure, it is commonly referred to in the industry as a “Dog Bone” or “Dovetail Spacer”.

Key Application Areas

Dry-Type Transformers and Reactors: Used as dovetail air duct spacers between winding coils. In addition to providing insulation, they secure the windings and prevent coil displacement caused by electromagnetic forces during operation or short-circuit conditions.

High-Voltage Motors and Generators: Used as slot wedges or end-support fixing components in stators and rotors.

Power Transmission and Distribution Equipment: Widely used in disconnect switches, medium-frequency furnaces, and other heavy-duty electrical equipment that require both ultra-high mechanical strength and high-temperature insulation performance.

II. Differences Between Epoxy Dog Bone Profiles and Standard Epoxy Rods

Although both products belong to epoxy fiberglass pultruded composites, they differ fundamentally in cross-sectional design, manufacturing focus, and functionality.

Thermal Management Advantages of the Geometry

When standard epoxy rods are stacked in parallel, the contact surfaces create enclosed dead zones that restrict airflow. In contrast, the recessed design of the dog bone profile naturally forms ventilation channels between high-voltage windings, allowing heat generated during transformer operation to dissipate quickly and significantly extending equipment service life.

Anti-Sliding and Partial Discharge (PD) Resistance Advantages

During transformer winding assembly, the dovetail structure of the dog bone profile acts like a locking mechanism that securely holds the coils in place and prevents movement under high mechanical stress. Premium dog bone profiles are fully cured under controlled conditions to achieve a void-free internal structure. Their rounded edge geometry effectively reduces electric field concentration, minimizing the risk of partial discharge (PD), electrical tracking, and dielectric breakdown under high-voltage conditions. In contrast, conventional epoxy rods are much more susceptible to interlayer displacement when exposed to complex multidirectional electromagnetic stresses.