Common Materials and Selection of Insulating Spacers for Dry-Type Transformers

Insulating spacers in dry-type transformers are mainly used for coil support, positioning, electrical insulation, and cushioning. Therefore, the materials used for these components need to provide excellent mechanical strength, electrical insulation, thermal resistance, and dimensional stability.

Depending on the transformer’s capacity, operating temperature, and insulation class, different materials may be selected. The most commonly used materials include epoxy fiberglass laminate, SMC/BMC molding compounds, and silicone rubber.

1. Epoxy Fiberglass Laminate

Epoxy fiberglass laminate is one of the most widely used materials for insulating spacers in dry-type transformers. Common grades include G10, G11, FR-4, and 3240 epoxy fiberglass sheets.

Material Composition

The material is manufactured by impregnating electrical-grade alkali-free fiberglass cloth with epoxy resin, followed by high-temperature and high-pressure lamination.

Key Features

• High mechanical strength with excellent compressive and flexural strength.
• Excellent electrical insulation and high dielectric strength.
• Low water absorption and good resistance to moisture.
• Good dimensional stability with low deformation.
• Can be machined into different shapes and dimensions according to design requirements.

Applications

Epoxy fiberglass laminates are widely used in medium- and high-voltage dry-type transformers, cast-resin transformers, motors, and other electrical equipment for insulation support and spacer applications.

Materials such as G10 and G11 offer excellent mechanical strength and thermal resistance, making them suitable for applications requiring high load-bearing capability and elevated temperature resistance.

2. SMC / BMC Molding Compounds

SMC (Sheet Molding Compound) and BMC (Bulk Molding Compound) are glass-fiber-reinforced thermosetting composite materials that are increasingly used in modern dry-type transformers.

Material Composition

They are generally made from unsaturated polyester resin, chopped glass fibers, mineral fillers, and various functional additives, and are cured through compression molding.

Key Features

• Good mechanical strength and impact resistance.
• Good electrical insulation properties.
• Good thermal and aging resistance.
• Complex structures can be produced directly through precision molds.
• Suitable for mass production with good dimensional consistency.
• Grooves, ribs, bosses, and other structures can be incorporated into the molded parts to meet insulation and creepage-distance requirements.

Applications

SMC/BMC materials are suitable for dry-type transformer insulating supports, spacers, and structural components that require complex geometries, high dimensional accuracy, and efficient mass production.

3. Silicone Rubber and Modified Silicone Rubber Composites

Silicone rubber materials are mainly used in some small- and medium-sized transformers or in insulation structures where cushioning, vibration damping, moisture resistance, and noise reduction are required.

Key Features

• Excellent elasticity with good cushioning and vibration-damping properties.
• Excellent aging resistance.
• Good resistance to moisture and environmental contamination.
• Helps reduce mechanical vibration and operating noise.
• Good adaptability to temperature variations.

Applications

Silicone rubber is mainly used in areas requiring flexible support, vibration damping, or cushioning. It can also be used together with rigid insulating materials to form composite support structures.

Important Note: The stiffness and load-bearing capacity of silicone rubber are generally lower than those of epoxy fiberglass laminates. Therefore, in large-capacity and heavily loaded dry-type transformers, conventional silicone rubber is generally not used alone as the primary load-bearing spacer material.

How to Select Materials for Dry-Type Transformer Insulating Spacers

Material selection should not be based solely on electrical insulation performance. Factors such as temperature class, mechanical load, operating voltage, creepage distance, environmental humidity, manufacturing method, and cost should also be considered.

In general:

• For high mechanical strength and rigid support: G10, G11, FR-4, and other epoxy fiberglass laminates are preferred.
• For higher temperature requirements: Select an appropriate heat-resistant epoxy fiberglass material according to the required temperature class.
• For complex structures and high-volume production: SMC/BMC molding compounds can be considered.
• For cushioning, vibration damping, and noise reduction: Silicone rubber or modified silicone rubber can be considered.
• For load-bearing components in large-capacity dry-type transformers: Rigid insulating composite materials with high mechanical strength and good dimensional stability are generally preferred.

Therefore, there is no single “best” material suitable for all dry-type transformer insulating spacer applications. The material should be selected based on a comprehensive evaluation of the transformer capacity, insulation class, temperature-rise requirements, mechanical load, and specific structural design.