Types of Transformer Interlayer Insulation materials

Compare the best transformer interlayer insulation materials. From cost-effective DDP to high-performance Nomex and FR4 rigid laminates, find the right solution for Class A to C...

Interlayer insulation materials for transformers come in various types, and the choice depends primarily on the transformer type (oil-immersed or dry-type), operating temperature class, and mechanical strength requirements.

The following are the common types of interlayer insulation materials and their characteristics:

1. Cellulose and Paper-Based Insulation (Commonly used in Oil-Immersed Transformers)

These materials are used in conjunction with transformer oil, offering excellent oil permeability and cost-effectiveness.
Electrical Pressboard: Made from pure cellulose, it provides superior mechanical and dielectric strength. It is the core insulation component for oil-immersed power transformers.
Diamond Dotted Paper (DDP): Insulation paper coated with diamond-shaped epoxy resin dots. During winding drying, the resin melts to bond the layers, enhancing the winding’s short-circuit resistance.
Kraft Paper / Cable Paper: Commonly used for interlayer wrapping or as basic insulation in small transformers.

2. Synthetic Fiber Insulation (Commonly used in Dry-Type or Special Transformers)

These materials typically offer high thermal resistance (Class F or H).
Nomex® Paper (Aramid Paper): Features excellent thermal stability (up to 220°C) and chemical stability. It is the standard for Class H dry-type transformers.
Composite Insulation (DMD / NMN / NHN):
DMD: A composite of polyester film and non-woven fabric; cost-effective and used for low-voltage interlayer insulation.
NMN: A composite of polyester film and Nomex, typically rated for Class F.
NHN: A composite of polyimide film and Nomex, offering extreme temperature and mechanical performance for premium Class H applications.

3. Rigid Laminates (Used for Structural Parts or Core Barriers)

These materials provide high physical strength, serving both as support and insulation.
FR4 / G10 / G11 Epoxy Glass Cloth Laminates: Extremely high mechanical strength with a wide temperature range (G11 up to 180°C). They are used for core insulation, spacers, or support strips in dry-type transformers.
3240 Epoxy Board: The traditional yellow epoxy board; cost-effective for general insulation where flame retardancy is not a critical requirement.
Electrical Laminated Wood: Offers good dielectric strength and excellent vibration resistance; commonly used for pressure plates and supports in large power transformers.

4. Film-Based Insulation

Polyester Film (PET Film): A typical Class E insulation, often used in small electronic transformers or as the center layer in composite materials.
Polyimide Film (PI Film): Provides outstanding thermal performance, used for ultra-thin interlayer insulation in high-performance transformers.

Core Comparison Table