Types of Transformer Interlayer Insulation materials

Interlayer insulation materials for transformers come in various types, and the choice depends primarily on the trans...

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