Dry-type transformers are the workhorse of modern power distribution, industrial plants, and renewable-energy systems. Unlike oil-filled units, they rely entirely on solid insulation to provide electrical isolation, mechanical support, and long-term thermal endurance. That makes the choice of insulation material one of the most important design decisions you will make — it directly determines the transformer’s thermal class, reliability, and service life.
Why Insulation Materials Decide Transformer Performance
The insulation system does three jobs at once: it separates live conductors, supports the winding mechanically under short-circuit forces, and resists heat over years of operation. If the material is under-rated for the operating temperature, the insulation ages prematurely and the transformer fails early. Selecting the right material — and the right thermal class — is therefore a reliability decision, not a cost decision.
The Main Insulation Material Categories
1. Flexible Composite Insulation (DMD, NMN, NHN)
Flexible laminates bond a polyester (Mylar) film between layers of paper or Nomex. DMD (Dacron–Mylar–Dacron) is the economical choice for Class B/F layer and slot insulation. NMN y NHN (Nomex–Mylar–Nomex) add high-temperature Nomex faces for Class F/H applications and better chemical resistance. These are used for layer insulation, phase insulation, and slot liners.
2. Laminates (FR4, GPO-3, SMC, 3240)
Rigid laminates provide structural strength and machined parts. FR4 / G10 / G11 epoxy glass cloth offers high mechanical and electrical strength for spacers, barriers, and PCB-type supports. GPO-3 polyester glass mat is arc- and track-resistant, ideal for barriers and terminal boards. SMC sheet molding compound is used for molded structural components. 3240 epoxy phenolic laminate is a general-purpose insulating board.
3. Insulating Paper (Cable, Crepe, DDP)
Cable paper wraps conductors and windings. Crepe paper is flexible and conformable, ideal for wrapping irregular winding shapes. Papel punteado con forma de diamante (DDP) has resin dots that bond under heat, making it excellent for layer insulation that needs to hold in place during processing.
4. Films (PET, PI)
PET polyester film is the standard slot-liner material. PI polyimide film (Kapton) handles much higher temperatures — essential for EV drive motors and Class H applications.
5. Tapes and Sleeving
Adhesive tapes (polyester, polyimide, glass cloth, aramid) secure windings and provide extra layer protection. Insulating sleeving (silicone fiberglass, heat-shrink, polyurethane) protects lead wires and connections.
How to Choose: Five Criteria
- Clase térmica — match the material’s temperature rating (B 130°C, F 155°C, H 180°C, N 200°C) to your winding’s hot-spot temperature.
- Dielectric strength — verify the material’s breakdown voltage (kV/mm) meets your design margin.
- Mechanical properties — tensile, flexural, and tear strength for winding and short-circuit forces.
- Environmental resistance — moisture, oil (ATF for EV motors), and chemical exposure.
- Standards compliance — IEC, UL, RoHS, and REACH for your target market.
Get the Right Material, Fast
Anwell Electric supplies the full range of transformer and motor insulation materials — flexible composites, laminates, papers, films, tapes, and sleeving — with complete technical data sheets, samples, and custom-cut or custom-machined parts. Contáctanos to discuss your application, and we’ll recommend the right material and thermal class for your design.