Insulation Materials for Transformers: Types and Applications

Time: 10-14 2025 Auther: Xujue Electrical

Transformer Insulation Materials play a critical role in ensuring electrical, thermal, and mechanical reliability. Th...

Transformer Insulation Materials play a critical role in ensuring electrical, thermal, and mechanical reliability. They prevent short circuits, reduce dielectric losses, and extend the service life of transformers. Below is a comprehensive overview categorized by transformer type and material function:

1. Classification by Transformer Type

Dry-Type Transformer Insulation Materials

Solid insulation only (no oil):

Epoxy resin (casting resin): used for coil encapsulation and insulation.

G10 / G11 Epoxy Glass Laminate: used for insulation supports, spacers, and structural parts.

DMD Insulation Paper (Polyester + Nomex): slot and interlayer insulation.

Nomex Paper (Aramid Paper): high thermal class (up to 220°C); used for interturn and layer insulation.

Mylar (Polyester Film): electrical insulation for windings.

Fiberglass Cloth / Tape: coil wrapping, reinforcement, and mechanical protection.

Silicone Rubber / Epoxy Mica Tape: for high-voltage end insulation.

Fiberglass Wound Tube in transformer

Oil-Immersed Transformer Insulation Materials

Combined solid + liquid insulation:

Insulating Oil (Mineral / Synthetic / Natural Ester): provides both cooling and insulation.

Kraft Paper (Electrical Grade): interlayer and conductor wrapping.

Pressboard (Transformer Board): used for spacers, barriers, and cylinders.

Crepe Paper / Wrinkled Paper: used around conductors for flexibility and oil absorption.

Wood Laminates (e.g., Beech or Maple): support structures.

Cotton Tape: binding and wrapping for leads.

Presspaper Tubes / Cylinders: for lead insulation and mechanical support.

pressboard use on oil-immersed transformers

2. Classification by Function

Function	Typical Materials	Application
Conductor Insulation	Enamel, Kraft Paper, DMD, Nomex	Wrapping around copper/aluminum wire
Interlayer Insulation	DMD, NMN, Mylar, Nomex	Between winding layers
Main Insulation	Pressboard, Resin, Mica	Between LV/HV windings and core
Structural Insulation	G10, G11, FR4, SMC	Supporting and mechanical components
Impregnation / Cooling Medium	Transformer Oil, Epoxy Resin, Silicone	Fills gaps, enhances dielectric strength
End Insulation / Barriers	Pressboard, Mica Tape	Terminal and end-turn insulation

3. Thermal Class (IEC 60085)

Class	Max. Operating Temp (°C)	Typical Materials
A	105	Cotton, Paper, Pressboard
E	120	Polyester Film (Mylar), DMD
B	130	Polyester Resin, Mica, Fiberglass
F	155	Epoxy Resin, Glass Fiber, DMD
H	180	Silicone Rubber, Nomex
C	>180	Mica, Ceramic, Aramid

4. Recommended Insulation Materials

If you’re building or maintaining transformers:

For Dry Type: G10 / G11 epoxy glass board, DMD insulation paper, epoxy resin cast parts.

For Oil Immersed: Pressboard, Kraft paper, crepe paper, epoxy-coated tubes, and transformer oil.

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