Transformer Kraft Paper vs. Thermally Upgraded Paper

Transformer Kraft Paper and Thermally Upgraded Paper (TUP) are both widely used cellulose-based insulation materials in oil-immersed transformers.

Transformer Kraft Paper vs. Thermally Upgraded Paper: Differences and Applications

Transformer Kraft Paper and Thermally Upgraded Paper (TUP) are both widely used cellulose-based insulation materials in oil-immersed transformers. The main difference lies in their thermal aging performance, allowable operating temperature, and insulation life under elevated temperatures.

1. Key Differences

Note: Actual temperature ratings and allowable hot-spot temperatures depend on the complete transformer insulation system, materials, design, and applicable standards. They should not be determined by the paper alone.

2. What Is Transformer Kraft Paper?

Transformer Kraft Paper is one of the most traditional and widely used cellulose insulation materials for oil-immersed transformers.

It offers:

Good dielectric strength
Good mechanical strength
Excellent compatibility with transformer oil
Good processability for insulation structures
Cost-effective performance

Main Applications

Transformer Kraft Paper is commonly used for:

Transformer winding insulation
Layer insulation
Turn-to-turn insulation
Conductor insulation
Interlayer insulation
End insulation
Lead insulation
Oil-immersed transformer insulation structures

For conventional oil-immersed transformers, Kraft Paper remains one of the fundamental cellulose insulation materials.

3. What Is Thermally Upgraded Paper?

Thermally Upgraded Paper (TUP) is a cellulose-based insulation paper that has been specially treated to improve its thermal aging resistance.

The main purpose of thermally upgrading the paper is not simply to make the paper withstand a higher instantaneous temperature. Instead, it is designed to reduce the rate of cellulose aging during long-term operation at elevated temperatures, helping to extend the service life of the transformer insulation system.

Main Applications

Thermally Upgraded Paper is particularly suitable for transformers that operate under higher thermal loads or have higher insulation-life requirements, including:

High-load transformers
Power transformers
Distribution transformers
Transformers operating at elevated temperatures
Transformers designed for extended insulation life
Transformers with higher permissible winding hot-spot temperatures

Summary

Transformer Kraft Paper is mainly used for the basic insulation requirements of conventional oil-immersed transformers, while Thermally Upgraded Paper is designed for transformers operating at higher temperatures and under heavier loads, offering improved thermal aging performance.

Buyer’s Recommendation: Select the appropriate insulation paper according to the transformer’s actual insulation requirements, operating temperature, load conditions, and expected service life.