The role of phenolic paper tube in transformers

The core function of phenolic paper tubes in transformers is to provide three key functions: electrical insulation, m...

The core function of phenolic paper tubes in transformers is to provide three key functions: electrical insulation, mechanical support, and heat and corrosion resistance.

1. Electrical Insulation

The main material of the phenolic paper tube is insulating paper impregnated with phenolic resin, a structure that gives it excellent insulation properties. Inside a transformer, the potential difference between windings of different voltage levels and between windings and the core can reach several kilovolts. The phenolic paper tube effectively prevents current leakage and short-circuit accidents by blocking direct contact between conductive components. For example, in oil-immersed transformers, it is often made into an insulating bushing to ensure absolute isolation between the high-voltage leads and the tank casing.

2. Mechanical Support

During transformer operation, the windings not only withstand temperature rises of up to 200°C but also short-circuit electrodynamic impacts of 5-10 times the rated current. The compressive strength of the phenolic paper tube can reach 150 MPa. This rigid support keeps the windings in a concentric circle structure, preventing inter-turn misalignment caused by electromagnetic vibration. The tubular structure formed by the special lamination process can also share the axial clamping force of the windings, preventing structural loosening caused by the creep of the insulation material.

3. Environmental Resistance

The cured phenolic resin allows the paper tube to remain uncarbonized for 3000 hours in a 155℃ heat aging test. For the potential naphthenic acid corrosion in transformer oil (pH < 4.5), its oil resistance is approximately 60% higher than that of ordinary insulating paper. Some specially formulated products can even resist the corrosion of hydrogen fluoride (HF) produced during the arc decomposition of SF6 gas, making them particularly suitable for sealed dry-type transformers.