Transformer Oil Filter Paper: Selection and Use Guide

Electrical Insulating Oil Filter Paper: Essential for Transformer Oil Purification

The filter paper used for transformer oil (insulating oil) is not ordinary industrial paper. It is known as electrical insulating oil filter paper, or transformer oil filter paper, designed specifically for oil purification in vacuum oil filters. The correct paper ensures transformer safety, insulation, and reliability.

Why Ordinary Filter Paper Is Unsuitable

Ordinary oil filter paper focuses on particle retention, but transformer oil filtration demands far higher standards:

High dielectric strength: Must not release fibers or conductive particles that reduce insulation.

Hydrophobic and oleophilic: Repels water yet allows oil to pass easily for efficient moisture removal.

High strength: Withstands vacuum suction and oil pressure without rupturing.

Chemical compatibility: Must not react with oil or additives.

Key Characteristics and Selection Criteria

1. Filter Fineness (Pore Size)

Determines particle removal size, usually 1–10 μm.

Routine filtration: 5–10 μm for smooth flow.

Deep purification: 1–3 μm for finer cleaning and higher dielectric strength.

(Note: finer paper clogs faster.)

2. Material Composition

Pure wood pulp: Strong, economical, and widely used.

Glass fiber blends: Higher porosity and temperature resistance, ideal for demanding tasks.

3. Thickness, Weight & Air Permeability

Heavier paper holds more dirt and lasts longer. Higher permeability increases flow but may reduce accuracy — balance both for best results.

4. Brands and Standards

Use filter paper from Pall, Hydac, Donaldson, or Wilbley. Always match your oil purifier’s specifications and follow IEEE Std 637 or equivalent standards.

Practical Use and Maintenance Tips

Match equipment: Confirm your vacuum oil purifier uses compatible filter paper sizes and models.

Set goals:

For moisture removal – rely on vacuum dehydration; paper removes solids.

For heavy contamination – use graded filtration: 10 μm first, then 3 μm or 1 μm for precision.

ｒｅｐｌａｃｅ when:

Oil flow drops or pressure rises.

Generally, every 24 hours of continuous use or after one full batch.

Summary

Always use electrical insulating oil filter paper for transformer oil filtration.

Selection steps:

Confirm purifier specifications.

Choose fineness (1–10 μm) by contamination level.

Use reputable brands.

Monitor flow and ｒｅｐｌａｃｅ promptly.

Proper selection and replacement maintain oil purity, restore insulation, and ensure safe transformer operation.