6 methods of insulating oil purification

The purification of insulating oil (such as transformer oil, switch oil, etc.) requires the selection of appropriate methods according to the type of pollution (water, particles, gas, oxidation products).

The current six mainstream purification technologies are:

Physical purification method

1. Vacuum dehydration and degassing

- Principle:

The oil is heated in a vacuum tank (50-65℃), and the water evaporates and is pumped out by a vacuum pump (vacuum degree reaches -0.095～-0.099 MPa).

- Effect:

- Water content from 500ppm→≤10ppm

- Gas content from 5%→≤0.1%

- Equipment: Two-stage vacuum oil filter (with condenser)

- Application: Pretreatment of new oil injection, rescue of damp oil

2. Precision filtration

- Filter element type:

- Cellulose filter paper (5μm)

- Glass fiber (1μm, β₅≥200)

- Standard: After treatment, the particle size reaches NAS 1638 Class 6

- Note: High viscosity oil needs to be heated to 40℃ first

Chemical purification method

1. White clay adsorption

- Process:

Add 3%-5% activated white clay, stir and heat (80-90℃) and filter.

- Objects to be removed:

- Oxides (acid value from 0.1→0.01 mg KOH/g)

- Colloidal substances (improvement of dielectric loss factor tanδ)

- Limitations: White clay waste residues need to be treated as hazardous waste

2. Solvent extraction

- Targeted problem: PCB (polychlorinated biphenyl) contaminated oil

- Solvent formula: n-hexane + isopropanol (volume ratio 3:1)

- Efficiency: PCB removal rate >99%

Combined process

1. Vacuum-coagulation combination

- Process:

`Coarse filtration→coagulation dehydration (to 50ppm)→vacuum deep dehydration (to 10ppm)`

- Advantages: 30% energy saving compared to the single vacuum method

2. Electrostatic adsorption + filtration

- Applicable: Regeneration of aged oil

- Effect:

- Breakdown voltage from 30kV→≥60kV

- Color restored from dark brown to light yellow

Method comparison table

| Method | Treatment cost (¥/ton) | Time consumption | Best applicable scenario |

|--------------------|------------------|------|--------------------------|

| Vacuum dehydration | 300-500 | 8-12h | Periodic maintenance of large transformers |

| White clay adsorption | 800-1200 | 24h | Acidified oil (acid value>0.1) |

| Portable agglomeration | 500-800 | 4-6h | Emergency repair of substation |

| Solvent extraction | 2000+ | 48h | PCB contaminated oil (special qualification required) |

Special working condition treatment

1. Low temperature environment:

- Heat to 30℃ before filtering (to prevent wax precipitation)

2. High altitude area:

- Use a booster vacuum pump (to compensate for the impact of low air pressure)

3. Online purification:

- Install a circulating filtration system (processing capacity = 5% of the tank volume/h)

Safety Tips

- Explosion-proof equipment is required to handle flammable oil (flash point <140℃)

- Waste clay/solvents belong to HW08 hazardous waste (code: 900-249-08)

Choosing a combined process based on the oil inspection report (water content, acid value, particle count) can extend the oil life by 3-5 times. For UHV equipment (≥500kV), a full-process solution of vacuum + electrostatic adsorption + online monitoring is recommended.