Transformer oil-water separation method

Transformer oil-water separation is a key step in maintaining the insulation performance of the oil, and the appropriate method must be selected based on the form of water (free water, dissolved water, emulsified water). The following is a professional-grade water separation technology and operation guide:

Water existence and detection

| Water type | Particle size | Content range | Detection method |

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

| Free water | >100μm | 0.1-1% | Visual inspection/centrifugal sedimentation method |

| Emulsified water | 1-100μm | 50-500ppm | ASTM D2709 (emulsification test) |

| Dissolved water | <1μm | 10-50ppm | Karl Fischer method (ASTM D6304)|

Mechanical separation method (for free water)

1. Gravity sedimentation

- Equipment: Cone bottom oil storage tank (with drain valve)

- Parameters:

- Standing time: 48 hours (20℃)

- Drainage frequency: Drain every 8 hours (until there is no visible water layer)

- Efficiency: can remove more than 90% of free water

2. Centrifugal separation

- Equipment: disc centrifuge (speed ≥8000rpm)

- Advantages:

- Short processing time (≤30 minutes)

- Can simultaneously remove particles ≥5μm

Physical and chemical method (for emulsified/dissolved water)

1. Vacuum dehydration

- Equipment: two-stage vacuum oil filter

- Core parameters:

- Vacuum degree: -0.095～-0.099 MPa

- Oil temperature: 50-60℃ (reduce viscosity, increase water vapor pressure)

- Effect:

- Dissolved water from 50ppm to <10ppm

- Processing capacity: 500-2000L/h (depending on the equipment model)

2. Coalescence separation

- Material: hydrophilic-oleophobic coalescing filter element (glass fiber material)

- Process:

1. Emulsified oil passes through the coalescer → small water droplets merge into large water droplets

2. Enter the separation tank → gravity stratification drainage

- Advantages:

- Not dependent on heating, suitable for synthetic ester oil with low flash point

3. Molecular sieve adsorption

- Adsorbent: 3Å molecular sieve (pore size 0.3nm, selective water absorption)

- Regeneration method:

- Bake at 180℃ for 4 hours (can be reused 50 times)

- Applicable scenarios:

- Trace water fine treatment (ultimately up to ≤5ppm)

Emergency treatment plan (sudden water inflow)

1. Freezing separation:

- Reduce the oil temperature to -10℃ (2 hours) → Free water crystallization → filtration

2. Demulsifier injection:

- Add 0.1% oil-soluble demulsifier (such as polyether) → Centrifugal separation

Performance comparison table

| Method | Treatment lower limit (ppm) | Energy consumption (kWh/ton oil) | Equipment cost |

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

| Gravity sedimentation | 500 | 5 | ¥20,000-50,000 |

| Vacuum dehydration | 10 | 30 | ¥150,000-500,000 |

| Coagulation separation | 50 | 15 | ¥80,000-200,000 |

| Molecular sieve | 5 | 10 (adsorption energy consumption) | ¥30,000-100,000 |

Safety and standards

1. Moisture control standards:

- New oil: ≤15ppm (IEC 60296)

- Operating oil: ≤35ppm (DL/T 596)

2. Explosion-proof requirements:

- ATEX-certified equipment is required when handling oil with a flash point <140°C

Maintenance recommendations

- Daily monitoring: Use a fast moisture meter (such as Vaisala MMT330) for weekly testing

- Equipment maintenance:

- The coalescing filter element should be replaced every 200 hours

- Vacuum pump oil should be replaced every 500 hours

Through combined processes (such as centrifugation + vacuum), the moisture content of transformer oil can be efficiently controlled below 10 ppm, meeting the insulation requirements of transformers above 500kV. For UHV equipment, it is recommended to configure an online moisture monitoring + automatic dehydration system.