What is transformer oil centrifugal separation?

Transformer oil centrifugal separation is a physical purification technology that uses centrifugal force to remove water, solid impurities and other pollutants from oil. It is mainly used to restore the insulation performance and chemical stability of transformer oil to ensure the safe operation of power equipment. The following is a detailed explanation from the aspects of principle, equipment, operation steps and precautions:

Centrifugal separation principle

1. Density difference separation

Using the density difference of transformer oil (density about 0.85-0.89 g/cm³), water (1.0 g/cm³) and solid particles (such as metal chips, dust), in a high-speed rotating centrifuge, impurities with high density are thrown to the outside, and pure oil is concentrated on the inside to achieve stratified separation.

- Free water: large water droplets are easy to separate;

- Emulsified water: demulsifier needs to be added or the centrifugation time is extended;

- Solid particles: particles usually >1μm can be effectively removed

2. Centrifugal force calculation

Centrifugal force \( F = m \cdot r \cdot \omega^2 \) (\( m \)-mass, \( r \)-radius of rotation, \( \omega \)-angular velocity), the separation efficiency can be controlled by adjusting the speed.

Types of centrifugal separation equipment

| Type | Features |

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

| Disc centrifuge | - Multi-layer conical discs, high separation efficiency; <br>- Suitable for continuous processing of large amounts of oil (such as power system maintenance). |

| Tubular centrifuge | - High speed (＞10000rpm), high separation accuracy; <br>- Suitable for small batches of high purity requirements (laboratories). |

| Basket centrifuge | - Simple structure, easy to maintain; <br>- Commonly used for on-site emergency treatment or small transformers. |

Operation steps (taking the disc centrifuge as an example)

1. Pretreatment

- Oil sample testing: Determine the water content (needed to be <5%) and particle size (ISO 4406 standard).

- Heating the oil: Raise the oil temperature to 50-60℃ (reduce viscosity and improve separation efficiency).

2. Equipment debugging

- Start the centrifuge and gradually increase it to the rated speed (such as 6000rpm).

- Adjust the oil inlet flow rate (usually 100-500L/h, adjusted according to the degree of pollution).

3. Separation process

- Dirty oil enters the centrifuge from the top, stratifies between the discs, impurities are deposited on the drum wall, and clean oil flows out from the center outlet.

- Slag discharge: Regularly stop the machine to remove the sludge in the drum (manual or automatic slag discharge function).

4. Post-processing

- Test the breakdown voltage (need ≥50kV/2.5mm) and water content (≤20ppm) of the purified oil.

- If it does not meet the standard, it can be recycled or combined with vacuum dehydration.

Advantages and Disadvantages of Centrifugal Separation

| Advantages | Limitations |

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

| 1. Efficient removal of free water and solid particles; | 1. Ineffective for dissolved water (<500ppm); |

| 2. No consumables (such as filter elements) are required, and the operating cost is low; | 2. Unable to remove chemical pollutants such as colloids and acidic substances.

| 3. Large processing volume, suitable for industrial scenarios. | 3. The equipment is large and inconvenient to move. |

Comparison with other purification technologies

| Technology | Applicable pollutants | Efficiency | Cost | Scenario |

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

| Centrifugal separation | Free water, large particles | High | Medium | Substation, factory batch processing |

| Vacuum dehydration | Dissolved water, gas | High | High | Deep dehydration of precision equipment |

| Precision filtration | Tiny particles (1-5μm) | Medium | Low (consumables) | Laboratory or small system maintenance |

| Adsorption treatment | Acidic substances, colloids | Low | High | Regeneration after oil aging |

Precautions

1. Safe operation

- The centrifuge needs to be fixed stably to avoid vibration caused by high-speed rotation;

- The oil temperature should not exceed 80℃ during heating to prevent oxidation or fire risks.

2. Environmental protection requirements

- The separated sludge (including heavy metals and oil residue) must be treated as hazardous waste and must not be dumped at will.

3. Maintenance

- Clean the drum and disc regularly to prevent impurities from hardening.

- Check the bearing lubrication to avoid wear.

Typical application scenarios

1. Transformer maintenance: Regularly remove moisture and dust inhaled during operation.

2. Fault repair: Clean carbides and metal debris in oil after a lightning strike or overload;

3. Oil regeneration: Extend the service life of transformer oil and reduce oil change costs.

Transformer oil centrifugal separation is one of the core technologies for oil treatment in power systems, which efficiently removes moisture and solid impurities through physical means. In practical applications, equipment parameters should be selected based on the type of oil contamination (such as mainly water-containing or mainly particle-containing), and vacuum dehydration or adsorption purification should be combined when necessary to meet the standard requirements of DL/T 429 "Technical Guidelines for Oil Purification for Power Use".