Main types of transformer oil purifiers

The main types of transformer oil (insulating oil) purifiers can be divided into the following categories according to their working principles, purification efficiency and applicable scenarios:

1. Classification by purification principle

(1) Vacuum oil filter

Principle: Remove moisture, gas and mechanical impurities from the oil through heating, vacuum dehydration and precision filtration.

Features:

- Applicable to medium and high voltage transformer oil (35kV~500kV).

- Can be deeply dehydrated and degassed (water content can be reduced to ≤5ppm, gas content ≤0.1%).

- Subtypes:

- Single-stage vacuum oil filter: single-stage vacuum tank, suitable for general purification (below 110kV).

- Two-stage high vacuum oil filter: Two-stage vacuum tanks are connected in series, with higher purification efficiency (UHV transformers above 500kV).

(2) Pressure oil filter

Principle: Remove particulate impurities through mechanical filtration through filter elements (such as glass fiber, stainless steel mesh).

Features:

- Mainly used to remove solid particles (filtration accuracy 1~5μm).

- Unable to dehydrate and degas, often used in conjunction with a vacuum oil filter.

(3) Centrifugal oil filter

Principle: Use centrifugal force to separate water and impurities in the oil (density difference).

Features:

- Suitable for the pretreatment of waste oil with high water content and many impurities.

- The dehydration effect is weaker than that of a vacuum oil filter and is gradually being eliminated.

(4) Coalescing and separation oil filter

Principle: The water droplets are combined and separated through a coalescing filter element, and then combined with precision filtration.

Features:

- Good at handling emulsified water (water content can be reduced to ≤50ppm).

- Mostly used for lubricating oil, less used in the transformer oil field.

2. Classification by function and structure

(1) Ordinary transformer oil filter

- Basic vacuum + pressure filtration, to meet routine maintenance (such as small distribution transformers).

(2) High-precision two-stage vacuum oil filter

- Two-stage vacuum + multi-stage filtration, used for ultra-clean treatment of ultra-high voltage transformers (such as 750kV, 1000kV) or before new oil injection.

(3) Live operation oil filter

- Can filter oil online when the transformer is live to ensure power supply continuity.

- Requires explosion-proof design and extremely high safety requirements.

(4) Mobile oil filter

- Vehicle-mounted or trailer-type design, suitable for on-site repairs at substations or operations in remote areas.

(5) Online monitoring oil filter system

- Integrated oil quality sensors (water content, particle size, dielectric loss), real-time monitoring and automatic purification.

3. Classification by processing capacity

| Type | Processing volume (L/h) | Applicable scenarios |

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

| Small oil filter           | 500~2000                | Distribution transformer, small unit maintenance                        |

| Medium oil filter      | 2000~6000              | 110kV~220kV main transformer maintenance                             |

| Large oil filter           | 6000~12000            | UHV transformer above 500kV                                                     |

| Super large oil filter | 12000~30000           | Converter station, nuclear power transformer batch processing |

4. Selection recommendations

- New oil injection: ｓｅｌｅｃｔ a two-stage high vacuum oil filter (to ensure cleanliness ≤5ppm).

- Operation and maintenance: single-stage vacuum oil filter + pressure filtration (economical and efficient).

- Waste oil regeneration: vacuum oil filter + centrifugal pretreatment (for highly polluted oil).

- UHV scenario: Double-stage high vacuum equipment (such as TR-300) must be used.