How to configure transformer oil filtration accuracy?

The selection of transformer oil filtration accuracy requires a comprehensive consideration of voltage level, oil contamination level, and the equipment manufacturer's requirements. The following is a specific selection guide:

Core Principles

1. Voltage Level Determines Baseline Accuracy

- ≤35kV: 5-10 microns (routine maintenance, removal of mechanical impurities).

- 110-220kV: 3-5 microns (control of particulate matter, avoidance of partial discharge).

- ≥500kV (UHV): 1-3 microns (requires vacuum dehydration, particle size ≤ NAS Class 7).

2. Dynamic Adjustment of Contamination Level

- Light contamination (ISO 18/16/13 particle count): 5-micron filter element + vacuum dehydration.

- Severe contamination (ISO 21/19/16 or emulsification): First, coarse filtration (20 microns) to remove large particles, then fine filtration to 1 micron.

Key Parameter Comparison

| Standard Reference |        Cleanliness Requirements         | Corresponding Filtration Accuracy |

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

| IEC 60422                 | Particle Count ≤5000/mL (≥110kV) | ≤3 microns                                     |

| GB/T 14542              | Moisture ≤15ppm (UHV)                 | Requires Vacuum + 1 micron         |

| ASTM D6786            | NAS 1638 Level 6 (UHV)                  | ≤1 micron                                       |

Scenario-Specific Selection Options

1. New Oil Injection

- Accuracy: 3-5 microns (removes impurities during transportation/storage).

- Equipment: Plate and Frame Oil Filter + Molecular Sieve Adsorption (controls moisture ≤20ppm).

2. Operating Oil Maintenance

- Routine Filtration: 5 microns (monthly inspection, combined with particle counting).

- Post-overhaul filtration: 1 micron + vacuum treatment (dissipation loss ≤ 0.5%).

3. Fault recovery

- Moisture/minor deterioration: 3 micron + vacuum oil filter (moisture ≤ 10 ppm).

- Carbonization/heavy contamination: 1 micron + clay adsorption (acid value ≤ 0.1 mg KOH/g).

Precautions

- Post-Filtration Testing:

- Particle Size (ISO 4406)

- Moisture (GB/T 7600)

- Dielectric Loss (IEC 60247)

Recommended Equipment Configuration

| Voltage Level | Filter Element Precision | Required Features                            | Target Specifications                                                  |

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

| 10kV              | 10 micron                       | Plate and Frame Filter                      | Particle Count ≤ ISO 20/18/15                                   |

| 220kV            | 3 micron                         | Vacuum + Glass Fiber Filter              | Moisture ≤ 15ppm, NAS Level 8                                |

| 1000kV          | 1 micron                         | Vacuum + Electrostatic Purification | Dielectric Loss ≤ 0.3%, Particle Count ≤ NAS Level 6 |

Transformer oil filtration accuracy should be tailored to the specific application, based on voltage levels and contamination data. A phased, progressive filtration approach is preferred, with regular oil filtration tests verifying effectiveness.