What is acceptable particle count in transformer oil?

The acceptable particle count in transformer oil typically adheres to the ISO 4406 standard, which classifies particles based on size. For most applications, a cleanliness level of ISO 14/12/9 is considered acceptable, indicating a maximum of 320 particles larger than 4 micrometers, 80 larger than 6 micrometers, and 20 larger than 14 micrometers per 100 milliliters of oil. Maintaining this standard is crucial for ensuring optimal transformer performance and longevity.