The “Chemical degradation of oil” criticality is caused mainly by the mechanisms of normal ageing and thermal stress of oil, and secondly by problems of cross-contamination and the use of improper practices in the handling of insulating liquids and the transformer. The aforementioned improper practices have an impact on the life cycle of the electrical equipment with insulating fluids:
| Causes of the “Chemical degradation of oil” criticality | When it may occur (life cycle phases) |
|---|---|
| Deficiency of requirements for purchase of new insulating liquid (seeIEC 60296) | Requirements and purchase |
| Deficiencies in quality control for individual lots or individual supplies of insulating oil | Acceptance of insulating oils |
| Deficiency in analytical procedures for checking chemical degradation of oil | Oil acceptance, factory test, installation and pre-energisation, operation, old age, post-mortem |
| Cross-contamination through the use of oil, plants, tanks or containers contaminated by oxidised, polar and/or incompatible compounds (for topping up, impregnating or filling) | Transformer construction, factory test, installation and pre-energisation, exercise, old age |
| Recycling of oil and other materials contaminated by oxidation products or polar compounds | | Post-mortem |
