Effect of impurity particles on transformer oil under normal operating conditions

A systematic survey was conducted of transformer oil samples taken from operating transformers and reactors used in Hydro-Quebec's transmission system. It was found that the particle content in the oil follows a distribution of the power function type and that it can be related to the dielectric strength of the oil and constitutes a good indication of the overall performance of the apparatus. Filtering the oil reduces the particle content and improves its dielectric strength.