Parameters governing the AC and LI flashover strength of interfaces between epoxy resin tubes and transformer oil

This paper reports on experimental investigations dealing with the impact of the temperature, the oil humidity, and the carbon content on the breakdown strength of oil gaps and the flashover behavior of glass-fiber reinforced epoxy resin tubes embedded in transformer oil. The measurements were carried out in a nearly uniform electrical field with an electrode arrangement being similar to the electrode/insulation configuration that is applied in on-load tap changers of power transformers. The contribution reveals that besides the breakdown values of the oil gap also the flashover behavior of the tubes is to a high extent determined by the relative oil humidity. Moreover it will be shown that in carbonized oil the flashover strength of the tubes needs not necessarily to be lower than in clean oil