Influence of Presence of Acids in Transformer Insulation: A study using Cole-Cole Plots

Failure of paper insulation is the end of design life of a transformer. Researchers have already stated that paper itself is the storehouse of moisture. Different operating variations over the service life in a transformer initiate degradation and breaking down of cellulosic chain of the paper. Degradation not only weakens the dielectric strength of solid insulation electrically but also produces different carboxylic acids. Organic acids that are produced as by product play a major role in insulation degradation. Among the organic acids produced, low molecular weight acids are found to be absorbed by paper. Over the past few years, attention has been focused to look into the causes of the detrimental effects of insulation ageing, but no such serious efforts have been made to look for the detrimental effects and to understand the influence on insulation ageing due to acid formation. Hence, an attempt has been made to look into the degrading effects caused by the acids by analyzing the dielectric response data obtained in time domain. To understand the physical behavior going on inside the dielectric material due to the influence of acid, time domain data is converted to frequency domain. The frequency domain parameters obtained are used to construct the Cole-Cole diagram to draw conclusions about the condition of ageing status of transformer oil-paper insulation.