Insulation geometry independent aging sensitive parameter evaluated from transfer function of Debye model for condition assessment of oil-paper insulation

Existing literature shows that lower time constant branches of insulation model represent condition of oil, whereas higher time constant branches are influenced by the condition of solid insulation. It is possible to assess the condition of oil-paper insulation by identifying the parameters of insulation model. It is understood that in addition to aging and moisture, factors like insulation geometry also affect the values of the branch parameters of insulation model. This implies parameters evaluated from one insulation model has limited potential in assessing the condition of a different transformer, even if the loading history and power rating of the two units are similar. The present paper introduces a performance parameter, which is less sensitive to insulation geometry. The parameter can be evaluated from the Transfer Function of the insulation model. It is shown that the parameter is influenced by condition of both oil and paper insulation. The performance of the proposed parameter is first tested using laboratory sample and then using data obtained from several real life power transformers.