Power Transformer Insulation Diagnosis Using De-Trapped Charge Affected Short-Duration Dielectric Response

The polarization and depolarization current (PDC) gets affected by de-trapped charges. Analysis of such currents leads to an inaccurate assessment of the transformer insulation condition. Existing insulation model-based methods assume the polarization current to be free of the de-trapped charges. This assumption does not always hold good; moreover, most of the time series forecasting methods available in the literature are based on this assumption. A novel method has been proposed for obtaining the depolarization current, which is less affected by the de-trapping current, from short-duration de-trapped charge affected polarization current. The result presented in the article demonstrates that the use of data that is less affected by de-trapped charges leads to reliable diagnosis. The proposed analysis has been formulated and tested on data collected from various real-life transformers.