Detrapped Charge-Affected Depolarization-Current Estimation Using Short-Duration Dielectric Response for Diagnosis of Transformer Insulation

Analysis of detrapped charge [evaluated from polarization-depolarization current (PDC)] is effective in carrying out insulation diagnosis. However, computation of detrapped charge requires PDC data for at least 1600 s (PDCs each measured for 800 s). Such a technique of obtaining detrapped charge from short-duration PDC data considers few assumptions (including modeling of detrapping current by a straight line), which might not always be true for real-life equipment. Furthermore, PDC data are susceptible to noise and other environmental factors. Hence, it may be practically difficult to allow a measurement time of 1600 s during field measurement. Therefore, it is advisable to reduce the measurement time as well as the volume of data required. In this article, a method has been proposed, which is capable of estimating detrapped charge using only polarization current measured for 600 s. In addition, some unique advantages offered by the proposed method are also discussed in this article. The proposed technique is tested on data collected from several real-life in-service transformers.