Condition Assessment of Power Transformer Using Polarization and Depolarization Current Measurement Technique

Abstract

Condition assessment is a process, which is used to monitor insulation condition in electrical machinery. Condition monitoring allows us to identify the insulation failure which would further lead to hardware failure. By using condition assessment, maintenance can be done in a scheduled manner or some other precautions can be taken up to avoid the failure. Moisture content and natural decay influence the dielectric characteristics of multi-layer insulation in a high voltage transformer. The observation and analysis of the dc conductivity and dielectric response function is a feasible way of diagnosis of a transformer main insulation condition. This research work is focused on polarization and depolarization current measurement which can be used for evaluating the quality of transformer insulation. This technique is a time domain based method for evaluating the conductivity of insulation and moisture content in solid insulation materials of a transformer. Prediction from this analysis provides a future course of action which includes oil refurbishment, drying or changing the paper insulation in the transformer. This work presents a description of the PDC measurement technique with the quantitative modelling and simulation studies of PDC measurements on several power transformers having different dielectric material with different conductivity among the insulation configuration.