Monitoring of Solar Photovoltaic Plant Power Transformers Using Sweep Frequency Response Analysis

Frequency response analysis is a popular technique for assessing the mechanical and electrical integrity of oil immersed power transformers. Although this diagnostic method is often used for transformer condition assessment, interpretation of the frequency responses remains one of the main challenges. In this paper, experimental results, following sweep frequency response analysis of four similar Dy11 vector type, with ratings of 2.7MVA, 33kV/655V power transformers are presented and discussed. The selected transformers were part of transformers that are in use in a solar photovoltaic plant. The four transformers include two non-faulty and two faulty transformers. The study aims at explaining transformer wideband frequency characteristics and identifying various failure modes from the plotted frequency responses. It is shown that measured transformer frequency characteristics can provide useful information to detect defects in the windings and therefore help greatly in maintenance.