Identification of the most sensitive frequency response measurement technique for diagnosis of interturn faults in power transformers

Interturn winding faults are one of the most prevalent and potentially destructive electrical faults in power transformers. This contribution is an initiative to explore the potential of the sweep frequency response analysis (SFRA) method in detecting interturn winding faults and also identifying the most appropriate measurement configuration for making sensitive frequency response measurements. This application enables timely warning of the rising failure and so is of particular importance, as these kinds of defects, if left undetected, can propagate and lead to catastrophic phase-ground or phase-phase faults which can finally cause the breakdown of the whole transformer. In this paper contribution is made to a better understanding of the transformer performance and modification of the transformer winding frequency response in the presence of interturn faults. The paper includes a full description of the details of the SFRA method and measuring procedure, along with principal experiments conducted on a 100 kVA distribution transformer. A large number of measurements with different transfer functions, various terminal configurations and three categories of measurement types was conducted to identify the most appropriate configuration for making SFRA measurements. The experimental results proved that the identified measurement configuration is sensitive to detect unambiguously interturn faults even down to 0.2% shorted turns along the winding.