Terminal measurements based modeling of single phase transformer for condition monitoring

The major limitation in the electromagnetic modeling of single phase transformers is the need for the design details and core specifications for accurate representation of its equivalent magnetic circuit. In this paper, a transformer modeling technique which requires only the terminal voltage and current measurements as the necessary inputs is proposed. The methodology is not only simple but also its implementation is non-invasive and can be performed without disconnecting the transformer from the supply. The underlying principle is to develop a magnetizing inductance profile based on these terminal measurements and use it in the circuit-based model of the transformer to simulate its dynamic performance. Effects of core saturation, core losses, magnetic core irregularities and imperfections are accounted for in the model, as these conditions are actually reflected in the terminal measurements themselves. For demonstrating the accuracy of the proposed method, it has been satisfactorily implemented on a 150 VA single-phase transformer. This suggests that the technique can be extended for modeling single and three phase transformers of higher ratings in future. The ultimate goal of such a model is to monitor the health of a transformer online and in real-time by comparing actual magnetizing current with the estimated healthy one.