Evaluating Internal Resonances in Power Transformers by Using Instrumental Variable Vector Fitting

Procedures for modeling potential/ power transformers and reactors in order to support electromagnetic transients analysis have been addressed by many recent researchers. Among all methods for obtaining black-box models, the Frequency Domain Vector Fitting (FD-VF) or, simply VF, has several successful application reports in electrical power systems. This article is two purpose: first to describe a procedure that combines instrumental variables to the VF method, called the Instrumental Variable VF (IV-VF). The main advantage of the IV-VF is the fact that if the iterative procedure converged, an optimal local solution is obtained. Also to present a case study based on actual single-phase transformer measurements (Benchmark JWG A2/C4.52 for Power Transformers) and a GIS installation, where IV-VF is used for evaluating internal resonances in power transformers due to high frequency transients. The knowledge of external and internal winding response to these transients contribute to insulation design and reliability in field operation.