Development and testing of a methodology to determine parameters of equivalent circuits of power transformers based on fault oscillograms for short-circuit current calculation

<jats:p>Currently, the Common Information Model of the United Power System of Russia is being actively implemented in the electric power industry. Data which is received from Common Information Model is used to develop calculation models for various grid and generating equipment (including unit transformers and interconnecting autotransformers of nuclear power plants) for short-circuit current calculation. However, in real-world practice, an electric power engineering entity does not possess sufficient data to completely instantiate Common Information Model. For example, for multi-winding transformers, determining the active resistances in the positive-sequence equivalent circuit is up-to-date issue, while for all three-phase transformers (including unit transformers of nuclear power plants), calculating the parameters of the zero-sequence equivalent circuit is crucial. When compiling and analyzing the equivalent circuit diagrams for multi-winding power transformers, the principles of classical theory of electrical circuit analysis and synthesis have been used. When determining the parameters of the transformer equivalent circuit diagrams, programs for viewing fault oscillograms (Waves, Transcop, etc.) have been used. Impedance values of the equivalent circuit of multi-winding transformers are determined using various methods, and their characteristics have been provided. A methodology to determine the parameters of equivalent circuits for power transformers using fault oscillograms has been proposed. A method to verify the grid calculation model for short-circuit current calculations has been formulated. The scope of application of fault oscillograms to verify the parameters of equivalent circuits for transformers has been outlined. The results of determining various parameters of equivalent circuits for power transformers using fault oscillograms have been presented. For some transformers, the active power losses during the short-circuit test may not match the same loss value calculated using the active resistance values of the individual transformer windings. Fault oscillograms are a sufficient tool to determine/verify the parameters of power transformer equivalent circuits (including zero-sequence circuits). However, there is a number of limitations in their use related to the magnitude of fault current and voltage components, as well as current transformer errors.</jats:p>