Broadband models of high voltage power transformers and their use in EMC system simulations of high voltage substations

In this paper we present and apply a methodology to create broadband models of power transformers in the frequency range from 9 kHz to 10 MHz. A power transformer of about 300 MVA rated power used at the interface between high voltage stations and AC-power grid is characterized in various operation modes by small signal measurements of the S-parameters. The measurement procedure is shown to provide passive and repeatable measurement data. We find that within the frequency range of interest the operation setting of the transformer like valve voltage or auxiliary power have only a minor impact on the measurements. The measured data is then post-processed to a black-box model describing the transformer as passive linear multiport. This model is then used in EMC system simulations of radiated emissions of full high voltage substations that are connected to the AC-grid by power transformers.