| A new method of power system equipment representation by node-to-node impedance functions (NIF) based on wide frequency range (50Hz-1MHz) external impedance measurements has been developed. The study includes measurement procedure development, a comprehensive field measurement program covering 22 transformers at 9 converter stations and at other locations, a collection of over 3,000 impedance functions, the analysis of frequency dependent impedance functions, the derivation and calculation of NIF models, and the application of the NIF model for converter station radio frequency interference (RFI) studies.;The regular structure, relatively small number of elements, and virtually unlimited frequency range are the most important features of the node-to-node impedance representation compared to the conventional RLC lumped circuit models.;The analysis of the test results has revealed many transformer impedance characteristics for the wide frequency range covered. Based on the analysis, prediction of the first resonant frequency of transformer windings is possible. Application of the NIF models is demonstrated by the review of RFI studies related to a high voltage DC converter station. |
