Mathematical Models for Current, Voltage, and Capacitively Coupled Voltage Transformers (TR117)

This report reviews and presents several mathematical models of instrument transformers, including those used to represent the nonlinear magnetic core of instrument transformers. The transient response of the instrument transformer is compared to test results recorded in the laboratory. The report provides practical guidelines as to which of the physical elements of instrument transformers are important to model during transient studies and which elements may be ignored without sacrificing the accuracy of the simulation results. The Electromagnetic Transients Program (EMTP) data files used to generate the models are also provided in an appendix to help new EMTP users model instrument transformers for evaluation of high-speed protective relaying systems.