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UBC Theses and Dissertations

Transformer modelling for transient studies Neves, Washington L. A.


Transformer modelling is a concern for the utility industry. The object of this work is to develop and investigate dynamic core models suitable for transient studies. A major advantage of the core models developed here is that they use readily available transformer test data as supplied by the manufacturer. For ferroresonance and inrush current studies, core saturation needs to be represented reasonably well. A direct approach to producing nonlinear peak flux-current and voltage-current characteristic of the iron core, taking iron losses into account, is presented. The algorithm is simple in concept, easy to implement, and may be useful for electromagnetic transient programs. A crude estimation of the transformer open circuit capacitance is also made from rated frequency data. It is useful for situations in which the transformer exciting current experiences strong capacitive effects. An iterative algorithm for more correctly representing the flux-linkage curve of a delta-connected transformer, suitable for situations in which the tests are performed with a closed delta, is developed. It uses positive sequence excitation test data as input and takes into consideration the removal of triplen harmonics from the line current. An approach to model frequency-dependent effects in the transformer core from transformer no-load loss data, is presented. Hysteresis and eddy current effects in the core are treated simultaneously. The flux-current trajectories are generated by circuit models with no need to pre-define them. Simulations using the developed models are compared to laboratory measurement of inrush current and to a ferroresonance field test.

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