Modeling of three-phase autotransformer for short-circuit studies

•The inductance matrix autotransformer model for short-circuit studies is presented.•The model was verified with symmetrical components.•Tertiary winding presence increases currents in faulty windings.•Tertiary winding presence reduces currents in un-faulted windings. In this paper a three-phase autotransformer is represented by inductance matrix for short-circuit studies. The inductance matrix consists of winding self-inductances and corresponding mutual inductances between windings. For single phase-to-ground fault the inductance matrix model results are compared to symmetrical components results, commonly used to analyze unsymmetrical faults in three-phase power systems. The influence of a delta connected tertiary winding on un-faulted phase voltages and asymmetrical fault current distribution is analyzed.