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.