Short-Circuit Performance Analysis of a Distribution Transformer Using Coupled Field-Circuit Approach

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The inability of power transformers to resist a short-circuit (SC) fault significantly impacts the safety of power systems. During SC faults, the leakage field undergoes significant distortion, resulting in large SC electromagnetic forces (EFs), which results in critical mechanical stresses. The finite element method (FEM) might be one of the best non-destructive numerical methods that enable designers to assess the transformer SC performance. Using the FEM, most SC performance analysis studies assume either the three-phase (LLL) or the single-phase-to-ground (LG) SC fault. Moreover, the existing studies use an excitation method that provides a high error rate due to the sensitivity of transient solvers. Furthermore, no considerable attention has been given to analyzing the influence of grounding the wye-connected windings on the SC performance. In this work, a non-linear-transient field-circuit coupled 3-D finite element model is created to analyze the SC performance of a delta-wye connected distribution transformer under various SC fault conditions. Results show that grounding the secondary windings significantly impacts the performance when a LG fault is applied. Except for the LG fault with wye configuration of the secondary windings, the windings SC current and EFs decay/rise over time with an exponential trend till reaching steady state.