Application limits for transient earth-fault analysis of symmetrical components in compensated grids under unbalanced conditions

Unbalanced grids may have variations in line and coupling impedances, as well as capacitances, requiring further considerations for symmetrical component calculations. This leads to deviations between the symmetrical component model and reality. These deviations are demonstrated on a medium-voltage grid and their respective values are determined. Due to the unbalance, a zero-sequence voltage occurs which varies with the grid conditions. Alternative methods of balancing the grid to reduce unbalances are analysed. Cable shield currents must be determined separately, as they are not directly obtained using symmetrical components. The impact of grid unbalances on the transient behavior during earth-fault initiation and clearing is also studied.