Influence of element grounding generator neutral and resistance of breakdown channel on fast transient process in unit-connected generator

In the paper the simulation results of ground-fault fast transients in stator windings of unit-connected generators are presented. The simulations were done for different elements connected between generator neutral and ground. Ungrounded neutral, neutral grounded through neutralisers or resistances were considered. The influence of the parameters of the particular grounding elements on the fast transient overvoltages during interrupted arcing ground-faults in the generator stator winding was determined. An additional capacitance to ground of the generator breakers, a real mechanism of ground-fault arc quenching, and real changes in its resistance during fast transients were also taken into account. Comparative simulations of the ground-fault overvoltages for units with the biggest difference in parameters (in range 30-1600 MVA) were carried out. It has been found that for the grounding elements analysed the maximum overvoltages will not exceed double amplitude of the generator phase voltage.