Assessing the Severity of Voltage Sags Due to Short Circuits in Transmission and Distribution Grids

Grid codes require power plants to stay connected during grid disturbances. Power generation units have to withstand voltage disturbances with very low remaining voltages at their terminals or point of common connection (PCC). The capability of power generation units to withstand a defined voltage-against-time-profile is specified by so called low-voltage-ride-through-(LVRT)-requirements. Typical are LVRT-profiles with remaining voltages around u=0.05 pu for a fault event duration in the range of 150-250 ms. This paper investigates the propagation of voltage sags through different voltage levels in a Central European power grid and the likelihood of such low voltages, as given by voltage-against-time-curves in grid codes. It is not intended to make statements about the LVRT-capability of power generation units in this paper. Simulations are performed on an actual power grid with real load flow data in the power systems analysis software DIgSILENT PowerFactory. Fault statistics are given for the analyzed power grid to provide a rough estimate about the probability of different types of faults and fault events in general.