Impact of Changed Reactive Power Flows on Protection Relays in the Future Distribution Grid

As part of the decarbonisation of the energy system, large power plants in the transmission grid are gradually being switched off and the resulting lack of reactive power demand is being covered by the sub-grid levels. These changes in the reactive power flows and the effects on the protection devices in the distribution grid were investigated in more detail in this paper. For this study, selected protection systems - overcurrent and distance protection relays - were implemented in two distribution grids at different grid interconnection points. With the help of the generation units in the grids, study cases with different resulting reactive power flows were simulated. The analyses have revealed that the overcurrent relays are influenced and, in some scenarios, display false tripping. Using new parameters or with a given limit value for the reactive power supply, it was possible to rectify this. In addition, it could be determined that these false tripping events usually occur on spur lines to which many generation plants are connected.