Requirements for Protection Concepts in High-Voltage Networks with High Penetration of Decentralized Generation Systems in Distribution Networks

The paper describes the approach and results of a study on the maximum fault clearing time in the distribution grid before generation capacities in system-critical power sizes disconnect from the grid.
Due to the energy transition, a large part of the generation capacity is expected to be connected to the distribution grids in the future. Until now, distribution network operators have assumed that faults within their networks do not lead to loss of generation with system-critical impact. Protection concepts have been designed to protect the elements in the distribution grid. However, long fault clearing times may go along with a loss of generation units, which stay connected under low voltage conditions only for a certain time period defined in fault-ridethrough (FRT) requirements and the plant protection settings. In order to determine how much generation capacity may get lost RMS simulations with 3-phase faults were used to determine the power disconnection from the grid over the duration of the fault. A grid model with a detailed high- and medium-voltage grid was used for the 2030 and 2045 scenarios. The disconnected power and the chronological sequence depend on the fault behaviour of the decentralized generators and their setting of the plant protection. Furthermore, it was shown that neighbouring grids must be taken into account. Even if there is no system-critical generation capacity in the grid that contains the fault, system-critical generation capacity can be disconnected from the grid due to the influence of neighbouring grids or plants. Possible adjustments and requirements to avoid such situations are described.