Grid protection is intended to protect the electrical energy system from damage. The study describes which topics need to be investigated in the near future in order to fulfill this protection task.
The task of grid protection is to protect equipment, installations and the electrical energy system in its functional unit from damage or to minimize the local damage that has usually already occurred in the event of hazardous conditions. This study describes for three subject areas which objects of investigation need to be considered in the foreseeable future in order to guarantee the protection task. In summary:
1. Short-circuit power
Increasing feed-in from power electronics is changing the short-circuit conditions in the grid. A reduction in the short-circuit power with a change in the feed-in will be partially compensated for by the increasing grid expansion and the resulting higher meshing; the short-circuit power of the node with the lowest short-circuit current in 2011 will not be undercut at any point in the grid in the future. In addition, the protection principles used in the extra-high voltage grid are largely independent of the level of current. The protection principles currently used and the sensitivity of the protection devices currently in use will continue to be sufficient in the future.
2. Harmonics and quality of short-circuit currents
With regard to the quality of short-circuit currents, there are currently no requirements for generation systems or for the robustness of protective devices. This can lead to malfunctions of protective devices due to increasing feed-in from power electronics. It is urgently recommended that this aspect be investigated further and, if necessary, incorporated into standardization.
On the other hand, protective devices require harmonic currents during fault-free operation of the grid in order to be able to distinguish between a hard operating state (e.g. switch-on surge of a transformer) and a short circuit. This can result in requirements for a more voltage source-like behavior of power electronic feeders, i.e. to react actively to harmonic voltages in the grid by damping them with harmonic currents. Here, too, it is recommended that this previously neglected effect be investigated further.
3. Higher utilization of the transmission grid
With the protection principles currently in use, it is in principle possible to increase the utilization of the transmission grid. This report describes several measures that can be taken by the grid operators and by the protection technology, including online monitoring (in the grid management system), the activation of droop blocks (if necessary) and an optimization of the pick-up characteristic (by the protection device manufacturers).