Protection philosophy in low short-circuit capacity distribution grids with high penetration of converter-interfaced distributed renewable energy sources

Abstract

The ever-growing penetration of converter-interfaced distributed renewable energy sources (CI-DRES) in distributionnetworks, despite the undoubted advantages, has a profound impact on the traditional protection systems. The protectionproblem becomes even more complicated as the increase in the CI-DRES penetration level leads to the decommissioning ofconventional power plants. Due to the limited current capability of CI-DRES, decommissioning of conventional units will lead toa transmission grid of significantly lower short-circuit level. This study proposes a novel protection philosophy for distributiongrids of low short-circuit capacity and high CI-DRES penetration. According to the proposed approach, CI-DRES are controlledto actively participate in the fault-clearing procedure, supporting the short-circuit capacity, in an aggregated form, through theinjection of controllable currents. Therefore, conventional overcurrent protection devices can be used, without any additionalinvestments for a protection system upgrade. The CI-DRES fault contribution is based on their relative position to the fault,respecting technical and protection-malfunction constraints. In addition to the short-circuit level, the effect of the feederparameters and the power factor of the injected fault current on the voltage recovery is also investigated. The proposedprotection philosophy is validated via detailed simulations in DIgSILENT PowerFactory.