Investigation of an ICT-based protection scheme for short-circuit events and an overload protection scheme to reduce cascading outages on HV/MV grids

This thesis is divided into two sub-parts, i.e., short-circuit protection scheme for the MV grid is addressed in the first part, and in the second part, an overload protection scheme and cascading effect for the HV grid is addressed. Non-directional overcurrent relays are the conventional relay type used in radial and open-ring distribution grids. In the future grid scenario with the incorporation of distributed energy resources, which leads to bi-directional power flows, the usage of these relays would result in unselective tripping during a fault. Directional overcurrent or distance relays are used to solve this problem and to isolate the faulty part. However, the directional overcurrent and the distance relays utilize the voltage phasor as a reference for the determination of the fault direction. This requires the usage of current and voltage transformers, which makes the protection design costlier and involves huge retrofitting and new installation in the existing grids. In this thesis, an ICT-based protection scheme is proposed as an extension for non-directional overcurrent relays to gain selective tripping in the case of a short-circuit in grids. The scheme uses the current phasor angle information exchange between two primary relays over the ICT to locate a fault in their protected areas. Furthermore, the primary scheme is extended with a backup protection scheme, which isolated the fault in the case of a failure of the primary relay. The proposed primary and backup scheme is evaluated with case studies using the power system tools pandapower and PowerFactory, to verify if the scheme is able to isolate short-circuit faults reliably and selectively. Overload cascades are among the most severe grid disturbances in interconnected power systems, which mostly results in a large load loss in the grid. The cascades are initiated by the tripping of protection relays in the grid during overloads. Their prevention is an important factor for grid stability. In this thesis, an overload protection scheme is proposed, which tries to solve overload cascades by load shedding through targeted relay tripping. The scheme uses a reduced subgraph which is affected by overload for the solution finding. The reduced subgraph of the grid has the advantage, that possible overload solutions can be determined reasonably fast. The proposed overload protection scheme is evaluated with case studies using the power system tool pandapower. Here, cascades with and without the protection scheme are analyzed to evaluate how the proposed solution reduces the load loss and solves the overload problem to avoid cascade overload tripping issues in the grid.