Design and analysis of UFLS scheme for a low-inertia based power grid

Due to the high penetrations of renewable energy sources, a significant change to power systems' dynamic behavior following a contingency event has become a major concern in modern days. A power system's inertia is getting weaker with the integrations of renewable generators. As a result, UFLS schemes may fail to protect the frequency decline below the threshold limits with conventional settings. Inadequate load shedding during frequency excursion process may lead a cascade tripping of remaining generators, leading to a possible blackout. This thesis addresses this problem and analyses the impacts of penetration of renewable energies into grid. Here, a modified load-shedding method is proposed by considering ROCOF and the total system's damping factor. Then, it models the under-frequency relay by using MILP techniques to provide complete freedom of relays while dealing with the same problem. Furthermore, this thesis also shows a comparison of performances of these three techniques (conventional, proposed and MILP). Here, a13-bus network from real power system is considered as a test system and several case studies are conducted using the PSS/E. From simulations it is found that the proposed on-line based UFLS scheme is more efficient and one of the promising solutions to avoid blackouts