Load Shedding and Load Recovery with Dynamic Simulations

Electric load shedding is implemented to maintain the generation power margin at nominated level when load demand is higher than electric supply. This prevents the widespread system collapse when a fault occurs. The scope of study consists of system analysis, design and simulation. Dynamic simulations are performed using the ERACS Power Analysis Software. When the frequency falls below preset level at a certain rate, a predetermined amount of load will be removed to restore the system frequency. Important design considerations for this scheme are the maximum anticipated overload, number of load sheading steps, size of load shed at each step and frequency relay settings. Load restoration after load shedding can only be executed after the system bas recovered completely and its normal frequency is restored. Loads should be restored in small blocks sequenced by time delay between successive restorations to allow frequency stabilization. A case study is carried out on PETRONAS Penapisan Melaka, whereby a load shedding scheme is designed for its upcoming cogeneration plant. Dynamic simulations performed indicate that the load shedding design is feasible and abIe to halt frequency collapse due to generation loss. The design strategy, calculations and justification are presented in this paper.