A decentralized hybrid load-shedding scheme for the prevention of blackouts in power grids

In normal conditions, the load and generation of a power system are kept in strict balance to have a constant system frequency. Any variation on the load side is compensated by automatic control loops on the generation side and load management by the System Operator (SO). However, in major system disturbances, the load-generation mismatch is much larger, and the control loops fall short of maintaining the required balance. During this time, if sufficient generation is not injected or the surplus load is not disconnected soon, system frequency drops below the permissible limits, and the whole system collapses resulting in a blackout. To maintain system balance and control system frequency during major disturbance events, the widely used technique to shed excessive load is Under-Frequency Load Shedding (UFLS). The conventional Load Shedding (LS) techniques have several shortcomings i.e. slow operation under-shedding and over-shedding. This paper proposes a Rate of Change of Frequency (ROCOF) driven, decentralized, faster, and reliable LS scheme to disconnect the surplus load of the network in successive stages during major system disturbance events to avoid system blackouts. The performance of the proposed LS scheme was tested on a hardware-based setup and implemented in the National Grid of Pakistan.