Hardware Implementation of an Automatic Adaptive Centralized Underfrequency Load Shedding Scheme

The underfrequency load shedding (UFLS) mostly used in industry is a decentralized deterministic scheme designed to shed a prespecified amount of load after a predetermined time delay. It sheds the same amount of load from the same location irrespective of how fast the frequency drops and without consideration of the disturbance location or dip in bus voltage. Recent studies focused on adaptive UFLS, but these studies are still based on software simulation. This study presents an implementation of a real-time centralized adaptive UFLS scheme using industry-grade hardware. It estimates the amount of load to be shed based on the rate of frequency decline and distributes the load to be shed among the load buses based on the voltage dip at these buses. The UFLS in this study is implemented using a real-time digital simulator, phasor measurement units embedded in the relays, a global positioning system clock, and a synchrophasor vector processor. The load is modelled as a mixture of dynamic and static load. The implemented scheme restored the system frequency and voltage. The results emphasize its adaptability and suitability for implementation in industry.