Adaptive UFLS Schemes in Modern Power Systems– Conceptual and Simulation Proved Comparison

In recent decades, the advantages of a fast development in the computer and communication technology have been successfully harvested in the majority of technological areas for updating various mechanisms and processes. Power system control and protection is no exception. However, actual implementation of modern technologies into power system control and protection mechanisms depends on a country - in some of them it is rather dare and open-minded, in some of them it is very conventional. This also goes for underfrequency load shedding protection. In case of a sudden underfre- quency conditions appearance in the power system only a centralized gathering of measurements and global actions (e.g. use of so-called WAMPAC technology - Wide Area Measurement Protection And Control) can represent an appropriate approach to a global problem. In such circumstances, underfrequency load shedding is often the last resort tool for avoiding a total power system blackout. It's appropriate actions are of great importance both from technological and economical point of view. In this paper several different adaptive approaches are presented and compared in their efficiency via testing on two different dynamic power system models. First scheme is a typical adaptive scheme with calculation of active power deficit and equal distribution of the calculated value among four different load shedding steps. Second scheme involves some modification of shedding steps amount according to frequency first time derivative change between two steps. Other two schemes are of predictive type and shed load according to the prediction of minimal frequency value after active power deficit occurrence. Tests have shown that predictive schemes yield best results and therefore should be strongly considered as an actual possibility for power system implementation in the future.