Predictive underfrequency load shedding scheme for islanded power systems with renewable generation

• Worst possible disturbance is estimated by the probabilistic approach to load flow,
• The presence of intermittent renewable energy sources is considered,
• On-line prediction of minimum frequency after the disturbance is performed,
• On-line prediction is achieved by solving a simple algebraic equation.

Underfrequency load shedding is one of the most important protection mechanisms in a power system. However, in the majority of power systems it has remained unchanged for decades, despite the advances in computer and communication technologies. Wide Area Monitoring System proved to be very useful and reliable in the last few years and this is why much effort is given into development of Wide Area Monitoring, Protection and Control concepts. Adaptive underfrequency load shedding is certainly a very suitable candidate for the task. In order to accelerate changes in this area, a proposal for an adaptive scheme has been developed, which is a good option from both the technical and economic points of view. In contrast to majority of adaptive schemes, it handles problems of active-power deficit estimation and its variations during the transient due to voltage dependent loads differently, i.e., by on-line forecasting the operating point trajectory in a phase space. The scheme has been tested on previously proven (by comparison to WAMS measurements) dynamic model of a part of a Slovenian power system and the results indicate a large improvement compared to the traditional scheme.