Assessment of General Feasibility for Robust Islanding

Intentional islanding is a concept where power system is divided, in case of a significant disturbance, into smaller segments in order to prevent a complete black-out. In this paper the results of three different approaches to assess the feasibility of intentional islanding is presented using generic power system model. The study targets to identify on high level the criteria for successful islanding based on the system's main characteristics with a wide variety of operating conditions. The operating conditions were executed by varying size of the studied system, imbalance level at the time of islanding and the response speed of the turbine governor. The conditions were derived so that they can be considered to represent on a general level, the possible regional islands and their generation portfolio in Finland. Size of the possible regional islands was represented by varying the kinetic energy of the rotating masses. The results showed that the frequency response stayed within tolerable limits when the total imbalance was maximum of 1.25 % of the total kinetic energy of the rotating masses, i.e. very a narrow range of the studied combinations. Based on the results, it can also be concluded that turbine speed control parameters, tuned for certain size of system, do not likely perform in an adequate manner when the rotational kinetic energy of the systems varies. Considering the results of the study, it seems that the required combinations for robust island may be very rarely available because of the present market-based electricity generation allocation and configuration. However, separate system specific studies to address the possibility of intentional islanding should be performed considering the actual availability and variations of generation and the actual power system configurations.