Design and real time performance evaluation of islanding and load shedding scheme

Industrial plant units are to be isolated from the grid as quickly as possible during grid disturbances. After islanding, load shedding is one the main actions that can be taken to prevent complete black out in industrial plants during such disturbances. The challenge for the islanding scheme is to island within the critical clearing time to avoid total system collapse. Islanding should not be done for every temporary disturbance in the grid as frequent islanding will reduce the reliability of the system. For sensing such conditions, careful selection of settings of the protective devices such as under frequency relay, over frequency relay, ±df/dt -rate of change of frequency relay, undervoltage and directional over current relays is required. Composite Islanding Load Management System (CILMS) implementing the logics for islanding and load shedding can be pre-commissioned and tuned, while connected to the Real Time Digital Simulator (RTDS) in a closed loop. In this paper, the results of the studies which formed the basis for arriving at the settings to be implemented in CILMS and performance evaluation of CILMS on Real Time Digital Simulator (RTDS) which helped in fine tuning the settings for a practical system are discussed.