The development of survivability analysis for power systems

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University of New Brunswick


The structural and operational natures of power systems make these systems prone to experience various types of transient events. Such undesired events include the loss of generation units, loss of transmission lines, load rejections, sudden and abrupt changes in load power demands, equipment failures, etc. The impacts of transient events start by creating frequency dynamics that can disrupt the generation, transmission and distribution of electric power in any power system. The conventional approaches to mitigate and damp frequency dynamics are set to restore the balance between power generation and demands so that a power system can regain a steadystate condition post any transient event. In general, the conventional approaches are usually designed and operated based on power system dynamics and stability analyses. These analyses are conducted with the assumption that frequency dynamics can be responded to by actions initiated by primary, secondary, or tertiary frequency controllers. The dynamics and stability analyses of power systems are widely used to design power system stabilizers, operate frequency controllers, and select settings for protective device. Conventional responses to frequency dynamics restore the balance between power generation and demands by either adjusting power generation (governor control), changing inter-area power exchange, or disconnecting loads. Such responses have shown a good capacity to effectively damp frequency dynamics and regain steadystate conditions in power systems. However, the recent trends of operating power systems have been shifting towards the de-regulated operation, which can offer integrating distributed generation units and deploy load-side control actions. Despite its advantages, the de-regulated operation of power systems faces several challenges, including the frequency dynamics. This challenge is created by the bi-directional power flows of load buses, as well as load-side control actions that may alter the active power injection into load buses. Frequency dynamics created by such activities can be difficult to damp using conventional responses. This difficulty is due to the fact that the disconnection of loads can (as a response) worsen the frequency dynamics. As a result, new responses are mandated to damp frequency dynamics created by load-side control activities. This thesis develops and tests a survivability-based method to model and analyze the impacts of load-side activities on frequency dynamics in power systems. The developed method introduces a survivability index to quantify the ability of a load bus to regain a steady-state condition, after experiencing a load-side activity. The survivability index is defined as the difference between pre-activity and post-activity power injection into a load bus. The boundary values of the survivability index are also defined in this thesis, and they are used to specify energy storage systems to enhance the survivability of certain load buses. The survivability-based method is implemented as a stand-alone software tool, and is being used by Barbados Power System. Several tests are conducted for integrating solar units and implementing demand response at several load buses. Test results show that the survivability index can accurately quantify the ability of load buses to regain steady-state conditions, and damp frequency dynamics created by load-side activities. Moreover, the survivability index is used to specify battery storage units for load buses with narrow survivability margins. Finally, test results demonstrate that the validity and accuracy of the survivability-based method is not affected by the ratings of integrated solar units and/or times and durations of demand response actions.