Summary So far, several line stability indices have been introduced and used for evaluating voltage stability status of power systems. The objective of this paper is to propose a comprehensive assessment of these indices and also to propose a modified line stability index to accurately assess the stability status of networks in different situations. To this purpose, the performance of several line indices at different conditions is analyzed. Also, to categorize system states to normal, alert, and emergency, proper thresholds are proposed for these indices. It will be shown that although line indices are able to properly assess the stability of a two‐bus system, they cannot detect the stability status in real networks. Therefore, a modified index has been proposed, which can accurately assess the stability status of power systems. The static and dynamic simulation results performed in the Institute of Electrical and Electronics Engineer (IEEE) 39‐ and 118‐bus test systems verify the performance of the proposed index.

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The main objective of this article is to propose a special protection system (SPS) to execute efficient remedial actions to prevent mid-term and long-term voltage instabilities. In this method, when the operating point (OP) leaves the normal operation state, the proposed SPS is initiated to execute the required corrective remedial actions to bring the OP back to a normal state and maintain bus voltages above prespecified thresholds. Considering the local nature of Volt/Var control and in order to execute fast remedial actions, in this approach, the required generation rescheduling or load shedding procedures were selected based on the electrical distance concept. This allows for remedial actions with the highest impact on volt/var control. In addition, in generation rescheduling procedures, the proposed method uses the ability of utility-scale photovoltaic resources, which can change their generation quickly. This plays a major role in maintaining stability of power systems. Efficiency of the proposed algorithm was validated through several scenarios performed in IEEE 39-bus, Nordic32, and PST 16 test systems using DIgSILENT PowerFactory software. Results of these dynamic simulations and their comparison with some previously published methods show the effectiveness of this method in timely executing appropriate remedial actions to maintain system stability.

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