Increasing demand for electricity and the modernization of power systems within competitive markets has induced power systems to operate close to their stability limits. Therefore, the continuous monitoring and control of power systems through voltage stability indices is urgently needed. This is the first-ever effort to examine more than 40 voltage stability indices based on their formulation, application, performance, and assessment measures. These indices are sorted based on a logical and chronological order considering the most recent indices to be applied worldwide. However, the generalizability of these indices in terms of multivariable objectives is limited. Despite its limitation, this study systematically reviews available indices in the literature within the past three decades to compile an integrated knowledge base with an up-to-date exposition. This is followed by a comparative analysis in terms of their similarity, functionality, applicability, formulation, merit, demerit, and overall performance. Also, a broad categorization of voltage stability indices is addressed. This study serves as an exhaustive roadmap of the issue and can be counted as a reference for planning and operation in the context of voltage stability for students, researchers, scholars, and practitioners.

The provision of electricity in a reliable and sustainable manner in provincial towns and villages in the small West Africa state of Sierra Leone requires the adoption of appropriate technologies. The rapid increase in electricity demand has generated great interest in how to tackle a possible long-lasting energy deficiency in the country. This paper aims at analyzing the techno-economic feasibility of a hybrid renewable energy system (HRES) for the sustainable rural electrification of Lungi Town, Port Loko District, Sierra Leone. Optimization, economic, reliability, and sustainability analyses were carried out using a genetic algorithm (GA), with the main objectives of minimizing the loss of power supply probability (LPSP) and cost of energy (COE). Three different case scenarios were configured, using a diesel generator (DG), wind/PV/DG/battery, and wind/PV/battery. Various combinations of these case scenarios were compared to determine which option was the most economically viable. In order to determine the case scenario with the lowest LPSP and COE, the operations and maintenance costs of the three cases were calculated. Using only DG for case one, the operations and maintenance cost amounted to USD 1050,348.12/year. The operation and maintenance cost for case two, which included wind/PV/DG/battery, was found to be USD 561,674.06/year. The operations and maintenance cost for case three, which included wind/PV/battery, was found to be USD 36,000/year. In standalone microgrids, however, the use of renewable energy sources is not reliable due to the uncertainty of renewable energy sources. Consequently, the simulation results show that the wind/PV/DG/battery-based HRES is the most cost-effective, reliable, and sustainable for the specific location in comparison to the current traditional method of electricity generation. Since there is abundant solar radiation with substantial wind speeds across the country, this HRES can be applied in most rural and remote areas in place of the current diesel generators (DGs) that are widely deployed in the country.

The integration of Distributed Generation (DG) units in the existing power system has made the reliable operation of the system more complex. This has necessitated a comprehensive approach in planning the expansion of the system with the incorporation of DG units for effective and reliable operation of the system. In this study, a robust Hybrid Islanding Detection Technique (HIDT) has been proposed for identifying the islanding event early and accurately in the distribution networks with DGs installed by a two‐step Genetic Algorithm (GA) process. As the reliability of power supply to the customer is of utmost importance, a priority‐based load shedding scheme is proposed. The proposed load shedding scheme sheds only the vulnerable loads in the island for regaining the frequency and voltage stabilities. By the proposed methods, a comprehensive solution for system planning and emergency control actions can be obtained for effective operation of the system with DG units. The proposed methods are investigated on standard IEEE 33 and 69 bus distribution systems under different loading conditions. The results obtained show that the proposed methods are able to identify the islanding event more effectively and also regain the stability in the island with less amount of load shedding.

Like most developing countries, Afghanistan still employs the traditional philosophy of supplying all its load demands whenever they happen. However, to have a reliable and cost-effective system, the new approach proposes to keep the variations of demand at the lowest possible level. The power system infrastructure requires massive capital investment; demand response (DR) is one of the economic options for running the system according to the new scheme. DR has become the intention of many researchers in developed countries. However, very limited works have investigated the employment of appropriate DR programs for developing nations, particularly considering renewable energy sources (RESs). In this paper, as two-stage programming, the effect of the time-of-use demand response (TOU-DR) program on optimal operation of Afghanistan real power system in the presence of RESs and pumped hydropower storage (PHS) system in the day-ahead power market is analyzed. Using the concept of price elasticity, first, an economic model indicating the behaviour of customers involved in TOU-DR program is developed. A genetic algorithm (GA) coded in MATLAB software is used accordingly to schedule energy and reserve so that the total operation cost of the system is minimized. Two simulation cases are considered to verify the effectiveness of the suggested scheme. The first stage programming approach leads case 2 with TOU-DR program to 35 MW (811 MW − 776 MW), $16,235 ($528,825 − $512,590), and 64 MW reductions in the peak load, customer bill and peak to valley distance, respectively compared to case 1 without TOU-DR program. Also, the simulation results for stage 2 show that by employing the TOU-DR program, the system’s total cost can be reduced from $317,880 to $302,750, which indicates a significant reduction in thermal units’ operation cost, import power tariffs and reserve cost.

Combating climate change issues resulting from excessive use of fossil fuels comes with huge initial costs, thereby posing difficult challenges for the least developed countries in Sub-Saharan Africa (SSA) to invest in renewable energy alternatives, especially with rapid industrialization. However, designing renewable energy systems usually hinges on different economic and environmental criteria. This paper used the Multi-Objective Particle Swarm Optimization (MOPSO) technique to optimally size ten grid-connected hybrid blocks selected amongst Photo-Voltaic (PV) panels, onshore wind turbines, biomass combustion plant using sugarcane bagasse, Battery Energy Storage System (BESS), and Diesel Generation (DG) system as backup power, to reduce the supply deficit in Sierra Leone. Resource assessment using well-known methods was done for PV, wind, and biomass for proposed plant sites in Kabala District in Northern and Kenema District in Southern Sierra Leone. Long term analysis was done for the ten hybrid blocks projected over 20 years whilst ensuring the following objectives: minimizing the Deficiency of Power Supply Probability (DPSP), Diesel Energy Fraction (DEF), Life Cycle Costs (LCC), and carbon dioxide (CO ${}_2$ ) emissions. Capacity factors of $27.41\%$ and $31.6\%$ obtained for PV and wind, respectively, indicate that Kabala district is the most feasible location for PV and wind farm installations. The optimum results obtained are compared across selected blocks for DPSP values of 0–50% to determine the most economical and environmentally friendly alternative that policy makers in Sierra Leone and the region could apply to similar cases.