Abstract
The 2025 blackout across the Iberian Peninsula marked a paradigm shift in the nature of power system failures, revealing how modern grids-dense with inverter-based resources and automated controls-can exhibit emergent instabilities that traditional design frameworks may not fully anticipate. This review examines the event through the lens of complex systems engineering, drawing on publicly available information and prior research to illustrate why a well-instrumented, high-renewables grid might still struggle to contain rapidly evolving disturbances. We begin by highlighting structural features-such as bottlenecks and asymmetric interconnections-that have been shown in the literature to influence the propagation of instability in transmission networks. Network-science tools, including algebraic connectivity, spectral radius and betweenness centrality, are discussed as methods used in previous studies to reveal latent fragilities. Attention then shifts to synchronization dynamics, where low-inertia conditions can amplify frequency deviations and interact with heterogeneous inverter response characteristics. Using models of cascading failures and percolation-type transitions, we outline how disruptions can propagate nonlocally, highlighting mechanisms identified in analytical and simulation studies. The analysis extends to fragility scoring systems, modular segmentation strategies and the spatial deployment of virtual inertia and fast-response resources-approaches proposed in prior research as part of a resilience toolkit aimed at containment and stabilization. Finally, we summarize emerging redesign directions emphasizing harmonized protection logic, regional operational cells and complexity-aware digital twins as increasingly important under conditions of uncertainty.

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Ensuring reliable and high-quality electricity service is critical for consumers and Distribution System Operators (DSO). The DSO's Plan for Development and Investment in the Distribution Network (PDIDN) plays a pivotal role in enhancing network reliability and resilience while balancing technical and financial aspects. This study proposes a novel probabilistic approach for quality-of-service (QoS) estimation in distribution systems, addressing the limitations of traditional deterministic methods. Leveraging Bayesian regression, specifically the Spike and Slab technique, the model incorporates prior knowledge to improve the prediction of key QoS indicators such as SAIDI, SAIFI, and TIEPI. Using historical network data, the model demonstrates superior predictive accuracy and robustness, offering realistic confidence intervals for strategic planning. This method enables informed investments, enhances regulatory compliance, and supports renewable integration. The findings underline the potential of probabilistic modeling in advancing QoS forecasting, encouraging its application in other areas of electric network management.

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This article explores the optimization of Battery Energy Storage Systems (BESS) in energy markets, emphasizing their role in decarbonization by storing excess renewable energy and mitigating grid constraints. BESS enables energy transition by facilitating energy arbitrage, frequency regulation, and grid stabilization, essential for integrating variable renewable sources. Focusing on the UK energy market, the study highlights the favorable policies and investments driving BESS deployment. It examines revenue streams, including Day-Ahead and Intraday markets, ancillary services, and balancing mechanisms, particularly dynamic services like frequency regulation. Challenges such as gas market volatility and regulatory hurdles are also discussed. The proposed market optimization model simulates BESS operations, revealing consistent revenue potential influenced by market conditions and regulatory frameworks. The study underscores BESSs critical role in stabilizing grids, supporting renewables, and enhancing energy security while calling for further research on equipment degradation and broader impacts on energy systems and pricing.

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This paper presents an experimental evaluation of the dielectric performance of a synthetic ester-based insulating fluid (Midel 7131) for power transformers subjected to lightning impulse voltages. The study is motivated by the search for sustainable and environmentally friendly alternatives to conventional mineral oils, particularly under extreme electrical stress conditions. A test setup was developed using Rogowski-type electrodes immersed in the fluid and subjected to positive and negative standard lightning impulses, following IEC 60060-1 and 60247. The dielectric dissipation factor (tan d) and partial discharge (PD) activity were measured before and after the impulses. Results showed that Midel 7131 maintained low dielectric loss values and exhibited stable PD behavior, even after repeated high-voltage (HV) impulses. These findings confirm the technical feasibility of synthetic esters as reliable insulating fluids for HV equipment, supporting sustainable practices in the electrical energy sector. © 2025 IEEE.