Power Quality assessment is very important for Extra High Voltage networks. We need to make sure these networks are reliable, efficient and meet standards. Disturbances like harmonics, voltage surges, flicker and transients can move across transmission systems. This affects loads and distributed generation integration. This review looks at ways to monitor Power Quality measures to compare performance, strategies to fix problems and case studies that are relevant, to Extra High Voltage substations. These pictures show how to watch over systems they use numbers and payment plans and that helps us understand how to measure power quality in places with really high voltage, like power plants.

Power quality (PQ) assessment in Extra High Voltage (EHV) networks is a multidimensional challenge that requires integrated monitoring, advanced benchmarking, and dynamic compensation strategies [1]-[11]. Traditional single -parameter indices such as THD or voltage sag duration provide useful insights but are insufficient to capture the complexity of PQ disturbances in large transmission systems [3],[5]. The evolution of compound indices and analytic models, supported by frameworks such as the Analytic Hierarchy Process (AHP), has enabled more holistic benchmarking across substations and transmission corridors [2],[5]. These approaches allow utilities to prioritize PQ concerns and align operational outcomes with IEEE 519 and IEC 61000 standards. Industrial case studies demonstrate the practical relevance of PQ management, particularly in sectors such as steel and glass manufacturing where nonlinear loads impose significant harmonic and reactive power burdens [6],[9]. Similarly, utility – level investigations highlight how disturbances in low -voltage feeders can propagate upstream into EHV substations, underscoring the need for coordinated monitoring across voltage levels [9],[10]. The integration of distributed generation (DG), especially inverter -based renewables, further complicates PQ management by introducing harmonics and voltage variability at the point of common coupling [10]. These real-world applications emphasize that PQ assessment cannot remain isolated at the transmission level but must incorporate industrial, utility, and DG perspectives into unified framework. Looking ahead, future research must focus on three critical directions. First, the development of standardized compound indices is essential to ensure consistency in PQ benchmarking across utilities and regions. Second, the adoption of predictive PQ analytics, leveraging machine learning and AI, will enable proactive identification of disturbances and optimization of compensation strategies. Third, the design of cyber -resilient PQ security frameworks are increasingly important as monitoring and control systems become more digitized and vulnerable to cyber -physical risks. By advancing these areas, EHV networks can maintain reliability, efficiency, and compliance in the face of growing complexity, renewable integration, and evolving market structures.

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