As electrification accelerates and distributed energy resources (DERs) become more prevalent, utility-scale dc microgrids (MGs) are emerging as a technically viable and forward-looking solution for modernizing grid infrastructure. These systems enable higher operational efficiency, streamlined integration of renewable energy and energy storage systems, and advanced control functionality. Their inherent characteristics make them particularly well suited to enhance grid resilience and operational flexibility. This article provides insights into the design, implementation, and operational experiences of utility-scale dc MGs, with a focus on their role in enhancing grid reliability and resilience. It reviews a range of electrical architectures currently deployed or proposed for such systems, analyzing their technical characteristics and implementation considerations. The article also explores hierarchical control strategies, utility interconnection methods, grounding and protection schemes, and the interoperability of dc systems with existing ac infrastructure in the context of a real-world utility dc MG. Contributions from utility operators, developers, and consultants offer a multistakeholder perspective on integration challenges, technology readiness, and long-term serviceability. A key highlight is the operational experience of Tampa Electric Company (TECO) in integrating a dc MG into its distribution system, providing valuable real-world insights into deployment practices. Finally, the article discusses future trends, including emerging applications such as data centers and meshed dc MG networks. By addressing both technical approaches and practical challenges, this work supports the broader adoption of utility-scale dc MGs as a key enabler of resilient, flexible, and decarbonized energy systems.
Historically, distribution alternating current (AC) networks were designed to operate in a predictable manner, making monitoring, protection, and control relatively straightforward. Radial AC feeders, a dominant source at the substation, and healthy/nominal fault currents gave protection engineers a solid starting point for protection settings and coordination. Time-current curves, fuse-recloser coordination, and a few well-placed directional elements were usually enough to ensure selective, secure, and reliable protection. That world is disappearing. Across the globe, distribution grids are being rewired with power-electronics-based components, including direct current (DC) links, electric vehicle (EV) fast chargers, data centers, and rooftop photovoltaic (PV) and battery systems, all competing for space on networks that were never designed for them. Hybrid AC-DC distribution networks play a key role in this transformation. DC feeders now support EV charging and building microgrids, while low-voltage DC (LVDC) schemes enhance efficiency. Medium-voltage DC (MVDC) branches provide power for large industrial and information and communication technology loads. These DC components are increasingly connected to existing AC networks via a dense layer of converters. These converters change the nature of fault current distribution, waveforms, and magnitudes. Short-circuit currents can be tightly limited; can last only a few milliseconds; and may not appear "large" compared with the normal load, i.e., the nominal current. Power can flow in multiple directions at once. An event on a DC branch can ripple back into the AC system via complex converter controls. Under these conditions, relying on traditional overcurrent-based protection coordination and fuse-recloser philosophies becomes dangerously optimistic. This article examines what protection coordination entails when the distribution network transitions to a hybrid AC-DC system and how this change impacts the principles that have guided protection engineers for generations. We first review the fundamentals of protection coordination in classical AC distribution networks, then explore the impact of hybrid architectures on selectivity requirements. Building on this, we present emerging concepts for zone- and time-based coordination across AC and DC segments, emphasize the crucial role of interface protection at converters, and illustrate these ideas with a stylized urban feeder example. Our goal is to demonstrate how the existing practices must be adapted: from a world where fault current alone determined where to trip, to one where coordination must be deliberately designed across new timescales, understanding how fault currents behave and how new technology can support protection coordination of future distribution networks.
With the rapid growth of renewable resources, the steady increase in electricity demand, including large-scale data centers and artificial intelligence training facilities, and the heightened occurrence of extreme weather events, today’s power systems are operating under conditions far more volatile than those of previous decades. Under such circumstances, state estimation has become critically important for ensuring the stable and secure operation of power systems.
As DC power sources and DC loads are connected to the power system on a large scale, the conventional AC distribution systems are reaching their limitations. In response, medium-voltage DC (MVDC) distribution systems are emerging as an alternative for the next-generation distribution system. In the Republic of Korea, the goal is to operate a hybrid AC/DC distribution system by 2030, and partially replacing existing AC distribution systems with DC distribution systems is being considered. This article investigates the issue of nearby transformer saturation that may occur when an MVDC distribution system replaces an existing AC distribution system and introduces countermeasures to prevent transformer saturation.
As medium-voltage (MV) dc networks gain traction in response to the rapid growth of distributed energy resources (DERs), data centers, and electric vehicles, MV hybrid ac/dc distribution networks—enabled by modular multilevel converters (MMCs)—are emerging as a key architecture for next-generation power systems. These hybrid systems integrate MVdc subsystems into existing ac infrastructures, creating new challenges in protection system design due to fundamentally different fault behaviors in dc networks and the lack of standardized fault analysis methods. Moreover, the interaction caused by ac/dc inverter alters fault characteristics of ac distribution system also. This article presents a comprehensive approach to fault current analysis in MMC-based hybrid ac/dc distribution networks. It introduces an equivalent circuit model-based fault current calculation methodology and highlights a dedicated fault calculation tool developed through a national research project in South Korea. The accuracy of this tool is verified against detailed electromagnetic transient simulations in PSCAD, demonstrating its practical applicability for protection studies in emerging hybrid grid environments.
Modern electrical distribution systems are transitioning toward hybrid AC/DC architectures to efficiently integrate renewable energy and DC-native technologies. This article provides an overview of the structural components and computational challenges inherent in these complex networks, focusing on the critical role of load flow analysis. It examines various modeling methodologies, such as sequential and unified frameworks, while addressing the unique impacts of active power electronic converters. Ultimately, these robust analytical tools serve as the foundation for essential applications including system planning, hosting capacity studies, and real-time grid optimization.
As the energy sector transitions toward increased renewable integration and bidirectional grid operation, the complexity and frequency of disturbance events rise, necessitating advanced situational awareness. Robust expert systems are needed that leverage a multilayered wide area monitoring, protection, and control (WAMPAC) architecture, integrating device-level detection, data aggregation, and an adaptive event classification and validation framework facilitated by dynamic incremental learning (DIL). These expert systems address challenges such as concept drift, catastrophic forgetting, and the need for human-in-the-loop oversight, enabling rapid and accurate identification of both known and novel disturbance events that can be expected in the future.
Transformer research is a specialized area of electrical engineering that requires a high level of investment in laboratory infrastructure. Many high-voltage (HV) and insulation research facilities have closed at numerous universities over the last three decades. However, due to the increasing proliferation of renewable energy sources, the need for power transformers has increased; concurrently, there has been a global shortage in the supply of new transformers. These issues therefore support the need for innovative research into power transformer design, particularly the use of transformer operation in a renewable-dominated power grid, as well as the use of sustainable materials for transformer construction, e.g., natural ester oil replacing mineral oil. The training of future engineers and the upskilling of the current workforce with specialist knowledge in transformer design and operation is becoming more important than ever. To this end, several global research-intensive universities have formed a virtual alliance, the University Transformer Research Alliance (UTRA), to share research and training expertise in power transformers. This article introduces power transformer research and training activities in eight universities across Asia, the Pacific, Europe, and North America.
AC-DC hybrid grids offer enhanced flexibility and efficiency for integrating both AC and DC generation and loads. However, the unique characteristics of these grids present significant challenges for protection and fault analysis. This article provides a comprehensive overview of the challenges associated with fault detection, location, and isolation in hybrid grids, considering the interaction between AC and DC components. It analyzes the impact of fault types, grid topologies, and control strategies on protection system performance. Furthermore, the article explores various solutions, including advanced protection schemes, fault current limiters (FCLs), and intelligent control strategies, designed to ensure the reliability and security of AC-DC hybrid grids. The effectiveness of the proposed solutions and future trends for the protection of hybrid grids are discussed. The article addresses protection challenges and solutions in AC-DC hybrid grids at both the transmission level [e.g., high-voltage (HV) DC and multiterminal DC systems] and the distribution level (e.g., hybrid microgrids and active distribution networks), with explicit clarification provided throughout where issues are domain specific.
The electric power system is essential for modern society, and a malfunction may immediately lead to severe financial damage and, in the worst case, personal injuries. For this reason, extensive measures are taken to ensure the highest possible level of system reliability. Global electricity consumption is expected to grow significantly by 2050 compared to today’s levels. Besides the amount of consumption, the load patterns will be more temperature sensitive and volatile. Furthermore, there is likely to be growth in domestic, selfsufficient, distributed, and clean electricity generation.
Wildfires have grown in frequency, scale, and impact, driven by climate change, expanding vegetation, and the spread of development into wildland-urban interface (WUI) areas. The WUI, where human development meets wildland vegetation, is especially vulnerable as it combines flammable fuels with dense infrastructure and population. Protecting these zones is critical because fires in WUI regions pose heightened risks to lives, property, and grid assets. Some of the most destructive wildfires in California have been attributed to distribution and transmission systems, underscoring the need for a system wide approach to mitigation. While electric infrastructure accounts for only a fraction of ignitions, these events often occur during extreme weather and can produce disproportionately large and destructive fires. This makes it imperative for utilities to revisit grid design, engineering practices, and protection strategies to reduce ignition risk under evolving environmental conditions. Addressing this challenge requires a coordinated effort that extends beyond utility boundaries, recognizing wildfire mitigation as a public priority supported by agencies, regulators, and communities. A robust, multi-stakeholder ecosystem, spanning research, manufacturing, utilities, and policy bodies, must work together to accelerate the development and deployment of effective solutions. Hierarchical policies should guide utilities in redefining operational processes, adopting advanced technologies, strengthening standards, and integrating wildfire risk reduction into every aspect of system planning and operation. This paper reviews wildfire incidents from multiple authoritative sources, examines the physical mechanisms by which electrical faults can ignite fires, and considers engineering, protection, and monitoring measures to reduce this risk. The discussion emphasizes proactive design and physical system strategies to move beyond incremental improvements, aiming for a fire-aware and resilient grid. Achieving this vision requires coordinated policy, targeted funding, and active stakeholder collaboration to address the challenge holistically.
[Most recently, there have been significant efforts by power system operators in studying generation and transmission uncertainties in operation planning. With the increasing penetration of weather-dependent renewable generation and frequent geo-climate events, power system operators have begun to predict weather changes and preventively mitigate their impacts on power generation and transmission. Uncertainty evaluation and subsequent preventive mitigation actions have become important tasks in operating regions with significant renewable generation. Amid these efforts, artificial intelligence and machine learning are playing instrumental roles in the development of new tools. Based on a handful of public reports, this article discusses the emerging new problem of operational uncertainties for power system operators and outlines a systematic approach that involves risk evaluation and mitigation in both generation scheduling and transmission operation. It is envisioned that risk-based operation will be the new paradigm for power system security assessment.
Distributed Energy Resources (DERS) have emerged as a fundamental component in modern energy systems, promoting decentralization, sustainability, and resilience. Establishing flexibility markets has become crucial in the global transition to a low-carbon future to optimize the integration and coordinate the utilization of DERs. This article provides a comparative analysis of local flexibility market developments in Europe and the United States, offering insights into innovative technologies, policy frameworks, business models, and practical experiences.
Maintaining transmission system reliability is becoming increasingly complex as utilities face unprecedented data center interconnection requests. These requests rival the scale of major generation projects, with individual sites exceeding thousands of megawatts and overall demand rising sharply. Proprietary designs, reliance on power electronic equipment, and uncertain dynamic behavior distinguish data centers from traditional industrial customers. This paper highlights the need for advanced modeling, early collaboration with developers, and updated planning practices to ensure reliable integration of these facilities into the grid.
The emerging penetration of converter-based generation through offshore wind turbines and battery energy storage systems (BESSs) aims to reduce carbon emissions in modern offshore oil and gas platforms (OOGPs). This system represents a unique and challenging test case for studies related to power system flexibility and resilience. The new onboard converter-interfaced devices together can provide various grid services, including voltage regulation, frequency response, reactive power control, and peak shaving. Moreover, in the event of an outage, BESS converters can help to restore power rapidly, thus enhancing power system resilience. It can be established that enhanced flexibility and resilience on modern OOGPs is possible only with cooperation of power electronic converters, such as those of variable frequency drives (VFDs), wind turbines, BESSs, and active power filters (APFs). By working together, these technologies can maximize their exploitability, enhance efficiency of gas turbine generators and/or reduce the need for them, and increase resilience by integrating BESSs endowed with grid-forming capability. Hence, this article explores diverse case study scenarios, providing valuable insights into the necessity and opportunities for cooperation among different devices on the platform. This marks a step forward in OOGPs’ green transition, potentially serving as a useful paradigm for several other autonomous systems.
The Ongoing Green Transition is arguably the largest change in the European power system for several decades. Traditional dispatchable generation sources like coal and nuclear power plants are being replaced by massive amounts of wind and solar generation with less predictability and no inertia. These renewable sources give larger and faster changes in flow patterns and balancing, and the power system operation is moving from a “generation must follow load” to “load must follow generation” paradigm. In addition to this fundamental change in the physical properties of the power system, common European rules and regulations for markets and system operation are being implemented, including flow-based market clearing, 15-min time resolution in day-ahead and intraday markets, and increased cross-border trading of both energy and reserves.
By integrating renewables in the era of digitalization, power infrastructure is becoming more connected to ensure a secure, efficient, and decarbonized future system. However, this increased connectivity also makes infrastructure more vulnerable. Over the past decade, geopolitical tensions and concerns about energy security have influenced power systems, prompting energy professionals to explore various solutions for maintaining a reliable and resilient future. Researchers and experts from the International Smart Grid Network (ISGAN), International Council on Large Electric Systems (CIGRE), as well as system operators and communities, are exploring various solutions that focus on flexibility options, resilience, and how these two aspects can support each other. In particular, they continue to work on energy system stakeholders’ interaction to identify a key pathway to a clean, reliable, and secure energy future. In ISGAN, the experience from flexibility definition and characterization started in 2019, and continued with flexibility for resilience in integrated systems activity supported by the International Energy Agency in 2022; recent outcomes from an ISGAN workshop held in 2023 on the topic of “Flexibility for Resilience and Power System Stakeholder Interaction” are summarized and discussed here. This article presents the results and best practices derived from collaboration and the exchange of experiences between countries. It highlights the potential, role, and actions being taken by various stakeholders, including academia, society, policymakers, regulators, urban planners, system operators, retailers, and consumers, in addressing the urgent need for power system resilience and the critical role of flexibility.
As the global power grid transforms, utilities face growing complexity in modeling, stability assessment, and operational planning. The increasing penetration of inverter-based resources (IBRs), power-electronics-interfaced devices (PEIDs), and distributed energy technologies exceeds the limits of traditional phasor-domain tools, which struggle to capture fast, nonlinear, and unbalanced behaviors. Electromagnetic transient (EMT) simulations have become essential, offering sub-cycle accuracy, detailed switching behavior, and multi-domain integration. EMT is now integrated into planning workflows, interconnection studies, protection coordination schemes, real-time platforms, and digital twin architectures, helping utilities, system operators, manufacturers, and research institutions address modern grid challenges at both device and system levels. This article provides a utility-focused overview of EMT simulation strategies for large-scale power grids, with a particular emphasis on practical implementation, model development and validation, hybrid co-simulation architectures, and digital twin integration. Drawing from real-world experience and evolving industry standards, the article also highlights use cases across the power system lifecycle from planning and protection to procurement and interconnection. Furthermore, it offers a roadmap for scaling EMT practices in support of the future grid reliability and performance.
The reliable and secure operation of large-scale, complex power systems increasingly relies on high-fidelity, synchronized data. Unlike traditional supervisory control and data acquisition (SCADA) systems, phasor measurement units (PMUs) provide real-time, high-sampling-rate data, which are crucial for the observability of dynamic phenomena. They offer precise, synchronized, and real-time measurements of fundamental electrical parameters, including three-phase voltage and current magnitudes, and phase angles, with much higher resolution than conventional systems. This enables immediate disturbance detection, grid stability monitoring, and accurate postevent analysis. Within this context, this article introduces the reader to the openWAMS project, an innovative open source wide area monitoring system (WAMS) implemented by Brazil’s independent system operator (ONS), operational in the control room since mid-2024. Its open source nature facilitates customization, adaptability, and future proofing, allowing engineers to customize the platform and integrate algorithms tailored to the country’s grid challenges. To provide context, the article first outlines the role of ONS and the current challenges in operating the National Interconnected Power System (NIPS). It then discusses the project’s implementation and operational impact, highlighting the migration experience of a multidisciplinary team and the rapid deployment of a minimum viable product (MVP). Furthermore, the article discusses its architecture, which integrates open source components for data acquisition and storage, along with an open source web-based user interface (UI) for visualization. Examples of dashboards currently used in control rooms are presented. Finally, the article provides a glimpse into real-time advanced applications (e.g., continuous assessment of PMU data quality and disturbance detection), highlighting the ongoing development of the WAMS platform.
Increased penetration of distributed renewable energy sources, electrification of the energy end uses, and the uptake of electric vehicles (EVs) represent relevant challenges to the method of operating low- and medium-voltage networks. To cope with them, grid operation procedures and the responsibilities of system operators are evolving. Thus, the development of innovative solutions for grid management and operation is becoming increasingly important, while infrastructure investments, including those in digital technologies, are a key option to face the mentioned challenges and to enhance the role of distribution system operators (DSOs) to support the security and adequacy of the entire energy system.
