Tennet (Germany)

ABSTRACT This study examines transient overvoltage phenomena in 525 kV high‐voltage direct current (HVDC) onshore cable systems, with particular emphasis on the influence of grounding configurations in two joint types: straight‐through and screen‐separated. Transient overvoltages arising from wave propagation and reflections are analysed, highlighting the impact of joint types, bonding cable configurations (coaxial vs. noncoaxial) and bonding cable length on the resulting overvoltage magnitudes. The necessity of modelling screen‐to‐earth representations of sectionalised cables at grounded joint locations in the vicinity of faults is emphasised, whereas simplified representations of ungrounded and grounded straight‐through joints are identified as sufficient for system‐level simulations. To address the computational challenges of detailed electromagnetic transient simulations, a stand‐alone simplified circuit is proposed to analyse grounded joint transients and to mitigate errors caused by insufficient time‐step resolution. The results provide practical insights for insulation coordination, supporting the reliable integration of HVDC technology into long‐distance cable‐based transmission networks while enhancing system resilience.

Zusammenfassung Das kurative Engpassmanagement ermöglicht es, Stromversorgungssysteme näher an ihren Betriebsgrenzen zu betreiben. Dieser Artikel analysiert die Online-Berechnung temporärer thermischer Grenzwerte für Freileitungen und erläutert einen Anwendungsfall für kurative Maßnahmen unter Verwendung von Netzkuppeltransformatoren zwischen Verteil- und Übertragungsnetzen.

This study presents sector-coupled PyPSA-Earth: a novel global open-source energy system optimization model that incorporates major demand sectors and energy carriers in high spatial and temporal resolution, to enable energy transition studies worldwide. The model includes a workflow that automatically downloads and processes the necessary demand, supply and transmission data to co-optimize investment and operation of energy systems of countries or regions of Earth. The workflow provides the user with tools to forecast future demand scenarios and allows for custom user-defined data in several aspects. Sector-coupled PyPSA-Earth introduces novelty by offering users a comprehensive methodology to generate readily available sector-coupled data and model of any region worldwide, starting from raw and open data sources. The model provides flexibility in terms of spatial and temporal detail, allowing the user to tailor it to their specific needs. The capabilities of the model are demonstrated through two showcases for Egypt and Brazil. The Egypt case quantifies the relevant role of PV, exceeding 35 GW, and electrolysis in Suez and Damietta regions, for meeting 16% of the EU hydrogen demand. Complementarily, the Brazil case confirms the model’s ability in handling hydrogen planning infrastructure, including repurposing of existing gas networks which results in 146 M€ lower costs than building new pipelines. The results prove the suitability of sector-coupled PyPSA-Earth to meet the needs of policymakers, developers, and scholars in advancing the energy transition. The authors invite the interested individuals and institutions to collaborate in the future developments of the model within PyPSA meets Earth initiative. • Open-source sector-coupled energy model with global coverage and high resolution. • Readily available workflow for supply, demand and transmission data worldwide. • Future demand scenario forecast tool with the option of custom data integration. • Global sub-national demand database with assets geo-locations, based on open data. • Showcases for hydrogen export and infrastructure expansion in Egypt and Brazil.

As a result of armed conflicts, huge amounts of Unexploded Ordnance devices (UXO) and Discarded Munition Material (DMM) are expected to be located on the seafloor, especially in coastal regions. During Offshore Construction, strategical site monitoring and systematic remediation activities, the behavior of such objects in waves and currents is of huge interest as potential mobilization of objects after a survey or clearance activity could change the situational picture again. From findings and reports it often is assumed that UXO and DMM tend to migrate over the seafloor for long distances. Here, anthropogenic effects like fishing or dredging activities are underestimated. More scientific approaches clearly show that mobilization and migration of UXO over long distances does not occur. However, theoretical analysis remain theories until they are proven by experiments. For this reason, three large representative objects were investigated under real scale wave conditions in the Delta Flume of Deltares. The objects represent real scale models of UXO found in the North Sea as well as academically shaped objects. All objects as well as the Flume Tank were intensively instrumented to measure the full environmental conditions as well as the behavior of the objects. The sediment represents typical sand as found in the North Sea and the seabed morphology and soil conditions were closely monitored during the experiments. The experiments support the theoretical models that predict burial but no mobilization also under extreme wave conditions.

Substation topology planning can be beneficial to reduce redispatch and better utilize existing infrastructure. This could lower the cost of grid operation and expansion. Various optimization methods are available to find substation topologies. These methods have in common that they are based on steady-state load flow calculations. It must be expected that an increasing grid utilization comes with negative effects on the dynamic stability. This study identifies these possible consequences of grid reconfiguration. A voltage stability study is performed, comparing a meshed grid against two reconfigured grid topologies. It shows that the greatest impact is expected to be on short-term voltage recovery. Depending on the system state and fault location, the permissible voltage limits may be exceeded. These effects are localized and depend on the changes in electrical distances. Such consequences can be mitigated by the use of dynamic reactive power compensation. However, it is clear that substation topologies based on steady-state optimizations need to be examined regarding the impact on voltage stability. With the topological changes, short-circuit currents can be reduced. This could be beneficial for some locations to comply the short-circuit breaker's capacities, but negative for others with an already low short-circuit ratio.

Abstract Die Dimensionierung von Höchstspannungs‐Gleichstrom‐Übertragungsleitungen (HGÜ) basiert auf detaillierten Kenntnissen des Baugrunds im Hinblick auf die Wärmeleitfähigkeit. Aufgrund dessen wurde für die Realisierung der Windstromleitung SuedLink mit einer Trassenlänge von ca. 700 km ein Messprogramm entwickelt, das eine sehr große Anzahl an reproduzierbaren Wärmeleitfähigkeitsuntersuchungen ermöglicht. Mithilfe eines hocheffizienten Versuchsstands können damit vom gesättigten bis zum ofentrockenen Zustand einer Bodenprobe die korrespondierenden Wärmeleitfähigkeitswerte ermittelt werden. Die Auswertung der Wärmeleitfähigkeits‐Wassergehalts‐Beziehung wurde maßgeblich weiterentwickelt, wobei die Steinanteile des Bodens und die Grundwasserverhältnisse Berücksichtigung finden. Die daraus gewonnenen Erkenntnisse fließen in die Planung der Kabeldimensionierung zur Optimierung von Kabelachsabständen ein und tragen somit zur Minimierung der Projektkosten und der Eingriffe in die Natur bei. Darüber hinaus dienen die zahlreichen Messergebnisse der Erweiterung bestehender Datenbanken für Wärmeleitfähigkeitswerte, um für zukünftige Erdkabelprojekte über sog. Pedotransferfunktionen die Anzahl der benötigten Messungen zu verringern.

In this chapter, we discuss how residential batteries within microgrids (MGs) can be used to provide flexibility to the DSO. On this lowest level of the grid hierarchy we only consider active power demand. In particular, we manipulate the aggregated power demand by charging and discharging residential batteries while neglecting the grid topology.

In this chapter, we describe how to determine the flexibility of a distribution grid given the flexibility of a set of microgrids (see Chap. 3 ). Specifically, we compute the minimum, maximum, and optimal active power demand of the entire distribution grid, i.e., the amount of power which must be supplied by the transmission grid.

This paper presents a set of self-adaptive methods to detect and damp power system resonances involving converters. Unlike previously reported methods that rely on impedance measurement and analysis to determine the resonance frequency and degree of damping required, the proposed methods detect the resonance directly by measuring the harmonics resulting from a system resonance. Both time- and frequency-domain techniques are presented for this purpose. Once a resonance is detected, damping is automatically applied in a selected narrow frequency range centered at the resonance frequency to avoid untended effects at other frequencies. The amount of damping to be applied is self-adjusted by a nonlinear feedback mechanism involving the detection circuit, and the damping function is automatically deactivated if the resonance has disappeared, e.g. due to changes in the network configuration or system operation conditions.

In the last decades, several developments have transformed electricity systems in Europe towards liberalized and decentralized systems that are coupled inter-sectorally and inter-regionally. These developments have yielded various significant benefits, such as increased efficiency and robustness. However, we argue that they have also caused new interdependencies and complexity with a corresponding increase in associated systemic risks, e.g., local failures may spread faster and more extensively throughout the system. In this paper, we illustrate how systemic risks may arise in European electricity systems by discussing three exemplary developments. We also discuss the decisive role of the digital transformation that, on the one hand, speeds up the transition of electricity systems and challenges electricity systems’ stability through rapid change, but on the other hand may also provide solutions to tackle systemic risks. We argue that, especially in a strongly interconnected world, policymakers must implement a global perspective on these critical and increasingly complex systems, requiring adequate cooperation with respect to data. Using an exemplary case from Germany, we finally illustrate how an intensified data exchange may help to address systemic risks. In this context, we draw a perspective on the potential of emerging digital technologies, like self-sovereign identities, blockchains, and privacy-enhancing technologies.