Transmission system operators (TSOs) are facing new challenges in day-to-day grid operation and operational planning. The security issues affecting the pan-European electricity transmission system are becoming more and more challenging due to:
• The growing contribution of less predictable and more variable renewable energy sources (RES);
• The need for the coordination of controllable devices such as phase-shifting transformers (PSTs), high-voltage direct-current (HVDC) lines and flexible alternating-current transmission systems (FACTSs);
• Partially controllable electricity demand;
• The increasing difficulty of building new transmission lines;
• The gradual integration of national markets into one common European electrical energy market;
• Market mechanisms not covering certain aspects of system security, leading to high deviations between scheduled and physical flows in terms of time, direction and volume.
As a consequence meteorological forecasting errors may lead to unforeseen violations of operating limits and trigger cascading outages in stressed-system situations. These new constraints, but also new opportunities, result in more complex operational planning and transmission system operation, take the system closer to its operational limits, cause remedial actions to be taken more frequently in order to relieve congestion and, as a result, make it necessary to revise operational rules and procedures. To be fully efficient, emerging Regional Security Cooperation Initiatives (RSCIs) need a new generation of tools to allow the different TSOs to increase coordination and react more quickly to the growing complexity of operational planning and system operation.
Hence, nine TSOs(1) from Central and Central- Eastern Europe, organised within their RSCI named TSO Security Cooperation (TSC), have joined forces with five universities (2) and one research institute (3) to to provide a coordinated solution to these increasing challenges in their target area. This research and development project, entitled “Innovative tools for the future coordinated and stable operation of the pan-European electricity transmission system” (UMBRELLA), is supported by the European Union as part of its Seventh Framework Programme (FP7). To cope with the above mentioned challenges
TSOs at first have to find an answer to the question: What will be the upcoming system state? This requires the modelling of uncertainties related to RES, load forecasting deviations and intraday trades. In this regard, the UMBRELLA Toolbox goes beyond state of the art by not just looking at one forecast. Instead, a wide range of deviations from the forecast and their probabilities are assessed by applying advanced deterministic and probabilistic methods.
Risk-based security assessment will allow the TSOs to answer the question whether the system will be secure. This includes a comparison of the well-known N-1 criterion with risk-based security criteria, taking into account both the probability of occurrence and the severity of outages, cascades and violations of operational limits. Additionally, the UMBRELLA Toolbox is capable of assessing additional operational costs that are the consequences of forecast deviations.
The complexity of congestion management in transmission systems is growing due to an increase in the amount of congestion and the number of available remedial measures. The enhanced optimal power flow (EOPF) algorithm developed may relieve TSOs’ workload significantly by using deterministic or probabilistic optimisation algorithms that take both uncertainty and risk measures into account.
The UMBRELLA Optimisation Framework aims to provide optimal topological and redispatch measures as well as the curtailment of RES infeed and load-shedding measures by taking into account numerous objectives, such as regulatory restrictions, the cost of redispatch and other factors, ranging from day-ahead operational planning to close-to-real-time operation.
The developed modules are synthesised in the UMBRELLA Toolbox. By testing the UMBRELLA Prototype on historical test cases (TCs), the general functionalities of the UMBRELLA Toolbox have been validated and key performance indicators (KPIs) attest the improvement achieved. The applied test system of nine TSOs’ control areas includes some 7000 nodes, approx. 3000 branches and around 1400 transformers of which 46 are phase-shifters. Some modules are tested using test systems of the Institute of Electrical and Electronics Engineers (IEEE). For the implementation and further exploitation of the UMBRELLA Toolbox within RSCIs, a stepwise approach is proposed.
As an result of the UMBRELLA and iTesla projects, a set of recommendations is provided for stakeholders such as regulators, policymakers, TSOs and the European Network of Transmission System Operators for Electricity (ENTSO-E) to foster the necessary harmonisation of the legal, regulatory and operative framework as well as to allow data exchange so that the innovative software tools developed can be applied by TSOs and within RSCIs
1) Amprion GmbH (Germany), Austrian Power Grid AG (Austria), CEPS (Czech Republic), Elektro-Slovenija (Slovenia), PSE S.A. (Poland), swissgrid (Switzerland), TenneT TSO B.V. (Netherlands), TenneT TSO GmbH (Germany; Coordinator) and TransnetBW GmbH (Germany)
2 ) Delft University of Technology (Netherlands), Graz University of Technology (Austria), ETH Zurich (Switzerland), RWTH Aachen (Germany) and University of Duisburg-Essen (Germany)
3 )FGH Forschungsgemeinschaft für elektrische Anlagen und Stromwirtschaft e.V. (Germany)

Project Context and Objectives:
Motivation and Summary
As part of the fight against climate change, the European Union is aiming to decarbonise its economy. An important aspect is to replace fossil-fuel-based electricity generation with RES such as wind and solar power. Therefore, European energy markets as well as energy grids have to be fit for renewables.