In 2019, the strategic digitalisation report of ENTSO-E addressed “Digitalisation Challenges, Opportunities and Projects from TSOs and ENTSO-E” [1]. It prioritised technologies and ranked Digital Twins third after Artificial Intelligence and Machine Learning. The pan-European Transmission system is a Cyber-Physical System (CPS) with standards already framing their development: the International Electrotechnical Commission (IEC) 60870-5-101 [2] and the IEC 60870-5-104 [3]. Today, the IEC standard 61850 is the successor of such developments [4]: 

• VDE released a paper based upon a study entitled “The Digital Twin in the Network and Electricity Industry” [5]   
• Several world-based network technology vendors have implemented the digital twin concept to, for instance, build a digital twin of the Australian energy grid [6], of an HVDC converter station [7, 8], or of a simulation environment to benefit the internal activities of energy players using the digital twin concept [9]. 

The Digital Twin (DT) is not a new paradigm, but to date there are many different definition and models of it [10]. The IEC and The International Organization for Standardization (ISO)/SC 41 committee have released the ISO/IEC 30173 “Digital Twin – Concepts and Terminology” [11] that defines the DT as “the digital representation of a target entity with data connections that enable convergence between the physical and digital states at an appropriate rate of synchronization”. 

A DT of the pan European Transmission system is a cyber-physical system, the development of which ought to follow the functional description proposed in Ref. [11] and is summarised in the diagram below for CPS.  It can be mapped to the 5C architecture such as “Standardized data protocols” at the Smart Connection Level (I), “AI-based decision support systems” at Cognition Level (IV) and “Back up procedures for automated systems” on the Configuration Level (V). However, it is the Cyber Level (III) that contains the concept of the DT and unlocks the full potential of the Cognition (IV) and Configuration Levels (V). 

Challenges to reach the scope when implementing DTs within TSOs: 

• Exchanging data and leveraging information coherently and efficiently, regardless of the platform individual systems are built on. 
• Ability of DTs to operate within larger ecosystems, connecting with the “internet of things (IoT)” devices, enterprise systems and other digital twins to create a comprehensive and interconnected digital representation of physical assets, processes and systems. 
• Interoperability within digital twins and TSOs to underpin the ability to achieve a holistic understanding of the operational ecosystem.

A DT located within each TSO: 

• Acquires and assimilates observational data from the asset (e.g. data from sensors or manual inspections) (Levels I and II). 
• Uses this information to continually update its internal models so that they reflect the evolving physical system with its own computing capability. This is a synergistic multi-way coupling between the physical system, the data collection, the computational models, and the decision-making systems [2] (Levels II and IV). 
• It then runs these up-to-date internal models for analysis, prediction, optimisation, and control of the physical system due to an appropriate computing capacity (Level V). 
• Improve the efficiency of the transmission network reducing the dispatching costs. 

By ensuring that digital twins can communicate and share data effectively [see Data Spaces factsheet], organisations can enhance decision-making, optimise operations, and foster an environment for innovation. 

The development of a pan-European DT is motivated by Digitalising the energy sector – European Union action plan. It will help develop a competitive market for digital energy services and digital energy infrastructure that are cyber-secure, efficient and sustainable. It will ensure the interoperability of energy data, platforms and services.

DT is often considered a piece of technology in hand of itself. It can be thought of as a system-of-systems, a set of several enabling technologies that construct a virtual representation of a physical entity and support a continuous bidirectional communication loop between the twins. 

The most common enabling technologies for DT development are listed below: 

• Broadband connections; 
• Internet of Things; 
• Cloud Computing; 
• Edge Computing; 
• Artificial Intelligence;  
• Real Time Digital Simulation; 
• High Performance Computing;  
• Big Data;  
• Data Spaces; and  
• Hardware-In-The-Loop 

The main technology enablers are primarily the vendors with DTs of technology components, IT solutions to develop DTs, and owning the practice of generic technologies needed to develop solutions for connected systems or integrated systems. 

When considering the interconnected transmission network, there are prerequisites to be met to ultimately develop Pan-European DT:   

• Investment costs: TSO are sometimes not incentivised to implement the DT because of its envisioned development costs and difficult-to-quantify Return on Investment. In fact, it is challenging to estimate the real cost of the DT because of its multi-disciplinary nature [12] at the smart connection level (I): The IEC 61850 must support the DT concept by incorporating standardised metadata within an object-oriented structure.  
• At the data-to-information Level (II): Data are the basis for the creation and operation of DTs. There are different maturity levels of data processing, starting with basic analytics such as Excel but also more sophisticated levels such as the data enrichment with big data infrastructure. DTs need a specific maturity level on data [13].  
• Interoperability and vendor Independency: each TSO operates a legacy system. Interoperability is the foundation required to develop effective and operationally federated DTs for each of TSO. This feature acts as a glue that allows diverse systems, devices and applications to communicate and work seamlessly. 

Organisational and process challenges of DT development: 

• Demanding expectations at the target level (high risk of disappointment). A common misunderstanding about the DT is that the digital copy should reflect the physical twin in its entirety, as well as that it should collect and elaborate all of its data in real-time. However, these performances are not currently feasible in some cases, and certainly not always necessary. 
• Standardisation represents another challenge that can decelerate the development of DT. The standardisation of platforms and interfaces necessary to exploit the full potential of DT is achieved through cross company collaboration and the networking of the DTs. A standard form shall be used to build, save and execute the model of the DT; this enables the interoperability and integration among the DTs of other TSO or other companies. 
• The high level of maturity of TSOs in all areas, from understanding and use through the target image and concepts towards implementation. 
• Ambiguity in responsibility of DT within a TSO. 
• Data ownership and governance.
• Data security. 

The technology is in line with milestones “Advanced reconfiguration and control of network and assets” and “Digital twin for optimisation of assets maintenance and replacement in operation” under Mission 1, milestones “Digital twin for monitoring and enhanced dynamic grid representation” and “Digital twin for grid control” under Mission 4 and milestone “Digital Twin application for enhanced grid flexibility” under Mission 5 of the ENTSO-E RDI Roadmap 2024-2034.

The increasing complexity of electrical equipment and systems (mainly introduced by inverter-based systems and, in general, by the energy transition paradigm) has made it necessary to adopt a more accurate and innovative approach on simulations, introducing the need to develop a DT of the electrical systems. 

There are several projects regarding the development of DTs on different industrial fields. Some of the main projects related to the DTs’ development on transmission grids are listed below: 

• TwinEU Project [14] as a flagship project of implementing the Digitalising the Energy System EU Action Plan. Its ultimate goal is to create the concept of the Pan-European DT based on the federation of local twins of the electricity system provided within the Consortium. 
• TU Delft owns a DT which is already operational to simulate a quarter of the Dutch grid. In the near future, this version is set to be replaced by a digital copy of the whole network operated by Tennet [15]. 
• A German consortium assumes that the inevitable transition of the power system toward a sustainable and renewable-energy centred power system is accompanied by huge versatility and significant challenges. DTs are a promising approach to realise CPS. In this paper, their applications in power systems are reviewed comprehensively [16]. 
• ISO formed a working group named ISO/IECJTC1/SC41/WG6 to focus on DT standardisation. The group is proposing a draft for a potential standard entitled ISO/IEC AWI 30173 (Digital Twin Concepts and terminology) [17].

TRL 7 for digital twins.

1. ENTSO-E, “The cyber physical system for the energy transition: Digitalisation challenges, opportunities and projects from TSOs and ENTSO-E,”, 2019.

2. IEC, “Standard IEC 60870-5-101.” Standard IEC 60870-5-101

3. ABB, “RER620 IEC 60870-5-101/104 Communication Protocol Manual.” RER620 IEC 60870-5-101/104 Communication Protocol Manual

4. Wikipedia. IEC 61850

5. VDE Association for Electrical, Electronic & Information Technologies: The Digital Twin in the Network and Electricity Industry, “The Digital Twin in the Network and Electricity Industry,” May, 2023. The Digital Twin in the Network and Electricity Industry M. G. Kapteyn, J. V. R. Pretorius and K. E. Willcox, “A probabilistic graphical model foundation for enabling predictive digital twins at scale,” Nature Computational Science, vol. 1, no. 5, pp. 1–11, May 2021. Predictive digital twins at scale

6. N. Flaherty. “Siemens to build digital twin of Australia’s energy grid.” eenewseurope.com. Siemens to build digital twin of Australia’s energy grid

7. “Hitachi Energy launches IdentiQ™ digital twin for sustainable, flexible and secure power grids.” hitachienergy.com. Hitachi Energy digital twin

8. F. Guay F, P. A. Chasson, N. Verville, S. Tremblay and P. Askvid, “New Hydro-Québec Real-Time Simulation Interface for HVDC Commissioning Studies,” in International Conference on Power Systems Transients (IPST2017), Seoul, Republic of Korea, June 26–29, 2017.

9. Opal-RT Technologies. “Digital Twins for Modern Power Systems”

10. M. Sjarov et al., “The Digital twin concept in industry – A review and systematization,” in 2020 25th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA), (Vienna, Austria), 2020, pp. 1789–1796, doi: 10.1109/ETFA46521.2020.9212089.

11. J. Ley et al., “A cyber-physical systems architecture for industry 4.0-based manufacturing systems,” Manufacturing Letters, vol. 3, pp. 18–23, 2015.

12. S. Mihai et al., “Digital Twins: A Survey on Enabling Technologies, Challenges, Trends and Future Prospects,” IEEE Communications Surveys & Tutorials, vol. 24, no. 4, pp. 2255–2291, Fourthquarter 2022, doi: 10.1109/COMST.2022.3208773.

13. M. Unterweger, “Digital Substations–their significance and benefits,” Siemens German Magazine, vol. 9, pp. 1–3, 2017.

14. ENTSO-E, ENTSO-E Research, Development, & Innovation Roadmap 2024-2034, July 2024.

15. Tu Delft. “Developing a digital twin for the electricity grid”

16. Z. Song et al., “Digital twins for the future power system: An overview and a future perspective,” vol. 15, no. 6, p. 5259, Mar. 2023.

17. ISO. “ISO/IEC 30173:2023 Digital twin — Concepts and terminology.”, iso.org