An alternating current (AC) circuit breaker refers to a mechanical switching device that is used to close or open a circuit. Circuit breakers are capable of carrying and breaking currents under normal circuit conditions. In case of specific abnormal conditions such as a short circuit, circuit breakers are capable of carrying the fault current for a specified time, as well as breaking currents.

Power transformers are crucial in alternating current power systems, enabling power exchange between different voltage levels while withstanding electrical stress from faults and transients. On-load tap changers (OLTCs) integrated into transformers regulate output voltage by adjusting windings, maintaining voltage stability regardless of load conditions.

Physical asset management is generally a holistic, integrated decision-making process.

Digital fault recorders (DFR) in the power system are devices that sample the analogue values of voltage and current and convert them to a digital format after being triggered by events or signals from protection relays. This digital data is then used for various analyses of electrical system performance. The analogue measurements are delivered by conventional voltage and current transformers or by modern sensors such as optical current transformers.

Dynamic Line Rating (DLR) for overhead lines (OHLs) is enabled by the variability of their current carrying capacity based on ambient conditions. While OHLs are constructed to endure the peak summer conditions, they frequently operate under less severe weather for the majority of the year, allowing for potential increases in line capacity by up to 200%.

The massive penetration of weather-dependent power generation from renewable energy sources (RES) creates several challenges for power system operation. The short-term forecasting of RES generation, a few minutes up to days ahead, is a cornerstone prerequisite for the secure and economic operation of power systems with high RES-penetration.

A fault current limiter (FCL) is an electrical device used to reduce the amplitude of the fault/short-circuit current to an acceptable level, especially for the circuit breaker that must clear the fault. Optimally, in normal operation, the FCL ought to be ‘invisible’ to the electrical system, having very low impedance or being bypassed. In case of a fault, the bypass is opened within a few milliseconds and significant impedance or resistance is made ‘visible’ to the system, causing a reduction of the fault current. After the fault current has been cleared, they typically return to normal operation.

Gas-insulated lines (GIL) describe technology for the transmission of electrical energy using conductors located in pipes filled with compressed gas as an insulating medium. The inner conductor is made of aluminium and is kept at the centre of the pipe using disc or support epoxy resin insulators. The pipes are made of aluminium or aluminium alloys to avoid magnetisation losses. Pipe diameters vary depending on the voltage level: 15 cm to 50 cm for 110 kV and 400 kV, respectively.

High Voltage Alternating Current (HVAC) cables are typically used as an alternative transmission technology when overhead lines are not appropriate, e. g. in densely populated and reserved areas, across a river or offshore. The extruded cables are insulated using cross-linked polyethylene (XLPE), providing electrical insulation, thermal stability, and protection from harsh environments. This is also the main design difference compared with mass-impregnated (MI) or oil cables, where wrapped paper insulation is used.

The High Voltage Direct Current (HVDC) circuit breaker is a switching device that interrupts the flow of normal and abnormal DC. The challenge in breaking DC is the absence of natural zero current crossing.

Superconducting cables are capable of carrying electrical current without electrical losses. In turn, to activate the superconductivity phenomenon, which is responsible for zero resistance, the cables need to be cooled down to very low temperatures (below -160°C), which requires an additional cooling system and additional electrical energy.

Hybrid alternating current/direct current (AC / DC) overhead lines (OHLs) carry at least two systems: one conventional AC circuit comprising three conductor bundles for each AC phase, and one DC circuit comprising three conductor bundles for a plus pole, minus pole, and neutral metallic return. Since the number of conductor bundles for AC and DC is the same and the air insulation is insensitive to voltage type, it is possible to convert the technologies from AC to DC, and vice versa. With a choice of appropriate insulators and voltage level, such voltage swipe can be realised immediately.

Direct Current (DC) overlay systems represent a radical evolution of the legacy of Alternating Current (AC) interconnected systems developed over the past few decades. Due to significant changes in the type and location of power generation, along with a shift towards a digitalised energy sector, continuing incremental AC interconnection upgrades may not provide the most cost-effective or timely solutions for managing the energy transition.

Line-commutated converters (LCCs) are the conventional, mature and well-established technology used to convert electric power from Alternating Current (AC) to Direct Current (DC) or vice versa. The term line-commutated indicates that the conversion process relies on a stable line voltage, with clear zero-crossings of the AC system to which the converter is connected to have a flow commutation from one switching element to another.

The main components of overhead lines (OHLs) are towers, tower foundation, conductors, and insulators. The task of the tower is to carry the conductors. In high voltage and extra high voltage applications, mainly lattice towers are used due to their high efficiency, security in operation, and cost-effectiveness.

A phase shifting transformer (PST) is a specialised type of transformer used to control the flow of active power in three-phase electric transmission networks. It does so by regulating the voltage angle and the voltage amplitude between two nodes of the system. The regulation range of angle and amplitude depend on the PST type. 

A STATic synchronous COMpensator (STATCOM) is a fast-acting device capable of providing or absorbing reactive current and thereby regulating the voltage at the point of connection to a power grid.

The static synchronous series compensator (SSSC) is a device that employs controllable power electronic components for series reactive power compensation. For this reason, the technology is categorised as a flexible alternating current transmission system (FACTS). It outputs a series-injected voltage that leads or lags the line current by 90°, thus emulating a controllable inductive or capacitive reactance. The SSSC is most commonly used to provide series compensation in power transmission lines.

A synchronous condenser (also called a synchronous capacitor or synchronous compensator) is a conventional solution that has been used for decades for regulating reactive power before there were any power electronics compensation systems.

Voltage Source Converters (VSCs) are self-commutated converters based on semiconductors, as insulated gate bipolar transistors (IGBTs), that can conduct or isolate independently on the current and voltage cycle. VSCs can generate Alternating Current (AC) voltages without the need to rely on an AC system. This allows for independent rapid control of both active and reactive power and black start capability. VSCs maintain a constant polarity of the Direct Current (DC) voltage and control the DC current flow. This ability enables the application of cross-linked polyethylene (XLPE) cables.

Artificial Intelligence (AI) enhances data-driven transmission network activities, including planning, operations, and asset maintenance, by extracting value from data collected through sensing systems. AI, as defined by IRENA, involves creating intelligent systems based on human behavior and data.

Massive amounts of data are generated every second by power transmission networks. In 2023, the world generated approximately 123 zettabytes of data, according to International Data Corporation [1]. Advanced data analytic algorithms are used to transform such data into information and knowledge, which can be then used for network operations and/or parent energy services. Such data analytics rely upon information and communication technologies (ICTs): they have a critical role in data collection, transfer and processing [2]. Computing is a critical function of ICTs: it determines how data analytics typical of transmission networks are performed, and thus becomes the foundation for transmission network operations and services.

“A data space is a virtual space leveraging existing standards and technologies, as well as governance models well-accepted in the data economy, to facilitate secure and standardised data exchange and data linkage in a trusted business ecosystem. It thereby provides a basis for creating smart-service scenarios and facilitating innovative cross-company business processes, while at the same time guaranteeing data sovereignty for data owners” [1].

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”.

Using the flexibility resources potentially provided by consumers and/or prosumers may enable network constraints to be met [1]. Consumers or prosumers are given an active, remunerated role in grid-balancing, whereas the aggregator is remunerated to stabilise the electricity system. The main issue is then securing such transactions. One solution may be the Distributed Ledger Technology, which includes the Blockchain option: both options support bidirectional information flows between different nodes in the energy systems while streamlining transactions [2].

The Internet of Things (IoT) is about connecting everyday objects to communication networks with the aim of providing a range of services or applications in energy areas such as smart grids, home automation or intelligent transportation.

Interoperability is the ability of a product or system to cooperate with other products or systems in terms of sharing resources. This term is suited to address a wide range of uses. The growth of renewable power generation will create an increasing demand for flexibility. So-called “cross-sector integration” [2,3] can provide cost-effective ways to increase the flexibility of the energy system but will require significant cooperation and information before it can be implemented.

Software-Defined Security is a generic security model within which information security is controlled and managed by security software. The well-known functions of network security devices, such as firewalling, intrusion detection, access controls and network segmentation, are extracted from hardware devices and framed into a software layer. Protection is based on logical policies which are no longer tied to any security device [1].

To enable the system operators, for the secure operation of the electrical grid, the existing IT infrastructure – mostly based on large monolithic systems with limited integration – needs to be adjusted for faster scaling and the ability to react to changes. A streaming platform can be exploited, as an expansion of a common understanding of a technology that allows data to be sent over the internet to be used immediately rather than having to download it or use it only when broadcast.