Grid Stabilization — The power grid is the backbone of the energy system, and we're making it stronger

Challenges in changing grids

The worldwide power sector has witnessed significant disruption, growth, and change in recent years, driven by decarbonization, electrification, and the increasing liberalization of energy markets. Integrating renewable energy sources — mainly photovoltaic and wind power — alters the operation of conventional power systems: renewables are intermittent, and their power-electronics grid interfaces decrease overall inertia due to a lack of rotating masses directly connected to the grid. These factors pose new challenges for grid stability along three domains: voltage stability, frequency stability, and load flow management (p. 4).

Voltage stability: the system voltage must be maintained within allowable ranges to ensure stable power system operation and safeguard people, equipment, and consumer devices; a sufficient supply of reactive power is needed to maintain voltage stability and leverage the transmission capacity of existing transformers and lines (p. 4). Frequency stability: frequency control ensures that power fed into the grid corresponds with power consumption; the rising fluctuation in generation capacity due to renewables has increased the demand for grid services (p. 5). Load flow management: thermal overloads and instances where frequency and voltage approach critically acceptable range limits may require costly redispatch interventions; system operators must optimize transmission-line utilization while maintaining maximum protection (p. 5).

The brochure summarizes the trends in electric energy supply — shutdown of conventional fossil and nuclear power plants, large-scale integration of renewables, increasing power demand in existing grids, continuous evolution of power market rules and regulations (p. 6) — and the grid stability risks they cause: decreased grid strength and frequency stability, increased inverter-connected generation, decreased voltage stability, and increased unbalanced load flows, congestion, and redispatch (p. 7).

Complexity in grid stabilizing — system services per stability domain

The challenges within frequency stability, voltage stability, and load flow management are highly complex. The brochure details the system services available to support reliable grid operation in a three-domain table (p. 8), transcribed below.

Voltage stability (2.1): keeping the voltage in the allowed bandwidth for which the devices in the electrical system are designed; the transition from big centralized to smaller decentralized power generation, longer transmission distances and the volatility of renewable sources make voltage stability in modern power system topologies a considerable challenge — dynamic reactive power compensation is the solution to tackle it (p. 9). Frequency stability (2.2): the strength of the system frequency, called system inertia, measures the system's sensitivity to generation/consumption mismatches; the reduction of rotating masses leads to higher deviations from the nominal frequency (p. 10). Load flow management (2.3): transmission grid operation follows the N-1 criterion, in which electrical components do not operate at maximum thermal capacity so they can withstand scenarios where one line is out of service (p. 11).

Pathways to solutions — technology vs. system service matrix

As a leader in the power transmission industry, Siemens Energy has developed modern, flexible, high-capacity grid stabilizing solutions, including Flexible AC Transmission Systems (FACTS), to prevent high voltage fluctuations and power failures, optimize network asset utilization, and mitigate load-induced disturbances. The solutions regulate voltage, impedance, and phase angle, providing inertia and short-circuit power (p. 12).

The brochure maps five technologies against the system services in a checkmark matrix (p. 13), transcribed below. The matrix prints double check marks in some cells and single check marks in others without a printed legend; the transcription preserves the distinction as ✓✓ (double check), ✓ (single check) and ✗ (cross). Footnotes on the matrix: *GFL: Grid-following, **GFM: Grid-forming. The check marks were read from a 200 dpi page render, as they are graphic glyphs not present in the PDF text layer.

Grid consulting and lifecycle services

Moving from the identification of grid challenges to the optimal solution definition raises many questions: which grid stabilizing devices are the best choice; how large should they be and how many are needed; which locations in the grid should they be installed; when are they required and how do they fit into the long-term grid development plan; what will the future energy system connected to the grid look like (e.g., generation mix, load forecast); and what are the costs and benefits of specific stabilization solutions. Applying simulation-based studies, Siemens Energy's grid consultants guide toward a tailor-made solution — from initial optioneering and component selection to full-scale long-term grid development masterplans (p. 14). The study portfolio spans strategic grid planning (data- and simulation-driven decision support), model development (digital representation of transmission and generation assets), solution design (dimensions, selection, design, and verification of transmission and generation solutions) and grid integration (grid interconnection of transmission and generation technologies) (p. 14).

Siemens Energy offers a single source for all necessary grid stabilizing solutions and complementary services across the full project lifecycle: consulting and feasibility studies, financing, project management, system design and engineering, civil design and works, procurement, factory testing, transport, installation supervision and works, commissioning & performance test, and after-sales services with condition-based maintenance and spare parts (pp. 16–17). Siemens Energy can deliver turnkey solutions, enabling timely grid stability improvements in rapidly changing energy systems (p. 17).

The new control and protection platform

Control and protection (C&P) systems are critical to managing power flows and protecting grid components in FACTS plants. System operators face three main challenges: quick reaction to market needs and short lead time of the C&P system; reliable and secure operations throughout the entire lifecycle while safeguarding low total cost of ownership; and easy expansion of new solutions and services (p. 18). The new modular C&P platform provides a common, proven basis; pre-integrated ready-to-use reference projects ("reference project lines") plus customer-specific delta engineering lead to significantly reduced engineering and lead times (p. 19).

Software applications use model-driven system engineering with MATLAB® and Simulink®, creating a single point of code transformation including software development, simulation, and offline testing; a digital twin escorts the system from the beginning, and hardware-independent software development means applications remain usable even with hardware changes (p. 19). Control-level hardware focuses on quick reaction, robustness, and secure functionality: scalable rail-mounted PC technology, internal standard protocols from IEC61850 to EtherCAT, and short bus cycle times of up to 250 µs enabling closed-loop control tasks. The primary hardware runs on an industrially proven open-source Unix operating system with no dependencies on other operating systems, continuous updates and life-long patch management (p. 20). The cloud-based engineering portal gives all stakeholders full transparency and parallel access to current data, and SensOTS, a cloud-based operator training simulator, trains staff in advance to operate the C&P system (p. 20).

For synchronous condensers, control capabilities cover voltage control, reactive power control, inertia response and fault current capacity, with requirements including fast and failsafe operation of rotating equipment, integration of excitation system and substation automation, remote operation, cybersecurity compliance, lifecycle maintenance coverage and remote diagnostics (p. 20). The Omnivise T3000 control system, at the core of the Omnivise family, simultaneously manages electrical equipment and fast control loops in one integrated architecture and supports communication protocols like IEC 61850, 60870-104, and DNP3 (p. 21).

Grid-forming control

For converter-based FACTS and HVDC applications, grid-forming controls are becoming the state-of-the-art solution. Siemens Energy has equipped three of its main power-electronics-based grid solutions with advanced grid-forming capabilities: STATCOM (SVC PLUS®), E-STATCOM (SVC PLUS FS®) and HVDC systems (HVDC PLUS®) (pp. 21–22). By providing a constant voltage source, grid-forming control allows a stabilizing current contribution, counteracting AC grid transients such as angle or amplitude changes in the grid voltage; the ideal transient behavior of a grid-forming converter at its terminals is similar to that of a rotating machine generator (p. 22).

The main grid-forming functionalities: inherent reaction counteracting grid disturbances (voltage and frequency); provide inertia for frequency stability (E-STATCOM and HVDC); inherent damping of system oscillations; operating in all grid conditions, including weak grids and islanding scenarios; support grid recovery; contribute short circuit power. Detailed information can be taken from the Siemens Energy white paper "Grid-forming converters" (p. 22).

The capability overview table (p. 22) is transcribed below. Check/cross marks were read from the page render. Footnote to the starred cell: "SVC PLUS® does have inherent short-term active power exchange with the grid. However, it does not have an additional storage to provide a notable active power support." The delta-topology cell prints as "A (Delta)" in the brochure's glyph set.

Digital engineering and cyber security

Digital engineering and execution mean working with all stakeholders on a common data platform for agile project collaboration and efficient operation, enabling reduction of execution time and steps, data exchange and access in the cloud, and improved efficiency. Examples include building information modeling (BIM) applications for planning, design, and construction (e.g., 4D time scheduling, 3D modeling, design, collaboration) and modeling tools for simulation (e.g., plant noise simulations) (p. 23).

Siemens Energy transmission offers a comprehensive security approach based on the "onion" principle of defense in depth, with multiple complementary security layers — plant security, network security, and system security — ensuring the three basic pillars of cybersecurity: availability, integrity, and confidentiality (pp. 24–26). The twelve security functions are: 01 network zone concept (networks segregated into distinct segments protected by firewall rules; all unnecessary services and ports blocked by default); 02 Identity Access Management (complex passwords and passphrases, documented only in encrypted formats); 03 data security and integrity protection (state-of-the-art secure protocols, public and private keys); 04 system hardening (BIOS boot order and passwords, Group Policy Objects enforced per the Center for Internet Security benchmark); 05 malicious code prevention and malware protection (whitelisting based on application control); 06 security update management (offline updates for Windows-based systems, continuous vulnerability monitoring); 07 Network Access Control (prevention of non-authorized access; unneeded switch ports closed by default); 08 security logging and monitoring (central logging solution, Syslog-server); 09 secure wireless access (wireless technology not recommended and in general not foreseen); 10 secure remote access (TLS and VPN, SSL VPN tunnel); 11 backup and recovery (online and offline backups, static configuration backups for embedded devices); 12 physical security (pp. 25–26).

SVC PLUS® (STATCOM)

Static synchronous compensator (STATCOM) technology is a dynamic solution for voltage control in the power grid by injecting and absorbing reactive power. SVC PLUS®, the well proven modular multilevel STATCOM, is based on VSC technology using high-performance transistors (IGBTs) as the primary semiconductor device (p. 28). SVC PLUS® control delivers: voltage control with superior under-voltage performance and voltage recovery after grid faults; grid-forming converter control offering inherent voltage support in both strong and weak grid conditions as well as provision of harmonic damping; power oscillation damping for increasing the transmission capability of the power system; additional control features such as active filtering (reducing the need for passive filters), external device control and unbalance control (e.g. negative phase sequence control); and continuously improved cyber security compliance. For mining and metal, specialized industry solutions of SVC PLUS® are available (p. 28). Headline benefits: optimal stability and quality; in harmony with harmonics — grid forming capability; fastest response — efficient solution (p. 29).

Wide range of reactive power: the reactive power range is scalable from 50 Mvar up to 425 Mvar per branch, with the possibility of converter branches in parallel, full turnkey project realization including all civil works, prefabricated containerized modular variants, and a Mobile STATCOM solution realized on truck trailers for quick relocation (p. 29). A typical installation comprises the SVC PLUS converter, control room, cooling, phase reactor yard, MV switchyard, power HV/MV transformer and connection to the HV switchyard (p. 29).

Siemens Energy introduced SVC PLUS® over 10 years ago; with more than 150 installations on all continents, it is a proven and trusted technology. Variants span highest reactive power ratings (up to 425 Mvar per branch), prefabricated modules for medium reactive power ratings (no building required), compact prefabricated modules for small ratings, and the relocatable Mobile STATCOM (p. 30). Realization is possible even for demanding constraints: very high system availability, seismic-compliant station design, noise-compliant realization, severe conditions (e.g., coastal conditions, high or low temperature sites, pollution, altitude), and electromagnetic compatibility with low radio frequency emissions (p. 31).

SVC PLUS FS® (E-STATCOM)

SVC PLUS FS® (Frequency Stabilizer) is an extended STATCOM (E-STATCOM) solution with voltage and frequency control in one unit. Because inverter-based resources have minimal inertia and cannot be used for frequency stabilization, new solutions are needed: using a bulk number of supercapacitors, the SVC PLUS frequency stabilizer® is a cost-efficient, compact solution supporting voltage and frequency grid stability. It combines a grid-forming converter (voltage source behavior with phase-correct instantaneous response to voltage magnitude or phase angle changes) with energy reserves — supercapacitors providing grid-scale active power output from milliseconds up to several seconds (p. 32).

Headline benefits: blackout prevention (dynamic voltage and frequency support combined in one unit); cost-effective solution (compact, space-saving installation with high power density, low losses, and easy maintenance); grid forming (inherent response time with high active power output over several seconds); high flexibility (adaptable through flexible adjustment of control parameters) (p. 33). Features include steady-state and dynamic voltage control through reactive current provision, frequency control using active current provision at frequency deviation, virtual synchronous machine behavior with natural inertial response, and stabilization of weak grids through voltage source behavior (p. 33). The technical data table (p. 32) is transcribed below.

Synchronous condenser (SynCon) and flywheel technology

With an increasing share of renewable power generation and the shutdown of large conventional and nuclear power plants, most power grids are experiencing a decreasing level of inertia and short-circuit power. Inertia reduces oscillation on grid frequency and prevents system blackouts, while short circuit power ensures reliable system protection. The synchronous condenser solution uses a generator to supply the necessary inertia with its rotating mass while also providing or absorbing reactive power: the generator is connected to the transmission network by a transformer, started by a static frequency converter, and once operating speed is achieved it is synchronized with the network, behaving like a synchronous motor with no load and providing reactive power, short-circuit power, and inertia (p. 34). Benefits: contribution of short-circuit power, voltage support, short-term overload capability, and inertia to the transmission system (p. 35).

To provide maximum inertia, Siemens Energy has extended the synchronous condenser solution with additional rotating mass from a flywheel — a highly effective method to maintain the required level of inertia and rate of change of frequency (RoCoF). Rotating mass provides an inherent synchronous inertial response, counteracting grid frequency fluctuations with active power injection or absorption during sudden load unbalance events. The flywheels operate in a partial vacuum to minimize air friction losses and reduce cooling efforts, enabling a safe emergency rundown in case of total power loss (grid blackout); the flywheel is designed for plug-and-play installation, delivered to site with the rotor installed, for minimal footprint and low supervision and maintenance effort (pp. 35–36). A typical plant comprises the generator hall, synchronous generator, generator circuit breaker, auxiliary transformer, flywheel and power transformer (p. 35). The technical data table (p. 35) is transcribed below.

Fixed Series Capacitor (FSC)

Series compensation technology provides higher transmission capacities for existing long-distance AC transmission lines and increased grid stability — without the costs and time requirements of building new lines. Power transfer with long overhead transmission lines is limited by the impedance that can lead to voltage drops; for decades, fixed series compensation has been the proven solution to maintain a minimum voltage profile and maximum utilization of transmission lines. The technology works by connecting a capacitor bank in series with the transmission line to partially compensate for inductive impedance while increasing the voltage at the point of connection (p. 38).

The capacitors are protected by metal oxide varistors (MOVs) and — in case of a severe fault — by a breaker which bypasses the FSC. For instant protection, a triggered spark gap bypasses capacitors and MOVs within less than 1 ms; gapless solutions are also possible where local requirements match. Main circuit elements: transmission line, capacitor bank, metal oxide varistor, spark gap, damping circuit (p. 39). Benefits: increases power transfer capability; reduces line voltage drops; limits load-dependent voltage drops; influences load flow in parallel transmission lines; reduces transmission angle, increasing stability; reduces transmission systems footprint; cost-effective; reliable and robust design even in seismic areas; headline benefits are increased maximum capacity, increased grid stability, and an economical solution (p. 39).

Global references (2012–2025)

Chapter 6 (pp. 40–55) presents 14 reference installations across nine countries. The table below transcribes each reference's technology, location, scope and special features verbatim from the per-project "Technical data" boxes. (The brochure names the customer/operator and customer project name for each reference and quotes two named executives; those names, project designations and quotes are omitted here per the customer-privacy guardrail — references are identified by technology and site location only.)

Notable technical context from the reference write-ups: the Rheinau installation is designed for a reactive power range of +/- 600 Mvar, making it among the most powerful systems in the world, and is the first-time application of grid-forming control for SVC PLUS® delta (p. 43); two of the four California STATCOMs together provide 848 megavolt-ampere (MVA) of dynamic reactive power support at a 500 kV substation (p. 44); the Mehrum E-STATCOM is the world's first with power supply via supercapacitors, stabilizing grid frequency by charging or discharging the stored 200 MW capacity (p. 46); the Moneypoint flywheel is described as the world's largest, supplying the same amount of rotating mass, inertia and short-circuit power as a coal turbine (p. 49); the Shannonbridge project combines a SynCon with a 160 MWh battery energy storage system in hybrid operation at a single grid connection — a world premiere at utility scale (p. 51); the Robertstown flywheels rotate in a negative pressure close to a perfect vacuum, reducing frictional heat and energy losses by 90 % (p. 52); and the Finland coastal-line upgrade from 220 kV to 400 kV used fixed series compensation because studies showed system limits are defined by voltage stability, not thermal overload (p. 54).

Figures & drawings

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