Svk Driftsäkerhet Augusti 2025

Svenska kraftnät’s report on grid operational security (driftsäkerhet) in the Swedish and Nordic power system, published August 2025. Covers the technical challenges arising from the transition to a high-inverter-based resource (IBR) system, and the tools and requirements Svk plans to use in response. The report is explicitly qualitative and written for non-specialist readers.

Core framing: six system needs

The report organizes operational security requirements around six fundamental system needs that any power system must satisfy:

Separately, the report divides power system stability into five categories (based on IEEE 2021): frequency stability, voltage stability, angular stability, resonance stability (oscillations in the 5–45 Hz range) and inverter stability. The last two have become increasingly relevant as inverter-connected generation has grown.

Grid-forming vs grid-following inverters

The central technical distinction in the report:

Grid-following (nätföljande omriktare)

• The dominant mode for all current wind, solar, and battery inverters
• Conventionally controlled inverters synchronize through measurements at the connection point and adapt to them, so they “follow” the grid
• Most inverters connected so far have implemented grid-following control, which has left several possible capabilities unused
• In a weak connection point it is harder for the inverter to adapt in time, because voltage changes both more and faster

Grid-forming (nätformande omriktare)

• Described in the report as a new generation of inverter control that can mimic physical properties of synchronous generators and contribute basic capabilities to the grid
• Simplified: synchronizes the inverter through internal measurement rather than by following the grid voltage
• Gives better synchronization in weaker grids and a better ability to contribute to island operation (ö-drift) and grid restoration
• All stability categories are affected, and several depend on inverters becoming grid-forming for a higher inverter share to be possible
• How grid-forming properties are defined determines the role inverter-connected plant can play, and underpins Svk’s own investments, requirements on others and economic incentives
• Related: “synthetic rotational energy” — using the energy buffer in wind turbine rotors (or batteries, hydrogen storage) for damping and fast frequency response

Why this matters now

As synchronous generation (hydro, nuclear, thermal) is displaced by IBR, the system loses:

• Rotational inertia (which naturally resists frequency changes)
• Built-in voltage regulation from synchronous machines
• Automatic damping from physical machine behavior

Grid-forming inverters can substitute for these properties if properly designed and controlled — but require explicit technical requirements from Svk.

Svk’s grid-forming development roadmap

Svk is developing requirements and conformance tests for grid-forming inverters in two steps (synchronization section):

1. First step — requirements for HVDC converters and STATCOMs
2. Next step — requirements for inverters of battery storage and solar and wind power

The requirements aim, among other things, for inverters to stay synchronized with the grid under varying connection-point conditions and during disturbances. The report stresses that a common definition needs continued cooperation across the Nordics and the wider power sector (see Grid-Forming Inverters for the CONDON position). It states no dates and does not say the requirements will be mandatory or how the segments are sequenced beyond these two steps.

Existing stability support mechanisms

Frequency regulation

• FCR-D (disturbances) and FCR-N (normal operation) are market-based stabilisation products; FCR-N volume is currently fixed at 600 MW, expected to grow with consumption and the share of solar and wind
• The technical requirements for FCR were revised in 2023; the new requirements include damping of frequency oscillations
• FFR (Fast Frequency Reserve): in use as a remedial measure since 2020, today delivered mainly by batteries at relatively low cost; a dynamic FFR (for higher volumes, over-frequency, emergency operation/restoration, and oscillation damping) is under consideration
• Frequency control in emergency operation (LFSM) has been introduced for generation; extension to consumption, storage and HVDC is planned

Reactive power and voltage

• Svk has invested in and procured voltage-regulating resources, for example three STATCOMs (no locations given)
• A large number of shunt reactors contracted in 2024, covering current needs and those from planned grid investments and connections up to 2032
• Voltage stabilisation (planned): via the transmission tariff, Svk plans to introduce in 2027 a voluntary opportunity for financial compensation for those who contribute voltage-regulating behaviour at the connection point
• Voltage maintenance (from 2027): an option to issue a penalty fee (vite) to actors that fail to limit their reactive power exchange with the transmission grid when Svk has requested it
• Both are framed as addressing the growing need for reactive resources as active power is transferred over longer distances

N-1 criterion

Svk’s dimensioning criteria are grounded in the N-1 criterion: the system must withstand all single disturbances, e.g. loss of a line or a production unit. Simultaneous faults with a common cause may be covered where probability and consequence are high enough; simultaneous independent faults (N-X) are generally not. The report notes that the system has historically withstood far larger disturbances than it was dimensioned for (example: the Hagby station disturbance of spring 2023, where more than 2000 MW of production was lost against a 1400 MW dimensioning fault) thanks to abundant inherent capabilities such as rotational energy, and that in a future system with many provided capabilities robustness falls to the level the system is designed for. This report treats N-1 as the operational baseline; for the EU-level push toward replacing it with probabilistic/stochastic risk assessment (ACER 2019, GARPUR, ENTSO-E, target end-2027) and the underlying risk-calculation methodology, see N-1 Criterion.

Relevance to wiki

• Grid-Forming Inverters — primary source for the concept page; defines the grid-forming/grid-following distinction and Svk’s requirements roadmap
• Svenska kraftnät — operational security program; planned 2027 voltage-regulation compensation and reactive-exchange penalty; STATCOM investments
• Balancing Markets — FFR in use since 2020, mainly battery-delivered; FCR requirement revisions 2023; FCR-N volume of 600 MW
• Island Operation — ö-drift capability as one of the six system needs; grid-forming inverters as enablers
• N-1 Criterion — the EU-level probabilistic-methodology successor to the N-1 standard this report treats as settled
• Electric Power Transmission — stability categories; six system needs framework

Data gaps

• Quantified inertia threshold at which Svk considers mandatory grid-forming requirements triggered
• Timeline for Svk publishing formal grid-forming technical requirements (HVDC phase)
• Whether FFR volumes in KMA2025 reflect grid-forming or grid-following battery assumptions