Electric Grid Structure

An overview of how the electrical grid is organized, from generation to consumption. Understanding this physical structure is essential context for Flexibility — flexibility mechanisms operate within and across these layers.

The three layers

Generation (2.3–30 kV)
    │
    ▼ step-up transformer
Transmission (110–765 kV)        ← TSO domain (Svenska kraftnät in Sweden)
    │
    ▼ transmission substation
Subtransmission (≈ Swedish regionnät)
    │
    ▼ distribution substation     ← TSO/DSO boundary
Distribution (2–33 kV)           ← DSO domain (elnätsföretag in Sweden)
    │
    ▼ distribution transformer
Utilization (230/400 V)          ← End customers

Each transition happens at a Substation. See Electric Power Transmission and Electric Power Distribution for details on each layer, and Distribution Transformer for the final step-down to utilization voltage.

Subtransmission has no fixed voltage boundary. A general engineering explainer (book excerpt) lists common subtransmission voltages of 34.5, 69, 115 and 138 kV and notes “much crossover in functionality and voltage” between subtransmission and transmission (one system sometimes serving both functions), with utilities using different voltage combinations. Topologically, it describes radial (simplest, cheapest, least reliable), dual-circuit, and looped or meshed arrangements, higher-voltage lines tending toward loop/mesh. The wiki’s own mapping treats Sweden’s regionnät (40–130 kV in E.ON’s plan) as falling within this subtransmission band; the article does not address Sweden. (Source - EEP Basics of Subtransmission Systems (web))

Why this structure matters for flexibility

The grid was designed for one-way power flow: large centralized generation → transmission → distribution → consumption. This assumption is embedded in the physical infrastructure (transformer ratings, protection schemes, voltage regulation).

The energy transition breaks this assumption:

1. Distributed generation (solar, wind) injects power at the distribution level, creating bidirectional flows.
2. Electrification (EVs, heat pumps) adds large new loads at the distribution level.
3. Variable renewables at transmission level require new balancing mechanisms.

The result: the distribution grid — historically passive — must become active. This is where Flexibility comes in: the ability to adjust consumption, generation, or storage in response to grid needs. Demand Response is one of the primary mechanisms, alongside energy storage and distributed generation.

TSO vs DSO

The coordination between TSO and DSO flexibility needs is one of the key open questions in European grid regulation. Both may need flexibility from the same resources (e.g., a battery at a distribution-connected customer), creating potential conflicts that regulation must resolve.

Sweden’s three levels vs. the EU’s two. Sweden has historically organised its grid into three levels — stam-/transmissionsnät, regionnät, lokalnät — while EU regulation is built around two: överföringssystem (transmission system) and distributionssystem (distribution system). Elmarknadslagen already introduces the two EU-aligned roles (systemansvarig för distributionssystem, systemansvarig för överföringssystem), under which the distribution-system operator becomes responsible for both lokalnät and regionnät, while Svenska kraftnät as transmission-system operator covers only stamnätet — in EU terms, 40–130 kV regionnät lines already read as part of the distribution system, not transmission. A July 2026 government inquiry (Dir. 2026:83) goes further, investigating whether Sweden should formally collapse to two grid levels — including whether Svk should take over higher-voltage regionnät lines (potentially funded by flaskhalsinkomster) and where the distribution/transmission voltage boundary should sit. Reporting deadline 24 November 2027.

Is subtransmission really a shared TSO-DSO problem — and does a Svk takeover fix it?

Dir. 2026:83 frames a Svk takeover mainly as a funding and boundary-line question (use flaskhalsinkomster to buy out regionnät assets; decide where the new voltage line sits). Two further pieces of evidence bear on the underlying technical premise — that subtransmission is a genuine shared TSO-DSO coordination problem today, and that consolidating ownership under Svk is the way to resolve it:

The problem is real and already quantified. An academic model of Sweden’s own grid — built on the CoordiNet project’s real Uppsala 70 kV subtransmission demonstration — shows the regionnät DSO (Vattenfall Eldistribution) already sits behind two separate TSO-DSO interfaces (2×315 MVA transformers at a 205 MW subscription, plus a 250 MVA transformer at 87 MW), a genuinely meshed-to-meshed topology with multiple boundary points, not the single clean substation the wiki’s own diagram simplifies to above. The study quantifies what happens without coordination: the DSO’s entire modelled cost when no local flexibility is available (1,674 k€/year) is subscription-penalty exposure — Svk’s “virtual congestion” mechanism functioning as a direct cost-shifting tool from the TSO to the DSO. That cost falls 52% (to 802 k€/year) once the DSO can procure local flexibility, and scaling available flexibility to 1.6× today’s level eliminates the penalty entirely. So yes — subtransmission is a live, measurable coordination problem, not a hypothetical one raised only by the current inquiry.

But the Nordic precedent doesn’t point toward ownership consolidation. Finland — the closest comparator — has not resolved this by having Fingrid absorb the 110 kV layer. Fingrid’s own structure names only two components (main grid; distribution networks spanning 0.4–110 kV, not a separate “regional grid” tier), and its 7,600 km of 110 kV main-grid lines sit alongside a DSO-operated share of the same 110 kV level that the page itself doesn’t quantify (a commonly cited ~80% DSO / ~20% Fingrid split remains unconfirmed against a primary source — see the source page’s data gap). Even on that unconfirmed figure, mixed operation at a shared voltage level looks like the stable Nordic norm, not a transitional state Sweden is unusual for being in. Finland’s actual answer to the coordination problem is a market mechanism, not a takeover: FinFlex, a joint Fingrid–Helen Electricity Network congestion market on NODES, lets TSO and DSO clear flexibility from the same order book without either owning the other’s assets — structurally close to the Netherlands’ GOPACS Common market model already documented in TSO-DSO Coordination — The Central Design Problem › EU taxonomy: four market coordination models.

Reading the two arguments together: a Svk takeover would remove the multi-interface coordination problem by definition — a single owner has no TSO-DSO boundary to coordinate across, which is a genuine safety/efficiency argument (one operator with full observability, one protection philosophy, one planning process). But the Uppsala case study also shows that procuring flexibility, not consolidating ownership, is what already closes most of the cost gap in practice (52% at today’s flexibility levels, ~100% at 1.6×) — and Finland demonstrates that a market-coordination fix scales without an ownership change. The stronger case for a takeover in Dir. 2026:83 may end up being economic and administrative (only six DSOs with more than 100,000 customers among 168 elnätsföretag, appeal-rights asymmetry, the EU’s two-level norm) rather than a safety necessity that only full Svk control can deliver — the safety/efficiency gain a takeover buys is real, but it looks more like a simplification of an already-manageable coordination problem than a fix for an unmanageable one.

HVDC interconnections

Cross-border HVDC links are critical infrastructure for Nordic/EU flexibility. They enable:

• Cross-border balancing (import/export to match supply and demand)
• Access to Norwegian hydropower as flexible backup
• Market coupling across price zones

Notable links involving Sweden: Baltic Cable (Sweden–Germany), NordBalt (Sweden–Lithuania), Fenno-Skan (Sweden–Finland), SwePol (Sweden–Poland), Konti-Skan (Sweden–Denmark). Several connections are planned for renewal or expansion: Konti-Skan Connect (~2036), Aurora Line 2 to Finland (~2036), and a potential new DE-SWE interconnector (under study). (Source - Svk Network Development Plan 2026-2035)

The Swedish grid today

Sweden’s grid is structured around four Bidding Areas (SE1–SE4) reflecting the north-south generation/consumption imbalance. The transmission grid is undergoing a massive expansion: Svenska kraftnät plans SEK 225 billion in investments over 2025–2035, including ~2,900 km of new lines and ~40 new substations. The NordSyd initiative is the centerpiece, aiming to increase north-south transfer capacity through four parallel routes. Available cross-border capacity is now calculated using Flow-Based Capacity Calculation (since October 2024). (Source - Svk Network Development Plan 2026-2035)