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 (33–138 kV)
    │
    ▼ 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.

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:

Distributed generation (solar, wind) injects power at the distribution level, creating bidirectional flows.
Electrification (EVs, heat pumps) adds large new loads at the distribution level.
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

	TSO	DSO
Operates	Transmission grid (high voltage)	Distribution grid (medium/low voltage)
Sweden	Svenska kraftnät (single national TSO, ~15,000 km at 220–400 kV)	~170 elnätsföretag (E.ON, Ellevio, Vattenfall, municipal utilities, etc.)
Traditional role	System balancing, frequency control, transmission capacity	Voltage quality, connection, fault management
Emerging role	Procuring flexibility for system balancing	Procuring flexibility for local congestion, becoming “neutral market facilitator”

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.

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)

Data gaps

Details on Nordic synchronous area vs. continental European grid
DSO-level grid capacity and congestion data