Electric Power Transmission
The bulk movement of electrical energy from generating sites to Substations, via high-voltage transmission lines. Distinct from Electric Power Distribution, which handles local delivery to consumers. Together they form the electrical grid.
How it works
Power is generated at relatively low voltage (2.3–30 kV), then stepped up by transformers to high voltage (115–765 kV) for efficient long-distance transport. High voltage reduces current and thus resistive losses (which scale with I²). At the destination, Substations step voltage back down for distribution.
Most transmission is three-phase AC. HVDC (high-voltage direct current) is used for long distances, submarine cables, and interconnecting asynchronous grids. HVDC is particularly relevant in the Nordics — see interconnectors like Baltic Cable, NorNed, Viking Link, and North Sea Link.
Grid structure
Transmission networks are organized as wide area synchronous grids. Europe has a single synchronous grid covering most of the continent; the Nordics operate as a separate synchronous area. These grids are interconnected via HVDC links.
The network is administered by Transmission System Operators (TSOs) — e.g., Svenska kraftnät in Sweden (~15,000 km at 220–400 kV). Since the 1990s liberalization, transmission is typically regulated separately from generation as a Natural Monopoly. Sweden is divided into four Bidding Areas (SE1–SE4) reflecting transmission bottlenecks between the surplus north and deficit south.
The fundamental constraint
Electrical energy must be generated at the same rate it is consumed.
The transmission system has very limited energy storage/buffering. Generation must continuously match load. This is the root reason Flexibility, Balancing Markets, and demand response exist — they are mechanisms to maintain this real-time balance.
Key numbers
- Transmission voltages: typically 110 kV and above
- Subtransmission: 33–138 kV
- US T&D losses: ~5% (2013–2019)
- 765 kV line: 0.5–1.1% loss over 160 km
- 345 kV line: 4.2% loss for same power/distance
EU grid investment scale
The European Commission’s 2023 Grid Action Plan and 2025 European Grids Package established the investment need for EU electricity grids:
| Metric | Value | Source |
|---|---|---|
| Total T+D investment needed (this decade) | €584 billion | COM/2023/757 |
| Distribution grid investment by 2030 | €375–425 billion | COM/2023/757 |
| Total T+D investment needed by 2040 | €1.2 trillion | COM/2025/1006 |
| Additional cross-border capacity needed by 2040 | 108 GW | COM/2025/1006 |
| Cross-border needs unaddressed by 2030 (current trajectory) | 41 of 88 GW | COM/2025/1006 |
| Net system cost saving from optimal grid investment | €8 bn/year (2040) | COM/2025/1006 |
40% of EU distribution grids are over 40 years old. Electricity consumption is expected to grow ~60% by 2030. Wind and solar must reach 1,000 GW by 2030 from 400 GW in 2022.
Energy Highways
The 2025 Grids Package identifies 8 priority cross-border infrastructure bottlenecks (Energy Highways) receiving targeted Commission support. Of Nordic relevance:
- Harmony Link — electricity interconnection of the Baltic states; boosts energy independence from Russia
- Bornholm Energy Island — transforms the Baltic Sea into an offshore wind interconnector hub (Germany and Denmark developing jointly)
Sweden is not an Energy Highway host but is adjacent: Bornholm lies in the Baltic Sea opposite Skåne, and Harmony Link affects the security of supply picture for the Nordic-Baltic area. (Source - European Grids Package COM2025-1005)
Relevance to flexibility
As variable renewables (wind, solar) replace dispatchable generation, the real-time balance becomes harder to maintain through traditional means. New flexibility mechanisms — storage, demand response, cross-border trading via HVDC interconnectors — become essential. Transmission constraints also create Congestion Management needs that drive local flexibility markets.
Sweden’s transmission grid is undergoing its largest-ever expansion, with Svenska kraftnät planning SEK 225 billion in investments over 2025–2035 and targeting 4,000 km of new transmission lines over 10 years — from a historical ~5,000 MSEK/year to 25,000+ MSEK/year investment pace. The explicit goal is to halve project lead times. The NordSyd initiative targets the critical north-south bottleneck with four parallel reinforcement routes. Available cross-border capacity is now determined by Flow-Based Capacity Calculation (replaced NTC in October 2024). Despite this investment, the connection queue (>175 GW applied, vs ~25 GW peak load) vastly exceeds buildout speed, making Flexibility essential to bridge the gap. (Source - Svk Network Development Plan 2026-2035, Source - Svk Strategi mot 2030 (2026))
HVDC interconnector projects on hold (May 2026): Three planned Svk interconnector projects — Konti-Skan Connect (Denmark), Aurora Line 2, and Fenno-Skan 3 (Finland) — were ordered excluded from Svk’s 2027–2029 investment plan by Regeringsbeslut I:6 (7 May 2026). The government’s stated reason is objections to the EU nätpaketet (network package, Commission proposal December 2025), particularly its restrictions on how member states may use flaskhalsinkomster (congestion revenues) and its centralization of electricity system planning at EU level. Existing interconnectors remain in operation. (Source - Svk Utlandskablar Uppdrag Reviderad Investeringsplan (2026))