Electric power transmission (Wikipedia)

Summary

Electric power transmission is the bulk movement of electrical energy from generating sites to Substations, via high-voltage transmission lines. The interconnected lines form a transmission network, administered by entities such as Transmission System Operators (TSOs) or regional transmission organizations (RTOs). Transmission is distinct from Electric Power Distribution, which handles local delivery to end customers.

Key points

Physics and efficiency

• High voltage reduces current and thus resistive (I²R) losses. A 765 kV line loses 0.5–1.1% over 160 km vs. 4.2% for the same power on 345 kV.
• Power stations generate at about 2.3–30 kV depending on unit size; the power-station transformer steps this up to 115–765 kV AC for transmission.
• Transmission-level voltages are typically 110 kV and above; subtransmission 33–138 kV; distribution below 33 kV.
• US T&D losses estimated at ~5% (2013–2019).

AC vs DC

• Most transmission is three-phase AC. Per the article, most North American lines are three-phase AC, “although single phase AC is sometimes used in railway electrification systems” (single-phase is otherwise used for distribution to end users).
• HVDC is used for: long distances (lower losses), submarine cables (>50 km), and interconnecting asynchronous grids. HVDC links stabilize grids and allow independent power flow control.
• Nordic relevance: the article mentions Baltic Cable (Germany–Sweden, 238 km submarine HVDC), NorNed (Norway–Netherlands, 580 km), Viking Link (UK–Denmark, 765 km), and North Sea Link (Norway–UK, 720 km).

Grid structure

• Wide area synchronous grids: one grid connects most of continental Europe. (Wiki context, not in the article: the Nordic synchronous area is a separate interconnection.)
• Base load served by large constant-output plants (nuclear, coal or hydroelectric). Peak load by faster-responding gas turbines.
• Electrical energy must be generated at the same rate it is consumed — the fundamental constraint driving the need for Balancing Markets and Flexibility (wiki framing, not an article claim). The raw text says electricity “typically” must be generated at the rate consumed.

Load balancing and distributed generation

• The transmission system has limited buffering capacity — generation must match load.
• Distributed generation (wind, solar, V2G, VPPs) can interact with the grid to reduce transmission losses and improve system operation.
• The article notes a slow move from a centralized to decentralized power systems (article wording) internationally.

Market structure

• Transmission is generally a Natural Monopoly, generally considered a natural monopoly but not inherently linked to generation; many countries regulate it separately, and from the 1990s many liberalized in ways that led to separate companies.
• Spain was the first country to establish a regional transmission organization (REE as TSO, OMEL as market operator, separate). In the US, FERC Order 888 (1996) spurred creation of RTOs.

Reconductoring

• Replacing existing transmission conductors with advanced materials (carbon fiber core instead of steel) has the potential to double capacity; advanced lines cost 2–4x more per unit, with total reconductoring under half the cost of a new line. Grid expansion can take 10 years.

Relevance to flexibility

The article establishes why flexibility is needed at a fundamental level: electricity must be generated at the same rate it is consumed, and the grid has limited buffering. As generation shifts from dispatchable plants to variable renewables, and as distributed generation grows, the need for new balancing mechanisms (flexibility markets, storage, demand response) increases. The HVDC interconnections are also directly relevant to Nordic/EU grid flexibility — they enable cross-border balancing.