Flex›Source - Electric power transmission (Wikipedia)

Source - Electric power transmission (Wikipedia)

Source: 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.
  • 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. Single-phase AC used only for some railway electrification.
  • 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. The Nordic synchronous area is a separate interconnection.
  • Base load served by large constant-output plants (nuclear, hydro). 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.

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 centralized to decentralized power systems” internationally.

Market structure

  • Transmission is generally a Natural Monopoly, regulated separately from generation since the 1990s liberalization.
  • Spain was first to establish a separate TSO. 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) can double capacity at less than half the cost of new lines. Increasingly relevant as 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.