Flex›Dynamic Line Rating

Dynamic Line Rating

Dynamic Line Rating (DLR) is a technique for calculating the real-time thermal capacity of overhead power lines based on actual weather conditions, rather than using a fixed worst-case assumption. By more accurately capturing how much current a line can carry at any given moment, DLR allows grid operators to utilize more of the line’s physical capacity without compromising safety.

How it works

The thermal capacity of an overhead conductor depends on how quickly heat can be dissipated:

  • Low ambient temperature → greater temperature margin → higher capacity
  • Higher wind speed → greater convective cooling → higher capacity
  • Solar radiation → additional heating → lower capacity
  • Precipitation → modest additional cooling effect

Traditional static line rating assumes conservative worst-case conditions (e.g., 25°C ambient, minimal wind) year-round. In practice, a line can carry significantly more current during cold, windy conditions. DLR replaces the static assumption with dynamic calculation using real-time sensor data — typically temperature sensors attached to the conductor and/or weather stations near the line.

Why it matters for flexibility

DLR reduces the number of situations classified as congestion. If a line’s true capacity is higher than its static rating at a given time:

In this sense DLR is a technical alternative to flexibility procurement — it expands the effective capacity envelope without hardware investment. It sits in the same category as grid reconfiguration (omkopplingar) as a non-wire solution.

Swedish implementation — E.ON

E.ON Energidistribution is deploying DLR across its regional grid. Status as of late 2024:

  • Currently deployed on 1 line in E.ON’s network
  • Ambition: deploy on all 130 kV lines during 2025

E.ON’s DNDP explicitly lists DLR alongside grid reconfiguration as one of the “tekniska alternativa lösningar” (technical alternative solutions) in its flexibility toolbox. (Source - E.ON Nätutvecklingsplan 2025-2034)

The 130 kV lines form the primary transmission backbone of E.ON’s regional network — spanning regions such as Skåne, Halland, Jönköping, and Kalmar — so full deployment at that voltage level represents a meaningful operational change.

Relationship to other tools

DLR is one layer of E.ON’s capacity management toolbox, alongside:

ToolTypeTimescale
DLRTechnical (line rating)Real-time / operational
Grid reconfigurationTechnical (switching)Operational / planned
Flexibility MarketMarket-basedDay-ahead / intraday
Villkorade AvtalRules-basedActivated post gate-closure
Grid reinforcementInfrastructureYears ahead

DLR does not eliminate the need for other tools but shifts the threshold at which they become necessary.

Limitations

  • Applies only to overhead lines (luftledningar) — underground cables (markkablar) and transformers are not equivalently weather-dependent for thermal capacity purposes, though E.ON notes that capacitive currents in cable-heavy networks are a separate constraint
  • Meshed regional networks require system-level analysis — knowing a single line’s DLR capacity is insufficient if flows can reroute through adjacent lines
  • Real-time monitoring infrastructure required at each line segment

Swedish sector baseline — Ei R2026:02 (2024)

Ei‘s first biennial smart grid monitoring report (Ei R2026:02, December 2025) provides the first official sector-wide count of DLR deployment in Sweden:

  • Only 2 regionnätsföretag use automated DLR, as defined by Ei’s indicator (a system that both automatically measures line capacity based on real conditions AND automatically operates the line based on that information)
  • No change between 2023 and 2024 for either company
  • One company applies DLR on 1 line segment; the other on 3 line segments
  • DLR is a regionnät/transmissionsnät indicator only — lokalnät are not tracked for DLR

The two companies are confirmed by Ei’s SGI dataset (EIFS 2022:5 annual reporting, No_DLR indicator): Skellefteå Kraft Elnät AB (1 line) and E.ON Energidistribution (3 lines) — unchanged in both 2023 and 2024. (Source - Ei SGI Data 2023-2024)

Ei’s assessment: “tekniken för dynamisk belastningsbarhet kan vara underutnyttjad” — the technology may be underutilized. Ei’s formal recommendation to the sector is that more widespread DLR deployment has potential to contribute to more efficient grid use and reduce the need for grid reinforcements.

This baseline establishes the 2024 starting point. The next report is due in 2027 (covering 2026 data).

The E.ON deployment plan (all 130 kV lines during 2025) post-dates this count. If realized, E.ON alone would significantly increase the number of DLR-equipped regionnätsföretag.

(Source - Ei R2026-02 Utvecklingen av Smarta Elnät (2025))

EU-level recognition

DLR features in two major 2024 EU documents as a priority technology:

ENTSO-E RDI Roadmap 2024–2034: DLR is a Mission 1 near-term milestone (Cluster 1 — Power Grid) under the theme of enhancing grid use and sustainability. The Roadmap also lists DLR in its Technopedia catalog as an “Asset technology” contributing to Mission 1. This makes DLR an officially mandated TSO research and deployment priority across all 40 ENTSO-E members. (Source - ENTSO-E RDI Roadmap 2024-2034 (2024))

EU DSO Entity Technical Vision (2024): The Technical Vision explicitly mentions “Dynamic Ratings” as an operations tool for DSOs: “Dynamic Ratings optimize asset use by allowing real-time adjustments to transformer and line limits, reducing conservatism and unlocking capacity.” Framed alongside power flow control as a digitalization-enabled operations capability. (Source - EU DSO Entity Technical Vision (2024))

The convergence of TSO (ENTSO-E) and DSO (EU DSO Entity) institutional recognition signals that DLR is expected to be deployed at both transmission and distribution voltage levels as part of the energy transition.