DLR-Based Reassessment of Continuous Current-Carrying Capacity for Improved RES Integration in Legacy HV Networks

Rating (SLR) assumptions.

This paper presents an alternative rating criterion for determining static line ratings for overhead high-voltage lines, based on long-term Dynamic Line Rating (DLR) data and electrical clearance constraints rather than fixed conductor design temperatures. The proposed ClearanceBased Static Line Rating (CB-SLR) method derives line-specific static ampacities from multiyear clearance-limited dynamic performance, incorporating meteorological conditions, conductor ageing effects, and a statistical assessment of acceptable operational risk.

The methodology is validated using extensive field data collected over 10 years from approximately 400 weather stations and DLR monitoring systems installed on more than 1 000 overhead lines owned by the three largest DSOs in Poland. High-resolution aerial inspection data are used to model conductor sag and ground clearance in critical spans accurately. CBSLR values are determined using a quantile-based risk framework, allowing a controlled probability of short-duration clearance non-compliance depending on the line owner's choice

(e.g. 1 % or 5 % of seasonal operating time).

Application of the method to selected 110 kV lines shows that conventional temperature-based static ratings may be either overly conservative or insufficiently safe, depending on local conditions and asset history. In many cases, CB-SLR reveals substantial unused transmission capacity that can be safely utilised, while in others it identifies elevated clearance-related risk not captured by legacy ratings.

The proposed approach provides transmission and distribution system operators with a practical, experience-based tool to reassess static line ratings, improve utilisation of existing assets, and support the integration of renewable generation while maintaining compliance with clearance regulations. The methodology is consistent with IEC TR 61597 and is transferable to other networks where long-term DLR and clearance data are available.