Assessment of conductor thermal models for grid studies

Abstract

Existing EMS applications resort to static network models built upon constant resistances whose values are specified beforehand. However, the steady-state thermal balance of overhead conductors requires that ohmic losses be dissipated by convection and radiation heat, leading to conductor resistances being a function both of environmental factors and transmitted current. Each term of the equation involved in the thermal balance of overhead conductors is analysed allowing the influence of conductor current on conductor temperature to be separated from that corresponding to environmental factors. As a result, three approximate thermal models are elaborated, which are compared on the Spanish transmission system. Test cases are included showing that the influence of the selected model on transmission losses may be significant enough, particularly when the transmission system spans areas with diverse loading levels and weather conditions.

Research on Transmission Line Loss and Carrying Current Based on Temperature Power Flow Model

“…In the steady state, the heat transfer of transmission line is determined by the heat balance equation [3],…”

“…r Q , c Q can be approximated as linear functions of the conductor temperature under certain environmental condition, the above factors can be expressed as [3],…”

“…Although the resistance of the branch is sensitive to the temperature, the resistance of the system is always treated as normal. Not promptly adjusting branch resistances may produce significant errors under high load conditions----up to 10% for the total system loss, 30% for the branch alone [2] [3].…”

A Novel Thermo-Mechanical Model to Assess the Dynamic Thermal Rating of Multi-Span Overhead Transmission Lines

“…All over the world, increasing the thermal rating of existing overhead transmission lines is considered a valid alternative to the construction of new lines [1,2].…”

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Abstract

Keywords

Ampacity, Dynamic Thermal Rating, Overhead lines

IntroductionAll over the world, increasing the thermal rating of existing overhead transmission lines is considered a valid alternative to the construction of new lines [1,2].The thermal rating of a transmission line is the highest current that the line can carry under assigned meteorological conditions, respecting all clearances. The ampacity is limited in practice by the maximum allowed operating temperature: if the temperature limit is exceeded, the distances between conductors and ground decrease to unacceptable values.

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