Mechanical Behaviour of Multi-Span Overhead Transmission Lines Under Dynamic Thermal Stress of Conductors Due to Power Flow and Weather Conditions

TLDR: In this paper, a dynamic model for calculating sags and tensions in a multi-span power line, for purposes of Dynamic Thermal Rating (DTR), is proposed. But the model considers not only the mechanical interaction between spans, due to rotation of strings, but also that the temperature of conductors can vary span by span, for different weather conditions.

Abstract: Dynamic Thermal Rating (DTR) of overhead transmission lines represents a significant improvement with respect to the traditional criteria used to assess the steady-state ampacity of conductors. In fact DTR uses actual operating conditions of the power line, rather than assumed conservative conditions. This is extremely promising for the secure operation of the power system: with DTR, TSOs can fully exploit the dynamic performances of conductors, i.e. currents significantly higher than the steady-state thermal limits, in the meantime that the system is redispatched. The present paper proposes a novel dynamic model for calculating sags and tensions in a multi-span power line, for purposes of DTR. The model considers not only the mechanical interaction between spans, due to rotation of strings, but also that the temperature of conductors can vary span by span, for different weather conditions. The problem was solved with a fast Newton-Raphson technique, rather than with conventional relaxation methods, in order to comply with the requirements of real-time operation. The developed tool is able to forecast the time trend of conductor temperatures, tensions, sags and clearances at each span, or to indicate which current can be carried for a given time, before a clearance or temperature constraint is violated. A case study compares the results of this novel method with the outcomes of the traditional "ruling span" technique.