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High-temperature low-sag (HTLS) conductors, which can double the ampacity of conventional conductors, are becoming a mature option to uprate thermally limited transmission lines. This paper addresses several issues related to the widespread use of HTLS conductors in existing power systems. The first part of the paper analyzes the influence of higher line resistances on power transfer capability as well as the accuracy of conventional network models, based on constant conductor temperatures. The second part deals with the problem planners are facing when considering existing network reinforcement options versus the new alternative offered by HTLS conductors, intended to replace Alloy Aluminum Conductor Steel Reinforced (ACSR) equipment in situ. This leads to a security-constrained optimization problem involving binary decision variables. The 57-bus system is used throughout the paper to illustrate the main ideas.