## 4 Considerations Relating to the Use of High-Temperature Low-Sag Conductors  
Conductors can be divided into three basic groups [20]:  
* Aluminium and its alloys,
* Aluminium-iron alloy conductors (aluminium-steel),
* High-temperature conductors. Conductors can be composed of wires of various shapes. The most used is wire with a circular cross-section. Other shapes include trapezoidal wires stranded into segments, known as segmental wires, or wires shaped like a Z, referred to as Z-shaped conductors [20]. The current trend reflects a continual escalation in energy consumption, accompanied by challenges such as unplanned large-scale transfers of electrical energy from one region of the power system to another. This often arises due to fluctuations in the production of renewable energy sources concentrated in specific locales. Consequently, there arises a critical need to augment the transmission capacity of overhead electrical lines. As mentioned previously, one viable approach to address this issue is the replacement of conductors. A promising solution lies in the adoption of HTLS conductors in lieu of traditional ACSR conductors, which operate within a temperature range of 80 \({}^{\circ}\)C to 100 \({}^{\circ}\)C [15; 19]. HTLS conductors are made from special materials to maintain their mechanical properties at elevated temperatures. Most have a similar construction to conventional ACSR conductors, but there is also a special type with a gap. The core of the conductor is made from various types of steel or composite materials to enhance mechanical properties, while the sheath is made from aluminium alloys to ensure conductivity [21]. To minimize the necessity for structural modifications to transmission lines, HTLS conductors must operate at significantly higher temperatures than conventional conductors, while ensuring compliance with permissible sag limits and without inducing substantial increases in original mechanical tension, ice loading, or wind loading. HTLS conductors are engineered for applications necessitating continuous operation at conductor temperatures exceeding 100 \({}^{\circ}\)C, designed to withstand emergency conditions at temperatures exceeding 150 \({}^{\circ}\)C. The appealing characteristics of high-temperature conductors come with elevated costs. However, these higher costs are deemed acceptable if they facilitate cost reduction or prevention of expenses associated with structural alterations to transmission lines [15]. Current commercially available types of HTLS conductors, as well as the materials employed in the construction of their cores and casings, are succinctly described in technical manuals such as CIGRE 425, CIGRE 331, and CIGRE 244 (Table 1). Additionally, CIGRE Technical Brochure 331 addresses the impact of HTLS conductors on insulators, providing comprehensive insights into their application and integration within existing power infrastructure [15]. In HTLS studies of conductors in transmission systems, the manufacturers' performance comparison of various HTLS and conventional conductors demonstrates that HTLS conductors are superior at handling high temperatures with minimal sag compared to conventional conductors. Among HTLS options, ACCC conductors perform the best, showing minimal sag at elevated temperatures due to the high-tensile strength of their hybrid carbon core strand. The geometric design of HTLS conductors helps address sagging issues and maintains good clearance at high temperatures, reducing structural weight and installation costs. Additionally, HTLS conductors provide better geometry configurations and excellent electrical conductivity. Other advantages of HTLS include lower maintenance costs, improved efficiency, and enhanced reliability in diverse environmental conditions. Additional benefits of HTLS conductors include the following [5]:  
* Excellent conductivity and low resistivity, enabling more current flow and optimizing carrying capacity.