Techno-economic analysis and methods for approximating limiting power transfer conditions in 110–220 kV overhead transmission lines

Abstract

Relevance: Overhead transmission lines rated at 110–220 kV are essential components of regional power systems and the electricity supply infrastructure of large industrial enterprises. Increasing demand, changing consumption patterns, the connection of new industrial facilities, and the expansion of distributed generation make their operating conditions increasingly variable. Rising electricity prices further increase the economic significance of technical losses, highlighting the need to determine optimal line loading.

Determining the optimal operating regime requires more than an assessment of average current. Relevant factors include daily and annual load profiles, equivalent full-load hours, projected electricity demand, ambient temperature, wind speed, solar radiation, the condition of conductors and connections, and actual line resistance. These factors influence transmission capacity, conductor temperature, energy losses, and operational reliability.

This integrated approach treats technical constraints as mandatory conditions and economic efficiency as the criterion for selecting the optimal solution. Its application can reduce energy losses and overall costs, improve the utilisation of existing network assets, extend equipment service life, and support technically and economically justified reconstruction and modernisation while maintaining the required supply reliability and power quality.

Aim: Develop and scientifically substantiate a methodology for determining the economically optimal current loading and rational current density in the phase conductors of existing 110–220 kV overhead transmission lines, using the minimization of discounted electricity transmission costs per unit of energy transmitted as the optimization criterion.

Methods: The study employed techno-economic and comparative analysis, economic–mathematical modelling, and optimization.

Results: Optimal current density was found to depend on maximum-load utilization duration, voltage, conductor type and cross-sectional area, electricity tariff, climate, and operating cost structure. Increasing conductor size and flattening the load curve reduce unit costs through lower losses and more efficient use of transmission capacity. Under the conditions considered, unit costs for 110 kV overhead lines were, on average, 10–12% higher than those for 220 kV lines. Since substantial deviations from the optimal current in either direction increase costs, maintaining the actual current within ±5% of its optimal value was recommended.