New Approach for Ampacity Calculation of Overhead Lines With Steel-Cored Conductors

Abstract

Due to increasing energy demand and penetration of renewable energy sources into the grid, the transmission system has often been operated closer to its operating limit. This scenario requires the accurate calculation of the lines' ampacity in order to ensure their safe operation and the full use of their capacity. This paper proposes a new approach for calculating the ampacity of overhead lines with steel-cored conductors, using an accurate resistance calculation model in a straightforward way. The alternating current (AC) resistance of this type of conductors can be affected by the core magnetization depending on factors such as the number of aluminum layers and the core magnetic properties, which are properly considered using the proposed model. Results for the conductor AC resistance variation with the carried current value and the ampacity for different scenarios are presented and compared with those obtained using the resistance calculation models proposed in ampacity calculation methods by IEEE and CIGRE´ . Results show that the lines' ampacity tends to be underestimated using the existing models. However, for conductors with one aluminum layer, the IEEE method may overestimate the line's ampacity by considering a constant conductor resistance value, bringing risks of accidents due to conductor overheating.