EHV transmission line capacity enhancement through increase in surge impedance loading level

The quantum of power that a given EHVAC transmission line can safely carry depends on various limits. These limits can be categorized into two types viz. thermal and stability/SIL limits. In case of long lines the capacity is limited by its SIL level only which is much below its thermal capacity due to large inductance. Decrease in line inductance and surge impedance shall increase the SIL and transmission capacity. This paper presents a mathematical model of increasing the SIL level towards thermal limit. Sensitivity of SIL on various configuration of sub-conductors in a bundle, bundle spacing, tower structure, spacing of phase conductors etc. is analyzed and presented. Various issues that need attention for application of high surge impedance loading (HSIL) line are also deliberated.