Abstract
Abstract With the increase of power demand and the shortage of transmission corridors, the multi-circuit transmission lines on the same tower are widely adopted in extra-high-voltage (EHV)/ultra-high-voltage (UHV) transmission systems. The chapter elaborates the reasons for current unbalance in multi-circuit transmission lines based on analyses of typical tower structure and feasible phase arrangements. In addition to the studies of system under normal operation condition, the unbalance currents of multi-circuit line under external fault are investigated. The severe impact of the current unbalance on pilot directional protection and zero-sequence overcurrent protection of is proven by simulation results and real field data. An improved scheme of pilot directional protection is proposed to overcome the impact of circulating unbalanced current.
Published Version
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