A Single-Circuit Extra-High Voltage Line of Increased Transmission Capacity

Abstract

Conventional single-circuit EHV AC lines, widely used around the world, feature an essential drawback: in the case of most probable single-phase sustained failures, the line is fully disconnected. An advanced single-circuit EHV line is proposed, one phase of which is made as two semi-phases operating in parallel to each other. In emergency modes, one of these semi-phases is used as a backup phase, and two usual phases are equipped in the line middle part with series compensation devices for balancing the line operation mode. An algorithm for calculating normal operation modes has been developed. Taking the example of an advanced 500 kV line, the ratio between the transmission capacities of the proposed line and a conventional single-circuit line is shown. A scheme is proposed, with which it becomes possible, in the case of a sustained damage to one of the semi-phases or in case of damage to one of the phases, to switch over for operation in the post-emergency mode with the possibility of transmitting at least 50% of the power of the initial maximum operation mode. A technical and economic comparison of a conventional double-circuit and the advanced single-circuit lines was carried out.