Upgradation of Power Flow in EHV AC Transmission

Transient stability plays key role for the loading of Extra High Voltage AC lines under their thermal limits. It is not possible to load these EHV lines near the thermal limits. But, with the proposed scheme in this paper, it is possible to load these lines very close to their thermal limits. Master current controller senses ac current and regulates the dc current orders for converters online such that conductor current never exceeds its thermal limit. In this scheme, the ac line conductors are superimposed with dc power flow and it doesn't cause any transient instability. This paper presents the converting of an ac line into composite ac-dc power transmission line to improve transient stability and damping out the oscillations. With Matlab/Simulink software the thermal limits are satisfactory and the gain in the load ability of the line is obtained.