Reactive compensation of overhead AC transmission lines using underground power cables

Overhead (OH) transmission lines when loaded always consume reactive power. An underground (UG) power cable on the other hand is in itself a huge capacitor and therefore a source of reactive power. This paper highlights the use of UG power cables in conjunction with overhead lines, where the reactive power requirement of overhead line is compensated by UG power cables. To realize this compensation, an overhead line is divided into n equal sections and UG power cables are inserted in between each section. The resulting compensation leads to three advantages: 1) Unity power factor at both sending and receiving ends; 2) Increase in overall power transfer; 3) Improvement in transient stability. In addition, it partially solves the land acquisition “not in my backyard” problems associated with construction of new or already existing lines. Key equations to determine the exact cable length are formulated and validated through simulation.