Analysis of the Voltage Profiles with Uprating Technique by Third Harmonic Voltage Injection
This paper presents a study concerning the transmission line uprating method by injection of third harmonic voltage (THV). The method has been recently employed as a more economically feasible proposal to raise the transmission voltage level without the requirement for changes in the structural elements of overhead lines. The superposition of a third harmonic voltage component with the fundamental component at the sending and receiving ends of the line increases the amplitude of the fundamental voltage component without exceeding the electrical insulation tolerance limits, which results in a rising of the power transfer capability. This work
shows a study on the behavior of the voltage profile of several OHTLs, represented by Bergeron's model, which were uprated by the THV technique. The results have shown that THV technique is a feasible option for OHTLs of up to 200-km length. For OHTLs longer than 200 km, phase voltages may exceed safety levels which imposes a limitation in the uprating of the long lines by this technique.