Relevant factors for temporary overvoltages due to fault-resonance conditions on half-wavelength transmission lines

Abstract

This article explains the phenomenon of severe temporary overvoltage (TOV) due to critical faults on a very long transmission line with half-wavelength properties. Such non-conventional AC lines are an alternative to bulk power transmission over very long distances and present excellent steady-state properties. However, half-wavelength lines can present fault cases with very different natures of the voltage response due to fault-resonance conditions. The present document introduces a further explanation of these fault-resonance conditions. First, this study analyses the resonance at the fundamental frequency and analytically determines the TOV considering the fault location, the type of fault, and a simple model of system components. Coherence of major phenomena is obtained with time-domain simulation. Then, a more detailed method for analysing overvoltages on half-wavelength lines under fault conditions is presented. Here, a sensitivity analysis is implemented using PSCAD/EMTDC with more accurate models of system components. Factors such as the type of fault, sequence circuit, fault location, short-circuit level, fault resistance, loading level, transformer saturation and ground resistivity are considered. Finally, the paper interprets the impact of those factors on fault-resonance conditions and TOV.