Fault Impedance Analysis in Half-Wavelength Transmission Lines

Abstract

Half-wavelength (HWL) line has excellent steady-state properties to power transmission over very long distances, and technical and economic advantages over HVDC very long lines. However, protection system based on impedance calculations need carefully attention due to specific behavior of HWL line under fault. This paper analyzes the fault impedance on HLW lines to produce more insight about the effect of the capacitance, the point of fault, the resonance phenomenon, the transmission line model and the phasor estimation to the impedance measurement process in protective devices. This paper shows that the phase impedance estimation suffers higher deviation from ideal values as faults are applied far away from terminals and transposition introduces an additional deviation. Three characteristic impedance zones can be observed in HWL line. The steady-state phase impedance can be measured with a small error in the first zone and the third zone. Faults in the second zone (the middle of line) introduce a very high deviation due to line transposition.