AC interference on gas pipelines due to phase to ground faults in overhead transmission lines

Abstract

The purpose of this research is to investigate the severity of voltages induced on gas pipeline (GPL) installed in parallel to a 115-kV overhead transmission line. The overhead transmission line (OHTL) is configured as a single-circuit with a single phase to ground fault occurred on one phase. Transmission of high voltage along the same right of way (ROW) with a metallic conductor may possibly introduce interference on the metallic conductor such as GPL due to power frequency voltage as well as due to phase faults and switching phenomena. Two main approaches were used to compute the induced voltages, namely the method of moment (MOM), which is based on the electromagnetic field theory, and the circuit based method. The simulation considers a 30-km-long OHTL and a 10-km-long GPL. The GPL is buried at 1-m depth in a homogenous earth structure with varying soil resistivites from 10 to 1000 I-m. The transmission line consists of 150 towers and 200-m span length. The separation distance between the GPL and OHTL is varied from 5 to 100 m. The phase to ground fault current was varied from 0.5 to 10 kA. Several observation points were made throughout the corridor to examine the induced voltages at different locations. The results show that, the soil resistivity, separation distance, and fault current had significant effects on the GPL induced voltage. In the case of the observation points lying on the soil or on the outer surface of the GPL coating, the induced voltage increases, when the soil resistivity increases, as expected. In contrast, for the observation points placed inside the GPL metal, and the GPL is well coated, the induced voltage decreases when the soil resistivity increases.