The capacitive coupling between EHV lines and nearby pipelines

This paper addresses the effect of the electrostatic field due to extra high voltage (EHV) overhead transmission lines on pipelines in the vicinity of those power lines. Two measures for this effect are used: the maximum electric field on the pipe surface and the total electric charge on the pipeline per unit length. A mathematical model is presented for assessing these two measures. The results of applying the model to a situation involving a single-circuit, six-bundle, three-phase, 750-kV EHV line with flat conductor configuration are presented and discussed. The first set of results refers to a parallel pipeline of radius 0.5 m. The dependence of both the maximum electric field (at the top of the pipe) and the charge per meter on the distance between the pipeline and the tower center is similar to the distribution of the electric field beneath the tower at the ground surface. It shows maxima of both quantities if the pipe is exactly under one of the outer phases of the power line. At a distance of about 35 m from the tower center, both the electric field and the charge per unit length drop to 50% of their maximum values. The electric field is found to increase almost linearly with the clearance between the pipeline and the ground surface. The charge changes in a more complicated way with the clearance. It decreases if the pipe clearance increases from 0 to 0.2 m, then increases steadily beyond this value. For a given distance from the 750-kV line and for a fixed clearance from the ground, both the electric field and the electric charge per unit length on the pipeline will increase with the pipe radius. This paper will deal also with the impact of the pipeline on the nearby EHV power line and its associated network. The results will show that for a solidly earthed power network, the presence of the pipeline will be accompanied by a slight increase in the neutral current. On the other hand, for a power network with an inductively earthed neutral, there will be a tendency toward a parallel resonance that can occur for particular values of the neutral inductance and pipe radius. This resonance will result in an increase in the system's neutral potential, which will be primarily limited by the network losses.