Induced Voltage in Overhead Power Lines with an Uneven Line Route Approach

This paper is concerned with an analysis of the induced voltage that may pose a hazard to personnel of a repair team during a repair job done on a deenergized power line exposed to the electical field of a neighboring operating network. For analysis, a number of assumptions were made. Only steady-state sinusoidal processes at a frequency of 50 Hz were considered. Other electromagnetic wave and phase processes were ignored. Reasonably long parallel-approach stretches of power lines were considered; end effects were ignored. All actual parameters were defined in terms of a plane-parallel field. Under normal operating conditions of a power network, the maximum permissible ground voltage of 42 V was taken as a safety criterion for conducting repair work [1]. In recent years, much interest has been focused on the problem as formulated above [2, 3]. In the first part of our study, we consider in some detail the physics of induced longitudinal voltage with allowance for the effects associated with the unevenness of line route approach. Special attention will be given to the design and parameters of equivalent schemes. In the second part, results of an induction analysis of an actual extensive network composed of a large number of power lines are given. It is a well-known fact that, as two or more power lines approach one another, longitudinal electromotive forces (EMF) are induced in each of them; these forces are associated with currents in the phase conductors of neighboring lines and with ground voltages that, in turn, are determined by the electric field of parallel power lines. By conventional terminology, we call the former effect an electromagnetic effect, and the latter — an electric effect. The problem we are concerned with is considered in terms of a linear model; therefore, each component can be analyzed separately, and the resulting voltage at each point along a line can be found using a vectorial addition technique. We assume that the route of the power line to be repaired (henceforth denoted RL) is sufficiently long (by convention, running along a straight line parallel to the x coordinate). Spaced apart at a specified distance y, an inductive line (IL) runs parallel to the RL. The IL phases are energized at voltage U k , and they pass current I k (effective complex values of the phase voltage and phase current in the IL kth conductor). The IL is assumed to operate in a symmetric regime. The mutual-induction EMF per unit length of the RL j-th conductor, induced by the I k current, is determined irrespective of the rest of conductors by the formula E jk ext = ZjkIk, where Z jk is the complex longitudinal resistance between the RL jth conductor and the IL kth which (for a single-bed ground and neglect of the end effect and ground-bias currents) can roughly be determined at a frequency of 50 Hz by the formula [4]