Steady state inductive influence of high voltage transmission lines

摘要

Harmonic current flows within High Voltage transmission lines induce voltages in neighbouring metallic conductors be they fences, pipelines, other transmission lines or telecommunications cables. These voltages may endanger organisms which come into contact with the conductors or impair the operation of electrical systems connected to them. Under steady state operating conditions the induced voltages are seldom of sufficient magnitude to be hazardous, however they are on occasions severe enough to impair telecommunications services. With the increasing use of non-linear loads within the power system, harmonic current flows and hence the incidence of telecommunication interference can be expected to rise. Many potential interference problems may be avoided by the coordination of telecommunication and electricity transmission systems. The most cost effective time to engineer solutions to interference problems is during the design of the system. A need exists therefore for methods which accurately quantify the ability of High Voltage transmission lines to cause interference. This thesis is concerned with methods, both experimental and analytical, for determining the Inductive Influence or ability of a transmission line to cause interference. Existing models for the mutual impedance of conductors in the presence of the earth are reviewed. Numerical studies of the factors effecting the inductive influence of single and three phase transmission lines are reported. Measures for reducing the inductive influence through the use of alternative transmission line geometries and continuously grounded earth wires are investigated. New measures for quantifying the inductive influence are proposed, which are superior to existing measures due to the inclusion of the effect of frequency, earth resistivity, current sequence and transmission line geometry on the inductive influence. Comparisons are made between a digital computer model of the New Zealand inter-island HVDC link, and measured currents using a non-invasive crossed loop antenna system. The accuracy of the new methods is confirmed, as is the need for sensitive equipment when undertaking such investigations.