ELECTROMAGNETIC INTERFERENCE PRODUCED ON A COMPLEX METALLIC PIPELINE NETWORK BY A FAULT IN A POWER SUBSTATION

摘要

It is known that metallic structures like pipes for oil,rnwater and gas distribution, telecommunication cablesrnmay be very close or even enter a power substationrnarea; due to the proximity of the substation earthingrngrid with the above mentioned structures, it is necessaryrnto take into account of possible problems ofrnelectromagnetic interference among the different plants.rnThis is a typical case of electromagnetic compatibilityrninvolving very large structures. In particular, in case ofrnfault in the substation, overvoltages and overcurrentsrnmay be induced and transferred along the victimrnstructure also for some hundreds of meters. The effectsrnof such interference can be danger for staff and/orrnpossibilities of damages to the induced structure itselfrnor to equipments connected to it.rnSo, it is important, mainly at the project stage of a newrnplant (inducing or induced), to be able to predictrnvoltages and currents which could be induced on thernvictim in order to arrange suitable protection means.rnTo this purpose, some algorithms already exis inrntechnical literature but their validity is restricted tornsimple cases where the involved plants arerncharacterized by a simple geometry (i.e. the pipelinernlayout is modeled by a simple broken line). In many realrncases the geometry is much more complex because thernpipes may form a branched structure and sometimesrnalso loops can be present. Thus, the aim of the paper isrnto overcome such restrictions by presenting a morerngeneral method to be applied to interferencerncalculations in stationary state in case of pipelinernnetworks with complex geometry.rnTwo are the main assumptions on which our work isrnbased:rn1. the electromagnetic influence of the pipelinernnetwork on the power plant is neglected;rn2. the quasi static analysis of the problem is valid.rnThe first assumption, valid when the earthing grid andrnpipeline network are not metallically connected, allowsrnus to calculate the inducing field produced by the powerrnsystem as if the victim plant would not exist. The secondrnassumption, which is generally valid due to the lowrnfrequency considered (16.67 Hz, 50 Hz, 60 Hz typically)rnallows us to separately calculate as a first step therninducing fields that is:rn1. the inductive component of the electric fieldrnproduced by the fault current flowing into thernpower line entering the substation; (such a fieldrnis responsible of the inductive coupling with thernpipeline network);rn2. the earth potential produced by the fault currentrninjected into the soil through the substationrnearthing grid; (such potential is responsible ofrnthe resistive (or conductive) coupling with thernpipeline network).rnBy taking into account of the hypotheses mentioned inrnthe previous paragraph, the calculation algorithm mayrnbe subdivided into the following main steps:rn1. calculation of the inducing fields;rn2. calculation of the ideal longitudinalrnelectromotive force (e.m.f.) and ideal transversalrncurrent generators which represent thernelectromagnetic influence produced by therninducing power system on the induced pipelinernnetwork;rn3. modeling the pipeline network by means of arnsuitable equivalent electric network;rn4. calculation of voltages and currents induced onrnthe pipeline network.rnThe paper also presents an example of applicationrnrelated to a real case project.