Συμβολή στον υπολογισμό της επαγωγικής επίδρασης γραμμών μεταφοράς ηλεκτρικής ενέργειας σε υπόγειους μεταλλικούς αγωγούς

Abstract

This PhD Dissertation deals with the problem of inductive interference of electric power lines, including transmission and distribution lines and electric traction lines, to underground metallic conductors, such as gas or oil pipelines, water pipes etc. The case of electromagnetic interference between electric lines and metallic conductors has been a topic of major concern since the early 60’s. The main reasons for that were: • The rapid increase in energy consumption, especially in western countries, which led to the adoption of higher load and short circuit current levels, thus making the problem more acute. • The ever increasing cost of rights-of-ways, suitable for power lines and pipelines, along with recent environmental regulations, aiming to protect nature and wildlife, has forced various utilities to share close or even common corridors for both power lines and pipelines. Therefore, situations where a pipeline is laid at close distance from a transmission line for several km are frequent nowadays. This electromagnetic interference is present both during normal operating conditions and faults and, generally, it consists of an inductive, a conductive and a capacitive component. Out of the three, the inductive part is the dominant one. The capacitive component may be ignored for buried pipelines, whereas the conductive part arises only in fault conditions and, specifically, in cases where the pipeline is located near the faulted structure. The inductive interference is the result of the magnetic field generated by the power line, which induces voltages in adjacent metallic conductors, like pipelines. Under fault conditions, high voltages and currents may be induced to nearby pipelines, which may result in hazards to people or working personnel touching the pipeline or other metallic structures connected to it. If the pipeline is electrically continuous, i.e. it is not separated by insulating flanges, then the induced voltages and currents “travel” throughout its length, even if the fault occurs far away from the pipeline. In addition, there is a high risk of damaging the pipeline coating, insulating flanges or rectifiers, whereas the corrosion of the metal is accelerated. Over the past years, the problem was examined by researchers that produced various reports, papers and standards. The widely known Carson’s relations [11] were the basis for the initial attempts to study this interference [12-17]. A technical recommendation was developed in Germany based on these studies, which was revised later [18], by utilizing more advanced and sophisticated analytical models in a computer program. During the late 70’s and early 80’s, two research projects of the Electrical Power Research Institute (EPRI) and the American Gas Association (AGA) introduced practical analytical expressions that could be programmed on hand held calculators [19- 23] and computerized techniques [24-26]. In the following years, EPRI and AGA joined forces and developed a computer program [27-29], which utilizes equivalent circuits with concentrated or distributed elements, with the self and mutual inductances being calculated using classic formulae from Carson [11], Pollaczek [12], Sunde [17] and Wait [31]. Furthermore, CIGRE’s Study Committee 36 produced a report detailing the different regulations existing in several countries [44] and some years later published a general guide on the subject [43], with a summary of its most important parts reproduced in [45]. Moreover, a universal algorithm was proposed in [42] that may be used to simulate uniformly both the inductive and conductive interference, whereas a more general method that may be applied to pipeline networks with complex geometries was proposed in [50].