Abstract
This work presents the feasibility study of an on-line monitoring technique aimed to discover unwanted variations of longitudinal impedance along the line (also named “impedance discontinuities”) and, possibly, incipient faults typically occurring on high voltage power transmission lines, like those generated by oxidated midspan joints or bolted joints usually present on such lines. In this paper, the focus is placed on the application and proper customization of a technique based on the time-domain reflectometry (TDR) technique when applied to an in-service high-voltage overhead line. An extensive set of numerical simulations are provided in order to highlight the critical points of this particular application scenario, especially those that concern the modeling of both the TDR signal injection strategy and the required high-voltage coupling devices, and to plan a measurement activity. The modeling and simulation approach followed for the study of either the overhead line or the on-line TDR system is fully detailed, discussing three main strategies. Furthermore, some measurement data that were used to characterize the specific coupling device selected for this application at high frequency—that is, a capacitive voltage transformer (CVT)—are presented and discussed too. This work sets the basic concepts underlying the implementation of an on-line remote monitoring system based on reflectometric principles for in-service lines, showing how much impact is introduced by the high-voltage coupling strategy on the amplitude of the detected reflected voltage waves (also named “voltage echoes”).
Highlights
It is a matter of fact that the natural evolution toward more and more sophisticated energy systems, such as smartgrids and supergrids, is pushing the market of electrical energy and the related handlers, namely the transmission system operators (TSO), to more advanced power line management strategies [1,2,3,4], and to more accurate monitoring techniques [5,6,7,8]
All infrastructure built to implement the national electric transmission lines are shaped to be rugged and reliable, the extremely high and ever increasing power demands are capable of overstressing the critical parts of the entire power grid, sometimes resulting in temporary hard faults or the breakdown of the grid itself, in this way causing a long list of obvious severe inconveniences
The actual status of advancement in this context is stuck in a controversial situation, where there are, on the one side, a lot of research efforts that explore a wide range of new and alternative monitoring techniques, such as the ones employing electromagnetic (EM) techniques [9,10,11,12,13,14], vibro-acoustic techniques [15], information technology (IT) solutions [16,17], and drones [17,18], whereas, on the other side, in the real-world, monitoring activity is mainly still linked with manual inspection methodologies using thermo-graphic cameras recordings [19,20]
Summary
It is a matter of fact that the natural evolution toward more and more sophisticated energy systems, such as smartgrids and supergrids, is pushing the market of electrical energy and the related handlers, namely the transmission system operators (TSO), to more advanced power line management strategies [1,2,3,4], and to more accurate monitoring techniques [5,6,7,8]. Among the new explored pathways, some appealing approaches have been the ones based on the application of electrical reflectometric techniques, like the ones employing time-domain reflectometry (TDR), which have already been successfully applied to fault-detection and localization applications in other fields of electric and electronic systems. Based on this technique, a test signal is injected into an electric line to catch the reflected waves produced by possible impedance variations along the line. It is a matter of fact that power lines can spread over hundreds of kilometers and are subject to environmental variables, so it is very difficult in practice to detect impedance variations due to incipient faults, which are the most common symptoms of power line degradation
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