Using Modal Analysis to Estimate Received Signal Levels for a Power-Line Carrier Channel on a 500-kV Transmission Line

This paper presents the results of a study on the use of modal analysis for estimating received signal levels of a power-line carrier (PLC) channel on high voltage transmission lines. The intent of the paper is to serve as a reference. Numerous papers have been written on modal analysis and signal propagation on overhead lines at PLC frequencies. However, for the information to be put to practical use requires reading numerous references, including references on transmission line modeling. Therefore, this paper provides information on transmission line modeling and modal analysis theory needed for using modal analysis for an actual calculation of received signal levels with results in the phase domain, which is the domain in which measurements are usually made. Modal analysis is used to calculate modal propagation constants, which are used in an equation that directly relates sending-end voltage to receiving-end voltage utilizing a multiphase reflection coefficient. To validate calculations using the described methods, field tests were performed on an energized 500-kV transmission line. Results from these tests in the form of a comparison of calculated versus measured voltage levels are provided.