Understanding Dynamic Performance of Power Line Carrier Protection Channels: A Real-World Application of Lossy Modal Analysis

Abstract: This paper presents details of a real-world application of “modal analysis” to resolve a decades-old power line carrier (PLC) protection issue. A certain PLC pilot protection channel on a critical line between two transmission utilities was inoperable for several months each year due to excessive signal attenuation. A “lossy” (complex) modal analysis indicated that the system might be experiencing a phenomenon called “mode cancellation”, and further indicated that changing the coupled phase of the carrier would resolve the issue. The coupling changes were implemented successfully, and the channel issues were resolved. Data from the analysis, on-site changes, and performance before and after the coupling change are presented in this paper. Modal simulations demonstrate how changes in conductor height and ground resistivity over time contribute to the periodic nature (diurnal / annual) of the observed channel issues. The paper concludes with a novel, four-dimensional method for estimating the performance risk due to mode cancellation on a given transmission line.