Frequency-Modulated Disturbance Analysis of the Ferranti Effect in Low-Inertia Power Grids

The Ferranti effect, i.e., receiving-end overvoltage on unloaded or lightly loaded long transmission lines, is regaining practical relevance in modern low-inertia power grids. This paper introduces an analytical framework that re-interprets the observed waveform dynamics at a point of interest-typically the receiving end-as an unintentional frequency modulation (FM) imposed on the nominal grid frequency carrier. By extracting the instantaneous frequency from the measured voltage via Hilbertbased processing, we define a compact scalar diagnostic index, the disturbance power P ∆f , which quantifies the "energy" of frequency deviations within short time windows. The approach is developed as a mathematical and inspectorial study: classical telegrapher-equation modeling provides the transmission-line basis, and theoretical/numerical examples illustrate how P ∆f can highlight dynamic severity beyond conventional magnitude-only indicators. The paper is intended as a first step toward experimental validation and collaboration on measurement chains and potential countermeasures, which are deliberately left outside the present scope.