Propagation of harmonics in electrical grids: a review of selected issues

Recent years saw increasing of harmonic distortion at transmission grids caused partly by a growing system undergrounding, leading to resonances at lower frequencies. Presently, the estimation of the harmonic distortion through simulations after significant grid changes is not sufficiently accurate, and the understanding of harmonics propagation is a topic under research. This hinders grid development by system operators, as it is not possible to assess fully the impact of new lines. This paper presents and analyses four harmonic-related phenomena: (1) impact of line asymmetry in long HVAC cables; (2) harmonic peak voltage/current along a line; (3) harmonic propagation between voltage levels; (4) fillter location. The paper summarizes the root causes and consequences of each phenomenon, together with tools and recommendations that can ease the assessment of harmonic propagation.