When Harmonic resonance strikes 33kv grid distribution system

When Harmonic resonance strikes a grid, at its 33kV power distribution system, it results in a massive total voltage harmonic distortion, THDv magnification, within the affected power system at the grid supply zone. The order or number of individual voltage harmonics, are around the grid's natural resonance frequency range. It results in a large voltage oscillation, and fluctuations in the forms of simultaneous incidents of voltage sags and swells. Which in turn results in electrical noise and vibrations with grid connected plant equipment due to humming electromagnetic interference - across all industries within the affected grid supply zone. The Grid harmonic resonance in turn, triggers a massive total current harmonic distortion, THDi magnification, at all grid connected transformers at various factories within the affected electrical power system zone.   

Metal and heavy industries at this industrial region have had a long history of grid transformer failures. At times their plant trips on fatal earth fault which happens due to transformer high voltage winding insulation failure- burn/flash/blast. Sometimes, even the transformer high voltage winding melts open due to heavy current flow, due to the short time magnification of THDi within individual factories. The incidence of Grid harmonic resonance typically prolongs from few minutes to about an hour, and in that process, it trips the plant on multiple relay operations. Some are nuisance tripping like over currents and over voltages. Few are fatal faults like earth faults and Buchholz relay trip.