Earth Potential Rise influence on High-Voltage rotating machines of a power plant caused due to lightning on a nearby tall object

During a heavy thunderstorm a 6.6kV High-Voltage Motor in a thermal power plant was damaged. Preliminary investigation revealed that effects caused on rotating machines were due to the influence of Earth Potential Rise (EPR) caused by lightning currents that strikes to close elevated structures of power stations flowing through the conductive-earthed structures over the ground and in grounding grids induced transients in rotating machines. Due to the impedances to remote earth, the current injection will result in an increased potential of the surrounding soil during the impact of the strike. This earth potential rise will have an impact on nearby motor installations in proximity of the grounding system, and will in severe cases damage the motors. This work presents some results showing that the front time of the lightning currents and the soil resistivity have a great influence on the tolerated lightning current along with the solutions proposed for lightning protection of thermal power plant equipment. Furthermore the transient performance of the grounding grid also has a great effect on the amplitude of the lightning overvoltage occurring at the equipment, based on this few recommendations for grounding system are made.