Experimental impulse response of grounding grids

Experimental tests, consisting in the impression of low amplitude impulsive currents with lightning-patterned waveforms on a real grounding grid, were performed to assess the grid transient response. Simultaneous waves of current and grounding potential rise were measured considering the current impression on different points along the grid electrodes (earth termination) to determine the impulsive grounding impedance. Currents with very short front-times were used to show strong propagation effects in the soil, responsible for values of grounding impedance always significantly larger than the measured low frequency resistance and strongly dependent on the position where current was impressed on the grid.