The effect of multilayer stratified ground on the harmonic impedance of grounding systems is evaluated. To this aim, the mixed-potential integral equation is used. The method is general as it allows taking into account 1) stratified soil structure with any number of layers and 2) grounding electrodes with arbitrary shapes. Moreover, the method has no limitation in terms of the maximum working frequency. The impressed-current model is used as the excitation and the harmonic impedance is directly obtained from the method of moments matrix. This is in contrast with the conventional methods where the harmonic impedance is calculated from the integration of the electric field at ground surface. The cases of horizontal and vertical electrodes buried in soils with different layers are analyzed. The accuracy of the proposed approach is validated by comparing the results with those obtained by independent numerical methods.
