On the Equivalence of a Conducting Plate in a Laboratory Experiment to a Real Earth

This paper investigates the validity and the application limit of experimental results on a scale model above a conducting plate, such as an aluminum (Al) or copper (Cu) plate, representing a real power system, which is too large for experimental measurements. The surge characteristics on a scale model of an overhead conductor above an Al plate are compared with that above a real earth. The experimental results are compared with analytical and numerical simulation results by the electromagnetic transients program and finite-difference time domain method. It is clear that the Al plate can represent the real earth only for an initial part of a surge waveform until reflection comes back from the other end of the conductor. The surge waveform on the Al plate noticeably deviates from that on the real earth as time passes. Correspondingly, the characteristic impedance of the Al plate differs from that on the real earth depending on the conductor height and the separation between the conductors.