Relationship between Surge Impedance and Impedance in Frequency Domain of Earthing System in Traction Substation

Abstract

The relationship between “surge impedance”, which is defined as the ratio between the maximum transient voltage and current in a time domain, and “impedance” in the frequency domain is discussed based on a set of measured transient responses of an earthing circuit in a traction substation. The frequency characteristics of the results are numerically determined using linearized Laplace transform (LLT). The results indicate that the rise time of the injected impulse current is a key parameter that determines the relationship between the surge impedance and the impedance in a frequency domain. The investigation shows that the surge impedance which can be easily obtainable in a field test is useful for characterizing the transient grounding characteristic by appropriately utilizing the relationship.