Modeling of transmission tower for electromagnetic transient simulations caused by atmospheric discharges

Abstract

The analysis of the transmission tower dynamic behavior is directly related to the studies of system protection caused by lightning. In the study of fast electromagnetic transients in transmission lines (lightning impulse), the towers should be modeled and taken into account in the simulation of the propagation of surge voltage and current along the line, as described in the technical standards as the International Electrotechnical Commission (IEC Standards). Conventionally, the concept of surge impedance of the tower in the time domain is used to characterize the electrical behavior of transmission tower. The main drawback in this definition is the dependence of the excitation waveform. In order to circumvent these limitations, frequency domain models are used. In this case, the surge impedance of the tower depends only on the geometry of the structure and the electromagnetic characteristics of the environment. The purpose of this project is to develop an electric model for transmission towers directly in the time domain, using the Numerical Electromagnetic Code (NEC) for numerical analysis of electromagnetic fields and the theory of transmission lines using Electromagnetic Transient Program (EMTP). Through representation of the surge impedance of the tower by a rational function, one can obtain the model of the tower making use of lumped elements RLC circuits, this technique is called in many references as vector fitting. Moreover, the proposed model is developed directly in the time domain without the use of inverse transforms.