Combining Baum–Liu–Tesche Model and Charge Simulation Method for Analysis of Electromagnetic Field Coupling to Transmission Lines Inside Underground Utility Tunnels

The intense electromagnetic fields above ground have the potential to induce overvoltage in the power/communication transmission line (TL) systems located within urban utility tunnels. Due to the presence of tunnel structure, the actual electromagnetic field incident on TL can undergo significant distortion, leading to substantial computational errors in the load voltage/current response when directly applying the classic Baum–Liu–Tesche (BLT) method without correcting the field perturbation. To tackle this challenge, this article introduces an integrated BLT and charge simulation method (CSM) model designed to capture coupling between the electromagnetic field and TL within underground utility tunnels. The proposed approach utilizes the refraction law to construct the unperturbed underground field distribution initially, it then defines correction coefficients to quantify the distortion of the transverse electric field introduced by tunnel's presence. This correction facilitates adjustments to the source vectors in the BLT model, ensuring accurate modeling of TL response. Moreover, CSM is developed to calculate the key variable correction coefficient. This article consolidates the accuracy of proposed model and explores its application in calculating response subjected to pulsed electromagnetic field. This research reveals the field-line coupling mechanisms in underground utility tunnels, providing an efficient tool for computational analysis.