Propagation properties of electromagnetic wave through T-branch in GIS

To investigate the transmission of electromagnetic waves excited by partial discharge through T branch section and L-shaped sections of a gas-insulated switchgear (GIS) bus structure, electromagnetic fields were numerically simulated. The modes of the simulated electromagnetic wave were found to transform to different modes, e.g., from TE11 to TE21, after transmission and reflection through T branch or L-shaped sections of a GIS. These characteristics found in the simulation, mode transformation and dependence of resonance frequency on excitation direction of partial discharge, were also confirmed experimentally. In the case of 90-degree bent direction, the characteristics of mode transformation in a T branch and those in an L shaped section are similar. In an obliquely angled tank although electromagnetic-wave propagation behavior becomes similar to that for the L shaped section, the ratio of mode transformation becomes smaller, and the transmitted component of the input mode tends to increase, as the tank shape becomes closer to straight