Multimode wave theory application to the analysis of very fast transients in lossless systems

This paper presents a new method of analyzing very fast transients in power systems by including the higher modes in the wave propagation analysis which, if ignored, can lead to erroneous results. A characteristic matrix is introduced to characterize the mode reflections and couplings to replace the scalar reflection and transmission coefficients used in the conventional traveling wave method. A sample transient calculation is carried out for a lossless coaxial cable terminated with a circular waveguide which shows the necessity to consider higher modes in very fast transient studies. The proposed approach also applies to more complicated structures such as gas insulated substations.