NILT - Based Transient Traveling Wave Calculation Method for Lightning Stroke on Coupled Transmission Lines in DC Systems

Overhead lines are the main way of power transmission in HVDC system. The fault traveling wave propagates along the line after lightning stroke, which may cause accidents. Fault identification and protection design rely on traveling wave analysis and calculation. The time domain solution of transmission line telegraph equations is complicated. Analysis in the complex frequency domain can reduce the computational difficulty. Firstly, this paper decouples the DC transmission line through phase-mode transformation and establishes the model. Then, the post-lightning boundary conditions are introduced and the calculation network is established. On this basis, it solves the expression of traveling wave based on nodal analysis method. Finally, with the numerical inverse Laplace transform, calculation results in complex frequency domain are converted into time domain. The proposed method can reflect the transient process after lightning stroke, which has engineering value for protection design.