Algorithms for fast calculation of energization overvoltage of hybrid overhead line-cable transmission lines based on full frequency-dependent parameters

This paper addresses the challenges associated with the time-consuming and complex nature of using electromagnetic transient (EMT) simulation software, such as PSCAD/EMTDC, for calculating transient overvoltages in complex power grids. To overcome these challenges, we propose a novel algorithm for fast calculation of energization overvoltages in hybrid overhead and cable transmission lines. The proposed algorithm begins by calculating the frequency-dependent parameters of the transmission lines in the full frequency domain. These parameters are then decoupled using phase-mode transformation. Subsequently, the algorithm derives the boundary conditions of the transmission line based on its topology, leading to corresponding complex frequencydomain voltage expressions. To obtain the calculation results of energization overvoltages along the hybrid transmission lines, the algorithm applies mode-phase transformation and an improved numerical inverse Laplace transform (NILT). To verify the accuracy and speed of the proposed algorithm, it is applied to a 330 kV hybrid overhead line and cable transmission system with a length of 56.8 km. The results demonstrate that the proposed algorithm achieves a maximum relative error of less than 0.261 % compared to the frequency-dependent phase model (FDPM) used in PSCAD. Additionally, the calculation time of the proposed algorithm is shown to be only 32.654 % - 58.649 % of the FDPM's calculation time.