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 frequency-domain 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.