Research On HVDC Transmission Line Models In Real-Time Digital Simulator (RTDS)

Power transmission lines are one of the most important components of electric power systems, in order to improve the accuracy of system calculation and simulation, it is necessary to research different transmission line mathematical models. This paper presents a theoretical analysis and comparison of the four HVDC transmission line models in Real-Time Digital Simulator (RTDS), also the steady-state and transient properties of four transmission line model are analyzed by simulation tests. Guidelines for DC transmission line model type selection and parameter setting in RTDS are given out.The commonly used transmission line models in RTDS include:PI model, Bergeron model, frequency dependent (mode) model and frequency dependent (phase)model. Through the transmission line equation the basic principles and equivalent circuit of the transmission line model can be deduced, and then the advantages, disadvantages and applications of each line model will be evaluated.According to the field data, the transmission line model of Three Gorges-Shanghai±500kV DC transmission project is built and short circuit tests are carried out to compare the steady-state characteristics of different line models. The Three Gorges-Shanghai project simulation models are built to compare characteristics of transmission line models while the project is in different operating conditions. The results show that, except the PI section model, the others are similar and close to filed data in most cases.When HVDC works in bipolar mode, an overvoltage will occur in one pole of HVDC overhead lines while a line-fault happens on the other do pole. Since the transmission lines are coupled and frequency-dependent, the overvoltage magnitude closely related to the lines. Line-faults are carried out in the Three Gorges-Shanghai project's simulation model to compare the simulation result with field recorded waves and analyze the accuracy of each transmission line model. Model selection and parameter setting are also considered to find out their influence on the overvoltage.The basic input parameters and meanings of transmission line models in RTDS are introduced and shortcomings of each model are summarized. At last guidelines for parameter setting of the DC transmission line model are put forward.