Analysis Of The Fault And The Relay Protection For Half Wavelength AC Transmission Line

With the rapid development of the global economy, the demand for energy increases year by year. The high-power, long-distance power transmission will become a major trend of the grid. Especially in the vast China where the energy bases are far from the power load centers, a way for the power’s long distance transmission with high-efficiency is taken more seriously.The half wavelength AC transmission (HWACT) has good transmission characteristics and excellent economic characteristics. It will bring a new change to the grid and become a possible transmission way suitable for future transmission needs.As a new technology, the HWACT has had many challenges remain to be studied. At first, this article describes the technical advantage and development history of HWACT. According to the current situation, the broad application prospect of the HWACT has been predicted. The existing good UHV protection technology provides a reference for the half-wavelength transmission line’s relay protection research. Then, the HWACT’s fault characteristics have been analyzed with the symmetrical component method and the uniform transmission line model. The voltage and current’s mathematical expressions are also given when the line is in fault conditions. In addition, the half wavelength AC transmission line’s model is built using the PSCAD/EMTDC software and various short-circuit faults have been simulated. The voltage and current’s curves at different fault point are drawn. Through comparative analyses, simulation results prove the correctness of the theory before. It can be concluded that the analysis of HWACT line must be based on the distributed parameter line model. The half wavelength line shows a big difference from the short-line’s fault characteristics and The traditional protection schemes no longer apply to it. On the basis of knowing well the half-wavelength transmission line’s fault characteristics, a improvement on the traditional distance protection’s criterion has been done. To eliminate the impact of capacitive current to the relay, a current differential protection principle based on the line’s Bergeron model has been proposesed. And the simulation rusults show that the protection principle can reflect the internal and external faults correctly and be suitable for the HWACT line.