Research On Characteristics Of Fault Transient And Travelling Wave Protection For Uhvdc Line

Compared with AC transmission, DC transmission is more suitable for long-distance cross-region power transmission; DC transmission system can realize rapid and various ways to regulate the entire AC-DC system. In 2010, China will run the world's first±800kV ultra-high-voltage direct current transmission system–- Yunnan-Guangdong HVDC project. The probability of accidents in Long distance power transmission such as short-circuit lines, lightning will greatly increase. The travelling wave protection (WFPDL) is used as the main protection of the±800kV UHVDC transmission system. Its principle is based on the transient characteristics of the line fault, which is the changes in the voltage and current caused by the travelling wave. But there are few theories and methods for the analysis of the transient characteristics of DC line fault. Based on characteristics of the fault transient, this paper futher study and reveal a characteristic of travelling wave protection, that is, the relationship between the critical transition resistance and the calculated frequency used by the wave protection.The research work and findings are as follows: The analytic formula of the travelling wave caused by internal and external region faults is derived through simplifing the electrical structure scientifically. The dispersion mechanism of the travelling wave on transmission lines is studied.The theory formula of refraction waves when rectangular waves incident rectifiers is derived, and the influence of ground lines on refractions is discussed. The formula of the rectifier's overshoot current of bidirectional 12-pluse DC system when DC line short-circuit fault occurs is derived. This paper evaluates the relationship between the fictitious critical transition resistance and the calculated frequency, using the analytic formula of the line terminal voltage casused by internal and external region faults.Then base on the line model decomposition of the travelling wave,the dispersion spread on the line and the line travelling wave's catadioptric are discussed, the critical transition resistance of the travelling wave protection- the characteristics of the calculated frequency are obtained. Based on the PSCAD/EMTDC electromagnetic simulation software, the simulation model for the±800kV UHVDC system is developed, and a large number of simulations are carried out. The simulation results strongly support the theoretical analysis.