Study On Characteristics And New Methods Of Traveling Wave Based On Protection For UHVDC Lines

The unbalanced characteristics on energy distribution and load center of china determines our resource optimization must implement the strategy of the power transmission from west to east. UHVDC has the characteristics of ultra-long-distance, large-capacity and high efficiency, these advantages just to meet the demand and make it has a very rapid development in recent years.Transmission line protection is the important guarantee for the safe and stable operation in high-voltage direct current power transmission system, but according to operation experiences of HVDC projects in recent years, the correct action rate of traveling wave protection were always low. Compared with traditional HVDC transmission system, UHVDC has many differences in system structures, parameters and operation methods, this make its protection system, especially main protection—traveling wave protection, face more complex operating environments. Therefore, it is necessary to study the action characteristics of traveling wave protection for UHVDC, and put forward coping approaches according to existing problems. The main contents of this paper are as follows:1,Based on the parameters of Yunguang UHVDC system,the electromagnetic transient simulation model of Yunguang±800k V UHVDC system is build, this model can accurately reflect the response characteristic of actual control and protection system. On the basis of analysing the influences of traveling wave protection on different factors,the author points out what the function of each criterion of traveling wave protection is,and explain the reason of refusing act when faults occurs with the critical transition resistance.2,Study the influences of traveling wave protection criterion on different sampling frequencies,and point out that the volatility of sampled data is inevitable. The analysis results show that too large or too small sampling frequency could lead to increased fluctuation of du/dt, but sampling frequency has little effect on the voltage and current variation. The author also point out that increasing sampling frequency is propitious to distinguish internal or external fault of DC line. In the last this research conclusion have certain reference significance on the development of device.3,Analyse the differences of wave head about internal fault and external fault of DC line, put forward a new principle with high sensitivity on traveling wave protection. This principle is better than existing traveling wave protection, it could endure bigger fault resistance,also can accurately and reliably act under various fault conditions. The new principle has practical value in engineering.