Study On The Fault Recovery Characteristics Of Ultra-high Voltage Direct Current System

The primary energy sources mainly distribute in west ,but the power requirement are major in east of China,thus it is unevitable to transmite power energy long-distance and large-capacity from west to east. In the view of STATE GRID, transmitting power from west to east, interconnection between north and south and the building of nation-wide poewer grid are the development trend. The China South Grid Corporation will put YunGuang UHVDC on June 2010, of which the voltage is±800kV and the bipolar capacity is 5000MW. Also,The State Grid Corporation will build six±800kV UHVDC lines to transmit the power from Wu Dong Dei,Bai He TAN,Xi Luo Du and Xiang Jia Ba to the load centers of East China and Central China.Due to the lack of the operation experience of±800kV UHVDC in world and the relevant research achievements are not so many, special the problem of fault recovery characteristics of system are concerned, this thesis set up detailed UHVDC model based on RTDS in order to study on the fault recovery characteristics that how to recover the maximum power level.The paper includes three parts as follow:(1) The reasons and the effect to system of commutation fault to UHVDC are studied on . The paper discuss the fault recovery characteristics after AC fault at UHVDC and the polar control stategy including current constant ,voltage constant,firing angle constant how to transform to restrain commutation fault. Also, the paper study on the effect of ESRC to the fault recovery characteristics and suggest the DC power support strategy to enhance the stability of system.(2) The faults at rectifier and inverter side are seperately simulated on , because the faults occur at differente place the responses are very difference. The fault current loop and the fault characteristics are very different of different faults, even the same fault occours at the moment of different valves swithing on/off the fault loop are not the same. Because of no complety fault analysis theory to guide the DC system protection, there would be no definite protection active to cooperate with control system at anticipated fault. This part solve the problem of it is unable to set valve faults to prove the fault recovery characteristics at scene.(3) The paper study on the fault characteristics of DC line and control system response, for the feature of long-distance DC line of UHVDC system . Also , the effect of different transition resistances, DC power level, fault times, and the styles of different connect line to the stategy of fault revovery restart are simulated on.