Analysis On Commutation Failures In Shandong Multi-Infeed HVDC System

HVDC has been playing a more important role in building a strong intelligence network, which has a remarkable advantage over long-distance and large-capability electricity transmission. Compared with the HVAC transmission system, HVDC system has lots of advantages such as the lower cost of the electric power line and transmission loss when the same power in transmission, able to limit short-circuit current, easily to construct by stages and be augmented. ±660kV Yindong HVDC system is the first HVDC project set into Shandong province. With the commissioning of the project, Shandong power system has stepped into the operation state of AC-DC hybrid power system. According to "foreign power into Shandong" plan, by 2015, ±800kV Humeng--Shandong UHVDC project will be completed and put into operation, Shandong power grid will be formed a typical multi-infeed hybrid grid, the grid structure and function will be changed tremendously. The access of Humeng UHVDC project makes the amount of electricity accepted by Shandong power system surge, the second and third defense line of Shandong power system will be greatly affected and the applicability of security control measures of Yindong HVDC project also be tested. Therefore, in-depth study of the voltage and angle stability of Shandong power system, mutual influence between the two HVDC project and the transient stability characteristics of the two HVDC project when Ximeng UHVAC project under normal or unnormal state after Humeng HVDC project set into is important to guarantee the security and stability of Shandong power system and north China power grid system as well as UHAV power grid system.Based on the above, the key of this paper is commutation failure problems of the two HVDC projects caused by three-phase short circuit fault at Shandong power grid and single phase short circuit fault at Shandong power grid and the tansmission line of Ximeng project, overvoltage problems caused by unipolar blocking. The specific research works are as follows:1. In power system electromagnetic transients simulation software PSCAD/EMTDC (abbreviations for Power Systems Computer Aided Design), we build the model of Shandong AC-DC hybrid power system including ± 660kV Yindong HVDC project and ±800kV Humeng UHVDC project.2. As to the Shandong power system, dynamic equivalence in PSASP (abbreviations for Power System Analysis Software Package) based on physical equivalent principle is made according to the research question. Converter bus,500kV bus and other grid nodes focused on are retained, and the rest parts of the system are replaced by equivalence. Then the model of Shandong power system in PSCAD is made according to the equivalence results above.3. In the model established, the response characteristics of HVDC system are simulated and analyzed under single-phase fault or three-phase fault at AC side. The possibility of commutation failure is also analyzed. The degree of influence on the two HVDC projects under the same AC fault is studied. The response characteristics of the two HVDC projects are analyzed when the UHVAC project is under single-phase fault.4. The various measures to prevent commutation failure is analyzed and eventually select the static reactive power compensation device SVC (abbreviations for Static Var Compensator) to suppress local commutation failure. By reference to the Cigre model in PSCAD, we build the SVC model of TCR/TSC type and the AC/DC hybrid model is simulated and analyzed after the installation of SVC devices on converter bus. The comparisons with the original prove that SVC devices are effective against local commutation failure. According to the current figure, we consider to disconnect the Weifang--aoshan, Daze--aiyang 500 kV line, to discuss the effect of preventing commutation failure at the same time by changing the MIIF between the two HVDC projects.5. Finally, the transient response characteristics of the two HVDC project under ground fault on DC line is analyzed, and the impact of one HVDC line ground fault on another HVDC project is analyzed emphasisly. A brief introduction about DC monopoles block has been made and takes unipolar atresia which occurred more as an example, overvoltage phenomenon due to this reason is discussed and using reactive power control links and SVC device is proposed.