| With the implementation of power grid interconnection and the power transmission from west to east, the national power grid of China has developed quickly in recent years. A hybrid AC/DC power grid will be formed in the future. According to the planning of State Grid Corporation, Shandong power grid will accept 4000MW from northwest power grid through the Ningxia-Shandong DC lines in 2010. Shandong power grid will gradually change to be receiving end and hybrid AC/DC power grid. Therefore, the stability studies of receiving end, which mainly considers the interactions between AC and DC systems, are important. Besides, with the operation of more and more DC lines, overvoltage caused by faults or operation becomes the main threat to device insulation of converter station. So, overvoltage research based on actual DC project is very useful.This thesis performs a study from two aspects of the interactions between AC and DC systems, including the stability of receiving end and the overvoltage of AC bus at converter station. The main contributions are stated below.Using a digital simulator PSASP, the stability strength of Shandong power grid and steady-state reactive power compensation at Qingdao converter station are studied based on the power grid planning of 2010. The influence of DC faults on the stability of receiving end, combined with the interactions between AC and DC systems, is mainly researched. Shandong power grid, as receiving end, has large power receiving capacity in 2010. Under DC bipolar operation mode, 12 sets of reactive power compensation equipment should be inputted at Qingdao converter station. Most faults of 500kV AC lines in Shandong power grid can cause commutation failures. But, the stability isn't damaged because DC system can recover from commutation failures after faults disappear. Generally, the fault of Ningxia-Shandong DC couldn't lead to the voltage or frequency stability problem in receiving end. But, it could make the voltage of load center drop. In order to overcome this problem, some reactive power compensation equipments are held at converter station. After the commission of Binzhou tie lines, Low-frequency oscillation may happen between Shandong and western inner Mongolia grid because of DC block. It can be presented as power oscillation of the tie lines between Shandong power grid and north China power grid. Besides, the maximum transmission power of the tie lines between Shandong power grid and north China power grid is analyzed.Electromagnetic transient model of Ningxia-Qingdao DC system is established based on a digital simulator EMTDC. The AC transient overvoltage at Qingdao converter station is researched from four aspects including load rejection overvoltage,overvoltage caused by energizing converter transformer,AC filter switching overvoltage and clearing overvoltage of AC earth fault. The maximum load rejection overvoltage is 1.268p.u. (Peak voltage is 569kV) at Qingdao converter station, which happens under DC bipolar overload operation mode. Therefore, there is no need to take measures to limit overvoltage. Both overvoltage caused by energizing converter transformer and AC filter switching overvoltage are very small, which can be controlled by paralleling resistance on breaker. The clearing overvoltage of AC earth fault is mainly concerned with the short-circuit current at fault clearing time and the distance between the bus and the fault point. The clearing overvoltage of AC earth fault, at Qingdao converter station, is 1.926p.u.(Peak voltage is 865kV) without arrester. But, it reduces to 1.625p.u.(Peak voltage is 730kV) after arresters installed on converter transformers and AC filters.
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