Upfc-based Non-symmetrical Short-circuit Fault Current Limiting

The rapid development of power system promotes economic rapid development and a great deal of progress, the obvious advantages of large power grids also has been brought by the formation of large power grids. The total capacity of power systems is increasing; the network structure has become more and more complex, which brings potential threats to the power system, so the loss of national economy caused by the power system failures is getting big. Power system fault, the asymmetry in a high proportion of failures, only single-phase ground fault on the account for about 70% of the EHV transmission line phase distance, and fault type of single-phase short circuit in the proportion of larger, can be as high as 90% more than a lot of three-phase symmetrical fault, and some caused by the collapse of the power system is also of major accidents developed by the asymmetry of the fault. Therefore, it has great significance to eliminate or limit the non-symmetric short-circuit fault current, and make the fault line maintain the continued operation of transmission power.Modern power electronic technology and the rapid development of control technology combined with the traditional impedance control components, power angle control components (series compensation capacitors, and also compensates the capacitance, reactance, phase shifters), there have been formed flexible AC transmission technology. Unified power flow controller in flexible AC transmission system is the most representative, it has a parallel compensation, series compensation and transfer the same basic functions, as well as the role of a combination of these features. Unified power flow controller has become the most powerful device in the FACTS controller.This paper introduced the fault current limiter, as well as reference [8] and references [4] proposed methods of fault current limiter based on both ends for the installation of UPFC devices are transmission lines, when there is non-symmetric short-circuit failure, the use of UPFC at both ends of the line asymmetry in tandem to provide voltage control circuit voltage in series at both ends of the negative sequence components and zero sequence components, so that fault current of negative sequence components and zero sequence components is 0, and fault current is sequence component as well as 0, so that fault current is 0. Although the fault current is 0, but the fault line on the transmission of positive sequence current is not 0, change the fault line in series at both ends of the positive sequence voltage component can change the transmission line fault positive sequence current, thereby changing the breakdown of power transmission lines. Optimization the positive sequence voltage component that was provided by the both ends of the tandem lines, not only make the fault current 0, must be bound to meet under the conditions of the power system can also run in the best condition.On the basis of examples of models establishment, this paper study simulation. Simulation results show that the use of UPFC installation of non-symmetric short-circuit fault current approach is correct, and have very good non-symmetric short-circuit fault current limiting effect, while the operation of power systems is in good condition.