The Study Of Transformer Differential Protection Based On Non-Periodic Current

As the frequently-used and essential element in the power system, the transformer is used to increase the voltage level in the transmission line and to decrease the voltage level in the distribution line, which is very meaningful for the whole power system. Besides, considering that the cost of a high-capacity power transformer, the transformer’s breaking down will result in large economic losses. The traditional power frequency transformer longitudinal differential protection in existing in the application of electromagnetic current transformer, current transformer, CT) saturated and excitation inrush current protection misoperation of the problem. Experts and scholars to solve these problems, a lot of research and achieved excellent results, but still exist many problems. So this article introduces a kind of aperiodic component differential protection to the transformer protection, the protection compared with the traditional protection has many advantages and can be very good deal with the issue of excitation inrush current.First, this thesis shows the working process of the traditional electromagnetic type CT as well as main problems and corresponding solutions, which leads to the optical CT characteristics of non-magnetic full and accurate measurement to obtain the advantages of aperiodic component fault current, on the basis of this analysis was based on aperiodic component current longitudinal differential protection, and select a full-wave inner integral method to extract the aperiodic component.Then, this thesis analyzes the current transformer longitudinal differential protection principle and criterion, analyzing the cause of excitation inrush current and unbalance current and their specific impact of transformer longitudinal differential protection, and then focuses on analyzing the existing excitation inrush current identification methods and their respective characteristics.Finally, the thesis applys the aperiodic component line differential protection to the transformer protection. Then the criterion and direction of the differential ratio differential protection is presented. By MATLAB/Simulink software to build the transformer power supply, single-ended power supply and interturn short circuit fault simulation model, simulation verified the correctness and reliability of the protection and the simulation analysis of the different time, different transition resistance and the influence of different fault types of the protective properties.Through the theory analysis and simulink verification, this thesis get the conclusion that the aperiodic-component-based transformer differential protection is better than the conventional protection in sensibility, which can identify the magnetizing inrush current without other methods, and the protection can be applied to the intertun cutting-out faults even when the number of turns is more than 3.6%. The research has certain significance on the application of aperiodic-component-based transformer differential protection, the identifications of the small interturn cutting-out faults and the magnetizing inrush current.