The New Transformer Differential Protection Based On The Time Difference Algorithm

Inrush current and current transformer saturation essentially all belong to the core saturation. In order to prevent transformer differential protection malfunction brought about by core saturation phenomenon, a series of settlement programs are put forward. Time difference method has been successfully applied to the bus differential protection as an effective identification method.Taking into account the excellent CT identification property of time difference method, it is introduced into transformer differential protection is this article. Because the problem that how to define time difference at internal fault and time difference at external fault exists when it is used to distinguish internal fault and external fault, an improved transformer differential protection is proposed in this paper based on a deep analysis. Through the re-definition the primary current and secondary current of transformer internal fault and external fault can be identified effectively.In the time difference method, the moment of abnormal state happening is needed to know. Many kinds of detecting method are employed in this paper, such as Wavelet method and Huang Hilbert transforms and so on. Although these methods have been widely used in its related field, duo to the lower sampling frequency and the higher real-time property, many detection methods are difficult to be effective. Sliding window iterative Fourier detection method has small calculation and rapid update speed so that it needs the requirement for real-time at low sampling frequency to detect abnormal state.In order to verify the correctness of the program proposed by this paper, the electromagnetic transient software (EMTP) is used for computer simulation. How to simulate the excitation slip is the critical issue of computer simulation. Type-96 components and non-linear resistance is selected to be as excitation slip through research the various components of the non-linear characteristics in EMTP. Not only the non-linear characteristics is considered but also the impact of residual magnetism Finally, dynamic test is set up under the situations of internal failure, external fault, closing with no-load. According to data collected by recording device, the correctness of the transformer differential protection program proposed by this paper is verified by MATLAB programming.