Study And Application Of The Identification Between Magnetizing Inrush And Sympathetic Inrush Of Transformers Based On Theory Of Wavelet

With the rapid development of the national economy, the demand for electricity is growing, the range of electric network is expanding, the transient process of the electromagnetic power is more complicated, and the electromagnetic decay is more slowly. In order to ensure the security and stability for the electricity lines, higher remand is necessary for the relay protection, but the traditional protection and fault diagnosis technology cannot meet the new requirements of the development of electricity. Thus, the relay protection technology based on wavelet theory is attracting more and more attention; lots of people are doing such research.Electricity Transformer is one of the most important equipments in electricity system, its safe operation is directly related to the system's security and stability. As it's very expensive, once it is damaged, the maintenance will be long and difficult, and it will greatly affect the stability of electricity supply and the normal running of system. So, the protection of Transformer is the priorities and difficulties for scholars and manufacturers. The correct action rate of Transformer protection is lower than other protection's, which is mainly caused by transformer inrush current. Differential protection as the main transformer protection, has good selectivity and liquid, but differential transformer inrush current protection is the main reason of maloperation, correctly distinguish inrush current and internal fault current transformer protection is the key to ensure the reliable action .Wavelet transform is a good analysis and time-frequency domain characteristics of the local, especially to extract transient signals in the process of mutation, and a good signal to the singularity. Transformer inrush current study shows that flow significantly different from the short-circuit current, the transient process, which is complicated, it is suitable for use wavelet packet for the extraction and analysis of signal processing.This article briefly analysis the mechanism of transformer producing excitation flows and establishes the simulation model of transformer excitation to flow and each kind of internal breakdown, according to different characteristic of the transformer excitation and the fault current, selecting a appropriate small wave packet to flow to the excitation and the fault current to restructure and analysis process, the massive simulation result indicated that the method of this article could distinguish the transformer excitation to flow under switching on different condition and the fault current fast and accurately .Two parallel or series transformer, when switching on, will produce flow phenomenon in another transformer possibly, which is also another important attribution to the differential motion protection. With flow not looking like the excitation to flow such obviously, only will be producing flow rapidly under specific operating condition and parameter, therefore there is quite few research. This article analyzed the mechanism of excitation to flow and the condition which occurs based on the former research , according to the profile characteristic of flow and good strange examination performance of wavelet transformation , contrastive analysis processing obtained between the Matlab simulation of flow and the fault current profile indicated that the low frequency part after flow wavelet transformation has the obvious characteristic of deviation time axis to one side, but the fault current did not have this characteristic, so according to the criterion of recognition of the excitation to flow and the fault current, massive simulation result has confirmed the accuracy of this method.