A method to identify and prevent transformer differential protection action caused by inrush current

Abstract

The invention discloses a method for identifying and preventing differential protection action of a transformer caused by inrush current. In the state of fault current, when the criterion is not satisfied, the differential protection is correctly blocked, and when the criterion is met, the protection is correctly opened; 2) Use the fundamental wave amplitude increment method to judge whether it is the inrush current, if the current is judged to be In response to inrush current, short-term enhancement of braking characteristics is adopted, and the next step is to judge TA saturation. If it is judged as exciting inrush current, the criterion of exciting inrush current is used to judge whether to act; 3) Use virtual braking criterion to judge TA saturation, if If the TA is saturated, the 2-level short-time enhanced braking characteristic is adopted, and if it is not saturated, the short-time enhanced braking characteristic is adopted; 4) The differential protection operates when the protection current falls in the action area, otherwise the differential protection does not operate. The invention can fundamentally solve the problem that the surge current will cause the differential protection to malfunction.

Description

technical field [0001] The invention relates to the technical field of relay protection of electric power systems, in particular to a method for identifying and preventing differential protection actions of transformers caused by surge currents. Background technique [0002] Transformer differential is a protection based on the basic principle of Kirchhoff's current law. It is simple and easy to implement, and it is one of the main transformer protections. The design regulation stipulates that generally the main transformer capacity above 6.3 MVA should be installed with longitudinal differential protection. Due to the use of the differential current generated during a fault to operate, the sensitivity of the transformer differential protection is high and the action is relatively rapid. However, due to various factors such as transformer error, protection device, transformer excitation inrush current, and inrush current due to its own reasons, the unbalanced current is an ...

AI Technical Summary

Problems solved by technology

[0015] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and proposes a method for identifying and preventing differential protection action of transformers caused by inrush current, which completely solves the problem of using the second harmonic difference in the fundamental wave incremental method. To judge the defect of inrush current, use the time difference method criterion instead of the second harmonic criterion to distinguish fault and inrush current, so as to judge more accurately, which can avoid the 2nd harmonic amount of inrush current caused by the influence of TA remanence less than 15%. Causes the problem that the differential protection cannot be blocked, and the fault and inrush current are misidentified, which leads to the malfunction of the differential protection

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