Transformer excitation inrush current identification method based on phase space reconstruction technology of differential current polar coordinate system

Abstract

Disclosed is a transformer inrush current identification method based on phase space reconstruction of a differential current polar coordinate system. The method includes the following steps: among Npoints every cycle, collecting secondary currents of current transformers on both sides of transformer differential protection and forming a differential current signal sequence I; judging whether a value of the differential current signal sequence I exceeds a setting value of a differential protection start-up element, and adopting criteria provided by the invention to judge false differential currents and inrush currents if the value of the differential current signal sequence I exceeds the setting value; reconstructing the differential current signal sequence into a two-dimensional phase space with a delay time of 1 / 4 period, converting the sequence into a polar coordinate form, taking the number n of points of polar angles within a specified range in a one-cycle wave phase space trajectory as a criterion of protection motion, comparing n with a set threshold value nset, performing protection motion if n>nset, otherwise, performing protection blocking. The method can accurately judge CT saturation of faults in a region, inrush currents and faults outside the region, thus ensuring the reliability of differential protection.

Description

technical field [0001] The invention discloses a transformer excitation inrush current identification method based on the phase space reconstruction technology of a differential current polar coordinate system, and relates to the field of transformer differential protection. Background technique [0002] In recent years, my country's economy has developed rapidly, the voltage level of the power grid has gradually increased, and the scale has gradually expanded. my country has also gradually formed a complete long-distance power transmission grid. With the formation of long-distance transmission network, the safe and stable operation of my country's power grid has become the focus of people's attention. Since the power grid has a large demand for transformers, and transformers are often at the core of the power grid, the safe operation of transformers is related to the stability of the power grid. [0003] The excitation inrush current is the excitation current comparable to...

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Problems solved by technology

However, the actual operation shows that the second harmonic braking criterion has limitations. For example, when the differential current is a symmetrical inrush current, the second harmonic content is low, which will lead to the failure of the second harmonic braking criterion and poor performance. When the transformer is switched on without load due to a fault in the high-resistance area of ​​the transformer, the differential current contains an obvious inrush current in addition to the fault current, which will increase the content of the second harmonic, resulting in an error in the second harmonic braking criterion. Latching Differential Protection

The inrush current criterion based on discontinuity angle principle and waveform symmetry principle also has similar limitations

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