Transformer magnetizing-inrush-current identification method based on MEEMD algorithm

Abstract

The invention discloses a power transformer magnetizing-inrush-current identification method based on an MEEMD algorithm, and belongs to the field of power system relaying protection. Through collecting differential current signals on two sides of a transformer, MEEMD decomposition is firstly carried out to obtain a set of approximately stationary IMF signals; and then a first IMF signal is extracted from a result of decomposition to carry out Hilbert transform to obtain instantaneous frequency thereof, a sudden-change point of the instantaneous frequency can reflect a sudden change of a phaseof the current signal, and accurate identification on magnetizing inrush currents and internal faults of the transformer can be realized according to a time interval between two adjacent sudden-change points of the instantaneous frequency monitored in real time. The method is not impacted by inrush-current dead angles, closing initial-phase-angles and non-periodic components, and can accurately,reliably and quickly distinguish the magnetizing inrush currents and internal short-circuit faults of the transformer.

Description

technical field [0001] The invention belongs to the field of relay protection of power systems, and in particular relates to a transformer excitation inrush current identification method based on the MEEMD algorithm. Background technique [0002] The identification of transformer excitation inrush current and internal short-circuit fault is the most critical part of transformer differential protection, and its safety is directly related to the safe and stable operation of the power grid. Traditional differential protection uses proportional braking and second harmonic braking to improve its performance. However, the improvement of the manufacturing level of the transformer reduces the content of the second harmonic in the excitation inrush current, which makes this method have certain limitations. In recent years, scholars at home and abroad have proposed many new principles and algorithms for identifying inrush current. For example, the wavelet differential protection sch...

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Problems solved by technology

For example, the wavelet differential protection scheme uses boundary discrete wavelet transform to calculate fault transient components to identify internal faults, but this scheme may malfunction when the fault angle is 0° or 180°; discontinuous angle identification method, but it is affected by current mutual inductance Influenced by the saturation of the transformer, it is limited in practical applications; the waveform symmetry method identifies the excitation inrush current and the fault in the area, and the action time is about 20ms or more, so it is difficult to increase the action speed

Using the EMD and Hilbert algorithm, the inrush current and internal faults are identified through the instantaneous frequency change rate, but the EMD algorithm itself has an endpoint effect, and the discontinuity angle of the inrush current will cause the modal aliasing phenomenon of the EMD algorithm, and its action time is about 20ms

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