Current transformer (CT) saturation detection method based on Hilbert-Huang transformation (HHT)

Abstract

The invention discloses a current transformer (CT) saturation detection method based on Hilbert-Huang transformation (HHT), and the method comprises the followings steps that instantaneous frequency spectrum, Hilbert spectrum and Hilbert marginal spectrum are obtained through EMD decomposition and Hilbert diversion by collecting differential current signals on both sides of a transformer; the detection of saturation faults and CT saturation outside a transformer area is completed respectively arranged to the three types of spectrum so as to realize the quick action and the reliable action of differential protection under CT saturation; the method serves as a preferential improvement to a traditional CT saturation detection method and combines instantaneous frequency criteria, Hilbert spectrum criteria and Hilbert marginal spectrum criteria in the forms of 'and' and 'or'; when a judgment result has errors, another method can correctly judge, so that the reliability of differential protection is improved; and in addition, fault current outside the transformer area, fault current in the area, conversion fault current and the like under the two circumstances of CT saturation and unsaturation are fully considered, and the CT saturation detection method based on HHT has the advantages of stronger functions, higher efficiency, higher reliability and the like.

Description

technical field [0001] The invention belongs to the field of relay protection of electric power systems, and in particular relates to an HHT-based CT saturation detection method. Background technique [0002] In the process of building a smart grid with the UHV grid as the backbone grid in my country, the expansion of the power system scale and the improvement of the voltage level objectively require the configuration of power equipment with larger capacity and higher voltage level. The operation of large-capacity transformers puts forward higher requirements for relay protection. The latest statistical data show that the average correct rate of operation of transformers of 220kV and above from 2001 to 2011 is 79.794%, which is about 20 percentage points lower than that of generator and line protection. At present, differential protection is one of the main protections for internal faults of transformers, and its reliability is affected by CT saturation. In the case of CT ...

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Problems solved by technology

[0003] At present, the ratio braking method is generally used in engineering practice to identify, but this method cannot guarantee the reliability of differential protection in the case of extreme CT saturation, and must be supplemented by other measures to identify CT saturation

In addition, the identification methods proposed at home and abroad include time difference method, harmonic braking method, wavelet singularity detection method, second-order or third-order derivative method, etc. These methods can basically guarantee the safety of transformer differential protection when experiencing faults , but there are still some problems in the rapidity or accuracy of the time, some of the above methods are too complicated and not suitable for practical applications

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