Morphological gradient-based identification method for magnetizing inrush current of transformer

Abstract

The invention discloses a morphological gradient-based identification method for the magnetizing inrush current of a transformer. The identification method comprises the following steps of: (1) acquiring a differential current signal I of current transformers arranged at two differential protection sides of the transformer; (2) sampling the differential current signal I; and (3) when the obtained differential current signal I exceeds a setting valve Icd of a differential-protection starting component, distinguishing the magnetizing inrush current. The step (3) specifically comprises the following steps of: (3-1) taking the differential current signal I of which a data window is a half of the length of a base frequency period to obtain a morphological gradient result of the I according to an improved mathematical morphology gradient algorithm; (3-2) introducing criterion sigma: determining that I is the magnetizing inrush current if sigma is greater than sigma set, and carrying out a step (3-3) otherwise; and (3-3) introducing criterion C: determining that I is the magnetizing inrush current if C is greater than C set, and determining that I is an inner fault signal otherwise. The method provided by the invention has the advantages of simple steps, small calculated quantity, short time delay, high reliability and the like, so that the magnetizing inrush current can be identified to realize the locking differential protection.

Description

Technical field [0001] The invention belongs to the technical field of transformer relay protection, and particularly relates to a method for identifying inrush current of a transformer based on a morphological gradient. Background technique [0002] As one of the important electrical equipment, the transformer is responsible for the important role of power transmission and voltage conversion, and its operation status directly affects the safety and stability of the power supply system. At the same time, the transformer itself is generally expensive, and once it is damaged due to a fault, it will be difficult and long to repair, which will cause serious economic losses. Therefore, researching new transformer protection schemes with reliable performance and advanced technology will have greater engineering and theoretical value. [0003] For a long time, the differential protection has been used as the main protection of the transformer because of its good selectivity and quick act...

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Problems solved by technology

But this method is not reliable in some cases, such as when the fault occurs not at the 0 degree closing angle, the first half wave of the current will not be reliably identified

[0009] The Chinese invention patent with the notification number CN 101567552A discloses a method for identifying inrush current and internal short circuit of a power transformer using morphological structure. The consistency between the original signal and the waveform of the morphological analysis results is taken, which essentially reflects the similarity between the original waveform signal and the sine wave, and the identification of the excitation inrush current and the internal fault current of the power transformer is realized by comparing the waveform consistency coefficient; It overcomes the deficiencies of some existing technologies, but its sampling data window is as long as 25ms, which causes a long time delay and cannot meet the requirements of high-voltage transformers for fast action. The long action time also aggravates the impact of internal fault current on the transformer. damage

When the transformer CT is saturated, the internal fault current will no longer be a sine wave. At this time, the excitation inrush current and the internal short-circuit current cannot be identified by the size of the waveform consistency coefficient. Therefore, the method of this invention patent is not suitable for use when the transformer CT is saturated.

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