Diagnosis method for fault area of ​​three-phase three-winding transformer

Abstract

A fault area diagnosis method for a three-phase three-winding transformer. First measure the negative sequence currents of the high voltage side, medium voltage side and low voltage side of the three-phase three-winding transformer, rotate the negative sequence current vectors of the high voltage side negative sequence current and the medium voltage side by 30° clockwise, and then use the high voltage after the clockwise rotation of 30° The phase relationship between the negative sequence current on the negative sequence side of the three-phase three-winding transformer, the negative sequence current on the medium-voltage side and the negative-sequence current on the low-voltage side after rotating 30° clockwise can accurately determine the fault area of ​​the three-phase three-winding transformer. In the calculation process, the present invention only uses the negative sequence current of the high voltage side, the medium voltage side and the low voltage side of the transformer, and does not need to use the three-phase full current of the three sides of the transformer, and the operation performance is not affected by the excitation current and the excitation inrush current. The invention utilizes the phase relationship between the negative sequence current on the high voltage side rotated 30° clockwise, the negative sequence current on the medium voltage side and the negative sequence current on the low voltage side after rotating 30° clockwise to accurately judge the fault area of ​​the three-phase three-winding transformer , not affected by load current and transition resistance.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a method for diagnosing a fault area of ​​a three-phase three-winding transformer. Background technique [0002] 220kV transformers widely used in power systems usually use three-phase three-winding transformers. In order to ensure that the phase potential is close to the sine wave and provide a path for the third harmonic, a set of windings of the three-phase three-winding transformer must be connected in delta, so its connection method is △ / Y / Y connection. [0003] The current differential protection is the main protection of the transformer. In order to make the current differential amount zero during normal operation, it is necessary to convert the current of the two groups of Y sides of the transformer to the △ side or convert the current of the △ side to the two groups of Y sides to eliminate the imbalance. current. In order to eliminate the...

AI Technical Summary

Problems solved by technology

In order to eliminate the unbalanced current, the current compensation method of converting the two groups of Y-side currents to the △ side and the current compensation method of converting the △-side current to the two groups of Y-sides are mainly used at present, but the current difference between the two conversion methods is The momentum cannot correctly reflect the influence of the transformer excitation current, which affects the reliability of the current differential protection as the main protection of the transformer, and also makes the method of using the second harmonic to distinguish the excitation inrush current and short-circuit fault less reliable.

[0004] Affected by the limitations of the current differential protection principle, the current differential protection can only treat the three-phase three-winding transformer as a whole to be protected, and can only distinguish whether the fault point is located in the protection area, but cannot accurately determine whether the fault location is in the third Which side of the three-phase three-winding transformer cannot provide accurate fault range information for fault judgment, making it difficult to find the fault point after a fault, which is not conducive to rapid troubleshooting and rapid power supply recovery

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