Differential protection speed-up method for unsymmetrical fault during oscillation
A differential protection and asymmetric technology, applied in the field of power transmission and transformation, can solve problems such as power system operation hazards, inability to act quickly, system oscillation deterioration, etc., achieve good application prospects, improve action speed, and accurately determine the effect
Active Publication Date: 2015-09-23
STATE GRID CORP OF CHINA +1
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Problems solved by technology
If an asymmetrical fault occurs during this period, the differential protection is easily blocked by the ratio braking curve and cannot act quickly
In severe cases, the system oscillation will deteriorate, and even cause system disconnection, etc., which will bring great harm to the operation of the power system
Method used
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[0037]For faults in the oscillation zone, the operation time of the conventional ratio brake differential protection is obviously delayed, and the operation delay is related to the oscillation cycle. In extreme cases, when the current peak fault occurs, the operation delay even reaches nearly half the oscillation cycle. figure 2 The comparison between the conventional ratio brake differential protection and the action characteristics of the negative sequence current directional element shown, the sampling frequency is 4000 (points / second), the conventional ratio brake differential protection operates 150ms after the ground fault in the zone (corresponding to the number of sampling points Counting 600 points), and the negative sequence current directional element is opened within 10ms of the fault.
[0038] image 3 Comparison of the operating characteristics of conventional ratio brake differential protection and negative sequence current directional element shown, the sampli...
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The invention relates to a protection method in the field of power transmission and transformation, and specifically relates to a differential protection speed-up method for an unsymmetrical fault during oscillation. The method comprises the following steps: (1) connecting a determining element during the start of differential protection, and determining negative sequence currents of differential protection branch circuits; (2) enabling the differential protection branch circuit with the highest negative sequence current amplitude to be equivalent to a virtual branch K; (3) summing the negative sequence currents of other differential protection branch circuits except the differential protection branch circuit with the highest negative sequence current amplitude, and enabling the summed negative sequence current branch to be equivalent to a virtual branch T; (4) connecting negative sequence current direction elements of the two virtual branches K and T to judge a fault position, and judging whether the locking differential protection is carried out or not according to the fault position. The method can achieve the quick collection and calculation of the negative sequence currents of all branches, can effectively recognize whether a fault point is within a differential protection region or not, can carry out speed-up differential protection operation in needs, and brings favorable influences to a power transmission and transformation system. The method is accurate in determination, is easy to implement, and is good in application prospect.
Description
technical field [0001] The invention relates to a protection method in the field of power transmission and transformation, in particular to an acceleration method for differential protection of an asymmetrical fault in oscillation. Background technique [0002] Differential protection is an important short-circuit protection. Its structure and working principle are simple, and it is less affected by the load current, so it is widely used in power systems. At present, the differential protection generally adopts the braking curve of the ratio between the differential current and the braking current to distinguish the internal and external faults. When the system oscillates, the braking current alternates periodically with the oscillation, and the alternating amplitude is large. During this period, an asymmetric fault occurs, and the differential protection is easily blocked by the ratio braking curve and cannot act quickly. In severe cases, the system oscillation will deteri...
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Inventor 李岩军周春霞詹荣荣周泽昕余越詹智华晁晖贾琰崔佳陈争光
Owner STATE GRID CORP OF CHINA