Method for detecting trailing amount of transformer

Abstract

The invention discloses a method for detecting a trailing amount of a transformer. The method comprises: (1), a monotonic property of a sample value is detected; (2), if the sample value has a monotone increasing characteristic or a monotone decreasing characteristic and a constant time value is exceeded, a sample current is determined to be a trailing amount. In addition, a method for detecting the monotonic property of the sample value includes: differences between a current sample point and previous N sample points are calculated; if the difference values are larger than zero, the current sample point has a monotone increasing characteristic; and otherwise, if the difference values are smaller than zero, the current sample point has a monotone decreasing characteristic. The N is larger than 1 and is smaller than the sampling point number per cycle. If the monotone increasing characteristic of the sampling point is larger than constant time value continuously, the sampling current is the trailing amount; and if the monotone decreasing characteristic of the sampling point is larger than constant time value continuously, the sampling current is the trailing amount. On the basis of the monotonic property of the trailing amount, the trailing amount can be detected rapidly; the return speed of a tripping protection command increases; and reliability of failure protection is improved.

Description

technical field [0001] The invention relates to the technical field of power grids, in particular to a method for detecting the trailing amount of a transformer. Background technique [0002] When a fault occurs in the power system, the relay protection detects the fault and the action outlet trips, and the circuit breaker is disconnected to remove the faulty electrical primary part. Theoretical and actual field recordings show that after the circuit breaker is disconnected, the electromagnetic current transformer may have a current tailing phenomenon, that is, after the primary device is disconnected, the secondary winding of the current transformer still has attenuated aperiodic equal current components. The reason for the current tailing phenomenon is that when the primary side circuit breaker is disconnected, the current of the secondary winding of the current transformer is not zero at this time, and the secondary load carried by the excitation winding, the secondary wi...

AI Technical Summary

Problems solved by technology

The disadvantage of this method is that the software filter can only filter out the DC component, and the tail current is an attenuated DC component, which cannot be completely eliminated. In extreme cases, if the tail current is very large and the failure setting is relatively low, At this time, it may still cause malfunction and misoperation

[0007] The article "Simulation Research on the Impact of Current Transformer Tailing on Circuit Breaker Failure Protection" in "Henan Science and Technology" No. 9, 2014 analyzed the reasons for the tailing current, and analyzed the advantages and disadvantages of the three algorithms. Method 1 is Composite voltage blocking criterion, the disadvantage of this method is that the sensitivity of complex voltage is not enough, which may lead to rejection

Method 2 is a differential full-cycle algorithm. The disadvantage of this method is that it cannot completely filter out the tail current, and there may be a risk of misoperation

Method 3 is zero-crossing detection. The disadvantage of this method is that the fault current may completely deviate to one side of the coordinate axis within 1 to 2 cycles after the fault in the system, which may cause failure or slow movement.

[0008] Chinese Patent Publication No. CN201410281034.2, published on November 5, 2014, the name of the invention is a method for preventing current transformer trailing current from affecting circuit breaker failure protection. The patent discloses a method for preventing current transformer trailing The method for the influence of tail current on circuit breaker failure protection, wherein the tail current judgment of the current transformer in claim 1 includes the zero-crossing judgment of the sampling value and the current reduction judgment, the disadvantage is that the fault current may occur in the system after the fault In the case of completely deflecting to one side of the coordinate axis within 1 to 2 cycles, the zero-crossing judgment may cause malfunction and refusal to move or the movement is very slow

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