Current transformer trailing current identification algorithm based on waveform characteristic difference

Abstract

A current transformer trailing current recognition algorithm based on waveform characteristic difference comprises the steps that firstly, the absolute value of the first 1/2 cycle wave of real-time sampling current of a transformer is obtained, the half-wave integral value, the maximum/minimum value and the maximum value deviation in a data window are calculated, and if the maximum value deviation is equal to 0, it is judged that the sampling current meets the maximum value criterion; secondly, every three continuous sampling points is taken as a section, the increase, decrease and convexityof the sampling points of the section are judged, and if the number of the sampling sections which are continuously and progressively decreased and have concave characteristics exceeds a set thresholdvalue, a judgment is made that the sampling current satisfies a subtraction-concavity criterion; further, a comprehsnive judgment is made that data meets the subtraction-concavity criterion, if the half-wave integral value is less than the set threshold, a judgment is made that that the current transformer current is the trailing current. A recognition algorithm is simple in principle, dual in criterion and high in reliability. The method only needs current magnitude information and is easy to implement in engineering.

Description

technical field [0001] The invention relates to a tailing current recognition algorithm of a current transformer based on waveform characteristic difference, which belongs to the field of relay protection of electric power system. Background technique [0002] When a fault occurs in the power system, the relay protection device will send a trip command to the corresponding circuit breaker after confirming the fault, and the circuit breaker will trip the faulty part of the primary side. According to theoretical analysis and on-site verification, due to the presence of inductance components in the current loop of the secondary side of the CT, a small amount of electric energy will be stored in the inductance components. The winding and the secondary load carried by the CT form a loop and release the energy stored in the current loop inductance, so the CT secondary side loop still has an attenuated non-periodic DC component after the circuit breaker disconnects the primary side...

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Problems solved by technology

[0003] When the initial current amplitude of the trailing current is high and the time constant of the secondary side of the CT is large, some protection misjudgments may be caused, such as circuit breaker failure, expanding the scope of power outages, and having a greater impact on the power system (Jiang Ziqiang , Liu Jianyong. Research on Failure Protection of Nanyang UHV Circuit Breaker[J]. Power System Protection and Control, 2015, 43(12): 117-122.)

[0004] At present, for the identification method of tailing current, it is generally to detect the zero-crossing point of the waveform, which requires a cycle of time, and the identification time is relatively long. In addition, once the non-periodic bias current in the fault current is too large, the fault current waveform will be in the One cycle or even a longer period of time will not cross the zero point, and the transmission error of the CT device may also cause the zero-crossing phenomenon of the trailing current that was originally no more than zero point, which will eventually lead to the failure of the zero-crossing criterion of the waveform (Wu Yani, Jiang Weiping, Wang Huawei, et al. Research on the delayed zero-crossing phenomenon of short-circuit current in 500kV AC line circuit breakers [J]. Power Grid Technology, 2013, 37(01): 195-200.)

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