Improved current transformer saturation characteristic recognition method

Abstract

The invention discloses an improved current transformer saturation characteristic recognition method. Firstly, all current transformers connected to a same bus belong to the same group, and current signals are collected; secondly, a kalman filtering algorithm is adopted for extracting fundamental components to carry out differential protection calculation, and a protection action signal is detected; finally, a data window is selected, corrected wavelet transformation and power function optimization are conducted on all the current transformers in the same group to obtain respective mutation detection results, the positions of all mutation points are determined, and the saturation characteristic of the current transformer is identified. The method can improve the real-time performance of differential protection calculation; traditional wavelet transform is corrected, and mutation point detection can be more accurate; defects of a time difference method can be overcome, different faultsand saturation moments can be recognized, fault types are correctly judged, and the method has high accuracy and applicability under various scenes.

Description

technical field [0001] The invention relates to the analysis of the saturation characteristics of a current transformer, in particular to an improved identification method for the saturation characteristics of a current transformer. technical background [0002] In the power system, current transformers are used in conjunction with relay protection devices and current metering devices to provide current information of the power grid and play a decisive role in the normal operation of secondary equipment such as relay protection devices and current monitoring devices. When the current transformer is saturated, due to its own nonlinear characteristics, it will lead to distortion of the output of the collected current data, affecting normal use. Especially when the current transformer oversaturation exceeds its maximum protection capacity due to excessive current, the secondary current waveform will be distorted. In this process, the function of the quick-break overcurrent prot...

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Problems solved by technology

When the current transformer is saturated, due to its own nonlinear characteristics, it will lead to distortion of the output of the collected current data, affecting normal use

Especially when the current transformer oversaturation exceeds its maximum protection capacity due to excessive current, the secondary current waveform will be distorted. In this process, the function of the quick-break overcurrent protection device will be affected by the distorted current , because the effective value of the current is reduced, the device will be difficult to function, and at the same time, the differential protection device will cause the differential protection to send an error signal due to the abnormal change of the current, which may also cause the current protection to refuse to operate. Major damage to the power grid

[0003] At this stage, scholars have proposed various current transformer saturation identification schemes, but there are still some shortcomings. For example, various schemes based on the time difference method still rely on a certain time difference between the fault and saturation. If the detected time difference If it is less than the threshold value, it is considered that the time difference does not exist

In the case of serious and rapid saturation or strong pulse interference, the detection method based on the time difference criterion will misjudge that the time difference does not exist, resulting in protection misoperation, and if the external fault causes the current transformer to saturate, then a conversion fault occurs When the protection may refuse to move for a long time

The current harmonic method only judges whether saturation occurs based on the harmonic components in the current signal, and cannot essentially identify the occurrence time of fault and saturation

However, when the saturation degree of the transformer is deep in the differential protection, the differential current may still be located in the trip area, resulting in protection misoperation

Signal disturbance detection based on wavelet modulus maxima to identify the waveform characteristics of the sudden change in the current transformer is currently a more effective method for detecting sudden change points. However, this method only relies on the current information of a single current transformer and has no more possibilities. The reference quantity is compared and screened, the anti-interference ability is poor, and the criterion may fail in some extreme cases

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