CN108880505B - Grounding grid potential difference filtering method based on starting judgment element and wavelet transformation - Google Patents

Grounding grid potential difference filtering method based on starting judgment element and wavelet transformation Download PDF

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CN108880505B
CN108880505B CN201810337245.1A CN201810337245A CN108880505B CN 108880505 B CN108880505 B CN 108880505B CN 201810337245 A CN201810337245 A CN 201810337245A CN 108880505 B CN108880505 B CN 108880505B
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王立辉
黄嘉宇
赵凯
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Abstract

本发明公开了一种基于启动判定元件和小波变换的接地网电位差滤波方法，该方法针对继电保护电流互感器的采集信号，根据启动元件连续五点的约束条件对信号是否满足稳态条件进行判断，不满足的采样数据通过基于波形系数的判定元件进行进一步的判断。若为正常数据，则直接输出；若为异常数据，则通过小波变换滤波处理后再输出。本发明在传统小波变换前加入启动判定元件，可对信号进行预判断，大大减少了计算量，克服了传统滤波算法时效性不好的缺点，同时利用小波变换可以有效地滤除接地网电位差导致的噪声信号，保证继电保护数据测量的准确性，避免继电保护设备的误操作。

Figure 201810337245

The invention discloses a grounding grid potential difference filtering method based on a start-up judging element and wavelet transformation. The method aims at the acquisition signal of a relay protection current transformer, and determines whether the signal satisfies the steady-state condition according to the constraint condition of five consecutive points of the start-up element. A judgment is made, and the unsatisfactory sample data is further judged by a judgment element based on the form factor. If it is normal data, it will be output directly; if it is abnormal data, it will be filtered and processed by wavelet transform and then output. The invention adds a start-up judging element before the traditional wavelet transform, which can pre-judgment the signal, greatly reduces the amount of calculation, overcomes the shortcoming of the traditional filtering algorithm with poor timeliness, and at the same time uses the wavelet transform to effectively filter out the potential difference of the grounding grid The resulting noise signal ensures the accuracy of the relay protection data measurement and avoids the misoperation of the relay protection equipment.

Figure 201810337245

Description

基于启动判定元件和小波变换的接地网电位差滤波方法A Filtering Method of Grounding Grid Potential Difference Based on Startup Decision Element and Wavelet Transform

技术领域technical field

本发明涉及一种基于启动判定元件和小波变换的接地网电位差滤波方法，属于继电保护设备滤波算法技术领域。The invention relates to a grounding grid potential difference filtering method based on a start-up determination element and wavelet transformation, and belongs to the technical field of filtering algorithms for relay protection equipment.

背景技术Background technique

特高压变电站普遍采用GIS(Gas insulated substation)开关设备，当隔离开关操作时，开关断口处将出现几十次乃至几百次燃弧和灭弧。其产生的骚扰电压在母线和短线上不断折反射，形成特快速暂态过电压VFTO(very fast transient over-voltage)。VFTO通过互感器一次侧的保护接地线泄入地网，导致地网局部电位升。由于特高压变电站的二次电缆普遍采用双端接地的方式，屏蔽层两端会产生接地网电位差。该电位差通过耦合在二次电缆中的信号芯线上感生出骚扰电流，导致继电保护数据测量不准确，易引起接地智能设备的误操作，因此有必要找出干扰信号的识别和消除方法，如硬件滤波方法和信号处理算法，其中信号处理算法因其简单高效，使用更为广泛。UHV substations generally use GIS (Gas insulated substation) switchgear. When the isolating switch is operated, dozens or even hundreds of arcing and arc extinguishing will occur at the switch fracture. The generated disturbance voltage is constantly refracted and reflected on the bus and short lines, forming a very fast transient over-voltage VFTO (very fast transient over-voltage). VFTO leaks into the ground grid through the protective grounding wire on the primary side of the transformer, causing the local potential of the ground grid to rise. Since the secondary cables of UHV substations are generally grounded at both ends, there will be a potential difference between the two ends of the shielding layer. This potential difference induces disturbance current through the signal core wire coupled in the secondary cable, which leads to inaccurate measurement of relay protection data and easily causes misoperation of grounded smart devices. Therefore, it is necessary to find out how to identify and eliminate interference signals. , such as hardware filtering methods and signal processing algorithms, among which signal processing algorithms are more widely used because of their simplicity and efficiency.

接地网电位差引起的骚扰信号主要表现为突变的高频暂态信号，传统基于时域的滤波算法针对该类信号效果不好，而小波变换可以根据电流与噪声的模极大值随尺度变化所表现出来的不同特性，对信号进行小波分解和重构处理，从而有效地滤除接地网电位差引起的噪声信号。在变电站实际工况下，骚扰信号占比极低，若直接采用小波变换对所有采样值进行滤波处理，计算效率不高，易导致继电保护处理延误。需要针对变电站的实际情况，对传统滤波算法进行改进，既保证电力系统继电保护的可靠性，又提高继电保护数据处理的时效性。The disturbance signal caused by the potential difference of the grounding grid is mainly manifested as a sudden high-frequency transient signal. The traditional filtering algorithm based on the time domain is not effective for this kind of signal, while the wavelet transform can change with the scale according to the maximum value of the current and noise. According to the different characteristics displayed, the signal is decomposed and reconstructed by wavelet, so as to effectively filter out the noise signal caused by the potential difference of the grounding grid. Under the actual working conditions of the substation, the proportion of disturbance signals is extremely low. If the wavelet transform is directly used to filter all the sampled values, the calculation efficiency is not high, and it is easy to cause delays in the processing of relay protection. It is necessary to improve the traditional filtering algorithm according to the actual situation of the substation, which not only ensures the reliability of the power system relay protection, but also improves the timeliness of the relay protection data processing.

发明内容SUMMARY OF THE INVENTION

为了解决上述技术问题，本发明提供一种基于启动判定元件和小波变换的接地网电位差滤波方法，在小波变换前加上了启动和判定元件，提前对信号进行了预处理，保证继电保护数据测量的时效性。In order to solve the above technical problems, the present invention provides a grounding grid potential difference filtering method based on a start-up judging element and wavelet transform. The start-up and judging elements are added before the wavelet transform, and the signal is preprocessed in advance to ensure the relay protection. Timeliness of data measurement.

本发明为解决上述技术问题采用以下技术方案：The present invention adopts the following technical solutions for solving the above-mentioned technical problems:

本发明提供一种基于启动判定元件和小波变换的接地网电位差滤波方法包括以下步骤：The present invention provides a grounding grid potential difference filtering method based on a start-up determination element and wavelet transformation, which includes the following steps:

步骤1，采集继电保护电流互感器信号；Step 1, collect the signal of the relay protection current transformer;

步骤2，根据启动元件连续五点的约束条件，对当前时刻采集到的继电保护电流互感器信号是否满足稳态条件进行判断：若当前时刻采集到的继电保护电流互感器信号满足稳态条件，则输出当前时刻采集到的继电保护电流互感器信号，并返回步骤1继续执行下一时刻的采集操作；反之则执行步骤3；Step 2, according to the constraints of five consecutive points of the starting element, judge whether the signal of the relay protection current transformer collected at the current moment satisfies the steady-state condition: if the signal of the relay protection current transformer collected at the current moment meets the steady-state condition If the conditions are met, output the relay protection current transformer signal collected at the current moment, and return to step 1 to continue to perform the acquisition operation at the next moment; otherwise, perform step 3;

步骤3，通过基于波形系数的判定元件，判断当前时刻采集到的继电保护电流互感器信号是否为正常数据：若是则输出当前时刻采集到的继电保护电流互感器信号，并返回步骤1继续执行下一时刻的采集操作；反之则执行步骤4；Step 3: Determine whether the current relay protection current transformer signal collected at the current moment is normal data through the determination element based on the waveform coefficient: if so, output the relay protection current transformer signal collected at the current moment, and return to step 1 to continue Execute the acquisition operation at the next moment; otherwise, execute step 4;

步骤4，通过小波变换，对当前时刻采集到的继电保护电流互感器信号进行滤波处理，然后输出滤波处理后的继电保护电流互感器信号，并返回步骤1继续执行下一时刻的采集操作。Step 4: Perform filtering processing on the current transformer signal of relay protection collected at the current moment through wavelet transformation, then output the signal of the relay protection current transformer after filtering processing, and return to step 1 to continue to perform the acquisition operation at the next moment. .

作为本发明的进一步技术方案，步骤1中通过采集系统对继电保护电流互感器信号进行实时采集，其中，采集系统包括依次连接的电流互感器、前置模拟低通滤波器、采样保持器、模数转换器、多路转换开关和单片机。As a further technical solution of the present invention, in step 1, the signal of the relay protection current transformer is collected in real time by the collection system, wherein the collection system includes the current transformers connected in sequence, the pre-analog low-pass filter, the sample holder, Analog-to-digital converters, multiplexers and microcontrollers.

作为本发明的进一步技术方案，步骤2具体为：As a further technical scheme of the present invention, step 2 is specifically:

2.1，启动元件连续五点的约束条件为：y′k＝-yk-4+2yk-3-2yk-2+2yk-1+2cos100πTs(yk-3-2yk-2+yk-1)，其中，y′k为k时刻继电保护电流互感器信号的预测值，yk-1、yk-2、yk-3、yk-4分别为k-1、k-2、k-3、k-4时刻采集到的继电保护电流互感器信号，Ts为继电保护电流互感器信号的采样周期；2.1, the constraints of the five consecutive points of the starting element are: y′ k = -y k-4 +2y k-3 -2y k-2 +2y k-1 +2cos100πT s (y k-3 -2y k-2 + y k-1 ), where y′ k is the predicted value of the relay protection current transformer signal at time k, y k-1 , y k-2 , y k-3 , y k-4 are respectively k-1, The relay protection current transformer signal collected at time k-2, k-3, k-4, T s is the sampling period of the relay protection current transformer signal;

2.2，如果

Figure BDA0001629583630000021
则k时刻采集到的继电保护电流互感器信号yk不满足稳态条件；否则yk满足稳态条件，输出yk并继续执行k+1时刻继电保护电流互感器信号yk+1的采集和信号是否满足稳态条件的判断；其中，Im为系统额定电流幅值，ε1为设定的第一阈值。2.2, if
Figure BDA0001629583630000021
Then the relay protection current transformer signal y k collected at time k does not satisfy the steady-state condition; otherwise, y k satisfies the steady-state condition, output y k and continue to execute the relay protection current transformer signal y k+1 at time k+1 The acquisition of and the judgment of whether the signal meets the steady-state condition; wherein, Im is the rated current amplitude of the system, and ε 1 is the set first threshold.

作为本发明的进一步技术方案，步骤3具体为：As a further technical solution of the present invention, step 3 is specifically:

如果R＞ε2，则k时刻采集到的继电保护电流互感器信号yk不是正常数据，继续执行步骤4；否则，输出yk并返回步骤2继续执行对k+1时刻采集到的继电保护电流互感器信号yk+1是否满足稳态条件的判断；其中，

Figure BDA0001629583630000022
α为畸变所占面积，
Figure BDA0001629583630000023
N为判断yk是否为正常数据所选定的判定元件数据窗长度，yk+2、yk+3、yk+4分别为k+2、k+3、k+4时刻采集到的继电保护电流互感器信号，Ts为继电保护电流互感器信号的采样周期，s为所选定的数据窗的波形面积，
Figure BDA0001629583630000024
ε2为设定的第二阈值。If R>ε 2 , then the relay protection current transformer signal y k collected at time k is not normal data, and proceed to step 4; Judgment of whether the electrical protection current transformer signal y k+1 satisfies the steady-state condition; among them,
Figure BDA0001629583630000022
α is the area occupied by the distortion,
Figure BDA0001629583630000023
N is the length of the data window of the judging element selected to judge whether y k is normal data, y k+2 , y k+3 , y k+4 are the data collected at times k+2, k+3, and k+4, respectively. Relay protection current transformer signal, T s is the sampling period of relay protection current transformer signal, s is the waveform area of the selected data window,
Figure BDA0001629583630000024
ε 2 is the set second threshold.

作为本发明的进一步技术方案，步骤4通过小波变换，对当前时刻采集到的继电保护电流互感器信号进行滤波处理，具体为：As a further technical solution of the present invention, step 4, through wavelet transformation, performs filtering processing on the signal of the relay protection current transformer collected at the current moment, specifically:

a)选择小波基函数，并确定小波分解层数l；a) Select the wavelet basis function, and determine the wavelet decomposition layer number l;

b)进行小波分解，对采集到的继电保护电流互感器信号Y进行等间隔抽样，然后对抽样序列进行离散小波变换，得到小波的展开系数和，分解公式为：b) Perform wavelet decomposition, sample the collected relay protection current transformer signal Y at equal intervals, and then perform discrete wavelet transform on the sampling sequence to obtain the expansion coefficient sum of the wavelet. The decomposition formula is:

Figure BDA0001629583630000031
Figure BDA0001629583630000031

其中，i＝1,2,…,l，M为小波变换数据窗的长度，cA0即为Y，cAi为分解的第i层低频小波系数，cDi为分解的第i层高频小波系数，hm-2为选定小波基对应的低频滤波器，gm-2为选定小波基对应的高频滤波器；Among them, i=1,2,...,l, M is the length of the wavelet transform data window, cA 0 is Y, cA i is the decomposed i-th layer of low-frequency wavelet coefficients, and cD i is the decomposed i-th layer of high-frequency wavelet coefficient, h m-2 is the low-frequency filter corresponding to the selected wavelet base, and g m-2 is the high-frequency filter corresponding to the selected wavelet base;

c)确定小波系数的阈值和选择阈值函数，阈值变换后的第i层高频小波系数的计算公式为

Figure BDA0001629583630000032
其中，th为阈值，
Figure BDA0001629583630000033
其中，σ为噪声标准差；c) Determine the threshold value of the wavelet coefficients and select the threshold value function. The calculation formula of the i-th layer high-frequency wavelet coefficients after the threshold value transformation is:
Figure BDA0001629583630000032
Among them, th is the threshold,
Figure BDA0001629583630000033
Among them, σ is the noise standard deviation;

d)根据

Figure BDA0001629583630000034
进行小波重构，l次重构后得到的cA0”即为滤波处理后的继电保护电流互感器信号Y'，其中，cAl”＝cAl，cDi'为阈值变换后的第i层高频小波系数，cAi-1”为重构后第i-1层低频小波系数，cAi”为重构后第i层低频小波系数。d) according to
Figure BDA0001629583630000034
Carry out wavelet reconstruction, and cA 0 ″ obtained after 1 reconstruction is the relay protection current transformer signal Y′ after filtering, wherein cA l ″=cA l , and cD i ' is the i-th signal after threshold transformation Layer high-frequency wavelet coefficients, cA i-1 ″ is the i-1 layer low-frequency wavelet coefficients after reconstruction, cA i ″ is the i-th layer low-frequency wavelet coefficients after reconstruction.

本发明采用以上技术方案与现有技术相比，具有以下技术效果：本发明在小波变换前加上了启动和判定元件，提前对信号进行了预处理，则正常信号可以直接进行输出，省去了滤波算法的计算时间，克服了传统小波变换时效性不好的问题，保证继电保护数据测量的准确性，提高电力系统继电保护的可靠性。Compared with the prior art, the present invention adopts the above technical solution, and has the following technical effects: the present invention adds a start-up and a determination element before the wavelet transform, and preprocesses the signal in advance, so that the normal signal can be output directly, eliminating the need for The calculation time of the filtering algorithm is reduced, the problem of poor timeliness of the traditional wavelet transform is overcome, the accuracy of the relay protection data measurement is ensured, and the reliability of the power system relay protection is improved.

附图说明Description of drawings

图1是本发明的方法流程图。Figure 1 is a flow chart of the method of the present invention.

具体实施方式Detailed ways

下面结合附图对本发明的技术方案做进一步的详细说明：Below in conjunction with accompanying drawing, the technical scheme of the present invention is described in further detail:

如图1所示，本发明的基于启动判定元件和小波变换的接地网电位差滤波算法，包括以下步骤：As shown in FIG. 1 , the grounding grid potential difference filtering algorithm based on the startup determination element and wavelet transform of the present invention includes the following steps:

步骤1，实时采集继电保护电流互感器信号；Step 1, collect relay protection current transformer signals in real time;

采集系统包括依次连接的电流互感器、前置模拟低通滤波器、采样保持器、模数转换器、多路转换开关和单片机。The acquisition system includes a current transformer, a pre-analog low-pass filter, a sample-and-hold, an analog-to-digital converter, a multiplexer switch and a single-chip microcomputer connected in sequence.

步骤2，启动元件对信号进行判断；Step 2, the starting element judges the signal;

由于在电力系统的稳态过程中，电网内流过稳定的工频电流，频率为50Hz，幅值由电源、负载和线路参数等因素决定，在稳态过程中保持不变。在接地网电位差干扰中，电网电流中除了含有工频稳态分量，还会产生暂态量，暂态量的幅值随时间衰减，最终达到零。电网电流的一般表达式可写成工频稳态分量与衰减非周期分量的叠加：During the steady state process of the power system, a stable power frequency current flows in the power grid, the frequency is 50Hz, and the amplitude is determined by factors such as power supply, load and line parameters, and remains unchanged in the steady state process. In the grounding grid potential difference interference, in addition to the power frequency steady-state component, the grid current will also generate transients. The amplitude of the transients decays with time and eventually reaches zero. The general expression of the grid current can be written as the superposition of the power frequency steady-state component and the decaying aperiodic component:

Figure BDA0001629583630000041
Figure BDA0001629583630000041

其中，A为工频电流的幅值，

Figure BDA0001629583630000042
为工频电流初相角，B为衰减非周期分量的初值，τ为衰减非周期分量的衰减时间常数。此表达式中共有四个未知量A，
Figure BDA0001629583630000043
B和τ，所以只要知道电流信号的前四个采样点数据，代入即可求解此电流表达式，第五个点的采样值也应满足此表达式，因此即可实现对采集信号的预测。写出其表达式，并进行泰勒展开，可得：Among them, A is the amplitude of the power frequency current,
Figure BDA0001629583630000042
is the initial phase angle of the power frequency current, B is the initial value of the attenuation aperiodic component, and τ is the attenuation time constant of the attenuation aperiodic component. There are four unknown quantities A in this expression,
Figure BDA0001629583630000043
B and τ, so as long as the data of the first four sampling points of the current signal are known, the current expression can be solved by substituting it, and the sampling value of the fifth point should also satisfy this expression, so the prediction of the collected signal can be realized. Write out its expression and perform Taylor expansion, we can get:

Figure BDA0001629583630000044
Figure BDA0001629583630000044

其中，yk、yk-1、yk-2、yk-3、yk-4为连续5个时刻的采样数据，Ts为采样周期。Among them, y k , y k-1 , y k-2 , y k-3 , and y k-4 are sampling data at five consecutive times, and T s is the sampling period.

整理上述表达式可得启动元件的约束条件为：yk′＝-yk-4+2yk-3-2yk-2+2yk-1+2cos100πTs(yk-3-2yk-2+yk-1)。所以如果k时刻的实际采样值yk和预测值y′k差的绝对值除以系统额定电流幅值Im大于设定的阈值ε1，即

Figure BDA0001629583630000045
表明该采样值yk不符合稳态条件，需要执行步骤3进行下一步的判定，判定其是否为正常数据。反之，直接输出yk，并继续执行k+1时刻继电保护电流互感器信号yk+1的采集和信号是否满足稳态条件的判断。Arranging the above expression, we can get the constraints of the starting element: y k ′=-y k-4 +2y k-3 -2y k-2 +2y k-1 +2cos100πT s (y k-3 -2y k-2 +y k-1 ). Therefore, if the absolute value of the difference between the actual sampling value y k and the predicted value y′ k at time k divided by the system rated current amplitude Im is greater than the set threshold ε 1 , that is,
Figure BDA0001629583630000045
It indicates that the sampled value yk does not meet the steady-state condition, and it is necessary to perform step 3 for the next step to determine whether it is normal data. On the contrary, directly output y k , and continue to perform the acquisition of the signal y k+1 of the relay protection current transformer at time k+1 and the judgment of whether the signal satisfies the steady-state condition.

步骤3，判定元件进行信号判断；Step 3, the judging element judges the signal;

如果一次系统在由稳态过程进入暂态过程的临界点，此时刻电流采样值对应的幅值和初始相位会发生变化，从而不满足启动元件的约束表达式，则可以采用波形系数对采集信号是否为正常数据进行判断。If the primary system is at the critical point from the steady-state process to the transient process, the amplitude and initial phase corresponding to the current sampling value at this moment will change, so that the constraint expression of the start-up element is not satisfied, the waveform coefficient can be used to measure the acquired signal. It is judged whether it is normal data.

波形系数的定义为：The form factor is defined as:

Figure BDA0001629583630000051
Figure BDA0001629583630000051

其中，α为畸变所占面积，通过

Figure BDA0001629583630000052
求得，其中，N为判断yk是否为正常数据所选定的数据窗长度，本发明选定为20个点，既保证准确度，又保证时效性。s为所选定的数据窗的波形面积，可通过对同一段数据窗内的采样值瞬时值进行积分获得，即
Figure BDA0001629583630000053
Among them, α is the area occupied by the distortion, through
Figure BDA0001629583630000052
Obtained, wherein, N is the length of the data window selected for judging whether y k is normal data, and the present invention selects 20 points to ensure both accuracy and timeliness. s is the waveform area of the selected data window, which can be obtained by integrating the instantaneous values of the sampled values in the same segment of the data window, namely
Figure BDA0001629583630000053

理想状态下，波形系数R的分子为零，其值也为零；若采样值中存在异常数据，R的值将不为零，且R越大，代表采样值畸变越严重。所以如果波形系数R大于设定的阈值ε2，即R＞ε2，表明该采样值yk不是正常数据，需要执行步骤4采用滤波算法对信号进行滤波处理。否则，yk是正常数据，返回步骤1继续执行下一次采集操作。Ideally, the numerator of the waveform coefficient R is zero, and its value is also zero; if there is abnormal data in the sampled value, the value of R will not be zero, and the larger the R, the more serious the distortion of the sampled value. Therefore, if the waveform coefficient R is greater than the set threshold ε 2 , that is, R>ε 2 , it indicates that the sampled value y k is not normal data, and step 4 needs to be performed to filter the signal by using a filtering algorithm. Otherwise, y k is normal data, and return to step 1 to continue the next acquisition operation.

步骤4，小波变换进行滤波处理；Step 4, wavelet transform performs filtering processing;

由于接地网电位差的干扰信号主要为突变的暂态信号，所以滤波算法选定为小波变换，主要分为4个部分：Since the interference signal of the grounding grid potential difference is mainly a sudden transient signal, the wavelet transform is selected as the filtering algorithm, which is mainly divided into 4 parts:

a)选择小波基函数，并确定小波分解层数l；a) Select the wavelet basis function, and determine the wavelet decomposition layer number l;

b)进行小波分解，对采集到的继电保护电流互感器信号Y进行等间隔抽样，然后对抽样序列进行离散小波变换，得到小波的展开系数和，分解公式为：b) Perform wavelet decomposition, sample the collected relay protection current transformer signal Y at equal intervals, and then perform discrete wavelet transform on the sampling sequence to obtain the expansion coefficient sum of the wavelet. The decomposition formula is:

Figure BDA0001629583630000054
Figure BDA0001629583630000054

其中，i表示第i层分解，分解过程中i＝1,2,…,l，M为小波变换数据窗的长度，cA0即为Y，cAi为分解的第i层低频小波系数，cDi为分解的第i层高频小波系数，hm-2为选定小波基对应的低频滤波器，gm-2为选定小波基对应的高频滤波器。按此方式，进行l次逐层分解；Among them, i represents the i-th layer decomposition, i=1,2,...,l in the decomposition process, M is the length of the wavelet transform data window, cA 0 is Y, cA i is the decomposed i-th layer low-frequency wavelet coefficient, cD i is the decomposed i-th layer high-frequency wavelet coefficient, h m-2 is the low-frequency filter corresponding to the selected wavelet base, and g m-2 is the high-frequency filter corresponding to the selected wavelet base. In this way, perform layer-by-layer decomposition for l times;

c)确定小波系数的阈值和选择阈值函数，阈值变换后的第i层高频小波系数的计算公式为

Figure BDA0001629583630000061
其中，th为阈值，
Figure BDA0001629583630000062
来计算阈值，其中，σ为噪声标准差；c) Determine the threshold value of the wavelet coefficients and select the threshold value function. The calculation formula of the i-th layer high-frequency wavelet coefficients after the threshold value transformation is:
Figure BDA0001629583630000061
Among them, th is the threshold,
Figure BDA0001629583630000062
to calculate the threshold, where σ is the noise standard deviation;

d)根据

Figure BDA0001629583630000063
进行小波重构，其中，重构过程中i＝l,l-1,…,1，cAl”＝cAl，cDi'为阈值变换后的第i层高频小波系数，cAi-1”为重构后第i-1层低频小波系数。按此方式，进行l次重构，得到的cA0”即为滤波处理后的继电保护电流互感器信号Y'，输出并返回步骤2继续执行对yk+1是否满足稳态条件的判断。d) according to
Figure BDA0001629583630000063
Carry out wavelet reconstruction, wherein, in the reconstruction process i=l,l-1,...,1, cA l "=cA l , cD i ' is the i-th layer high-frequency wavelet coefficient after threshold transformation, cA i-1 ” is the low-frequency wavelet coefficient of the i-1th layer after reconstruction. In this way, carry out 1 reconstructions, and the obtained cA 0 ″ is the filtered relay protection current transformer signal Y', output and return to step 2 to continue to judge whether y k+1 satisfies the steady-state condition .

本发明方法在小波变换前加上了启动和判定元件，对信号进行了预处理，正常信号可以直接进行输出，大大减少滤波算法的计算量，克服传统小波变换时效性不好的问题，既保证了继电保护数据测量的准确性，又提高了电力系统继电保护的可靠性。The method of the invention adds a start-up and a judgment element before the wavelet transform, preprocesses the signal, and the normal signal can be output directly, which greatly reduces the calculation amount of the filtering algorithm, overcomes the problem of poor timeliness of the traditional wavelet transform, and not only ensures the It improves the accuracy of relay protection data measurement and improves the reliability of power system relay protection.

以上所述，仅为本发明中的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉该技术的人在本发明所揭露的技术范围内，可理解想到的变换或替换，都应涵盖在本发明的包含范围之内，因此，本发明的保护范围应该以权利要求书的保护范围为准。The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited to this, any person familiar with the technology can understand the transformation or replacement that comes to mind within the technical scope disclosed by the present invention, All should be included within the scope of the present invention, therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (4)

1. The ground net potential difference filtering method based on the starting judgment element and the wavelet transformation is characterized by comprising the following steps of:
step 1, collecting signals of a relay protection current transformer;
step 2, judging whether the relay protection current transformer signal acquired at the current moment meets a steady state condition according to the constraint condition of five continuous points of the starting element: if the relay protection current transformer signal acquired at the current moment meets the steady state condition, outputting the relay protection current transformer signal acquired at the current moment, and returning to the step 1 to continue to execute the acquisition operation at the next moment; otherwise, executing the step 3; the method specifically comprises the following steps:
2.1, the constraint condition of five continuous points of the starting element is as follows: y'k＝-yk-4+2yk-3-2yk-2+2yk-1+2cos100πTs(yk-3-2yk-2+yk-1) Wherein, y'kFor the predicted value y of the relay protection current transformer signal at the moment kk-1、yk-2、yk-3、yk-4Respectively are relay protection current transformer signals T acquired at k-1, k-2, k-3 and k-4sSampling period of relay protection current transformer signals;
2.2, if
Figure FDA0003289118380000011
The relay protection current transformer signal y acquired at the moment kkA steady state condition is not satisfied; otherwise ykSatisfy the steady state condition, output ykAnd continuing to execute the relay protection current transformer signal y at the k +1 momentk+1Whether the signal meets the steady state condition is judged; wherein I is the rated current amplitude of the system, epsilon1Is a set first threshold;
and 3, judging whether the relay protection current transformer signal acquired at the current moment is normal data or not through a judgment element based on the waveform coefficient: if yes, outputting a relay protection current transformer signal acquired at the current moment, and returning to the step 1 to continue to execute the acquisition operation at the next moment; otherwise, executing the step 4;
and 4, filtering the relay protection current transformer signal acquired at the current moment through wavelet transformation, outputting the filtered relay protection current transformer signal, and returning to the step 1 to continue to execute the acquisition operation at the next moment.
2. The grounding grid potential difference filtering method based on the start judgment element and the wavelet transformation as claimed in claim 1, wherein in step 1, the relay protection current transformer signal is collected in real time through a collection system, wherein the collection system comprises a current transformer, a pre-analog low pass filter, a sample holder, an analog-to-digital converter, a multi-way switch and a single chip microcomputer which are connected in sequence.
3. The earth grid potential difference filtering method based on the start-up decision element and the wavelet transform as claimed in claim 1, wherein step 3 is specifically:
if R > ε2And the relay protection current transformer signal y acquired at the moment kkIf the data is not normal data, continuing to execute the step 4; otherwise, output ykAnd returning to the step 2 to continue executing the relay protection current transformer signal y acquired at the moment of k +1k+1Judging whether a steady state condition is met; wherein,
Figure FDA0003289118380000021
alpha is the area occupied by the distortion,
Figure FDA0003289118380000022
n is judgment ykDecision element data window length, y, selected for normal datak+2、yk+3、yk+4Respectively the relay protection current transformer signals T collected at the moments of k +2, k +3 and k +4sIs the sampling period of the relay protection current transformer signal, s is the waveform area of the selected data window,
Figure FDA0003289118380000023
ε2is a set second threshold.
4. The grounding grid potential difference filtering method based on the start judgment element and the wavelet transformation as claimed in claim 1, wherein the step 4 is to perform filtering processing on the relay protection current transformer signal acquired at the current moment through the wavelet transformation, specifically:
a) selecting a wavelet basis function and determining the wavelet decomposition layer number l;
b) performing wavelet decomposition, performing equal-interval sampling on the acquired relay protection current transformer signal Y, and then performing discrete wavelet transform on a sampling sequence to obtain an expansion coefficient sum of wavelets, wherein the decomposition formula is as follows:
Figure FDA0003289118380000024
where i is 1,2, …, l, M is the length of the wavelet transform data window, cA0Namely Y, cAiFor decomposed i-th layer low-frequency wavelet coefficients, cDiFor the i-th layer of decomposed high-frequency wavelet coefficients, hm-2For low-frequency filters corresponding to selected wavelet bases, gm-2A high frequency filter corresponding to the selected wavelet basis;
c) determining the threshold value of the wavelet coefficient and selecting a threshold value function, wherein the calculation formula of the ith layer of high-frequency wavelet coefficient after threshold value transformation is as follows
Figure FDA0003289118380000025
Wherein, th is a threshold value,
Figure FDA0003289118380000026
wherein σ is a noise standard deviation;
d) according to
Figure FDA0003289118380000027
Performing wavelet reconstruction to obtain cA after l times of reconstruction0The signal is the relay protection current transformer signal Y' after filtering treatment, wherein cAl″＝cAl，cDi' is the ith layer high frequency wavelet coefficient, cA after threshold value transformationi-1"is the reconstructed i-1 th layer low-frequency wavelet coefficient, cAiAnd the' is the i-th layer low-frequency wavelet coefficient after reconstruction.
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