CN108490311B - Extraction and Separation Method of Weak Shock Signal Based on Power Frequency Sampling - Google Patents

Abstract

The invention provides a method for extracting and separating weak impulse signals based on power frequency sampling, including: collecting line signals through a high-speed sampling module, processing the sampled signals with an oversampling algorithm, changing the sampling frequency and precision of the signals, The transient signal in the sampled signal is processed by the peak integrator to obtain the maximum value of the transient signal modulo, compare the signal changes, and start the algorithm to make judgments according to the signal changes and give the corresponding response. The invention can effectively extract the transient signal, and the oversampling algorithm expands the dynamic range of startup, so that the dynamic range of the transient signal exceeds 60dB. The device has high response sensitivity to transient signals, and can respond to transient signals with a power frequency signal amplitude of 0.1%. The equipment has high operation stability and strong anti-interference ability.

Description

Extraction and Separation Method of Weak Shock Signal Based on Power Frequency Sampling

technical field

The invention relates to the technical field of power equipment, in particular to power fault location equipment, and in particular to a method for extracting and separating weak impulse signals based on power frequency sampling.

Background technique

There are two main types of fault location methods in power system: fault analysis method and traveling wave location. In recent years, the traveling wave method has become more popular. The traveling wave method is a new method to measure the distance according to the propagation time of the high-frequency transient traveling wave signal generated during the fault. In practice, the length of the traveling wave propagation line and the size of the transition resistance will affect the shape and amplitude of the traveling wave head. For traveling wave ranging, the more seriously the traveling wave head is affected, the more difficult it is to identify the traveling wave head, especially noise interference. In severe cases, misjudgment is likely to occur, affecting the accuracy of waveform analysis. How to extract traveling wave effectively is the precondition for traveling wave fault location. The energy of the traveling wave signal is much smaller than that of the power frequency signal. Only the amplitude threshold is as low as possible to ensure that the traveling wave signal is responded. When the amplitude threshold is low and the interference signal is relatively large, false alarms are likely to occur. Ranging equipment requires the starting weak signal to be as small as possible, and the anti-interference ability is strong.

SUMMARY OF THE INVENTION

In order to better respond to transient signals, improve anti-interference ability, and ensure stable and reliable operation of equipment, the present invention proposes a method for extracting and separating weak impulse signals based on power frequency sampling.

The present invention adopts following technical scheme:

The method for extracting and separating weak impulse signals based on power frequency sampling includes the following steps:

Step 1. Obtain the voltage or current signal of the line under test;

Step 2: Perform oversampling processing on the acquired voltage or current signal;

Step 3, filtering out the power frequency signal contained in the oversampling signal of step 2 through the digital start filter, and extracting the transient signal in the oversampling signal;

Step 4: Perform peak value processing on the transient signal;

Step 5: Determine the type of the signal by comparing the intensity changes of the current sampling point signal and the reference sampling point signal, so as to realize the extraction and separation of weak impact signals based on power frequency sampling.

Further, in the step 1, acquiring the voltage or current signal of the line under test includes: a power frequency signal, a traveling wave signal and a noise signal.

Further, in the second step, an oversampling process is performed on the acquired voltage or current sampling signal, and a low-frequency oversampling signal with a high sampling number is obtained through an oversampling algorithm.

Further, in the third step, the transient signal in the oversampling signal is extracted, and the specific method is: processing the low-frequency oversampling signal through a digital start filter, filtering out the power frequency signal in the signal, and leaving the signal including the traveling wave. Transient signal of signal and noise signal.

Further, in the fourth step, peak value processing is performed on the transient signal, specifically: the extracted transient signal is processed by a peak integrator to obtain the maximum value of the modulo value of the transient signal at the current sampling time.

Further, in the step 5, by comparing the intensity changes of the current sampling point signal and the reference sampling point signal, it is determined that the type of the signal is specifically:

Judging the value of e according to the algorithm formula e=U _a -3U _(a-3) ; wherein, U _a is the current sampling point signal, and U _(a-3) is the reference sampling point signal;

e≥0 is judged as fault traveling wave;

It is determined that e<0 is an interference signal.

Further, the current sampling point signal is a sampling value closest to the current moment, and the reference sampling point is set as the fourth last sampling value.

Beneficial effects of the present invention:

1. The signal bandwidth coverage of the sampling channel is wide, which can meet the analysis requirements based on the time domain, reaching 20Hz to 1MHz.

2. The startup sensitivity is high, and the fault location device can be started when the transient signal is 0.1% of the power frequency signal amplitude. The equipment has high running stability and accurate judgment of transient signals.

3. The dynamic range of the separated transient signal exceeds 60dB. The response bandwidth of the transient signal is better than 1KHz~1MHz, which meets the analysis requirements of the power system.

Description of drawings

The accompanying drawings that form a part of the present application are used to provide further understanding of the present application, and the schematic examples and descriptions of the present application are used to explain the present application and do not constitute a limitation to the present application.

Fig. 1 is a flow chart of weak impulse signal extraction and separation based on power frequency sampling;

Fig. 2 is the filter attenuation curve diagram of the startup filter;

Figure 3(a)-(c) are the sampled power frequency signal, step shock and its coupled signal waveforms respectively;

Fig. 4 is the signal waveform diagram processed by the start filter;

Figure 5 is a waveform diagram of the signal processed by the peak integrator.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

The specific implementation is described with reference to the flow chart of FIG. 1 . In this example, the line voltage signal is sampled, and the current signal processing is similar. The weak impulse signal adopts the step signal of VP ₌ 500 and the period=15ms, and the power frequency signal adopts the voltage signal of VP ₌ 20000; the sampling frequency of the high-speed A/D module is 1MHz, the sampling number is 16Bit, and the sampling value is recorded as u _b ; The low frequency oversampling frequency is 10KHz, the sampling number is 23, and the sampling value is recorded as U _a ;

The weak impulse signal extraction and separation based on power frequency sampling is characterized by the following steps:

Step 1: Obtain the voltage (current) signal of the line under test.

Step 2: Oversampling processing of the voltage (current) sampling signal.

Step 3: Extract the transient signal in the oversampled signal.

Step 4: Processing the peak value of the transient signal.

Step 5: Start condition analysis and judgment.

Complete the extraction and separation of weak impulse signals based on power frequency sampling.

The specific method of acquiring the voltage signal of the line to be measured in step 1 is: collecting the voltage signal in the power grid through a voltage sensor, wherein the voltage sensor has a passband of 15Hz... The high-speed A/D module of , obtains 16-bit voltage sampling values (sampling points are recorded as 0, 1...999999, and the sampling values are recorded as u ₀ , u ₁ ... u ₉₉₉₉₉₉ ). Here the sampled value _ub is a signed number. The voltage signal includes power frequency signal, traveling wave signal and noise. Figure 3(a)-(c) are the waveform diagrams of the power frequency signal, the step impulse signal and the coupled signal, respectively.

将连续100个高频采样值u_b合并成一个过采样值U_a，过采样值U_a为有符号数。过采样处理后的电压信号仍然包含工频信号、行波信号及噪声。The specific method for over-sampling processing of the voltage sampling signal in step 2 is: performing sampling processing on the high-frequency voltage sampling signal obtained in step 1, so that the sampling frequency of the voltage signal becomes 10KHz and the number of sampling bits is 23. The change in sampling frequency and number of bits is achieved through an oversampling algorithm. Algorithm based on formula

Combine 100 consecutive high-frequency sampling values _ub into one over-sampling value U _a , and the over-sampling value U _a is a signed number. The voltage signal after oversampling still includes power frequency signal, traveling wave signal and noise.

单极点滤波器对工频信号衰减超过80dB，归一化频率为1000Hz；其衰减曲线如图2。通过衰减获得行波信号及噪声等弱冲击信号(暂态信号)。Wherein, step 3 extracts the transient signal in the oversampling signal, and the specific method is as follows: filtering out the power frequency signal included in the oversampling signal in step 2 through a digital start filter, the filter is designed as a single-pole filter, and the attenuation pole is 50Hz, The single-pole filter transfer function is

The single-pole filter attenuates the power frequency signal by more than 80dB, and the normalized frequency is 1000Hz; its attenuation curve is shown in Figure 2. Weak impulse signals (transient signals) such as traveling wave signals and noise are obtained by attenuation.

Among them, in step 4, the peak value processing of the transient signal, the specific method is: after passing through the digital start filter, the power frequency signal is attenuated, the weak shock signal is retained, the obtained weak signal is processed by the peak integrator, and the maximum value of the modulo value of the weak shock signal at the current moment is obtained. . The signal processed by the peak integrator is shown in Figure 5. The processed signal only has amplitude and no direction.

Wherein, step 5 starts the condition analysis and judgment, and the specific method is: comparing the current sampling point U _a and the reference sampling point U _(a-3) (the fourth last sampling point at the current moment) through the comparator, the signal strength change, and relying on the starting algorithm to separate Interference signal and fault traveling wave signal, judge the signal type.

Both the current sampling point and the reference sampling point are peak processed signals. The oversampling frequency is 10khz, there are 10,000 corresponding sampling points in 1s, the current sampling point is the latest sampling value, and the reference sampling point is set to the fourth last sampling value. Assuming that there are currently 500 sample values, the current sample value is the 500th sample value, and the reference sample point is the 497th sample value.

Judge the value of e according to the algorithm formula e=U _a -3U _(a-3) . e≥0 is considered as fault traveling wave, and the equipment starts; if e<0, it is considered as interference signal, and the equipment does not start.

Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to pay creative work. Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (5)

1. the weak impulse signal extraction and separation method based on power frequency sampling, is characterized in that, comprises the steps: Step 1. Obtain the voltage or current signal of the line under test; Step 2: Perform oversampling processing on the acquired voltage or current signal; Step 3, filtering out the power frequency signal contained in the oversampling signal of step 2 through the digital start filter, and extracting the transient signal in the oversampling signal; Step 4: Perform peak value processing on the transient signal; Step 5. Determine the type of the signal by comparing the intensity changes of the current sampling point signal and the reference sampling point signal, and realize the extraction and separation of weak shock signals based on power frequency sampling; In the step 1, acquiring the voltage or current signal of the line under test includes: a power frequency signal, a traveling wave signal and a noise signal; In the fifth step, by comparing the intensity changes of the current sampling point signal and the reference sampling point signal, it is determined that the type of the signal is specifically: Judging the value of e according to the algorithm formula e=U _a -3U _(a-3) ; wherein, U _a is the current sampling point signal, and U _(a-3) is the reference sampling point signal; e≥0 is judged as fault traveling wave; It is determined that e<0 is an interference signal. 2 . The method for extracting and separating weak impulse signals based on power frequency sampling according to claim 1 , wherein, in the second step, an oversampling process is performed on the acquired voltage or current sampling signal, and an oversampling algorithm is used to obtain an oversampling algorithm. 3 . A low frequency oversampled signal with a high number of sample bits. 3. The method for extracting and separating weak impulse signals based on power frequency sampling as claimed in claim 1, characterized in that, in the step 3, the transient signal in the oversampling signal is extracted, and the specific method is: start filtering by digitally The low-frequency oversampling signal is processed by the controller, the power frequency signal in the signal is filtered out, and the transient signal including the traveling wave signal and the noise signal is left. 4. The method for extracting and separating weak impulse signals based on power frequency sampling according to claim 1, wherein in the step 4, peak processing is performed on the transient signal, specifically: the extracted transient signal passes through the The peak value integrator processes to obtain the maximum value of the transient signal modulo at the current sampling time. 5. The method for extracting and separating weak impulse signals based on power frequency sampling according to claim 1, wherein the current sampling point signal is a sampling value closest to the current moment, and the reference sampling point is set to the penultimate Four sample values.

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