CN108880505A - Grounded screen potential difference filtering method based on starting decision element and wavelet transformation - Google Patents
Grounded screen potential difference filtering method based on starting decision element and wavelet transformation Download PDFInfo
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- CN108880505A CN108880505A CN201810337245.1A CN201810337245A CN108880505A CN 108880505 A CN108880505 A CN 108880505A CN 201810337245 A CN201810337245 A CN 201810337245A CN 108880505 A CN108880505 A CN 108880505A
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- relay protection
- wavelet
- transducer signal
- protection current
- current transducer
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H17/00—Networks using digital techniques
- H03H17/02—Frequency selective networks
- H03H17/0211—Frequency selective networks using specific transformation algorithms, e.g. WALSH functions, Fermat transforms, Mersenne transforms, polynomial transforms, Hilbert transforms
Abstract
The invention discloses a kind of grounded screen potential difference filtering methods based on starting decision element and wavelet transformation; this method is directed to the acquisition signal of relay protection current transformer; judge that whether signal meets limit, ungratified sampled data is further judged by the decision element based on form factor according to continuous 5 points of the constraint condition of starting element.If normal data, then directly export；If abnormal data, then exported again after being handled by wavelet transform filtering.Starting decision element is added in the present invention before traditional wavelet; signal can be judged in advance; greatly reduce calculation amount; overcome the bad disadvantage of traditional filtering algorithm timeliness; noise signal caused by grounded screen potential difference can be effective filtered out using wavelet transformation simultaneously; the accuracy for guaranteeing relay protection DATA REASONING, avoids the maloperation of relay protection device.
Description
Technical field
The present invention relates to it is a kind of based on starting decision element and wavelet transformation grounded screen potential difference filtering method, belong to after
Electric protection equipment filtering algorithm technical field.
Background technique
Ultra-high voltage transformer station generallys use GIS (Gas insulated substation) switchgear, works as disconnecting switch
When operation, tens times or even several hundred secondary arcings and arc extinguishing will occur in switch incision position.Its disturbance voltage generated is in bus and short
Continuous catadioptric on line is formed very fast transient overvoltage VFTO (very fast transient over-voltage).
VFTO leaks into earth mat by the protective ground wire of mutual inductor primary side, leads to earth mat local potential liter.Due to ultra-high voltage transformer station
Secondary cable generally use the mode of two sides earth, shielded layer both ends can generate grounded screen potential difference.The potential difference passes through coupling
It closes and generates harassing and wrecking electric current on the signal core line in secondary cable, cause relay protection DATA REASONING inaccurate, easily cause to connect
The maloperation of ground smart machine, it is therefore necessary to identification and the removing method for finding out interference signal, such as hardware filtering method and letter
Number Processing Algorithm, wherein for signal processing algorithm because it is simple and efficient, use is more extensive.
Harassing and wrecking signal caused by grounded screen potential difference is mainly shown as the high frequency transient signal of mutation, and tradition is based on time domain
Filtering algorithm is bad for such signal effect, and wavelet transformation can be according to the modulus maximum of electric current and noise with dimensional variation
The different characteristics showed carry out wavelet decomposition and reconstruction processing to signal, to effective filter out grounded screen potential difference
Caused noise signal.Under substation's actual condition, harassing and wrecking signal accounting is extremely low, adopts if directlying adopt wavelet transformation to all
Sample value is filtered, and computational efficiency is not high, easily leads to relay protection processing delay.Need the practical feelings for substation
Condition, improves traditional filtering algorithm, has not only guaranteed the reliability of relay protection of power system, but also improve at relay protection data
The timeliness of reason.
Summary of the invention
In order to solve the above technical problem, the present invention provides a kind of grounded screens based on starting decision element and wavelet transformation
Potential difference filtering method added starting and decision element before wavelet transformation, be pre-processed in advance to signal, guarantee after
The timeliness of electric protection DATA REASONING.
The present invention uses following technical scheme to solve above-mentioned technical problem：
The present invention provide it is a kind of based on starting decision element and wavelet transformation grounded screen potential difference filtering method include with
Lower step：
Step 1, relay protection current transducer signal is acquired；
Step 2, mutual to current time collected relay protection electric current according to continuous 5 points of the constraint condition of starting element
Whether sensor signal, which meets limit, is judged：If current time, collected relay protection current transducer signal met
Limit, then export current time collected relay protection current transducer signal, and return step 1 continue to execute it is next
The acquisition at moment operates；Otherwise then follow the steps 3；
Step 3, by the decision element based on form factor, judge current time collected relay protection Current Mutual Inductance
Whether device signal is normal data：If then exporting current time collected relay protection current transducer signal, and return
Step 1 continues to execute the acquisition operation of subsequent time；Otherwise then follow the steps 4；
Step 4, by wavelet transformation, place is filtered to current time collected relay protection current transducer signal
Reason, the relay protection current transducer signal after then output is filtered, and return step 1 continues to execute adopting for subsequent time
Collection operation.
As further technical solution of the present invention, relay protection current transformer is believed by acquisition system in step 1
It number is acquired in real time, wherein acquisition system includes sequentially connected current transformer, preposition simulation low-pass filter, sampling
Retainer, analog-digital converter, multicircuit switch and single-chip microcontroller.
As further technical solution of the present invention, step 2 is specially：
2.1, continuous 5 points of the constraint condition of starting element is：y′k=-yk-4+2yk-3-2yk-2+2yk-1+2cos100πTs
(yk-3-2yk-2+yk-1), wherein y 'kFor the predicted value of k moment relay protection current transducer signal, yk-1、yk-2、yk-3、yk-4
Respectively k-1, k-2, k-3, k-4 moment collected relay protection current transducer signal, TsFor relay protection Current Mutual Inductance
The sampling period of device signal；
2.2, ifThen k moment collected relay protection current transducer signal ykIt is unsatisfactory for stable state
Condition；Otherwise ykMeet limit, exports ykAnd continue to execute k+1 moment relay protection current transducer signal yk+1Acquisition
Whether meet the judgement of limit with signal；Wherein, ImFor system nominal current amplitude, ε1For the first threshold of setting.
As further technical solution of the present invention, step 3 is specially：
If R > ε2, then k moment collected relay protection current transducer signal ykIt is not normal data, continues to execute
Step 4；Otherwise, y is exportedkAnd return step 2 is continued to execute to k+1 moment collected relay protection current transducer signal
yk+1Whether the judgement of limit is met；Wherein,α is distortion occupied area,
N is to judge ykIt is
No is the selected decision element data window length of normal data, yk+2、yk+3、yk+4Respectively k+2, k+3, k+4 moment collect
Relay protection current transducer signal, TsFor the sampling period of relay protection current transducer signal, s is selected data
The waveform area of window,ε2For the second threshold of setting.
As further technical solution of the present invention, step 4 protects current time collected relay by wavelet transformation
Shield current transducer signal is filtered, specially：
A) wavelet basis function is selected, and determines wavelet decomposition number of plies l；
B) wavelet decomposition is carried out, systematic sampling is carried out to collected relay protection current transducer signal Y, it is then right
Sampled sequence carry out wavelet transform, obtain small echo expansion coefficient and, decomposition formula is：
Wherein, i=1,2 ..., l, M are the length of wavelet transformation data window, cA0As Y, cAiFor i-th layer of low frequency of decomposition
Wavelet coefficient, cDiFor i-th layer of high-frequency wavelet coefficient of decomposition, hm-2To select the corresponding low-frequency filter of wavelet basis, gm-2For choosing
Determine the corresponding high frequency filter of wavelet basis；
C) threshold value and selection threshold function table of wavelet coefficient, the meter of i-th layer of high-frequency wavelet coefficient after threshold transformation are determined
Calculating formula isWherein, th is threshold value,Wherein, σ is that noise criteria is poor；
D) basisCarry out wavelet reconstruction, the cA obtained after l reconstruct0" i.e.
For the relay protection current transducer signal Y' after filtering processing, wherein cAl"=cAl, cDi' for i-th layer after threshold transformation
High-frequency wavelet coefficient, cAi-1" it is (i-1)-th layer of low-frequency wavelet coefficients after reconstruct, cAi" it is i-th layer of low-frequency wavelet coefficients after reconstruct.
The invention adopts the above technical scheme compared with prior art, has the following technical effects：The present invention becomes in small echo
It added starting and decision element before changing, signal pre-processed in advance, then normal signal can be exported directly, be saved
The calculating time for having removed filtering algorithm overcomes the bad problem of traditional wavelet timeliness, guarantees that relay protection data are surveyed
The accuracy of amount improves the reliability of relay protection of power system.
Detailed description of the invention
Fig. 1 is flow chart of the method for the present invention.
Specific embodiment
Technical solution of the present invention is described in further detail with reference to the accompanying drawing：
As shown in Figure 1, the grounded screen potential difference filtering algorithm of the invention based on starting decision element and wavelet transformation, packet
Include following steps：
Step 1, relay protection current transducer signal is acquired in real time；
Acquisition system includes sequentially connected current transformer, preposition simulation low-pass filter, sampling holder, modulus turn
Parallel operation, multicircuit switch and single-chip microcontroller.
Step 2, starting element judges signal；
Due to flowing through stable power current in the steady-state process of electric system, in power grid, frequency 50Hz, amplitude by
The factors such as power supply, load and line parameter circuit value determine, remain unchanged in steady-state process.In the interference of grounded screen potential difference, power grid
In addition to containing power frequency steady-state component in electric current, transient can be also generated, the amplitude of transient decays at any time, is finally reached zero.
The general expression of power network current can be write as being superimposed for power frequency steady-state component and Attenuation-corrected algorithm：
Wherein, A is the amplitude of power current,For power current initial phase angle, B is the initial value of Attenuation-corrected algorithm, and τ is
The damping time constant of Attenuation-corrected algorithm.It is total in this expression formula there are four unknown quantity A,B and τ, so only it is to be understood that electricity
The first four sample point data of signal is flowed, substitution can solve this current expression, and the sampled value of the 5th point should also meet this
Expression formula, therefore the prediction to acquisition signal can be realized.Its expression formula is write out, and carries out Taylor expansion, can be obtained：
Wherein, yk、yk-1、yk-2、yk-3、yk-4For the sampled data at continuous 5 moment, TsFor the sampling period.
It arranges above-mentioned expression formula and can obtain the constraint condition of starting element and be：yk'=- yk-4+2yk-3-2yk-2+2yk-1+
2cos100πTs(yk-3-2yk-2+yk-1).So if the actual sample value y at k momentkWith predicted value y 'kAbsolute value of the difference divided by
System nominal current amplitude ImGreater than the threshold epsilon of setting1, i.e.,Show sampled value ykLimit is not met,
The judgement that step 3 carries out next step is needed to be implemented, determines whether it is normal data.Conversely, directly exporting yk, and continue to execute
K+1 moment relay protection current transducer signal yk+1Acquisition and signal whether meet the judgement of limit.
Step 3, decision element carries out signal judgement；
If primary system is in the critical point for entering transient process by steady-state process, this corresponding width of moment current sampling data
Value and initial phase can change, then can be using form factor to adopting to be unsatisfactory for the constraint expression formula of starting element
Integrate whether signal is judged as normal data.
The definition of form factor is：
Wherein, α is distortion occupied area, is passed through
It acquires, wherein N is to judge ykIt whether is the selected data window length of normal data, the present invention is chosen to be 20 points, both guaranteed
Accuracy, and guarantee timeliness.S is the waveform area of selected data window, can be by the sampling in same one piece of data window
Value instantaneous value carries out integral acquisition, i.e.,
Ideally, the molecule of form factor R is zero, and value is also zero；If there are abnormal data in sampled value, R's
Value will be not zero, and R is bigger, and it is more serious to represent sampled value distortion.So if form factor R is greater than the threshold epsilon of setting2, i.e. R
> ε2, show sampled value ykIt is not normal data, needs to be implemented step 4 and signal is filtered using filtering algorithm.It is no
Then, ykIt is normal data, return step 1 continues to execute acquisition operation next time.
Step 4, wavelet transformation is filtered；
Since the interference signal of grounded screen potential difference is mainly the transient signal being mutated, so filtering algorithm is chosen to be small echo
Transformation, is broadly divided into 4 parts：
A) wavelet basis function is selected, and determines wavelet decomposition number of plies l；
B) wavelet decomposition is carried out, systematic sampling is carried out to collected relay protection current transducer signal Y, it is then right
Sampled sequence carry out wavelet transform, obtain small echo expansion coefficient and, decomposition formula is：
Wherein, i indicates i-th layer of decomposition, i=1 in decomposable process, and 2 ..., l, M are the length of wavelet transformation data window, cA0
As Y, cAiFor i-th layer of low-frequency wavelet coefficients of decomposition, cDiFor i-th layer of high-frequency wavelet coefficient of decomposition, hm-2To select small echo
The corresponding low-frequency filter of base, gm-2To select the corresponding high frequency filter of wavelet basis.In this way, l times is carried out successively to decompose；
C) threshold value and selection threshold function table of wavelet coefficient, the meter of i-th layer of high-frequency wavelet coefficient after threshold transformation are determined
Calculating formula isWherein, th is threshold value,To calculate threshold value, wherein σ is noise
Standard deviation；
D) basisCarry out wavelet reconstruction, wherein i=l in restructuring procedure,
L-1 ..., 1, cAl"=cAl, cDi' for i-th layer of high-frequency wavelet coefficient after threshold transformation, cAi-1" low for (i-1)-th layer after reconstruct
Frequency wavelet coefficient.In this way, l reconstruct, obtained cA are carried out0" be filtered after relay protection current transformer
Signal Y', exports and return step 2 is continued to execute to yk+1Whether the judgement of limit is met.
The method of the present invention added starting and decision element before wavelet transformation, be pre-processed to signal, normal to believe
It number can directly be exported, greatly reduce the calculation amount of filtering algorithm, overcome the problems, such as that traditional wavelet timeliness is bad,
Not only it ensure that the accuracy of relay protection DATA REASONING, but also improved the reliability of relay protection of power system.
The above, the only specific embodiment in the present invention, but scope of protection of the present invention is not limited thereto, appoints
What is familiar with the people of the technology within the technical scope disclosed by the invention, it will be appreciated that expects transforms or replaces, and should all cover
Within scope of the invention, therefore, the scope of protection of the invention shall be subject to the scope of protection specified in the patent claim.
Claims (5)
1. the grounded screen potential difference filtering method based on starting decision element and wavelet transformation, which is characterized in that including following step
Suddenly：
Step 1, relay protection current transducer signal is acquired；
Step 2, according to continuous 5 points of the constraint condition of starting element, to current time collected relay protection current transformer
Whether signal, which meets limit, is judged：If current time, collected relay protection current transducer signal met stable state
Condition then exports current time collected relay protection current transducer signal, and return step 1 continues to execute subsequent time
Acquisition operation；Otherwise then follow the steps 3；
Step 3, by the decision element based on form factor, judge current time collected relay protection current transformer letter
It number whether is normal data：If then exporting current time collected relay protection current transducer signal, and return step 1
Continue to execute the acquisition operation of subsequent time；Otherwise then follow the steps 4；
Step 4, by wavelet transformation, current time collected relay protection current transducer signal is filtered,
Then the relay protection current transducer signal after output filtering processing, and return step 1 continues to execute the acquisition of subsequent time
Operation.
2. the grounded screen potential difference filtering method according to claim 1 based on starting decision element and wavelet transformation,
It is characterized in that, relay protection current transducer signal is acquired in real time by acquisition system in step 1, wherein acquisition system
System includes sequentially connected current transformer, preposition simulation low-pass filter, sampling holder, analog-digital converter, multipath conversion
Switch and single-chip microcontroller.
3. the grounded screen potential difference filtering method according to claim 1 based on starting decision element and wavelet transformation,
It is characterized in that, step 2 is specially：
2.1, continuous 5 points of the constraint condition of starting element is：y′k=-yk-4+2yk-3-2yk-2+2yk-1+2cos100πTs(yk-3-
2yk-2+yk-1), wherein y 'kFor the predicted value of k moment relay protection current transducer signal, yk-1、yk-2、yk-3、yk-4Respectively
K-1, k-2, k-3, k-4 moment collected relay protection current transducer signal, TsFor relay protection current transducer signal
Sampling period；
2.2, ifThen k moment collected relay protection current transducer signal ykIt is unsatisfactory for limit；
Otherwise ykMeet limit, exports ykAnd continue to execute k+1 moment relay protection current transducer signal yk+1Acquisition and letter
Number whether meet the judgement of limit；Wherein, I is system nominal current amplitude, ε1For the first threshold of setting.
4. the grounded screen potential difference filtering method according to claim 1 based on starting decision element and wavelet transformation,
It is characterized in that, step 3 is specially：
If R > ε2, then k moment collected relay protection current transducer signal ykIt is not normal data, continues to execute step
4；Otherwise, y is exportedkAnd return step 2 continues to execute relay protection current transducer signal y collected to the k+1 momentk+1It is
The no judgement for meeting limit；Wherein,α is distortion occupied area,
N is to judge ykIt is
No is the selected decision element data window length of normal data, yk+2、yk+3、yk+4Respectively k+2, k+3, k+4 moment collect
Relay protection current transducer signal, TsFor the sampling period of relay protection current transducer signal, s is selected data
The waveform area of window,ε2For the second threshold of setting.
5. the grounded screen potential difference filtering method according to claim 1 based on starting decision element and wavelet transformation,
It is characterized in that, step 4 is filtered place to current time collected relay protection current transducer signal by wavelet transformation
Reason, specially：
A) wavelet basis function is selected, and determines wavelet decomposition number of plies l；
B) wavelet decomposition is carried out, systematic sampling is carried out to collected relay protection current transducer signal Y, then to sampling
Sequence carry out wavelet transform, obtain small echo expansion coefficient and, decomposition formula is：
Wherein, i=1,2 ..., l, M are the length of wavelet transformation data window, cA0As Y, cAiFor i-th layer of low frequency wavelet of decomposition
Coefficient, cDiFor i-th layer of high-frequency wavelet coefficient of decomposition, hm-2To select the corresponding low-frequency filter of wavelet basis, gm-2It is small to select
The corresponding high frequency filter of wave base；
C) threshold value and selection threshold function table of wavelet coefficient are determined, the calculating of i-th layer of high-frequency wavelet coefficient after threshold transformation is public
Formula isWherein, th is threshold value,Wherein, σ is that noise criteria is poor；
D) basisCarry out wavelet reconstruction, the cA obtained after l reconstruct0" it is to filter
Wave treated relay protection current transducer signal Y', wherein cAl"=cAl, cDi' for i-th layer of high frequency after threshold transformation
Wavelet coefficient, cAi-1" it is (i-1)-th layer of low-frequency wavelet coefficients after reconstruct, cAi" it is i-th layer of low-frequency wavelet coefficients after reconstruct.
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Cited By (1)
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