CN101162838A - Low current neutral grounding system fault route selecting method by wavelet package decompose and correlation analysis - Google Patents

Abstract

The present invention relates to a small current grounding system fault line selecting method by wavelet package decomposition and relevant analysis, belonging to the power system relay protection technical field. The method comprises: starting the fault line selecting device and recording wave to acquire transient zero-order current on each of the feeder lines when bus zero-order voltage transient value exceeds limit; calculating energy on each of frequency bands of the transient zero-order current after wavelet package decomposition, summing the energy of transient zero-order current on all the lines according to frequency bands and selecting the frequency bands with the maximum and secondary value of energy and values as the characteristic frequency bands, applying relevant analysis method to line transient zero-order current on the selected characteristic frequency bands in order; and finally determining fault point integrating the relevant analysis results of two frequency bands. The method uses wavelet package decomposition and relevant analysis, thereby effectively using information (amplitude and phase) contained in fault transient process and reflecting differences between fault line and non-fault line to maximum degree. Principle analysis and simulations demonstrate that the method has precise and reliable line selection.

Description

A kind of low current neutral grounding system fault route selecting method that utilizes WAVELET PACKET DECOMPOSITION and correlation analysis

Technical field:

The present invention relates to a kind of low current neutral grounding system fault route selecting method that utilizes WAVELET PACKET DECOMPOSITION and correlation analysis, belong to the relay protection of power system technical field.

Background technology:

A large amount of research has been done by China aspect low-current ground fault line selection in recent years, has obtained certain achievement, but the problem of route selection accurately and reliably still is not well solved.Can not detect the development that earth fault has not only hindered power distribution automation rapidly and accurately, and safety, the stable operation of electrical network is had threat.

During small current neutral grounding system generation single phase ground fault, total system all residual voltage will occur, flow through in the electric current of fault point and contain the higher transient state amount of amplitude, fainter steady-state quantity after the relative fault, fault signature can fully be extracted and delineate to the transient state amount more, therefore uses the transient state amount will help to improve route selection sensitivity and reliability ^[1]

Wavelet packet analysis provides a kind of meticulousr analytical method for signal on the multiresolution analysis basis, frequency band is divided at many levels, therefore can not have the HFS of segmentation to do further decomposition to multiresolution analysis, can extract the transient state amount after the fault more accurately and efficiently.Mostly research in the past is route selection on a frequency band ^[2-8]Because the frequency content and the size of transient state amount are subjected to influence of various factors such as network parameter, fault moment, the frequency distribution of different circuit transient state amounts is always not in full accord yet.The characteristic spectra concentrated is always consistent because the complexity of transient process, each circuit transient current distribute, therefore only route selection under a frequency band, and its result is also unreliable, and should route selection on multiband ^[9-11]Document [9-11] route selection on the basis of multiband, but all only utilized the amplitude or the polarity of transient current, only utilized the part transient information, can not distinguish faulty line and non-fault line to greatest extent.

List of references:

[1]Chaari?O，Meunier?M，Brouaye?F?Wavelets：A?New?Tool?for?the?Resonant?GroundedPower?Distribution?Systems?Relaying[J].IEEE?Trans.On?Power?Delivery.1996，11(3).

[2] Yu Xiaorong, Liao Peijin, Peng Shutao etc. the application [J] of wavelet analysis in low current neutral grounding system fault route selecting. Power System and its Automation journal .2003,15 (4): 24-26.

[3] Jia Qingquan, Xiao Peng, Yang Yihan etc. the small echo selection method [J] of low current neutral grounding electric network single-phase earth fault. relay .2001,29 (3): 5-8.

[4] neat Zheng, Yang Yihan, Lin Rong etc. based on the single-phase grounded malfunction in grounded system of low current route selection research [J] of wavelet transformation and Wiener filtering technology. electric power network technique .2004,28 (13): 23-26.

[5] Wu Ling, Sun Ying. the application [J] of continuous wavelet transform in the single-phase grounded malfunction in grounded system of low current route selection. relay .2003,31 (11): 20-24.

[6] Song Hongyun, Lv Yanping, Xia Yunfei. the research [J] of 2 single-phase earth fault line selections of small current neutral grounding system. relay .2005,33 (10), 31-35.

[7] Su Zhantao, Lv Yanping. a kind of low current neutral grounding electric network single-phase earth fault route selection new method [J] based on wavelet packet analysis. electric power network technique .2004,28 (12); 30-33.

[8] lift a sail Pan Zhencun, Zhang Huifen etc. based on the small current earthing wire-selecting new criterion [J] of zero-sequence current transient state maximum. Automation of Electric Systems .2006,30 (4): 45-48.

[9] Wang Yaonan, Huo Bailin, Wang Hui etc. based on the new criterion [J] of the low current neutral grounding system fault route selecting of wavelet packet. Proceedings of the CSEE .2004,20 (6): 56-58.

[10] Pan Lu, Lv Yanping is in virtue. based on the low current neutral grounding system fault route selecting [J] of phase-frequency characteristic and multiband analysis. and Automation of Electric Systems .2007,31 (4): 76-79.

[11] Dai Jianfeng, Zhang Yanxia. study [J] based on the self adaptation distribution network fault line selection that multi-frequency is analyzed. Proceedings of the CSEE .2003,23 (5): 44-47.

[12] to shine year Cao Meiyue. electric power system resonance grounding [M]. Beijing: China Electric Power Publishing House, 2000.

[13] Cui Jintai (U.S.). wavelet analysis introduction [M]. Xi'an: publishing house of Xi'an Communications University, 1995

[14] Jia Qingquan, Xiao Peng, Yang Yihan. etc. the small echo selection method [J] of low current neutral grounding electric network single-phase earth fault. relay, 2001,29 (3): 5-8.

[15] Hu Changhua, Zhang Junbo, Xia Jun etc. based on the Design ﹠ Analysis of System [M] of MATLAB. Xi'an: publishing house of Xian Electronics Science and Technology University, 1999.

[16] hair roc, Sun Yaming, Zhang Zhaoning etc. the application [J] of wavelet packet in the one-phase earthing failure in electric distribution network route selection. electric power network technique, 2000,24 (6): 9-13.

[17] Wu Xiangqi. signal, system and signal processing [M]. Beijing: Electronic Industry Press .2000.

[18] Xue Yongrui, Xu Bingyin, low current grounding transient state direction protection principle researchs [J] such as Feng Zuren. Proceedings of the CSEE, 2003.23 (7): 51-56.

Summary of the invention

In order to overcome the deficiency of existing low current neutral grounding system fault route selecting method, the present invention proposes a kind of single-phase ground fault line selecting method of small-electric current grounding system that utilizes WAVELET PACKET DECOMPOSITION and correlation analysis.

Technical scheme of the present invention is as follows: a kind of method of utilizing WAVELET PACKET DECOMPOSITION that low current grounding is carried out route selection, carry out failure line selection by on-line measuring device, and it is characterized in that realizing through following process:

A, with bus residual voltage instantaneous value u _n(t) greater than K _uU _nAs the entry condition of fault, wherein K _uValue is 0.15, U _nBe the bus rated voltage, note each feeder line zero-sequence current of 1 cycle in fault front and back by line selection apparatus;

B, employing db10 wavelet packet are done 4 layers of decomposition to each feeder line transient zero-sequence current, and the route selection frequency bandwidth is 125Hz;

C, be calculated as follows each transient zero-sequence current, press frequency band again the energy of all circuit transient zero-sequence currents on each frequency band is sued for peace at the energy that removes on (4,0) outer each frequency band:

$\mathrm{\ϵ}=\underset{n}{\mathrm{\Σ}}{\left[{\mathrm{\ω}}_k^{\left(j\right)}\left(n\right)\right]}^2$

ω in the formula _k ^(j)(n) be WAVELET PACKET DECOMPOSITION (j, the k) coefficient under the sub-band, with the frequency band at the maximum of energy and value and second largest value place as feature band;

D, successively on the feature band of step C to fault after each bar circuit zero sequence current temporary state component waveform---wavelet coefficient carries out correlation analysis, ask for the coefficient correlation between the circuit, form correlation matrix M ₁, M ₂, ask for the integrated correlation coefficient ρ (j) of every circuit according to correlation matrix with respect to All other routes, j=1,2 ..., n, and with the mean value of the coefficient correlation that defines this circuit and the All other routes integrated correlation coefficient as this circuit:

Integrated correlation coefficient is found the solution by the following method: ask earlier M respectively ₁, M ₂The mean value of the every row element of matrix obtains ρ ₁, ρ ₂, use ρ again ₁, ρ ₂Average after the corresponding element addition and obtain integrated correlation coefficient ρ;

The integrated correlation coefficient ρ of E, each bar circuit of comparison, when the difference Δ ρ of minimax integrated correlation coefficient greater than threshold values ρ _SetThe time, then the circuit of Zui Xiao integrated correlation coefficient correspondence is faulty line; When the difference Δ ρ of minimax integrated correlation coefficient less than threshold values ρ _SetThe time, then decision-making system generation busbar grounding fault, wherein threshold values ρ _SetBe 0.5.

Theory analysis of the present invention is as follows:

1, single phase ground fault analysis

From the transient process of single-phase earthing, the transient state amount of earth current is bigger a lot of times than steady-state quantity, the time very short (1-2 cycle) that false voltage and fault current transient process continue, but contain abundant one of transient characteristic quantity.

System with neutral by arc extinction coil grounding is an example below, the transient process of analysis of failure.At instant of failure, both there had been power frequency component in the transient state earth current that flows through the fault point, also had higher-order of oscillation component.The transient state earth current that flows through the fault point be by fault relatively capacitance discharges electric current, non-fault relatively the charging current of electric capacity and the transient state inductive current of arc suppression coil are formed by stacking ^[12]The transient state earth current distributes and sees Fig. 1.

The expression formula of transient state earth current is:

In the formula: I _CmBe electric capacity stable state amplitude; ω _fAngular frequency for transient state free component oscillating component; τ _CTime constant for capacitor loop; I _LmSteady-state value for inductive current; τ _LTime constant for inductor loop.

From (1) formula as can be seen, the transient state amount of earth current equals the transient DC component sum of the transient state free component and the inductive current of capacitance current, and both amplitudes not only can not be cancelled out each other, and can also superpose, and the transient current amplitude can be bigger.Approach maximum during moment when fault occurs in phase voltage, the transient state capacitance current is more a lot of greatly than transient state inductive current, and the frequency of transient state is also very high, and the electric current that at this moment flows through arc suppression coil is very little, and is inoperative to transient state.So at the initial stage of fault, inductive current and capacitance current can not compensate mutually, the characteristic of its transient state earth current mainly is that the characteristic by the transient state capacitance current is determined.

Isolated neutral system is not because there is arc suppression coil, so its transient state earth current is exactly the transient state capacitance current.Therefore, no matter be that resonant earthed system or the isolated neutral system transient current can utilize fault the time comes route selection.

Analysis chart 1 can be drawn a conclusion:

(1) zero-sequence current appears in faulty line and non-fault line, and the non-fault line zero-sequence current equals the capacitive earth current of this circuit itself, and the faulty line zero-sequence current is the summation of total system non-fault line capacitive earth current.

(2) the leading residual voltage of non-fault line zero-sequence current is 90 °; 90 ° of faulty line zero-sequence current hysteresis residual voltages, promptly fault and non-fault zero-sequence current differ 180 °.

According to above analysis, the amplitude and the polarity that can fully utilize transient zero-sequence current realize route selection.

During single-phase earthing, the zero-sequence current of faulty line and certain non-fault line distributes and sees Fig. 2.

2, WAVELET PACKET DECOMPOSITION

2.1 the proposition of wavelet packet

The just global feature of signal of Fourier transform reflection, therefore be mainly used in the analysis of stationary signal, for the transient state non-stationary signal, it can't demarcate time location that changes and the violent degree that changes, and promptly Fourier transform is not demarcated and tolerance power the local distortion of signal.Multiresolution analysis can carry out effective time-frequency to signal and decompose, but owing to its yardstick changes by binary system, so relatively poor in its frequency resolution of high band, and relatively poor in its time resolution of low-frequency range.Wavelet packet analysis can provide a kind of meticulousr analytical method for signal, frequency band is divided at many levels, therefore can there be the HFS of segmentation to do further to decompose to multiresolution analysis, and can be according to the feature of analyzed signal, select frequency band adaptively, make it to be complementary with signal spectrum, thus when having improved-frequency resolution, have using value widely.

2.2 the definition of wavelet packet

With yardstick subspace V _jWith wavelets Subspace W _j, with a new subspace U _j ⁿThe unified sign, definition subspace U _j ⁿIt is function U _n(t) closure space, and U _j ²ⁿIt is function U _2n(t) closure space, and make U _n(t) satisfy following two yardstick equations ^[13]

$\left\{\begin{array}{c}{U}_{2n}\left(t\right)=\sqrt{2}\underset{k\∈Z}{\mathrm{\Σ}}h\left(k\right)U_n(2t-k)\\ U_{2n+1}\left(t\right)=\sqrt{2}\underset{k\∈Z}{\mathrm{\Σ}}g\left(k\right)U_n(2t-k)\end{array}\right.---\left(2\right)$

G (k) is the high pass filter coefficient in the formula (2); H (k) is a low-pass filter coefficients; G (k)=(1) ^kH (1-k), promptly two coefficients have orthogonality relation.Sequence { U by formula (1) structure _n(t) } (n ∈ Z wherein ₊) be called by basic function U _o(t)=the definite Orthogonal Wavelet Packet of Ф (t).

2.3 the decomposition of wavelet packet

By formula (2) as can be known, to n ∈ Z arbitrarily ₊(nonnegative integer) has

$U_{j+1}^n=U_j^{2n}\⊕U_j^{2n+1},j\∈Z;n\∈Z_{+}---\left(3\right)$

The various decomposition of wavelets Subspace are as follows like this

$\left\{\begin{array}{c}{W}_j=U_{j-1}^2\&CirclePlus;U_{j-1}^3\\ W_j=U_{j-k}^{2^k}\&CirclePlus;U_{j-k}^{2^k+1}\&CirclePlus;...\&CirclePlus;U_{j-k}^{2^{k+1}-1}\\ W_j={\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="S2007100664040E00011.png,S2007100664040E00021.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^{2^j}\&CirclePlus;{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="S2007100664040E00011.png,S2007100664040E00021.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^{2^j+1}\&CirclePlus;...\&CirclePlus;{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="S2007100664040E00011.png,S2007100664040E00021.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^{2^{j+1}-1}\end{array}\right.---\left(4\right)$

Corresponding to W _j, the j frequency range just be broken down into 2 ^kIndividual frequency sub-band, thus its localization property strengthened, overcome the deficiency of orthogonal wavelet transformation.The WAVELET PACKET DECOMPOSITION tree as shown in Figure 2.

2.4 choosing of wavelet function

Compare with the standard Fourier transform, used wavelet function has not uniqueness in the wavelet analysis, i.e. the selection of wavelet function has diversity.Analyze same problem with different wavelet basiss and can produce different effects, do not select wavelet function, adopt qualitative analysis in the reality in conjunction with experiment way relatively so have an acceptable principle at present.The little wave system of dbN is to use more wavelet function on the engineering ^[14], the characteristics of this little wave system are energy non-destructive and complimentary ^[11], and along with the increase of sequence number N, the time domain bearing length is elongated, the temporal locality variation; Filter length is elongated; The vanishing moment exponent number increases; Regularity increases, and the frequency domain locality improves.It is not very strict that the application of this paper requires temporal locality, the frequency domain locality is then had relatively high expectations, to prevent frequency alias.By adopting multiple small echo to carry out repeatedly emulation experiment relatively, basis experience in the past determines to select for use the db10 small echo again.

Fault transient state current from zero sequence current mutual inductor or the acquisition of zero-sequence current pass filter is carried out WAVELET PACKET DECOMPOSITION, its essence is and allow signal pass through the conjugation orthogonal filter group of one group high low pass combination, constantly division of signal is on different frequency ranges, the every effect of bank of filters once, sampling interval doubles, and number of data points then reduces by half ^[15]For similar frequency bands, what of the number of coefficient of wavelet decomposition are relevant with the filter length of used small echo, and filter length is long more, and then number is many more, and the sensitivity of route selection criterion is corresponding high more.But can not pursue the length of filter simply,, reduce the reliability of criterion because for the more and more serious distribution network system of Harmonic Interference, the increase of the number of coefficient of wavelet decomposition also may be introduced more disturbing factor.This also is an one of the main reasons of selecting the db10 small echo.

2.5 the WAVELET PACKET DECOMPOSITION number of plies

Consider that the free-running frequency of transient state capacitance current generally concentrates on 300-1500Hz ^[12], getting sample frequency in the emulation is 4000Hz, sampled data window length is got each 1 week of short circuit front and back: when carrying out WAVELET PACKET DECOMPOSITION, what choose is the db10 small echo; Consider that the frequency bandwidth that finally is used for failure line selection should select suitably, if meticulous, then the corresponding sampling number of frequency band is very few, will reduce the reliability of failure line selection; If wide, then information content increases, and will be unfavorable for further signal analysis ^[16], the comprehensive pros and cons of this two aspect, the route selection frequency bandwidth is decided to be 125Hz, according to two fens characteristics of frequency of wavelet packet, decomposes the number of plies and should be 4 layers.

Adopt the db10 wavelet packet that the circuit transient zero-sequence current is done 4 layers of decomposition, remove the lowest band (4,0) at power frequency place after, the frequency band that energy is bigger has comprised the principal character of transient state capacitance current ^[18]Can get rid of the influence of power frequency amount and other non-feature bands after the WAVELET PACKET DECOMPOSITION.

2.6 determining of feature band

Adopt the db10 wavelet packet that the circuit transient zero-sequence current is done 4 layers of decomposition, remove the lowest band (4,0) at power frequency place after, the frequency band that energy is bigger has comprised the principal character of transient state capacitance current ^[18]Therefore, press frequency band with the summation of the energy of all circuit transient zero-sequence currents, energy and the bigger inevitable concentrated expression of frequency band the constitutive relations between each circuit.Calculate each circuit transient zero-sequence current at the energy that removes on (4,0) outer each frequency band by (5) formula, and calculate the energy and the value of all circuit transient zero-sequence currents on each frequency band by frequency band, selecting the energy and the maximum of value and the frequency band at second largest value place is feature band.

$\mathrm{\&epsiv;}=\underset{n}{\mathrm{\&Sigma;}}{\left[{\mathrm{\&omega;}}_k^{\left(j\right)}\left(n\right)\right]}^2---\left(5\right)$

ω in the formula (5) _k ^(j)(n) be WAVELET PACKET DECOMPOSITION (j, k) coefficient under the sub-band.

Faulty line and certain non-fault line zero-sequence current, the coefficient of wavelet decomposition on two feature bands is shown in Fig. 4,5.

3, correlation analysis

Correlation function is the very important numerical characteristic that time-frequency is described the random signal statistical nature.Deterministic signal can be regarded as stably and has the special case of ergodic random signal, thereby its basic conception and definition (stationary random process) equally also are suitable for deterministic signal and do correlation analysis ^[17]The physical meaning that its inherence is arranged from the theory of correlation analysis, establishing x (t) and y (t) is the real signal waveform of 2 finite energies.For studying the difference between them, weigh it at difference similarity degree constantly, introduce

ε＝x(t)-λy(t+τ) (6)

ε is a constant in the formula (6).

According to the mean square error minimum criteria, get ε ²Time average W weigh similitude between the two, then have

$W=\frac{1}{2T}{\&Integral;}_{-T}^T{\mathrm{\&epsiv;}}^2\mathrm{dt}=\frac{1}{2T}{\&Integral;}_{-T}^T{[x\left(t\right)-\mathrm{\&lambda;y}(t+t)]}^2\mathrm{dt}---\left(7\right)$

Order $\frac{\mathrm{dW}}{\mathrm{dt}}=0,$ Try to achieve best λ _OptMake two waveforms the most similar, and with its substitution formula (7), the W that obtains minimum is

$W_{\min }=\frac{1}{2T}{\&Integral;}_{-T}^T{x}^2\left(t\right)\mathrm{dt}[1-{\mathrm{\&rho;}}_{\mathrm{xy}}^2\left(\mathrm{\&tau;}\right)]---\left(8\right)$

ρ in the formula (8) _XyThe expression formula of the discrete sampling sequence of respective signal x (t) and y (t) in certain data window is

${\mathrm{\&rho;}}_{\mathrm{xy}}=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}x\left(n\right)y\left(n\right){\left[\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}x{\left(n\right)}^2\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}y{\left(n\right)}^2\right]}^{-1/2}---\left(9\right)$

By formula (9) as can be known, ρ is big more, and W is more little, and two waveforms are similar more.When ρ=1, then W=0 illustrates that x (t) is similar fully with y (t).ρ is defined as coefficient correlation for this reason.Formula (9) has been represented the dependency relation that x (t), y (t) waveform are sampled in certain data window inter-sync, combined reaction the comprehensive phase relation and the amplitude information of each frequency component in 2 signals, and be not the simple phase relation of single-frequency, effectively overcome the defective that the single information that only relies on fault-signal is come detection failure.

4, route selection criterion

According to above 3 point analysis, to the transient zero-sequence current of WAVELET PACKET DECOMPOSITION, carry out correlation analysis after, can form the route selection criterion:

1), ρ _Max-ρ _Min＞ρ _Set, j=1,2 ..., n, ρ _MinCorresponding feeder line is fault feeder (ρ _SetGet 0.5);

2), ρ _Max-ρ _Min＜ρ _Set, j=1,2 ..., n judges busbar fault (ρ _SetGet 0.5).

The present invention compared with prior art has following advantage:

1), usually, when near phase voltage is crossed null value single phase ground fault taking place, the fault transient state current amplitude is very little, causes the route selection difficulty, and the present invention can overcome the little influence of fault transient state current under the situation of glitch angle effectively, realizes correct route selection.

2), the present invention has stronger arc resistant grounded capacity; Be subjected to the influence of neutral point operational mode less; The free-running frequency of transient state capacitance current generally concentrates on 300-1500Hz ^[12], adopt 12 A/D to record ripple with the 4kHz sample frequency, be enough to meet the demands.

3), the present invention when the short-term fault, can overcome of the influence of sound long line to earthing capacitance current; Very strong noise resisting ability is arranged; Also correctly route selection during high resistance ground.

4), the present invention utilizes WAVELET PACKET DECOMPOSITION; removed the influence of power frequency amount and other non-feature bands; and utilize relevant function method; can effectively utilize the information (amplitude, phase place) that comprises in the fault transient process more; reflect the difference of faulty line and non-fault line to greatest extent, improve protection nargin.Simultaneously, the situation that causes fault signature to be fallen into oblivion because of interference and measure error can not appear in the route selection on two frequency bands of this method, can improve the sensitivity and the reliability of failure line selection.

Description of drawings:

Fig. 1 single-phase-to-ground current distributes.

Fig. 2 circuit zero-sequence current.

Fig. 3 wavelet packet binary tree.

The coefficient of wavelet decomposition of Fig. 4 circuit zero-sequence current on first feature band.

The coefficient of wavelet decomposition of Fig. 5 circuit zero-sequence current on second feature band.

Fig. 6 failure line selection algorithm flow chart.

Embodiment:

During small current neutral grounding system generation single phase ground fault, utilize above-mentioned principle can realize perfect failure line selection.The specific implementation flow process as shown in Figure 6.

Specific implementation step of the present invention is as follows:

1. as bus residual voltage instantaneous value u _n(t) greater than K _uU _n, fault line selection device starts immediately, notes each feeder line zero-sequence current, wherein K of 1 cycle in fault front and back _uGeneral value is 0.15, U _nExpression bus rated voltage;

2. with the db10 small echo each feeder line zero-sequence current is carried out four layers of wavelet decomposition.

3. after removing the lowest band (4,0) at power frequency place, the frequency band that energy is bigger has comprised the principal character of transient state capacitance current ^[18]Therefore, press frequency band with the summation of the energy of all circuit transient zero-sequence currents, energy and the bigger inevitable concentrated expression of frequency band the constitutive relations between each circuit.Calculate each circuit transient zero-sequence current at the energy that removes on (4,0) outer each frequency band by (5) formula, and calculate the energy and the value of all circuit transient zero-sequence currents on each frequency band by frequency band, selecting the energy and the maximum of value and the frequency band at second largest value place is feature band.

$\mathrm{\&epsiv;}=\underset{n}{\mathrm{\&Sigma;}}{\left[{\mathrm{\&omega;}}_k^{\left(j\right)}\left(n\right)\right]}^2---\left(5\right)$

ω in the formula (5) _k ^(j)(n) be WAVELET PACKET DECOMPOSITION (j, k) coefficient under the sub-band.

Successively on two feature bands to fault after the waveform (wavelet coefficient) of each bar circuit zero sequence current temporary state component carry out correlation analysis in twos, ask for the coefficient correlation in twos between the circuit, form correlation matrix M ₁, M ₂, ask for every circuit relatively and the integrated correlation coefficient ρ (j) of All other routes according to the pairwise correlation coefficient matrix, j=1,2 ..., n.(mean value of coefficient correlation that defines this circuit and All other routes is as the integrated correlation coefficient of this circuit)

Integrated correlation coefficient is found the solution by the following method: ask earlier M respectively ₁, M ₂The mean value of the every row element of matrix obtains ρ ₁, ρ ₂, use ρ ₁, ρ ₂Average after the corresponding element addition and obtain integrated correlation coefficient ρ.

5. the integrated correlation coefficient ρ of each bar circuit relatively, when the difference Δ ρ of minimax integrated correlation coefficient greater than a threshold values ρ _Set(ρ _SetGet 0.5) time, the circuit of minimum integrated correlation coefficient correspondence is faulty line.When the difference Δ ρ of minimax integrated correlation coefficient less than a threshold values ρ _Set(ρ _SetGet 0.5) time, decision-making system generation busbar grounding fault then.

Claims (1)

1. a method of utilizing WAVELET PACKET DECOMPOSITION that low current grounding is carried out route selection is carried out failure line selection by on-line measuring device, it is characterized in that realizing through following process:

A, with bus residual voltage instantaneous value u _n(t) greater than K _uU _nAs the entry condition of fault, wherein K _uValue is 0.15, U _nBe the bus rated voltage, note each feeder line zero-sequence current of 1 cycle in fault front and back by line selection apparatus;

B, employing db10 wavelet packet are done 4 layers of decomposition to each feeder line transient zero-sequence current, and the route selection frequency bandwidth is 125Hz;

C, be calculated as follows each transient zero-sequence current, press frequency band again the energy of all circuit transient zero-sequence currents on each frequency band is sued for peace at the energy that removes on (4,0) outer each frequency band:

$\mathrm{\&epsiv;}=\underset{n}{\mathrm{\&Sigma;}}{\left[{\mathrm{\&omega;}}_k^{\left(j\right)}\left(n\right)\right]}^2$

ω in the formula _k ^(j)(n) be WAVELET PACKET DECOMPOSITION (j, the k) coefficient under the sub-band, with the frequency band at the maximum of energy and value and second largest value place as feature band;

D, successively on the feature band of step C to fault after each bar circuit zero sequence current temporary state component waveform---wavelet coefficient carries out correlation analysis, ask for the coefficient correlation between the circuit, form correlation matrix M ₁, M ₂, ask for the integrated correlation coefficient ρ (j) of every circuit according to correlation matrix with respect to All other routes, j=1,2 ..., n, and with the mean value of the coefficient correlation that defines this circuit and the All other routes integrated correlation coefficient as this circuit:

Integrated correlation coefficient is found the solution by the following method: ask earlier M respectively ₁, M ₂The mean value of the every row element of matrix obtains ρ ₁, ρ ₂, use ρ again ₁, ρ ₂Average after the corresponding element addition and obtain integrated correlation coefficient ρ;

The integrated correlation coefficient ρ of E, each bar circuit of comparison, when the difference Δ ρ of minimax integrated correlation coefficient greater than threshold values ρ _SetThe time, then the circuit of Zui Xiao integrated correlation coefficient correspondence is faulty line; When the difference Δ ρ of minimax integrated correlation coefficient less than threshold values ρ _SetThe time, then decision-making system generation busbar grounding fault, wherein threshold values ρ _SetBe 0.5.

Images