CN116908605A - Fault line identification method, device, terminal and medium based on transient small current - Google Patents
Fault line identification method, device, terminal and medium based on transient small current Download PDFInfo
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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Abstract
The invention discloses a fault line identification method, a device, a terminal and a medium based on transient small current, wherein the method is characterized in that a DWT is utilized to decompose the fault line identification method by collecting bus zero sequence voltage of a power system and transient zero sequence current signals of all outgoing lines, a wavelet energy spectrum of the line is drawn, wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrum are selected to reconstruct the signal, a Prony algorithm is adopted to fit the reconstructed signal, the amplitude and the phase of the reconstructed signal are estimated, the zero sequence transient admittance of the line is calculated, and the fault line is selected according to preset setting admittance and line selection criteria. Therefore, the embodiment of the invention can preprocess zero sequence voltage and zero sequence current transient signals by utilizing wavelet decomposition, retain fault characteristic information by wavelet packet energy spectrum and wavelet reconstruction, estimate transient zero sequence admittance by utilizing Prony algorithm, select fault lines and improve the accuracy of small current grounding fault line selection.
Description
Technical Field
The invention relates to the technical field of line faults, in particular to a fault line identification method, device, terminal and medium based on transient small current.
Background
Of all faults occurring in the distribution network of the power system, the single-phase ground fault occupies a maximum of 70%. When single-phase earth fault occurs, the residual current is still small, the line voltage is symmetrical, and the power system can still work for 1-2 h. With the development of economy and the implementation of the policy of "up-down" and down-up ", the cable lines are becoming widely used, and the capacitive current generated after a single-phase earth fault occurs in the power system is also increased, and the long-term indirect operation of the capacitive current causes more serious two-phase short circuit and intermittent overvoltage. Therefore, a faulty line must be found and excluded in time.
When single-phase earth fault occurs, an obvious transient process often exists, the process contains rich fault information, and the earth fault line can be selected by extracting fault characteristics. At present, the error rate of the low-current ground fault line selection method is higher, the traditional trial-and-error method has to be used for judging the fault line again, the time and the labor are wasted, and the power supply reliability of a power system is seriously affected. To solve this problem, researches for improving the accuracy of the small current ground fault line selection are increasing. The first research is on a line selection method based on the zero sequence current fundamental component, however, the line selection becomes unreliable due to the small signal amplitude. In addition, the signal parameter estimation method is widely applied to a transient system, and the Prony algorithm is widely applied because the estimation parameter is accurate, but the method is extremely easy to be influenced by noise, and the Prony algorithm is difficult to find the optimal order, easy to cause misjudgment and difficult to be applied to engineering practice. Therefore, how to improve the accuracy of small current ground fault line selection still has a great challenge.
Disclosure of Invention
The invention provides a fault line identification method, device, terminal and medium based on transient small current, which are characterized in that the transient signals of zero sequence voltage and zero sequence current are preprocessed by utilizing wavelet decomposition, fault characteristic information is reserved by wavelet packet energy spectrum and wavelet reconstruction, the transient zero sequence admittance is estimated by utilizing Prony algorithm, a fault line is selected, and the accuracy of small current grounding fault line selection is improved.
In order to achieve the above object, in a first aspect, an embodiment of the present invention provides a fault line identification method based on transient small current, including:
collecting bus zero sequence voltage of a power system and transient zero sequence current signals of all outgoing lines;
decomposing the first half-wave periodic signals of the zero-sequence voltage and transient zero-sequence current signals by using a DWT, drawing a wavelet energy spectrum of a circuit, and selecting wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrum for signal reconstruction;
fitting the reconstructed signal by adopting a Prony algorithm, estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the circuit according to the amplitude and the phase;
judging whether the line has a ground fault or not according to a preset setting admittance and a line selection criterion, if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line.
As an improvement of the above scheme, the decomposing the first half-wave periodic signal of the zero-sequence voltage and transient zero-sequence current signals by using DWT, drawing a wavelet energy spectrum of a line, and selecting a wavelet coefficient of maximum energy and sub-maximum energy of the wavelet energy spectrum to reconstruct the signal, specifically includes:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
As an improvement of the above scheme, the fitting of the reconstructed signal by using the Prony algorithm, estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase, specifically includes:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sample function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is the conjugate of the linear combination of the exponential functions of the p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signal, r (p, p) is the (p, p) th sample function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1)] T 。
As an improvement of the above solution, the method for setting the preset setting admittance specifically includes:
according to the zero sequence voltage and zero sequence current of single-phase earth fault, obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of arc suppression coils set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
In a second aspect, an embodiment of the present invention provides a fault line identification device based on transient small current, including:
the acquisition module is used for acquiring the bus zero sequence voltage of the power system and the transient zero sequence current signals of all outgoing lines;
the decomposition module is used for decomposing the first half-wave periodic signal of the zero-sequence voltage and transient zero-sequence current signals by utilizing a DWT, drawing a wavelet energy spectrum of a circuit, and selecting the wavelet coefficients of the maximum energy and the sub-maximum energy of the wavelet energy spectrum for signal reconstruction;
the fitting module is used for fitting the reconstructed signals by adopting a Prony algorithm, estimating the amplitude and the phase of the reconstructed signals, and calculating the zero sequence transient admittance of the circuit according to the amplitude and the phase;
the judging module is used for judging whether the line has a ground fault or not according to preset setting admittance and line selection criteria, if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line.
As an improvement of the above solution, the decomposition module is specifically configured to:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
As an improvement of the above solution, the fitting module is specifically configured to:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sampleThe function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is the conjugate of the linear combination of the exponential functions of the p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signal, r (p, p) is the (p, p) th sample function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1)] T 。
As an improvement of the above solution, the method for setting the preset setting admittance specifically includes:
according to the zero sequence voltage and zero sequence current of single-phase earth fault, obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of arc suppression coils set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
In a third aspect, an embodiment of the present invention correspondingly provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, where the processor implements the above-mentioned fault line identification method based on transient small currents when executing the computer program.
In addition, the embodiment of the invention also provides a computer readable storage medium, which comprises a stored computer program, wherein the equipment where the computer readable storage medium is located is controlled to execute the fault line identification method based on the transient small current when the computer program runs.
Compared with the prior art, the fault line identification method, device, terminal and medium based on transient small current are disclosed in the embodiment of the invention, through collecting bus zero sequence voltage of a power system and transient zero sequence current signals of all outgoing lines, decomposing first half-wave periodic signals of the zero sequence voltage and the transient zero sequence current signals by using a DWT, drawing a wavelet energy spectrum of a line, selecting wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrum for signal reconstruction, fitting the reconstructed signals by adopting a Prony algorithm, estimating amplitude and phase of the reconstructed signals, calculating zero sequence transient admittance of the line according to the amplitude and the phase, judging whether the line has a ground fault according to preset setting admittance and line selection criteria, if the zero sequence admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line. Therefore, the embodiment of the invention can preprocess zero sequence voltage and zero sequence current transient signals by utilizing wavelet decomposition, retain fault characteristic information by wavelet packet energy spectrum and wavelet reconstruction, estimate transient zero sequence admittance by utilizing Prony algorithm, select fault lines and improve the accuracy of small current grounding fault line selection.
Drawings
Fig. 1 is a schematic flow chart of a fault line identification method based on transient small current according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a fault line identification device based on transient small current according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that the terms "comprises" and "comprising," along with any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed or inherent to such process, method, article, or apparatus, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
It should be noted that, in the system without grounding, a single-phase earth fault occurs, and the first half-wave period of the zero-sequence current and the zero-sequence voltage contains fault characteristic information, that is, the transient zero-sequence current of the fault line is greater than that of the non-fault line, the phase of the zero-sequence current of the fault line is 180 degrees different from that of the transient zero-sequence voltage, and the non-fault line is in phase with the zero-sequence voltage. Because the Prony algorithm can accurately estimate the first half-wave period signal parameter, the Prony algorithm can be utilized to estimate parameters for transient zero-sequence current and transient zero-sequence voltage signals. Meanwhile, in order to improve the practicability of the method, the wavelet packet decomposition can be utilized to preprocess the zero sequence voltage and the zero sequence current, and a novel DWT-Prony method for extracting the transient zero sequence voltage and the transient zero sequence current parameters based on the wavelet packet and the Prony algorithm is further provided. The time window cuts off the acquired zero-sequence voltage and zero-sequence current data to decompose wavelet packets, acquires an energy spectrum, reserves two wavelet coefficients with the largest duty ratio in the energy spectrum, and reconstructs signals. And carrying out parameter estimation on the reconstructed signal by adopting a Prony algorithm to obtain a transient zero sequence admittance, judging the transient zero sequence admittance, and selecting a fault line.
Referring to fig. 1, fig. 1 is a flow chart of a fault line identification method based on transient small current according to an embodiment of the present invention, where the fault line identification method based on transient small current includes steps S11 to S14:
s11: collecting bus zero sequence voltage of a power system and transient zero sequence current signals of all outgoing lines;
in the half-cycle signal after the occurrence of the small-current ground fault, the zero-sequence voltage and current signals are generally hundreds to thousands of hertz, in order to ensure that the acquired signals are not distorted, a sampling frequency of 10kHz is adopted in simulation, and a sampling frequency-reducing method is selected to reduce to 5kHz in analysis in consideration of Nyquist criterion.
Meanwhile, it should be noted that determination of the number of parent wavelet and decomposition level is also important, daubechies (dbN) is selected as parent wavelet to perform DWT, N is the order of wavelet, dbN is a biorthogonal wavelet, the higher the value of N, the smaller the overlapping area of the frequency band overlapping frequency band, the higher the regularity, and the smoother the wavelet base and the reconstructed signal, so db44 is selected as parent wavelet.
S12: decomposing the first half-wave periodic signals of the zero-sequence voltage and transient zero-sequence current signals by using a DWT, drawing a wavelet energy spectrum of a circuit, and selecting wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrum for signal reconstruction;
Specifically, in step S12, specifically, the method includes:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
Note that, given a certain original signal s= (S) 1 ,S 2 ,S 3 ,□,S N ) Decomposing it into an approximation signal a by Discrete Wavelet Transform (DWT) n And n detail signals D y Then approximate signal A n And detail signal D y Is of the frequency bandwidth of
The energy characteristic value of each frequency band is defined as:
where y=1, 2, n, E (D y ) For the i-th bandEnergy characteristic value D corresponding to the node signal y For the detail signal of the i-th band,
the original signal satisfies the relation as
S＝A n +D n +D n-1 +…+D 1 。
The number of decomposition layers is mainly determined by the power frequency, and excessive number of decomposition layers can reduce the inherent change and trend of signals, and the excessive number of decomposition layers can lead to the decomposition of signals to reach the desired effect. The specific method of reconstructing the signal is to keep the interested approximate signal, the needed line selection characteristic information is generally contained in the largest first two wavelet coefficients, and the high-frequency detail signal threshold value during reconstruction is directly selected to be 0, namely, other detail signals are reset to zero, so that the reconstruction of the signal is completed. Thus, the reconstructed signal only retains the power frequency and transient main frequency signals.
S13: fitting the reconstructed signal by adopting a Prony algorithm, estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the circuit according to the amplitude and the phase;
Specifically, in step S13, specifically, the method includes:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sample function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is the conjugate of the linear combination of the exponential functions of the p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signal, r (p, p) is the (p, p) th sample function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1)] T 。
It should be noted that, the Prony algorithm was first proposed by Prony, a french mathematicist, to construct a mathematical model of a signal using a linear combination of exponential functions, and for a linear combination of exponential functions of p arbitrary magnitudes, phases, frequencies, and attenuation factors, the general expression is:
wherein f w Represents the w-th frequency, A w 、θ w The amplitude and the phase of the w-th frequency component, alpha w As an attenuation factor Δt is the time interval of sampling.
The constant coefficient linear difference equation is
S14: judging whether the line has a ground fault or not according to a preset setting admittance and a line selection criterion, if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line.
Specifically, in step S14, the preset setting method of the setting admittance specifically includes:
according to the zero sequence voltage and zero sequence current of single-phase earth fault, obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of arc suppression coils set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
It should be noted that, after the neutral point is not effectively grounded, the fault zero sequence voltage and zero sequence current can be expressed as a direct current component, a power frequency component and a transient main frequency component attenuated exponentially, namely:
wherein u is dc 、i dc Represents the direct current component, u 01 、i 01 Represents the power frequency component, u 0d 、i 0d Representing the transient dominant frequency component.
The above can be further written as:
wherein omega is u01 、ω i01 、ω u0d 、ω i0d 、α u0d 、α i0d Representing the corresponding frequency, phase and attenuation factors.
Due to transient main frequency zero sequence voltage frequency omega u0d Attenuation factor alpha u0d And transient main frequency zero sequence current frequency omega i0d Attenuation factor alpha i0d Approximately equal, collectively denoted ω u0d And alpha u0d . The transient dominant frequency component may be written as:
definition of transient dominant frequency admittance Y 0d The ratio of the transient main frequency current phasor to the transient main frequency voltage phasor is:
when a single-phase grounding fault occurs in a low-current grounding system, the line resistance and attenuation factor components are ignored, and the transient main frequency admittance of the fault line can be written as:
the transient dominant frequency admittance of the non-faulty line is:
wherein C is 0Σ 、C 0f 、C 0h The sum of the earth capacitances of all lines in the power system, the earth capacitance of the fault line and the earth capacitance of the non-fault line are respectively;
the transient state dominant frequency admittance of the fault line and the transient state dominant frequency admittance of the non-fault line have obvious differences, and the amplitude of the transient state dominant frequency admittance of the fault line is large and is positioned on the negative half axle of the admittance vector diagram; the transient dominant frequency admittance amplitude of the non-fault line is small and is positioned on the positive half axle of the admittance vector diagram.
When the number of the wire outlet loops of the complex system or the same bus is large, the influence of the arc suppression coil needs to be considered, and a preset setting admittance Y is set set ：
Where Lk is the arc suppression coil inductance.
Fig. 2 is a schematic structural diagram of a fault line identification device based on transient small current, which is provided by an embodiment of the present invention, and includes:
The acquisition module 21 is used for acquiring bus zero sequence voltage of the power system and transient zero sequence current signals of all outgoing lines;
the decomposition module 22 is configured to decompose the first half-wave periodic signal of the zero-sequence voltage and transient zero-sequence current signals by using a DWT, draw a wavelet energy spectrum of a line, and select a wavelet coefficient of maximum energy and sub-maximum energy of the wavelet energy spectrum to perform signal reconstruction;
the fitting module 23 is configured to fit the reconstructed signal by using a Prony algorithm, estimate an amplitude and a phase of the reconstructed signal, and calculate a zero sequence transient admittance of the line according to the amplitude and the phase;
the judging module 24 is configured to judge whether the line has a ground fault according to a preset tuning admittance and a line selection criterion, if the zero-sequence transient admittance is smaller than the preset tuning admittance, the line is a faulty line, and if the zero-sequence transient admittance is greater than the preset tuning admittance, the line is a non-faulty line.
As a preferred embodiment, the decomposition module 22 is specifically configured to:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
Decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
As a preferred embodiment, the fitting module 23 is specifically configured to:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
Calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sample function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is a co-ordination of the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signalYoke, r (p, p) is the (p, p) th sample function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1) ] T 。
As a preferred embodiment, the method for setting the preset setting admittance specifically includes:
according to the zero sequence voltage and zero sequence current of single-phase earth fault, obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of arc suppression coils set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
The fault line identification device based on the transient small current provided by the embodiment of the invention can realize all the processes of the fault line identification method based on the transient small current in the embodiment, and the actions and the realized technical effects of each module in the device are respectively corresponding to the actions and the realized technical effects of the fault line identification method based on the transient small current in the embodiment, and are not repeated here.
The embodiment of the invention correspondingly provides a terminal device, which comprises: a processor, a memory, and a computer program stored in the memory and executable on the processor. The steps in the fault line identification method embodiment based on transient small current are realized when the processor executes the computer program. Or the processor executes the computer program to realize the functions of each module in the fault line identification device embodiment based on the transient small current.
The terminal equipment can be computing equipment such as a desktop computer, a notebook computer, a palm computer, a cloud server and the like. The terminal device may include, but is not limited to, a processor, a memory. It will be appreciated by those skilled in the art that the schematic diagram is merely an example of a terminal device and does not constitute a limitation of the terminal device, and may include more or less components than illustrated, or may combine certain components, or different components, e.g., the terminal device may further include an input-output device, a network access device, a bus, etc.
The processor may be a central processing unit, but also other general purpose processors, digital signal processors, application specific integrated circuits, field programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general purpose processor may be a microprocessor or the processor may be any conventional processor or the like, which is a control center of the terminal device, and which connects various parts of the entire terminal device using various interfaces and lines.
The memory may be used to store the computer program and/or module, and the processor may implement various functions of the terminal device by running or executing the computer program and/or module stored in the memory and invoking data stored in the memory. The memory may mainly include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program (such as a sound playing function, an image playing function, etc.) required for at least one function, and the like; the storage data area may store data (such as audio data, phonebook, etc.) created according to the use of the handset, etc. In addition, the memory may include high-speed random access memory, and may also include non-volatile memory, such as a hard disk, memory, plug-in hard disk, smart memory card, at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage device.
It should be noted that the above-described apparatus embodiments are merely illustrative, and the units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed over a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
The embodiment of the invention also provides a computer readable storage medium, which comprises a stored computer program, wherein the computer program is used for controlling equipment where the computer readable storage medium is located to execute the fault line identification method based on the transient small current according to the embodiment.
In summary, the method, the device, the terminal and the medium for identifying a fault line based on transient small current disclosed in the embodiments of the present invention are used to collect bus zero sequence voltage of an electric power system and transient zero sequence current signals of each outgoing line, decompose first half-wave periodic signals of the zero sequence voltage and the transient zero sequence current signals by using DWT, draw wavelet energy spectrums of the line, select wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrums to reconstruct the signal, fit the reconstructed signal by adopting Prony algorithm, estimate amplitude and phase of the reconstructed signal, calculate zero sequence transient admittance of the line according to the amplitude and phase, judge whether the line has a ground fault according to preset setting admittance and line selection criteria, and if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line. Therefore, the embodiment of the invention can preprocess zero sequence voltage and zero sequence current transient signals by utilizing wavelet decomposition, retain fault characteristic information by wavelet packet energy spectrum and wavelet reconstruction, estimate transient zero sequence admittance by utilizing Prony algorithm, select fault lines and improve the accuracy of small current grounding fault line selection.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.
Claims (10)
1. The fault line identification method based on the transient small current is characterized by comprising the following steps of:
collecting bus zero sequence voltage of a power system and transient zero sequence current signals of all outgoing lines;
decomposing the first half-wave periodic signals of the zero-sequence voltage and transient zero-sequence current signals by using a DWT, drawing a wavelet energy spectrum of a circuit, and selecting wavelet coefficients of maximum energy and sub-maximum energy of the wavelet energy spectrum for signal reconstruction;
fitting the reconstructed signal by adopting a Prony algorithm, estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the circuit according to the amplitude and the phase;
judging whether the line has a ground fault or not according to a preset setting admittance and a line selection criterion, if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line.
2. The fault line identification method based on transient small current according to claim 1, wherein the decomposing the first half-wave periodic signal of the zero sequence voltage and transient zero sequence current signals by using DWT, and drawing a wavelet energy spectrum of the line, selecting a wavelet coefficient of maximum energy and sub-maximum energy of the wavelet energy spectrum, and performing signal reconstruction specifically includes:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
3. The fault line identification method based on transient low current according to claim 1, wherein the fitting of the reconstructed signal by using a Prony algorithm estimates the amplitude and phase of the reconstructed signal, and calculates the zero sequence transient admittance of the line according to the amplitude and phase, specifically comprising:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sample function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is the conjugate of the linear combination of the exponential function of the p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signal, r (p, p) is the (p, p) th sampleThe function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1)] T 。
4. The fault line identification method based on transient low current according to claim 1, wherein the preset setting method of setting admittance specifically comprises:
According to the zero sequence voltage and zero sequence current of single-phase earth fault, obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of arc suppression coils set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
5. A transient low current based fault line identification device, comprising:
the acquisition module is used for acquiring the bus zero sequence voltage of the power system and the transient zero sequence current signals of all outgoing lines;
the decomposition module is used for decomposing the first half-wave periodic signal of the zero-sequence voltage and transient zero-sequence current signals by utilizing a DWT, drawing a wavelet energy spectrum of a circuit, and selecting the wavelet coefficients of the maximum energy and the sub-maximum energy of the wavelet energy spectrum for signal reconstruction;
the fitting module is used for fitting the reconstructed signals by adopting a Prony algorithm, estimating the amplitude and the phase of the reconstructed signals, and calculating the zero sequence transient admittance of the circuit according to the amplitude and the phase;
The judging module is used for judging whether the line has a ground fault or not according to preset setting admittance and line selection criteria, if the zero sequence transient admittance is smaller than the preset setting admittance, the line is a fault line, and if the zero sequence transient admittance is larger than the preset setting admittance, the line is a non-fault line.
6. The fault line identification device based on transient low current as claimed in claim 5, wherein the decomposition module is specifically configured to:
preprocessing the first half-wave periodic signals of the zero sequence voltage and transient zero sequence current signals by using a DWT (discrete wavelet transform) to obtain approximate signals and detail signals;
decomposing the approximate signals according to a decomposition layer number formula to obtain the approximate signals of different frequency bands;
according to the definition of the energy characteristic values, calculating the energy corresponding to the approximate signals of different frequency bands, and drawing a wavelet energy spectrum; the approximate signal of the maximum energy of the wavelet energy spectrum is a transient main frequency signal, and the approximate signal of the secondary maximum energy is a power frequency signal;
carrying out signal reconstruction on wavelet coefficients of the transient main frequency signal and the power frequency signal;
wherein the formula of the decomposition layer number is
The energy characteristic value is defined by the formula
Wherein, I d The number of decomposition layers of the approximation signal, f s For sampling the frequency of the signal, f 1 For the frequency of the power frequency signal, E (A n ) An energy characteristic value corresponding to the approximation signal of the ith band, A n For the approximation signal of the i-th band, N n For the data length of the number of decomposition levels,n is the total number of frequencies of the sampled signal and N is the total number of detail signals.
7. The fault line identification device based on transient low current as claimed in claim 5, wherein the fitting module is specifically configured to:
fitting the reconstructed signal by adopting a Prony algorithm to obtain a Prony model of the reconstructed signal, defining a sample function of the Prony model, constructing a normal equation of the sample function, and solving coefficients of the normal equation and a minimum error energy estimated value;
calculating the root of the characteristic polynomial of the coefficient, calculating the parameter of the root according to a parameter formula, thereby estimating the amplitude and the phase of the reconstructed signal, and calculating the zero sequence transient admittance of the line according to the amplitude and the phase;
wherein the sample function is
The normal equation of the sample function is
The characteristic polynomial of the coefficient is
1+a 1 z 1 -1 +a 2 z 2 -2 …+a p z p -p ＝0，
The parameter formula is
b＝(Z T Z) -1 Z T x，
Wherein r (w, v) is the (w, v) th sample function, Q is the number of samples of the reconstructed signal, x (Q-v) is the linear combination of the exponential functions of p arbitrary amplitudes, phases, frequencies and attenuation factors of the Q-v th reconstructed signal, x * (q-w) is the conjugate of the linear combination of the exponential functions of the p arbitrary amplitudes, phases, frequencies and attenuation factors of the q-w th reconstructed signal, r (p, p) is the (p, p) th sample function, a 1 For the 1 st said coefficient, a 1 For the 1 st said coefficient a p Epsilon is the p-th coefficient p For the minimum error energy, a 2 For the 2 nd said coefficient, z 1 Being the root of the coefficient of 1, z 2 Being the root of the coefficient of 2, z p For the p-th root of the coefficient, b is the parameter set of the root of the coefficient, Z is the matrix of the root set of the coefficient,Z T as the transpose of the root set of coefficients, x is the transpose of a linear combination set of the exponential functions of p arbitrary amplitudes, phases, frequencies, and attenuation factors of the Q reconstructed signals, x= [ x (0), x (1), …, x (Q-1)] T 。
8. The fault line identification device based on transient low current as claimed in claim 5, wherein the preset setting method of setting admittance specifically comprises:
Based on the zero sequence voltage and zero sequence current at which the single-phase earth fault occurs,obtaining transient main frequency components of the zero sequence voltage and the zero sequence current, obtaining transient main frequency phase voltage and transient main frequency phase current of the transient main frequency components, obtaining transient main frequency admittance, and setting preset setting admittance as Y by considering the influence of an arc suppression coil set ，
Wherein omega is 0d For the transient main frequency zero sequence voltage frequency, C 0Σ L is the sum of all the line-to-ground capacitances in the power system k Is the arc suppression coil inductance.
9. A terminal device comprising a processor, a memory and a computer program stored in the memory and configured to be executed by the processor, the processor implementing the transient low current based fault line identification method according to any one of claims 1-4 when the computer program is executed.
10. A computer readable storage medium, characterized in that the computer readable storage medium comprises a stored computer program, wherein the computer program, when run, controls a device in which the computer readable storage medium is located to perform the transient low current based fault line identification method according to any one of claims 1-4.
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| CN117110797B (en) * | 2023-10-23 | 2024-01-12 | 武汉格蓝若智能技术股份有限公司 | Multi-criterion-based single-phase earth fault positioning method and device for power distribution network |
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