CN113740660A - Line fault positioning method and device for low-voltage direct-current system at user side - Google Patents
Line fault positioning method and device for low-voltage direct-current system at user side Download PDFInfo
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Abstract
The invention relates to a line fault positioning method and a device of a low-voltage direct-current system at a user side. The fault positioning method provided by the invention is irrelevant to wave velocity, and can achieve a better distance measurement effect. Compared with the empirical mode decomposition method in the prior art, the method can more accurately position the fault line under different transition resistances, different fault distances and different fault types, and the positioning error is smaller as the position of the fault point is closer to the middle point of the line.
Description
Technical Field
The invention relates to the technical field of power system fault detection, in particular to a method and a device for positioning a line fault of a low-voltage direct-current system on a user side.
Background
With the rapid development of current social economy and the progress of modern science and technology, infrastructure construction in all aspects of China is increasingly perfect, higher and higher operation requirements are provided for electric power systems in China, the electric power systems in China are increasingly enlarged in scale, the regional distribution is increasingly wide, the transmission distance of a power transmission line is increasingly far, the transmission energy and voltage levels are greatly improved, and a power transmission network is increasingly huge and complex. The fault of the power system will affect the stable and safe operation of the whole power system, and in severe cases will affect the national economy of China, so the fault type and the fault position need to be determined quickly and accurately, and the fault can be repaired in the shortest time, so as to prevent serious accidents or damages caused by the expansion of the fault range.
Scholars at home and abroad have a great deal of scientific achievements for the problem of fault location of the power transmission line, and provide a great number of effective location methods. The rapid development of the GPS clock correction technology and the GPS positioning technology enables the time synchronization precision to be accurate to a nanosecond level, and the double-end traveling wave distance measurement method needs to accurately record the time when voltage or current traveling waves reach two ends of a line and only needs to accurately record the time when a first wave head reaches a collection point, so that the method is simple, and the application of the double-end traveling wave distance measurement method in fault positioning of a power transmission line is more common at present. In practical application, the signal sampling frequency and the traveling wave speed are very easy to influence the fault positioning result of double-end ranging, and particularly the traveling wave speed is influenced greatly.
Disclosure of Invention
Based on the above situation in the prior art, an object of the present invention is to provide a method and an apparatus for locating a line fault in a low-voltage dc system on a user side, in which a traveling wave head capture model based on a variational modal decomposition-Hilbert transform algorithm (VMD-Hilbert algorithm) is constructed, so as to effectively improve a signal-to-noise ratio of a traveling wave signal and effectively capture the traveling wave head, and the locating method is independent of a wave velocity, and can achieve a better ranging effect.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method for locating a line fault of a user-side low voltage dc system, including the steps of:
when a line has an internal fault, sampling line transient signals at two ends of the line;
decomposing the transient signals sampled at two ends by adopting a variational modal decomposition method to obtain an intrinsic modal function component BLIMF with limited bandwidth;
respectively deriving intrinsic mode function component BLIMF obtained by decomposing two ends of the line, taking module value, and reading module value maximum point as time t when traveling wave reaches two ends of the line1、t2；
According to the time t1、t2The distance of each end from the fault point is calculated.
Further, the method for decomposing the transient signals sampled at the two ends by using the variational mode decomposition method to obtain the intrinsic mode function and the component BLIMF with limited bandwidth comprises the following steps:
decomposition of a transient signal f (t) into k BLIMF components u with a center frequency and a limited bandwidthk(t) satisfying that the sum of BLIMF components equals f (t) and the wideband sum of BLIMF components is minimal, expressed as:
wherein the content of the first and second substances,
is the partial derivative of the function over time t; omegakA set of center frequencies for each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
Further, the deriving and modulus taking intrinsic mode function component BLIMF obtained by decomposing the two ends of the line respectively includes:
performing spectrum processing on the intrinsic mode function component BLIMF;
decoupling through Kerenbel transformation, and selecting a line mode component;
hilbert transformation is carried out on each intrinsic mode function component BLIMF, and an amplitude spectrum and an instantaneous frequency of a corresponding analytical function are solved to obtain a Hilbert spectrum H (omega, t) of a signal;
and (3) carrying out derivation and modulus on a first mode function component in the Hilbert spectrum H (omega, t) of the signal.
Further said dependent time t1、t2Calculating the distance of each end from the fault point, including calculating the distance l' of each end from the fault point according to the following formula:
where, t is1-t2L is the total length of the line and v is the speed of the traveling wave propagating in the line.
According to another aspect of the invention, a line fault positioning device for a user-side low-voltage direct-current system is provided, which comprises a transient signal acquisition module, an intrinsic mode function component calculation module and a fault positioning module;
the transient signal acquisition module samples line transient signals at two ends of the line when the line has an internal fault;
the intrinsic mode function component calculation module adopts a variational mode decomposition method to decompose the transient signals sampled at two ends to obtain an intrinsic mode function component BLIMF with limited bandwidth; respectively deriving intrinsic mode function component BLIMF obtained by decomposing two ends of the line, taking module value, and reading module value maximum point as time t when traveling wave reaches two ends of the line1、t2；
The fault positioning module is used for positioning the fault according to the time t1、t2The distance of each end from the fault point is calculated.
Further, the module for calculating the eigenmode function component decomposes the transient signals sampled at two ends by using a variational mode decomposition method to obtain the eigenmode function component BLIMF with a limited bandwidth, which includes:
decomposition of a transient signal f (t) into k BLIMF components u with a center frequency and a limited bandwidthk(t) satisfying that the sum of BLIMF components equals f (t) and the wideband sum of BLIMF components is minimal, expressed as:
wherein the content of the first and second substances,
is the partial derivative of the function over time t; omegakA set of center frequencies for each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
Further, the deriving and modulus taking of the intrinsic mode function component BLIMF obtained by decomposing the two ends of the line by the intrinsic mode function component calculating module respectively includes:
performing spectrum processing on the intrinsic mode function component BLIMF;
decoupling through Kerenbel transformation, and selecting a line mode component;
hilbert transformation is carried out on each intrinsic mode function component BLIMF, and an amplitude spectrum and an instantaneous frequency of a corresponding analytical function are solved to obtain a Hilbert spectrum H (omega, t) of a signal;
and (3) carrying out derivation and modulus on a first mode function component in the Hilbert spectrum H (omega, t) of the signal.
Further, the fault positioning module is used for positioning the fault according to the time t1、t2Calculating the distance of each end from the fault point comprises:
the distance l' of each end from the fault point is calculated according to the following formula:
where, t is1-t2L is the total length of the line and v is the speed of the traveling wave propagating in the line.
In summary, the invention provides a line fault positioning method and device for a low-voltage direct-current system on a user side, which effectively improve the signal-to-noise ratio of a traveling wave signal and can effectively capture the traveling wave head by constructing a traveling wave head capture model based on a VMD-Hilbert algorithm, so as to determine the time when a fault traveling wave reaches monitoring points at two ends of a line and perform fault positioning according to the time. The fault positioning method provided by the invention is irrelevant to wave velocity, and can achieve a better distance measurement effect. Compared with an Empirical Mode Decomposition (EMD) method in the prior art, the method can more accurately position the fault line under different transition resistances, different fault distances and different fault types, and the positioning error is smaller as the position of the fault point is closer to the midpoint of the line.
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FIG. 1 is a flow chart of a line fault location method for a user side low voltage DC system according to the present invention;
FIG. 2 is a block diagram of the line fault locating device of the low-voltage DC system at the user side according to the present invention;
FIG. 3 shows waveforms of IMF components obtained by VMD decomposition of line mode current components obtained at the M end of the line; wherein FIGS. 3 a-3 d are the current line modulus IMF1, IMF2, IMF3, and IMF4 components, respectively;
FIG. 4 shows waveforms of IMF components obtained by VMD decomposition of line mode current components obtained at the N-terminal of the line; 4 a-4 d are the components of the current line modulus IMF1, IMF2, IMF3, and IMF4, respectively;
FIG. 5 is a schematic diagram of the derivative of the two-terminal current α modulus IMF1 component; where FIG. 5a is the derivative of the M-terminal current line modulus IMF1 component and FIG. 5b is the derivative of the N-terminal current line modulus IMF1 component.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. According to an embodiment of the present invention, there is provided a method for locating a line fault of a user-side low-voltage dc system, where a flowchart of the method is shown in fig. 1, and the method includes the following steps:
when the line has an internal fault, line transient signals are sampled at two ends of the line. In actual sampling, the traveling wave signals are all from the secondary side of the transformer. For the electromagnetic mutual inductor, a voltage mutual inductor and a current mutual inductor can well transmit high-frequency signals, and at the moment, traveling wave signals can adopt both voltage signals and current signals. For a capacitor transformer, a current transformer can well transmit high-frequency signals, but the voltage transformer has an internal nonlinear energy storage element, so that traveling waves can generate leading edges and oscillation under a transient condition, the arrival time of a wave head observed on a secondary side is inconsistent with that of a primary side, and the current transformer cannot be applied, and the current signal is selected. In this embodiment, a capacitor transformer is taken as an example, and a transient current signal is used as a traveling wave signal for calculation. The speed v of the traveling wave propagating in the line can be determined according to the following formula:
where L represents the inductance of the line per unit length and C represents the capacitance of the line per unit length.
And decomposing the transient signals sampled at two ends by adopting a variation modal decomposition method to obtain an intrinsic mode function component BLIMF with limited bandwidth. In the embodiment, the traveling wave head of the transient signal can be effectively captured by constructing the traveling wave head capturing model based on the VMD-Hilbert algorithm. The traveling wave information has the characteristics of richness and complexity, mutation exists, whether the traveling wave head is detected or not can be detected or not is the criterion, and the time when the mutation point is detected is the arrival time of the corresponding traveling wave. The method provided by the embodiment replaces the problem of capturing the traveling wave head with the problem of detecting the traveling wave abrupt change point. The characteristics of the abrupt change signal can be well reflected by a small wave mode maximum value method, and the time when the traveling wave head reaches the detection point is the time when the abrupt change signal appears.
The fault signal has large fluctuation and poor linearity, and the VMD algorithm can adaptively decompose the signal and extract the most important characteristics held by the signal according to the attribute characteristics of the signal. Constructing a variational modal decomposition model and solving the variational modal decomposition model is a main problem of a VMD algorithm, and adaptively decomposing signals through a preset scale to form BLIMF components of k different frequency bands. The method comprises the following specific steps:
let it be assumed that the transient signal f (t) is decomposed into k BLIMF components u with a center frequency and a finite bandwidthk(t) if the sum of BLIMF components is equal to f (t) and the sum of the wide bands of the BLIMF components is minimum, constructing a variational modal decomposition model with constraint conditions as follows:
in the formula (I), the compound is shown in the specification,
is the partial derivative of the function over time t; f is the center frequency of each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
The steps of solving the optimal solution for the variational modal decomposition model are as follows:
introducing a Lagrange multiplication operator lambda and a secondary penalty factor, wherein a variational modal decomposition model without constraint conditions is as follows:
updating by a multiplier algorithm of alternating directions
And
the 'saddle point' of the Lagrange expression, namely the optimal solution of the variational modal decomposition model is obtained, and the detailed process is shown as follows.
The updated expression of each modal component, namely the optimal solution of the variation modal decomposition model is as follows:
wherein the content of the first and second substances,
the expression of the frequency domain is obtained through Fourier transform, and the expression is as follows:
the center frequency of each BLIMF component updated in the frequency domain is obtained in the same way
The expression for the lagrange multiplier λ is:
where τ is a noise margin parameter.
Hilbert transform and calculation of instantaneous frequency:
for real signal u (t), its Hilbert transform is defined:
the inverse transform is:
combining v (t) and u (t) into a complex signal:
x(t)＝u(t)+jv(t)＝a(t)ejθ(t)
wherein:
then define the instantaneous frequency fiComprises the following steps:
hilbert transform is performed on each IMF, and the amplitude spectrum and instantaneous frequency of the corresponding analytical function, i.e. Hilbert spectrum H (ω, t) of the signal, are solved:
the embodiment of the invention adopts a VMD-Hilbert algorithm to analyze fault transient traveling wave signals, monitor the sudden point of traveling wave frequency, capture the traveling wave head and realize fault positioning. The VMD-Hilbert algorithm consists of two parts, VMD (variational modal decomposition) and Hilbert (Hilbert transform), the former decomposing a complex non-stationary signal containing multiple modal aliasing into many BLIMF components, each containing only a single mode, which are arranged in a series from high to low frequencies, the high frequency component being contained in the first BLIMF. The latter, Hilbert transform, is mainly to perform spectral processing on the previously obtained IMF to obtain a time-frequency spectrum according to the formula H (ω, t). The time-frequency maps are shown in fig. 3 and 4, for example. 3 a-3 d show waveforms of IMF components obtained by VMD decomposition of line mode current components obtained at one end of a line, for example, the M end; fig. 4 a-4 d show waveforms of IMF components obtained by VMD decomposition of line mode current components obtained at the other end of the line, e.g. the N-terminal.
In the selection of the mode, for the Kerenbel transformation, the voltage and the current of the positive and negative two-pole line are decoupled into a zero-mode component and a line-mode component, and the decoupled integral modulus is not influenced by electromagnetic coupling.
Respectively deriving intrinsic mode function component BLIMF1 obtained by decomposing two ends of the line, taking module value, and reading module value maximum point as time t when traveling wave reaches two ends of the line1、t2(ii) a According to the time t1、t2The distance of each end from the fault point is calculated. The specific steps can be carried out as follows: derivation and modulus taking are performed on the first mode function component in the Hilbert spectrum H (ω, t) of the signal, that is, derivation and modulus taking are performed on the current line mode component IMF1 at the two ends of M, N, and the derivation and modulus taking are shown in fig. 5.
When calculating the distance between each end and a fault point, a fault location method based on double-end positioning is adopted, specifically, the basic location principle belongs to a traveling wave location B-type location method, namely, the location is carried out by the time difference and the wave speed when the traveling wave reaches the two ends of the line for the first time, and the location formula is as follows:
wherein the content of the first and second substances,
△t＝t1-t2
and delta t represents the time difference of the traveling wave reaching the two ends of the line, L represents the total length of the line, v represents the wave speed of the traveling wave propagating in the line, and L' represents the ranging result.
According to another embodiment of the present invention, a line fault location device for a low-voltage dc system on a user side is provided, and a block diagram of the device is shown in fig. 2, and the device includes a transient signal acquisition module, an eigenmode function component calculation module, and a fault location module.
The transient signal acquisition module is used for sampling line transient signals at two ends of the line when the line has an internal fault.
The intrinsic mode function component calculation module adopts a variational mode decomposition method to decompose the transient signals sampled at two ends to obtain an intrinsic mode function component BLIMF with limited bandwidth; respectively to the lineObtaining intrinsic mode function component BLIMF derivation and modulus value from two-end decomposition, reading maximum value point of modulus value as time t of traveling wave reaching two ends of line1、t2. The intrinsic mode function component calculation module adopts a variational mode decomposition method to decompose the transient signals sampled at two ends to obtain intrinsic mode function components BLIMF with limited bandwidth, and specifically, the transient signals f (t) are decomposed into k BLIMF components u with central frequency and limited bandwidthk(t) satisfying that the sum of BLIMF components equals f (t) and the wideband sum of BLIMF components is minimal, expressed as:
wherein the content of the first and second substances,
is the partial derivative of the function over time t; omegatIs the center frequency of each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
Performing spectrum processing on the intrinsic mode function component BLIMF;
decoupling through Kerenbel transformation, and selecting a line mode component;
hilbert transformation is carried out on each intrinsic mode function component BLIMF, and an amplitude spectrum and an instantaneous frequency of a corresponding analytical function are solved to obtain a Hilbert spectrum H (omega, t) of a signal;
and (3) carrying out derivation and modulus on a first mode function component in the Hilbert spectrum H (omega, t) of the signal.
A fault positioning module for respectively deriving the intrinsic mode function component BLIMF obtained by decomposing the two ends of the line and taking the module value, and reading the maximum value point of the module value as the time t when the traveling wave reaches the two ends of the line1、t2And according to the time t1、t2Calculating the distance between each end and the fault point, and calculating the distance l' between each end and the fault point according to the following formula:
where, t is1-t2L is the total length of the line and v is the speed of the traveling wave propagating in the line.
The simulation result of a specific example is used to explain the fault location effect of the present invention. The method of the above embodiment was simulated using a voltage rating of 750V. The parameters are set as follows: sampling frequency 106Hz; lines 4-5 are 100km, lines 4-6 are 60km, lines 5-7 are 80km, lines 6-9 are 100km, lines 7-8 are 60km, and lines 8-9 are 120 km. Different fault types of fault resistors are set, and simulation tests are continuously carried out, and the results are shown in tables 1-3.
Table 1750V simulation result in line ground fault
Table 2750V line interpolar fault simulation result
From the simulation results in tables 1-2, it can be seen that the ranging result is basically unchanged and is not affected by different fault modes, different fault transition resistances and the like. The absolute errors of the distance measurement are all within 150m, and in most cases, the absolute errors are only dozens of meters.
TABLE 3 simulation results based on EMD method for 750V line grounding short circuit
Compared with the EMD method, the VMD-based double-end positioning algorithm provided by the invention can more accurately position the fault line under different transition resistances, different fault distances and different fault types, and the positioning error is smaller as the position of the fault point is close to the midpoint of the line.
In summary, the invention relates to a line fault positioning method and device for a low-voltage direct-current system at a user side, and the method and device effectively improve the signal-to-noise ratio of a traveling wave signal and can effectively capture the traveling wave head by constructing a traveling wave head capture model based on a VMD-Hilbert algorithm, so as to determine the time when a fault traveling wave reaches monitoring points at two ends of a line, and perform fault positioning according to the time. The fault positioning method provided by the invention is irrelevant to wave velocity, and can achieve a better distance measurement effect. Compared with an Empirical Mode Decomposition (EMD) method in the prior art, the method can more accurately position the fault line under different transition resistances, different fault distances and different fault types, and the positioning error is smaller as the position of the fault point is closer to the midpoint of the line.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
Claims (8)
1. A line fault positioning method for a user side low-voltage direct current system is characterized by comprising the following steps:
when a line has an internal fault, sampling line transient signals at two ends of the line;
decomposing the transient signals sampled at two ends by adopting a variational modal decomposition method to obtain an intrinsic modal function component BLIMF with limited bandwidth;
respectively solving intrinsic mode function component BLIMF obtained by decomposing two ends of the lineLeading and taking module value, reading module value maximum value point as time t of traveling wave arriving at two ends of line1、t2；
According to the time t1、t2The distance of each end from the fault point is calculated.
2. The method according to claim 1, wherein the transient signal sampled at two ends is decomposed by using a variational modal decomposition method to obtain a bandwidth-limited eigenmode function and component BLIMF, comprising the steps of:
decomposition of a transient signal f (t) into k BLIMF components u with a center frequency and a limited bandwidthk(t) satisfying that the sum of BLIMF components equals f (t) and the wideband sum of BLIMF components is minimal, expressed as:
wherein the content of the first and second substances,
is the partial derivative of the function over time t; omegakA set of center frequencies for each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
3. The method of claim 2, wherein deriving and modulo the intrinsic mode function component BLIMF separately from the line end decomposition comprises:
performing spectrum processing on the intrinsic mode function component BLIMF;
decoupling through Kerenbel transformation, and selecting a line mode component;
hilbert transformation is carried out on each intrinsic mode function component BLIMF, and an amplitude spectrum and an instantaneous frequency of a corresponding analytical function are solved to obtain a Hilbert spectrum H (omega, t) of a signal;
and (3) carrying out derivation and modulus on a first mode function component in the Hilbert spectrum H (omega, t) of the signal.
4. Method according to claim 1, characterised in that said function is based on the time t1、t2Calculating the distance of each end from the fault point, including calculating the distance l' of each end from the fault point according to the following formula:
where, t is1-t2L is the total length of the line and v is the speed of the traveling wave propagating in the line.
5. A line fault positioning device of a user side low-voltage direct current system is characterized by comprising a transient signal acquisition module, an intrinsic mode function component calculation module and a fault positioning module;
the transient signal acquisition module samples line transient signals at two ends of the line when the line has an internal fault;
the intrinsic mode function component calculation module adopts a variational mode decomposition method to decompose the transient signals sampled at two ends to obtain an intrinsic mode function component BLIMF with limited bandwidth; respectively deriving intrinsic mode function component BLIMF obtained by decomposing two ends of the line, taking module value, and reading module value maximum point as time t when traveling wave reaches two ends of the line1、t2；
The fault positioning module is used for positioning the fault according to the time t1、t2The distance of each end from the fault point is calculated.
6. The apparatus of claim 5, wherein the eigenmode function component calculating module decomposes the transient signals sampled at two ends by using a variational mode decomposition method to obtain a bandwidth-limited eigenmode function component BLIMF, and includes:
decomposition of a transient signal f (t) into k BLIMF components u with a center frequency and a limited bandwidthk(t) satisfying that the sum of BLIMF components equals f (t) and each BLThe sum of the wide bands of the IMF components is minimal, expressed as:
wherein the content of the first and second substances,
is the partial derivative of the function over time t; omegakA set of center frequencies for each BLIMF component; is a convolution symbol; δ (t) is a unit pulse function; j is an imaginary unit.
7. The apparatus according to claim 6, wherein the module for calculating the eigenmode function component derives and takes the modulo value of the eigenmode function component BLIMF decomposed at two ends of the line respectively comprises:
performing spectrum processing on the intrinsic mode function component BLIMF;
decoupling through Kerenbel transformation, and selecting a line mode component;
hilbert transformation is carried out on each intrinsic mode function component BLIMF, and an amplitude spectrum and an instantaneous frequency of a corresponding analytical function are solved to obtain a Hilbert spectrum H (omega, t) of a signal;
and (3) carrying out derivation and modulus on a first mode function component in the Hilbert spectrum H (omega, t) of the signal.
8. The apparatus of claim 5, wherein the fault location module is configured to locate the fault based on time t1、t2Calculating the distance of each end from the fault point comprises:
the distance l' of each end from the fault point is calculated according to the following formula:
where, t is1-t2L is total line length and v is traveling wave velocity propagating in the line。
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