Transformer partial discharge positioning method and device based on bushing CT acquisition

Abstract

The invention provides a transformer partial discharge positioning method and device based on bushing CT acquisition. The method comprises the following steps: acquiring a high-frequency partial discharge pulse signal of a current transformer at a transformer bushing; background noise of the pulse signal is removed, amplitude correction is carried out, and a corrected pulse signal is obtained; judging whether the partial discharge belongs to external interference or internal partial discharge based on the polarity distribution rule of the corrected pulse signal; if the interference is external interference, comparing the amplitudes of the correction acquisition signals corresponding to the bushings, and taking the position corresponding to the current transformer with the maximum amplitude as an interference source injection position; if partial discharge occurs in the transformer, calculating the distance proportion from the partial discharge position to the head end of the winding according to the attenuation characteristic of the pulse signal propagating in the winding and the pre-injected calibration square wave signal so as to determine the discharge position. According to the method, the method for determining the partial discharge position of the transformer is simplified, external interference and internal partial discharge signals can be quickly identified, and misoperation of a protection device is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer discharge positioning in a power system, and particularly to a method and device for local discharge positioning of a transformer based on bushing CT acquisition. Background Art

[0002] A transformer is a crucial device in a power system, and its safe and stable operation is essential for the overall operation of the power system. As the main cause of transformer failures, local discharge is an important detection method for indicating the insulation state of a transformer. When a transformer undergoes local discharge, the urgent problem to be solved is to determine the location of the local discharge and judge whether the local discharge signal comes from inside the transformer.

[0003] Existing methods for local discharge positioning of transformers mainly include ultrasonic positioning method, UHF signal positioning method, and high-frequency multi-terminal detection technology. The ultrasonic positioning method receives ultrasonic signals generated by local discharge through ultrasonic sensors, and solves a corresponding system of equations based on the time differences of the signals received by each sensor to obtain the specific coordinates of the local discharge location. The UHF positioning method receives UHF electromagnetic signals generated by local discharge inside the transformer through an antenna, and realizes positioning by combining the time of arrival and amplitude attenuation differences. The principle of the high-frequency multi-terminal detection technology is that high-frequency local discharge pulses occurring in multiple windings of a transformer will propagate to the first and last ends of each terminal, forming a local discharge monitoring network. By simultaneously measuring the high-frequency local discharge pulse signals of multiple terminals and comparing the characteristic information such as the amplitude and polarity of the local discharge pulses, external interference can be distinguished, and the discharge type and corresponding occurrence location of the local discharge can be judged.

[0004] However, although the ultrasonic positioning method has good anti-electromagnetic interference ability, its detection sensitivity for internal discharge of transformers is low, and the error in solving the system of equations is large. The UHF positioning method is easily interfered by on-site UHF electromagnetic signals, has high requirements for receiving devices such as antennas, and also needs to solve a system of equations, which limits the positioning accuracy. Finally, the current high-frequency multi-terminal detection technology measures local discharge signals through high-frequency current sensors led out from the bushing end screen. The device has insufficient reliability, serious electromagnetic interference, and high signal attenuation, reducing the receiving performance. Summary of the Invention

[0005] In view of this, the present invention provides a method and device for local discharge positioning of a transformer based on bushing CT acquisition to solve at least one of the above-mentioned problems.

[0006] To achieve the above object, the present invention adopts the following solutions: According to a first aspect of the present invention, there is provided a method for local discharge location of a transformer based on bushing CT acquisition. The method includes: collecting high-frequency partial discharge pulse signals at the secondary side terminals of the current transformers of the transformer bushings, where the transformer bushings include high-voltage side bushings, medium-voltage side bushings, neutral point bushings, low-voltage side first-end bushings, and low-voltage side end bushings; performing discrete wavelet decomposition on the high-frequency partial discharge pulse signals to obtain wavelet coefficients; selecting a soft threshold function to perform threshold processing on the wavelet coefficients to remove background noise; reconstructing a signal using the wavelet coefficients after removing the background noise to obtain the high-frequency partial discharge pulse signal after removing the background noise; performing amplitude correction on the high-frequency partial discharge pulse signal after removing the background noise based on the frequency response characteristics of the current transformer to obtain a corrected pulse signal; determining whether the local discharge of the transformer belongs to external interference or internal local discharge based on the polarity distribution law of the corrected pulse signal; if it is determined to be external interference, then compare the amplitudes of the corrected acquisition signals corresponding to each bushing, and the position corresponding to the current transformer of the bushing with the largest amplitude is the interference source injection position; if it is determined to be internal local discharge of the transformer, then according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding, combined with the pre-injected calibration square wave signal, calculate the distance ratio from the local discharge position to the first end of the winding to determine the discharge position.

[0007] As an embodiment of the present invention, the amplitude correction of the high-frequency partial discharge pulse signal after removing the background noise based on the frequency response characteristics of each bushing current transformer in the above method includes: injecting a calibration pulse signal into the end of any selected bushing of the transformer and calculating the spectrum of the calibration pulse signal; collecting the induced signal at the secondary side port of the selected bushing and calculating the spectrum of the induced signal; calculating the frequency response of the selected bushing using the spectrum of the calibration pulse signal and the spectrum of the induced signal; calculating the spectrum of the high-frequency partial discharge pulse signal of the selected bushing; calculating the spectrum of the original pulse transmitted to the selected bushing using the spectrum of the high-frequency partial discharge pulse signal and the frequency response; obtaining a time-domain signal through inverse discrete Fourier transform based on the spectrum of the original pulse; taking the modulus of the time-domain signal and finding the maximum value to obtain the corrected amplitude.

[0008] As an embodiment of the present invention, determining whether the local discharge of the transformer belongs to external interference or internal local discharge based on the polarity distribution law of the corrected pulse signal in the above method includes: judging whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the local discharge of the transformer belongs to external interference. If they are not the same, it is determined that the local discharge of the transformer belongs to internal local discharge of the transformer.

[0009] As an embodiment of the present invention, in the above method, according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding and in combination with the pre-injected calibration square wave signal, calculating the distance ratio from the partial discharge position to the head end of the winding to determine the discharge position includes: before the partial discharge detection test starts, injecting calibration square wave signals with the same charge amount into the head end and the tail end of the winding to be measured respectively, and obtaining the electric field intensities at the head end and the tail end of the winding to be measured; obtaining the electromagnetic energy of the high-frequency partial discharge pulse signals collected at the bushings at the head end and the tail end of the winding to be measured based on the electric field intensities; obtaining the signal energies at the head end and the tail end of the winding to be measured based on the length of the winding to be measured, the electromagnetic energy and the electric field intensity amplitude of the high-frequency pulse at the partial discharge position; obtaining the distance ratio from the partial discharge position to the head end of the winding based on the electromagnetic energy and the signal energy, and further determining the discharge position.

[0010] According to the second aspect of the present invention, there is provided a transformer partial discharge positioning device based on bushing CT acquisition. The device includes: a signal acquisition unit for acquiring high-frequency partial discharge pulse signals at the secondary side terminals of the current transformers of the transformer bushings, where the transformer bushings include a high-voltage side bushing, a medium-voltage side bushing, a neutral point bushing, a low-voltage side head end bushing and a low-voltage side tail end bushing; a wavelet decomposition unit for performing discrete wavelet decomposition on the high-frequency partial discharge pulse signals to obtain wavelet coefficients; a denoising unit for selecting a soft threshold function to perform threshold processing on the wavelet coefficients to remove background noise; a signal reconstruction unit for reconstructing a signal using the wavelet coefficients after removing the background noise to obtain the high-frequency partial discharge pulse signals after removing the background noise; an amplitude correction unit for performing amplitude correction on the high-frequency partial discharge pulse signals after removing the background noise based on the frequency response characteristics of each bushing current transformer to obtain corrected pulse signals; a discharge type judgment unit for judging whether the transformer partial discharge belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signals; a first positioning unit for, when the discharge type judgment unit determines it to be external interference, comparing the amplitudes of the corrected acquisition signals corresponding to each bushing, and the position corresponding to the bushing current transformer with the largest amplitude is the interference source injection position; a second positioning unit for, when the discharge type judgment unit determines it to be internal partial discharge of the transformer, calculating the distance ratio from the partial discharge position to the head end of the winding according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding and in combination with the pre-injected calibration square wave signal to determine the discharge position.

[0011] As an embodiment of the present invention, the above-mentioned amplitude correction unit includes: a first spectrum calculation module that injects a calibration pulse signal into the end of any selected bushing of the transformer and calculates the spectrum of the calibration pulse signal; a second spectrum calculation module that is used to collect the induced signal at the secondary side port of the selected bushing and calculate the spectrum of the induced signal; a frequency response calculation module that is used to calculate the frequency response of the selected bushing by using the spectrum of the calibration pulse signal and the spectrum of the induced signal; a third spectrum calculation module that is used to calculate the spectrum of the high-frequency partial discharge pulse signal of the selected bushing; a fourth spectrum calculation module that is used to inversely deduce the spectrum of the original pulse transmitted to the selected bushing by using the spectrum of the high-frequency partial discharge pulse signal and the frequency response; an inverse transformation module that is used to obtain a time-domain signal through inverse discrete Fourier transform based on the spectrum of the original pulse; an amplitude correction module that is used to take the modulus of the time-domain signal and find the maximum value to obtain the corrected amplitude.

[0012] As an embodiment of the present invention, the above-mentioned discharge type judgment unit is specifically used for: judging whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the partial discharge of the transformer belongs to external interference. If they are not the same, it is determined that the partial discharge of the transformer belongs to internal partial discharge of the transformer.

[0013] As an embodiment of the present invention, the above-mentioned second positioning unit includes: an electric field strength acquisition module that, before the start of the partial discharge detection test, injects calibration square wave signals with the same charge amount into the head end and the tail end of the winding to be measured, respectively, to obtain the electric field strengths at the head end and the tail end of the winding to be measured; an electromagnetic energy acquisition module that, based on the electric field strength, obtains the electromagnetic energy of the high-frequency partial discharge pulse signals collected at the bushings at the head end and the tail end of the winding to be measured; a signal energy acquisition module that, based on the length of the winding to be measured, the electromagnetic energy, and the electric field strength amplitude of the high-frequency pulse at the partial discharge location, obtains the signal energies at the head end and the tail end of the winding to be measured; a discharge position determination module that, based on the electromagnetic energy and the signal energy, obtains the distance ratio from the partial discharge position to the head end of the winding, and further determines the discharge position.

[0014] According to the third aspect of the present invention, there is provided an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the above method are implemented.

[0015] According to the fourth aspect of the present invention, there is provided a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are implemented.

[0016] According to a fifth aspect of the present invention, there is provided a computer program product comprising a computer program / instructions which, when executed by a processor, implement the steps of the above method.

[0017] The method and device for local discharge location of a transformer based on bushing CT acquisition proposed by the present invention reduce the interference factors of background noise, eliminate the influence of bushing current transformers on receiving high-frequency partial discharge pulse signals, and simplify the method for determining the local discharge location of a transformer. Specifically, through polarity discrimination, it helps to quickly identify external interference and internal partial discharge signals, avoid misoperation of protection devices, and provide a basis for fault analysis and maintenance work. For external interference, by comparing the signal amplitudes of each bushing current transformer, the injection location of the interference source can be directly determined. For internal discharge, using the attenuation characteristics of high-frequency pulse signals in the winding and combining with calibration signals, the distance ratio from the discharge point to the head end of the winding is calculated, achieving precise positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts. In the drawings: Figure 1 is a schematic flow chart of a method for local discharge location of a transformer based on bushing CT acquisition provided by an embodiment of the present application; Figure 2 is a schematic wiring diagram of high-frequency partial discharge pulse signal acquisition provided by an embodiment of the present application; Figure 3 is a schematic flow chart of amplitude correction for high-frequency partial discharge pulse signals provided by an embodiment of the present application; Figure 4 is a schematic diagram of the polarity of a winding when the transformer is subject to external interference provided by an embodiment of the present application; Figure 5 is a schematic diagram of the polarity of a winding when there is internal partial discharge in the transformer provided by an embodiment of the present application; Figure 6 is a schematic diagram of the location of the discharge point of the winding provided by an embodiment of the present application; Figure 7 is a schematic flow chart of calculating the distance ratio from the local discharge location to the head end of the winding provided by an embodiment of the present application; Figure 8 is a schematic structural diagram of a device for local discharge location of a transformer based on bushing CT acquisition provided by an embodiment of the present application; Figure 9It is a schematic structural diagram of the amplitude correction unit provided by an embodiment of the present application; Figure 10 It is a schematic structural diagram of the second positioning unit provided by an embodiment of the present application; Figure 11 It is a schematic structural diagram of an electronic device provided by an embodiment of the present invention. Specific embodiments

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer and more understandable, the following further describes the embodiments of the present invention in detail with reference to the accompanying drawings. Herein, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

[0020] Since in the existing transformer partial discharge location methods, the ultrasonic location method has low detection sensitivity for internal transformer discharges and large errors in solving the equations; the UHF location method is easily interfered by on-site UHF electromagnetic signals, has high requirements for receiving devices such as antennas, and also requires solving equations, which limits the positioning accuracy; the high-frequency multi-terminal detection technology measures partial discharge signals through high-frequency current sensors led out from the bushing end shields, and the device reliability is insufficient, the electromagnetic interference is serious, and the signal attenuation degree is high, reducing the receiving performance. Therefore, the purpose of the present application is to provide a transformer partial discharge location method and device that can quickly identify external interference and internal partial discharge signals, are not affected by electromagnetic interference, and have accurate discharge location.

[0021] As Figure 1 shown is a schematic flow diagram of a transformer partial discharge location method based on bushing CT acquisition provided by an embodiment of the present application. The method includes the following steps: Step S101: Collect high-frequency partial discharge pulse signals at the secondary side terminals of the current transformers of the transformer bushings. The transformer bushings include high-voltage side bushings, medium-voltage side bushings, neutral point bushings, low-voltage side head bushings, and low-voltage side end bushings.

[0022] In this embodiment, the secondary side wiring terminals of the current transformers at these bushings can be connected to observation devices such as oscilloscopes through protective resistors, and then the corresponding high-frequency partial discharge pulse signals can be collected. As Figure 2 shown is a schematic wiring diagram for collecting high-frequency partial discharge pulse signals provided by an embodiment of the present application. Figure 2 It is a wiring diagram drawn to avoid repeated intersections with the capacitor branch and does not represent the actual position. Figure 2Among them, a, x, Am, A, and X respectively represent the bushing lead terminals of the transformer at the low-voltage head end, low-voltage tail end, medium voltage, high voltage, and neutral point. L1 and L2 represent the low-voltage windings, L3 and L4 represent the common windings of the high voltage and medium voltage (abbreviated as common windings), and L5 and L6 represent the high-voltage series windings. C1, C2, C3, and C4 respectively represent the capacitances between the low-voltage winding and the iron core, the common winding and the low-voltage winding, the high-voltage series winding and the common winding, and the box shell and the high-voltage series winding.

[0023] Step S102: Perform discrete wavelet decomposition on the high-frequency partial discharge pulse signal to obtain wavelet coefficients.

[0024] Since the collected high-frequency partial discharge pulse signal usually contains relatively large low-frequency background noise, which will mask the polarity characteristics of the pulse signal and is not conducive to the subsequent polarity discrimination. Therefore, this application needs to remove the background noise of the high-frequency partial discharge pulse signal. In this embodiment, the wavelet threshold denoising algorithm is used to remove the background noise.

[0025] Since the collected high-frequency partial discharge pulse signal is a time series, it can be denoted as x(t), where t = 1, 2,..., N, and N is the signal length.

[0026] In this step, the original signal x(t) is first subjected to discrete wavelet decomposition through the following formula (1) to obtain wavelet coefficients: (1) In the above formula a j ( n ) is the approximation coefficient, d j ( n ) is the detail coefficient, h is the low-pass filter, g is the high-pass filter, j is the decomposition level.

[0027] Step S103: Select a soft threshold function to perform threshold processing on the wavelet coefficients for denoising.

[0028] Specifically, this step can be represented by the following formula (2): (2) In the above formula W j,k represents the j th k wavelet coefficient w j,k The corresponding wavelet coefficient after denoising, sgn(.) is the sign function; λ is a threshold in a fixed form, and the value is: (3) In the above formula, σ is the standard deviation of the noise signal, N and is the signal length.

[0029] Step S104: Reconstruct the signal using the denoised wavelet coefficients to obtain the high-frequency partial discharge pulse signal after removing the background noise.

[0030] The formula for signal reconstruction is shown in the following formula (4): (4) In the above formula, y ( t ) is the reconstructed signal, J is the total number of decomposition levels. In this embodiment, the wavelet basis function is selected as the db4 wavelet, and the total number of decomposition levels is set to , where is the floor function.

[0031] Step S105: Based on the frequency response characteristics of the current transformer, perform amplitude correction on the high-frequency partial discharge pulse signal after removing the background noise to obtain a corrected pulse signal.

[0032] In actual operation, the models of the current transformers of each bushing of the transformer are different, resulting in different transmission capabilities for high-frequency partial discharge pulse signals.

[0033] Preferably, in order to eliminate the influence of this factor, this embodiment corrects the pulse signal amplitude based on the characteristic that the frequency response of the bushing current transformer remains unchanged. As Figure 3 shown, this step may further include the following sub-steps: Step S1051: Inject a calibration pulse signal into the end of any selected bushing of the transformer and calculate the spectrum of the calibration pulse signal.

[0034] Let the injected calibration pulse signal be p ( t ), and use the following formula (5) to calculate the spectrum of the calibration pulse p ( jω ): (5) In the above formula, j is the imaginary unit, ω is the normalized angular frequency.

[0035] Step S1052: Collect the induced signal at the secondary side port of the selected bushing and calculate the spectrum of the induced signal. Specifically, the spectrum of the induced signal is calculated according to the following formula (6): (6) In the above formula, R (jω ) is the spectrum of the induction signal, r ( t ) is the induction signal at the selected secondary side port of the casing.

[0036] Step S1053: Calculate the frequency response of the selected casing by using the spectrum of the calibration pulse signal and the spectrum of the induction signal. Specifically, the frequency response of the selected casing is calculated according to the following formula (7): (7) In the above formula, H ( jω ) is the frequency response of the selected casing.

[0037] Step S1054: Calculate the spectrum of the high-frequency partial discharge pulse signal of the selected casing. The high-frequency partial discharge pulse signal here refers to the pulse signal after removing the background noise. Therefore, the calculated spectrum is also the spectrum after removing the noise. Specifically, it is calculated according to the following formula (8): (8) In the above formula, Y ( jω ) is the spectrum of the high-frequency partial discharge pulse signal after removing the background noise, y ( t ) is the corresponding high-frequency partial discharge pulse time-domain signal, j is the imaginary unit, ω is the normalized angular frequency, N is the signal length.

[0038] Step S1055: Calculate the spectrum of the original pulse transmitted to the selected casing by using the spectrum of the high-frequency partial discharge pulse signal and the frequency response. Specifically, the spectrum of the original pulse of the selected casing is obtained according to the following formula (9): (9) In the above formula, Z ( jω ) is the spectrum of the original pulse of the selected casing.

[0039] Step S1056: Obtain the time-domain signal through the inverse discrete Fourier transform based on the spectrum of the original pulse. Specifically, the time-domain signal is obtained according to the following formula (10): (10) In the above formula, z ( t ) is the time-domain signal.

[0040] Step S1057: Take the modulus of the time-domain signal and find the maximum value to obtain the corrected amplitude, as shown in the following formula (11): (11) In the above formula, N is the signal length, M is the corrected amplitude.

[0041] Step S106: Determine whether the partial discharge of the transformer belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signal. If it belongs to external interference, go to step S107; if it belongs to internal partial discharge, go to step S108.

[0042] When the transformer is under external interference or internal partial discharge occurs, the high-frequency partial discharge pulse signals induced in different bushing current transformers will show different polarity characteristics.

[0043] When the transformer is under external interference, the interference signal invades from the top of a certain bushing, reaches the other end of the winding along the winding direction, and reaches other sensing positions through the capacitance between windings, the capacitance between the winding and the box shell, and the capacitance between the winding and the iron core. During this period, the current direction does not change, making the polarity of the pulse signals flowing through each bushing current transformer the same. Taking the high-voltage series winding and the common winding as an example, the current polarity can be seen in Figure 4 shown.

[0044] When internal discharge occurs in the transformer, the partial discharge location can be regarded as a pulse source, sending high-frequency current pulse signals with opposite polarities to both sides, causing the pulse signals between each bushing current transformer to have opposite polarities. Taking the high-voltage series winding and the common winding as an example, the current polarity can be seen in Figure 5 shown, where the dotted line and the solid line represent high-frequency partial discharge pulse signals with opposite propagation directions.

[0045] Therefore, this step can further include: judging whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the partial discharge of the transformer belongs to external interference; if they are different, it is determined that the partial discharge of the transformer belongs to internal partial discharge of the transformer.

[0046] Step S107: Compare the amplitudes of the corrected acquisition signals corresponding to each bushing. The position corresponding to the bushing current transformer with the largest amplitude is the interference source injection position.

[0047] The amplitude of the bushing current transformer into which the external interference signal is injected is the highest, significantly greater than that of other bushing current transformers. The following is an example for illustration: Denote the amplitudes of the corrected acquisition signals of the high-voltage, medium-voltage, and low-voltage primary bushing current transformers as M A 、MA m、M a , taking the current transformer of the high-voltage side bushing as an example, if the following conditions are met simultaneously: M A > K M MA m and M A > K M M a ; it is determined that the interference signal invades from the high-voltage side. In the above formula, K M is the amplitude coefficient, usually in the range of 1.1 to 1.2.

[0048] Step S108: According to the attenuation characteristics of the high-frequency pulse signal propagating in the winding and in combination with the pre-injected calibration square-wave signal, calculate the distance ratio from the partial discharge position to the head end of the winding to determine the discharge position.

[0049] When partial discharge occurs inside the transformer, the high-frequency pulse signal generated by the discharge source will propagate along both sides of the winding to the current transformer of the bushing. Since the electric field strength and magnetic field strength of the high-frequency pulse decay exponentially with the increase of the propagation distance, the amplitudes of the pulse signals received by the current transformers of the bushings at both ends of the winding will be different. Taking the Figure 2 corresponding low-voltage winding as an example, as Figure 6 shown, denote the total length of the winding as l , and the distance from the discharge point position to the head end of the winding as d .

[0050] As Figure 7 shown, this step may further include the following sub-steps: Step S1081: Before the partial discharge detection test starts, inject calibration square-wave signals with the same charge amount into the head end and the tail end of the winding to be measured respectively, and obtain the electric field strengths at the head end and the tail end of the winding to be measured.

[0051] In this embodiment, the winding to be measured is described by taking the low-voltage winding as an example, that is, calibration square-wave signals with the same charge amount are injected into the head end and the tail end of the low-voltage winding respectively in this step. Denote the attenuation constant of the electromagnetic wave in the low-voltage winding as , and at this time, there is: (12) In the above formula, E a , E x are the electric field strengths at the head end and the tail end of the low-voltage winding respectively.

[0052] Step S1082: Obtain the electromagnetic energy of the high-frequency partial discharge pulse signals collected at the bushing at the head and the end of the winding under test based on the electric field strength.

[0053] The electromagnetic energy of the high-frequency partial discharge pulse signal is proportional to the square of the electric field strength, that is: (13) (14) In the above formula, C is a constant; , are the electromagnetic energies of the high-frequency partial discharge pulse signals from the current transformers at the low-voltage head and end bushings, defined as: (15) (16) where z a ( i ), z x ( i ), i= 1, 2,... N is the time series of the pulse signals collected by the current transformers at the low-voltage head and end bushings after amplitude correction.

[0054] Thus, it can be obtained that: (17) In the above formula is the attenuation constant of the electromagnetic wave in the low-voltage winding.

[0055] Step S1083: Obtain the signal energies at the head and the end of the winding under test based on the length of the winding under test, the electromagnetic energy, and the electric field strength amplitude of the high-frequency pulse at the partial discharge location.

[0056] If a discharge occurs at a distance of d from the head of the low-voltage winding during the partial discharge detection test, record the signal energies at the head and the end of the low-voltage winding during the test as , respectively, then there is: (18) (19) In the above formula , are defined in the same way as , ; c is a constant; E mis the amplitude of the electric field strength of the high-frequency pulse at the partial discharge location.

[0057] Step S1084: Obtain the distance ratio from the partial discharge location to the winding head based on the electromagnetic energy and the signal energy, and then determine the discharge location.

[0058] After simplifying and combining the above formulas (18) and (19), we have: (20) (21) In the above formula, x is the distance between the partial discharge location and the winding head.

[0059] From this, the proportion of the partial discharge location from the winding head can be obtained as: (22) The common winding and the high-voltage series winding also have the same law as the above-mentioned low-voltage winding. For example, in the present invention, the head of the common winding can be defined as the middle-voltage side bushing lead-out terminal A m , and the end is the neutral point bushing lead-out terminal X; the head of the high-voltage series winding is defined as A, and the end is defined as A m .

[0060] As can be seen from the above, the method for local discharge location of a transformer based on bushing CT acquisition proposed by the present invention reduces the interference factors of background noise, eliminates the influence of the bushing current transformer on receiving high-frequency partial discharge pulse signals, and simplifies the method for determining the local discharge location of a transformer. Specifically, through polarity discrimination, it helps to quickly identify external interference and internal partial discharge signals, avoid misoperation of protection devices, and provides a basis for fault analysis and maintenance work. For external interference, by comparing the signal amplitudes of each bushing current transformer, the injection location of the interference source can be directly determined. For internal discharge, using the attenuation characteristics of high-frequency pulse signals in the winding and combining with calibration signals, the distance ratio from the discharge point to the winding head is calculated, realizing precise positioning.

[0061] As Figure 8 shown in the structural schematic diagram of a local discharge location device for a transformer based on bushing CT acquisition provided by an embodiment of the present application, the device includes: a signal acquisition unit 810, a wavelet decomposition unit 820, a denoising unit 830, a signal reconstruction unit 840, an amplitude correction unit 850, a discharge type judgment unit 860, a first positioning unit 870, and a second positioning unit 880. Among them: The signal acquisition unit 810 is used to acquire high-frequency partial discharge pulse signals from the secondary side terminals of the current transformers of the transformer bushings, and the transformer bushings include high-voltage side bushings, middle-voltage side bushings, neutral point bushings, low-voltage side head bushings, and low-voltage side end bushings.

[0062] A wavelet decomposition unit 820 is configured to perform discrete wavelet decomposition on the high-frequency partial discharge pulse signal to obtain wavelet coefficients.

[0063] A denoising unit 830 is configured to select a soft threshold function to perform threshold processing on the wavelet coefficients to remove background noise.

[0064] A signal reconstruction unit 840 is configured to reconstruct a signal by using the wavelet coefficients after removing background noise, so as to obtain the high-frequency partial discharge pulse signal after removing background noise.

[0065] An amplitude correction unit 850 is configured to perform amplitude correction on the high-frequency partial discharge pulse signal after removing background noise based on the frequency response characteristics of each bushing current transformer, so as to obtain a corrected pulse signal.

[0066] A discharge type determination unit 860 is configured to determine whether the partial discharge of the transformer belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signal.

[0067] A first positioning unit 870 is configured to, when the discharge type determination unit determines that it is external interference, compare the amplitudes of the corrected acquisition signals corresponding to each bushing, and the position corresponding to the bushing current transformer with the largest amplitude is the injection position of the interference source.

[0068] A second positioning unit 880 is configured to, when the discharge type determination unit determines that it is internal partial discharge of the transformer, calculate the distance ratio from the partial discharge position to the head end of the winding according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding and in combination with a pre-injected calibration square wave signal, so as to determine the discharge position.

[0069] Preferably, as Figure 9 shown, the above-mentioned amplitude correction unit 850 may further include: A first spectrum calculation module 851 injects a calibration pulse signal into the end of any selected bushing of the transformer and calculates the spectrum of the calibration pulse signal.

[0070] A second spectrum calculation module 852 is configured to collect the induced signal at the secondary side port of the selected bushing and calculate the spectrum of the induced signal.

[0071] A frequency response calculation module 853 is configured to calculate the frequency response of the selected bushing by using the spectrum of the calibration pulse signal and the spectrum of the induced signal.

[0072] A third spectrum calculation module 854 is configured to calculate the spectrum of the high-frequency partial discharge pulse signal of the selected bushing.

[0073] The fourth spectrum calculation module 855 is configured to calculate the spectrum of the original pulse transmitted to the selected bushing by using the spectrum of the high-frequency partial discharge pulse signal and the frequency response.

[0074] The inverse transformation module 856 is configured to obtain a time-domain signal through an inverse discrete Fourier transform based on the spectrum of the original pulse.

[0075] The amplitude correction module 857 is configured to take the modulus of the time-domain signal and find the maximum value to obtain a corrected amplitude.

[0076] Preferably, the above-mentioned discharge type determination unit 860 is specifically configured to: determine whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the partial discharge of the transformer belongs to external interference. If they are different, it is determined that the partial discharge of the transformer belongs to internal partial discharge of the transformer.

[0077] Preferably, as Figure 10 shown, the above-mentioned second positioning unit 880 may further include: The electric field strength acquisition module 881 is configured to inject calibration square wave signals with the same charge amount into the head end and the tail end of the winding to be measured before the partial discharge detection test starts, so as to obtain the electric field strengths at the head end and the tail end of the winding to be measured.

[0078] The electromagnetic energy acquisition module 882 is configured to obtain the electromagnetic energy of the high-frequency partial discharge pulse signals collected at the bushings at the head end and the tail end of the winding to be measured based on the electric field strength.

[0079] The signal energy acquisition module 883 is configured to obtain the signal energies at the head end and the tail end of the winding to be measured based on the length of the winding to be measured, the electromagnetic energy, and the electric field strength amplitude of the high-frequency pulse at the partial discharge location.

[0080] The discharge position determination module 884 is configured to obtain the distance ratio from the partial discharge position to the head end of the winding based on the electromagnetic energy and the signal energy, and further determine the discharge position.

[0081] As can be seen from the above, the transformer partial discharge positioning device based on bushing CT acquisition proposed by the present invention reduces the interference factors of background noise, eliminates the influence of the bushing current transformer on receiving high-frequency partial discharge pulse signals, and simplifies the method for determining the transformer partial discharge position. Specifically, through polarity discrimination, it helps to quickly identify external interference and internal partial discharge signals, avoid misoperation of the protection device, and provides a basis for fault analysis and maintenance work. For external interference, by comparing the signal amplitudes of each bushing current transformer, the injection position of the interference source can be directly determined. For internal discharge, by using the attenuation characteristics of high-frequency pulse signals in the winding and combining with calibration signals, the distance ratio from the discharge point to the head end of the winding is calculated, realizing precise positioning.

[0082] Figure 11 It is a schematic diagram of the electronic device provided by the embodiment of the present invention. Figure 11 The shown electronic device is a general data processing device, which includes a general computer hardware structure, and at least includes a processor 801 and a memory 802. The processor 801 and the memory 802 are connected through a bus 803. The memory 802 is adapted to store one or more instructions or programs executable by the processor 801. The one or more instructions or programs are executed by the processor 801 to implement the steps in the above-mentioned transformer partial discharge positioning method based on bushing CT acquisition.

[0083] The above-mentioned processor 801 can be an independent microprocessor or a set of one or more microprocessors. Thus, the processor 801 executes the commands stored in the memory 802 to execute the method flow of the embodiment of the present invention as described above to implement data processing and control of other devices. The bus 803 connects the above-mentioned multiple components together and at the same time connects the above-mentioned components to a display controller 804, a display device, and an input / output (IO) device 805. The input / output (IO) device 805 can be a mouse, a keyboard, a modem, a network interface, a touch input device, a somatosensory input device, a printer, and other devices well-known in the art. Typically, the input / output (IO) device 805 is connected to the system through an input / output (IO) controller 806.

[0084] Among them, the memory 802 can store software components, such as an operating system, a communication module, an interaction module, and application programs. Each of the above-mentioned modules and application programs corresponds to a set of executable program instructions for completing one or more functions and the methods described in the embodiment of the invention.

[0085] The embodiment of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned transformer partial discharge positioning method based on bushing CT acquisition are implemented.

[0086] The embodiment of the present invention also provides a computer program product, including a computer program / instructions. When the computer program / instructions are executed by a processor, the steps of the above-mentioned transformer partial discharge positioning method based on bushing CT acquisition are implemented.

[0087] The method and device for local discharge location of transformers based on bushing CT acquisition proposed by the present invention reduce the interference factors of background noise, eliminate the influence of bushing current transformers on receiving high-frequency partial discharge pulse signals, and simplify the method for determining the local discharge location of transformers. Specifically, through polarity discrimination, it helps to quickly identify external interference and internal partial discharge signals, avoid misoperation of protection devices, and provide a basis for fault analysis and maintenance work. For external interference, by comparing the signal amplitudes of each bushing current transformer, the injection location of the interference source can be directly determined. For internal discharge, using the attenuation characteristics of high-frequency pulse signals in the winding and combining with calibration signals, the distance ratio from the discharge point to the head end of the winding is calculated to achieve precise positioning.

[0088] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings. Many features and advantages of these embodiments are clear from this detailed description, and thus the claims are intended to cover all such features and advantages that fall within the true spirit and scope of these embodiments. In addition, since many modifications and changes are readily envisioned by those skilled in the art, the embodiments of the present invention are not to be limited to the exact structures and operations illustrated and described, but may cover all suitable modifications and equivalents that fall within their scope.

[0089] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0090] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate means for realizing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0091] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction device that implements the functions specified in one or more of the processes and / or blocks Figure 1 in one or more of the processes and / or blocks Figure 1 specified in the function.

[0092] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one or more of the processes and / or blocks Figure 1 in one or more of the processes and / or blocks Figure 1 specified in the function.

[0093] The specific embodiments described above further elaborate on the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for local discharge location of a transformer based on casing CT acquisition, characterized in that, The method includes: Collecting high-frequency partial discharge pulse signals at the secondary terminal of the current transformer of the transformer bushing, where the transformer bushing includes a high-voltage side bushing, a medium-voltage side bushing, a neutral point bushing, a low-voltage side first-end bushing, and a low-voltage side end bushing; Performing discrete wavelet decomposition on the high-frequency partial discharge pulse signals to obtain wavelet coefficients; Selecting a soft threshold function to perform threshold processing on the wavelet coefficients to remove background noise; Reconstructing the signal using the wavelet coefficients after removing background noise to obtain the high-frequency partial discharge pulse signals after removing background noise; Performing amplitude correction on the high-frequency partial discharge pulse signals after removing background noise based on the frequency response characteristics of the current transformer to obtain corrected pulse signals; Determining whether the partial discharge of the transformer belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signals; If it is determined to be external interference, then compare the amplitudes of the corrected acquisition signals corresponding to each bushing, and the position corresponding to the current transformer of the bushing with the largest amplitude is the interference source injection position; If it is determined to be internal partial discharge of the transformer, then according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding, combined with the pre-injected calibration square wave signal, calculate the distance ratio from the partial discharge position to the winding head end to determine the discharge position.

2. The method for local discharge location of a transformer based on sleeve CT acquisition according to claim 1, wherein, The amplitude correction of the high-frequency partial discharge pulse signals after removing background noise based on the frequency response characteristics of each bushing current transformer includes: Injecting a calibration pulse signal into the end of any selected bushing of the transformer and calculating the spectrum of the calibration pulse signal; Collecting the induced signal at the secondary side port of the selected bushing and calculating the spectrum of the induced signal; Calculating the frequency response of the selected bushing using the spectrum of the calibration pulse signal and the spectrum of the induced signal; Calculating the spectrum of the high-frequency partial discharge pulse signal corresponding to the selected bushing; Calculating the spectrum of the original pulse transmitted to the selected bushing using the spectrum of the high-frequency partial discharge pulse signal and the frequency response; Obtaining a time-domain signal through inverse discrete Fourier transform based on the spectrum of the original pulse; Taking the modulus of the time-domain signal and finding the maximum value to obtain the corrected amplitude.

3. The method for local discharge location of a transformer based on sleeve CT acquisition according to claim 1, wherein The determination of whether the partial discharge of the transformer belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signals includes: Judging whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the partial discharge of the transformer belongs to external interference. If they are different, it is determined that the partial discharge of the transformer belongs to internal partial discharge of the transformer.

4. The method for local discharge location of a transformer based on casing CT acquisition according to claim 1, wherein, The calculation of the distance ratio from the partial discharge position to the winding head end to determine the discharge position according to the attenuation characteristics of the high-frequency pulse signal propagating in the winding, combined with the pre-injected calibration square wave signal, includes: Before the start of the partial discharge detection test, injecting calibration square wave signals with the same charge amount into the head end and the end of the winding to be measured, and obtaining the electric field strengths at the head end and the end of the winding to be measured; Obtaining the electromagnetic energies of the high-frequency partial discharge pulse signals collected at the head end and the end bushings of the winding to be measured based on the electric field strengths; Obtain the signal energy at the head and end of the winding to be measured based on the length of the winding to be measured, the electromagnetic energy, and the amplitude of the electric field strength of the high-frequency pulse at the partial discharge location; Based on the electromagnetic energy and the signal energy, obtain the distance ratio from the partial discharge location to the head of the winding, and then determine the discharge location.

5. A partial discharge location device for a transformer based on sleeve CT acquisition, characterized in that, The device includes: A signal acquisition unit for acquiring high-frequency partial discharge pulse signals at the secondary side terminals of the current transformers of the transformer bushings, where the transformer bushings include high-voltage side bushings, medium-voltage side bushings, neutral point bushings, low-voltage side head bushings, and low-voltage side end bushings; A wavelet decomposition unit for performing discrete wavelet decomposition on the high-frequency partial discharge pulse signals to obtain wavelet coefficients; A denoising unit for selecting a soft threshold function to perform threshold processing on the wavelet coefficients to remove background noise; A signal reconstruction unit for reconstructing a signal using the wavelet coefficients after removing background noise to obtain the high-frequency partial discharge pulse signal after removing background noise; An amplitude correction unit for performing amplitude correction on the high-frequency partial discharge pulse signal after removing background noise based on the frequency response characteristics of each bushing current transformer to obtain a corrected pulse signal; A discharge type judgment unit for determining whether the partial discharge of the transformer belongs to external interference or internal partial discharge based on the polarity distribution law of the corrected pulse signal; A first positioning unit for, when the discharge type judgment unit determines it to be external interference, comparing the amplitudes of the corrected acquisition signals corresponding to each bushing, and the position corresponding to the bushing current transformer with the largest amplitude is the interference source injection position; A second positioning unit for, when the discharge type judgment unit determines it to be internal partial discharge of the transformer, calculate the distance ratio from the partial discharge location to the head of the winding based on the attenuation characteristics of the high-frequency pulse signal propagating in the winding and in combination with a pre-injected calibration square wave signal to determine the discharge location.

6. The partial discharge localization device of a transformer based on casing CT acquisition according to claim 5, characterized in that, The amplitude correction unit includes: A first spectrum calculation module for injecting a calibration pulse signal into the end of any selected bushing of the transformer and calculating the spectrum of the calibration pulse signal; A second spectrum calculation module for collecting the induced signal at the secondary side port of the selected bushing and calculating the spectrum of the induced signal; A frequency response calculation module for calculating the frequency response of the selected bushing using the spectrum of the calibration pulse signal and the spectrum of the induced signal; A third spectrum calculation module for calculating the spectrum of the high-frequency partial discharge pulse signal of the selected bushing; A fourth spectrum calculation module for calculating the spectrum of the original pulse transmitted to the selected bushing using the spectrum of the high-frequency partial discharge pulse signal and the frequency response; An inverse transform module for obtaining a time-domain signal through inverse discrete Fourier transform based on the spectrum of the original pulse; An amplitude correction module for taking the modulus of the time-domain signal and finding the maximum value to obtain a corrected amplitude.

7. The partial discharge localization device for transformer based on bushing CT acquisition according to claim 5, characterized in that The discharge type judgment unit is specifically used for: judging whether the polarities of the corrected pulse signals corresponding to each bushing are the same. If they are the same, it is determined that the partial discharge of the transformer belongs to external interference. If they are not the same, it is determined that the partial discharge of the transformer belongs to internal partial discharge of the transformer.

8. The partial discharge localization device of a transformer based on casing CT acquisition according to claim 5, characterized in that, The second positioning unit includes: An electric field strength acquisition module is used to inject a calibration square wave signal with the same charge amount into the head end and the tail end of the winding to be tested before the partial discharge detection test starts, so as to obtain the electric field strength of the head end and the tail end of the winding to be tested; An electromagnetic energy acquisition module, used to obtain the electromagnetic energy of the high-frequency partial discharge pulse signal collected at the head end and the end bushing of the winding to be tested based on the electric field strength; A signal energy acquisition module, used to obtain the signal energy of the head end and the tail end of the winding to be measured based on the length of the winding to be measured, the electromagnetic energy and the electric field strength amplitude of the high-frequency pulse at the partial discharge; The discharge position determination module is used to obtain the distance ratio from the local discharge position to the winding head end based on the electromagnetic energy and the signal energy, and then determine the discharge position.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, the steps of the method according to any one of claims 1 to 4 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

11. A computer program product, comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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