Cable partial discharge positioning method based on time-frequency domain matched filter

Abstract

The invention discloses a cable partial discharge positioning method based on a time-frequency domain matched filter, and relates to the technical field of cable detection, and the method comprises the steps: obtaining an original discharge signal of a target cable; filtering the original discharge signal by using a zero phase filter to obtain a de-noised discharge signal; constructing a plurality of time-frequency domain matched filters based on the de-noised discharge signals; performing matched filtering on the de-noised discharge signal based on a plurality of time-frequency domain matched filters to obtain a plurality of filtering results; and positioning a discharge position according to a filtering result. According to the invention, the noise-containing partial discharge signal is preprocessed by using the zero-phase filter, the phase information of the partial discharge signal is reserved while the noise is effectively reduced, and the result of subsequent matched filtering is ensured to be more accurate, so that higher-precision positioning is realized; by constructing the matched filter for matched filtering, the pulse arrival time can be prevented from being extracted under the condition of low signal-to-noise ratio, so that the anti-noise interference capability and the positioning precision are remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of cable detection technology, and in particular to a cable partial discharge positioning method based on time-frequency domain matching filters. Background Art

[0002] In the related technologies, partial discharge is one of the important manifestations of the deterioration of the insulation materials of power cables, and its accurate positioning is crucial for cable maintenance and fault prevention. The traditional cable partial discharge positioning method based on time-frequency domain matching filters is the time domain reflection method, which locates partial discharge by estimating the time difference between the partial discharge traveling wave and its terminal reflected wave. Therefore, it is necessary to calculate the pulse arrival time of the partial discharge incident wave and the reflected wave. The common calculation methods currently include the threshold method, the energy method, the correlation method, etc.

[0003] However, when the noise on site is serious, due to the serious attenuation of the local discharge signal, the signal-to-noise ratio of the collected pulse signal is low, making it difficult to accurately extract the pulse start time, making it difficult to obtain accurate positioning results.

[0004] Therefore, how to locate the position of partial discharge more accurately is a problem that needs to be solved urgently. Summary of the invention

[0005] The main purpose of the present application is to provide a cable partial discharge location method based on a time-frequency domain matched filter, aiming to solve the technical problem of how to locate the position of partial discharge more accurately.

[0006] To achieve the above objectives, the present application proposes a cable partial discharge location method based on a time-frequency domain matched filter. The cable partial discharge location method based on a time-frequency domain matched filter includes: Obtain the original discharge signal of the target cable; Using a zero-phase filter to filter the original discharge signal to obtain a denoised discharge signal; Based on the denoised discharge signal, construct a plurality of time-frequency domain matched filters, wherein each of the time-frequency domain matched filters corresponds to a different cable length; Based on the multiple time-frequency domain matched filters, performing matched filtering on the denoised discharge signal to obtain multiple filtering results; The discharge position is located according to the filtering result.

[0007] In some embodiments, the zero-phase filter is a finite impulse response bandpass filter; the step of filtering the original discharge signal using the zero-phase filter to obtain a denoised discharge signal includes: Using a finite impulse response bandpass filter to forward filter the original discharge signal to obtain an intermediate output signal; The intermediate output signal is inversely filtered using the finite impulse response bandpass filter to obtain the denoised discharge signal.

[0008] In some embodiments, the constructing of multiple time-frequency domain matched filters based on the denoised discharge signal includes: Calculating target parameters corresponding to cables of multiple target lengths according to standard parameters, wherein the standard parameters correspond to the target cables of unit length, and the multiple target lengths are different; For each of the target lengths, a time-frequency domain matched filter corresponding to the target length is constructed based on the corresponding target parameters and the denoised discharge signal.

[0009] In some embodiments, for each of the target lengths, based on the corresponding target parameters and the denoised discharge signal, constructing a time-frequency domain matched filter corresponding to the target length includes: Performing Fourier transform on the denoised discharge signal to obtain a frequency domain signal; For each of the target lengths, taking the product of the target parameter corresponding to the target length and the frequency domain signal as a reference frequency domain signal; Performing an inverse Fourier transform on the reference frequency domain signal to obtain a reference time domain signal corresponding to the target length; Performing short-time Fourier transform on the reference time domain signal, and using the complex conjugate of the transform result as the time-frequency domain matched filter corresponding to the target length.

[0010] In some embodiments, the denoised discharge signal is subjected to matched filtering based on the multiple time-frequency domain matched filters to obtain multiple filtering results, including: Performing short-time Fourier transform on the denoised discharge signal to obtain a transformed signal; For each of the time-frequency domain matched filters, the transformed signal is multiplied by the corresponding time-frequency domain matched filter to obtain a corresponding filtering result.

[0011] In some embodiments, locating the discharge position according to the filtering result includes: Calculate the maximum value of the modulus of each of the plurality of filtering results; The time-frequency domain matched filter corresponding to the filtering result with the highest modulus value maximum is used as the target time-frequency domain matched filter; The preset proportional position of the cable length corresponding to the target time-frequency domain matched filter is determined as the discharge position corresponding to the original discharge signal.

[0012] One or more technical solutions proposed in this application have at least the following technical effects: By using a zero-phase filter to preprocess the noisy partial discharge signal, the phase information of the partial discharge signal is retained while effectively reducing the noise, ensuring that the results of subsequent matched filtering are more accurate, thereby achieving higher-precision positioning; in addition, by constructing a matched filter for matched filtering, it can be applied to partial discharge signals with non-stationary characteristics, and avoids extracting pulse arrival time when the signal-to-noise ratio is low, thereby significantly improving the anti-noise interference ability and positioning accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 A schematic flow chart of a cable partial discharge location method based on a time-frequency domain matched filter provided in an embodiment of the present application is shown.

[0016] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0017] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0018] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0019] The main solution of the embodiment of the present application is: obtaining the original discharge signal of the target cable; filtering the original discharge signal with a zero-phase filter to obtain a denoised discharge signal; constructing multiple time-frequency domain matched filters based on the denoised discharge signal, wherein each time-frequency domain matched filter corresponds to a different cable length; based on the multiple time-frequency domain matched filters, matching filtering is performed on the denoised discharge signal to obtain multiple filtering results; and locating the discharge position according to the filtering results.

[0020] In the related technologies, partial discharge is one of the important manifestations of the deterioration of the insulation materials of power cables, and its accurate positioning is crucial for cable maintenance and fault prevention. The traditional cable partial discharge positioning method based on time-frequency domain matching filters is the time domain reflection method, which locates partial discharge by estimating the time difference between the partial discharge traveling wave and its terminal reflected wave. Therefore, it is necessary to calculate the pulse arrival time of the partial discharge incident wave and the reflected wave. The common calculation methods currently include the threshold method, the energy method, the correlation method, etc.

[0021] However, in the related art, when the on-site noise is serious, due to the serious attenuation of the local discharge signal, the signal-to-noise ratio of the collected pulse signal is low, and it is difficult to accurately extract the pulse start time, thereby making it difficult to obtain accurate positioning results.

[0022] In summary, how to locate the position of partial discharge more accurately is a problem that needs to be solved urgently.

[0023] Based on this, the present application provides a solution to enable the location where partial discharge occurs in the cable to be located more accurately.

[0024] It should be noted that the execution subject of this embodiment can be a computing service device with data processing, network communication and program running functions, such as a tablet computer, a personal computer, a mobile phone, etc., or a cable partial discharge locating device based on a time-frequency domain matching filter that can realize the above functions. The following takes the cable partial discharge locating device based on a time-frequency domain matching filter as an example to illustrate this embodiment and the following embodiments.

[0025] Reference Figure 1 , Figure 1 The schematic diagram of the flow chart of the cable partial discharge location method based on the time-frequency domain matching filter provided by an embodiment of the present application is shown. The cable partial discharge location method based on the time-frequency domain matching filter can be applied to the cable partial discharge location device based on the time-frequency domain matching filter, including the following steps S110 to S150: Step S110, obtaining the original discharge signal of the target cable.

[0026] The target cable refers to the cable to be tested. The cable partial discharge locating device based on the time-frequency domain matched filter in the embodiment of the present application can be set for a single cable to be tested, or can be set for multiple cables to be tested at the same time, which is not limited in this embodiment.

[0027] In this embodiment, the target cable may have partial discharge at a certain position of the target cable due to known or unknown reasons (such as cable aging, mechanical damage, etc.). The staff can detect this partial discharge through a preset measuring device and collect the signal generated by the partial discharge, that is, the original discharge signal.

[0028] The preset measuring device may be a high-frequency current transformer. When the high-frequency current transformer is used to collect the signal generated by the partial discharge, the complete signal of the incident wave and the reflected wave of the partial discharge can be collected, that is, the original discharge signal contains the complete signal of the incident wave and the reflected wave of the partial discharge.

[0029] Step S120, filtering the original discharge signal with a zero-phase filter to obtain a denoised discharge signal.

[0030] Among them, the zero-phase filter refers to a special digital filter that does not introduce additional phase delay during the filtering process, that is, the phase difference between the output signal and the input signal is zero. In the actual application of the zero-phase filter, the filter is usually applied twice in the forward and reverse directions to eliminate the distortion caused by the phase accumulation in a single filtering process.

[0031] In some implementations, the zero-phase filter is a finite impulse response bandpass filter; it is understandable that the bandpass filter can be customized by the staff, and this is not set in this embodiment.

[0032] It is understandable that the use of a zero phase filter to pre-process the noisy partial discharge signal in step S120 can retain the phase information of the partial discharge signal while effectively reducing the noise, ensuring that the subsequent matched filtering result is more accurate, thereby achieving higher precision positioning.

[0033] In this embodiment, a finite impulse response bandpass filter may be used to forward filter the original discharge signal to obtain an intermediate output signal; and a finite impulse response bandpass filter may be used to reverse filter the intermediate output signal to obtain a denoised discharge signal.

[0034] Specifically, the original discharge signal is defined as x[n], which contains n signal samples, and the forward filtering can be expressed as follows:

[0035] in, That is, the intermediate output signal corresponding to the nth signal sample; is the preset coefficient of the bandpass filter, and N is the length of the bandpass filter.

[0036] After obtaining the intermediate output signals corresponding to all signal samples, the same finite impulse response bandpass filter is used to Perform reverse filtering, that is, perform filtering from the last signal sample forward. Reverse filtering can be expressed as follows:

[0037] in, That is the denoised discharge signal corresponding to the nth signal sample.

[0038] Step S130: construct multiple time-frequency domain matched filters based on the denoised discharge signal.

[0039] In some implementations, before executing step S130, standard parameters may be acquired for the target cable, wherein the standard parameters correspond to the target cable per unit length.

[0040] Specifically, a three-dimensional model may be constructed for the target cable (for example, a COMSOL Multiphysics tool may be used to construct a COMSOL model). The following further describes the COMSOL model as an example.

[0041] By analyzing the target cable based on the COMSOL model, the cable per unit length can be obtained. Parameters, that is, standard parameters in this embodiment. Among them, the unit length can be set by the staff, and this embodiment does not limit it here. Parameters refer to the ability of a signal to be transmitted from one port to another, and can be measured by running simulations based on the COMSOL model.

[0042] In some embodiments, after obtaining the standard parameters Afterwards, target parameters corresponding to cables of multiple target lengths can be calculated based on the standard parameters.

[0043] Wherein, the multiple target lengths are different, and the multiple target lengths can be different integer multiples of the unit length, for example, n unit lengths of cables, where n is a positive integer. In some embodiments, the target parameter of a cable having a length L is defined as: ,but It can be calculated by the following expression:

[0044] in, It represents the transmission gain per unit length of cable. Indicates the phase shift per unit length of cable.

[0045] After obtaining the target parameters corresponding to the cables of multiple target lengths respectively through the above method, a time-frequency domain matched filter corresponding to the target length can be constructed for each target length based on the corresponding target parameters and the denoised discharge signal.

[0046] In some implementations, the de-noised discharge signal may be subjected to Fourier transform to obtain a frequency domain signal. Specifically, referring to the definitions of the parameters and variables in the above expression, the frequency domain signal may be obtained using the following expression:

[0047] In some embodiments, for each target length, the product of the target parameter corresponding to the target length and the frequency domain signal is used as a reference frequency domain signal; the reference frequency domain signal is inverse Fourier transformed to obtain a reference time domain signal corresponding to the target length; the reference time domain signal is short-time Fourier transformed, and the complex conjugate of the transformation result is used as the corresponding time-frequency domain matched filter.

[0048] Specifically, based on the target parameters and the denoised discharge signal, constructing the corresponding time-frequency domain matched filter (for each target length) can include the following steps: ① Frequency domain signal With target parameters Multiply to get the reference frequency domain signal The expression is:

[0049] ②For the reference frequency domain signal Perform inverse Fourier transform to obtain the reference time domain signal The expression is:

[0050] ③For the reference time domain signal Perform short-time Fourier transform and take the complex conjugate to obtain the time-frequency domain matched filter. The expression is:

[0051] in, is the window function.

[0052]

[0053] For each length, based on the above steps, the corresponding time-frequency domain matched filter can be obtained.

[0054] Step S140: performing matched filtering on the denoised discharge signal based on multiple time-frequency domain matched filters to obtain multiple filtering results.

[0055] In some implementations, the denoised discharge signal may be subjected to a short-time Fourier transform to obtain a transformed signal; and for each of the time-frequency domain matched filters, the transformed signal may be multiplied by the corresponding time-frequency domain matched filter to obtain a corresponding filtering result.

[0056] Specifically, the short-time Fourier transform of the denoised discharge signal can be calculated by the following expression:

[0057] The filtering result can be obtained by the following expression:

[0058] Step S150, locating the discharge position according to the filtering result.

[0059] In some implementations, the maximum value of the modulus of each of the plurality of filtering results may be calculated first. Specifically, the maximum value of the modulus calculated for each filtering result may be calculated by the following expression:

[0060] After obtaining the maximum modulus value of each filtering result, multiple maximum modulus values ​​are sorted according to numerical values, and the time-frequency domain matched filter corresponding to the filtering result with the highest maximum modulus value is used as the target time-frequency domain matched filter.

[0061] The preset proportional position of the cable length corresponding to the target time-frequency domain matched filter is determined as the discharge position corresponding to the original discharge signal.

[0062] The preset proportional position may be 50%, that is, the distance from the location where the partial discharge signal occurs to the end of the cable (ie, the collection end) is 50% of the corresponding cable length.

[0063] This embodiment provides a cable partial discharge positioning method based on time-frequency domain matched filter. By using a zero-phase filter to preprocess the noisy partial discharge signal, the phase information of the partial discharge signal is retained while effectively reducing the noise, ensuring that the results of subsequent matched filtering are more accurate, thereby achieving higher-precision positioning; in addition, by constructing a matched filter for matched filtering, it can be applicable to partial discharge signals with non-stationary characteristics, and avoids extracting pulse arrival time when the signal-to-noise ratio is low, thereby significantly improving the anti-noise interference capability and positioning accuracy.

[0064] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A cable partial discharge location method based on time-frequency domain matched filter, characterized in that: The cable partial discharge positioning method based on time-frequency domain matched filter includes: Obtain the original discharge signal of the target cable; Using a zero-phase filter to filter the original discharge signal to obtain a denoised discharge signal; Based on the denoised discharge signal, construct a plurality of time-frequency domain matched filters, wherein each of the time-frequency domain matched filters corresponds to a different cable length; Based on the multiple time-frequency domain matched filters, performing matched filtering on the denoised discharge signal to obtain multiple filtering results; The discharge position is located according to the filtering result.

2. The cable partial discharge location method based on time-frequency domain matched filter according to claim 1, characterized in that: The zero-phase filter is a finite impulse response bandpass filter; The step of filtering the original discharge signal with a zero phase filter to obtain a denoised discharge signal comprises: Using a finite impulse response bandpass filter to forward filter the original discharge signal to obtain an intermediate output signal; The intermediate output signal is inversely filtered using the finite impulse response bandpass filter to obtain the denoised discharge signal.

3. The cable partial discharge location method based on time-frequency domain matched filter according to claim 1, characterized in that: The method of constructing a plurality of time-frequency domain matched filters based on the denoised discharge signal comprises: Calculating target parameters corresponding to cables of multiple target lengths according to standard parameters, wherein the standard parameters correspond to the target cables of unit length, and the multiple target lengths are different; For each of the target lengths, a time-frequency domain matched filter corresponding to the target length is constructed based on the corresponding target parameters and the denoised discharge signal.

4. The cable partial discharge location method based on time-frequency domain matched filter according to claim 3 is characterized in that: For each of the target lengths, based on the corresponding target parameters and the denoised discharge signal, a time-frequency domain matched filter corresponding to the target length is constructed, including: Performing Fourier transform on the denoised discharge signal to obtain a frequency domain signal; For each of the target lengths, taking the product of the target parameter corresponding to the target length and the frequency domain signal as a reference frequency domain signal; Performing an inverse Fourier transform on the reference frequency domain signal to obtain a reference time domain signal corresponding to the target length; Performing short-time Fourier transform on the reference time domain signal, and using the complex conjugate of the transform result as the time-frequency domain matched filter corresponding to the target length.

5. The cable partial discharge location method based on time-frequency domain matched filter according to claim 1, characterized in that: The method further comprises performing matched filtering on the denoised discharge signal based on the multiple time-frequency domain matched filters to obtain multiple filtering results, including: Performing short-time Fourier transform on the denoised discharge signal to obtain a transformed signal; For each of the time-frequency domain matched filters, the transformed signal is multiplied by the corresponding time-frequency domain matched filter to obtain a corresponding filtering result.

6. The cable partial discharge location method based on time-frequency domain matched filter according to claim 1, characterized in that: The locating the discharge position according to the filtering result comprises: Calculate the maximum value of the modulus of each of the plurality of filtering results; The time-frequency domain matched filter corresponding to the filtering result with the highest modulus value maximum is used as the target time-frequency domain matched filter; The preset proportional position of the cable length corresponding to the target time-frequency domain matched filter is determined as the discharge position corresponding to the original discharge signal.

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