Cable insulation on-line monitoring method based on broadband oscillation signal injection

Abstract

The invention discloses a cable insulation on-line monitoring method based on broadband oscillation signal injection, and belongs to the field of power systems, and the method comprises the steps: obtaining and filtering a common-mode leakage current through injecting a broadband oscillation signal subjected to signal attenuation compensation and leakage inductance influence compensation correction; after the resonant frequency is extracted, the frequency variation is calculated in combination with the historical reference value, and the insulation aging state of the cable is quantitatively evaluated, so that the problem that the insulation aging degree is difficult to accurately and quantitatively evaluate due to signal attenuation, noise interference and leakage inductance coupling in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to an on-line monitoring method for cable insulation based on injection of broadband oscillation signals. Background Art

[0002] In modern power systems, the insulation state of underground power cables is directly related to the safety and stability of power grid operation. As the service time of the cables increases, the insulation layer gradually deteriorates due to factors such as electrical aging, thermal aging, and environmental erosion, resulting in changes in key parameters such as insulation capacitance and conductance. In severe cases, insulation breakdown accidents may occur.

[0003] In the prior art, the on-line monitoring method based on injection of broadband oscillation signals evaluates the insulation state by analyzing the frequency response characteristics of the cable common-mode impedance. However, due to the complexity of cable transmission characteristics and the influence of on-site operating environments, this technology has significant defects in practical applications: First, when broadband signals propagate in long-distance cables, amplitude attenuation will occur due to factors such as conductor resistance loss and insulation medium polarization effect, resulting in insufficient signal strength at the end to support accurate measurement; Second, high-frequency noise in the complex on-site electromagnetic environment is superimposed on the common-mode leakage current signal, causing deviation in impedance calculation results; In addition, additional resonance points formed by the coupling of the system transformer leakage inductance and cable distributed parameters will cause distortion of the measured resonance frequency. Due to the combined action of the above multiple factors, it is difficult for the existing monitoring methods to achieve accurate quantitative evaluation of the cable insulation aging degree. Summary of the Invention

[0004] The present invention provides an on-line monitoring method for cable insulation based on injection of broadband oscillation signals, which can solve the problem in the prior art that it is difficult to accurately quantitatively evaluate the aging degree of underground power cable insulation.

[0005] In a first aspect, an embodiment of the present invention provides an on-line monitoring method for cable insulation based on injection of broadband oscillation signals, including:

[0006] Obtaining a first common-mode leakage current in an underground power cable, and processing the first common-mode leakage current through a noise filtering method to obtain a second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first broadband oscillation signal into the underground power cable, and the first broadband oscillation signal is obtained by correcting a second broadband oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method;

[0007] Determining a resonance frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal;

[0008] Determine the change in the resonant frequency based on the resonant frequency and the pre-resonant frequency, and obtain the insulation state of the underground power cable according to the change in the resonant frequency.

[0009] In the embodiments of the present application, online monitoring of the insulation state of underground power cables is achieved by injecting broadband oscillation signals. The beneficial effects are as follows: First, through the signal attenuation compensation method and the leakage inductance influence compensation method, it is ensured that the first broadband oscillation signal maintains a stable amplitude in a complex transmission path and avoids the system interference frequency band; Second, the first common-mode leakage current is processed by combining a noise filtering method, providing a reliable data basis for the subsequent resonant frequency; Third, the resonant frequency characteristics are determined based on the corrected broadband signal and the processed current data to achieve a quantitative evaluation of the insulation state; Finally, by comparing the change in the current resonant frequency with the historical reference value, different aging stages such as mild and moderate are effectively identified. In summary, the present application can complete the monitoring without power outage or damaging the cable structure, injects signals in a non-invasive manner, and proposes compensation measures for adverse effects such as signal attenuation, noise interference, and leakage inductance, which can solve the problem in the prior art that it is difficult to accurately quantify and evaluate the insulation aging degree of underground power cables.

[0010] As a preferred example of the first aspect, the processing of the first common-mode leakage current by the noise filtering method to obtain the second common-mode leakage current includes:

[0011] Process the first common-mode leakage current using digital filtering technology to obtain a third common-mode leakage current;

[0012] Remove the high-frequency noise components in the third common-mode leakage current through the fast Fourier transform method to obtain the second common-mode leakage current.

[0013] In this preferred example, digital filtering technology is used to reduce the noise of the common-mode leakage current, effectively suppressing power frequency interference and environmental noise; then, frequency domain analysis is performed through the fast Fourier transform (FFT) to accurately separate the effective components within the target frequency band and remove high-frequency noise pollution, providing a reliable data basis for subsequent impedance calculation.

[0014] As a preferred example of the first aspect, the first broadband oscillation signal is obtained by correcting the second broadband oscillation signal using the signal attenuation compensation method and the leakage inductance influence compensation method, including:

[0015] According to the length and material characteristics of the underground power cable, obtain the attenuation value of the second broadband oscillation signal in the underground power cable, and adjust the second broadband oscillation signal according to the attenuation value to obtain a third broadband oscillation signal;

[0016] Adjust the frequency range of the third broadband oscillation signal according to the preset leakage inductance parameter to obtain a first broadband oscillation signal.

[0017] In this preferred example, signal attenuation compensation is performed based on the cable length and material characteristics, and the broadband oscillation signal is dynamically adjusted to ensure that the signal strength still meets the measurement requirements after long-distance transmission; furthermore, the frequency range of the broadband oscillation signal is optimized in combination with the leakage inductance parameter to avoid the resonant frequency offset area caused by the leakage inductance; in this way, the influence of signal attenuation and leakage inductance is effectively eliminated through a dual compensation mechanism, ensuring the reliability of subsequent resonant frequency extraction.

[0018] As a preferred example of the first aspect, determining the resonant frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal includes:

[0019] Obtain the common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal;

[0020] Adopt a frequency analysis method to extract the resonant frequency from the common-mode impedance, and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve;

[0021] Extract the peak point of the impedance amplitude from the frequency response curve, and determine the resonant frequency through the peak point.

[0022] In this preferred example, by extracting the peak point of the impedance amplitude through the frequency response curve, the resonant frequency can be accurately located, which is directly related to the cable insulation capacitance and can effectively reflect the degree of insulation aging.

[0023] As a preferred example of the first aspect, determining the resonant frequency change amount through the resonant frequency and the pre-resonant frequency, and obtaining the insulation state of the underground power cable according to the resonant frequency change amount includes:

[0024] Subtract the resonant frequency from the pre-resonant frequency to obtain the frequency change amount; wherein, the pre-resonant frequency is obtained from a preset historical database;

[0025] If the frequency change amount is greater than a preset first frequency threshold and less than a preset second frequency threshold, it is determined that the underground power cable is slightly aged; if the frequency change amount is greater than or equal to the preset second frequency threshold, it is determined that the underground power cable is moderately aged; otherwise, it is determined that the underground power cable is not aged.

[0026] In this preferred example, by comparing the current resonant frequency with the historical reference value and calculating the frequency change in real time, the aging trend of the cable insulation capacitance can be dynamically tracked, and the early deterioration of the insulation performance can be effectively identified. Secondly, based on the quantitative evaluation mechanism with a preset threshold, the aging state of the cable can be accurately distinguished.

[0027] Secondly, the embodiment of the present application also provides an on-line monitoring device for cable insulation based on wide-frequency oscillation signal injection, including: a data acquisition module, a frequency extraction module, and a state judgment module;

[0028] The data acquisition module is used to acquire the first common-mode leakage current in the underground power cable, and process the first common-mode leakage current through a noise filtering method to obtain a second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first wide-frequency oscillation signal into the underground power cable, and the first wide-frequency oscillation signal is obtained by correcting a second wide-frequency oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method;

[0029] The frequency extraction module is used to determine the resonant frequency according to the second common-mode leakage current and the voltage amplitude of the first wide-frequency oscillation signal;

[0030] The state judgment module is used to determine the resonant frequency change amount through the resonant frequency and the pre-resonant frequency, and obtain the insulation state of the underground power cable according to the resonant frequency change amount.

[0031] As a preferred example of the second aspect, the data acquisition module includes: a first data processing unit and a second data processing unit;

[0032] The first data processing unit is used to process the first common-mode leakage current by using digital filtering technology to obtain a third common-mode leakage current;

[0033] The second data processing unit is used to remove the high-frequency noise component in the third common-mode leakage current by using the fast Fourier transform method to obtain a second common-mode leakage current.

[0034] As a preferred example of the second aspect, the data acquisition module further includes: a first adjustment unit and a second adjustment unit;

[0035] The first adjustment unit is used to obtain the attenuation value of the second wide-frequency oscillation signal in the underground power cable according to the length and material characteristics of the underground power cable, and adjust the second wide-frequency oscillation signal according to the attenuation value to obtain a third wide-frequency oscillation signal;

[0036] The second adjustment unit is configured to adjust the frequency range of the third broadband oscillation signal according to a preset leakage inductance parameter to obtain a first broadband oscillation signal.

[0037] As a preferred example of the second aspect, the frequency extraction module includes: an impedance acquisition unit, a curve acquisition unit, and a frequency determination unit;

[0038] The impedance acquisition unit is configured to obtain a common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal;

[0039] The curve acquisition unit is configured to extract a resonance frequency from the common-mode impedance by using a frequency analysis method and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve;

[0040] The frequency determination unit is configured to extract a peak point of the impedance amplitude from the frequency response curve and determine the resonance frequency through the peak point.

[0041] As a preferred example of the second aspect, the state judgment module includes: a change amount determination unit and a judgment unit;

[0042] The change amount determination unit is configured to subtract the resonance frequency from the pre-resonance frequency to obtain the frequency change amount; wherein, the pre-resonance frequency is obtained from a preset historical database;

[0043] The judgment unit is configured to determine that the underground power cable is slightly aged if the frequency change amount is greater than a preset first frequency threshold and less than a preset second frequency threshold; determine that the underground power cable is moderately aged if the frequency change amount is greater than or equal to the preset second frequency threshold; otherwise, determine that the underground power cable is not aged.

[0044] In summary, the embodiment of the present application realizes on-line monitoring of the insulation state of underground power cables through wide-frequency oscillation signal injection, and its beneficial effects are reflected in the following aspects: First, through the signal attenuation compensation method and the leakage inductance influence compensation method, it is ensured that the first wide-frequency oscillation signal maintains a stable amplitude in a complex transmission path and avoids the system interference frequency band; Second, the first common-mode leakage current is processed in combination with the noise filtering method, providing a reliable data basis for the subsequent resonance frequency; Third, the resonance frequency characteristics are determined based on the corrected wide-frequency signal and the processed current data to realize the quantitative evaluation of the insulation state; Finally, by comparing the change amount of the current resonance frequency with the historical reference value, different aging stages such as mild and moderate are effectively identified. In summary, the present application can complete the monitoring without power outage or cable structure damage, and proposes compensation measures for adverse effects such as signal attenuation, noise interference, and leakage inductance, which can solve the problem that it is difficult to accurately quantitatively evaluate the insulation aging degree of underground power cables in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the present application, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0046] Figure 1 is a flowchart of a cable insulation on-line monitoring method based on wide-frequency oscillation signal injection provided by some embodiments of the present application;

[0047] Figure 2 is a block diagram of an on-line monitoring system for the insulation of underground power cables based on wide-frequency oscillation signal injection provided by some embodiments of the present application;

[0048] Figure 3 is a block diagram of a simulation system for the insulation of underground power cables based on wide-frequency oscillation signal injection provided by some embodiments of the present application;

[0049] Figure 4 is a structural diagram of a cable insulation on-line monitoring device based on wide-frequency oscillation signal injection provided by some embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the following will clearly and completely describe the technical solutions in this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts belong to the scope of protection of this application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0052] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means more than two, unless otherwise specifically defined.

[0053] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0054] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0055] In the description of the embodiments of this application, the term "a plurality of" refers to more than two (including two). Similarly, "a plurality of groups" refers to more than two groups (including two groups), and "a plurality of pieces" refers to more than two pieces (including two pieces).

[0056] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0057] Embodiment 1

[0058] See Figure 1 , to solve the problem that it is difficult to accurately quantify and evaluate the insulation aging degree of underground power cables in the prior art, a cable insulation on-line monitoring method based on wide-frequency oscillation signal injection provided by an embodiment of the present invention includes:

[0059] S1. Obtain the first common-mode leakage current in the underground power cable, and process the first common-mode leakage current through a noise filtering method to obtain a second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first wide-frequency oscillation signal into the underground power cable, and the first wide-frequency oscillation signal is obtained by correcting a second wide-frequency oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method;

[0060] Further, in some embodiments of the present application, the processing the first common-mode leakage current through a noise filtering method to obtain a second common-mode leakage current includes:

[0061] Process the first common-mode leakage current by using digital filtering technology to obtain a third common-mode leakage current;

[0062] Remove the high-frequency noise components in the third common-mode leakage current through a fast Fourier transform method to obtain a second common-mode leakage current.

[0063] Further, in some embodiments of the present application, the first wide-frequency oscillation signal is obtained by correcting a second wide-frequency oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method, including:

[0064] According to the length and material characteristics of the underground power cable, obtain the attenuation value of the second wide-frequency oscillation signal in the underground power cable, and adjust the second wide-frequency oscillation signal according to the attenuation value to obtain a third wide-frequency oscillation signal;

[0065] Adjust the frequency range of the third wide-frequency oscillation signal according to the preset leakage inductance parameters to obtain a first wide-frequency oscillation signal.

[0066] Specifically, in actual application scenarios, such as Figure 2 As shown, the injected signal propagates through the cable, and the common-mode leakage current caused by it is measured. The device for injecting the first broadband oscillation signal into the underground power cable may include a DC power supply, a digital signal processor (DSP), and a switching device controlled by a chirp pulse width modulation (PWM) signal. Among them, the DSP generates a chirp signal with a frequency range of 1000 Hz to 5000 Hz, and controls the switching device through the PWM signal to convert the voltage of the DC power supply into the required broadband oscillation signal and inject it into the cable system.

[0067] Specifically, in the simulation scenario, MATLAB / Simulink is used to build the experimental environment and conduct the simulation, such as Figure 3 As shown, the simulation results are used to verify the effectiveness of the proposed monitoring method under different system operating conditions. A three-phase transformer (with a capacity of 100 kVA and a voltage level of 10 kV / 0.4 kV) is used to connect the simulated cable section and the real cable section. The simulated cable section consists of multiple 1-km-long XLPE cable models, and each model contains resistance (R0), inductance (L0), insulation capacitance (C), and insulation conductance (G) elements, and the parameters are set according to the actual cable characteristics. The broadband oscillation signal is injected into the cable system through an isolation transformer to ensure that the signal is injected in a common-mode manner and avoid affecting the load. The broadband oscillation signal injection unit consists of a DSP controller and a MOSFET switch, and can generate a chirp signal with a frequency range of 1000 Hz to 3000 Hz. The current measurement unit uses a high-precision common-mode current probe (with a bandwidth of 10 kHz) and a data acquisition card (with a sampling rate of 100 kHz).

[0068] Start the DSP controller, generate the chirp signal, and inject the signal into the cable system through the MOSFET switch. The amplitude of the injected signal is adjusted according to the cable length to ensure that the amplitude of the signal at the end of the cable meets the measurement requirements. Use the common-mode current probe to measure the common-mode leakage current caused by the injected signal, and record the current waveform through the data acquisition card. At the same time, measure the voltage amplitude of the injected signal for subsequent impedance calculation. Perform low-pass filtering on the collected current signal to remove high-frequency noise components. For example, use a low-pass filter with a cut-off frequency of 5 kHz to ensure that the frequency components of the signal are concentrated within the target frequency band.

[0069] Add a load at the end of the cable to simulate the signal attenuation situation in actual operation. Verify the effectiveness of the signal attenuation compensation measure by adjusting the amplitude of the injected signal. For example, increase the amplitude of the injected signal by 20% to ensure that the amplitude of the signal at the end of the cable meets the measurement requirements.

[0070] Introduce a high-frequency noise source into the cable system to simulate the noise interference in actual operation. Through a low-pass filter and FFT analysis, verify the effectiveness of the noise filtering measures. For example, after filtering, the noise components are effectively removed, and the measurement accuracy of the resonant frequency is improved. Add a leakage inductance element (1.68 mH) between the system transformer and the cable to verify the effectiveness of the leakage inductance compensation measures. By adjusting the signal injection frequency range, avoid the resonant frequency offset area caused by the leakage inductance. For example, after adjusting the signal injection frequency range to 1200 Hz to 4800 Hz, the measured value of the resonant frequency is consistent with the theoretical value, which verifies the effectiveness of the leakage inductance compensation measures.

[0071] S2. Determine the resonant frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal;

[0072] Further, in some embodiments of the present application, the determining the resonant frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal includes:

[0073] Obtain the common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal;

[0074] Adopt a frequency analysis method to extract the resonant frequency from the common-mode impedance, and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve;

[0075] Extract the peak point of the impedance amplitude from the frequency response curve, and determine the resonant frequency through the peak point.

[0076] Specifically, in actual application scenarios and simulation scenarios, the obtaining the common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal can be calculated according to Ohm's law, and the specific calculation formula is as follows:

[0077]

[0078] where I CM is the second common-mode leakage current, U inj is the voltage amplitude of the first broadband oscillation signal, and Y CM is the common-mode impedance.

[0079] Specifically, in the simulation scenario, the collected common-mode leakage current signal is subjected to fast Fourier transform (FFT) to obtain its frequency response curve. FFT analysis can clearly display the current amplitude and phase characteristics at different frequencies. Locate the peak point of the current amplitude on the frequency response curve to determine the resonant frequency. For example, for the cable in the initial state, the resonant frequency is 2500 Hz. Use the moving average method to smooth the frequency response curve to reduce the influence of measurement noise. For example, use a data window with a length of 30 for moving average to ensure the accuracy of the resonant frequency.

[0080] S3. Determine the change in the resonant frequency based on the resonant frequency and the pre-resonant frequency, and obtain the insulation state of the underground power cable according to the change in the resonant frequency.

[0081] Further, in some embodiments of the present application, the determining the change in the resonant frequency based on the resonant frequency and the pre-resonant frequency, and obtaining the insulation state of the underground power cable according to the change in the resonant frequency includes:

[0082] Subtract the resonant frequency from the pre-resonant frequency to obtain the change in frequency; wherein, the pre-resonant frequency is obtained from a preset historical database;

[0083] If the change in frequency is greater than a preset first frequency threshold and less than a preset second frequency threshold, determine that the underground power cable is slightly aged; if the change in frequency is greater than or equal to the preset second frequency threshold, determine that the underground power cable is moderately aged; otherwise, determine that the underground power cable is not aged.

[0084] Specifically, in the actual application scenario, the preset first frequency threshold can be 100 Hz, and the preset second frequency threshold can be 200 Hz.

[0085] Specifically, in the simulation scenario, the aging process of the cable can be simulated by changing the insulation capacitance of the simulated cable segment. For example, increase the insulation capacitance from the initial value of 10 nF to 12 nF to simulate the aging degree of the cable. Repeat the above measurement and analysis steps, and record the resonant frequency after aging. For example, when the insulation capacitance increases by 20%, the resonant frequency drops to 2300 Hz. Evaluate the aging degree of the cable according to the change in the resonant frequency. For example, a 200 Hz decrease in the resonant frequency indicates that the cable enters the slightly aged stage; when the decrease exceeds 300 Hz, it enters the moderately aged stage.

[0086] In summary, the embodiments of the present application realize the online monitoring of the insulation state of underground power cables through the injection of broadband oscillation signals. The beneficial effects are reflected in the following aspects: First, through the signal attenuation compensation method and the leakage inductance influence compensation method, it is ensured that the first broadband oscillation signal maintains a stable amplitude in the complex transmission path and avoids the system interference frequency band. Second, the first common-mode leakage current is processed by combining the noise filtering method, providing a reliable data basis for the subsequent resonance frequency. Third, the resonance frequency characteristics are determined based on the corrected broadband signal and the processed current data to realize the quantitative evaluation of the insulation state. Finally, by comparing the change amount of the current resonance frequency with the historical reference value, different aging stages such as mild and moderate are effectively identified. In summary, the present application can complete the monitoring without power outage or damaging the cable structure, and proposes compensation measures for adverse effects such as signal attenuation, noise interference, and leakage inductance, which can solve the problem that it is difficult to accurately quantify and evaluate the insulation aging degree of underground power cables in the prior art.

[0087] Embodiment 2

[0088] As Figure 4 shown, based on the above method item embodiments, corresponding device item embodiments are provided;

[0089] An embodiment of the present invention provides a cable insulation online monitoring device based on the injection of broadband oscillation signals, including: a data acquisition module 11, a frequency extraction module 12, and a state judgment module 13;

[0090] Further, in some embodiments of the present application, the data acquisition module 11 is used to acquire the first common-mode leakage current in the underground power cable and process the first common-mode leakage current by the noise filtering method to obtain the second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first broadband oscillation signal into the underground power cable, and the first broadband oscillation signal is obtained by correcting a second broadband oscillation signal using the signal attenuation compensation method and the leakage inductance influence compensation method; the frequency extraction module 12 is used to determine the resonance frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal; the state judgment module 13 is used to determine the resonance frequency change amount through the resonance frequency and the pre-resonance frequency, and obtain the insulation state of the underground power cable according to the resonance frequency change amount.

[0091] Further, in some embodiments of the present application, the data acquisition module 11 includes a first data processing unit and a second data processing unit; the first data processing unit is configured to process the first common-mode leakage current by using a digital filtering technique to obtain a third common-mode leakage current; the second data processing unit is configured to remove high-frequency noise components in the third common-mode leakage current by using a fast Fourier transform method to obtain a second common-mode leakage current.

[0092] Further, in some embodiments of the present application, the data acquisition module 11 further includes a first adjustment unit and a second adjustment unit; the first adjustment unit is configured to obtain an attenuation value of the second broadband oscillation signal in the underground power cable according to the length and material characteristics of the underground power cable, and adjust the second broadband oscillation signal according to the attenuation value to obtain a third broadband oscillation signal; the second adjustment unit is configured to adjust the frequency range of the third broadband oscillation signal according to a preset leakage inductance parameter to obtain a first broadband oscillation signal.

[0093] Further, in some embodiments of the present application, the frequency extraction module 12 includes: an impedance acquisition unit, a curve acquisition unit, and a frequency determination unit; the impedance acquisition unit is configured to obtain a common-mode impedance according to the voltage amplitude of the second common-mode leakage current and the first broadband oscillation signal; the curve acquisition unit is configured to extract a resonance frequency from the common-mode impedance by using a frequency analysis method, and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve; the frequency determination unit is configured to extract a peak point of the impedance amplitude from the frequency response curve, and determine the resonance frequency through the peak point.

[0094] Further, in some embodiments of the present application, the state judgment module 13 includes: a change amount determination unit and a judgment unit; the change amount determination unit is configured to subtract the resonance frequency from the pre-resonance frequency to obtain the frequency change amount; wherein, the pre-resonance frequency is obtained from a preset historical database; the judgment unit is configured to determine that the underground power cable is slightly aged if the frequency change amount is greater than a preset first frequency threshold and less than a preset second frequency threshold; determine that the underground power cable is moderately aged if the frequency change amount is greater than or equal to the preset second frequency threshold; otherwise, determine that the underground power cable is not aged.

[0095] It can be understood that the above device item embodiments correspond to the method item embodiments of the present invention, and can implement the cable insulation on-line monitoring method based on broadband oscillation signal injection provided by any one of the above method item embodiments of the present invention.

[0096] It should be noted that the device embodiments described above are merely illustrative. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the attached drawings of the device embodiments provided by the present invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0097] In summary, it can be seen that the embodiment of the present application realizes the online monitoring of the insulation state of underground power cables through the injection of broadband oscillation signals, and its beneficial effects are reflected in the following aspects: First, through the signal attenuation compensation method and the leakage inductance influence compensation method, it is ensured that the first broadband oscillation signal maintains a stable amplitude in a complex transmission path and avoids the system interference frequency band; Second, the first common-mode leakage current is processed in combination with the noise filtering method, providing a reliable data basis for the subsequent resonance frequency; Third, the resonance frequency characteristics are determined based on the corrected broadband signal and the processed current data to realize the quantitative evaluation of the insulation state; Finally, by comparing the change amount of the current resonance frequency with the historical reference value, different aging stages such as mild and moderate are effectively identified. In summary, the present application can complete the monitoring without power outage or cable structure damage, and proposes compensation measures for adverse effects such as signal attenuation, noise interference, and leakage inductance, and can solve the problem that it is difficult to accurately quantitatively evaluate the insulation aging degree of underground power cables in the prior art.

[0098] Embodiment III

[0099] Based on the above embodiment of the cable insulation online monitoring method based on broadband oscillation signal injection, another embodiment of the present invention provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it realizes the cable insulation online monitoring method based on broadband oscillation signal injection according to any embodiment of the present invention.

[0100] Exemplarily, in this embodiment, the computer program can be divided into one or more modules, and the one or more modules are stored in the memory and executed by the processor to complete the present invention. The one or more module elements can be a series of computer program instruction segments capable of performing specific functions, and these instruction segments are used to describe the execution process of the computer program in the terminal device.

[0101] The terminal device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The terminal device may include, but is not limited to, a processor and a memory.

[0102] The so-called processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The processor is the control center of the terminal device and connects various parts of the entire terminal device through various interfaces and lines.

[0103] Embodiment 4

[0104] Based on the above method item embodiments, another embodiment of the present invention provides a computer-readable storage medium, including a stored computer program, wherein when the computer program runs, it controls the device where the computer-readable storage medium is located to execute the cable insulation on-line monitoring method based on broadband oscillation signal injection described in any one of the above method item embodiments of the present invention.

[0105] Among them, if the modules / units integrated in the device / terminal device are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes in the above embodiment methods of the present invention, it can also be completed by a computer program instructing relevant hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0106] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An on-line monitoring method for cable insulation based on injection of broadband oscillation signals, characterized in that, Including: Obtain the first common-mode leakage current in the underground power cable, and process the first common-mode leakage current by a noise filtering method to obtain a second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first broadband oscillation signal into the underground power cable, and the first broadband oscillation signal is obtained by correcting a second broadband oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method; Determine the resonance frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal; Determine the resonance frequency change amount through the resonance frequency and the pre-resonance frequency, and obtain the insulation state of the underground power cable according to the resonance frequency change amount.

2. The on-line cable insulation monitoring method based on broadband oscillation signal injection according to claim 1, wherein The processing the first common-mode leakage current by a noise filtering method to obtain a second common-mode leakage current includes: Process the first common-mode leakage current by using a digital filtering technique to obtain a third common-mode leakage current; Remove the high-frequency noise component in the third common-mode leakage current by a fast Fourier transform method to obtain a second common-mode leakage current.

3. The on-line cable insulation monitoring method based on broadband oscillation signal injection according to claim 1, characterized in that, The first broadband oscillation signal is obtained by correcting a second broadband oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method, including: Obtain the attenuation value of the second broadband oscillation signal in the underground power cable according to the length and material characteristics of the underground power cable, and adjust the second broadband oscillation signal according to the attenuation value to obtain a third broadband oscillation signal; Adjust the frequency range of the third broadband oscillation signal according to the preset leakage inductance parameter to obtain a first broadband oscillation signal.

4. The on-line cable insulation monitoring method based on injection of broadband oscillation signals according to claim 1, characterized in that, The determining the resonance frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal includes: Obtain the common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal; Extract the resonance frequency from the common-mode impedance by using a frequency analysis method, and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve; Extract the peak point of the impedance amplitude from the frequency response curve, and determine the resonance frequency through the peak point.

5. The on-line cable insulation monitoring method based on injection of broadband oscillation signal as claimed in claim 1, wherein, The determining the resonance frequency change amount through the resonance frequency and the pre-resonance frequency, and obtaining the insulation state of the underground power cable according to the resonance frequency change amount includes: Subtract the resonance frequency from the pre-resonance frequency to obtain the frequency change amount; wherein, the pre-resonance frequency is obtained from a preset historical database; If the frequency change amount is greater than a preset first frequency threshold and less than a preset second frequency threshold, determine that the underground power cable is slightly aged; if the frequency change amount is greater than or equal to the preset second frequency threshold, determine that the underground power cable is moderately aged; otherwise, determine that the underground power cable is not aged.

6. An on-line cable insulation monitoring device based on injection of broadband oscillation signals, characterized in that, Including: A data acquisition module, a frequency extraction module and a state judgment module; The data acquisition module is used to acquire the first common-mode leakage current in the underground power cable, and process the first common-mode leakage current by a noise filtering method to obtain a second common-mode leakage current; wherein, the first common-mode leakage current is caused by injecting a first broadband oscillation signal into the underground power cable, and the first broadband oscillation signal is obtained by correcting a second broadband oscillation signal by using a signal attenuation compensation method and a leakage inductance influence compensation method. The frequency extraction module is used to determine the resonance frequency according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal. The state judgment module is used to determine the resonance frequency change amount through the resonance frequency and the pre-resonance frequency, and obtain the insulation state of the underground power cable according to the resonance frequency change amount.

7. The on-line cable insulation monitoring device based on wide-band oscillation signal injection according to claim 6, wherein The The data acquisition module includes: a first data processing unit and a second data processing unit. The first data processing unit is used to process the first common-mode leakage current by using digital filtering technology to obtain a third common-mode leakage current. The second data processing unit is used to remove the high-frequency noise component in the third common-mode leakage current by using the fast Fourier transform method to obtain a second common-mode leakage current.

8. The on-line cable insulation monitoring device based on injection of broadband oscillation signals as claimed in claim 6, wherein The data acquisition module further includes: a first adjustment unit and a second adjustment unit. The first adjustment unit is used to obtain the attenuation value of the second broadband oscillation signal in the underground power cable according to the length and material characteristics of the underground power cable, and adjust the second broadband oscillation signal according to the attenuation value to obtain a third broadband oscillation signal. The second adjustment unit is used to adjust the frequency range of the third broadband oscillation signal according to the preset leakage inductance parameter to obtain a first broadband oscillation signal.

9. The on-line cable insulation monitoring device based on injection of broadband oscillation signal as claimed in claim 6, wherein, The frequency extraction module includes: an impedance acquisition unit, a curve acquisition unit and a frequency determination unit. The impedance acquisition unit is used to obtain the common-mode impedance according to the second common-mode leakage current and the voltage amplitude of the first broadband oscillation signal. The curve acquisition unit is used to extract the resonance frequency from the common-mode impedance by using a frequency analysis method, and perform a fast Fourier transform on the common-mode impedance to obtain a frequency response curve. The frequency determination unit is used to extract the peak point of the impedance amplitude from the frequency response curve, and determine the resonance frequency through the peak point.

10. The on-line cable insulation monitoring device based on broadband oscillation signal injection according to claim 6, characterized in that, The state judgment module includes: a change amount determination unit and a judgment unit. The change amount determination unit is used to subtract the resonance frequency from the pre-resonance frequency to obtain the frequency change amount; wherein, the pre-resonance frequency is obtained from a preset historical database. The judgment unit is used to determine that the underground power cable is slightly aged if the frequency change amount is greater than a preset first frequency threshold and less than a preset second frequency threshold; determine that the underground power cable is moderately aged if the frequency change amount is greater than or equal to the preset second frequency threshold; otherwise, determine that the underground power cable is not aged.

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