Cable insulation state detection method, device and system

Abstract

The invention provides a cable insulation state detection method, device and system, and relates to the technical field of power transmission and distribution cable detection. The method comprises the following steps: based on a power transmission and distribution cable defect continuous frequency modulation leakage current detection mode, obtaining leakage current waveform time-frequency characteristics of a to-be-detected cable under broadband voltage excitation; constructing an amplitude frequency curve of the leakage current of the to-be-detected cable according to the leakage current waveform time frequency characteristics; judging whether an abnormal frequency band exists in the amplitude frequency curve or not according to the amplitude fluctuation trend of the leakage current in the amplitude frequency curve; under the condition that the abnormal frequency band exists, determining the fault type of the to-be-detected cable according to the center frequency of the abnormal frequency band and a preset frequency range; the fault types comprise cable overheating, cable damping and cable buffer layer ablation. The cable insulation state detection efficiency can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power transmission and distribution cable detection, and in particular to a cable insulation state detection method, device and system. BACKGROUND

[0002] In the process of power transmission and distribution, cable insulation state monitoring and evaluation is a key link to ensure the safe, stable and reliable operation of the power grid. The good or bad of the cable insulation state directly affects the normal operation of the power system. Poor insulation state may cause cable failure, and thus cause power outage accidents, causing great losses to society and economy.

[0003] At present, the cable insulation state monitoring and evaluation work has been plagued by operation and maintenance personnel. The existing technology has many limitations and cannot meet the actual needs. The existing cable insulation state detection technology mainly includes partial discharge monitoring, insulation resistance testing and dielectric loss testing. The partial discharge monitoring technology has serious signal attenuation, requires multiple detections or complex signal enhancement, and has high analysis requirements and time and labor consumption. The insulation resistance test can only be evaluated as a whole and cannot accurately locate the fault. The dielectric loss test has limited single frequency information and insufficient sensitivity, and requires multiple detections or combination with other means. These problems result in low detection efficiency of the existing cable insulation state detection technology. SUMMARY

[0004] The embodiments of the present application provide a cable insulation state detection method, device and system to solve the problem of low cable insulation state detection efficiency.

[0005] In a first aspect, the embodiments of the present application provide a cable insulation state detection method, comprising:

[0006] Based on the power transmission and distribution cable defect continuous frequency leakage current detection method, the leakage current waveform time-frequency feature of the cable to be detected under wide frequency voltage excitation is obtained. The leakage current waveform time-frequency feature includes the frequency of the voltage excitation signal and the leakage current flowing out of the insulation layer of the cable to be detected collected at the corresponding frequency.

[0007] According to the leakage current waveform time-frequency feature, the amplitude-frequency curve of the leakage current of the cable to be detected is constructed.

[0008] According to the amplitude fluctuation trend of the leakage current in the amplitude-frequency curve, it is judged whether there is an abnormal frequency band in the amplitude-frequency curve.

[0009] In the case of an abnormal frequency band, the fault type of the cable to be detected is determined according to the center frequency of the abnormal frequency band and the preset frequency range. The fault type includes cable overheating, cable damp and cable buffer layer ablation.

[0010] In a second aspect, the embodiments of the present application provide a cable insulation state detection device, comprising:

[0011] The time-frequency feature acquisition module is configured to acquire time-frequency features of a leakage current waveform of the cable to be detected under a wideband voltage excitation based on a power transmission and distribution cable defect continuous frequency modulation leakage current detection method, wherein the time-frequency features of the leakage current waveform include a frequency of the voltage excitation signal and a leakage current flowing out of an insulation layer of the cable to be detected collected at the corresponding frequency.

[0012] The curve construction module is configured to construct an amplitude-frequency curve of the leakage current of the cable to be detected according to the time-frequency features of the leakage current waveform.

[0013] The abnormality judgment module is configured to determine whether an abnormal frequency band exists in the amplitude-frequency curve according to a fluctuation trend of the amplitude of the leakage current in the amplitude-frequency curve.

[0014] The fault judgment module is configured to determine a fault type of the cable to be detected according to a center frequency of the abnormal frequency band and a preset frequency range in a case where the abnormal frequency band exists, wherein the fault type includes cable overheating, cable dampness and cable buffer layer ablation.

[0015] In a third aspect, an embodiment of the present application provides a cable insulation state detection system, which comprises a high-voltage amplifier, a picoammeter and the cable insulation state detection device, one end of the high-voltage amplifier is connected with a cable core of a cable to be detected, one end of the picoammeter is connected with a copper shielding layer of the cable to be detected, the other end of the picoammeter is connected with the other end of the high-voltage amplifier, and the picoammeter is electrically connected with the cable insulation state detection device.

[0016] In the embodiment of the present application, when the insulation state of the power transmission and distribution cable is detected, the time-frequency features of the leakage current waveform of the cable to be detected under the wideband voltage excitation can be acquired based on the power transmission and distribution cable defect continuous frequency modulation leakage current detection method, then the amplitude-frequency curve of the leakage current of the cable to be detected can be constructed according to the time-frequency features of the leakage current waveform, and then the fault types such as cable overheating, cable dampness and cable buffer layer ablation can be quickly determined according to the center frequency of the abnormal frequency band in the amplitude-frequency curve and the preset frequency range, so that the detection efficiency of the cable insulation state is greatly improved, and the cable operation and inspection efficiency can be improved, and the stable operation of the power system is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an implementation flowchart of the cable insulation state detection method provided by the embodiment of the present application;

[0018] Figure 2a is a schematic diagram of the amplitude-frequency curve of the leakage current when the cable is defect-free and provided by the embodiment of the present application;

[0019] Figure 2b is a schematic diagram of the amplitude-frequency curve of the leakage current when the cable is overheated and provided by the embodiment of the present application;

[0020] Figure 2c is a schematic diagram of the amplitude-frequency curve of the leakage current when the cable is wet, provided by an embodiment of the present application;

[0021] Figure 2d is a schematic diagram of the amplitude-frequency curve of the leakage current when the buffer layer of the cable is ablated, provided by an embodiment of the present application;

[0022] Figure 3 is a schematic diagram of the structure of the cable insulation state detection device, provided by an embodiment of the present application;

[0023] Figure 4 is a schematic diagram of the electronic device, provided by an embodiment of the present application;

[0024] Figure 5 is a schematic diagram of the cable insulation state detection system, provided by an embodiment of the present application;

[0025] Figure 6a is a schematic diagram of the relationship between the leakage current amplitude and the cable position when the cable is defect-free, provided by an embodiment of the present application;

[0026] Figure 6b is a schematic diagram of the relationship between the leakage current amplitude and the cable position when the cable is overheated, provided by an embodiment of the present application;

[0027] Figure 6c is a schematic diagram of the relationship between the leakage current amplitude and the cable position when the cable is wet, provided by an embodiment of the present application;

[0028] Figure 6d is a schematic diagram of the relationship between the leakage current amplitude and the cable position when the buffer layer of the cable is ablated, provided by an embodiment of the present application. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0030] Referring to Figure 1 , which shows an implementation flowchart of the cable insulation state detection method provided by an embodiment of the present application, and is described in detail as follows:

[0031] Step 101: Based on the defect continuous frequency leakage current detection mode of the power transmission and distribution cable, the time-frequency characteristics of the leakage current waveform of the cable to be detected under wideband voltage excitation are obtained; wherein the time-frequency characteristics of the leakage current waveform include the frequency of the voltage excitation signal, and the leakage current flowing out of the insulation layer of the cable to be detected collected at the corresponding frequency.

[0032] In this embodiment, by obtaining the time-frequency characteristics of the leakage current waveform of the cable to be detected under wideband voltage excitation, the leakage current information of the cable under different frequency voltage excitation signals is obtained, which reflects the response characteristics of the cable insulation layer under different frequencies.

[0033] Step 102: According to the time-frequency characteristics of the leakage current waveform, the amplitude-frequency curve of the leakage current of the cable to be detected is constructed.

[0034] Specifically, the obtained leakage current is sorted in order of frequency from small to large, ensuring that the leakage current amplitude corresponding to each frequency point can be accurately corresponded. Professional data processing and drawing software can be used, which can conveniently draw the amplitude-frequency curve. In the selected drawing tool, the frequency is taken as the horizontal axis, and the amplitude of the leakage current is taken as the vertical axis. The sorted data points are input and the curve is drawn. Each point on the curve represents the amplitude of the leakage current at a certain frequency. In order to make the curve smoother and more representative, the data points can be curve-fitted. Select an appropriate fitting method, such as polynomial fitting, spline fitting, etc., to better reflect the overall trend of the leakage current amplitude changing with frequency.

[0035] In this embodiment, first, according to the time-frequency characteristics of the obtained leakage current waveform, including the frequency of the voltage excitation signal and the leakage current at the corresponding frequency, the amplitude-frequency curve of the leakage current of the cable to be detected is constructed. This curve takes the frequency as the horizontal coordinate and the amplitude of the leakage current as the vertical coordinate, and directly shows the change of the leakage current amplitude at different frequencies. Finally, through the amplitude-frequency curve, the fluctuation trend of the leakage current amplitude and the abnormal frequency band and other key features can be more easily identified.

[0036] Step 103: According to the fluctuation trend of the amplitude of the leakage current in the amplitude-frequency curve, it is determined whether there is an abnormal frequency band in the amplitude-frequency curve.

[0037] Specifically, after obtaining the amplitude-frequency curve of the leakage current, the overall shape of the amplitude-frequency curve is observed to understand the general law of the change of the leakage current amplitude with frequency. Under normal circumstances, the leakage current amplitude of the cable may present an oscillation decay trend with frequency, without obvious mutation points. If there is a significant change in the curve, such as severe decay, there may be an abnormal frequency band. According to the above analysis, it is determined whether there is an abnormal frequency band in the amplitude-frequency curve. If there is, the start frequency, end frequency and center frequency of the abnormal frequency band are recorded for subsequent fault diagnosis.

[0038] In this embodiment, according to the fluctuation trend of the amplitude of the leakage current in the constructed amplitude-frequency curve of the leakage current, it is determined whether there is a frequency band in the amplitude-frequency curve that is significantly different from the normal cable insulation state, i.e. an abnormal frequency band. These abnormal frequency bands indicate that the cable has insulation defects.

[0039] Step 104: in the presence of an abnormal frequency band, the center frequency of the abnormal frequency band and the preset frequency range are determined to determine the fault type of the cable to be detected; wherein the fault type includes cable overheating, cable moisture and cable buffer layer ablation.

[0040] In this embodiment, after determining the center frequency of the abnormal frequency band, the preset frequency range corresponding to each type of fault is confirmed. The center frequency of the abnormal frequency band is compared with the preset frequency range of each type of fault. By judging whether the center frequency falls within a certain preset frequency range, the corresponding fault type is determined. This step can accurately determine the specific type of cable fault, and the maintenance personnel can prepare the corresponding maintenance tools and materials in advance according to the determined fault type, thereby improving the maintenance efficiency.

[0041] In the embodiment of the present application, when detecting the insulation state of the power transmission and distribution cable, the frequency modulation leakage current detection method based on the defect of the power transmission and distribution cable can be used to obtain the time-frequency characteristics of the leakage current waveform of the cable to be detected under wide frequency voltage excitation. Then, according to the time-frequency characteristics of the leakage current waveform, the amplitude-frequency curve of the leakage current of the cable to be detected is constructed. Then, according to the center frequency of the abnormal frequency band and the preset frequency range in the amplitude-frequency curve, the fault types such as cable overheating, cable moisture and cable buffer layer ablation can be quickly judged, thereby greatly improving the detection efficiency of the cable insulation state, and further improving the cable operation and maintenance efficiency and ensuring the stable operation of the power system.

[0042] In a possible implementation, the preset frequency range includes a first preset range, a second preset range and a third preset range; wherein the range intervals of the first preset range, the second preset range and the third preset range are independent of each other; different fault types correspond to different frequency ranges; the center frequency of the abnormal frequency band and the preset frequency range are used to determine the fault type of the cable to be detected, and the specific processing is as follows: when the center frequency is located in the first preset range, it is determined that the fault type of the cable to be detected is cable overheating; when the center frequency is located in the second preset range, it is determined that the fault type of the cable to be detected is cable moisture; when the center frequency is located in the third preset range, it is determined that the fault type of the cable to be detected is cable buffer layer ablation.

[0043] Specifically, the center frequency of the cable leakage current response of different defects has obvious difference, and the main reason is that the capacitance change caused by cable overheating, cable moisture and cable buffer layer ablation has significant difference. At the same time, the center frequency of the cable leakage current response to a specific defect changes within a certain range, which is mainly affected by the length and severity of the cable defect. The analysis of the center frequency of the cable leakage current response of different defects is shown in Table 1.

[0044] Table 1

[0045] Serial number Cable overheating (kHz) Cable moisture absorption (kHz) Cable buffer ablation (kHz) 1 10.6 4.6 15.3 2 9.8 4.7 15.2 3 8.7 4.6 15.5 4 9.3 5.2 15.1 5 9.2 6.4 14.6 6 10.1 5.6 14.8 7 10.3 5.4 15.7 8 9.2 6.2 16.2 9 9.0 5.0 16.5 10 9.1 6.1 15.8 Frequency range 8.7～10.6 4.6～6.4 14.6～16.5

[0046] As shown in Figure 2a , when the power cable is defect-free, the amplitude spectrum presents a trend of oscillatory decay as the frequency increases, without obvious mutation points. As shown in Figure 2b , for the overheating caused by the local aging of the cable line, the amplitude spectrum presents a trend of oscillatory decay as the frequency increases, and presents more serious decay in the frequency range f1-f2, such as 8.7-10.6 kHz. As shown in Figure 2c , for the cable line partially subjected to moisture intrusion or immersion, the amplitude spectrum presents a trend of oscillatory decay as the frequency increases, and presents more serious decay in the frequency range f3-f4, such as 4.6-6.4 kHz. As shown in Figure 2d , for the ablation of the buffer layer of the cable line, the amplitude spectrum presents a trend of oscillatory decay as the frequency increases, and presents more serious decay in the frequency range f5-f6, such as 14.6-16.5 kHz.

[0047] In this embodiment, by comparing the center frequency of the abnormal frequency band with the preset frequency range, and according to the fault type corresponding to the preset frequency range, such as the first preset range corresponding to cable overheating, the second preset range corresponding to cable moisture, and the third preset range corresponding to cable buffer layer ablation, the specific fault type of the cable can be accurately determined. The maintenance personnel can prepare the corresponding maintenance tools and materials in advance according to the determined fault type, and the maintenance efficiency is improved.

[0048] In a possible implementation, if it is judged that there is no abnormal frequency band in the amplitude frequency curve, a detection result that the insulation state of the to-be-detected cable is normal is generated.

[0049] In this embodiment, after the amplitude frequency curve of the leakage current is constructed, the analysis result of the amplitude frequency curve, i.e., whether there is an abnormal frequency band, is confirmed. If the judgment result shows that there is no abnormal frequency band, the generation process of the normal insulation state detection result is triggered, and the detection result that the cable insulation state is normal is generated. This result can be presented in the form of a textual description, a state identifier, such as "normal" and "no fault", or a specific code form, so as to facilitate the user to quickly understand the insulation state of the cable.

[0050] In a possible implementation, the fault position of the to-be-detected cable can also be located, and the corresponding processing can be as follows: calculating the frequency domain impedance spectrum of the head end of the to-be-detected cable according to the cable parameters of the to-be-detected cable, and determining the fault position of the to-be-detected cable according to the frequency domain impedance spectrum of the head end; wherein the cable parameters include distributed resistance, distributed inductance, distributed conductance and distributed capacitance.

[0051] In the embodiment, the cable parameters of the cable to be detected are usually provided by the cable manufacturer or measured by professional equipment. By calculating the frequency domain impedance spectrum of the head end, the fault position in the cable can be accurately located according to the frequency domain impedance spectrum of the head end, the cable segment needing repair or replacement can be quickly found, and the repair time and cost are reduced.

[0052] In a possible implementation, the calculation of the frequency domain impedance spectrum of the head end of the cable to be detected according to the cable parameters of the cable to be detected is specifically processed as follows: obtaining the voltages at both ends of the cable to be detected under wide frequency voltage excitation; calculating the propagation coefficient and wave impedance of the cable to be detected according to the cable parameters; calculating the frequency domain impedance spectrum of the head end of the cable to be detected according to the voltages at both ends of the cable to be detected, the propagation coefficient and the wave impedance; and determining the fault position of the cable to be detected according to the frequency domain impedance spectrum of the head end, which is specifically processed as follows: obtaining the real part of the frequency domain impedance spectrum of the head end of the cable to be detected; performing discrete Fourier transform on the real part of the frequency domain impedance spectrum of the head end of the cable to be detected to obtain the corresponding relationship between the leakage current amplitude and the position of the cable to be detected; and determining the peak point according to the fluctuation trend of the leakage current amplitude, and determining the position of the cable to be detected corresponding to the peak point as the fault position.

[0053] Specifically, the formula for calculating the propagation coefficient and the wave impedance of the cable to be detected according to the cable parameters is as follows:

[0054]

[0055] In the formula, k is the propagation coefficient of the cable to be detected, R is the distributed resistance, L is the distributed inductance, G is the distributed conductance, C is the distributed capacitance, and the wave impedance of the cable to be detected is Z0.

[0056] The propagation coefficient describes the attenuation and phase change characteristics of the electromagnetic wave in the cable, and the wave impedance reflects the impedance characteristics of the cable to the electromagnetic wave.

[0057] The frequency domain impedance spectrum of the head end of the cable to be detected is as follows:

[0058]

[0059] In the formula, l is the length of the cable to be detected, and V(f) is the voltage at both ends of the cable to be detected.

[0060] The distributed resistance R, the distributed inductance L, the distributed conductance G and the distributed capacitance C caused by different defects of the cable insulation have serious frequency dependence. Therefore, the leakage current of the cable contains relevant information about the degree and position of the change of the cable parameters, and reading the information of the leakage current can effectively identify the change point of the cable parameters.

[0061] Since there are multiple characteristic parameters in the leakage current that can represent the transmission characteristics of the cable, the present application only selects the real part of the leakage current as the discussion object. The real part of the frequency domain impedance spectrum of the head end is obtained, which contains the amplitude of the leakage current in the cable and the relevant information of the cable position, and can be used for positioning the fault point. The real part of the frequency domain impedance spectrum of the head end is:

[0062]

[0063] Take Re(I(0)) as a function of time variable, and its frequency f' is exactly 2l / v. Under high frequency, v tends to a constant, so f' is a constant value. Discrete Fourier Transform (DFT) is performed on Re(I(0)) to obtain the corresponding relationship S(l) of the leakage current amplitude along the cable direction:

[0064] S(l) = DFT[Re(I(0))]

[0065] After spectrum analysis, by finding the peak points in the corresponding spectrum, the cable position corresponding to these peak points is the fault position, because the cable parameters at the fault point change, resulting in a significant change in the leakage current amplitude, so the position of the cable defect can be determined, thereby realizing the cable defect positioning.

[0066] In the embodiment, by calculating the frequency domain impedance spectrum of the head end and performing discrete Fourier transform, the fault position in the cable can be accurately positioned, the cable segment that needs to be repaired or replaced can be quickly found, and the repair time and cost are reduced.

[0067] In one possible implementation, the leakage current waveform time-frequency characteristics of the cable to be detected under wide frequency voltage excitation are obtained, and the specific processing is as follows: a plurality of frequency voltage excitation signals are obtained, and a preset period of leakage current flowing out of the insulation layer of the cable to be detected is collected under each frequency voltage excitation signal, and the root mean square value of the leakage current collected under each frequency is calculated; according to the frequency of the voltage excitation signal and the corresponding root mean square value, the leakage current waveform time-frequency characteristics are determined.

[0068] Specifically, a signal generator, such as a function generator or an arbitrary waveform generator, is used to generate a voltage excitation signal in a wide frequency range, generally 0.1 Hz to 30 kHz, and the amplitude range is generally 0 to 20 kV. A logarithmic sweep mode can be used to cover the entire frequency range, so that data can be effectively obtained at both low and high frequencies. The voltage signal output by the signal generator is amplified to the required amplitude range, such as 0-20 kV, to provide a wide frequency voltage excitation for the cable. For each frequency of the voltage excitation signal, a GPS clock module is used to align the voltage and current signal phases, and the leakage current waveform is collected for a predetermined number of cycles, such as 10 cycles. The selection of the predetermined number of cycles should be based on the stability and repeatability of the signal to ensure that the collected data is representative. For each frequency of the collected leakage current data, the root mean square value is calculated. The root mean square value reflects the effective value of the leakage current and is an important indicator of the current size. Each frequency and its corresponding leakage current root mean square value is arranged into a data pair to construct a time-frequency feature dataset of the leakage current waveform. These data pairs depict the change in leakage current amplitude at different frequencies, forming a time-frequency feature curve of the leakage current.

[0069] In this embodiment, by obtaining the time-frequency features of the leakage current in a wide frequency range, data support is provided for subsequent fault diagnosis and positioning.

[0070] In one possible implementation, when the frequency of the voltage excitation signal is higher than a predetermined frequency threshold, the frequency interval of the voltage excitation signal is a first value; when the frequency of the voltage excitation signal is lower than the predetermined frequency threshold, the frequency interval of the voltage excitation signal is a second value.

[0071] In this embodiment, starting from a specific power frequency, such as 50 Hz, a logarithmic sweep mode is used to cover 0.1 Hz-30 kHz, where the high frequency interval is 1 kHz and the low frequency interval is 0.5 Hz. The voltage excitation is applied, and the voltage dynamic compensation is adjusted in real time to ensure stable operation of the system, as follows:

[0072]

[0073] where V 50Hz is the voltage at 50 Hz frequency, and f is the frequency.

[0074] In one possible implementation, the cable insulation state detection method can further perform the following processing: determining an aging value of the insulation of the cable to be detected according to the amplitude-frequency curve of the leakage current; and determining whether the cable needs to be maintained or replaced according to the aging value and a predetermined aging threshold.

[0075] Specifically, the amplitude-frequency curve is quantitatively analyzed to calculate a value that reflects the aging degree of the cable insulation, i.e., an aging value, such as:

[0076] Integral method: the leakage current in a certain frequency range is integrated to obtain a total leakage current indicator. The formula is as follows:

[0077]

[0078] Wherein, I(f) is the leakage current amplitude corresponding to the frequency f.

[0079] Weighted summation method: the leakage current amplitudes at different frequencies are weighted and summed, and the weights can be set according to the influence degree of frequency on aging. The formula is as follows:

[0080]

[0081] Wherein, w i is the weight of frequency f i , I(f i ) is the leakage current amplitude at frequency f i .

[0082] In this embodiment, by comparing with the preset aging threshold, a clear decision basis is provided for the maintenance or replacement of the cable, helping the management personnel to reasonably arrange the maintenance plan and avoiding excessive maintenance or insufficient maintenance.

[0083] The present application provides a kind of cable insulation state detection method;Establish a set of cable defect state analysis diagnostic criteria;According to diagnostic criteria, the cable defect category and position are clearly given.The present application pays attention to broadband voltage excitation, such as the leakage current response characteristics under the condition of voltage range 0-20kV, frequency range 0-30kHz, the analysis object is leakage current signal, and the leakage current response characteristics are obvious due to high voltage excitation signal amplitude, which is sensitive to cable overheating, cable damp, cable buffer layer ablation and other defects, and has relatively obvious frequency response, suitable for new operation or operation cable damp, cable overheating and cable buffer layer ablation defect detection and rapid determination.The method uses cable insulation state detection method to solve the problem in practical engineering application, and the detection process is simple, which provides reliable basis for power cable defect rapid processing and fault early warning.

[0084] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0085] The following is a device embodiment of the present application, and for details not described in detail, reference can be made to the corresponding method embodiments described above.

[0086] Figure 3A structural schematic diagram of the cable insulation state detection device provided by the embodiment of the present application is shown. For ease of illustration, only parts related to the embodiment of the present application are shown, and the details are as follows.

[0087] As shown in Figure 3 , the cable insulation state detection device 3 comprises:

[0088] The time-frequency feature acquisition module 31 is configured to acquire a leakage current waveform time-frequency feature of the cable to be detected under a wide-frequency voltage excitation based on a power transmission and distribution cable defect continuous frequency modulation leakage current detection method. The leakage current waveform time-frequency feature comprises a frequency of the voltage excitation signal and a leakage current flowing out of the insulation layer of the cable to be detected collected at the corresponding frequency.

[0089] The curve construction module 32 is configured to construct an amplitude-frequency curve of the leakage current of the cable to be detected according to the leakage current waveform time-frequency feature.

[0090] The anomaly judgment module 33 is configured to judge whether there is an abnormal frequency band in the amplitude-frequency curve according to a fluctuation trend of the amplitude of the leakage current in the amplitude-frequency curve.

[0091] The fault judgment module 34 is configured to determine a fault type of the cable to be detected according to a center frequency of the abnormal frequency band and a preset frequency range in the case that there is the abnormal frequency band. The fault type comprises cable overheating, cable damp and cable buffer layer ablation. The preset frequency range comprises a first preset range, a second preset range and a third preset range. The range intervals of the first preset range, the second preset range and the third preset range are independent of each other. Different fault types correspond to different frequency ranges.

[0092] In a possible implementation manner, the fault judgment module 34 is further configured to:

[0093] determine that the fault type of the cable to be detected is cable overheating when the center frequency is located in the first preset range.

[0094] determine that the fault type of the cable to be detected is cable damp when the center frequency is located in the second preset range.

[0095] determine that the fault type of the cable to be detected is cable buffer layer ablation when the center frequency is located in the third preset range.

[0096] In a possible implementation manner, the fault judgment module 34 is further configured to:

[0097] generate a detection result that the insulation state of the cable to be detected is normal in the case that there is no abnormal frequency band.

[0098] In a possible implementation manner, the fault judgment module 34 is further configured to:

[0099] The frequency domain impedance spectrum of the head end of the cable to be detected is calculated according to the cable parameters of the cable to be detected, and the fault position of the cable to be detected is determined according to the frequency domain impedance spectrum of the head end.

[0100] In a possible implementation, the fault judgment module 34 is further configured to:

[0101] The voltages at both ends of the cable to be detected are obtained.

[0102] The propagation coefficient and the wave impedance of the cable to be detected are calculated according to the cable parameters.

[0103] The frequency domain impedance spectrum of the head end of the cable to be detected is calculated according to the voltages at both ends of the cable to be detected, the propagation coefficient and the wave impedance.

[0104] The real part of the frequency domain impedance spectrum of the head end of the cable to be detected is obtained.

[0105] The real part of the frequency domain impedance spectrum of the head end of the cable to be detected is subjected to a discrete Fourier transform to obtain a corresponding relationship between the leakage current amplitude and the position of the cable to be detected.

[0106] The peak point is determined according to the fluctuation trend of the leakage current amplitude, and the position of the cable to be detected corresponding to the peak point is determined as the fault position.

[0107] In a possible implementation, the time-frequency feature acquisition module 31 is further configured to:

[0108] The voltage excitation signals of multiple frequencies and the leakage currents of a preset period flowing out of the insulation layer of the cable to be detected collected under each frequency of the voltage excitation signals are obtained, and the root mean square values of the collected leakage currents under each frequency are calculated.

[0109] The time-frequency features of the leakage current waveform are determined according to the frequencies of the voltage excitation signals and the corresponding root mean square values.

[0110] In a possible implementation, the time-frequency feature acquisition module 31 is further configured to:

[0111] When the frequency of the voltage excitation signal is higher than a preset frequency threshold, the frequency interval of the voltage excitation signal is a first value.

[0112] When the frequency of the voltage excitation signal is lower than the preset frequency threshold, the frequency interval of the voltage excitation signal is a second value.

[0113] In a possible implementation, the fault judgment module 34 is further configured to:

[0114] The aging value of the insulation of the cable to be detected is determined according to the amplitude-frequency curve of the leakage current.

[0115] According to the aging value and the preset aging threshold, it is judged whether the cable needs to be maintained or replaced.

[0116] In the embodiment of the present application, when detecting the insulation state of the power transmission and distribution cable, the continuous frequency modulation leakage current detection mode based on the power transmission and distribution cable defect can be used to obtain the time-frequency characteristics of the leakage current waveform of the cable to be detected under wideband voltage excitation, and then the amplitude-frequency curve of the leakage current of the cable to be detected is constructed according to the time-frequency characteristics of the leakage current waveform. Then, the center frequency of the abnormal frequency band in the amplitude-frequency curve and the preset frequency range can be used to quickly judge the fault types such as cable overheating, cable damp, and cable buffer layer ablation, thereby greatly improving the detection efficiency of the cable insulation state, and further improving the cable operation and inspection efficiency and ensuring the stable operation of the power system.

[0117] Figure 4 is a schematic diagram of an electronic device provided by an embodiment of the present application. As shown in Figure 4 The electronic device 4 of this embodiment includes a processor 40 and a memory 41. The memory 41 stores a computer program 42. The processor 40 implements the steps in each of the method embodiments described above when executing the computer program 42. Alternatively, the processor 40 implements the functions of each module / unit in each of the device embodiments described above when executing the computer program 42.

[0118] For example, the computer program 42 can be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present application. The one or more modules / units can be a series of computer program instruction segments that can complete a specific function, which are used to describe the execution process of the computer program 42 in the electronic device 4.

[0119] The electronic device 4 can include, but is not limited to, the processor 40 and the memory 41. Those skilled in the art can understand that Figure 4 The electronic device 4 is only an example and does not constitute a limitation on the electronic device 4, and can include more or fewer components than shown, or combine certain components, or different components, for example, the electronic device 4 can also include an input / output device, a network access device, a bus, etc.

[0120] Figure 5 A schematic diagram of a cable insulation state detection system provided by an embodiment of the present application is shown. For ease of illustration, only parts related to the embodiments of the present application are shown, and are described in detail as follows:

[0121] As shown in Figure 5As shown, the cable insulation state detection system comprises a high-voltage amplifier, a picoammeter and the cable insulation state detection device, one end of the high-voltage amplifier is connected with the core of the cable to be detected, one end of the picoammeter is connected with the copper shielding layer of the cable to be detected, the other end of the picoammeter is connected with the other end of the high-voltage amplifier, and the picoammeter is electrically connected with the cable insulation state detection device.

[0122] The high-voltage amplifier is selected as the excitation power supply, the frequency range is 0-30 kHz, the amplitude range is 0-20 kV, C1 and C2 are voltage dividers, the voltage dividers are used to measure the voltage value applied to the two ends of the cable to be detected through the capacitor voltage division principle, the voltage value at the two ends of C2 is obtained, and the voltage after C1 and C2 are connected in series is calculated, and then the voltage value at the two ends of the cable to be detected is obtained, C3 is a filter capacitor, R1 is a protective water resistance, and the size is 10 kΩ. The leakage current is collected by the picoammeter, the resolution is 10 fA, the maximum measured current is 20 mA, when the range is set to 2 μA, the accuracy of the device is 0.15%+100 pA, the sensor in the instrument is connected to the copper shielding layer of the defect model, and the leakage current flowing out of the insulation layer is collected and grounded. The outer periphery of the copper shielding layer is the outer protective layer.

[0123] The cable insulation state detection technology mainly uses the leakage current response characteristics of the detected material, and does not damage or affect the structure and use performance of the detected material as the basic premise, so as to detect and quickly determine the cable damp, cable overheating and cable buffer layer ablation defects of the detected material.

[0124] As shown in Figure 6a , there is a relatively obvious reflection peak at the head of the spatial domain graph, reflecting the impedance mismatching condition of the picoammeter and the connecting line, the connecting line and the cable. There is a reflection peak with a larger amplitude at the end, reflecting the impedance mismatching condition of the end grounding point and the cable. The middle part of the cable line shows a relatively flat performance, reflecting that the capacitance of the defect-free cable has no mutation, and the leakage current amplitude of each frequency band has no obvious difference. As shown in Figure 6b , the middle part of the spatial domain shows a relatively obvious peak value, reflecting that the capacitance of the cable in this section changes obviously, and the leakage current amplitude changes obviously. As shown in Figure 6c , the middle part of the spatial domain shows a relatively obvious continuous peak value, reflecting that the cable in this section is long in the damp section and the capacitance changes obviously, and the leakage current amplitude changes obviously. As shown in Figure 6d , the middle part of the spatial domain shows a relatively obvious non-continuous peak value, reflecting that the buffer layer of the cable in this section is non-continuous ablation, the capacitance presents non-continuous change, and the leakage current amplitude changes obviously.

[0125] For the convenience and brevity of description, only the above-mentioned division of each functional module / unit is exemplified, and in actual application, the above-mentioned functions can be completed by different functional modules / units according to needs. The above-mentioned modules / units can be realized in the form of hardware, software or a combination of hardware and software.

[0126] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments. If there is no special description and logical conflict, the terms and / or descriptions of different embodiments are consistent and can be mutually referred to, and the technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationship.

[0127] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method of detecting a state of insulation of a cable, characterized by, The method comprises: Based on the power transmission and distribution cable defect continuous frequency leakage current detection mode, the leakage current waveform time-frequency characteristics of the cable to be detected under wide frequency voltage excitation are obtained; wherein the leakage current waveform time-frequency characteristics include the frequency of the voltage excitation signal, and the leakage current flowing out of the insulation layer of the cable to be detected collected at the corresponding frequency; According to the leakage current waveform time-frequency characteristics, the amplitude-frequency curve of the leakage current of the cable to be detected is constructed; According to the amplitude fluctuation trend of the leakage current in the amplitude-frequency curve, it is judged whether there is an abnormal frequency band in the amplitude-frequency curve; in the case of abnormal frequency band, the fault type of the cable to be detected is determined according to the center frequency of the abnormal frequency band and the preset frequency range; wherein the fault type includes cable overheating, cable damp and cable buffer layer ablation.

2. The method of claim 1, wherein The preset frequency range includes a first preset range, a second preset range and a third preset range; wherein the range intervals of the first preset range, the second preset range and the third preset range are independent of each other; different fault types correspond to different frequency ranges; The determination of the fault type of the cable to be detected according to the center frequency of the abnormal frequency band and the preset frequency range comprises: When the center frequency is located in the first preset range, it is determined that the fault type of the cable to be detected is cable overheating; When the center frequency is located in the second preset range, it is determined that the fault type of the cable to be detected is cable damp; When the center frequency is located in the third preset range, it is determined that the fault type of the cable to be detected is cable buffer layer ablation.

3. The method of claim 1, wherein The method further comprises: In the case where there is no abnormal frequency band, a detection result that the insulation state of the cable to be detected is normal is generated.

4. The method of claim 1, wherein The method further comprises: According to the cable parameters of the cable to be detected, the frequency domain impedance spectrum of the head end of the cable to be detected is calculated, and the fault position of the cable to be detected is determined according to the frequency domain impedance spectrum of the head end; wherein the cable parameters include distributed resistance, distributed inductance, distributed conductance and distributed capacitance.

5. The method of claim 4, wherein The method further comprises: Obtaining the voltage at both ends of the cable to be detected under wide frequency voltage excitation; The calculation of the frequency domain impedance spectrum of the head end of the cable to be detected according to the cable parameters of the cable to be detected comprises: According to the cable parameters, the propagation coefficient and wave impedance of the cable to be detected are calculated; According to the voltage at both ends of the cable to be detected, the propagation coefficient and the wave impedance, the frequency domain impedance spectrum of the head end of the cable to be detected is calculated; The determination of the fault position of the cable to be detected according to the frequency domain impedance spectrum of the head end comprises: Obtaining the real part of the frequency domain impedance spectrum of the head end of the cable to be detected; Discrete Fourier transform is performed on the real part of the frequency domain impedance spectrum of the head end of the cable to be detected to obtain the correspondence between the leakage current amplitude and the position of the cable to be detected; According to the fluctuation trend of the leakage current amplitude, the peak point is determined, and the position of the cable to be detected corresponding to the peak point is determined as the fault position.

6. The method of claim 1, wherein The acquisition of the leakage current waveform time-frequency characteristics of the cable to be detected under wide frequency voltage excitation comprises: acquire a plurality of voltage excitation signals of different frequencies, and a plurality of leakage currents of a preset period flowing out of the insulation layer of the cable under each voltage excitation signal, and calculate the root mean square value of the leakage current under each voltage excitation signal; determine the time-frequency feature of the leakage current waveform according to the frequency of the voltage excitation signal and the corresponding root mean square value.

7. The method of claim 6, wherein The method further comprises: when the frequency of the voltage excitation signal is higher than a preset frequency threshold, the frequency interval of the voltage excitation signal is a first value; when the frequency of the voltage excitation signal is lower than a preset frequency threshold, the frequency interval of the voltage excitation signal is a second value.

8. The method of claim 1, wherein The method further comprises: determine the aging value of the insulation of the cable to be detected according to the amplitude-frequency curve of the leakage current; determine whether the cable needs to be maintained or replaced according to the aging value and a preset aging threshold.

9. A cable insulation condition detection device characterized by comprising: comprise: a time-frequency feature acquisition module configured to acquire the time-frequency feature of the leakage current waveform of the cable to be detected under a wide-frequency voltage excitation based on a power transmission and distribution cable defect continuous frequency modulation leakage current detection method, wherein the time-frequency feature of the leakage current waveform comprises the frequency of the voltage excitation signal and the leakage current flowing out of the insulation layer of the cable to be detected under the corresponding frequency; a curve construction module configured to construct the amplitude-frequency curve of the leakage current of the cable to be detected according to the time-frequency feature of the leakage current waveform; an abnormality judgment module configured to determine whether there is an abnormal frequency band in the amplitude-frequency curve according to the amplitude fluctuation trend of the leakage current in the amplitude-frequency curve; a fault judgment module configured to determine the fault type of the cable to be detected according to the center frequency of the abnormal frequency band and a preset frequency range when there is an abnormal frequency band, wherein the fault type comprises cable overheating, cable damp and cable buffer layer ablation.

10. A cable insulation condition detection system characterized by, comprise a high-voltage amplifier, a picoammeter and a cable insulation state detection device as claimed in claim 9, one end of the high-voltage amplifier is connected with the core of the cable to be detected, one end of the picoammeter is connected with the copper shielding layer of the cable to be detected, the other end of the picoammeter is connected with the other end of the high-voltage amplifier, and the picoammeter is electrically connected with the cable insulation state detection device.

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