Direct-current cable leakage current full-band detection method and device based on multi-sensor fusion

Abstract

The invention relates to the technical field of power equipment state monitoring, and discloses a direct-current cable leakage current full-band detection method and device based on multi-sensor fusion, and the method comprises the steps: enabling a fluxgate sensor, a power frequency current transformer and a high-frequency current transformer to be connected in series, a grounding wire of a direct-current cable sequentially penetrates through the centers of the annular magnetic cores of the three sensors to form a single series loop; a fluxgate sensor is used for collecting leakage current signals of a direct-current frequency band, a power frequency current transformer is used for collecting leakage current signals of a frequency band of 50 Hz to 1 kHz, a high-frequency current transformer is used for collecting leakage current signals of a frequency band of 1 kHz to 30 MHz, low-pass filtering, band-pass filtering and high-pass filtering processing are carried out respectively, time domain alignment is achieved through a synchronous collection unit, and the leakage current signals of the frequency band of 50 Hz to 1 kHz are collected. And a composite waveform of the full-band leakage current is generated through superposition. According to the invention, the full-band DC cable leakage current waveform can be accurately and losslessly measured.

Description

Technical Field

[0001] The present application relates to the technical field of power equipment status monitoring, and in particular to a method and device for full-band detection of DC cable leakage current based on multi-sensor fusion. Background Art

[0002] In modern HVDC transmission systems, DC cables serve as the core carrier for power transmission, and their insulation performance directly determines the safety and reliability of the power system. With the rapid development of technologies such as renewable energy generation and cross-regional grid interconnection, the application scenarios of HVDC cables are expanding, voltage levels are constantly increasing, and operating environments are becoming more complex. In this context, accurate leakage current detection has become a key method for assessing cable insulation status and predicting potential faults.

[0003] The leakage current of a DC cable is often composed of both DC and AC components. The primary DC component is determined by the insulation's conductivity and reflects the insulation's aging or moisture content. The AC component, on the other hand, consists of high-frequency pulse signals generated by power frequency harmonics, surge overvoltage transients, and partial discharges, with frequencies ranging from 50 Hz to the MHz level. Detecting these different components offers complementary benefits for insulation condition diagnosis. For example, an abnormal DC component may indicate overall insulation degradation, while a high-frequency AC component is closely associated with localized defects such as partial discharges.

[0004] However, traditional methods often use a microammeter connected in series with the circuit to measure DC cable leakage current. This not only makes it difficult to detect the high-frequency components of the leakage current, but also introduces additional ground impedance, affecting the DC cable's grounding structure. The industry urgently needs a leakage current measurement method that can achieve accurate measurement while addressing issues affecting the grounding system and making full-band measurement difficult, thus meeting the needs of intelligent operation and maintenance of high-voltage DC cables. Summary of the Invention

[0005] The purpose of this application is to provide a full-band detection method and device for DC cable leakage current based on multi-sensor fusion, so as to develop an accurate, non-destructive, full-band measurement method that can simultaneously diagnose the overall degradation and local defects of DC cables, thereby enabling timely repair and replacement, providing important guarantees for the stable operation of the power grid.

[0006] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0007] In a first aspect, the present application provides a full-band detection method for DC cable leakage current based on multi-sensor fusion, comprising the following steps:

[0008] Arrange the fluxgate sensor, the power frequency current transformer, and the high frequency current transformer in series, so that the ground wire of the DC cable passes through the center of the annular magnetic cores of the three sensors in sequence to form a single series loop;

[0009] The fluxgate sensor is used to collect leakage current signals in the DC frequency band, the power frequency current transformer is used to collect leakage current signals in the 50 Hz to 1 kHz frequency band, and the high frequency current transformer is used to collect leakage current signals in the 1 kHz to 30 MHz frequency band;

[0010] The leakage current signal, the leakage current signal and the leakage current signal are respectively subjected to low-pass filtering, band-pass filtering and high-pass filtering, and time domain alignment is achieved through a synchronous acquisition unit, and a composite waveform of the full-band leakage current is superimposed.

[0011] Furthermore, an electromagnetic shielding layer is provided between the fluxgate sensor and the power frequency current transformer, and an isolation layer is provided between the high frequency current transformer and the power frequency current transformer.

[0012] Furthermore, the signal output by the fluxgate sensor is low-pass filtered and amplified with a cutoff frequency of 10 Hz to extract the DC component; the signal output by the power frequency current transformer is band-pass filtered and amplified from 50 Hz to 1 kHz to extract the power frequency harmonics and switching overvoltage transient signals; the signal output by the high-frequency current transformer is high-pass filtered and amplified with a cutoff frequency of 1 kHz to extract the partial discharge signal and lightning overvoltage transient signal.

[0013] Furthermore, the synchronous acquisition unit adopts a multi-channel synchronous acquisition card, in which the DC channel sampling rate is greater than 1kS / s, the power frequency channel sampling rate is greater than 10kS / s, and the high frequency channel sampling rate is greater than 10MS / s, so as to realize synchronous time domain acquisition of three signals.

[0014] Furthermore, when the grounding wire passes through the center of the annular magnetic cores of the three sensors, it is fixed by a clamp to ensure that the coaxiality deviation of the magnetic cores of each sensor is ≤0.1 mm.

[0015] In a second aspect, the present application provides a full-band DC cable leakage current detection device based on multi-sensor fusion, comprising:

[0016] A sensor group includes a fluxgate sensor, a power frequency current transformer, and a high frequency current transformer arranged in series, wherein the center of the annular magnetic core of the fluxgate sensor, the power frequency current transformer, and the high frequency current transformer is used to pass the ground wire of the DC cable;

[0017] an electromagnetic compatibility optimization unit, comprising an electromagnetic shielding layer provided between the fluxgate sensor and the power frequency current transformer, and an isolation layer provided between the high frequency current transformer and the power frequency current transformer;

[0018] The signal processing module includes a low-pass filter circuit, a band-pass filter circuit and a high-pass filter circuit respectively connected to the fluxgate sensor, the power frequency current transformer and the high-frequency current transformer, and a synchronous acquisition unit for achieving time domain alignment of the three signals.

[0019] Furthermore, the fluxgate sensor is installed at the head end of the grounding wire to detect the DC component.

[0020] The power frequency current transformer is arranged downstream of the fluxgate sensor, adopts a toroidal ferrite core, and has a frequency band covering 50Hz-1kHz, and is used to extract power frequency harmonics and switching overvoltage transient signals.

[0021] The high-frequency current transformer is installed at the end of the grounding wire, with a frequency band covering 1kHz-30MHz, and is used to extract partial discharge signals and lightning overvoltage transient signals.

[0022] Furthermore, the cut-off frequency of the low-pass filter circuit is 10 Hz;

[0023] The cut-off frequency of the band-pass filter circuit is 50 Hz to 1 kHz;

[0024] The cut-off frequency of the high-pass filter circuit is 1 kHz.

[0025] Furthermore, the synchronous acquisition unit adopts a multi-channel synchronous acquisition card, in which the DC channel sampling rate is greater than 1kS / s, the power frequency channel sampling rate is greater than 10kS / s, and the high-frequency channel sampling rate is greater than 10MS / s, so as to realize synchronous time domain acquisition of three signals; wherein, the DC channel is the channel connecting the multi-channel synchronous acquisition card and the fluxgate sensor, the power frequency channel is the channel connecting the multi-channel synchronous acquisition card and the power frequency current transformer, and the high-frequency channel is the channel connecting the multi-channel synchronous acquisition card and the high-frequency current transformer.

[0026] Furthermore, when the grounding wire passes through the center of the annular magnetic core of the three sensors, it is fixed by a clamp to ensure that the coaxiality deviation of the magnetic core of each sensor is ≤0.1mm.

[0027] This application achieves accurate and non-destructive full-band measurement of DC cable leakage current, with the following significant technical effects:

[0028] (1) Full frequency band coverage: All-band signals from DC to 30 MHz can be detected at one time, enabling simultaneous detection and analysis of DC leakage, power frequency harmonics, and partial discharge.

[0029] (2) Simplified structure: multiple sensors are connected in series using a common ground wire, which reduces installation space and cost, and eliminates position errors and redundant arrangements.

[0030] (3) Nondestructive testing: Using a ground wire through the coil of the multi-sensor, compared to the traditional measurement method of connecting the microammeter in series to the ground wire, it avoids affecting the original grounding system of the cable.

[0031] (4) Anti-interference capability: By eliminating ground impedance differences and using frequency division filtering and signal isolation technology, crosstalk between AC and DC components can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the sensor group structure of a device for detecting full-band DC cable leakage current based on multi-sensor fusion according to an embodiment of the present application is shown;

[0033] Figure 2 A structural diagram of a signal processing module of a DC cable leakage current full-band detection device based on multi-sensor fusion according to an embodiment of the present application is shown;

[0034] Figure 3 The structure diagram of a signal processing module of a DC cable leakage current full-band detection device based on multi-sensor fusion according to an embodiment of the present application when provided with an amplification circuit is shown;

[0035] Figure 4 A flowchart of a method for full-band detection of DC cable leakage current based on multi-sensor fusion according to an embodiment of the present application is shown;

[0036] Figure 5 Another flow chart of a method for full-band detection of DC cable leakage current based on multi-sensor fusion according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0038] The specific implementation of the present application is further described in detail below with reference to the accompanying drawings and examples.

[0039] Example 1:

[0040] This embodiment of the present application provides a full-band DC cable leakage current detection device based on multi-sensor fusion. This device enables full-band DC cable leakage current detection. By utilizing a series common ground connection layout of a fluxgate sensor, a power-frequency current transformer (CT), and a high-frequency current transformer (HFCT), combined with frequency-division signal processing technology, it achieves simultaneous, high-precision detection of both AC and DC components. The device includes a sensor group 100, an electromagnetic compatibility optimization unit 200, and a signal processing module 300.

[0041] like Figure 1 As shown, the sensor group 100 is installed in an electromagnetic shielding shell 400. The sensor group 100 includes a fluxgate sensor 101, a power frequency current transformer 102 and a high frequency current transformer 103 arranged in series. The center 104 of the annular magnetic core of the fluxgate sensor 101, the power frequency current transformer 102 and the high frequency current transformer 103 is used to pass the ground wire of the DC cable; the electromagnetic compatibility optimization unit 200 includes an electromagnetic shielding layer 201 arranged between the fluxgate sensor and the power frequency current transformer, and an isolation layer 202 arranged between the high frequency current transformer and the power frequency current transformer.

[0042] like Figure 2 As shown, the signal processing module 300 includes a low-pass filter circuit 301, a band-pass filter circuit 302 and a high-pass filter circuit 303 respectively connected to the fluxgate sensor 101, the power frequency current transformer 102 and the high-frequency current transformer 103, and a synchronous acquisition unit 304 for achieving time domain alignment of the three signals.

[0043] This embodiment effectively solves the two core problems of frequency band coverage and electromagnetic compatibility in wide-band (DC-MHz) leakage current measurement through the series multi-sensor fusion design of the fluxgate sensor 101, the power frequency current transformer 102, and the high-frequency current transformer 103, combined with precise inter-layer electromagnetic shielding / isolation and external overall shielding. Assisted by targeted frequency division filtering and strict synchronous acquisition, it ultimately achieves full-band, high-precision, low-noise, and time-synchronized measurement of the DC cable grounding wire leakage current. This provides a powerful technical means for comprehensively evaluating the health of cable insulation, especially for early detection of different types of defects such as electrochemical aging, moisture, and partial discharge, significantly improving the level and reliability of power cable status monitoring and fault warning.

[0044] Specifically, the sensor group 100 is used to achieve multi-band signal capture, in which the fluxgate sensor 101 is used to detect weak leakage currents in the extremely low frequency band. It is very sensitive to DC and slow-changing currents close to DC, and can accurately measure the tiny DC components or ultra-low frequency components generated by the electrochemical aging of cable insulation materials. The power frequency current transformer 102 is used to detect the leakage current component of the power frequency and its low-order harmonics. This is the main frequency band for detecting a significant increase in leakage current caused by overall moisture, contamination, and concentrated defects (such as penetrating water trees) in the insulation. The high-frequency current transformer 103 is used to detect leakage current pulses in the high-frequency band, which mainly corresponds to the steep pulse current signal generated by partial discharge (PD) of the cable, and is an important sign of microscopic defects such as air gaps, impurities, and spikes inside the insulation. The three sensors are connected in series on the same ground wire of the DC cable. This structure ensures that they measure exactly the same ground wire current path, providing a physical basis for subsequent multi-source signal fusion.

[0045] The electromagnetic shielding layer 201 prevents the strong alternating magnetic field generated by the power-frequency CT from interfering with the magnetic-field-sensitive fluxgate sensor, ensuring that the fluxgate can accurately measure weak low-frequency / DC signals. The isolation layer 202 suppresses interference from the strong high-frequency electromagnetic field generated by the high-frequency CT during operation, while also reducing the potential saturation effect of the power-frequency magnetic field on the high-frequency CT. This isolation layer typically has high-frequency absorption or reflection properties.

[0046] The electromagnetic shielding shell 400 wraps the entire sensor group, shielding it from external electromagnetic interference, while also suppressing the magnetic field generated by the internal sensors from radiating outward and interfering with other devices.

[0047] Signal processing module 300 is used for signal conditioning and fusion. A low-pass filter circuit 301, connected to fluxgate sensor 101, allows only low-frequency / DC signals to pass through, filtering out high-frequency noise and interference. A bandpass filter circuit 302, connected to power-frequency current transformer 102, has a center frequency near the power frequency and a bandwidth covering its key harmonics, filtering out spurious signals outside the power frequency range. A high-pass filter circuit 303, connected to high-frequency current transformer 103, filters out low-frequency and power-frequency signals, retaining only high-frequency pulse components and improving the signal-to-noise ratio.

[0048] The synchronous acquisition unit 304 is key to achieving full-band information fusion. Using a common clock source, it samples the three filtered signals simultaneously and in phase at high speed. This ensures time alignment and phase consistency. Time alignment means that different frequency events occurring on the ground wire at the same moment are accurately mapped to the same point in time in the three signals. Phase consistency means that the correct phase relationship is maintained for periodic signals.

[0049] In some embodiments, a fluxgate sensor 101 is installed at the head end of the grounding wire to detect the DC component. A power frequency current transformer 102, located downstream of fluxgate sensor 101 and utilizing a toroidal ferrite core, operates in the 50 Hz to 1 kHz frequency range and is used to extract power frequency harmonics and switching overvoltage transients. A high-frequency current transformer 103, installed at the end of the grounding wire and operating in the 1 kHz to 30 MHz frequency range, is used to extract partial discharge signals and lightning overvoltage transients.

[0050] In some embodiments, the grounding wire of the DC cable passes through the centers of the annular magnetic cores of the three sensors in sequence to form a single series loop, thereby eliminating the problem of different grounding impedances caused by different installation positions of the multiple sensors.

[0051] In some embodiments, shielding layers are provided between the fluxgate sensor 101 and the power frequency current transformer 102 and between the power frequency current transformer 102 and the high frequency current transformer 103 and metal shielding is provided outside the coil to suppress mutual influence between signals and interference from external signals.

[0052] In some embodiments, as Figure 3 As shown, the output signal of the fluxgate sensor 101 passes through a low-pass filter circuit 301 with a cutoff frequency of 10 Hz and an integrating amplifier circuit 305 to extract the DC component. The output signal of the power frequency current transformer 102 passes through a band-pass filter circuit 302 with a cutoff frequency of 50 Hz-1 kHz and a first amplifier 306 to extract the signal waveform. The output signal of the high-frequency current transformer 103 passes through a high-pass filter circuit 303 with a cutoff frequency of 1 kHz and then passes through a second amplifier 307 to extract the signal waveform.

[0053] In some embodiments, the synchronous acquisition unit 304 uses a multi-channel synchronous acquisition card (sampling rate: DC channel greater than 1kS / s, power frequency channel greater than 10kS / s, high frequency channel greater than 10MS / s) to achieve synchronous time domain acquisition of three signals through continuous acquisition.

[0054] Example 2:

[0055] The present application embodiment provides a full-band detection method for DC cable leakage current based on multi-sensor fusion, which can be implemented based on the detection device described in any embodiment of embodiment 1, such as Figure 4 As shown, the detection method includes the following steps:

[0056] S10: Arrange the fluxgate sensor, the power frequency current transformer, and the high frequency current transformer in series, so that the ground wire of the DC cable passes through the center of the annular magnetic cores of the three sensors in sequence to form a single series loop.

[0057] Step S10 is used to connect the sensor to the ground wire in series. In some embodiments, step S10 can be implemented by sequentially passing the DC cable ground wire through the center of the annular magnetic core 104 of the fluxgate sensor 101, the power frequency current transformer 102, and the high frequency current transformer 103, ensuring that the ground wire has no branches or parallel paths. The ground wire is secured to each sensor using a fixture, ensuring that the coaxial deviation of each sensor's magnetic core is ≤0.1 mm to reduce magnetic leakage interference.

[0058] S20: using the fluxgate sensor to collect leakage current signals in the DC frequency band, using the power frequency current transformer to collect leakage current signals in the 50 Hz to 1 kHz frequency band, and using the high frequency current transformer to collect leakage current signals in the 1 kHz to 30 MHz frequency band.

[0059] S30: performing low-pass filtering, band-pass filtering and high-pass filtering on the leakage current signal, leakage current signal and leakage current signal respectively, and achieving time domain alignment through a synchronous acquisition unit, and superimposing to generate a composite waveform of the full-band leakage current.

[0060] In some embodiments, the fluxgate sensor 101 detects the DC leakage current in the ground wire and outputs it to the data recording unit after low-pass filtering to extract the DC component. The extracted DC component is the leakage current signal in the DC frequency band. The power frequency current transformer 102 captures the AC signal of 50Hz-1kHz and separates the power frequency harmonics and the switching overcurrent component through bandpass filtering to extract the power frequency component. The extracted power frequency component is the leakage current signal in the 50Hz to 1kHz frequency band. The high-frequency current transformer 103 collects the high-frequency transient signal of 1kHz-30MHz and separates the partial discharge and lightning impulse current components through high-pass filtering and waveform pattern recognition to extract the high-frequency component. The extracted high-frequency component is the leakage current signal in the 1kHz to 30MHz frequency band. The time axes of the three signals are aligned by the synchronous acquisition unit 304 and superimposed to generate a composite waveform of the leakage current in the full frequency band.

[0061] In some embodiments, as Figure 5 As shown, it shows another flow chart of a full-band detection method for DC cable leakage current based on multi-sensor fusion. The detection method can be implemented by the following steps:

[0062] S1. Start.

[0063] Start the detection system and initialize the sensor, signal processing module and synchronous acquisition unit.

[0064] S2. The sensor assembly is installed in series with the ground wire.

[0065] Arrange the fluxgate sensor, power-frequency current transformer (CT), and high-frequency current transformer (HFCT) in series, with the DC cable grounding wire passing through the center of the annular magnetic cores of the three in sequence. Secure the grounding wire with a clamp, and calibrate the coaxiality of the magnetic core to ensure that its deviation is ≤0.1mm, completing the mechanical connection and electrical circuit construction.

[0066] S3. Frequency division signal acquisition and processing.

[0067] In step 3, the three sensor signals are processed in parallel:

[0068] In the fluxgate sensor channel, a 0-10 Hz low-pass filter is applied to the output signal to extract the DC component;

[0069] In the power frequency CT channel, a 50Hz-1kHz bandpass filter is applied to the output signal to extract the power frequency harmonics (including switching overvoltage transient signals);

[0070] The HFCT channel applies a 1kHz-30MHz high-pass filter to the output signal to capture high-frequency pulses (including partial discharge and lightning overvoltage signals).

[0071] S4. Synchronous acquisition and time domain alignment.

[0072] Start the multi-channel synchronous acquisition unit, synchronously acquire the three filtered signals at the preset sampling rate, and achieve time domain waveform alignment through timestamp calibration; among which, the preset sampling rate is ≥1kS / s for DC channel, ≥10kS / s for power frequency channel, and ≥10MS / s for high frequency channel.

[0073] S5. Data fusion and composite waveform generation.

[0074] The aligned DC component, power frequency harmonics, and high-frequency pulse signals are superimposed to generate a composite leakage current waveform covering the entire frequency band of 0Hz-30MHz.

[0075] S6. Fault feature extraction and diagnosis.

[0076] Characteristic parameters (such as DC offset, harmonic distortion rate, high-frequency pulse amplitude / frequency, etc.) are extracted from the composite waveform and combined with preset fault models (such as partial discharge identification and insulation aging analysis) to diagnose the cable insulation status.

[0077] S7. End.

[0078] Output the test report (including full-band waveform, fault type, location results, etc.) to complete the single test process.

[0079] The above implementation modes are only used to illustrate the present application and are not intended to limit the present application. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, all equivalent technical solutions also fall within the scope of the present application, and the scope of patent protection of the present application shall be defined by the claims.

Claims

1. A full-band detection method for DC cable leakage current based on multi-sensor fusion, characterized in that: The following steps are involved: Arrange the fluxgate sensor, the power frequency current transformer, and the high frequency current transformer in series, so that the ground wire of the DC cable passes through the center of the annular magnetic cores of the three sensors in sequence to form a single series loop; The fluxgate sensor is used to collect leakage current signals in the DC frequency band, the power frequency current transformer is used to collect leakage current signals in the 50 Hz to 1 kHz frequency band, and the high frequency current transformer is used to collect leakage current signals in the 1 kHz to 30 MHz frequency band; The leakage current signal, the leakage current signal and the leakage current signal are respectively subjected to low-pass filtering, band-pass filtering and high-pass filtering, and time domain alignment is achieved through a synchronous acquisition unit, and a composite waveform of the full-band leakage current is superimposed.

2. The detection method according to claim 1, wherein An electromagnetic shielding layer is provided between the fluxgate sensor and the power frequency current transformer, and an isolation layer is provided between the high frequency current transformer and the power frequency current transformer.

3. The detection method according to claim 1, wherein The signal output by the fluxgate sensor is low-pass filtered and amplified with a cutoff frequency of 10 Hz to extract the DC component; the signal output by the power frequency current transformer is band-pass filtered from 50 Hz to 1 kHz and amplified to extract the power frequency harmonics and switching overvoltage transient signals; the signal output by the high-frequency current transformer is high-pass filtered and amplified with a cutoff frequency of 1 kHz to extract the partial discharge signal and lightning overvoltage transient signal.

4. The detection method according to claim 1, wherein The synchronous acquisition unit adopts a multi-channel synchronous acquisition card, in which the DC channel sampling rate is greater than 1kS / s, the power frequency channel sampling rate is greater than 10kS / s, and the high frequency channel sampling rate is greater than 10MS / s, so as to realize the synchronous time domain acquisition of three signals.

5. The detection method according to claim 1, wherein When the grounding wire passes through the center of the annular magnetic core of the three sensors, it is fixed by a clamp to ensure that the coaxiality deviation of the magnetic core of each sensor is ≤0.1mm.

6. A full-band DC cable leakage current detection device based on multi-sensor fusion, characterized in that: include: A sensor group includes a fluxgate sensor, a power frequency current transformer, and a high frequency current transformer arranged in series, wherein the center of the annular magnetic core of the fluxgate sensor, the power frequency current transformer, and the high frequency current transformer is used to pass the ground wire of the DC cable; an electromagnetic compatibility optimization unit, comprising an electromagnetic shielding layer provided between the fluxgate sensor and the power frequency current transformer, and an isolation layer provided between the high frequency current transformer and the power frequency current transformer; The signal processing module includes a low-pass filter circuit, a band-pass filter circuit and a high-pass filter circuit respectively connected to the fluxgate sensor, the power frequency current transformer and the high-frequency current transformer, and a synchronous acquisition unit for achieving time domain alignment of the three signals.

7. The detection device according to claim 6, characterized in that The fluxgate sensor is installed at the head end of the grounding wire and is used to detect the DC component. The power frequency current transformer is arranged downstream of the fluxgate sensor, adopts a toroidal ferrite core, and has a frequency band covering 50Hz-1kHz, and is used to extract power frequency harmonics and switching overvoltage transient signals. The high-frequency current transformer is installed at the end of the grounding wire, with a frequency band covering 1kHz-30MHz, and is used to extract partial discharge signals and lightning overvoltage transient signals.

8. The detection device according to claim 6, characterized in that The cut-off frequency of the low-pass filter circuit is 10 Hz; The cut-off frequency of the band-pass filter circuit is 50 Hz to 1 kHz; The cut-off frequency of the high-pass filter circuit is 1 kHz.

9. The detection device according to claim 6, characterized in that The synchronous acquisition unit adopts a multi-channel synchronous acquisition card, wherein the DC channel sampling rate is greater than 1kS / s, the power frequency channel sampling rate is greater than 10kS / s, and the high-frequency channel sampling rate is greater than 10MS / s, so as to realize the synchronous time domain acquisition of three signals; wherein, the DC channel is the channel connecting the multi-channel synchronous acquisition card and the fluxgate sensor, the power frequency channel is the channel connecting the multi-channel synchronous acquisition card and the power frequency current transformer, and the high-frequency channel is the channel connecting the multi-channel synchronous acquisition card and the high-frequency current transformer.

10. The detection device according to claim 6, characterized in that: When the grounding wire passes through the center of the annular magnetic core of the three sensors, it is fixed by a clamp to ensure that the coaxiality deviation of the magnetic core of each sensor is ≤0.1mm.

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