High-voltage cable single-end grounding system resistor live-line detection method

Abstract

The invention discloses a high-voltage cable single-end grounding system resistor live-line detection method, which belongs to the technical field of high-voltage cable grounding system detection, and comprises the following steps: simultaneously arranging measurement clamps in a three-phase grounding loop of a high-voltage cable metal sheath; any two-phase grounding loop is selected as an injection loop, and a direct current constant current source is injected into the injection loop; measuring a direct-current voltage between the third-phase grounding loop which is not injected into the direct-current constant-current source after the multi-stage filtering processing and any phase injection loop by using a measuring clamp; and based on the current value injected into the direct current constant current source and the direct current voltage between the third-phase grounding loop and any phase injection loop, calculating the resistance value of the third-phase grounding loop which is not injected into the direct current constant current source. According to the method, the resistance value of each phase grounding loop can be accurately measured in the running state of the high-voltage cable.

Description

Technical Field

[0001] The present invention belongs to the technical field of high - voltage cable grounding system detection, and particularly relates to a method for live detection of the resistance of a single - end grounding system of high - voltage cables. Background Art

[0002] There are two ways for the high - voltage cable grounding system: single - end and cross - bonding. The single - end grounding system means that one end of the metal sheath of the high - voltage cable is directly grounded, and the other end is protected grounded. If any connection defect (such as loose bolts, poor soldering, poor lead sealing, etc.) is not detected in time, it may lead to power outage accidents. In order to timely detect and eliminate the defects of poor grounding in the grounding loop and ensure the safe and reliable operation of high - voltage cables, it is necessary to frequently detect the grounding resistance of the grounding loop under the operating state of high - voltage cables.

[0003] The existing technology calculates the resistance by injecting current into two phases and measuring the voltage, but there are the following problems: (1) When the grounding resistance of a certain phase fluctuates, the measurement results of other phases have large errors; (2) The induced voltage interference leads to too long measurement time and insufficient accuracy. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for live detection of the resistance of a single - end grounding system of high - voltage cables, which can accurately measure the resistance values of each phase grounding loop under the operating state of high - voltage cables and ensure the safe operation of the power system.

[0005] To achieve the above - mentioned purpose, the present invention provides the following technical solutions: A method for live detection of the resistance of a single - end grounding system of high - voltage cables, comprising: Simultaneously set measuring clamps in the three - phase grounding loops of the metal sheath of the high - voltage cable; Select any two - phase grounding loops as the injection loop, and inject a DC constant current source into the injection loop; Use the measuring clamp to measure the DC voltage between the third - phase grounding loop that has not been injected with the DC constant current source and any one of the injection loops after multi - stage filtering processing; Based on the current value of the DC constant current source injected into the injection loop and the DC voltage between the third - phase grounding loop that has not been injected with the DC constant current source and any one of the injection loops, calculate the resistance value of the third - phase grounding loop that has not been injected with the DC constant current source.

[0006] The method for live detection of the resistance of a single - end grounding system of high - voltage cables provided by the present invention, by directly measuring the voltage of the phase without injected current, avoids the errors caused by the coupling of three - phase resistance calculation in the existing technology, can improve the measurement accuracy of single - phase grounding resistance, is especially suitable for the scenario where the grounding resistance fluctuates, and ensures that the detection results are not interfered by other phases.

[0007] Further, the multi-stage filtering process includes: Using a passive multi-stage filtering module to suppress the induced voltage generated by the metal sheath of the high-voltage cable; Using an active switched-capacitor filtering module to filter out the residual interference signals of the induced voltage; Wherein, a DC signal amplification module is arranged between the passive multi-stage filtering module and the active switched-capacitor filtering module, and is used to amplify the DC signal after the induced voltage is suppressed by the passive multi-stage filtering module.

[0008] The method for detecting the resistance of the single-end grounded system of the high-voltage cable provided by the present invention adopts a dual filtering mechanism combining a passive multi-stage filtering module and an active switched-capacitor filtering module, which can effectively suppress the high-frequency induced voltage and power-frequency interference on the metal sheath of the high-voltage cable, shorten the filtering time (from dozens of seconds to several seconds), and at the same time improve the signal-to-noise ratio of weak signals through the DC signal amplification module to ensure the measurement accuracy.

[0009] Further, the passive multi-stage filtering module adopts an LC filtering circuit, and the cut-off frequency of the LC filtering circuit is less than the frequency range of the induced voltage.

[0010] The method for detecting the resistance of the single-end grounded system of the high-voltage cable provided by the present invention, through the low cut-off frequency characteristic of the LC filtering circuit, specifically filters out the common induced voltage (such as power frequency 50Hz and its harmonics) during the operation of the high-voltage cable, avoids the impact of high-frequency interference on the subsequent signal processing module, and prolongs the service life of the equipment.

[0011] Further, before injecting a DC constant current source into the injection loop, an automatic calibration process is performed, including: Disconnect all external connections of the single-end grounded system of the high-voltage cable, and measure the background noise and offset voltage of the internal loop of the single-end grounded system of the high-voltage cable; Adjust the gain of the DC signal amplification module according to the background noise; Perform zero position compensation on the analog-to-digital conversion module according to the offset voltage; Reconnect the measurement fixture and lock the gain parameters; Wherein, the analog-to-digital conversion module is used to convert the DC signal amplified by the DC signal amplification module into a digital signal.

[0012] The automatic calibration process can eliminate the background noise and zero drift inside the equipment, solve the problem of baseline offset caused by temperature change or device aging, ensure the measurement consistency during long-term use, reduce the on-site manual calibration frequency, and reduce the maintenance cost.

[0013] Further, the injection direction of the DC constant current source is switched through a channel control module, and the channel control module is connected to the measurement fixture and is used to select different injection loop combinations.

[0014] The method for detecting the resistance of a single - end grounded system of high - voltage cables provided by the present invention realizes automatic switching of multiple circuits through a channel control module, reduces manual operation steps, avoids measurement errors caused by human switching mistakes, and at the same time supports flexible selection of any two - phase injection currents to adapt to complex on - site environments.

[0015] Furthermore, the channel control module adopts a multi - path relay switch, and the multi - path relay switch supports automatic cyclic switching of the combination of two - phase injection circuits in a three - phase grounding loop.

[0016] The automatic switching function of the multi - path relay switch can ensure the efficiency of three - phase combination cyclic measurement, shorten the overall detection period (single measurement ≤ 5 seconds), and improve the operation and maintenance efficiency.

[0017] Furthermore, when calculating the resistance value of the third - phase grounding loop without injecting a DC constant - current source, a dynamic weighted average algorithm is adopted, including: Continuously collect multiple DC voltage sampling values within a preset time period; Regard the DC voltage sampling values that exceed the preset deviation range as abnormal sampling values and eliminate them; Perform weighted averaging on the remaining DC voltage sampling values, and the weights decrease according to the proximity of the sampling time; Calculate the final resistance value based on the weighted average value.

[0018] The dynamic weighted average algorithm effectively suppresses the influence of instantaneous interference (such as electromagnetic pulses or load mutations) on the resistance value through eliminating abnormal sampling points and time - weighted processing, ensuring the long - term stability of the measurement results, and is especially suitable for high - interference environments.

[0019] Furthermore, if the calculated resistance value of the third - phase grounding loop without injecting a DC constant - current source is greater than the preset threshold, an alarm is triggered, and the resistance value greater than the preset threshold is recorded as abnormal data.

[0020] The dynamic threshold alarm mechanism can real - time identify abnormal fluctuations in the grounding resistance (such as resistance mutations caused by loose connections), trigger an alarm and record data, helping operation and maintenance personnel quickly locate defects and reducing the risk of power outage accidents.

[0021] Furthermore, the contact impedance of the measuring fixture is less than 1 mΩ, and the connection method with the metal sheath of the high - voltage cable is magnetic adsorption connection or bolt - fastening connection.

[0022] The magnetic adsorption or bolt - fastening fixture with low contact impedance (< 1 mΩ) can ensure the reliable connection between the measurement loop and the cable metal sheath, avoid additional resistance errors introduced by poor contact, and at the same time adapt to the on - site installation requirements of different - specification cables.

[0023] Further, the output current range of the DC constant current source is 10 mA to 1 A, and the adjustment accuracy is -0.5% to +0.5%.

[0024] The high-precision DC constant current source (-0.5% to +0.5%) can ensure the stability of the injected current, avoid measurement errors caused by current fluctuations. At the same time, the wide-range output (10 mA to 1 A) can adapt to the detection requirements of different lengths of cables.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for detecting the resistance of a single-ended grounded system of a high-voltage cable provided by the present invention systematically solves the problems of large measurement errors, long time consumption, and weak anti-interference ability in the prior art through innovations in multiple dimensions such as direct measurement optimization, anti-interference filtering, and automatic control, improving the detection accuracy, efficiency, and reliability, and is applicable to on-line monitoring of the grounding state of high-voltage cables under complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the prior art detection method provided by an embodiment of the present application; Figure 2 is a schematic diagram of the method for detecting the resistance of a single-ended grounded system of a high-voltage cable provided by an embodiment of the present application; Figure 3 is a schematic diagram of the device for detecting the resistance of a single-ended grounded system of a high-voltage cable provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions of the present application will be further described in detail below in conjunction with the specific embodiments.

[0028] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary only for explaining the present application and should not be construed as limiting the present application. Without conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0029] An embodiment of the present application provides a method for detecting the resistance of a single-ended grounded system of a high-voltage cable, including: Simultaneously setting measurement clamps in the three-phase grounding circuit of the metal sheath of the high-voltage cable; Selecting any two-phase grounding circuits as the injection circuits and injecting a DC constant current source into the injection circuits; Using the measurement clamps to measure the DC voltage between the third-phase grounding circuit that has not been injected with the DC constant current source after multi-stage filtering processing and any one of the injection circuits; Calculate the resistance value of the third-phase grounding loop without injecting a DC constant current source based on the current value of the DC constant current source injected into the injection loop and the DC voltage between the third-phase grounding loop without injecting the DC constant current source and any one-phase injection loop. Repeat the above steps to obtain the resistance values of each phase grounding loop in turn, and complete the live detection of the resistance of the high-voltage cable single-end grounding system.

[0030] The live detection method for the resistance of the high-voltage cable single-end grounding system provided by the embodiments of the present application systematically solves the problems of large measurement errors, long time consumption, and weak anti-interference ability in the prior art through innovations in multiple dimensions such as direct measurement optimization, anti-interference filtering, and automatic control, improving the detection accuracy, efficiency, and reliability, and is applicable to the on-line monitoring of the grounding state of high-voltage cables under complex working conditions.

[0031] In a possible embodiment, the multi-stage filtering process includes: Use a passive multi-stage filtering module to suppress the induced voltage generated by the metal sheath of the high-voltage cable; Use an active switched-capacitor filtering module to filter out the residual interference signals of the induced voltage; Wherein, a DC signal amplification module is arranged between the passive multi-stage filtering module and the active switched-capacitor filtering module for amplifying the DC signal after suppressing the induced voltage by the passive multi-stage filtering module.

[0032] The live detection method for the resistance of the high-voltage cable single-end grounding system provided by this embodiment adopts a dual filtering mechanism combining a passive multi-stage filtering module and an active switched-capacitor filtering module, which can effectively suppress the high-frequency induced voltage and power frequency interference on the metal sheath of the high-voltage cable, shorten the filtering time (from dozens of seconds to several seconds), and at the same time improve the signal-to-noise ratio of weak signals through the DC signal amplification module to ensure the measurement accuracy.

[0033] In this embodiment, the passive multi-stage filtering module adopts an LC filtering circuit, and the cut-off frequency of the LC filtering circuit is less than the frequency range of the induced voltage.

[0034] The live detection method for the resistance of the high-voltage cable single-end grounding system provided by this embodiment specifically filters out the common induced voltages (such as power frequency 50Hz and its harmonics) during the operation of the high-voltage cable through the low cut-off frequency characteristic of the LC filtering circuit, avoids the impact of high-frequency interference on the subsequent signal processing module, and prolongs the service life of the equipment.

[0035] In a possible embodiment, before injecting a DC constant current source into the injection loop, an automatic calibration process is performed, including: Disconnect all external connections of the high-voltage cable single-end grounding system and measure the background noise and offset voltage of the internal loop of the high-voltage cable single-end grounding system; Adjust the gain of the DC signal amplification module according to the background noise. Perform zero compensation on the analog-to-digital conversion module according to the offset voltage; Reconnect the measurement fixture and lock the gain parameter; Among them, the analog-to-digital conversion module is used to convert the DC signal amplified by the DC signal amplification module into a digital signal.

[0036] The automatic calibration process can eliminate the background noise and zero drift inside the device, solve the baseline offset problem caused by temperature changes or device aging, ensure the measurement consistency during long-term use, reduce the on-site manual calibration frequency, and lower the maintenance cost.

[0037] In this embodiment, the injection direction of the DC constant current source is switched through the channel control module, and the channel control module is connected to the measurement fixture and is used to select different injection loop combinations.

[0038] The method for detecting the resistance of the single-ended grounded system of the high-voltage cable provided in this embodiment realizes multi-loop automatic switching through the channel control module, reduces the manual operation steps, avoids measurement errors caused by human switching mistakes, and at the same time supports flexible selection of any two-phase injection currents to adapt to complex on-site environments.

[0039] Specifically, the channel control module adopts a multi-channel relay switch, and the multi-channel relay switch supports the automatic cyclic switching of two-phase injection loop combinations in the three-phase grounding loop.

[0040] The automatic switching function of the multi-channel relay switch can ensure the efficiency of the three-phase combination cyclic measurement, shorten the overall detection cycle (single measurement ≤ 5 seconds), and improve the operation and maintenance efficiency.

[0041] In a possible embodiment, when calculating the resistance value of the third-phase grounding loop without injecting the DC constant current source, a dynamic weighted average algorithm is adopted, including: Continuously collect multiple DC voltage sampling values within a preset time period; Regard the DC voltage sampling values exceeding the preset deviation range as abnormal sampling values and eliminate them; Perform weighted average on the remaining DC voltage sampling values, and the weights decrease according to the proximity of the sampling time; Calculate the final resistance value based on the weighted average value.

[0042] The dynamic weighted average algorithm effectively suppresses the influence of instantaneous interference (such as electromagnetic pulses or load mutations) on the resistance value through eliminating abnormal sampling points and time weighting processing, ensures the long-term stability of the measurement results, and is especially suitable for high-interference environments.

[0043] In this embodiment, if the calculated resistance value of the third-phase grounding loop without injecting the DC constant current source is greater than the preset threshold, an alarm is triggered, and the resistance value greater than the preset threshold is recorded as abnormal data.

[0044] The dynamic threshold alarm mechanism can identify abnormal fluctuations in the grounding resistance in real time (such as sudden resistance changes caused by loose connections), trigger alarms and record data, helping maintenance personnel quickly locate defects and reducing the risk of power outage accidents.

[0045] In a possible embodiment, the contact impedance of the measuring fixture is less than 1 mΩ, and the connection method with the metal sheath of the high-voltage cable is magnetic adsorption connection or bolt fastening connection.

[0046] The magnetic adsorption or bolt fastening fixture with low contact impedance (<1 mΩ) can ensure the reliable connection between the measuring circuit and the cable metal sheath, avoid additional resistance errors caused by poor contact, and at the same time adapt to the on-site installation requirements of different specifications of cables.

[0047] In a possible embodiment, the output current range of the DC constant current source is 10 mA to 1 A, and the adjustment accuracy is -0.5% to +0.5%.

[0048] The high-precision DC constant current source (-0.5% to +0.5%) can ensure the stability of the injected current, avoid measurement errors caused by current fluctuations, and at the same time the wide range of output (10 mA to 1 A) can adapt to the detection requirements of different lengths of cables.

[0049] The embodiment of the present application provides a resistive live detection device for a single-end grounded system of high-voltage cables, including: A DC constant current source module for injecting current into a selected two-phase grounding loop; A multi-stage filtering module, including a passive filtering unit and an active switched-capacitor filtering unit; A signal amplification module for amplifying the filtered DC voltage signal; An analog-to-digital conversion module for converting the amplified signal into a digital signal; A control unit for controlling channel switching, data processing and result display.

[0050] The modular design integrates the constant current source, filtering, amplification and control units, which can realize the lightweight and integration of the portable detection device, meet the portable requirements of live detection, and the cooperation of each module improves the system stability.

[0051] As Figure 1 shown, the existing methods for detecting the single-end grounding resistance of cables include the following steps: Step 1: Inject a DC constant current source i into the A and B phase grounding loops, measure the loop voltage Uab, and calculate: Rab = Uab / i, where Rab is the series resistance of the A and B phases; Step 2: Inject a DC constant current source \(i\) into the grounded circuits of phases A and C, measure the circuit voltage \(U_{ac}\), and calculate: \(R_{ac}=U_{ac} / i\), where \(R_{ac}\) is the series resistance of phases A and C; Step 3: Inject a DC constant current source \(i\) into the grounded circuits of phases B and C, measure the circuit voltage \(U_{bc}\), and calculate: \(R_{bc}=U_{bc} / i\), where \(R_{bc}\) is the series resistance of phases B and C; Step 4: Since \(R_{ab}\), \(R_{ac}\), and \(R_{bc}\) are known, and \(R_{ab}=R_a + R_b\), \(R_{ac}=R_a + R_c\), \(R_{bc}=R_b + R_c\), the grounding resistances \(R_a\), \(R_b\), and \(R_c\) of phases A, B, and C can thus be calculated.

[0052] Problems that may be encountered in the practical application of the prior art include: During the live detection of the cable operating state, there will be an induced voltage on the cable metal sheath. To prevent its damage to the measurement circuit and its adverse effects on the measurement accuracy, it is necessary to suppress the induced voltage. Usually, it takes dozens of seconds to measure one loop. During the measurement of three loops, if the grounding resistances of the three phases are stable without fluctuations, the measurement results are correct. However, if there is a poor grounding situation in a certain phase and its grounding resistance value fluctuates, it may cause large deviations in the measurement results of other phases.

[0053] For example: Assume that phases A and B are well grounded, and the resistances of the grounded circuits are both stable at 30 mΩ, and the grounded circuit of phase C is poorly connected and the resistance is unstable. When detecting the grounded circuits of phases A and B, the resistance of phase C is 100 mΩ. When detecting the grounded circuits of phases A and C, the resistance of phase C is also 100 mΩ. When detecting the grounded circuits of phases B and C, the resistance of phase C fluctuates to 120 mΩ. By measuring the three loops, we can get \(R_{ab}=30 + 30 = 60\), \(R_{ac}=30 + 100 = 130\), \(R_{bc}=30 + 120 = 150\). Substitute into the formulas \(R_a + R_b = 60\), \(R_a + R_c = 130\), \(R_b + R_c = 150\), and thus calculate \(R_a = 20\) mΩ, \(R_b = 40\) mΩ, \(R_c = 110\) mΩ. The results show that for phases A and B with good grounding, the measured values also deviate greatly from the actual values.

[0054] To overcome the deficiencies of the prior art, the present application provides a method that can accurately measure the resistance value of each phase's grounded circuit in a live state, regardless of whether the grounding conditions of the three phases are good or not and whether the resistance of the grounded circuit is stable.

[0055] As Figure 2 shown, measurement jigs are simultaneously added to the three-phase grounded circuits. Inject a DC constant current source between any two phases, and take one phase and the other phase without the constant current source, and measure the voltage value between the two, then the grounding resistance value of a certain phase can be known.

[0056] The specific operation process includes: Step 1: Inject a DC constant current source \(i\) into the grounded circuits of phases A and B, measure the DC voltage \(U_{ac}\) of the AC circuit. \(U_{ac}=U_a + U_c\). Since the DC constant current source does not flow through the C-phase circuit, so \(U_c = 0\) and \(U_{ac}=U_a\). Calculate: \(R_a=U_a / i = U_{ac} / i\); Step 2: Inject a DC constant current source \(i\) into the grounded circuits of phases B and C, measure the DC voltage \(U_{ba}\) of the BA circuit. \(U_{ba}=U_b + U_a\). Since the DC constant current source does not flow through the A-phase circuit, so \(U_a = 0\) and \(U_{ba}=U_b\). Calculate: \(R_b=U_b / i = U_{ba} / i\); Step 3: Inject a DC constant current source \(i\) into the grounded circuits of phases C and A, measure the DC voltage \(U_{cb}\) of the CB circuit. \(U_{cb}=U_c + U_b\). Since the DC constant current source does not flow through the B-phase circuit, so \(U_b = 0\) and \(U_{cb}=U_c\). Calculate: \(R_c=U_c / i = U_{cb} / i\).

[0057] Although this new scheme avoids the factors that make the existing scheme unsatisfactory, new problems arise and still need to be solved, that is, the interference problem of the phase circuit through which the DC constant current source does not flow, which is similar to measuring a weak DC voltage signal over a long distance through a wire with a high input impedance of hundreds of meters or even longer, and there are large interference signals on the long-distance wire.

[0058] For the suppression of interference such as induced voltage in the prior art, passive multi-stage filtering is adopted. The higher the induced voltage, the longer the filtering time required, and the measurement of a single circuit requires dozens of seconds. If only this filtering method is used in the new scheme, first, the signal-to-noise ratio of the useful signal is extremely low, and the measurement time needs to be increased significantly, which will lead to too long waiting time for on-site operation and poor working experience; second, even so, the detection accuracy index is difficult to meet the requirements.

[0059] In addition to retaining passive multi-stage filtering as the first-stage filtering in signal processing for the new scheme, active switched-capacitor filtering is added as the second-stage filtering, and a DC small-signal amplification link is also added between the two kinds of filtering, which solves the problems of extremely low signal-to-noise ratio and inability to meet the detection accuracy requirements.

[0060] Such as Figure 3 the signal from the fixture after channel switching may have a very high induced voltage. First, use passive multi-stage filtering to reduce these induced voltages to a range that can be used by the subsequent circuit.

[0061] After passive multi-stage filtering, the signal-to-noise ratio is improved to a certain extent, but the DC signal to be detected does not change and is still very weak, and there are still certain interference signals. At this time, by amplifying the DC signal, then passing through active switched-capacitor filtering, and then performing analog-to-digital conversion, the result can meet the detection accuracy requirements.

[0062] By this method, when one or more phases of the cable have poor grounding and the grounding resistance value fluctuates to a certain extent, not only can this fluctuation value be correctly detected, but also the detection data of other phases with good grounding will not be affected.

[0063] On-site application case: In the detection of a single-ended grounding system of a 110 kV cable, the method provided in this embodiment was used to find that the grounding resistance of phase C fluctuated from 30 mΩ to 120 mΩ. After inspection, it was found that the poor sealing lead caused a virtual connection. After repair, the re-measured resistance was stable at 32 mΩ, verifying the effectiveness of the present invention.

[0064] The method provided in this embodiment is applicable to the on-line monitoring of the grounding state of high-voltage cables in the power system, which can greatly shorten the detection time (single measurement ≤ 5 seconds), with an accuracy of -1 mΩ to +1 mΩ, and significantly improve the operation and maintenance efficiency and safety.

[0065] The above is only the preferred embodiment of the present application. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the technical principle of the present application, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present application.

Claims

1. A method for detecting the resistance of a high-voltage cable single-end grounding system, characterized in that: include: A measuring fixture is simultaneously set in the three-phase grounding loop of the metal sheath of the high-voltage cable; Select any two-phase grounding loop as the injection loop, and inject a DC constant current source into the injection loop; The DC voltage between the third phase grounding loop without DC constant current source injected after multi-stage filtering and any phase injection loop is measured by using a measuring fixture; The resistance value of the third phase grounding loop without the DC constant current source is calculated based on the current value of the DC constant current source injected into the injection loop and the DC voltage between the third phase grounding loop without the DC constant current source injected and any phase injection loop.

2. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1 is characterized in that: The multi-stage filtering process includes: A passive multi-stage filter module is used to suppress the induced voltage generated by the metal sheath of the high-voltage cable; Active switched capacitor filter module is used to filter out residual interference signals of induced voltage; Among them, a DC signal amplification module is arranged between the passive multi-stage filtering module and the active switched capacitor filtering module, and is used to amplify the DC signal after the induced voltage is suppressed by the passive multi-stage filtering module.

3. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 2 is characterized in that: The passive multi-stage filter module adopts an LC filter circuit, and the cut-off frequency of the LC filter circuit is less than the frequency range of the induced voltage.

4. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 2 is characterized in that: Before injecting the DC constant current source into the injection loop, perform an automatic calibration process, including: Disconnect all external connections of the high-voltage cable single-ended grounding system and measure the background noise and offset voltage of the internal loop of the high-voltage cable single-ended grounding system; Adjust the gain of the DC signal amplification module according to the background noise; Perform zero compensation on the analog-to-digital conversion module according to the offset voltage; Reconnect the measurement fixture and lock the gain parameters; The analog-to-digital conversion module is used to convert the DC signal amplified by the DC signal amplification module into a digital signal.

5. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1 is characterized in that: The injection direction of the DC constant current source is switched by a channel control module, and the channel control module is connected to the measuring fixture to select different injection circuit combinations.

6. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 5 is characterized in that: The channel control module adopts a multi-way relay switch, which supports automatic cyclic switching of a two-phase injection loop combination in a three-phase grounding loop.

7. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1 is characterized in that: The dynamic weighted average algorithm is used to calculate the resistance value of the third phase grounding loop without the DC constant current source injected, including: Continuously collecting multiple DC voltage sampling values ​​within a preset time period; The DC voltage sampling values ​​exceeding the preset deviation range are regarded as abnormal sampling values ​​and are eliminated; The remaining DC voltage sampling values ​​are weighted averaged, with the weight decreasing according to the sampling time; The final resistance value is calculated based on the weighted average.

8. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1 is characterized in that: If the calculated resistance value of the third phase grounding loop without the DC constant current source injected is greater than a preset threshold, an alarm is triggered, and the resistance value greater than the preset threshold is recorded as abnormal data.

9. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1, characterized in that: The contact impedance of the measuring fixture is less than 1mΩ, and the connection method with the metal sheath of the high-voltage cable is magnetic adsorption connection or bolt fastening connection.

10. The method for detecting the resistance charge of a high-voltage cable single-end grounding system according to claim 1, characterized in that: The output current range of the DC constant current source is 10mA~1A, and the adjustment accuracy is -0.5%~+0.5%.

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