Multi-core cable withstand voltage automatic test system

Abstract

The invention belongs to the technical field of cable testing, and particularly relates to a multi-core cable withstand voltage automatic testing system, which comprises a processing module, a data acquisition module and a determination module, and is characterized in that the processing module comprises a direct current charging unit and a damped oscillation unit; the determination module is used for calculating insulation resistance characteristics and partial discharge characteristics of the to-be-tested core wires according to the voltage signals and the partial discharge signals, and judging whether the to-be-tested multi-core cable passes a voltage withstanding test or not based on the insulation characteristics and the partial discharge characteristics of the to-be-tested core wires; the core wire does not generate capacitive current, so that the numerical value of the required direct-current high voltage is reduced relative to that of the alternating current, the size of the power supply of the test system can be reduced, damped oscillation processing is performed, and compared with a low-frequency long voltage withstand test, the required test time is reduced relative to the time required by an ultra-low-frequency test, and the test efficiency is improved. Therefore, the test time of the withstand voltage test of each core wire of the multi-core cable is shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of cable testing, and in particular relates to an automatic voltage withstand testing system for multi-core cables. Background Art

[0002] The main methods for voltage withstand testing of multi-core cables include DC voltage withstand test, ultra-low frequency voltage withstand test, oscillation wave voltage withstand test, power frequency series resonance test, and frequency modulation resonance voltage withstand test. Among them, the cable series resonance test device adjusts the power supply frequency to make the inductor and the equivalent capacitance of the test cable resonate, obtaining high voltage and low current on the test product. The ultra-low frequency method generally uses a test power supply with a frequency of 0.1Hz to replace the power frequency AC voltage withstand test. The capacitive current decreases significantly as the frequency decreases, the equivalent capacitive reactance of the cable increases, and the test current decreases. The volume and weight of the power supply equipment to achieve the same test effect are smaller than those of the AC resonance method.

[0003] Although the capacitive current is small, it still exists. The test equipment still needs to withstand high transient voltages, and the equipment capacity is still very high. If the equipment capacity is not enough to support the capacitance requirements of the cable test product, the protection mechanism (such as overcurrent protection) may be triggered due to excessive current, resulting in test interruption and the need to readjust the parameters, which will slow down the test process and extend the test time. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a multi-core cable withstand voltage automatic testing system to solve the problems of large test equipment size and long test time when performing withstand voltage testing on cables.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A multi-core cable withstand voltage automatic testing system, comprising: Processing module, including: A DC charging unit applies a DC high voltage to the core wires to be tested of the multi-core cable to be tested within a first predetermined time; a damped oscillation unit, applying a damped oscillation process to the core wire to be tested at intervals for a plurality of times after a first predetermined time; Data acquisition module, including: A first acquisition unit is configured to collect voltage signals of the core wires in different channels within the first predetermined time period; a second acquiring unit, configured to acquire partial discharge signals of the cable under test at different times at a start time of the second predetermined time period and after an end time of the damped oscillation process; A determination module is used to calculate the insulation resistance characteristics and partial discharge characteristics of each of the core wires to be tested according to the voltage signal and the partial discharge signal, and to determine whether the multi-core cable to be tested passes the withstand voltage test based on the insulation characteristics and partial discharge characteristics of each of the core wires to be tested.

[0006] Preferably, the determination module calculates the insulation resistance characteristics of each core wire according to the voltage signal and the partial discharge signal, including: Determine, based on the voltage signal, a voltage relationship curve for each core wire of the multi-core cable to be tested, wherein the voltage relationship curve is used to represent a curve of voltage variation over time within a first predetermined time, and the determination module determines, based on the voltage relationship curve and an input voltage curve of a DC charging unit, whether a nonlinear offset occurs in the core wire within the first predetermined time, wherein the nonlinear offset is used to represent a difference between a measured voltage and an actual voltage of the cable to be tested; determining, based on the partial discharge signal, whether concentrated discharge occurs in the core wire within a second predetermined time period; If at least one of the nonlinear offset and the concentrated discharge does not occur in each core wire of the multi-core cable to be tested, it is determined that the multi-core cable to be tested passes the withstand voltage test.

[0007] Preferably, the second acquisition unit collects the partial discharge signal in the zero voltage stage.

[0008] Preferably, the determining module determines whether the core wire has a nonlinear offset within a first predetermined time according to the DC high voltage curve and the voltage relationship curve of the DC charging unit, including calculating the drift time : ; in, is the theoretical charging voltage corresponding to the t-th moment on the theoretical charging curve, is the actual voltage of the core wire at the tth moment; When the offset time is greater than a preset time threshold, it is determined that the nonlinear offset occurs in the cable to be tested within a first predetermined time period.

[0009] Preferably, the partial discharge signal includes the partial discharge amount and the partial discharge position of the core wire, and determining whether concentrated discharge occurs in the core wire within the second predetermined time period according to the partial discharge signal includes: When the amount of partial discharge is greater than a discharge amount threshold and the number of partial discharge locations is greater than a number threshold, it is determined that concentrated discharge occurs in the core wire within the second predetermined time period.

[0010] Preferably, the determination module calculates the insulation resistance value of the core wire to be measured by dynamically compensating for the displacement current generated by the distributed capacitance of the cable: ; in, is the actual current of the core wire at the tth moment, is the rate of change of the high voltage of the pre-charging process applied by the DC charging unit to the core wire, and C is the calibrated equivalent capacitance of the core wire.

[0011] Preferably, the DC charging unit includes a pre-charging process for the selected core wire before the first predetermined time, and the real-time voltage of the pre-charging process is and real-time current The first acquisition unit also includes acquiring the steady-state voltage of the core line after the pre-charging process and steady-state current ; The calibration capacitance C determined by the determination module includes: Calculate the equivalent resistance: ; Calibration capacitor .

[0012] Preferably, it also includes a temperature compensation module, which is used to test the surface temperature T of the multi-core cable to be tested and transmit the surface temperature T to the determination module, and the determination module calculates the compensation resistance according to the surface temperature T : ; in, is the reference test temperature The test resistance of the core wire under test, is the temperature coefficient of resistance of the conductor material; The determination module also includes a The temperature-compensated discharge amount is obtained by supplementing the calculation of the single discharge amount of the core wire to be measured and temperature compensation of the energy density based on the temperature compensated discharge amount.

[0013] Preferably, the second acquisition unit includes a high-frequency current sensor and a capacitive coupler.

[0014] The beneficial effects of the present invention are: When using a DC power supply for charging, the capacitive current generated by the core wire to be tested will be very small, and the required DC high voltage will be lower than the value of AC power, which can reduce the size of the power supply of the test system; Moreover, by performing damped oscillation treatment on the multiple core wires of the multi-core cable to be tested, the test time required for the low-frequency long withstand voltage test will be reduced compared to the time required for the ultra-low frequency test, thereby shortening the test time of the withstand voltage test of each core wire of the multi-core cable. By performing parallel DC voltage treatment and damped oscillation treatment on the multiple core wires of the multi-core cable to be tested, the test time of the multi-core cable can be effectively shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0016] Figure 1 This is a system structure diagram of the present invention. DETAILED DESCRIPTION

[0017] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0018] See also Figure 1 This embodiment provides a multi-core cable withstand voltage automatic test system, including: a processing module for parallel processing of each core wire of the multi-core cable to be tested, including: The DC charging unit includes an independent high-voltage DC power supply configured for each core to ensure that the voltage of each core is independently adjustable, including using a DC high-voltage power supply to apply a DC high voltage to the selected core within a first predetermined time. The voltage on the current test core of the cable under test will gradually increase from 0 to a preset DC high voltage target value: The damped oscillation unit is used to apply damped oscillation processing at multiple intervals after a first predetermined time. When the voltage reaches a preset value, the high-voltage electronic switch is closed, and the core wires and inductance of the multi-core cable to be tested at the current moment form an LC damped oscillation circuit to generate an oscillation wave. The damped oscillation unit forms a damped oscillation voltage wave with the test cable through a high-voltage inductor, a high-voltage real-time solid-state switch, and applies a sinusoidal voltage wave of approximately industrial frequency to the test cable to stimulate a discharge signal at a potential defect in the cable.

[0019] Before performing high-voltage DC and damped oscillation processing on the multi-core cable under test, the other cores of the multi-core cable under test need to be grounded. All untested cores, the cable shield, and the metal armor layer need to be connected to the ground terminal. All untested cores are short-circuited (connected in parallel) and then grounded. The shield and armor layers are also grounded. It is also necessary to disconnect the multi-core cable under test from other equipment and check the insulation condition of the multi-core cable under test to ensure that it meets the test conditions to prevent test accidents when performing high-voltage DC and damped oscillation processing on the multi-core cable under test.

[0020] Data acquisition module, including: A first acquisition unit: within a first predetermined time, using a high-voltage voltage divider and a multi-channel ADC, collects the voltage of each core line to ground in a time-sharing or parallel manner, including acquiring the voltage signal of the core line at specific intervals within the first predetermined time; a second acquisition unit, which acquires partial discharge signals of the cable under test at different times at a start time of a second predetermined time period after an end time of the damped oscillation processing, wherein the second acquisition unit includes a high-frequency current sensor and a capacitive coupler, and uses the high-frequency current sensor and the capacitive coupler to acquire the partial discharge pulse signal at a zero voltage stage before the damped oscillation processing is performed; The first acquisition unit and the second acquisition unit use a unified clock source for all their acquisition channels to ensure that the time of data collected by each acquisition sub-unit can be aligned, which facilitates the subsequent further processing of the data by the determination module.

[0021] The determination module is used to calculate the insulation resistance characteristics and partial discharge characteristics of each core wire based on the voltage signal and partial discharge signal, and determine whether the multi-core cable under test passes the voltage withstand test based on the insulation characteristics and partial discharge characteristics. This includes: Determine, based on the voltage signal, a voltage relationship curve for each core wire of the multi-core cable to be tested, the voltage relationship curve being used to characterize a curve of voltage variation over time within a first predetermined time, and determine, based on a theoretical charging curve equation and the voltage relationship curve, whether a nonlinear offset occurs in the core wire within the first predetermined time, wherein the nonlinear offset is used to characterize the difference between the measured voltage and the actual voltage of a single core wire of the cable to be tested; determining, based on the partial discharge signal, whether concentrated discharge occurs in the multi-core cable to be tested within a second predetermined time period; If at least one of nonlinear offset and concentrated discharge does not occur in the multi-core cable to be tested, it is determined that the multi-core cable to be tested passes the withstand voltage test.

[0022] The multi-core cable to be tested is equivalent to a very large capacitor, so the multi-core cable to be tested will generate capacitive current during the AC charging process. Therefore, if an AC power supply is used for the withstand voltage test, the required target high voltage is very high, which causes the capacity of the detection equipment to increase, and then causes the footprint of the detection equipment to increase. Therefore, in this embodiment, when a DC power supply is used for charging, the capacitive current generated by the core wire to be tested will be very small, and then the required DC high voltage will be lower than the value of the AC power, and then the volume of the power supply of the test system can be reduced.

[0023] Moreover, by performing damped oscillation treatment on the multiple core wires of the multi-core cable to be tested, the test time required for the low-frequency long withstand voltage test will be reduced compared to the time required for the ultra-low frequency test, thereby shortening the test time of the withstand voltage test of each core wire of the multi-core cable. By performing parallel DC voltage treatment and damped oscillation treatment on the multiple core wires of the multi-core cable to be tested, the test time of the multi-core cable can be effectively shortened.

[0024] The nonlinear offset of the cable under test may cause uneven voltage distribution inside the core of the cable under test, which may cause overvoltage at a certain position of the cable core, leading to the risk of partial discharge or breakdown. If the nonlinear characteristics of the cable insulation material cause the electric field strength of the local electric field to increase, overvoltage may be generated in certain areas, affecting the test results. Therefore, in the withstand voltage test, further concentration discharge is measured to determine whether it occurs. Concentrated discharge usually indicates defects or weaknesses in the cable insulation. The defects may be due to manufacturing defects, mechanical damage or aging of the cable caused by environmental factors, and they need to be identified.

[0025] In one embodiment, when receiving the test data from the first acquisition unit, the determination module processes and determines the received partial discharge pulse signal, where the processing and determination include: S1: Signal preprocessing and pulse extraction: Bandpass filtering: Design a bandpass filter to retain the characteristic frequency band of the partial discharge signal and filter out low-frequency power frequency noise and high-frequency interference; Baseline correction: Sensor detection drift and power frequency interference can introduce low-frequency baseline offset. Correction eliminates the DC component of the signal and improves pulse detection accuracy. Therefore, the signal baseline (low-frequency drift) must be calculated using a sliding window method or polynomial fitting and subtracted from the original signal. Eliminate power frequency interference: When the power frequency interference amplitude exceeds the partial discharge signal, targeted filtering is required in the time-frequency domain to avoid drowning out the real pulse; Pulse extraction and separation: Set a pulse threshold and intercept the pulse band that exceeds the threshold. Since partial discharge pulses have a steep rising edge, in order to accurately locate transient pulses and solve the problem of missed detection in the threshold method, wavelet transform can be used to separate partial discharge pulses through threshold triggering and wavelet changes; S2: Calculation of discharge capacity and energy density analysis of the core wire: Modeling of the damped oscillation current of the damped oscillation unit: Based on the set RLC oscillation circuit, the damped oscillation current waveform is extracted, and the attenuation coefficient is fitted using an exponential decay model; Calculation of discharge capacity: For the oscillating current of the core to be measured that is damped by the damped oscillation unit, the single discharge capacity of the core to be measured is calculated. The single discharge capacity of the core to be measured reflects the severity of the insulation defect of the core. The calculation formula for the single discharge capacity of the core to be measured is: ; From time Time is the single duration of the damped oscillation wave; Count the number of discharges N in the time window T and calculate the unit discharge energy density: ; in, is the single discharge amount of the core wire to be tested after the i-th damped oscillation waveform passes through, It is the amplitude corresponding to the discharge pulse of the core wire to be tested. The discharge intensity of the core wire to be tested is evaluated by comprehensive estimation of energy density, thereby estimating the insulation aging degree of the core wire to be tested. S3: Phase analysis and discharge type identification of the core under test, including: Phase distribution and distribution statistics: For the synchronous power frequency voltage phase, obtain the phase position of each pulse and generate a phase-amplitude histogram; Discharge type identification: Identify whether the core wire under test is surface discharge or internal discharge based on the phase-amplitude histogram: Because the phase distribution of surface discharge is concentrated at the positive and negative peaks of the power frequency voltage, the amplitude is higher, while the phase distribution of internal discharge is wider, there may be voltage rising or falling edges, and the amplitude is lower; S4: Threshold value judgment and partial discharge determination: The discharge number threshold and discharge amount threshold of the core wire are set to compare and judge the discharge number and discharge amount of the core wire to be tested respectively. The determination module determines that the core wire to be tested has partial discharge if the discharge amount exceeds the discharge amount threshold or the discharge number exceeds the discharge number threshold.

[0026] Trigger the sound and light alarm, mark the faulty core number and the corresponding cable to be tested, discharge parameters and corresponding timestamp, and classify and store the original partial discharge waveform and characteristic parameters for subsequent corresponding analysis. For concentrated discharge, the fluctuation of the input voltage of the damped oscillation unit exceeds the safety threshold range. The safety threshold range can be set to , the system immediately cuts off the high-voltage output of the damped oscillation unit to prevent accidents.

[0027] If any core wire triggers the centralized discharge judgment, the entire cable under test is judged to be unqualified, that is, the cable under test fails the voltage withstand test.

[0028] In one embodiment, the determination module determines the DC high voltage curve of the DC charging unit. and an input voltage curve of the DC charging unit to determine whether the core wire has a nonlinear offset within a first predetermined time: Because when the DC charging unit is charging the core wire to be tested with DC high voltage, the theoretical voltage value of the core wire to be tested is calculated by the input voltage and the electrical parameters of each core wire of the cable to be tested. satisfy: ; in, is the time constant, which characterizes the rate at which the core wire to be tested is charged to a stable state, and the first acquisition unit obtains the real-time voltage value of the core wire to be tested. Conduct testing, It is the voltage response of the core wire to be tested under actual working conditions.

[0029] Determine module calculation drift time The formula is: ; in, is the theoretical voltage value of the cable core at the tth moment, is the actual voltage of the core wire at the tth moment; If the offset time is greater than a preset time threshold, the cable under test is determined to have experienced nonlinear offset within a first predetermined time period. The determination module uses nonlinear offset to characterize the difference between the theoretical voltage and the actual voltage of the cable under test. This allows for determining whether nonlinear offset has occurred in the cable under test.

[0030] The cause of partial discharge in the core to be tested is usually caused by air gaps, cracks, impurities or mechanical damage in the cable insulation layer. By locating the location where PD occurs, the specific insulation weak points can be quickly identified to avoid the waste of resources caused by replacing the entire cable. Therefore, in one embodiment, the partial discharge signal also includes the partial discharge position of the multi-core cable to be tested. By detecting the partial discharge position of the core to be tested, the PD at different positions may correspond to different types of defects, such as surface discharge of the core to be tested, air gap discharge inside, or electrical tree discharge. After positioning, the severity of the defect can be analyzed by the discharge mode to determine whether the cause of the partial discharge is to be repaired or continuously monitored. The system detects the partial discharge position of the core to be tested by the time difference method, including: The discharge position of the core wire is calculated by capturing the arrival time difference of the partial discharge pulse signal through multiple sensors. The pulse signal is collected by using a high-frequency current transformer installed at both ends of the cable or at the middle joint. Then, the electromagnetic wave signal is captured by setting capacitive couplers distributed on the surface of the core wire. Assume that the distance between the sensors is d and the pulse arrival time difference is , the propagation speed of the pulse is v, and the distance between the discharge position and the sensor is calculated using the time and spacing formula.

[0031] In order to, in one embodiment, the DC charging unit includes a pre-charging process for the selected core line before the first predetermined time, and the real-time voltage of the pre-charging process is and real-time current =The first acquisition unit also includes acquiring the steady-state voltage of the core line after the pre-charging process and steady-state current ; The calibration capacitor C determined by the determination module includes: Calculate the equivalent resistance: ; Calibration capacitor ; Then, the insulation resistance of the core wire to be measured is calculated by dynamically compensating for the displacement current generated by the distributed capacitance of the cable: ; in, is the actual current of the core wire at the tth moment, is the rate of change of the high voltage applied by the DC charging unit to the core wire during the pre-charging process, C is the calibrated equivalent capacitance of the core wire, .

[0032] Because the cable under test is within the test chamber, even when high DC or AC voltage (no power frequency current) is applied during a withstand voltage test, a small leakage current may still exist within the cable insulation. According to Joule's law, this leakage current generates heat as it passes through the insulation, causing the cable to heat up. For example, although the current generated by the DC charging unit in the cable under test is very small, heat will still accumulate in the cable under test as the high-voltage DC charging time increases. Furthermore, if the contact resistance of the cable connector or test fixture under test is excessive, such as if there is poor contact between the test fixture and the cable, or if there is an oxidation reaction in the test fixture, the current will generate heat during the test, further increasing the temperature of the cable under test.

[0033] However, when the temperature of the cable to be tested rises, the thermal motion of the molecules inside the insulation material will intensify, the free charge will increase, and the insulation resistance of the cable to be tested will decrease. Therefore, when the DC charging unit applies high-voltage DC power to the core to be tested, the leakage current of the core to be tested will increase significantly with the increase in temperature, and the resistance of the cable to be tested will increase with the increase in temperature. The change in resistance will affect the calculation error of the current by the determination module, and thus affect the single discharge amount of the core to be tested. calculation, which leads to system misjudgment.

[0034] Therefore, in one embodiment, the test system further includes a temperature compensation module, which is used to test the surface temperature T of the multi-core cable to be tested and transmit the surface temperature T to the determination module, and the determination module performs temperature compensation calculation based on the surface temperature T: a: Temperature compensation resistor for the test resistor : ; in, is the reference test temperature The test resistance of the core wire under test, It is the temperature coefficient of resistance of the conductor material, such as 0.00393 / ℃ for copper and 0.00403 / ℃ for aluminum; b: Based on The temperature-compensated discharge amount is obtained by supplementing the calculation of the single discharge amount of the core wire to be measured : ; c: Energy density is temperature compensated based on the temperature compensated discharge capacity.

[0035] The determination module uses the temperature compensation module to detect the surface temperature of the cable to be tested in real time, and dynamically corrects the conductor resistance, single discharge amount and energy density of the core to be tested to reduce the impact of the temperature change of the core to be tested on its own resistance, thereby reducing the error in the determination module's determination result caused by the change in conductor resistance. The system uses a formulated temperature compensation strategy to ensure the reliability and comparability of partial discharge detection and withstand voltage test results at different ambient temperatures, providing a scientific basis for long-term monitoring of cable insulation status. The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A multi-core cable withstand voltage automatic testing system, characterized by: include: Processing module, including: A DC charging unit applies a DC high voltage to the core wires to be tested of the multi-core cable to be tested within a first predetermined time; a damped oscillation unit, applying a damped oscillation process to the core wire to be tested at intervals for a plurality of times after a first predetermined time; Data acquisition module, including: A first acquisition unit: within the first predetermined time, collecting the voltage signal of each core wire in a channel-by-channel manner; a second acquiring unit, configured to acquire partial discharge signals of the cable under test at different times at a start time of the second predetermined time period and after an end time of the damped oscillation process; A determination module is used to calculate the insulation resistance characteristics and partial discharge characteristics of each of the core wires to be tested according to the voltage signal and the partial discharge signal, and to determine whether the multi-core cable to be tested passes the withstand voltage test based on the insulation characteristics and partial discharge characteristics of each of the core wires to be tested.

2. The multi-core cable withstand voltage automatic testing system according to claim 1, characterized in that: The determination module calculates the insulation resistance characteristics of each core wire according to the voltage signal and the partial discharge signal, including: Determine, based on the voltage signal, a voltage relationship curve of each core wire of the multi-core cable to be tested, wherein the voltage relationship curve is used to represent a voltage-time relationship curve within a first predetermined time, and the determination module determines, based on the voltage relationship curve and an input voltage curve of a DC charging unit, whether a nonlinear offset occurs in the core wire within the first predetermined time, wherein the nonlinear offset is used to represent a difference between a measured voltage and a true voltage of the cable to be tested; determining, based on the partial discharge signal, whether concentrated discharge occurs in the core wire within a second predetermined time period; When at least one of the nonlinear offset and the concentrated discharge does not occur in each core wire of the multi-core cable to be tested, it is determined that the multi-core cable to be tested passes the withstand voltage test.

3. The multi-core cable withstand voltage automatic testing system according to claim 1, characterized in that: The second acquisition unit acquires the partial discharge signal in the zero voltage stage.

4. The multi-core cable withstand voltage automatic testing system according to claim 1, characterized in that: The determination module determines whether the core line has a nonlinear offset within the first predetermined time based on the DC high voltage curve and the voltage relationship curve of the DC charging unit, including calculating the drift time : ； in, is the theoretical charging voltage corresponding to the t-th moment on the theoretical charging curve, is the actual voltage of the core wire at the tth moment; When the offset time is greater than a preset time threshold, it is determined that the nonlinear offset occurs in the cable to be tested within a first predetermined time period.

5. The multi-core cable withstand voltage automatic testing system according to claim 1, characterized in that: The partial discharge signal includes a partial discharge amount and a partial discharge position of the core wire. Determining whether concentrated discharge occurs in the core wire within a second predetermined time period based on the partial discharge signal includes: When the partial discharge amount is greater than a discharge amount threshold and the number of the partial discharge locations is greater than a number threshold, it is determined that concentrated discharge occurs in the core wire within the second predetermined time period.

6. The multi-core cable withstand voltage automatic testing system according to claim 3, characterized in that: The determination module calculates the insulation resistance value of the core wire to be measured by dynamically compensating for the displacement current generated by the distributed capacitance of the cable: ； in, is the actual current of the core wire at the tth moment, is the rate of change of the high voltage of the pre-charging process applied by the DC charging unit to the core wire, and C is the calibrated equivalent capacitance of the core wire.

7. The multi-core cable withstand voltage automatic testing system according to claim 6, characterized in that: The DC charging unit includes a pre-charging process for the selected core line before the first predetermined time, and the real-time voltage of the pre-charging process and real-time current The first acquisition unit also includes acquiring the steady-state voltage of the core line after the pre-charging process and steady-state current ; The calibration capacitance C determined by the determination module includes: Calculate the equivalent resistance: ; Calibration capacitor .

8. The multi-core cable withstand voltage automatic testing system according to claim 6, characterized in that: The temperature compensation module is used to test the surface temperature T of the multi-core cable to be tested and transmit the surface temperature T to the determination module, and the determination module calculates the compensation resistance according to the surface temperature T. : ； in, is the reference test temperature The test resistance of the core wire under test, is the temperature coefficient of resistance of the conductor material; The determination module also includes a The temperature-compensated discharge amount is obtained by supplementing the calculation of the single discharge amount of the core wire to be measured and temperature compensation of the energy density based on the temperature compensated discharge amount.

9. The multi-core cable withstand voltage automatic testing system according to claim 1, characterized in that: The second acquisition unit includes a high-frequency current sensor and a capacitive coupler.

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