Test method and system for micro-discharge failure of conductive slip ring under extreme alternating air pressure

Abstract

The application discloses a test method and system for micro-discharge failure of a conductive slip ring under extreme alternating air pressure. The test method comprises the following steps: placing a conductive slip ring to be tested in a vacuum chamber, and pumping the vacuum chamber according to a preset air pressure-time curve; in the pumping process, a combined voltage stress of a basic working voltage and a transient pulse overvoltage is synchronously applied to a test channel; a high-frequency current signal of the test channel is monitored in real time, and a micro-discharge trigger signal is generated when an ultra-high-frequency tiny current mutation is detected; in response to the micro-discharge trigger signal, a time-domain reflected waveform signal is captured based on a pre-trigger acquisition mechanism; and the spatial position where the micro-discharge occurs is calculated based on the time difference between an incident pulse characteristic point and a reflected pulse characteristic point. The test method provided by the application can accurately excite micro-discharge by coupling dynamic alternating air pressure and combined electric stress, capture a transient waveform by using a pre-trigger mechanism, and realize high-probability excitation, non-missing capture and high-precision positioning of micro-discharge.

Description

Technical Field

[0001] This application relates to the field of electrical connection and rotational conduction testing technology, and in particular to a testing method and system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure. Background Technology

[0002] As a core precision component for transmitting electrical signals and energy between two relatively rotating mechanisms, conductive slip rings are widely used in aerospace, medical equipment, wind power, and radar. In specific applications such as aerospace, equipment undergoes a rapid ascent from atmospheric pressure at ground level to low pressure at high altitudes as the aircraft travels, requiring conductive slip rings to operate reliably under extreme alternating pressure environments.

[0003] According to Paschen's law of gas discharge, under a specific product of gas pressure and gas gap width, the gas breakdown voltage will drop to an extremely low value. Due to the small insulation spacing inside conductive slip rings, micro-discharges (corona discharges or micro-sparks) are easily induced between the ring tracks and between the brushes and ring grooves when the gas pressure crosses near the lowest point of the Paschen curve. These micro-discharges lead to accelerated oxidation of the contact surfaces, aging of the insulation material, a sharp deterioration in the signal-to-noise ratio of the transmitted signal, and even instantaneous step loss, making them a hidden killer that induces early slip ring failure.

[0004] Currently, reliability testing for conductive slip rings mainly focuses on contact resistance testing, wear life testing, or steady-state high-voltage breakdown testing under normal atmospheric pressure. Existing technologies have the following significant drawbacks: 1. Difficulty in effectively inducing micro-discharge: Breakdown tests under static constant air pressure cannot reproduce the Paschen breakdown effect caused by dynamic changes in air pressure during the aircraft's climb, often resulting in the inability to detect micro-discharge; 2. Transient signals are easily lost: Micro-discharge is a transient physical process on the order of nanoseconds to microseconds. The conventional detection and judgment before triggering acquisition mode has a processing delay. By the time the judgment is completed and the acquisition is attempted, the incident wave and the reflected wave have already ended, which can easily lead to waveform loss and make it impossible to obtain a complete time-domain reflection signal. 3. Inability to accurately locate the discharge point: The internal structure of the slip ring is compact and the channels are dense. Existing technologies mostly rely on macroscopic current / voltage fluctuation monitoring, which can only determine whether micro-discharge has occurred, but cannot determine which ring channel or which air gap is discharging, resulting in aimless troubleshooting.

[0005] Therefore, there is an urgent need for a testing method and system that can accurately excite micro-discharges under extreme alternating gas pressures, capture transient waveforms without omission, and achieve high-precision positioning. Summary of the Invention This application provides a test method and system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure, in order to solve the problems of difficulty in effective excitation, easy loss of transient waveforms, and inability to accurately locate micro-discharges in current micro-discharge tests.

[0006] To address the aforementioned technical problems, this application provides a technical solution: a test method for micro-discharge failure of a conductive slip ring under extreme alternating gas pressure. This test method includes: S1: placing the conductive slip ring under test in a vacuum chamber and evacuating the chamber according to a preset pressure-time curve to simulate an extreme alternating gas pressure environment; S2: during evacuation, simultaneously applying a combined voltage stress to the test channel of the conductive slip ring under test, the combined voltage stress including the base operating voltage and transient pulse overvoltage; S3: real-time monitoring of the high-frequency current signal of the test channel, generating a micro-discharge trigger signal when a sudden change in ultra-high frequency micro-current is detected; S4: responding to the micro-discharge trigger signal, capturing the time-domain reflection waveform signal within the test channel based on a pre-triggered acquisition mechanism; S5: calculating the spatial location of the micro-discharge based on the time difference between the incident pulse characteristic point and the reflected pulse characteristic point in the time-domain reflection waveform signal.

[0007] In some embodiments, in step S1, the preset pressure-time curve is generated based on the aircraft's flight climb profile; the pumping process causes the pressure inside the vacuum chamber to drop from atmospheric pressure to low pressure at a non-linear rate in order to reproduce the breakdown pressure zone of the Paschen curve.

[0008] In some embodiments, step S2, applying a combined voltage stress to the test channel of the conductive slip ring under test, includes: A periodic transient pulse overvoltage is superimposed on the DC base operating voltage; wherein the amplitude of the transient pulse overvoltage is 1.5 to 3 times the DC base operating voltage, and the pulse width of the transient pulse overvoltage is in the microsecond or nanosecond range.

[0009] In some embodiments, step S2 further includes: As the air pressure inside the vacuum chamber decreases, the amplitude of the transient pulse overvoltage is dynamically increased according to Paschen's law, so that the applied combined voltage stress always approaches the critical value of the gas breakdown voltage corresponding to the current air pressure.

[0010] In some embodiments, prior to step S3, the method further includes: Under static conditions where no transient pulse overvoltage is applied and no air is pumped out, the high-frequency background noise signal of the test channel is acquired, and the average amplitude of the high-frequency background noise signal is calculated as the background noise reference value. In step S3, generating a micro-discharge trigger signal when a sudden change in ultra-high frequency micro-current is detected includes: When the amplitude of the current in the high-frequency current signal with a frequency in the range of hundreds of megahertz to gigahertz exceeds a preset multiple of the background noise reference value, the micro-discharge trigger signal is generated.

[0011] In some embodiments, prior to step S4, the method further includes: Under normal pressure and non-discharge conditions, a calibration probe pulse is sent to the test channel to collect and store the background reflection waveform generated only by the inherent impedance discontinuity of the test channel. After step S4, the following also includes: The captured original time-domain reflection waveform signal is subjected to wavelet denoising processing, and the waveform of the denoised time-domain reflection waveform signal is differentially subtracted from the background reflection waveform to cancel the interference of the inherent impedance discontinuity point and extract the abnormal reflection pulse signal caused only by micro-discharge.

[0012] In some embodiments, prior to step S5, the method further includes: Before testing, a standard short-circuit point is created at the known length end of the conductive slip ring under test. A calibration pulse is sent and the calibration time difference is obtained. The propagation speed of the high-frequency signal in the slip ring channel and the lead wire is calculated based on the known length from the standard short-circuit point and the calibration time difference. In step S5, calculating the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal includes: The extracted incident pulse waveform is used as a reference template, and a sliding cross-correlation operation is performed with the waveform of the abnormal reflected pulse signal. The time shift corresponding to the peak value of the cross-correlation function is taken as the feature point time difference. The equivalent transmission distance from the micro-discharge point to the measurement end is the product of the propagation speed and half the time difference of the feature point.

[0013] In some embodiments, the method further includes: determining the impedance change characteristics of the micro-discharge point based on the polarity of the abnormal reflection pulse signal; If the polarity of the abnormal reflected pulse is opposite to that of the incident pulse, it is determined that the characteristic impedance of the micro-discharge point decreases, and a gas gap conduction type discharge occurs; if the polarity of the abnormal reflected pulse is the same as that of the incident pulse, it is determined that the characteristic impedance of the micro-discharge point increases, and a discharge burnout type defect is cleared.

[0014] In some embodiments, the method further includes: assessing the severity of the micro-discharge based on the amplitude of the reflection coefficient of the abnormal reflected pulse signal; the larger the amplitude of the reflection coefficient, the deeper the air gap conduction or the stronger the discharge energy.

[0015] To address the aforementioned technical problems, another technical solution adopted in this application is: providing a test system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure, used to implement the method described above. The test system includes: a gas pressure simulation module for evacuating the vacuum chamber containing the conductive slip ring under test according to a preset gas pressure-time curve; a voltage stress application module for simultaneously applying a combined voltage stress of basic operating voltage and transient pulse overvoltage to the test channel of the conductive slip ring under test during evacuation; a micro-discharge excitation monitoring module for real-time monitoring of the high-frequency current signal of the test channel and generating a micro-discharge trigger signal when a sudden change in ultra-high frequency micro-current is detected; a waveform capture module for capturing the time-domain reflected waveform signal within the test channel based on a pre-triggered acquisition mechanism in response to the micro-discharge trigger signal; and a discharge location calculation module for calculating the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal.

[0016] The beneficial effects of this application are as follows: Unlike existing technologies, this application discloses a testing method and system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure. The embodiments of this application simulate alternating gas pressure by pumping air according to a preset pressure-time curve and simultaneously applying the combined stress of the base working voltage and transient pulse overvoltage, accurately reproducing the Paschen breakdown critical region and achieving high-probability excitation of micro-discharge. By utilizing high-frequency current mutation triggering and capturing the time-domain reflection waveform based on a pre-trigger acquisition mechanism, the omission of transient waveforms is avoided, and reliable acquisition of the complete time-domain reflection signal is achieved. Based on the time difference calculation of the characteristic points of the incident pulse and the reflected pulse, high-precision positioning of the micro-discharge spatial location is achieved. This application completely abandons the traditional static testing model, which cannot reproduce real working conditions, and the conventional monitoring model, which cannot locate the discharge point. It avoids the risk of missed detection due to low excitation rate and the problem of positioning failure due to waveform loss, significantly improving the accuracy and reliability of micro-discharge failure diagnosis. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic flowchart of an embodiment of the test method for micro-discharge failure of conductive slip ring under extreme alternating gas pressure provided in this application; Figure 2 This is a schematic diagram of an embodiment of the test system for testing the micro-discharge failure of a conductive slip ring under extreme alternating gas pressure provided in this application. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] To address the problems in existing technologies, such as the difficulty in effectively exciting micro-discharges under extreme alternating gas pressures, the easy loss of transient signals, and the inability to accurately locate discharge points, this application provides a micro-discharge testing scheme based on dynamic stress coupling excitation, pre-triggered capture, and high-precision positioning. This testing scheme accurately excites micro-discharges by simulating real flight profiles, utilizes a pre-triggered mechanism to ensure complete waveform capture, and achieves high-precision positioning through characteristic point time difference calculation. It only requires a conventional vacuum chamber, high-voltage source, and high-frequency acquisition equipment, significantly reducing the difficulty and cost of micro-discharge failure diagnosis.

[0022] Specifically, this application provides a test method for micro-discharge failure of conductive slip rings under extreme alternating gas pressure, see reference. Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the test method for testing the micro-discharge failure of a conductive slip ring under extreme alternating gas pressure provided in this application. The test method includes: Step S1: Place the conductive slip ring to be tested inside the vacuum chamber and evacuate the vacuum chamber according to the preset pressure-time curve to simulate an extreme alternating pressure environment.

[0023] The preset pressure-time curve is generated based on the aircraft's flight climb profile; the pumping process reduces the pressure inside the vacuum chamber from atmospheric pressure to low pressure at a non-linear rate to reproduce the breakdown pressure zone of the Paschen curve.

[0024] Specifically, when conductive slip rings are used in the aerospace field, the air pressure environment they face is not static and constant, but undergoes rapid nonlinear changes as the aircraft climbs, cruises, and descends. Traditional tests often use static low air pressure maintenance, which deviates greatly from the actual working conditions.

[0025] According to Paschen's law of gas discharge, the breakdown voltage is a function of the product of the gas pressure and the gas gap distance. Within a specific gas pressure range, the breakdown voltage drops to an extremely low value; this range is the breakdown pressure region near the lowest point of the Paschen curve. For the micrometer- to millimeter-scale insulating gas gap inside a conductive slip ring, this breakdown pressure region is typically located at 10... 3 Pa to 10 4 Within the Pa range. If the pumping rate in the vacuum chamber is too fast, the test channel of the conductive slip ring will have a very short dwell time at the Pa-Sing breakdown critical point, and the micro-discharge will not have enough time to develop before it crosses the pressure zone, resulting in a very low excitation probability; if the pumping rate is constant and not targeted, it is impossible to accurately simulate the worst working conditions.

[0026] Therefore, in this embodiment, the evacuation process causes the air pressure inside the vacuum chamber to decrease from 10... 5 Pa decreases to 10 at a nonlinear rate. 2 Below Pa, and above 10 Pa. 3 Pa to 10 4 When the pressure reaches the Pa range, the pumping rate is reduced to increase the dwell time in the critical pressure zone. The specific pressure inflection point and pumping rate can be set according to the actual climb profile of different aircraft models, or the optimal dwell parameters can be obtained through preliminary simulation calculations based on the air gap parameters of the conductive slip ring under test.

[0027] Extensive experimental verification has shown that when the air pressure crosses 10... 3 Pa to 10 4When the pressure range is within 1 / 5 to 1 / 3 of the normal rate, the duration of this pressure range is extended to 3 to 10 minutes. This allows sufficient time for the air gap inside the conductive slip ring to discharge at the pressure point corresponding to the lowest breakdown voltage, increasing the micro-discharge activation probability from less than 15% in traditional static testing to over 85%. If the residence time in this dangerous pressure range is less than 1 minute, the activation probability is still less than 40%; if the residence time exceeds 10 minutes, although the activation probability increases, the increase slows down and severely affects the testing efficiency.

[0028] Furthermore, the vacuum chamber is equipped with a high-precision pressure sensor and a variable frequency vacuum pump unit. The pressure closed-loop controller outputs a non-linear pumping control signal to the variable frequency vacuum pump unit based on a preset pressure-time curve. (The last sentence appears to be incomplete and possibly refers to a pressure control system operating at atmospheric pressure up to 10...) 4 During the Pa stage, a higher pumping rate is used to shorten the time consumed in non-critical areas; upon entering the 10 stage... 4 Pa to 10 3 In the hazardous area of ​​Pa, the air pressure closed-loop controller reduces the pump frequency to achieve slow air extraction; below 10 Pa... 3 After Pa, the pumping rate is increased again until the target low pressure value is reached. This nonlinear pumping strategy maximizes the probability of micro-discharge in the dangerous pressure zone while ensuring test efficiency, and realistically and strongly reproduces the fault causes under actual working conditions.

[0029] Step S2: During the evacuation process, a combined voltage stress is simultaneously applied to the test channel. The combined voltage stress includes the base operating voltage and the transient pulse overvoltage.

[0030] During the evacuation process, if only changes in ambient air pressure are relied upon without the application of electrical stress, micro-discharges are often difficult to initiate due to the lack of initial free electrons and the maintenance of an electric field. Although traditional steady-state high-voltage breakdown tests can provide a strong electric field, steady-state high voltage can easily trigger penetrating breakdown directly when the air pressure drops to a critical point, causing permanent damage to the insulating material of the conductive slip ring. This is not the micro-discharge phenomenon that this application aims to detect.

[0031] Therefore, this embodiment employs a combined voltage stress application method, specifically: superimposing periodic transient pulse overvoltages onto the DC base operating voltage. The base operating voltage is used to simulate the rated operating state of the conductive slip ring in an actual circuit, providing a base electric field for the air gap; the transient pulse overvoltage is used to provide transient high-intensity electric field energy when the air pressure reaches the critical region, triggering local ionization.

[0032] The transient pulse overvoltage amplitude is 1.5 to 3 times the DC base operating voltage, the pulse width is in the microsecond or nanosecond range, and the waveform is preferably a step pulse or a double exponential pulse. Specifically, the transient pulse overvoltage amplitude can be 1.5 times, 1.8 times, 2.0 times, 2.2 times, 2.5 times, or 3.0 times, etc.

[0033] Extensive experimental verification has shown that if the pulse overvoltage amplitude is less than 1.5 times the basic operating voltage, the transient electric field energy provided is insufficient to induce effective electron avalanche in the tiny air gap, thus failing to excite micro-discharge; if the pulse overvoltage amplitude is more than 3 times the basic operating voltage, it is very easy to directly cause the slip ring insulation material to break down and burn out at slightly lower air pressure, resulting in destructive damage and deviating from the original intention of non-destructive testing of micro-discharge.

[0034] For example, when the base operating voltage is 270V (typical aviation DC voltage), the amplitude of transient pulse overvoltage should be controlled between 405V and 810V.

[0035] Microsecond (e.g., 1 μs to 10 μs) or nanosecond (e.g., 100 ns to 500 ns) pulse widths ensure the concentrated release of electric field energy within an extremely short time. If the pulse width is too wide, such as reaching the millisecond level, the energy release time is too long, easily leading to the development of local ionization into a penetrating discharge. If the pulse width is too narrow, such as the picosecond level, although the energy is extremely concentrated, the hardware requirements for the pulse generator are extremely high, and narrow pulses exhibit severe dispersion in the slip ring transmission line, resulting in waveform distortion. Therefore, selecting microsecond or nanosecond pulse widths can generate a strong ionization excitation effect in the air gap while effectively suppressing the development towards breakdown.

[0036] Furthermore, as the air pressure inside the vacuum chamber decreases, the amplitude of the transient pulse overvoltage is dynamically increased according to Paschen's law, so that the applied combined voltage stress always approaches the critical value of the gas breakdown voltage corresponding to the current air pressure.

[0037] Specifically, the system has a pre-stored lookup table of Paschen breakdown voltage curves under typical air gaps of conductive slip rings. During the pumping process, the current air pressure value is read in real time, and the theoretical breakdown voltage under the current air pressure is calculated by interpolation through the lookup table. Based on this, the output amplitude of the pulse generator is dynamically adjusted. By dynamically adjusting the amplitude of transient pulse overvoltage, just the right intelligent excitation is achieved, avoiding destructive breakdown caused by applying excessively high voltage at low pressure, and also avoiding the problem of insufficient pulse energy to excite discharge at high pressure.

[0038] Furthermore, the conductive slip ring under test typically contains multiple test channels, ranging from a dozen to hundreds. To improve testing efficiency, this embodiment uses a multi-channel switching matrix to sequentially apply the combined voltage stress to different test channels, achieving multi-channel polling excitation testing.

[0039] The multi-channel switching matrix employs high-voltage vacuum relays or optically controlled solid-state relay arrays, providing high-voltage isolation and rapid switching capabilities. During polling, the dwell time of each test channel can be set according to the repetition frequency of the pulse generator, typically set to switch to the next test channel after applying 10 to 50 pulse cycles. At the moment of switching, the system is set with a blanking time, such as 1ms to 5ms, to prevent transient interference from relay operation from being misinterpreted as micro-discharge signals.

[0040] This embodiment maximizes the excitation probability of micro-discharge by precisely coupling dynamic alternating air pressure and combined voltage stress, without damaging the slip ring insulation, thus laying a solid signal foundation for subsequent waveform capture and precise positioning.

[0041] Step S3: Monitor the high-frequency current signal of the test channel in real time. When a sudden change in ultra-high frequency micro current is detected, generate a micro-discharge trigger signal.

[0042] Micro-discharge is essentially a localized ionization breakdown phenomenon that occurs in a gas gap under the influence of a strong electric field. At the moment of breakdown, the electron avalanche process within the gap generates a large number of charged particles in an extremely short time (on the order of nanoseconds to microseconds), causing a sharp increase in the gap current. This sudden change in current contains extremely rich high-frequency components, and its spectral range is typically distributed in the order of hundreds of megahertz (MHz) to gigahertz (GHz).

[0043] However, during the testing of conductive slip rings, a certain level of background noise always exists in the test circuit due to factors such as external power supply ripple, mechanical vibration interference from the vacuum pump, high-frequency harmonics from the frequency converter, and spatial electromagnetic interference. Without effective noise suppression and feature extraction, the micro-discharge signal is easily submerged in the background noise, leading to missed detections or misjudgments.

[0044] Therefore, before performing real-time high-frequency current monitoring on the test channel, a background noise calibration step is also included: under static conditions where no transient pulse overvoltage is applied and no air is pumped out, the high-frequency background noise signal of the test channel is acquired, and the average amplitude of the high-frequency background noise signal is calculated as the background noise reference value.

[0045] Specifically, under steady-state conditions with normal pressure, only the base operating voltage applied, and no pulses applied, a high-frequency current sensor continuously collects the loop current signal for a period of time, for example, 1000 power frequency cycles. The signal is then converted to the frequency domain using a Fast Fourier Transform (FFT), and the noise power spectral density of each frequency band is statistically analyzed. The root mean square (RMS) value of the current amplitude for the entire frequency band or a specific high-frequency band (e.g., greater than 100 MHz) is calculated and used as the background noise reference value. This calibration process provides a dynamic reference for subsequent micro-discharge determination and can effectively adapt to changes in electromagnetic interference under different test environments.

[0046] In this embodiment, a broadband high-frequency current sensor is used to non-contactly acquire the high-frequency current signal of the test circuit. Specifically, this broadband high-frequency current sensor uses a high-bandwidth Rogowski coil. Based on Faraday's law of electromagnetic induction, the Rogowski coil indirectly measures current by measuring the alternating magnetic field generated around the conductor. It has an extremely wide bandwidth (up to hundreds of MHz or even GHz), an extremely fast response time (nanosecond level), and good electrical isolation characteristics. Because the Rogowski coil has no iron core, there is no magnetic saturation problem, thus enabling it to capture steep high-frequency current pulses generated by micro-discharges without distortion.

[0047] By connecting the Rogowski coil to the lead wire of the slip ring test channel, the induced voltage signal is processed by a broadband amplifier and a bandpass filter, and then sent to a high-speed analog-to-digital converter (ADC) for real-time sampling.

[0048] When the current amplitude in the high-frequency current signal with a frequency in the range of hundreds of megahertz to gigahertz exceeds a preset multiple of the background noise reference value, such as a preset multiple of 3 or 4 times, a micro-discharge trigger signal is generated.

[0049] In this embodiment, the preset multiplier is 3-4 times, and the selection of 3-4 times the background noise reference value as the judgment standard is based on statistics and extensive experimental verification. If the threshold is set too low, such as 1 or 2 times the background noise reference value, due to the random fluctuation of background noise, it is very easy to be falsely triggered by occasional strong electromagnetic interference pulses, causing the system to erroneously start waveform capture when no micro-discharge occurs, wasting storage resources and interfering with subsequent analysis. If the threshold is set too high, such as 5 or 10 times the background noise reference value, it may miss the early weak corona discharge signal, because the current change amplitude in the early stage of corona discharge is often small and difficult to break through the high threshold, resulting in the inability to capture the initial stage of micro-discharge.

[0050] Extensive experimental verification has shown that within the 100 MHz to 1.5 GHz frequency band, a background noise reference value of 3-4 times can filter out most random noise pulses, while effectively identifying early micro-discharge current mutations with amplitudes of only tens of milliamperes.

[0051] In one specific implementation, a field-programmable gate array (FPGA) receives sampled data from a high-speed analog-to-digital converter (ADC) in real time, calculates the current amplitude in the high-frequency band in parallel, and compares it with a stored background noise reference value that is a preset multiple. If the value exceeds the reference value, the FPGA outputs a TTL-level micro-discharge trigger signal within a nanosecond delay. This trigger signal is synchronously sent to the waveform capture module to initiate the recording of the time-domain reflection waveform. This hardware-based high-speed real-time determination mechanism ensures an extremely short delay from the occurrence of the micro-discharge to the generation of the trigger signal, providing a precise time reference for subsequent pre-triggered capture.

[0052] Step S4: In response to the micro-discharge trigger signal, capture the time-domain reflection waveform signal in the test channel based on the pre-trigger acquisition mechanism.

[0053] Micro-discharge is a transient physical process on the order of nanoseconds to microseconds. Traditional data acquisition systems typically employ a trigger-delay-acquisition model, where the ADC is only activated to sample the signal after it exceeds a threshold. Due to the inherent microsecond-level delay in the microprocessor's response to interrupts and register configuration, by the time the system actually begins acquisition, the incident and reflected waves generated by the micro-discharge have often already propagated, resulting in significant waveform loss and making it impossible to obtain complete time-domain reflection characteristics.

[0054] This embodiment adopts a high-speed waveform acquisition technology based on a pre-triggered acquisition mechanism. The core of the pre-triggered acquisition mechanism is that, regardless of whether a micro-discharge occurs, the high-speed ADC in the waveform acquisition module is always in a continuous sampling state and writes the sampled data into the ring buffer memory in a loop.

[0055] When the micro-discharge excitation monitoring module generates a micro-discharge trigger signal, this trigger signal serves only as a time anchor point, notifying the waveform capture module to lock the current moment. Based on this time anchor point, the system extracts waveform data from the ring buffer for a period of time before the trigger point (and waveform data for a period of time after the trigger point; the waveform data for the period of time before the trigger point is pre-trigger data, which includes the incident wave and the background conditions before the discharge occurs; the waveform data for the period of time after the trigger point is post-trigger data, which includes the reflected wave and the discharge development process). The pre-trigger data and post-trigger data are then spliced ​​together to form a complete time-domain reflection waveform, which is recorded and stored.

[0056] The pre-trigger depth and post-trigger depth can be configured according to the physical length of the slip ring channel and the signal propagation speed. Typically, the pre-trigger point is set at 10% to 30% of the entire recording window to ensure complete coverage of the incident wave and all possible reflected waves. This mechanism completely eliminates the waveform omission problem caused by acquisition delay, achieving complete capture of micro-discharge transient signals.

[0057] Furthermore, before capturing the time-domain reflection waveform signal within the test channel based on the pre-triggered acquisition mechanism, a background reflection calibration step is also included. The internal structure of the conductive slip ring is complex, containing numerous physical interfaces such as leads, insulating sheets, loop transition points, and solder joints. According to transmission line theory, when a high-frequency signal propagates at these interfaces with impedance discontinuities, partial reflection occurs, generating background reflection waves. These background reflection waves objectively exist after the slip ring is manufactured, and their reflection positions and amplitudes are fixed until structural damage occurs. If these background reflections are not eliminated, when a micro-discharge occurs, the resulting abnormal reflection wave will superimpose with the background reflection wave, leading to an extremely complex waveform, making it difficult to distinguish the true discharge point location, and easily causing false or mis-localization.

[0058] Therefore, in this embodiment, under normal pressure and non-discharge conditions, a calibration probe pulse is sent to the test channel to collect and store the background reflection waveform generated only by the inherent impedance discontinuity of the test channel.

[0059] Specifically, the breakdown field strength of gas under normal pressure is extremely high. At this time, the low-pressure calibration pulse applied will not cause any discharge. For example, a fast-edge step pulse with an amplitude of 5V to 10V will propagate in the channel and the reflected wave generated when it encounters the impedance discontinuity is the pure background reflection waveform. This background reflection waveform is stored according to the channel number and used as the reference template for subsequent differential cancellation.

[0060] After capturing the time-domain reflection waveform at the time of micro-discharge, the transient pulse overvoltage in the applied combined voltage stress is actually multiplexed as the incident detection signal for time-domain reflection measurement.

[0061] Specifically, the leading edge energy of the applied transient pulse overvoltage is used to excite micro-discharge. When this leading edge reaches the micro-discharge point, the characteristic impedance at that point changes instantaneously due to the ionization and conduction of the air gap, abruptly changing from a high-impedance insulating state to a low-impedance arc state or a locally ionized state. This transient impedance discontinuity causes some of the incident pulse energy to be reflected back to the measurement end, forming an abnormal reflected pulse. Therefore, the transient pulse overvoltage acts as both an excitation source and a detection source. This dual-purpose design eliminates the need for an additional independent TDR signal generator, greatly simplifying the hardware architecture of the test system and fundamentally ensuring strict synchronization between the excitation and detection times, avoiding the timing jitter problem that is difficult to avoid in multi-source systems.

[0062] Furthermore, wavelet denoising is performed on the captured original time-domain reflection waveform signal, and the waveform of the denoised time-domain reflection waveform signal is differentially subtracted from the background reflection waveform to cancel the interference of the inherent impedance discontinuity point and extract the abnormal reflection pulse signal caused only by micro-discharge.

[0063] Specifically, since slip ring channels are typically several meters long, high-frequency signals inevitably experience attenuation and dispersion during transmission, leading to tailing and high-frequency oscillations in the reflected waveform. Wavelet denoising techniques are employed, selecting appropriate wavelet bases (such as db6 or sym8 wavelets) and decomposition levels (such as 5 to 8 levels) to perform multi-resolution decomposition on the original waveform. High-frequency detail components composed of thermal noise and quantization noise are filtered out using soft or hard thresholding functions, preserving the main contour features of the original time-domain reflected waveform signal.

[0064] The waveform of the denoised time-domain reflection waveform signal contains both background reflection information and micro-discharge abnormal reflection information. The denoised waveform and the background reflection waveform are precisely aligned in the time domain. Usually, the optimal alignment offset is found by using a cross-correlation registration algorithm to eliminate the small clock deviation between the two acquisitions. Then, differential subtraction is performed point by point.

[0065] Because the shape and amplitude of the background reflection waveform are highly repeatable under the same channel physical structure and the same probe pulse excitation, after subtraction, the inherent structural reflection wave is completely canceled out, and the remaining significant waveform feature is the abnormal reflection pulse generated only by the impedance change caused by micro-discharge.

[0066] The innovative background reflection calibration and differential subtraction mechanism proposed in this embodiment eliminates the background reflection waveform of the slip ring itself from the complex TDR waveform, allowing the abnormal reflection pulse signal of micro-discharge to be completely exposed, thus clearing the biggest obstacle for subsequent high-precision positioning.

[0067] Step S5: Calculate the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal.

[0068] After extracting the pure anomalous reflected pulse signal, it is necessary to accurately calculate the time difference between the incident pulse and the anomalous reflected pulse. However, the waveform of the reflected pulse generated by micro-discharge usually undergoes severe distortion and broadening after long-distance transmission and passing through multiple impedance mismatch interfaces. The traditional method of directly reading the 50% amplitude of the rising edge of the waveform as a feature point is greatly affected by waveform distortion, and the time difference reading error may be as high as several nanoseconds. In high-frequency transmission lines, a 1 nanosecond time error corresponds to a positioning error of about 0.15 meters, which is completely unacceptable for conductive slip rings with internal spacing of only millimeters.

[0069] Therefore, a propagation speed calibration step is included before calculating the time difference. The propagation speed of high-frequency signals in the slip ring channel and leads is not the ideal speed of light in a vacuum, but is significantly affected by the equivalent dielectric constant and geometry of the transmission line.

[0070] Specifically, before testing, a standard short-circuit point is created at the known length end of the conductive slip ring under test, for example, at the end of the loop at a precise distance L0 from the measuring end. A calibration pulse is sent to this channel, and the total internal reflection pulse generated at the standard short-circuit point is acquired. The calibration time difference Δt0 between the incident pulse and the total internal reflection pulse is measured. Based on the known length L0 and the calibration time difference Δt0, the propagation velocity v = 2L0 / Δt0 is calculated. This experimental calibration method fully considers the delay effect of the complex medium inside the slip ring (such as insulating sheets, air gaps, potting compound, etc.) on electromagnetic wave propagation, eliminating systematic errors caused by theoretical calculations.

[0071] In this embodiment, the cross-correlation algorithm is used to calculate the feature point time difference Δt. The cross-correlation algorithm is a statistical method for measuring the similarity between two waveforms, exhibiting strong robustness to local waveform distortion and amplitude fluctuations. The specific steps are as follows: the extracted incident pulse waveform is used as a reference template x(t), and the waveform of the abnormal reflected pulse signal is used as the signal to be matched y(t). In the time domain, y(t) is slid relative to x(t), and for each time shift τ, the cross-correlation function R(τ) is calculated. When the waveform reaches a specific time shift Δt, the overlap between the two waveforms is highest, and their shapes are most similar; at this point, the cross-correlation function R(τ) reaches its peak. The time shift corresponding to this peak value is taken as the feature point time difference Δt.

[0072] The advantage of using the cross-correlation algorithm lies in its utilization of the energy and shape information of the entire waveform for matching, rather than relying on the judgment of a single amplitude point. Even if the rising edge of an abnormal reflected pulse becomes slower due to dispersion or the amplitude decreases due to attenuation, as long as the overall waveform characteristics are preserved, the cross-correlation algorithm can accurately find the optimal matching position. Numerous experiments have shown that, with a signal-to-noise ratio greater than 3dB, the time difference resolution of the cross-correlation algorithm can reach the sub-nanosecond level, and the corresponding spatial positioning accuracy can reach the centimeter or even millimeter level.

[0073] The equivalent transmission distance L from the micro-discharge point to the measurement end is the product of the propagation speed v and half the feature point time difference Δt. That is, the formula for calculating the location of the micro-discharge is: L = v × Δt / 2. Here, L is the equivalent transmission distance from the micro-discharge point to the measurement end, v is the calibrated propagation speed, and Δt is the feature point time difference extracted by the cross-correlation algorithm. Dividing by 2 is because the signal travels a round trip from the measurement end to the micro-discharge point and then reflects back to the measurement end.

[0074] This formula allows for the precise mapping of microscopic discharge events onto the macroscopic physical structure of the slip ring, enabling high-precision spatial location of hidden faults.

[0075] Furthermore, on the basis of achieving high-precision positioning of the spatial location of microdischarges, the embodiments of the present application further provide a method for qualitatively diagnosing the type of microdischarges. The impedance change characteristics of the microdischarge points are judged according to the polarity of the abnormal reflection pulses after differential subtraction.

[0076] Furthermore, the impedance change characteristics of the microdischarge points are judged according to the polarity of the abnormal reflection pulse signals after differential subtraction.

[0077] According to the transmission line theory, when a high-frequency signal encounters an impedance discontinuity point on the transmission line, reflection will occur. The definition of the reflection coefficient Γ is , where Z L is the equivalent load impedance after the discontinuity point, and Z0 is the characteristic impedance of the transmission line.

[0078] At the moment when the microdischarge occurs, the original insulation state of the microdischarge point is broken, and its equivalent impedance changes suddenly. If the abnormal reflection pulse and the incident pulse have opposite polarities, it means that the reflection coefficient Γ < 0, that is, Z L < Z0, it is determined that the characteristic impedance of the microdischarge point decreases, and a discharge of the air-gap conduction type occurs.

[0079] This is the most typical physical process of microdischarges. The air gap is ionized and broken down to form a conductive channel, which is equivalent to connecting a low-impedance branch in parallel at the discharge point. According to the depth of conduction, it can be further subdivided: if the amplitude of the reflection coefficient is small, it is usually a corona discharge with local weak ionization; if the amplitude of the reflection coefficient is large and the waveform front edge is steep, it is usually a spark discharge with complete breakdown.

[0080] If the abnormal reflection pulse and the incident pulse have the same polarity, it means that the reflection coefficient Γ > 0, that is, Z L > Z0, it is determined that the characteristic impedance of the microdischarge point increases, and a discharge burn-off type defect is cleared. This situation is relatively special. Usually, it is caused by a low-impedance bridging due to metal burrs or conductive contaminants originally existing at the discharge point. Initially, it is a negative reflection. Under the action of the pulse energy, a microdischarge occurs, instantly vaporizing and burning off the burrs or contaminants, removing the low-impedance path, and making the impedance at this point recover to a high-impedance state or even locally open, thus generating a positive reflection.

[0081] This embodiment reveals the direction of impedance mutation caused by discharge through the determination of the reflection wave polarity, which provides a key basis for the slip ring designers to judge the initial state of insulation defects. Among them, the high-impedance corona discharge indicates that there is local field strength concentration but a small air gap inside the slip ring. If it exists for a long time, it will cause slow deterioration of the insulating material and surface carbonization; the low-impedance spark discharge indicates that the slip ring has serious insulation defects or large-size air gaps, which may cause the equipment to fail instantly in a short time. For different types of discharges, the subsequent improvement strategies are completely different; for example, the corona discharge focuses on optimizing the electrode shape or surface coating, and the spark discharge focuses on increasing the creepage distance or improving the potting process.

[0082] Furthermore, the severity of the micro-discharge is assessed based on the amplitude of the reflection coefficient of the abnormal reflected pulse signal.

[0083] Specifically, by measuring the peak-to-peak value of the differentially reflected pulse signal and comparing it with the peak-to-peak value of the incident pulse waveform, the absolute value of the actual reflection coefficient can be calculated.

[0084] For air gap conducting discharge (negative reflection), the larger the amplitude, the deeper the air gap conduction or the stronger the discharge energy, indicating a more severe impedance reduction caused by the discharge, a deeper degree of air gap ionization, and a higher degree of micro-discharge severity.

[0085] Furthermore, by combining the current air pressure parameters and using the inverse model of Paschen's law, the range of the equivalent air gap physical size where micro-discharge occurs can be roughly estimated.

[0086] For example, a spark discharge occurring at 5000 Pa may have an equivalent breakdown gap between 0.1 mm and 0.5 mm.

[0087] Furthermore, the location, discharge type, and equivalent gap variation of micro-discharge events excited at different pressure points on the same test channel were statistically analyzed to generate a three-dimensional micro-discharge characteristic map of pressure-voltage-location. In this three-dimensional map, the X-axis represents spatial location, the Y-axis represents air pressure (corresponding to flight altitude), and the Z-axis represents voltage stress or discharge intensity. Different colors are used to indicate the discharge type (e.g., blue represents corona, and red represents spark). This map comprehensively depicts the weak points in the insulation of the slip ring throughout the entire flight altitude profile.

[0088] By analyzing the distribution of moderate intensity lines in the spectrum, it is possible to intuitively identify which section of the slip ring is the most severely affected by discharge and which pressure range is the most sensitive. This characteristic spectrum is equivalent to the micro-discharge gene spectrum of the slip ring, providing a quantitative indicator system for batch improvement, quality consistency screening, and life prediction of products.

[0089] Based on the above method embodiments, this application also provides an embodiment of a test system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure. See also... Figure 2 , Figure 2This is a schematic diagram of an embodiment of a test system for testing the micro-discharge failure of a conductive slip ring under extreme alternating gas pressure provided in this application. The test system 100 is applied to the test method described above. The test system 100 includes a gas pressure simulation module 10, a voltage stress application module 20, a micro-discharge excitation monitoring module 30, a waveform capture module 40, and a discharge location calculation module 50. The gas pressure simulation module 10 is used to evacuate the vacuum chamber containing the conductive slip ring under test according to a preset gas pressure-time curve. The voltage stress application module 20 is used to simultaneously apply a combined voltage stress of the base working voltage and transient pulse overvoltage to the test channel of the conductive slip ring under test during the evacuation process. The micro-discharge excitation monitoring module 30 is used to monitor the high-frequency current signal of the test channel in real time and generate a micro-discharge trigger signal when a sudden change in ultra-high frequency micro-current is detected. The waveform capture module 40 is used to capture the time-domain reflected waveform signal within the test channel based on a pre-triggered acquisition mechanism in response to the micro-discharge trigger signal. The discharge location calculation module 50 is used to calculate the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal.

[0090] The pressure simulation module 10 includes a vacuum chamber, a variable frequency vacuum pump group, and a pressure closed-loop controller. The vacuum chamber adopts a stainless steel horizontal structure with polished inner walls to reduce gas adsorption and is equipped with a high-transparency observation window for high-speed camera observation. The variable frequency vacuum pump group consists of a dry screw pump and a molecular pump connected in series to achieve a wide range of pumping from atmospheric pressure to high vacuum. The pressure closed-loop controller adopts a PID algorithm and internally stores multiple preset pressure-time curves corresponding to flight profiles of different aircraft models.

[0091] During the evacuation process, the pressure closed-loop controller reads the pressure feedback value from the high-precision capacitive thin-film gauge inside the vacuum chamber in real time. After comparing it with the set curve, it dynamically adjusts the output frequency of the frequency converter to achieve non-linear and precise control of the evacuation rate, especially at 10... 3 Pa to 10 4 This module can smoothly decelerate and precisely remain in the dangerous pressure range of Pa. By accurately reproducing the extreme alternating pressure environment, it provides a physical basis for the high-probability excitation of micro-discharges.

[0092] The voltage stress application module 20 includes a DC high-voltage source, a pulse generator, a directional coupler, and a multi-channel switching matrix. The DC high-voltage source provides an adjustable base operating voltage from 0 to 1000V with a ripple factor of less than 0.1%. The pulse generator adopts an all-solid-state Marx generator architecture, capable of outputting transient pulse overvoltages with a leading edge of less than 50ns and an amplitude adjustable from 0 to 3000V. The pulse repetition frequency can be set between 1Hz and 100Hz. The directional coupler, as a key component, has its main circuit connected in series in the test circuit, coupling the DC high voltage and transient pulse to the slip ring channel without distortion. Its coupling branch extracts the weak high-frequency signal reflected back from the channel and sends it to the waveform capture module. The multi-channel switching matrix uses a high-voltage optically controlled solid-state relay array with an on-resistance of less than 0.1Ω and an inter-channel isolation greater than 80dB. Under system control, it sequentially applies the combined voltage stress to each channel of the slip ring, achieving high-speed automatic polling. A blanking time of 1ms to 5ms is set at the moment of switching to effectively suppress transient interference during switching.

[0093] The micro-discharge excitation monitoring module 30 includes a Rogowski coil broadband high-frequency current sensor, a bandpass filter, a spectrum analysis unit, and a comparator. The Rogowski coil is connected to the main circuit of the voltage stress application module 20 and the slip ring, with a bandwidth covering 1MHz to 2GHz and a sensitivity of 0.1V / A. The bandpass filter is a high-frequency co-cavity filter with a passband set from 100MHz to 1.5GHz, used to filter out low-frequency power supply ripple and high-frequency spatial radiation interference. The spectrum analysis unit performs detection and envelope extraction on the filtered signal. The comparator uses a high-speed ultrafast comparator chip, with its inverting input connected to a dynamic reference level generated by the background noise calibration step, and its non-inverting input connected to the detected real-time signal. Once the real-time signal exceeds the threshold, the comparator flips within a nanosecond delay and outputs a TTL micro-discharge trigger signal.

[0094] The waveform capture module 40 includes a high-frequency digital oscilloscope and a trigger controller. The high-frequency digital oscilloscope has a bandwidth of no less than 4 GHz, a real-time sampling rate of no less than 20 GSa / s, and is equipped with a large-capacity deep memory (no less than 1 G sampling points). The trigger controller receives a micro-discharge trigger signal and controls the oscilloscope to enter the pre-trigger acquisition mode. The ADC is always in a continuous sampling and cyclic writing state. When the trigger signal arrives, it locks the ring buffer and extracts waveform data of a preset window length before and after the trigger point. The reflected signal extracted by the directional coupler is amplified by a low-noise broadband amplifier (LNA) and then sent to the signal input terminal of the oscilloscope, ensuring reliable capture of weak reflected waveforms.

[0095] The discharge location calculation module 50 includes a background cancellation unit, a velocity calibration unit, a cross-correlation delay calculation unit, and a spectrum generation unit. Its hardware architecture adopts a heterogeneous computing platform of "FPGA + high-performance CPU". The background cancellation unit and the cross-correlation delay calculation unit are implemented by FPGA hardware logic to leverage its advantages in parallel processing and pipelined operation. The FPGA receives the waveform data stream transmitted from the oscilloscope, first performs fast alignment and differential subtraction with the background template in the time domain, and then sends the differential incident wave and reflected wave data into the FPGA-based cross-correlation calculation engine. Through FFT frequency domain multiplication and inverse IFFT transformation, the cross-correlation function curve is calculated at a speed of microseconds, and the delay Δt corresponding to the peak position is accurately extracted. The CPU is responsible for velocity calibration, position calculation, discharge polarity logic judgment, and the drawing and storage of three-dimensional feature spectrum. This hardware and software collaborative architecture enables the test system to achieve efficient real-time processing of simultaneous acquisition, calculation, and result output during multi-channel polling testing.

[0096] The test system 100 for micro-discharge failure of conductive slip rings under extreme alternating gas pressure provided in this embodiment has a compact structure and a high degree of automation. It can complete the entire test closed loop from environmental simulation, stress application, signal acquisition to location analysis without manual intervention. The entire system consists of only conventional vacuum equipment, high voltage source, oscilloscope and computer. It does not require expensive multi-type lasers or complex mechanical scanning mechanisms, which greatly reduces equipment investment and operating costs. It is particularly suitable for the research and development verification and factory screening of aerospace-grade conductive slip rings.

[0097] Unlike existing technologies, this application discloses a testing method and system for micro-discharge failure of conductive slip rings under extreme alternating gas pressure. The embodiments of this application simulate alternating gas pressure by pumping air according to a preset pressure-time curve and simultaneously applying the combined stress of the base working voltage and transient pulse overvoltage, accurately reproducing the Paschen breakdown critical region and achieving high-probability excitation of micro-discharge. High-frequency current abrupt triggering and a pre-triggered acquisition mechanism are used to capture the time-domain reflection waveform, avoiding the omission of transient waveforms and achieving reliable acquisition of the complete time-domain reflection signal. Based on the time difference calculation of the characteristic points of the incident and reflected pulses, high-precision positioning of the micro-discharge spatial location is achieved. This application completely abandons the traditional static testing model, which cannot reproduce real working conditions, and the conventional monitoring model, which cannot locate the discharge point. It avoids the risk of missed detection due to low excitation rate and the problem of positioning failure due to waveform loss, significantly improving the accuracy and reliability of micro-discharge failure diagnosis.

[0098] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A test method for micro-discharge failure of a conductive slip ring under extreme alternating gas pressure, characterized in that, include: S1: Place the conductive slip ring to be tested in the vacuum chamber and evacuate the vacuum chamber according to the preset pressure-time curve to simulate an extreme alternating pressure environment. S2: During the evacuation process, a combined voltage stress is simultaneously applied to the test channel of the conductive slip ring under test, the combined voltage stress including the basic operating voltage and transient pulse overvoltage; S3: Real-time monitoring of the high-frequency current signal of the test channel; when a sudden change in ultra-high frequency micro current is detected, a micro-discharge trigger signal is generated. S4: In response to the micro-discharge trigger signal, capture the time-domain reflection waveform signal in the test channel based on the pre-trigger acquisition mechanism; S5: Calculate the spatial location where the micro-discharge occurs based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal.

2. The method according to claim 1, characterized in that, In step S1, the preset pressure-time curve is generated based on the aircraft's flight climb profile; the pumping process causes the pressure inside the vacuum chamber to drop from atmospheric pressure to low pressure at a non-linear rate in order to reproduce the breakdown pressure zone of the Paschen curve.

3. The method according to claim 1, characterized in that, In step S2, applying a combined voltage stress to the test channel of the conductive slip ring under test includes: A periodic transient pulse overvoltage is superimposed on the DC base operating voltage; wherein the amplitude of the transient pulse overvoltage is 1.5 to 3 times the DC base operating voltage, and the pulse width of the transient pulse overvoltage is in the microsecond or nanosecond range.

4. The method according to claim 3, characterized in that, Step S2 also includes: As the air pressure inside the vacuum chamber decreases, the amplitude of the transient pulse overvoltage is dynamically increased according to Paschen's law, so that the applied combined voltage stress always approaches the critical value of the gas breakdown voltage corresponding to the current air pressure.

5. The method according to claim 1, characterized in that, Before step S3, the following is also included: Under static conditions where no transient pulse overvoltage is applied and no air is pumped out, the high-frequency background noise signal of the test channel is acquired, and the average amplitude of the high-frequency background noise signal is calculated as the background noise reference value. In step S3, generating a micro-discharge trigger signal when a sudden change in ultra-high frequency micro-current is detected includes: When the amplitude of the current in the high-frequency current signal with a frequency in the range of hundreds of megahertz to gigahertz exceeds a preset multiple of the background noise reference value, the micro-discharge trigger signal is generated.

6. The method according to claim 1, characterized in that, Before step S4, the following is also included: Under normal pressure and non-discharge conditions, a calibration probe pulse is sent to the test channel to collect and store the background reflection waveform generated only by the inherent impedance discontinuity of the test channel. After step S4, the following also includes: The captured original time-domain reflection waveform signal is subjected to wavelet denoising processing, and the waveform of the denoised time-domain reflection waveform signal is differentially subtracted from the background reflection waveform to cancel the interference of the inherent impedance discontinuity point and extract the abnormal reflection pulse signal caused only by micro-discharge.

7. The method according to claim 6, characterized in that, Before step S5, the following is also included: Before testing, a standard short-circuit point is created at the known length end of the conductive slip ring under test. A calibration pulse is sent and the calibration time difference is obtained. The propagation speed of the high-frequency signal in the slip ring channel and the lead wire is calculated based on the known length from the standard short-circuit point and the calibration time difference. In step S5, calculating the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal includes: The extracted incident pulse waveform is used as a reference template, and a sliding cross-correlation operation is performed with the waveform of the abnormal reflected pulse signal. The time shift corresponding to the peak value of the cross-correlation function is taken as the feature point time difference. The equivalent transmission distance from the micro-discharge point to the measurement end is the product of the propagation speed and half the time difference of the feature point.

8. The method according to claim 7, characterized in that, Also includes: The impedance change characteristics of the micro-discharge point are determined based on the polarity of the abnormal reflected pulse signal. If the polarity of the abnormal reflected pulse is opposite to that of the incident pulse, it is determined that the characteristic impedance of the micro-discharge point decreases, and a gas gap conduction type discharge occurs; if the polarity of the abnormal reflected pulse is the same as that of the incident pulse, it is determined that the characteristic impedance of the micro-discharge point increases, and a discharge burnout type defect is cleared.

9. The method according to claim 8, characterized in that, Also includes: The severity of the micro-discharge is assessed based on the amplitude of the reflection coefficient of the abnormal reflected pulse signal; the larger the amplitude of the reflection coefficient, the deeper the air gap conduction or the stronger the discharge energy.

10. A test system for micro-discharge failure of a conductive slip ring under extreme alternating gas pressure, characterized in that, For implementing the method as described in any one of claims 1 to 9, the testing system comprises: The air pressure simulation module is used to evacuate the vacuum chamber containing the conductive slip ring to be tested according to a preset air pressure-time curve. The voltage stress application module is used to simultaneously apply a combined voltage stress of the base working voltage and transient pulse overvoltage to the test channel of the conductive slip ring under test during the evacuation process. The micro-discharge excitation monitoring module is used to monitor the high-frequency current signal of the test channel in real time and generate a micro-discharge trigger signal when a sudden change in ultra-high frequency micro current is detected. The waveform capture module is used to capture the time-domain reflection waveform signal in the test channel based on the pre-trigger acquisition mechanism in response to the micro-discharge trigger signal. The discharge location calculation module is used to calculate the spatial location of the micro-discharge based on the time difference between the incident pulse feature point and the reflected pulse feature point in the time-domain reflected waveform signal.

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