Integrated detection system and method for insulation defects of valve side sleeve

Abstract

The invention relates to an integrated detection system and method for insulation defects of a valve side sleeve, and belongs to the technical field of insulation detection. A test platform under a controllable environment condition is constructed through integrated alternating current and direct current superposition voltage generation, partial discharge measurement, a shielding cabin body and a temperature and air pressure control structure; on the basis, alternating current and direct current 1: 1 superposed voltage is selected as a preferable detection working condition, and typical defects are quantitatively distinguished by utilizing a relative decreasing amplitude index of partial discharge initial voltage, so that engineering diagnosis of the insulation defects of the valve side bushing is realized. According to the method, the controllability of a test environment and the stability of partial discharge measurement are ensured, so that the detection system and method based on the 1: 1 superposition working condition and the K criterion have relatively high defect identification sensitivity, and also have relatively good engineering implementation and repeatability; and beneficial technical support can be provided for insulation state evaluation and operation maintenance of the valve side sleeve in an extra-high voltage direct current transmission project.

Description

Technical Field

[0001] This invention belongs to the field of insulation testing technology, and relates to an integrated detection system and method for insulation defects in valve-side bushings. Background Technology

[0002] In ultra-high voltage direct current (UHVDC) transmission projects, the valve-side bushing of the converter transformer, as a key insulating component connecting the converter transformer to the valve hall and valve tower, endures long-term combined electrical stresses from power frequency AC voltage, smoothed DC voltage, and harmonics and voltage fluctuations during operation. Defects in the internal or interface insulation of the valve-side bushing can trigger partial discharge or even insulation breakdown, directly threatening the safe and stable operation of the UHVDC transmission project. Therefore, establishing an effective insulation condition detection method for valve-side bushings is of significant engineering importance.

[0003] In current engineering practice, the insulation condition of valve-side bushings is mainly assessed through factory tests and periodic tests. Typical methods include power frequency AC withstand voltage and partial discharge tests, DC withstand voltage tests, and dielectric loss and capacitance tests. For partial discharge detection, existing research has proposed conducting valve-side bushing tests under various AC / DC composite voltage conditions to extract multiple characteristic parameters such as initial partial discharge voltage, average discharge quantity, discharge repetition rate, and phase distribution spectrum. These parameters are then analyzed in conjunction with routine test parameters such as power frequency dielectric loss and capacitance. A feature library is established using time-frequency feature clustering or pattern recognition methods to assess defect types and insulation conditions. While these methods are comprehensive in terms of feature dimensions, they rely on multiple test conditions and a large number of features, resulting in complex data processing and difficulty in obtaining timely and intuitive judgments. This makes it unsuitable for quickly determining the type of internal defects in bushings under engineering field conditions.

[0004] On the other hand, some studies focus on evaluating the operating performance of valve-side bushings under real or simulated electrical conditions. For example, by using an AC / DC superimposed voltage generation circuit and a high-voltage, high-current closed circuit, a superimposed AC / DC high voltage and AC high current are applied to the bushing of the converter transformer under test. Electrical quantities such as partial discharge pulses and leakage currents are measured to evaluate the bushing's operating condition under complex electrical stress. These test systems often adopt an open or semi-open layout, mainly focusing on electrical indicators such as voltage, current, and partial discharge. They give less consideration to the control and monitoring of environmental conditions and internal temperature rise of the bushing during the test. Changes in test oil temperature, chamber pressure, and local bushing temperature are often not adequately managed. The influence of bushing temperature and surrounding medium conditions on the development process of partial discharge is difficult to quantify, affecting the comparability of test results.

[0005] Existing valve-side bushing insulation testing technologies suffer from several drawbacks. Firstly, the numerous characteristic parameters and complex processing procedures hinder rapid on-site assessment. Secondly, the often open testing environments lack effective control and monitoring of environmental factors such as temperature and air pressure, as well as internal bushing temperature rise, resulting in limited stability and comparability of criteria based on partial discharge characteristics. Therefore, it is necessary to propose an integrated valve-side bushing insulation defect detection system and method that features simple parameter extraction under AC / DC composite voltage, clear criteria, and can be implemented in a controlled environment. This would improve the effectiveness of typical defect identification and enhance its engineering applicability. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an integrated detection system and method for valve side bushing insulation defects. By integrating AC / DC superimposed voltage generation, partial discharge measurement, shielded chamber and temperature and pressure control structure, a test platform under controllable environmental conditions is constructed. On this basis, AC / DC 1:1 superimposed voltage is selected as the preferred detection condition, and typical defects are quantitatively distinguished by the relative decrease index of partial discharge initiation voltage, so as to realize the engineering diagnosis of valve side bushing insulation defects.

[0007] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides an integrated detection system for insulation defects of valve side bushings, including an AC / DC superimposed voltage generation unit, a metal shielded test chamber, and a control and data processing unit; the metal shielded test chamber is equipped with a test bushing and oil tank unit, a partial discharge measurement unit, a temperature control and monitoring unit, and an internal air pressure control unit; The AC / DC superimposed voltage generating unit is used to output AC voltage and DC voltage with adjustable amplitude, and to form AC / DC superimposed test voltage through superimposed circuit; The metal shielding test chamber is used to shield the test sleeve and its external connecting devices as a whole, forming a closed test space; The test sleeve and oil tank unit is used to install the test valve side sleeve and provide it with an oil-paper insulation environment; The partial discharge measurement unit is used to acquire the high-frequency current signal caused by partial discharge in the grounding circuit of the end screen, and to perform partial discharge quantity measurement and phase analysis. The temperature control and monitoring unit is used to control the temperature of the casing itself and the temperature of the oil inside the tank during the test. The cabin pressure control unit is used to regulate the gas pressure inside the sealed cabin; The control and data processing unit is used to control each module, process the received data, and detect defects.

[0008] Furthermore, the AC / DC superimposed voltage generating unit includes a first test transformer, a second test transformer, a first voltage divider, a second voltage divider, a third voltage divider, a high-voltage silicon stack rectifier module, a filter capacitor, and a DC blocking capacitor. The first test transformer is connected to the first voltage divider, which is sequentially connected to the high-voltage silicon stack rectifier module, the filter capacitor, and the second voltage divider, thereby outputting a controllable DC voltage. The second test transformer is connected to the third voltage divider, which is connected to the second voltage divider through the DC blocking capacitor, thereby outputting a controllable AC voltage.

[0009] Furthermore, the test bushing and oil tank unit includes an oil tank, an oil-immersed test specimen mounting flange, and a grounding structure; the oil-immersed test specimen mounting flange is located at the upper end of the oil tank and is used to install the test valve-side bushing on the oil tank, so that the lower part of the bushing is immersed in insulating oil; the grounding structure is used to ground the test valve-side bushing.

[0010] Furthermore, the partial discharge measurement unit includes a high-frequency current transformer, a coupling capacitor, a partial discharge detector, and a data acquisition and analysis device; The high-frequency current transformer is connected to the grounding structure through a partial discharge measurement cable to sense the high-frequency pulse current signal generated by partial discharge. The coupling capacitor provides a coupling path for high-frequency partial discharge signals while blocking power frequency voltage and DC components. The partial discharge detector is used to amplify, filter, and shape the raw signal output by the high-frequency current transformer, and to identify and mark partial discharge pulses in real time. The data acquisition and analysis device is used to digitally acquire, store, and statistically analyze the results output by the partial discharge detector, extract the starting voltage, K value, and other characteristics for defect determination and result archiving.

[0011] Furthermore, the temperature control and monitoring unit includes a circulating oil pump, a heater, a cooler, a heat exchanger, and multiple temperature sensors arranged at different heights along the axial direction of the casing and inside the oil tank; The circulating oil pump is used to circulate the insulating oil in the oil tank; the heater and cooler are used to heat or cool the insulating oil to control the oil temperature; the heat exchanger is used to exchange heat with the outside of the system to regulate the temperature inside the test chamber and control the temperature of the test sleeve.

[0012] Furthermore, the control and data processing unit is used to execute the boost procedure, adjust environmental parameters, acquire and extract partial discharge signals, calculate the initial voltage drop, and determine defects.

[0013] On the other hand, the present invention provides an integrated detection method for insulation defects in valve-side bushings, comprising the following steps: Step 1: Obtain the starting partial discharge voltage of the reference bushing: Select a valve-side bushing with the same structure as the bushing under test and good insulation as the reference bushing. Conduct an AC / DC superimposed partial discharge test under preset environmental conditions such as oil temperature and tank pressure. Apply an AC / DC superimposed voltage of 1:1, and synchronously increase the AC and DC components according to the preset voltage step size. Maintain each voltage level for a certain period of time, and use the partial discharge measurement unit to monitor the high-frequency partial discharge signal in the grounding circuit of the end screen. When a stable partial discharge that meets the preset repetition rate and duration conditions is detected, record the effective value of the AC component at this time as the starting partial discharge voltage U0 of the reference bushing under AC / DC superimposed conditions. Step Two: Measuring the Initial Partial Discharge Voltage of the Bushing Under Test: Under the same test system and environmental conditions as in Step One, install the bushing on the valve side under test in the oil tank and connect it to the AC / DC superposition test circuit; apply an AC / DC 1:1 superposition voltage, using the same stepped voltage increase method as the reference bushing, synchronously increasing the AC and DC components with the same voltage step size, maintaining each voltage level for a predetermined time, and monitoring the partial discharge signal through the partial discharge measurement unit; when the discharge pulse repetition rate is detected to be greater than or equal to the preset threshold and lasts for multiple AC cycles, this voltage level is identified as the partial discharge initiation voltage of the bushing under test under AC / DC 1:1 conditions, and the effective value U of the AC component at this time is recorded. d ; Step 3: Calculate the initial voltage drop index: Based on the initial voltage U0 of the reference bushing and the initial voltage U of the bushing under test... d Calculate the initial voltage drop index K of the bushing under test; Step 4: Determine the defect type: Statistical analysis of test data for normal casing and casings with different types of defects is performed to obtain the K value distribution range corresponding to different defect types; based on the distribution results, a threshold is set to determine the defect type.

[0014] Furthermore, in step three, K is the dimensionless relative decrease, calculated using the following formula:

[0015] When K is positive, it indicates that the partial discharge initiation voltage of the bushing under test is lower than that of the reference bushing under AC / DC 1:1 superposition conditions, and the insulation margin has decreased; the magnitude of K reflects the degree of decrease in initiation voltage.

[0016] Furthermore, in step four, a first threshold T1 and a second threshold T2 are set, satisfying T1>T2>0, and the following defect type determination rule is constructed: when At that time, it was determined that the tested bushing had a serious internal insulation defect, such as a core crack. when At that time, it was determined that the tested bushing had a localized field strength concentration defect of metal particles; when At that time, it is determined that the insulation condition of the bushing under test is basically normal or has only minor defects.

[0017] Furthermore, in step four, under AC / DC 1:1 superposition conditions, the partial discharge phase distribution spectrum of the bushing under test is further acquired, and the phase concentration interval, discharge quantity, and repetition rate of the discharge pulse are analyzed to assist in the determination of the defect type.

[0018] The beneficial effects of this invention are as follows: By applying a 1:1 superimposed voltage with essentially equal AC and DC component amplitudes to the valve-side bushing within an integrated shielding and environmental control test system, this invention systematically analyzes the partial discharge initiation voltage characteristics of normal bushings and typical defective bushings under this condition. It proposes a concise defect determination method based on the relative drop in initiation voltage K, and verifies the method's effective ability to distinguish between metal particle defects and core crack defects using a 72.5kV valve-side bushing test. Simultaneously, the coordination of the metal shielding test chamber, temperature control and monitoring unit, and chamber pressure control unit ensures the controllability of the test environment and the stability of partial discharge measurements. This makes the detection system and method based on the 1:1 superimposed condition and K criterion possess both high defect identification sensitivity and good engineering feasibility and repeatability, providing valuable technical support for the insulation status assessment and operation and maintenance of valve-side bushings in UHVDC transmission projects.

[0019] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a framework diagram of an integrated detection system for insulation defects in valve-side bushings. Figure 2 This is a schematic diagram of the AC / DC superposition voltage generation unit. Figure 3 This is a schematic diagram of the metal-shielded test chamber and other unit structures; Figure 4 Flowchart of integrated detection method for insulation defects in valve-side bushings; Figure 5 The AC voltage component of the partial discharge initiation voltage under different AC / DC ratios in each bushing; Figure 6(a) and (b) are PRPD diagrams of different bushings under a 35kV:35kV composite voltage. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0023] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0024] Example 1: This invention provides an integrated detection system for insulation defects in valve-side bushings. Under controllable temperature and pressure conditions, the system applies a 1:1 AC / DC composite voltage to the valve-side bushing of a converter transformer. By extracting the partial discharge initiation voltage drop index, it achieves quantitative identification of typical internal insulation defects. This system is applicable to the insulation fault diagnosis of valve-side bushings in UHV converter transformers and provides core technical support for improving the insulation reliability of valve-side bushings in UHV DC transmission projects.

[0025] An integrated AC / DC superimposed voltage generation, partial discharge measurement, shielded chamber, and temperature and pressure control structure are used to construct a test platform under controllable environmental conditions. Based on this, an AC / DC 1:1 superimposed voltage is selected as the preferred test condition. The relative drop of the partial discharge initiation voltage is used to quantitatively distinguish typical defects, thereby realizing the engineering diagnosis of valve side bushing insulation defects.

[0026] like Figure 1 As shown, the integrated detection system for valve-side bushing insulation defects includes: (1) AC / DC superposition voltage generation unit like Figure 2 As shown, this unit outputs adjustable AC and DC voltages and forms an AC / DC superimposed test voltage through a superposition circuit. The unit includes a first test transformer, a second test transformer, a first voltage divider, a second voltage divider, a third voltage divider, a high-voltage silicon rectifier module, a filter capacitor, and a DC blocking capacitor. The first test transformer is connected to the first voltage divider, which is sequentially connected to the high-voltage silicon rectifier module, the filter capacitor, and the second voltage divider, thus outputting a controllable DC voltage. The second test transformer is connected to the third voltage divider, which is connected to the second voltage divider through the DC blocking capacitor, thus outputting a controllable AC voltage. This unit can superimpose an adjustable DC bias onto the power frequency AC voltage and simultaneously increase the AC and DC voltage components according to a set ratio.

[0027] (2) Test sleeve and oil tank unit like Figure 3 As shown, this unit is used to install the bushing on the side of the valve under test and to provide it with an oil-paper insulation environment similar to that in actual operation. The unit includes an oil tank, an oil-immersed test specimen mounting flange, and a grounding structure, ensuring that the electric field distribution on the bushing of the valve under test in the oil is reasonable and the external insulation conditions are controllable during the test.

[0028] (3) Partial discharge measurement unit This unit is used to acquire high-frequency current signals caused by partial discharge in the grounding loop of the final screen, and to perform partial discharge quantity measurement and phase analysis. It includes a high-frequency current transformer, coupling capacitors, a partial discharge detector, and a data acquisition and analysis device.

[0029] The high-frequency current transformer is connected to the grounding structure through a partial discharge measurement cable to sense the high-frequency pulse current signal generated by the partial discharge. Coupling capacitors provide a coupling path for high-frequency partial discharge signals while blocking power frequency voltage and DC components; Partial discharge detectors are used to amplify, filter, and shape the raw signal output from high-frequency current transformers, and to identify and mark partial discharge pulses in real time. The data acquisition and analysis device is used to digitally acquire, store, and statistically analyze the results output by the partial discharge detector, extract the starting voltage, K value, and other characteristics for defect judgment and result archiving.

[0030] The bandwidth of the high-frequency current transformer is preferably covered to 16kHz to 30MHz, and the sampling rate of the partial discharge detector is preferably not less than 100MS / s to ensure effective capture of high-frequency partial discharge pulses.

[0031] (4) Metal shielding test chamber This device is used to provide overall shielding for the tested bushing and its external connections, forming a closed test space and reducing the impact of external electromagnetic interference on partial discharge measurements. The test chamber is made of conductive material, and the shell is connected to the ground grid through a reliable grounding point. The chamber is equipped with insulated through-wall bushings and shielded connectors for high-voltage and measurement cable outgoings. Observation windows or monitoring interfaces are reserved inside the chamber for installing sensors and observing the operating status of the test sample.

[0032] (5) Temperature control and monitoring unit This unit is used to control the temperature of the bushing itself and the oil temperature inside the tank during the test, preventing excessive temperature rise of the bushing during the experiment from affecting the partial discharge characteristics. It includes a circulating oil pump, heater, cooler, heat exchanger, and multiple temperature sensors arranged at different axial heights of the bushing and inside the tank. The circulating oil pump circulates the insulating oil within the tank; the heater and cooler heat or cool the insulating oil to control its temperature; the heat exchanger exchanges heat with the external environment to regulate the temperature inside the test chamber and control the temperature of the test bushing. The control system adjusts the oil flow rate and heating / cooling power based on multi-point temperature measurements to ensure that the temperature difference during the test does not exceed a set threshold.

[0033] (6) In-cabin air pressure control unit Connected to a metal-shielded test chamber, this unit is used to regulate the gas pressure within the sealed chamber. It includes a gas source, pressure regulating valve, pressure sensor, and control device. By introducing or releasing gas into the chamber, the internal gas pressure can be regulated and stabilized within a certain range to reduce the impact of pressure fluctuations on partial discharge behavior.

[0034] (7) Control and data processing unit This unit coordinates the operation of the AC / DC superposition voltage generation unit, temperature control and monitoring unit, cabin pressure control unit, and partial discharge measurement unit, performing functions such as voltage boosting, environmental parameter adjustment, partial discharge signal acquisition and feature extraction, initial voltage drop calculation, and defect determination. This unit can utilize an industrial control computer or a programmable logic controller (PLC), and is equipped with a human-machine interface for setting test parameters and displaying test results.

[0035] Through the coordinated operation of the above-mentioned units, the integrated detection system of the present invention can conduct partial discharge tests on valve-side bushings under good electromagnetic shielding and controllable temperature, humidity and air pressure environments, and provide a stable and reliable partial discharge measurement data basis for subsequent defect identification.

[0036] Example 2: like Figure 4 As shown, the present invention also provides a method for detecting insulation defects in valve-side bushings based on the above-mentioned integrated detection system, which is applied to the insulation condition assessment of valve-side bushings in converter transformers, and includes the following steps: Step 1: Obtaining the initial partial discharge voltage of the reference bushing In the integrated testing system, a valve-side bushing with the same structure and good insulation as the bushing under test is selected as the reference bushing. An AC / DC superimposed partial discharge test is conducted under preset environmental conditions, including oil temperature and chamber pressure. A 1:1 AC / DC superimposed voltage is applied, and the AC and DC components are increased synchronously according to preset voltage steps. Each voltage level is maintained for a certain time, and the high-frequency partial discharge signal in the grounding circuit of the final screen is monitored using the partial discharge measurement unit. When a stable partial discharge meeting the preset repetition rate and duration conditions is detected, the effective value of the AC component at this time is recorded as the partial discharge initiation voltage U0 of the reference bushing under AC / DC superimposed conditions.

[0037] After conducting preliminary tests on different AC / DC superposition ratios, this invention selects a 1:1 superposition condition where the effective value of the AC component and the amplitude of the DC component are basically equal as the detection condition. Under this condition, the initial partial discharge voltage has a more obvious ability to distinguish different typical defects.

[0038] Step 2: Measurement of the initial partial discharge voltage of the bushing under test Under the same test system and environmental conditions as in step one, the bushing of the valve under test is installed in the oil tank and connected to the AC / DC superposition test circuit. A 1:1 AC / DC superposition voltage is applied, using the same stepped voltage increase method as the reference bushing, synchronously increasing the AC and DC components with the same voltage step size. Each voltage level is maintained for a predetermined time, and the partial discharge signal is monitored by the partial discharge measurement unit. When the discharge pulse repetition rate is detected to be greater than or equal to a preset threshold and lasts for multiple AC cycles, this voltage level is considered the partial discharge initiation voltage of the bushing under test under the 1:1 AC / DC condition, and the effective value U of the AC component at this time is recorded. d .

[0039] Step 3: Calculation of the initial voltage drop index Based on the starting voltage U0 of the reference bushing and the starting voltage U of the bushing under test d Calculate the initial voltage drop index K of the bushing under test. K is a dimensionless relative drop, which can be calculated in this embodiment using the following formula:

[0040] When K is positive, it indicates that the partial discharge initiation voltage of the bushing under test is lower than that of the reference bushing under AC / DC 1:1 superposition conditions, and the insulation margin has decreased; the magnitude of K reflects the degree of decrease in initiation voltage.

[0041] Step 4: Determining the type of defect Statistical analysis of test data from normal casings and casings with different types of defects was conducted to obtain the distribution range of K values ​​corresponding to different defect types. Based on this distribution, a first threshold T1 and a second threshold T2 (satisfying T1>T2>0) were set, and the following defect type determination rule was constructed: when At that time, it was determined that the tested bushing had a serious internal insulation defect, such as a core crack. when At that time, it was determined that the tested bushing had a localized field strength concentration defect of metal particles; when At that time, it is determined that the insulation condition of the bushing under test is basically normal or has only minor defects.

[0042] When necessary, under AC / DC 1:1 superposition conditions, the partial discharge phase distribution spectrum of the tested bushing can be further acquired to assist in the analysis of the phase concentration range of the discharge pulse, the discharge quantity, and the repetition rate, which can be used to corroborate the defect type determination results.

[0043] Example 3: This embodiment uses a converter transformer valve-side bushing with a nominal voltage level of 72.5kV as the test object. In the integrated test system of this invention, AC / DC 1:1 superimposed partial discharge tests are performed on normal bushings, bushings with metal particle defects, and bushings with core crack defects to verify the applicability of the method and the effectiveness of the criteria of this invention.

[0044] The 72.5kV valve-side bushing under test is installed at the upper flange of the oil tank, with the lower part of the bushing immersed in insulating oil. The oil tank and the upper part of the bushing are housed inside a metal-shielded test chamber. The high-voltage lead is led out through an insulated through-wall bushing on the top of the chamber, and the partial discharge measurement cable is led out of the chamber through a shielded connector and connected to the partial discharge detector. The temperature control and monitoring unit ensures a constant oil temperature. Multi-point temperature sensors display that the temperature change inside the bushing is less than 5°C throughout the experiment; otherwise, the test is automatically terminated. The chamber pressure control unit regulates the chamber pressure to a predetermined value and maintains it stable to reduce the impact of pressure fluctuations on partial discharge behavior. The partial discharge measurement unit connects a high-frequency current transformer in series in the bushing's end-screen grounding circuit, and the output signal is sent to the partial discharge detector. The partial discharge detector amplifies, filters, and synchronously samples the signal, measuring the charge value characterizing the partial discharge and generating a partial discharge phase distribution spectrum.

[0045] In the above system, the normal bushing is used as the reference bushing, and a 1:1 AC / DC stepped voltage increase test is performed according to step one of the testing method. After the oil temperature and tank pressure stabilize, the amplitudes of the AC and DC components are kept approximately equal, and the AC and DC voltages are synchronously increased in 1kV steps starting from zero voltage, with each voltage level held for approximately 5 minutes. At each voltage level, the partial discharge measurement unit continuously monitors the partial discharge signal in the grounding circuit of the final screen. When a discharge pulse repetition rate greater than or equal to 5 times / second is detected and discharge occurs in three consecutive AC cycles, that voltage level is considered the partial discharge initiation voltage. Figure 5 As shown, in this embodiment, the partial discharge initiation voltage (AC component) of the reference bushing under AC / DC 1:1 superposition conditions is approximately 29.8kV, denoted as U0.

[0046] Under the same system and environmental conditions, a 72.5kV valve-side bushing simulating metal particle defects inside the core was installed in the system, and the AC / DC 1:1 step-up voltage program was repeatedly executed. The partial discharge initiation voltage was measured to be approximately 25.4kV, denoted as U. d1 Calculated according to the formula:

[0047] A 72.5kV valve-side bushing simulating an internal core crack defect was then installed in the system. Under the same conditions, the partial discharge initiation voltage was measured to be approximately 14.2kV, denoted as U. d2 The corresponding reduction indicator is:

[0048] As can be seen, when the AC / DC voltage ratio is 1:1, there are significant differences in the partial discharge initiation voltage of the three bushings: approximately 29.8 kV for the normal bushing, approximately 25.4 kV for the bushing with metal particle defects in the core, and approximately 14.2 kV for the bushing with core crack defects. The corresponding K values ​​are approximately 0, 0.15, and 0.52, respectively, showing a relatively stable gradient difference among the normal bushing, the bushing with metal particle defects, and the bushing with core crack defects.

[0049] like Figure 6 As shown in (a) and (b), further partial discharge phase distribution measurements were performed under a combined AC / DC voltage of 35kV. The discharge pulse signals of normal bushings were mainly distributed in the 320°–360° phase range, while the discharge pulse signals of bushings with metal particle defects in the core were mainly distributed in the 30°–80° phase range, providing auxiliary evidence for the K criterion in terms of phase characteristics. Based on the comprehensive experimental results, the second threshold T2 can be selected to be approximately 0.1, and the first threshold T1 can be approximately 0.4. For any 72.5kV valve-side bushing under test, the starting voltage U was measured under AC / DC 1:1 conditions. dAfter calculating the K value, a value of K < 0.1 is considered basically normal, a value of 0.1 ≤ K < 0.4 is considered to indicate the presence of metal particle defects, and a value of K ≥ 0.4 is considered to indicate the presence of core crack defects. In actual tests, the above criteria were used to inspect multiple 72.5kV valve-side bushings. The results were basically consistent with the disassembly inspection or existing defect information, indicating that the method of the present invention has good accuracy and engineering feasibility.

[0050] Example 4: An electronic device, comprising a memory and a processor; The memory is used to store computer programs; The processor is configured to implement the method described in Embodiment 1 when executing the computer program.

[0051] Example 5: A computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0052] Example 6: A computer program product includes a computer program that, when executed by a processor, implements the method described in Example 1.

[0053] In the above embodiments, the reference to "this embodiment" in the specification indicates that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least some embodiments, but not necessarily all embodiments. Multiple appearances of "this embodiment" do not necessarily refer to the same embodiment.

[0054] In the above embodiments, although the invention has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory structures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed. The embodiments of the invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims.

[0055] As will be understood by those skilled in the art, the computer-readable storage medium described in this embodiment allows for the implementation of all or part of the steps in the above method embodiments by computer program-related hardware. The aforementioned computer program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0056] The electronic terminal provided in this embodiment includes a processor, a memory, a transceiver, and a communication interface. The memory and the communication interface are connected to the processor and the transceiver and complete communication between them. The memory is used to store computer programs, the communication interface is used to perform communication, and the processor and the transceiver are used to run the computer programs, so that the electronic terminal performs the steps of the above method.

[0057] In this embodiment, the memory may include random access memory (RAM) and may also include non-volatile memory, such as at least one disk storage device.

[0058] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0059] This invention can be used in a wide range of general-purpose or special-purpose computing system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices, etc.

[0060] This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A valve side bushing insulation defect integrated detection system, characterized in that: The device comprises an AC-DC superimposed voltage generating unit, a metal shielding test cabin and a control and data processing unit; the metal shielding test cabin is internally provided with a test bushing and oil tank unit, a partial discharge measurement unit, a temperature control and monitoring unit and a cabin internal air pressure control unit; The AC-DC superimposed voltage generating unit is used for outputting an AC voltage and a DC voltage with adjustable amplitude, and forming an AC-DC superimposed test voltage through a superimposed circuit; The metal shielding test cabin is used for shielding the test bushing and its external connecting device as a whole to form a closed test space; The test bushing and oil tank unit is used for installing the valve side bushing to be measured and providing an oil paper insulation environment for the valve side bushing to be measured; The partial discharge measurement unit is used for collecting high-frequency current signals caused by partial discharge in a ground loop of a terminal screen and performing partial discharge measurement and phase analysis; The temperature control and monitoring unit is used for controlling the temperature of the bushing itself and the temperature of the oil in the oil tank during the test; The cabin internal air pressure control unit is used for adjusting the air pressure in the closed cabin body; The control and data processing unit is used for controlling each module and processing the received data to detect defects.

2. The valve-side bushing insulation defect integrated detection system of claim 1, wherein: The AC-DC superimposed voltage generating unit comprises a first test transformer, a second test transformer, a first voltage divider, a second voltage divider, a third voltage divider, a high-voltage silicon stack rectifier module, a filter capacitor and a DC blocking capacitor; the first test transformer is connected with the first voltage divider; the first voltage divider is connected with the high-voltage silicon stack rectifier module, the filter capacitor and the second voltage divider in sequence to output a controllable DC voltage; the second test transformer is connected with the third voltage divider; the third voltage divider is connected with the second voltage divider through the DC blocking capacitor to output a controllable AC voltage.

3. The valve side can insulation defect integrated detection system of claim 1, wherein: The test bushing and oil tank unit comprises an oil tank, an oil-immersed test product mounting flange and a grounding structure; the oil-immersed test product mounting flange is arranged on the upper end of the oil tank and used for mounting the valve side bushing to be measured on the oil tank so that the lower part of the bushing is immersed in insulating oil; the grounding structure is used for grounding the valve side bushing to be measured.

4. The valve side can insulation defect integrated detection system of claim 1, wherein: The partial discharge measurement unit comprises a high-frequency current transformer, a coupling capacitor, a partial discharge detector and a data acquisition and analysis device; The high-frequency current transformer is connected with the grounding structure through a partial discharge measurement cable to induct high-frequency pulse current signals generated by partial discharge; The coupling capacitor provides a coupling channel for high-frequency partial discharge signals and blocks power frequency voltage and DC components at the same time; The partial discharge detector is used for amplifying, filtering and shaping original signals output by the high-frequency current transformer, identifying and marking partial discharge pulses in real time; The data acquisition and analysis device is used for digitizing, storing and statistically analyzing the results output by the partial discharge detector, extracting starting voltage, K value and other characteristics for defect judgment and result archiving.

5. The valve side can insulation defect integrated detection system of claim 1, wherein: The temperature control and monitoring unit comprises a circulating oil pump, a heater, a cooler, a heat exchanger and multiple temperature sensors arranged at different axial heights of the bushing and in the oil tank; The circulating oil pump is used to realize the circulation of the insulating oil in the oil tank; the heater and the cooler are used to heat or cool the insulating oil, so as to realize the control of the oil temperature; and the heat exchanger is used to realize the heat exchange with the outside of the system, so as to realize the temperature adjustment of the test cabin and the temperature control of the test sleeve.

6. The valve-side bushing insulation defect integration detection system of claim 1, wherein: The control and data processing unit is used to perform the voltage boosting program, the environmental parameter adjustment, the partial discharge signal acquisition and feature extraction, the initial voltage drop calculation and the defect judgment.

7. A method of integrated detection of valve side bushing insulation defects, characterized by: The method comprises the following steps: Step one: obtaining the initial partial discharge voltage of the reference sleeve: selecting a valve-side sleeve with the same structure as the measured sleeve and good insulation state as the reference sleeve, and performing the AC-DC superimposed partial discharge test under the preset environmental conditions such as oil temperature and cabin pressure; applying the AC-DC 1:1 superimposed voltage, synchronously increasing the AC and DC components according to the preset voltage step, keeping for a certain time at each voltage level, and monitoring the high-frequency partial discharge signal in the ground loop of the back screen by using the partial discharge measuring unit; when the stable partial discharge meeting the preset repetition rate and duration conditions is detected, the effective value of the AC component at this time is recorded as the initial partial discharge voltage U0 of the reference sleeve under the AC-DC superimposed condition; Step two: measure the starting partial discharge voltage of the measured bushing: under the same test system and environmental conditions as step one, install the measured valve side bushing in the oil tank and connect it to the AC-DC superimposed test circuit; apply AC-DC 1:1 superimposed voltage, use the same step-by-step voltage increasing method as the reference bushing, synchronously increase the AC component and DC component with the same voltage step, keep at each voltage level for a predetermined time, monitor the partial discharge signal through the partial discharge measurement unit; when the discharge pulse repetition rate is greater than or equal to the preset threshold and lasts for multiple AC cycles, it is determined that this voltage level is the starting partial discharge voltage of the measured bushing under AC-DC 1:1 condition, and the effective value U d of the AC component at this time is recorded. Step three: Calculate the starting voltage drop amplitude index: according to the starting voltage U0 of the reference bushing and the starting voltage U of the measured bushing, calculate the starting voltage drop amplitude index K of the measured bushing d ; Step four: judging the defect type: by statistically analyzing the test data of the normal sleeve and the different types of defect sleeves, the distribution interval of the K value corresponding to different defect types is obtained; according to the distribution result, the threshold value is set, and the defect type is judged.

8. The valve-side sleeve insulation defect integrated detection method of claim 7, wherein: In step three, K is the dimensionless relative drop amount, which is calculated according to the following formula: When K is positive, it indicates that the initial partial discharge voltage of the measured sleeve under the AC-DC 1:1 superimposed condition is lower than that of the reference sleeve, and the insulation margin decreases; the size of K reflects the degree of initial voltage drop.

9. The valve-side sleeve insulation defect integrated detection method of claim 7, wherein: In step four, the first threshold T1 and the second threshold T2 are set, which satisfy T1>T2>0, and the following defect type judgment rule is constructed: When a core crack type serious internal insulation defect exists in the measured casing; When a metal particle type local field intensity concentration defect exists in the measured casing; When the insulation condition of the measured casing is basically normal or only has slight defects.

10. The valve-side sleeve insulation defect integrated detection method of claim 7, wherein: In step four, under the AC-DC 1:1 superimposed condition, the partial discharge phase distribution atlas of the measured sleeve is further collected, and the phase concentration interval, discharge amount and repetition rate of the discharge pulse are analyzed, which are used to prove the defect type judgment result.

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