Breakdown fault analysis and switch screening method of bypass switch for low-frequency power transmission

Abstract

The invention relates to a low-frequency power transmission bypass switch breakdown fault analysis and switch screening method, which comprises the steps of appearance inspection, withstand voltage detection between an auxiliary loop and a main loop, X-ray test, vacuum degree test of a vacuum arc extinguish chamber, disassembly of the vacuum arc extinguish chamber and vacuum arc extinguish chamber contact roughness test in sequence. An analysis conclusion is obtained according to the detection result, whether breakdown of the vacuum arc-extinguishing chamber in the bypass switch occurs or not is determined, and the breakdown reason is that the mechanical structure of the bypass switch is unstable or the problem of the vacuum arc-extinguishing chamber exists or the two reasons exist; and by utilizing the characteristics of small direct current leakage current and sensitivity, the bypass switch with the breakdown risk is visually and quantitatively eliminated so as to deal with the risk of breakdown of the bypass switch in an engineering field.

Description

Technical Field

[0001] The present invention relates to the technical field of low-frequency power transmission, and in particular to a bypass switch breakdown fault analysis and switch screening method for low-frequency power transmission. Background Art

[0002] The bypass switch is a mechanical switch device connected across the terminals of a power unit, which transfers the current to the bypass switch when the power unit is out of operation. The bypass switch is a very critical component in the low-frequency power transmission system. Through its protection action, it ensures that the system will not trip in the event of a power unit failure of the converter valve.

[0003] Figure 1 The figure shows the topology of the half-bridge power module. Under normal operating conditions, the main contact of the bypass switch S1 is disconnected and bears the voltage of the power module port. At this time, the primary requirement for the bypass switch is not to have faults such as malfunction and breakdown that interfere with normal operation. However, in many engineering applications, the bypass switch has breakdown. In the field of low-frequency power transmission technology, both ends of the bypass switch need to withstand square waves. There is little research on the ability of the core component of the vacuum interrupter in the bypass switch to withstand square waves, and there is no relevant theoretical support. Since the breakdown fault occurs instantaneously and destructively, after a suspected bypass switch breakdown fault occurs in an engineering application, the vacuum interrupter is directly disassembled destructively to further confirm it. However, the disassembly process will destroy the evidence for finding the cause of the breakdown. This results in that even if it is determined that the vacuum interrupter is broken down, it is impossible to determine whether the breakdown is caused by the vacuum interrupter itself or the mechanical assembly problem, or the combination of the two.

[0004] In addition, since the actual working withstand voltage of the bypass switch is a square wave, the traditional AC withstand voltage cannot detect the reliability of the bypass switch when it withstands square waves. Since the leakage current base value of a normal bypass switch tested under AC voltage and square wave voltage is large, the bypass switch with a breakdown risk cannot be reflected by the leakage current with a large base value. A more sensitive parameter is needed to intuitively and quantitatively eliminate bypass switches with a breakdown risk. Summary of the invention

[0005] The present invention provides a bypass switch breakdown fault analysis and switch screening method for low-frequency power transmission, which can quickly determine whether a bypass switch breakdown occurs, and quickly and accurately determine the cause of the bypass switch breakdown. At the same time, bypass switches with a breakdown risk are screened out in advance through DC leakage current, thereby reducing the occurrence of bypass switch breakdown faults.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for analyzing breakdown failure of a bypass switch for low-frequency power transmission comprises the following steps:

[0008] 1) Appearance inspection: Check the appearance of the bypass switch for low-frequency power transmission. If there are traces of discharge, it is determined that the external insulation design of the bypass switch is unqualified;

[0009] 2) Withstand voltage test between auxiliary circuit and main circuit: measure the withstand voltage between the main circuit and auxiliary switch, coil, magnet and shell. If the withstand voltage fails, it is determined that there is a problem in the withstand voltage design between the bypass switch auxiliary components and the main circuit;

[0010] 3) Using X-ray testing: Use X-ray testing to test the opening distance of the moving and static contacts of the bypass switch for low-frequency power transmission. If the test shows that the mechanical structure of the moving and static contacts is unstable, it is determined that the breakdown will be caused by the unstable mechanical structure;

[0011] 4) Test the vacuum degree of the vacuum interrupter: When the vacuum degree of the vacuum interrupter is greater than 1.33×10^-3Pa, it is determined that the vacuum interrupter itself causes breakdown;

[0012] 5) Disassemble the vacuum interrupter: Open the vacuum interrupter to check the contact status of the vacuum interrupter. If there are traces of ablation on the contacts of the vacuum interrupter, the bypass switch has a vacuum interrupter breakdown fault;

[0013] 6) Test the roughness of the vacuum interrupter contact: If the roughness of the vacuum interrupter contact is less than 1μm, it is determined that the vacuum interrupter itself causes the breakdown.

[0014] Furthermore, the discharge marks include black or arc burns.

[0015] Furthermore, the X-ray test projects the two surfaces of the bypass switch at 90° angles to each other.

[0016] Furthermore, the X-ray test evenly selects 4 to 6 points on the obtained X-ray projection image to measure the distance between the moving and static contacts;

[0017] When any projection image shows that the deviation between the opening distance and the design value is greater than 10%, and the deviation between the measured data of 4 to 6 points and their average value is greater than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value and the skew between the contacts;

[0018] When any projection image shows that the deviation between the opening distance and the design value is greater than 10%, and the deviation between the measured data of 4 to 6 points and their average value is less than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value;

[0019] When the deviation between the open distance and the design value in any projected image is less than 10%, and the deviation between the measured data of 4 to 6 points and their average value is greater than 10%, it means that the mechanical structure is unstable, resulting in skew between the contacts;

[0020] When the X-ray projection test images of the two surfaces have an opening distance deviation from the design value of less than 10%, and the measurement data of 4 to 6 points deviate from their average value by less than 10%, it means that the mechanical structure is stable, the contact opening distance is normal and there is no skew.

[0021] A method for screening bypass switches for low-frequency power transmission adopts a DC voltage of 4.5 to 5 times the rated AC voltage to test the DC leakage current of the bypass switches for low-frequency power transmission, and screens out the bypass switches for low-frequency power transmission with a DC leakage current greater than 0.1 mA.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) For bypass switches suspected of breakdown failure, a step-by-step analysis method is adopted to obtain various information first, rather than directly destroying the fault site to determine whether a vacuum interrupter breakdown failure has occurred. This retains the key evidence for fault analysis, so that it can be accurately determined whether the breakdown of the vacuum interrupter is caused by its own reasons or the instability of the mechanical structure of the bypass switch, or the combination of the two reasons.

[0024] 2) By performing an X-ray projection test on two surfaces of the bypass switch at 90° to each other and evenly selecting 4 to 6 points for the open distance test, it can be effectively determined whether the breakdown is caused by the instability of the mechanical mechanism;

[0025] 3) Through the vacuum degree test of the vacuum interrupter and the contact roughness test, it can be quickly and accurately determined whether the breakdown is caused by the problem of the vacuum interrupter itself;

[0026] 4) This method comprehensively and completely realizes the problem analysis of bypass switch breakdown failure for low-frequency power transmission;

[0027] 5) The detection method of measuring the sensitive parameter DC leakage current to eliminate bypass switches with breakdown risk is simple and efficient, and uses quantitative data to reduce the risk of breakdown failure of bypass switches on the project site. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the circuit structure of a traditional half-bridge power module where the bypass switch is located.

[0029] Figure 2 The present invention is a flowchart of the method for analyzing breakdown failure of a bypass switch for low-frequency power transmission.

[0030] Figure 3 It is a schematic diagram of the opening distance when the X-ray projection image of the present invention proves that the mechanical structure is stable.

[0031] Figure 4 It is a schematic diagram of the opening distance when the X-ray projection image of the present invention proves that the mechanical structure is unstable.

[0032] Figure 5 It is a schematic diagram of the DC leakage current screening curve of the present invention. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0034] See Figure 2 , is a flow chart of the method for analyzing the breakdown fault of a bypass switch for low-frequency power transmission of the present invention. The method for analyzing the breakdown fault of a bypass switch for low-frequency power transmission of the present invention comprises the following steps:

[0035] 1) Appearance inspection: Check whether there are any discharge marks on the appearance of the low-frequency power transmission bypass switch suspected of breakdown fault. By inspecting the appearance of the bypass switch shell, it can be effectively judged whether the bypass switch suspected of breakdown fault has external insulation problems. When there are black marks or arc burns on the bypass switch shell, it is determined that the bypass switch has external insulation design problems. When there are no such marks, it is determined that the bypass switch does not have external insulation design problems. Regardless of whether there are external insulation design problems or not, the next step of analysis is carried out.

[0036] 2) Withstand voltage test between the auxiliary circuit and the main circuit: In order to further eliminate other interference factors that may cause breakdown, the withstand voltage between each auxiliary component and the main circuit is tested, and the withstand voltage between the auxiliary switch, coil, magnet, shell and the main circuit is measured respectively. If the withstand voltage test is passed, it means that the auxiliary components and the main circuit inside the bypass switch are sufficiently resistant and there is no breakdown between the auxiliary components and the main circuit; if the withstand voltage test is not passed, it means that there is a problem with the withstand voltage design between the auxiliary components of the bypass switch and the main circuit. Regardless of whether there is a breakdown problem between the auxiliary circuit and the main circuit, the next step of analysis is carried out to obtain more comprehensive information.

[0037] 3) Using X-ray test: At this time, it is uncertain whether the vacuum interrupter inside the bypass switch has been broken down. However, in order to obtain relevant information without destroying the fault site so as to determine the cause of the breakdown fault later, an X-ray projection test is performed on two surfaces of the bypass switch that are 90° to each other, and the state inside the vacuum interrupter is observed by X-ray.

[0038] During the test, the bypass switch needs to be tested by X-ray projection on two sides at 90° to each other. Figure 3 , which is a schematic diagram of the normal opening distance of the X-ray projection image. For the obtained X-ray projection image, 5 points are evenly selected to measure the opening distance between the moving and static contacts.

[0039] (1) When any projection image shows that the deviation between the opening distance and the design value is greater than 10%, and the deviation between the five-point measurement data and its average value is greater than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value and the presence of skew between the contacts;

[0040] (2) When the deviation between the opening distance and the design value of any projection image is greater than 10%, and the deviation between the five-point measurement data and their average value is less than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value;

[0041] (3) When the deviation between the open distance and the design value of any projection image is less than 10%, and the deviation between the measured data of the five points and their average value is greater than 10%, it means that the mechanical structure is unstable, resulting in skew between the contacts;

[0042] (4) When the X-ray projection test images of the two surfaces show that the deviation between the opening distance and the design value is less than 10%, and the deviation between the measured data of the five points and their average value is less than 10%, it means that the mechanical structure is stable, the contact opening distance is normal and there is no skew;

[0043] When any of (1), (2), and (3) occurs, it indicates that the bypass switch mechanical structure is not designed properly, resulting in unstable contact opening distance, which can point to the bypass switch mechanical structure being unstable and causing breakdown. When (4) occurs, it indicates that the bypass switch mechanical structure can support the dynamic and static contact opening distance to be stable and not deviate, and it can be further suspected that the vacuum interrupter itself causes the bypass switch breakdown. Figure 4 This is a schematic diagram of abnormal opening distance in X-ray projection. No matter whether the mechanical structure of the bypass switch is stable or unstable, proceed to the next step.

[0044] 4) Test the vacuum degree of the vacuum interrupter: When the vacuum degree is greater than 1.33×10^-3Pa, the vacuum degree of the vacuum interrupter is sufficient, and there is a risk of causing the vacuum interrupter to break down. Regardless of the measured vacuum degree, proceed to the next step.

[0045] 5) Disassemble the vacuum interrupter: Check the contact status of the vacuum interrupter. If there are symmetrical ablation marks on the static and dynamic ends or ablation marks on the static and dynamic end shielding covers, it means that the vacuum interrupter has been broken down. If not, it means that the vacuum interrupter has not been broken down.

[0046] 6) Test the roughness of the vacuum interrupter contact: If the roughness of the vacuum interrupter contact is less than 1μm, it is determined that the vacuum interrupter itself causes the breakdown.

[0047] During the overall analysis process, insulation problems of the bypass switch main circuit and other components and the outside were eliminated through appearance inspection and voltage resistance test between the auxiliary circuit and the main circuit. The vacuum interrupter was disassembled to confirm whether the vacuum interrupter had been broken down. Then, based on the X-ray test results obtained before disassembly, the vacuum test results obtained before disassembly, and the contact roughness test results obtained after disassembly, it was concluded that the breakdown was caused by the unstable mechanical structure of the bypass switch, the vacuum interrupter itself, or both.

[0048] A method for screening bypass switches for low-frequency power transmission does not use leakage current under AC voltage and square wave voltage, but uses DC leakage current as a sensitive parameter. By applying DC voltage to test its leakage current, it is determined whether the bypass switch has a breakdown risk. The applied DC voltage is 4.7 times the rated AC voltage. When the DC leakage current is greater than 0.1mA, breakdown is likely to occur in the square wave application field of low-frequency power transmission. When the DC leakage current is less than 0.1mA, breakdown is not likely to occur in the square wave application field of low-frequency power transmission. Therefore, bypass switches for low-frequency power transmission with DC leakage current greater than 0.1mA are screened out.

[0049] Two batches of bypass switches were tested for leakage current. The number of each batch was 30. One batch was a normal production batch, and the other batch was a batch with a certain link not properly assembled. The bypass switches with breakdown risks were screened out based on the leakage current test results. The screening results are as follows: Figure 5 shown.

[0050] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A method for analyzing breakdown failure of a bypass switch for low-frequency power transmission, characterized in that: The steps include: 1) Appearance inspection: Check the appearance of the bypass switch for low-frequency power transmission. If there are traces of discharge, it is determined that the external insulation design of the bypass switch is unqualified; 2) Withstand voltage test between auxiliary circuit and main circuit: measure the withstand voltage between the main circuit and the auxiliary switch, coil, magnet and housing. If the withstand voltage fails, it is determined that there is a problem in the withstand voltage design between the bypass switch auxiliary components and the main circuit; 3) Using X-ray testing: Use X-ray testing to test the opening distance of the moving and static contacts of the bypass switch for low-frequency power transmission. If the mechanical structure of the moving and static contacts is unstable, it is determined that it will cause breakdown; 4) Test the vacuum degree of the vacuum interrupter; when the vacuum degree of the vacuum interrupter is greater than 1.33×10^-3Pa, it is determined that the vacuum interrupter itself causes breakdown; 5) Disassemble the vacuum interrupter: Open the vacuum interrupter to check the contact status of the vacuum interrupter. If there are traces of ablation on the contacts of the vacuum interrupter, the bypass switch has a vacuum interrupter breakdown fault; 6) Test the roughness of the vacuum interrupter contact: If the roughness of the vacuum interrupter contact is less than 1μm, it is determined that the vacuum interrupter itself causes the breakdown.

2. A method for analyzing breakdown failure of a bypass switch for low-frequency power transmission according to claim 1, characterized in that: The discharge marks include black or arc burns.

3. A method for analyzing breakdown failure of a bypass switch for low-frequency power transmission according to claim 1, characterized in that: The X-ray test is performed by projecting two surfaces of the bypass switch at 90° to each other.

4. A method for analyzing breakdown failure of a bypass switch for low-frequency power transmission according to claim 3, characterized in that: The X-ray test evenly selects 4 to 6 points on the obtained X-ray projection image to measure the distance between the moving and static contacts; When any projection image shows that the deviation between the opening distance and the design value is greater than 10%, and the deviation between the measured data of 4 to 6 points and their average value is greater than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value and the skew between the contacts; When any projection image shows that the deviation between the opening distance and the design value is greater than 10%, and the deviation between the measured data of 4 to 6 points and their average value is less than 10%, it means that the mechanical structure is unstable, resulting in the opening distance not being consistent with the design value; When the deviation between the open distance and the design value in any projected image is less than 10%, and the deviation between the measured data of 4 to 6 points and their average value is greater than 10%, it means that the mechanical structure is unstable, resulting in skew between the contacts; When the X-ray projection test images of the two surfaces have an opening distance deviation from the design value of less than 10%, and the measurement data of 4 to 6 points deviate from their average value by less than 10%, it means that the mechanical structure is stable, the contact opening distance is normal and there is no skew.

5. A method for screening bypass switches for low-frequency power transmission, characterized in that: A DC voltage of 4.5 to 5 times the rated AC voltage is used to test the DC leakage current of the low-frequency power transmission bypass switch, and the low-frequency power transmission bypass switches with a DC leakage current greater than 0.1mA are screened out.

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