Contact detection method and device for on-load tap changer

Abstract

This invention provides a method and apparatus for detecting the contacts of an on-load tap changer, belonging to the field of equipment evaluation. The method includes: acquiring the stage voltage, operating current, transition resistance, bridging time, and switching count when the on-load tap changer is in operation; inputting the stage voltage, operating current, transition resistance, bridging time, and switching count into a pre-trained regression prediction model to obtain the actual contact resistance and mass loss of the contacts in the on-load tap changer; the regression prediction model determining the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time, and switching count when the switch is in operation; and determining the degree of contact erosion in the on-load tap changer based on the actual contact resistance and mass loss. This invention can detect the degree of contact erosion in real time, ensuring the safe operation of the OLTC (On-Load Tap Changer).

Description

Technical Field

[0001] This invention relates to the field of equipment evaluation technology, and in particular to a method and apparatus for detecting the contacts of an on-load tap changer. Background Technology

[0002] On-load tap changers (OLTCs) are a key component and the only moving part of a transformer, playing a crucial role in regulating reactive power and stabilizing grid voltage in power systems. OLTCs are widely used in HVDC converter transformers, step-up transformers in new energy power plants, traditional generation transformers, and distribution transformers. With the increasing demand for refined grid voltage control in power systems, the operating frequency of OLTCs has significantly increased. During the current-carrying switching and voltage regulation process, repeated arc interruptions can easily lead to contact erosion, resulting in changes in contact surface morphology, shortening of length, and increased contact resistance. This reduces the contact breaking capacity, and in severe cases, may cause tap-switching failure or even tank explosion, affecting the safe and stable operation of the power grid.

[0003] Currently, the detection of contact corrosion in OLTCs mainly relies on periodic power outages for maintenance. The degree of corrosion is determined by measuring the contact resistance. This makes it difficult to detect severe contact corrosion during OLTC operation in a timely manner, thus affecting the safe and stable operation of the OLTC. Summary of the Invention

[0004] This invention provides a contact detection method and apparatus for on-load tap changers to solve the problem that the degree of contact erosion cannot be detected in real time during the operation of an OLTC, thus affecting the safe operation of the OLTC.

[0005] In a first aspect, embodiments of the present invention provide a contact detection method for an on-load tap changer, comprising:

[0006] Obtain the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation.

[0007] The stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching operations are input into a pre-trained regression prediction model to obtain the actual contact resistance and mass loss of the contacts in the on-load tap changer. The regression prediction model determines the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the switch is in the operating state.

[0008] The degree of erosion of the contacts in the on-load tap changer is determined based on the actual contact resistance and mass loss of the contacts.

[0009] In one possible implementation, before inputting the stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching operations into the pre-trained regression prediction model, the method further includes:

[0010] Based on the on-load tap changer test system, the actual contact resistance and contact mass loss of the test on-load tap changer are obtained when it is subjected to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times.

[0011] The actual contact resistance and contact quality loss of the contacts corresponding to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times are used as the training sample set;

[0012] The regression prediction model is trained based on the training sample set to obtain the trained regression prediction model.

[0013] In one possible implementation, the on-load tap changer test system includes: a voltage regulator, a test transformer, an on-load tap changer under test, a test on-load tap changer, a load simulation device, and a control acquisition unit.

[0014] The three-phase input terminal of the voltage regulator is used to connect to a three-phase power supply, and the three-phase output terminal of the voltage regulator is connected to the three-phase input terminal of the test transformer.

[0015] The first phase output terminal of the three-phase output terminal of the test transformer is connected to the first terminal of the load simulation device; the second phase output terminal of the three-phase output terminal of the test transformer is connected to the first fixed node of the on-load tap changer and the first fixed node of the on-load tap changer; and the third phase output terminal of the three-phase output terminal of the test transformer is connected to the second fixed node of the on-load tap changer and the second fixed node of the on-load tap changer.

[0016] The contact node of the on-load tap changer is connected to the second end of the load simulation device;

[0017] The contact node of the on-load tap changer in the test is connected to the third terminal of the load simulation device;

[0018] The control acquisition unit is connected to the control acquisition terminal of the voltage regulator, the control acquisition terminal of the test transformer, the control acquisition terminal of the on-load tap changer under test, the control acquisition terminal of the on-load tap changer under test, and the control acquisition terminal of the load simulation device.

[0019] In one possible implementation, the low-voltage side windings of the test transformer are interconnected in a star configuration.

[0020] In one possible implementation, the load simulation device includes: a current-limiting resistor, an adjustable capacitor, and an adjustable inductor;

[0021] One end of the current-limiting resistor is connected to the first phase output terminal of the three-phase output terminal of the test transformer, and the other end of the current-limiting resistor is connected to one end of the adjustable capacitor and one end of the adjustable inductor respectively.

[0022] The other end of the adjustable capacitor is connected to the contact node of the on-load tap changer under test;

[0023] The other end of the adjustable inductor is connected to the contact node of the test on-load tap changer.

[0024] In one possible implementation, the on-load tap changer test system further includes: a high-voltage switchgear;

[0025] The input terminal of the high-voltage switchgear is used to connect to a three-phase power supply, and the output terminal of the high-voltage switchgear is used to connect to the three-phase input terminal of the voltage regulator.

[0026] The control acquisition terminal of the high-voltage control rail is connected to the control acquisition device.

[0027] In one possible implementation, the regression prediction model is trained based on the training sample set to obtain a trained regression prediction model, including:

[0028] Based on the training sample set, the first and second parameters of the regression prediction model are iteratively optimized to obtain the optimal solutions for the first and second parameters.

[0029] The optimal solutions for the first parameter and the second parameter are applied to the regression prediction model, and the training sample set is input into the regression prediction model for model training to obtain a trained regression prediction model.

[0030] In one possible implementation, determining the degree of contact erosion based on the actual contact resistance and the mass loss includes:

[0031] When the actual contact resistance is greater than the first preset value, or the mass loss is greater than the second preset value, the degree of erosion of the contact is determined to be severe erosion.

[0032] When the actual contact resistance is less than or equal to a first preset value and the mass loss is less than or equal to a second preset value, the initial contact resistance of the contact is obtained, and the contact resistance loss is calculated based on the initial contact resistance and the actual contact resistance.

[0033] Calculate the ratio of the contact resistance loss to the initial contact resistance, and determine the ratio as the contact resistance index;

[0034] The degree of erosion of the contact is determined based on the contact resistance index and the mass loss.

[0035] In one possible implementation, determining the degree of contact erosion based on the contact resistance index and the mass loss includes:

[0036] When the contact resistance index is less than a third preset value and the mass loss is less than or equal to a fourth preset value, the degree of erosion of the contact is determined to be mild erosion; the fourth preset value is less than the second preset value.

[0037] When the contact resistance index is less than a third preset value, the mass loss is greater than a fourth preset value, and the mass loss is less than or equal to a second preset value, the degree of erosion of the contact is determined to be moderate erosion.

[0038] When the contact resistance index is greater than or equal to the third preset value, and the contact resistance index is less than the fifth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be moderate erosion.

[0039] When the contact resistance index is greater than or equal to the fifth preset value and the mass loss is less than the sixth preset value, the degree of erosion of the contact is determined to be moderate erosion; the sixth preset value is less than the second preset value and the sixth preset value is greater than the fourth preset value;

[0040] When the contact resistance index is greater than or equal to the fifth preset value, the mass loss is greater than or equal to the sixth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be severe erosion.

[0041] Secondly, embodiments of the present invention provide a contact detection device for an on-load tap changer, comprising:

[0042] The acquisition module is used to acquire the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation.

[0043] The prediction module is used to input the stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching times into a pre-trained regression prediction model to obtain the change in contact resistance and mass loss of the contacts in the on-load tap changer; the regression prediction model determines the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time, and number of switching times when the switch is in the operating state.

[0044] The determination module is used to determine the degree of erosion of the contacts in the on-load tap changer based on the actual contact resistance and mass loss of the contacts.

[0045] This invention provides a method and apparatus for detecting the contacts of an on-load tap changer. By taking the stage voltage, operating current, transition resistance, bridging time, and switching frequency of the on-load tap changer when it is in operation as influencing factors on the degree of contact erosion, and taking the actual contact resistance and mass loss of the contacts as characterizing quantities of the degree of contact erosion, the method can detect the degree of contact erosion in real time based on the operating parameters of the on-load tap changer when it is in operation, thereby ensuring the safe operation of the on-load tap changer. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a flowchart illustrating the implementation of the contact detection method for an on-load tap changer provided in this embodiment of the invention.

[0048] Figure 2 This is a schematic diagram of the process of the tap changer contacts interrupting the electric arc provided in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the on-load tap changer testing system provided in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the on-load tap changer testing system provided in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the connection of the low-voltage side winding of the test transformer provided in an embodiment of the present invention;

[0052] Figure 6 This is a schematic diagram of the contact detection device for an on-load tap changer provided in an embodiment of the present invention. Detailed Implementation

[0053] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0055] Figure 1 The implementation flowchart of the on-load tap changer contact detection method provided in the embodiment of the present invention is described in detail below:

[0056] Step 101: Obtain the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation.

[0057] The erosion of contacts in on-load tap changers is mainly caused by the frequent interruption of electric arcs during the operation of the on-load tap changer. Figure 2 The process of interrupting the arc by the contacts of an on-load tap changer is shown. According to... Figure 2 It can be seen that each time the on-load tap changer interrupts the arc, the contact nodes in the on-load tap changer sequentially pass through main contact 1, transition contact 2, transition contact 3, and main contact 4, completing one switching process. Alternatively, the contact nodes in the on-load tap changer sequentially pass through main contact 4, transition contact 3, transition contact 2, and main contact 1, completing one switching process. That is, each time the on-load tap changer switches, the contacts in the on-load tap changer need to go through… Figure 2 The five states in the text.

[0058] The inventors discovered that when the contact nodes of an on-load tap changer are in state I, the breaking current of the main contact 1 is I. The breaking currents of the transition contacts 2, 3, and 4 are all 0. When the contact nodes are in state II, the breaking current of the transition contact 2 is I. The breaking currents of the main contact 1, 3, and 4 are all 0. When the contact nodes are in state III, the breaking current of the transition contact 2 is (I + U) / 2. st / R) / 2. The breaking current of the transition contact 3 is (IU) st / R) / 2. The breaking current of both main contact 1 and main contact 4 is 0. When the contact node is in state IV, the breaking current of transition contact 3 is I. The breaking current of main contact 1, transition contact 2, and main contact 4 is 0. When the contact node is in state V, the breaking current of main contact 4 is I. The breaking current of main contact 1, transition contact 2, and transition contact 3 is 0.

[0059] In other words, the breaking current of the main contacts in an on-load tap changer is equal to the operating current of the on-load tap changer. The breaking current of the transition contacts is related to the operating current of the on-load tap changer and the stage voltage U of the on-load tap changer. st It is also related to the transition resistance R in the on-load tap changer.

[0060] Therefore, this embodiment of the invention uses the stage voltage, operating current, and transition resistance of the on-load tap changer as influencing factors for detecting the degree of contact erosion of the on-load tap changer. Simultaneously, this embodiment of the invention also uses bridging time and the number of switching operations as influencing factors for the degree of contact erosion of the on-load tap changer. Here, bridging time refers to the time required to complete one switching process. The number of switching operations refers to the number of switching operations since the on-load tap changer was put into operation.

[0061] Step 102: Input the stage voltage, operating current, transition resistance, bridging time, and number of switching operations into the pre-trained regression prediction model to obtain the actual contact resistance and mass loss of the contacts in the on-load tap changer. The regression prediction model determines the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the switch is in operation.

[0062] When the contacts of an on-load tap changer erode, their contact resistance and mass change accordingly. Therefore, in this embodiment of the invention, the actual contact resistance and mass loss of the contacts are used as indicators of the degree of erosion.

[0063] The regression prediction model is used to fit the mapping relationship between the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the switch is in operation, and the actual contact resistance and mass loss of the switch contacts. The stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation are input into the pre-trained regression prediction model to obtain the actual contact resistance and mass loss of the contacts.

[0064] In some embodiments, prior to step 102, the method further includes:

[0065] Based on the on-load tap changer test system, the actual contact resistance and contact mass loss of the test on-load tap changer are obtained when it is subjected to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times.

[0066] The actual contact resistance and contact quality loss of the contacts corresponding to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times are used as the training sample set.

[0067] The regression prediction model is trained based on the training sample set, and the trained regression prediction model is obtained.

[0068] To train the regression prediction model, this embodiment of the invention constructs an on-load tap changer test system to obtain the actual contact resistance and contact mass loss of the on-load tap changer when it is under different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times, so as to train the regression prediction model.

[0069] In some embodiments, see Figure 3 The on-load tap changer test system includes: a voltage regulator 31, a test transformer 32, an on-load tap changer for testing 33, a test on-load tap changer 34, a load simulation device 35, and a control acquisition unit 36.

[0070] The three-phase input terminal of the voltage regulator 31 is used to connect to a three-phase power supply, and the three-phase output terminal of the voltage regulator 31 is used to connect to the three-phase input terminal of the test transformer 32.

[0071] The first phase output terminal of the three-phase output terminal of the test transformer 32 is connected to the first terminal of the load simulation device 35. The second phase output terminal of the three-phase output terminal of the test transformer 32 is connected to the first fixed node of the on-load tap changer 33 and the first fixed node of the on-load tap changer 34 respectively. The third phase output terminal of the three-phase output terminal of the test transformer 32 is connected to the second fixed node of the on-load tap changer 33 and the second fixed node of the on-load tap changer 34 respectively.

[0072] The contact nodes of the on-load tap changer 33 are connected to the second end of the load simulation device 35;

[0073] The contact nodes of the on-load tap changer 34 are connected to the third terminal of the load simulation device 35.

[0074] The control acquisition unit 36 ​​is connected to the control acquisition terminal of the voltage regulator 31, the control acquisition terminal of the test transformer 32, the control acquisition terminal of the on-load tap changer 33, the control acquisition terminal of the on-load tap changer 34, and the control acquisition terminal of the load simulation device 35, respectively.

[0075] The three-phase power supply passes sequentially through voltage regulator 31 and test transformer 32 to generate a three-phase test voltage. The first phase output terminal A of the test transformer 32 is connected to the first terminal of the load simulation device 35, and the voltage corresponding to the first phase output terminal A is used to control the operating current flowing through the on-load tap changer 33 and the test on-load tap changer 34. The second phase output terminals B and C of the test transformer 32 are connected to the on-load tap changer 33 and the test on-load tap changer 34 to generate their respective voltage levels. The on-load tap changer 23 and the test on-load tap changer 24 are synchronously operating on-load tap changers of the same model.

[0076] The control acquisition unit 36 ​​can control the output voltage of the voltage regulator 31, thereby controlling the three-phase output voltage of the three-phase output terminal of the test transformer 32. This allows for adjustment of the stage voltages of the on-load tap changer 33 and the test on-load tap changer 34. The control acquisition unit 36 ​​can also control the load simulation device 35, thereby adjusting the operating current of the on-load tap changer 33 and the test on-load tap changer 34. Furthermore, the control acquisition unit 36 ​​can control the on-load tap changer 33 and the test on-load tap changer 34 to perform switching actions, and correspondingly acquire the bridging time and switching frequency of the test on-load tap changer 34.

[0077] When an on-load tap changer is in operation, its stage voltage is typically less than or equal to 4000V, and its maximum rated operating current is typically less than or equal to 600A. Considering design margins, the on-load tap changer test system in this embodiment sets the maximum stage voltage of the tested on-load tap changer 34 to 6000V, and its operating current range to 400A to 800A.

[0078] In some embodiments, see Figure 4 The load simulation device 35 includes: a current-limiting resistor 351, an adjustable capacitor 352, and an adjustable inductor 353.

[0079] One end of the current-limiting resistor 351 is connected to the first phase output terminal A of the three-phase output terminals of the test transformer 32, and the other end of the current-limiting resistor 351 is connected to one end of the adjustable capacitor 352 and one end of the adjustable inductor 353 respectively.

[0080] The other end of the adjustable capacitor 352 is connected to the contact node of the on-load tap changer 33 under test;

[0081] The other end of the adjustable inductor 353 is connected to the contact node of the test on-load tap changer 34.

[0082] The on-load tap changer 33 is connected to an adjustable capacitor 352, and the on-load tap changer 34 is connected to an adjustable inductor 353. The on-load tap changer 33 and the on-load tap changer 34 are connected in parallel. This means that the vector sum of the operating currents of the on-load tap changer 33 and the on-load tap changer 34 is the total current supplied by the three-phase power supply. Furthermore, the direction of the operating current of the on-load tap changer 33 is opposite to the direction of the operating current of the on-load tap changer 34. That is, the difference between the amplitude of the operating current of the on-load tap changer 34 and the amplitude of the operating current of the on-load tap changer 33 is the amplitude of the total current supplied by the three-phase power supply. This is because, in this embodiment of the invention, the on-load tap changer test system is limited by hardware settings and cannot provide power supply equipment with an operating current range of 400A to 800A. Therefore, a companion on-load tap changer 23 is set up with the opposite operating current to the test on-load tap changer 24, so that the operating current requirements of the on-load tap changer can be met by using a small-capacity three-phase power supply, voltage regulator and test transformer, thereby improving the convenience of testing and obtaining a sufficient amount of operating current data.

[0083] The controller 36 can adjust the operating current of the on-load tap changer by adjusting the current-limiting resistor 351 and the adjustable inductor 353. The parameter calculation formula of the adjustable inductor 353 can be expressed as: L=U / ωI. Where L represents the inductance value of the adjustable inductor, U represents the voltage corresponding to the first phase output terminal A, ω represents the angular frequency, calculated according to the power frequency, ω=2πf, f represents the AC voltage frequency, and I represents the operating current of the on-load tap changer. For example, the operating current of the on-load tap changer is usually 400A~800A, and correspondingly, the inductance value of the adjustable inductor can be in the range of 15.92mH~31.83mH. For easy adjustment, different ranges can be set on the adjustable inductor. For example, 500kvar, 1000kvar, and 2000kvar.

[0084] The control acquisition unit 36, through the adjustable capacitor 352, can perform reactive power compensation, thereby reducing the power capacity of the three-phase power supply and improving the convenience of testing. The parameter calculation formula for the adjustable capacitor can be expressed as: C=1 / ω 2 L. Where C represents the capacitance value of the adjustable capacitor. For example, the adjustable capacitor and its value range can be 318.64nF to 637.29nF. Different settings can be set on the adjustable capacitor for easy adjustment, such as 500kvar, 1000kvar, and 2000kvar.

[0085] Based on reactive power compensation using adjustable capacitors, the formula for calculating the capacity of the three-phase power supply can be expressed as S = (1-η)UI. Where S represents the capacity of the three-phase power supply, η represents the reactive power compensation rate of the adjustable capacitor (which can be 70% of the rated capacity), U represents the voltage corresponding to the first phase output terminal A, and I represents the operating current of the on-load tap changer during testing. Based on the maximum operating current, the maximum capacity of the power supply needs to be set to 960kVA. Therefore, in this embodiment of the invention, the configuration capacity of the three-phase power supply, voltage regulator, and test transformer is set to 1000kVA.

[0086] It should be noted that, Figure 3 and Figure 4 The accompanying drawings are provided as illustrative examples to illustrate the connection relationships between the various test devices and are not intended to limit the connection method of the low-voltage winding of the test transformer.

[0087] In some embodiments, see Figure 5 The low-voltage windings of the test transformer are interconnected in a star configuration.

[0088] Figure 5 A schematic diagram of the low-voltage side winding connection of the test transformer is shown. (Using...) Figure 5 The star connection shown indicates the line voltage U between the first phase output terminal A and the second phase output terminal B of the test transformer. AB Equal to the line voltage U between the first phase output terminal A and the third phase output terminal AC By adjusting the line voltage U AC The operating current of the on-load tap changer can be adjusted. The line voltage U between the second-phase output terminal B and the third-phase output terminal C of the test transformer... BC This refers to the stage voltage of the on-load tap changer.

[0089] In this embodiment of the invention, the low-voltage windings of the test transformer are interconnected in a star connection, so that the line voltage U used to adjust the operating current is... AC and U used for regulating stage voltage BC They can be adjusted independently without affecting each other, thus independently adjusting the working current and stage voltage of the on-load tap changer in the test.

[0090] To adjust the operating current and voltage of the on-load tap changer separately, this embodiment of the invention can set multiple voltage divider taps on the low-voltage side winding of the test transformer. The controller can adjust the output voltage U of the test transformer by controlling the movement of the voltage divider taps on the low-voltage side winding. AC and U BC For example, each phase winding in the low-voltage side winding is provided with 3 taps, and the tap positions are respectively set at 0.25 times, 0.5 times and 0.75 times the number of turns of the current phase winding.

[0091] In some embodiments, see Figure 4 The on-load tap changer testing system also includes: high-voltage switchgear 36.

[0092] The input terminal of the high-voltage switchgear 37 is used to connect to a three-phase power supply, and the output terminal of the high-voltage switchgear 36 is used to connect to the three-phase input terminal of the voltage regulator 31.

[0093] The control acquisition terminal of the high-voltage control cabinet 37 is connected to the control acquisition device 35.

[0094] The controller 36 controls the high-voltage switchgear 37 to switch three-phase power supplies. The high-voltage switchgear 37 is equipped with overcurrent protection, short-circuit protection, and instantaneous tripping functions to ensure the safe operation of the on-load tap changer testing system. For example, the specifications of the high-voltage switchgear can be 12kV / 630A.

[0095] For example, the parameters and functions of some devices in the on-load tap changer test system can be found in Table 1.

[0096] Table 1 Equipment Parameter Function Table

[0097]

[0098] In this embodiment of the invention, when acquiring a training sample set using an on-load tap changer test system, the stage voltage and operating current of the test on-load tap changer can be controlled and adjusted via the control acquisition unit 36. The output voltage U of the test transformer can be adjusted accordingly. BC The stage voltage can be adjusted. This is achieved by adjusting the output voltage U of the test transformer. AC The operating current can be adjusted. Alternatively, the operating current can also be controlled by adjusting the adjustable inductor. See also... Figure 4 Current transformers CT1 and CT2, and voltage transformers PT1 and PT2 can be installed on the on-load tap changer to measure the stage voltage and operating current when the on-load tap changer is in operation. By controlling the operation of the on-load tap changer, the bridging time and switching count can be obtained. By changing the transition resistor in the on-load tap changer, this influencing factor can be changed. After each set of experiments, the mass loss and actual contact resistance of the contacts in the on-load tap changer are measured. The mass loss of the contacts is the average of the mass losses of main contact 1, transition contact 2, transition contact 3, and main contact 4. The actual contact resistance of the contacts is the average of the actual contact resistances of contacts 1, transition contact 2, transition contact 3, and main contact 4.

[0099] Based on the aforementioned on-load tap changer test system, the actual contact resistance and contact mass loss of the on-load tap changer under different voltage levels, operating currents, transition resistances, bridging times, and switching times can be obtained and used as a training sample set to train the regression prediction model. For example, tests can be conducted according to the test parameters in Table 2, and after each test, the actual contact resistance and mass loss of the contacts in the on-load tap changer can be measured to obtain the training sample set.

[0100] Table 2 Experimental Parameter Settings

[0101] Operating current 400A, 600A, 800A Level voltage 3000V, 400V, 5000V Transition resistance 2Ω, 3Ω, 4Ω, 5Ω Bridging time 22.4ms, 27.9ms, 30.6ms Switching times 1000、3000、5000

[0102] In some embodiments, the above-mentioned training of the regression prediction model based on the training sample set to obtain the trained regression prediction model may include:

[0103] The first and second parameters of the regression prediction model are iteratively optimized based on the training sample set to obtain the optimal solutions for the first and second parameters.

[0104] The optimal solutions for the first and second parameters are applied to the regression prediction model, and the training sample set is input into the regression prediction model for model training, resulting in a trained regression prediction model.

[0105] The regression prediction model in this embodiment of the invention can be a kernel ridge regression model. The first and second parameters can be the regularization parameter and Gaussian kernel parameter in the kernel ridge regression model. The kernel ridge regression model maps the input data to a high-dimensional kernel space and performs linear regression in the high-dimensional kernel space. When training the kernel ridge regression model using the training sample set, the Gaussian kernel function is used to map each group of training sample data to the high-dimensional kernel space, resulting in each group of sample data in the high-dimensional kernel space. The inner product of each group of sample data in the high-dimensional kernel space is calculated. The inner product of all groups of sample data in the high-dimensional kernel space constitutes the kernel matrix, and a penalty function is constructed based on the kernel matrix. The model parameters in the kernel ridge regression model are iteratively updated until the penalty function is less than a preset value, at which point training is complete, and a trained regression prediction model is obtained.

[0106] The Gaussian kernel function can be expressed as:

[0107] Where k(x,y) represents a set of sample data in a high-dimensional kernel space, x represents the independent variable in the input set of training data, such as stage voltage, operating current, transition resistance, bridging time and number of switching, y represents the dependent variable in the input set of training data, such as actual contact resistance and mass loss, and σ represents the Gaussian kernel parameter.

[0108] The penalty function can be expressed as: minα J(α) = ||y - Kα|| 2 +ααKα+λ||α|| 2 .

[0109] Where J(α) represents the penalty function, K represents the kernel matrix, α represents the weight vector to be adjusted, and λ represents the regularization parameter.

[0110] In this embodiment of the invention, the Gaussian kernel parameters and regularization parameters in the kernel ridge regression model are pre-optimized. Then, based on the optimized Gaussian kernel parameters and regularization parameters, the kernel ridge regression model is trained to adjust the weight vector α, thereby improving the prediction accuracy of the kernel ridge regression model.

[0111] When optimizing the Gaussian kernel parameters and regularization parameters in the kernel ridge regression model, ant colony optimization (ACO) or genetic algorithms can be used. Taking ACO as an example, when optimizing the Gaussian kernel parameters and regularization parameters, an initial solution is generated randomly beforehand, and parameters such as pheromone concentration and maximum number of iterations are set. The pheromone concentration for each path is calculated separately. The pheromone concentration of traversed paths is enhanced according to the success rate, and the pheromone concentration on all paths evaporates according to a certain rule, thereby updating the pheromone concentration of each path until the preset number of iterations is reached, or the algorithm converges, yielding the optimal Gaussian kernel parameters and regularization parameters.

[0112] In this embodiment of the invention, after obtaining the trained regression prediction model, a test sample set is used to test the regression prediction model. The test sample data is input into the regression prediction model, and the model calculates the inner product of the test sample and each training sample in the kernel space, obtaining the kernel vector k of the test sample and training samples. test And according to Calculate the output model predictions. The regression prediction model training is complete when the model predictions meet the required accuracy. Otherwise, retrain the regression prediction model.

[0113] Step 103: Determine the degree of erosion of the contacts in the on-load tap changer based on the actual contact resistance and mass loss of the contacts.

[0114] Based on the actual contact resistance and mass loss of the contacts in an on-load tap changer, the contacts are classified into mild, moderate, or severe corrosion. Mild corrosion only requires routine maintenance. Moderate corrosion requires close monitoring of the contact condition and replacement of the contacts during the next power outage maintenance. Severe corrosion requires immediate replacement of the contacts.

[0115] In some embodiments, step 103 may include:

[0116] When the actual contact resistance is greater than the first preset value, or the mass loss is greater than the second preset value, the degree of contact corrosion is determined to be severe corrosion.

[0117] When the actual contact resistance is less than or equal to the first preset value and the mass loss is less than or equal to the second preset value, the initial contact resistance of the contact is obtained, and the contact resistance loss is calculated based on the initial contact resistance and the actual contact resistance.

[0118] Calculate the ratio of contact resistance loss to initial contact resistance, and determine the ratio as the contact resistance index.

[0119] The degree of contact erosion is determined based on contact resistance and mass loss.

[0120] In other words, when the actual contact resistance or mass loss of the contact is too high, the degree of contact erosion can be directly determined as severe erosion. Otherwise, the contact resistance index is calculated based on the actual contact resistance and the initial contact resistance, and the degree of contact erosion is further classified based on the contact resistance index and mass loss. The initial contact resistance refers to the contact resistance in the initial state when the on-load tap changer is not in operation. For example, the first preset value can be 500 μΩ. The second preset value can be 5 g.

[0121] In some embodiments, determining the degree of contact erosion based on contact resistance and mass loss may include:

[0122] When the contact resistance is less than the third preset value and the mass loss is less than or equal to the fourth preset value, the degree of contact corrosion is determined to be mild corrosion; the fourth preset value is less than the second preset value.

[0123] When the contact resistance is less than the third preset value, the mass loss is greater than the fourth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be moderate corrosion.

[0124] When the contact resistance index is greater than or equal to the third preset value, and the contact resistance index is less than the fifth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be moderate corrosion.

[0125] When the contact resistance is greater than or equal to the fifth preset value and the mass loss is less than the sixth preset value, the degree of contact corrosion is determined to be moderate corrosion; the sixth preset value is less than the second preset value and greater than the fourth preset value.

[0126] When the contact resistance is greater than or equal to the fifth preset value, and the mass loss is greater than or equal to the sixth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be severe corrosion.

[0127] For example, the third preset value can be 0.2g. The fourth preset value can be 1g. The fifth preset value can be 0.5g. The sixth preset value can be 3g. The above grading standards can be found in Table 3.

[0128] Table 3. Grading Standards for Contact Erosion Degree

[0129]

[0130] Where R1 represents the actual contact resistance, ΔR / R or This represents the contact resistance index, and Δm represents the mass loss.

[0131] Compared to existing technologies, this invention uses the stage voltage, operating current, transition resistance, bridging time, and switching frequency of the on-load tap changer when it is in operation as influencing factors on the degree of contact erosion, and uses the actual contact resistance and mass loss of the contacts as characterizing quantities of the degree of contact erosion. This allows for real-time detection of the degree of contact erosion based on the operating parameters of the on-load tap changer when it is in operation, thereby ensuring the safe operation of the on-load tap changer.

[0132] Meanwhile, in this embodiment of the invention, when testing the on-load tap changer, a companion on-load tap changer with the opposite direction of its operating current is set up. This reduces the configuration capacity of the three-phase power supply, voltage regulator, and test transformer, freeing them from the limitations of laboratory hardware. Furthermore, the low-voltage winding of the test transformer adopts a star connection, allowing independent adjustment of the stage voltage and operating current of the on-load tap changer.

[0133] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0134] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0135] Figure 6 A schematic diagram of the contact detection device for an on-load tap changer provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below:

[0136] like Figure 6 As shown, the contact detection device 6 for an on-load tap changer includes: an acquisition module 61, a prediction module 62, and a determination module 63.

[0137] The acquisition module 61 is used to acquire the stage voltage, operating current, transition resistance, bridging time and switching count when the on-load tap changer is in the working state.

[0138] Prediction module 62 is used to input stage voltage, operating current, transition resistance, bridging time and switching number into a pre-trained regression prediction model to obtain the change in contact resistance and mass loss of the contacts in the on-load tap changer; the regression prediction model determines the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time and switching number when the switch is in the working state.

[0139] Module 63 is used to determine the degree of erosion of the contacts in the on-load tap changer based on the actual contact resistance and mass loss of the contacts.

[0140] In one possible implementation, prediction module 62 is specifically used for:

[0141] Based on the on-load tap changer test system, the actual contact resistance and contact mass loss of the test on-load tap changer are obtained when it is subjected to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times.

[0142] The actual contact resistance and contact quality loss of the contacts corresponding to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times are used as the training sample set;

[0143] The regression prediction model is trained based on the training sample set, and the trained regression prediction model is obtained.

[0144] In one possible implementation, an on-load tap changer test system includes: a voltage regulator, a test transformer, an on-load tap changer under test, a test on-load tap changer, a load simulation device, and a control acquisition unit.

[0145] The three-phase input terminal of the voltage regulator is used to connect to a three-phase power supply, and the three-phase output terminal of the voltage regulator is used to connect to the three-phase input terminal of the test transformer.

[0146] The first phase output terminal of the three-phase output terminal of the test transformer is connected to the first terminal of the load simulation device. The second phase output terminal of the three-phase output terminal of the test transformer is connected to the first fixed node of the on-load tap changer under test and the first fixed node of the on-load tap changer under test respectively. The third phase output terminal of the three-phase output terminal of the test transformer is connected to the second fixed node of the on-load tap changer under test and the second fixed node of the on-load tap changer under test respectively.

[0147] The contact nodes of the on-load tap changer are connected to the second end of the load simulation device.

[0148] The contact nodes of the on-load tap changer are connected to the third terminal of the load simulation device.

[0149] The control acquisition unit is connected to the control acquisition terminal of the voltage regulator, the control acquisition terminal of the test transformer, the control acquisition terminal of the on-load tap changer under test, the control acquisition terminal of the on-load tap changer under test, and the control acquisition terminal of the load simulation device.

[0150] In one possible implementation, the low-voltage side windings of the test transformer are interconnected in a star configuration.

[0151] In one possible implementation, the load simulation device includes: a current-limiting resistor, an adjustable capacitor, and an adjustable inductor;

[0152] One end of the current-limiting resistor is connected to the first phase output terminal of the three-phase output terminal of the test transformer, and the other end of the current-limiting resistor is connected to one end of the adjustable capacitor and one end of the adjustable inductor respectively.

[0153] The other end of the adjustable capacitor is connected to the contact node of the on-load tap changer under test;

[0154] The other end of the adjustable inductor is connected to the contact node of the on-load tap changer.

[0155] In one possible implementation, the on-load tap changer test system also includes: a high-voltage switchgear;

[0156] The input terminals of the high-voltage switchgear are used to connect to the three-phase power supply, and the output terminals of the high-voltage switchgear are used to connect to the three-phase input terminals of the voltage regulator.

[0157] The control acquisition terminal of the high-voltage control cabinet is connected to the control acquisition device.

[0158] In one possible implementation, prediction module 62 is specifically used for:

[0159] The first and second parameters of the regression prediction model are iteratively optimized based on the training sample set to obtain the optimal solutions for the first and second parameters.

[0160] The optimal solutions for the first and second parameters are applied to the regression prediction model, and the training sample set is input into the regression prediction model for model training, resulting in a trained regression prediction model.

[0161] In one possible implementation, module 63 is specifically used for:

[0162] When the actual contact resistance is greater than the first preset value, or the mass loss is greater than the second preset value, the degree of contact corrosion is determined to be severe corrosion.

[0163] When the actual contact resistance is less than or equal to the first preset value and the mass loss is less than or equal to the second preset value, the initial contact resistance of the contact is obtained, and the contact resistance loss is calculated based on the initial contact resistance and the actual contact resistance.

[0164] Calculate the ratio of contact resistance loss to initial contact resistance, and determine the ratio as the contact resistance index.

[0165] The degree of contact erosion is determined based on contact resistance and mass loss.

[0166] In one possible implementation, module 63 is specifically used for:

[0167] When the contact resistance is less than the third preset value and the mass loss is less than or equal to the fourth preset value, the degree of contact corrosion is determined to be mild corrosion; the fourth preset value is less than the second preset value.

[0168] When the contact resistance is less than the third preset value, the mass loss is greater than the fourth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be moderate corrosion.

[0169] When the contact resistance index is greater than or equal to the third preset value, and the contact resistance index is less than the fifth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be moderate corrosion.

[0170] When the contact resistance is greater than or equal to the fifth preset value and the mass loss is less than the sixth preset value, the degree of contact corrosion is determined to be moderate corrosion; the sixth preset value is less than the second preset value and greater than the fourth preset value.

[0171] When the contact resistance is greater than or equal to the fifth preset value, and the mass loss is greater than or equal to the sixth preset value, and the mass loss is less than or equal to the second preset value, the degree of contact corrosion is determined to be severe corrosion.

[0172] Compared to existing technologies, the prediction module 62 uses the stage voltage, operating current, transition resistance, bridging time, and switching frequency of the on-load tap changer when it is in operation as influencing factors on the degree of contact erosion, and uses the actual contact resistance and mass loss of the contact as characterizing quantities of the degree of contact erosion. Thus, it can detect the degree of contact erosion in real time based on the operating parameters of the on-load tap changer when it is in operation, so as to ensure the safe operation of the on-load tap changer.

[0173] Meanwhile, in this embodiment of the invention, when testing the on-load tap changer, a companion on-load tap changer with the opposite direction of its operating current is set up. This reduces the configuration capacity of the three-phase power supply, voltage regulator, and test transformer, freeing them from the limitations of laboratory hardware. Furthermore, the low-voltage winding of the test transformer adopts a star connection, allowing independent adjustment of the stage voltage and operating current of the on-load tap changer.

[0174] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0175] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0176] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the above embodiments of the on-load tap changer contact detection method. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0177] The above-described 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for detecting the contacts of an on-load tap changer, characterized in that, include: Obtain the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation. The stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching operations are input into a pre-trained regression prediction model to obtain the actual contact resistance and mass loss of the contacts in the on-load tap changer. The regression prediction model determines the actual contact resistance and mass loss of the switch contacts based on the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the switch is in the operating state. The degree of erosion of the contacts in the on-load tap changer is determined based on the actual contact resistance and mass loss of the contacts. Determining the degree of contact erosion based on the actual contact resistance and the mass loss includes: When the actual contact resistance is greater than the first preset value, or the mass loss is greater than the second preset value, the degree of erosion of the contact is determined to be severe erosion. When the actual contact resistance is less than or equal to a first preset value and the mass loss is less than or equal to a second preset value, the initial contact resistance of the contact is obtained, and the contact resistance loss is calculated based on the initial contact resistance and the actual contact resistance. Calculate the ratio of the contact resistance loss to the initial contact resistance, and determine the ratio as the contact resistance index; The degree of erosion of the contact is determined based on the contact resistance index and the mass loss. Determining the degree of erosion of the contact based on the contact resistance index and the mass loss includes: When the contact resistance index is less than a third preset value and the mass loss is less than or equal to a fourth preset value, the degree of erosion of the contact is determined to be mild erosion; the fourth preset value is less than the second preset value. When the contact resistance index is less than a third preset value, the mass loss is greater than a fourth preset value, and the mass loss is less than or equal to a second preset value, the degree of erosion of the contact is determined to be moderate erosion. When the contact resistance index is greater than or equal to the third preset value, and the contact resistance index is less than the fifth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be moderate erosion. When the contact resistance index is greater than or equal to the fifth preset value and the mass loss is less than the sixth preset value, the degree of erosion of the contact is determined to be moderate erosion; the sixth preset value is less than the second preset value and the sixth preset value is greater than the fourth preset value; When the contact resistance index is greater than or equal to the fifth preset value, the mass loss is greater than or equal to the sixth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be severe erosion.

2. The contact detection method for an on-load tap changer according to claim 1, characterized in that, Before inputting the stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching operations into the pre-trained regression prediction model, the method further includes: Based on the on-load tap changer test system, the actual contact resistance and contact mass loss of the test on-load tap changer are obtained when it is subjected to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times. The actual contact resistance and contact quality loss of the contacts corresponding to different voltage levels, different operating currents, different transition resistances, different bridging times, and different switching times are used as the training sample set; The regression prediction model is trained based on the training sample set to obtain the trained regression prediction model.

3. The contact detection method for an on-load tap changer according to claim 2, characterized in that, The on-load tap changer test system includes: a voltage regulator, a test transformer, an on-load tap changer under test, a test on-load tap changer, a load simulation device, and a control acquisition unit; The three-phase input terminal of the voltage regulator is used to connect to a three-phase power supply, and the three-phase output terminal of the voltage regulator is connected to the three-phase input terminal of the test transformer. The first phase output terminal of the three-phase output terminal of the test transformer is connected to the first terminal of the load simulation device; the second phase output terminal of the three-phase output terminal of the test transformer is connected to the first fixed node of the on-load tap changer and the first fixed node of the on-load tap changer; and the third phase output terminal of the three-phase output terminal of the test transformer is connected to the second fixed node of the on-load tap changer and the second fixed node of the on-load tap changer. The contact node of the on-load tap changer is connected to the second end of the load simulation device; The contact node of the on-load tap changer in the test is connected to the third terminal of the load simulation device; The control acquisition unit is connected to the control acquisition terminal of the voltage regulator, the control acquisition terminal of the test transformer, the control acquisition terminal of the on-load tap changer under test, the control acquisition terminal of the on-load tap changer under test, and the control acquisition terminal of the load simulation device.

4. The contact detection method for an on-load tap changer according to claim 3, characterized in that, The low-voltage windings of the test transformer are interconnected in a star configuration.

5. The contact detection method for an on-load tap changer according to claim 3 or 4, characterized in that, The load simulation device includes: a current-limiting resistor, an adjustable capacitor, and an adjustable inductor; One end of the current-limiting resistor is connected to the first phase output terminal of the three-phase output terminal of the test transformer, and the other end of the current-limiting resistor is connected to one end of the adjustable capacitor and one end of the adjustable inductor respectively. The other end of the adjustable capacitor is connected to the contact node of the on-load tap changer under test; The other end of the adjustable inductor is connected to the contact node of the test on-load tap changer.

6. The contact detection method for an on-load tap changer according to claim 3 or 4, characterized in that, The on-load tap changer testing system also includes: a high-voltage switchgear; The input terminal of the high-voltage switchgear is used to connect to a three-phase power supply, and the output terminal of the high-voltage switchgear is used to connect to the three-phase input terminal of the voltage regulator. The control acquisition terminal of the high-voltage switchgear is connected to the control acquisition device.

7. The contact detection method for an on-load tap changer according to any one of claims 2-4, characterized in that, The regression prediction model is trained based on the training sample set to obtain the trained regression prediction model, including: Based on the training sample set, the first and second parameters of the regression prediction model are iteratively optimized to obtain the optimal solutions for the first and second parameters. The optimal solutions for the first parameter and the second parameter are applied to the regression prediction model, and the training sample set is input into the regression prediction model for model training to obtain a trained regression prediction model.

8. A contact detection device for an on-load tap changer, characterized in that, include: The acquisition module is used to acquire the stage voltage, operating current, transition resistance, bridging time, and number of switching operations when the on-load tap changer is in operation. The prediction module is used to input the stage voltage, the operating current, the transition resistance, the bridging time, and the number of switching times into a pre-trained regression prediction model to obtain the change in contact resistance and mass loss of the contacts in the on-load tap changer. The regression prediction model determines the actual contact resistance and quality loss of the switch contacts based on the voltage, current, transition resistance, bridging time, and number of switching operations when the switch is in operation. The determination module is used to determine the degree of erosion of the contacts in the on-load tap changer based on the actual contact resistance and mass loss of the contacts in the on-load tap changer. Determining the degree of contact erosion based on the actual contact resistance and the mass loss includes: When the actual contact resistance is greater than the first preset value, or the mass loss is greater than the second preset value, the degree of erosion of the contact is determined to be severe erosion. When the actual contact resistance is less than or equal to a first preset value and the mass loss is less than or equal to a second preset value, the initial contact resistance of the contact is obtained, and the contact resistance loss is calculated based on the initial contact resistance and the actual contact resistance. Calculate the ratio of the contact resistance loss to the initial contact resistance, and determine the ratio as the contact resistance index; The degree of erosion of the contact is determined based on the contact resistance index and the mass loss. Determining the degree of erosion of the contact based on the contact resistance index and the mass loss includes: When the contact resistance index is less than a third preset value and the mass loss is less than or equal to a fourth preset value, the degree of erosion of the contact is determined to be mild erosion; the fourth preset value is less than the second preset value. When the contact resistance index is less than a third preset value, the mass loss is greater than a fourth preset value, and the mass loss is less than or equal to a second preset value, the degree of erosion of the contact is determined to be moderate erosion. When the contact resistance index is greater than or equal to the third preset value, and the contact resistance index is less than the fifth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be moderate erosion. When the contact resistance index is greater than or equal to the fifth preset value and the mass loss is less than the sixth preset value, the degree of erosion of the contact is determined to be moderate erosion; the sixth preset value is less than the second preset value and the sixth preset value is greater than the fourth preset value; When the contact resistance index is greater than or equal to the fifth preset value, the mass loss is greater than or equal to the sixth preset value, and the mass loss is less than or equal to the second preset value, the degree of erosion of the contact is determined to be severe erosion.

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