A method for evaluating the ablation state of SF6 circuit breaker contacts

Abstract

The application discloses an evaluation method for a SF6 circuit breaker contact ablation state, and the method comprises the following steps: acquiring a dynamic capacitance simulation curve of a SF6 circuit breaker contact fracture; calculating a dynamic capacitance measurement curve of the SF6 circuit breaker contact fracture through a capacitance measurement loop; inputting the dynamic capacitance simulation curve and the dynamic capacitance measurement curve into a preset BP neural network to acquire the ablation state of the SF6 circuit breaker contact. The application combines theoretical calculation with experimental measurement, verifies the rationality of the dynamic capacitance curve, adopts a BP neural network intelligent prediction algorithm to process data, deeply mines information of the dynamic capacitance curve, avoids interference of human factors on the result, and improves the objectivity and accuracy of evaluation of the high-voltage SF6 circuit breaker contact ablation state.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage SF6 circuit breaker insulation performance evaluation, in particular to an evaluation method for the ablation state of SF6 circuit breaker contacts. BACKGROUND

[0002] Currently, researchers have used the dynamic resistance-travel curve in the process of opening to assist in judging the ablation state of the contacts. Generally, the dynamic resistance refers to the resistance calculated by measuring the loop current and the voltage across the arc extinguishing chamber during the breaking process. Since the electrical contact performance of the circuit breaker contacts changes during the movement process, it is different from the static main loop resistance. The resistance value fluctuates within the measurement duration, and rich contact state information can be extracted. The dynamic resistance value is only in the micro-ohm level, which requires extremely high measurement accuracy. Generally, four-wire method is used to eliminate the interference of current lead resistance. However, different measurement models of circuit breakers or different test currents will cause measurement errors. Currently, it is still in the stage of technical research and has not been widely recognized. There are still many problems to be overcome before it can be put into field application. The dynamic resistance curve focuses on the period from the beginning of separation to the complete separation of the contacts. Then, until the end of the contact travel, the gap between the contacts is not fully utilized. The resistance between the breaks in this stage is the resistance of the SF6 insulating medium, which is extremely large and has no reference value. Then, there is a capacitance between the breaks in this stage, which decreases with the decreasing gap. The ablation of the contacts reduces the relative area between the two breaks, and the SF6 gas also produces some relative dielectric constant impurities in the process of ablation, which will cause the dynamic capacitance curve of the circuit breaker breaks to change under different contact ablation states. Therefore, it is necessary to propose an evaluation method for the ablation state of SF6 circuit breaker contacts, which uses the characteristic parameters in the whole breaking process to more accurately predict the insulation performance of SF6 circuit breakers. SUMMARY

[0003] The present application provides an evaluation method for the ablation state of SF6 circuit breaker contacts. The present application combines theoretical calculation with experimental measurement to verify the rationality of the dynamic capacitance curve. The BP neural network intelligent prediction algorithm is used to process data, which can deeply mine the information of the dynamic capacitance curve, avoid the interference of human factors on the results, and improve the objectivity and accuracy of evaluating the ablation state of high-voltage SF6 circuit breaker contacts.

[0004] The present application provides an evaluation method for the ablation state of SF6 circuit breaker contacts, which comprises:

[0005] Obtaining a dynamic capacitance simulation curve of the SF6 circuit breaker contact breaks;

[0006] Calculating a dynamic capacitance measurement curve of the SF6 circuit breaker contact breaks through a capacitance measurement loop;

[0007] The to-be-tested capacitance curve is input into a preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact.

[0008] Optionally, before the to-be-tested capacitance curve is input into the preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact, the method further comprises:

[0009] The capacitance measurement curve is taken as a test sample set, and the test sample set is divided into a training set and a verification set;

[0010] The training set is input into an initial BP neural network for training to obtain a trained BP neural network;

[0011] The verification set is input into the trained BP neural network for verification to obtain a preset BP neural network.

[0012] Optionally, the obtaining of the dynamic capacitance simulation curve of the SF6 circuit breaker contact fracture comprises:

[0013] The dynamic capacitance simulation curve of the SF6 circuit breaker contact fracture is obtained through a preset two-dimensional axisymmetric simulation calculation model.

[0014] Optionally, after the capacitance measurement curve of the SF6 circuit breaker contact fracture is calculated through the capacitance measurement circuit, the method further comprises:

[0015] It is judged whether the curve trend of the capacitance measurement curve and the capacitance simulation curve is consistent;

[0016] The to-be-tested capacitance curve is input into a preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact, comprising:

[0017] If yes, the to-be-tested capacitance curve is input into a preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact.

[0018] Optionally, after it is judged whether the curve trend of the capacitance measurement curve and the capacitance simulation curve is consistent, the method further comprises:

[0019] If no, the capacitance measurement curve of the SF6 circuit breaker contact fracture is recalculated.

[0020] From the above technology: obtain the dynamic capacitance simulation curve of the SF6 circuit breaker contact fracture; calculate the dynamic capacitance measurement curve of the SF6 circuit breaker contact fracture through the capacitance measurement loop; input the dynamic capacitance simulation curve and the dynamic capacitance measurement curve into a preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact. The present application combines theoretical calculation with experimental measurement to verify the rationality of the dynamic capacitance curve, uses a BP neural network intelligent prediction algorithm to process data, can deeply mine the information of the dynamic capacitance curve, avoids the interference of human factors on the results, and improves the objectivity and accuracy of evaluating the ablation state of the high-voltage SF6 circuit breaker contact. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a simulation model structure diagram of the present application;

[0022] Figure 2 It is a theoretical basis analysis diagram of the present application;

[0023] Figure 3 It is a measurement and analysis circuit arrangement diagram of the present application;

[0024] Figure 4 It is a preset BP neural network structure diagram of the present application;

[0025] Figure 5 It is a flowchart of an embodiment of the SF6 circuit breaker contact ablation state evaluation method in the present application. DETAILED DESCRIPTION

[0026] The embodiment of the present application provides an SF6 circuit breaker contact ablation state evaluation method, which combines theoretical calculation with experimental measurement to verify the rationality of the dynamic capacitance curve, uses a BP neural network intelligent prediction algorithm to process data, can deeply mine the information of the dynamic capacitance curve, avoids the interference of human factors on the results, and improves the objectivity and accuracy of evaluating the ablation state of the high-voltage SF6 circuit breaker contact.

[0027] Please refer to Figures 1 to 5 The SF6 circuit breaker contact ablation state evaluation method in the embodiment of the present application includes:

[0028] 101. Obtain the dynamic capacitance simulation curve of the SF6 circuit breaker contact fracture through a preset two-dimensional axisymmetric simulation calculation model;

[0029] In order to simplify the calculation, considering that the structure of the arc extinguishing chamber is an axisymmetric structure, a preset two-dimensional axisymmetric calculation model is used to reduce the calculation amount; in combination with Figure 1As shown, in order to reduce the non-linear degree of calculation, the right part symmetrical to the symmetry axis 8 is described; priority is given to the simultaneous movement of the static arc contact 1 and the static main contact 2, and the dynamic arc contact 4 and the dynamic main contact 3 and the large nozzle 5 and the small nozzle 6 remain stationary; when measuring, the current is small, and no arc is generated during the breaking process, but the movement of the contacts and the compression of the pressure cylinder still cause the SF6 arc-extinguishing medium 7 to change the local pressure. When calculating the capacitance simulation curve, the electric field and the flow field are considered, but the coupling between the two is not considered.

[0030] The capacitance simulation curve of the SF6 circuit breaker contact breaking dynamics is calculated, specifically:

[0031] 1> Static electric field calculation: the arc contact is applied with a 1V potential terminal, and the static contact is applied with a 0V ground, then the entire medium space satisfies:

[0032]

[0033] In the formula: is the potential, V.

[0034] The constitutive relation of D-E is considered:

[0035] D = ε0ε r E (2)

[0036] In the formula: D is the electric displacement vector. ε0 is the vacuum dielectric constant, 8.854187817×10-12 F / m; ε r is the relative dielectric constant, no mass.

[0037]

[0038] In the formula: ρ v is the charge density of the space body.

[0039] The above three formulas are the basis for solving the static electric field, and the electric field value and potential of any point in the space can be obtained. According to the definition formula of capacitance, the following formula is calculated:

[0040] C = Q / U (4)

[0041] In the formula: Q is the charge amount; U is the potential difference.

[0042] 2> Boundary physical condition setting: the initial pressure value of the SF6 gas in the arc-extinguishing chamber is set to 0.5 MPa, and the corresponding cylinder internal pressure change curve is set according to the measured internal pressure change of the pressure cylinder during the no-load breaking of the manufacturer. According to the measured contact moving speed and opening distance during the breaking process of the manufacturer, the moving speed and stroke size of the corresponding contact are set.

[0043] 3> flow field calculation: for the flow field in the arc extinguishing chamber, it has the characteristics of transonic, compressible, viscous, and complex boundary conditions of flow path, etc., two-dimensional compressible Navier-Stokes equation set and k-ε turbulence equation are used to describe, in which N-S is composed of mass conservation equation, momentum conservation equation and energy conservation equation, and k-ε turbulence equation is composed of turbulence kinetic energy equation and turbulence dissipation equation.

[0044] The mass conservation equation of N-S equation in two-dimensional cylindrical coordinate system is:

[0045]

[0046] In the formula: is the material derivative, which is physically the rate of change of a SF6 fluid micro-cluster over time; ρ is the SF6 gas density; v r , v θ , v z are the flow velocities of the fluid micro-cluster in the r, θ, and z axis directions respectively; r is the coordinate axis, is the reciprocal of the r-axis coordinate value.

[0047] The momentum conservation equation is:

[0048]

[0049]

[0050] In the formula: F r , F θ , F z are the projections of the volume force in the r, θ, and z axis directions respectively; μ is the gas dynamic viscosity coefficient; is the second dynamic viscosity coefficient.

[0051] The energy conservation equation is:

[0052]

[0053] In the formula: h is the gas enthalpy value; k is the gas thermal conductivity; C p is the gas constant pressure heat capacity; Q is the unit volume arc energy term, which is not considered during measurement.

[0054] Turbulence kinetic energy equation:

[0055]

[0056] Turbulence dissipation equation:

[0057]

[0058] μ t =C μ ρk2 / ε (12)

[0059] Where: k is the turbulent kinetic energy; ε is the turbulent dissipation power; C1, C2, C μ 、C K 、C ε is an empirical constant in the turbulence model.

[0060] 4> According to formula 4, the dynamic capacitance value between the fractures under the contact movement distance of each time step is calculated, and a dynamic capacitance-stroke curve, that is, a capacitance simulation curve, is drawn.

[0061] 5> Change the contact ablation angle in the model, repeat steps 1> to 4>, record the different ablation states, and obtain the dynamic capacitance-stroke curve, that is, the capacitance simulation curve.

[0062] 102. Calculate the capacitance measurement curve of the SF6 circuit breaker contact break dynamics through the capacitance measurement circuit;

[0063] See Figure 3 The fracture capacitance is on the order of magnitude of 10-100pF. The charge on the capacitor plates has an obstructive effect (resistance) on the directional movement of charges. Alternating current can pass through the capacitor, but it also has a certain obstructive effect. The higher the frequency of the alternating current, the smaller the capacitance obstruction. Since the capacitance of the capacitor is extremely small, a high-frequency power supply is required to measure the capacitance value. The fracture dynamic capacitance detection module consists of a high-frequency signal test power supply and a high-speed acquisition module. A high-frequency test signal power supply is applied between the fractures of the circuit breaker to control the circuit breaker to perform closing and opening operations, measure the fracture voltage and current, and the movement stroke of the circuit breaker contacts, measure the fracture capacitance-time and stroke-time waveforms, and calculate the fracture capacitance-stroke curve. The measuring device is equipped with a Bluetooth wireless data transmission interface, and the measurement data is collected, analyzed, displayed, and managed by a handheld device via Bluetooth.

[0064] In this embodiment, the capacitance measurement circuit is a dynamic capacitance measurement circuit for a high-voltage SF6 circuit breaker. A high-frequency signal power supply is used to output a stable 100V amplitude and 1-10MHz frequency signal. Since the port capacitance value is tens or hundreds of pF, the minimum current that can be measured in the final circuit is at the 10-1A level. The power supply is connected to both ends of the high and low voltage terminal blocks of the circuit breaker. Specifically:

[0065] Calculate the capacitance measurement curve of the SF6 circuit breaker contact break dynamics through the capacitance measurement circuit:

[0066] 1> Use a high-frequency acquisition card to collect the loop current value after the contacts are separated;

[0067] 2> apply high-frequency test signal power between the breaking gap of the circuit breaker, control the circuit breaker to perform the on-off operation, measure the gap voltage and current and the breaking gap movement stroke of the circuit breaker; further transmit the power voltage data and loop current data to the handheld data collection and analysis device by using the Bluetooth transmission module. The device automatically synchronizes the time sequence data of the voltage and current, calculates the capacitance value at each time by using formula (13), and converts the capacitance value into the capacitance-stroke curve, i.e. the capacitance measurement curve, according to the movement speed of the contact, and formula (13) is as follows:

[0068]

[0069] 103, determine whether the curve trend of the capacitance measurement curve is consistent with that of the capacitance simulation curve; if not, execute step 102; if yes, execute step 104;

[0070] In order to further determine that the capacitance measurement curve is more in line with the theory, so that the evaluation result is more accurate, since the capacitance simulation curve is obtained by theoretical calculation, i.e. the capacitance simulation curve is a theoretical curve, therefore, the curve trend of the capacitance measurement curve is compared with that of the capacitance simulation curve, when the curve trend of the capacitance measurement curve is consistent with that of the capacitance simulation curve, it indicates that the capacitance measurement curve is in line with the rationality; if the curve trend of the capacitance measurement curve is not consistent with that of the capacitance simulation curve, it indicates that the capacitance measurement curve is not in line with the rationality, when it is determined that the capacitance measurement curve is not in line with the rationality, the SF6 circuit breaker is adjusted, and step 102 is returned to recalculate the capacitance measurement curve of the SF6 circuit breaker contact breaking gap, until the capacitance measurement is in line with the rationality.

[0071] 104, if yes, the capacitance measurement curve is taken as a test sample set, and the test sample set is divided into a training set and a verification set;

[0072] When it is determined that the capacitance measurement curve is in line with the rationality, the capacitance measurement curve is taken as a test sample set before step 106 of training the initial BP neural network is executed; since the trained BP neural network needs to be verified after the initial BP neural network is trained, in the embodiment, the test sample set is divided into a training sample set and a verification sample set, wherein the training sample set includes a first training sample and a second training sample; the verification sample set includes a first verification sample and a second verification sample.

[0073] In the embodiment, the training sample set can contain the sample content of the verification sample set; the verification sample set can also contain the sample content of the training sample set, which is not specifically limited here.

[0074] 105, input the training set into the initial BP neural network to train and obtain a trained BP neural network;

[0075] Reference Figure 4, artificial neural network can find the mathematical relationship between the input parameters and the output parameters based on its own characteristics, without having to provide accurate mathematical expressions as other methods do, while ensuring good accuracy. Neural networks have good processing capacity for complex nonlinear problems with multiple inputs and outputs, and can build a relationship model between dynamic capacitance parameters and contact state indicator parameters to achieve the goal of circuit breaker contact state evaluation.

[0076] The training set is input into the initial BP neural network for training, specifically:

[0077] 1> From the capacitance measurement curves under different ablation states, the following parameters are extracted: (1) the capacitance value at the moment of contact separation (maximum value); (2) the stroke position where the maximum capacitance value appears; (3) the average capacitance value; (4) the area enclosed by the capacitance and the stroke.

[0078] 2> The data of (1), (2), and (3) of the training sample set are input into the initial BP neural network to obtain the evaluation result of the SF6 contact state;

[0079] 3> Determine whether the above evaluation result meets the preset result. If yes, it is determined that the training BP neural network tends to be stable, and step 106 is performed. If not, adjust the parameters of the training BP neural network and re-input the training sample set into the adjusted BP neural network.

[0080] 106, input the verification set into the training BP neural network for verification to obtain the preset BP neural network;

[0081] When the training BP neural network tends to be stable through the training set, in order to further determine the stability of the training BP neural network, the verification set is input into the training BP neural network, and the verification effect of the training BP neural network is verified. The verification effect is compared with the prediction effect. If the relative error is not more than 10%, it is considered that the training is completed, that is, the preset BP neural network is determined. If it exceeds, more capacitance measurement curves are obtained in step 102, and the BP neural network is retrained.

[0082] 107, input the dynamic capacitance curve of the SF6 circuit breaker contact fracture to be measured into the preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact.

[0083] When the preset BP neural network is determined, the dynamic capacitance curve to be measured of the SF6 circuit breaker contact fracture is obtained, and the capacitance curve to be measured is input into the preset BP neural network to obtain the output evaluation result, that is, the ablation state of the SF6 circuit breaker contact.

[0084] The application proposes to use the dynamic capacitance curve of the high-voltage SF6 circuit breaker port to evaluate the contact ablation state, and finally obtain the insulation breaking performance of the circuit breaker. The evaluation method can better utilize the information after the contact separation in the breaking process, can assist the dynamic resistance curve, and can more accurately judge the contact ablation state. The evaluation method of the SF6 circuit breaker contact ablation state proposed by the application has a clear evaluation process, is progressive, combines theoretical calculation and experimental measurement, verifies the rationality of the dynamic capacitance curve, processes data by using the BP neural network intelligent prediction algorithm, can deeply mine the information of the dynamic capacitance curve, avoids the interference of human factors on the result, and has important significance for the evaluation of the high-voltage SF6 circuit breaker contact ablation state.

[0085] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described system, device and unit can refer to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0086] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of the units is only a logical function division, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

[0087] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or can be distributed on a plurality of network units. According to actual needs, part or all of the units can be selected to achieve the purpose of the embodiment scheme.

[0088] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0089] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM, read-only memory), a random access memory (RAM, random access memory), a magnetic disk or an optical disk, and various media that can store program codes.

Claims

1. A method of evaluating the arcing condition of SF6 circuit breaker contacts, characterized by, The method comprises the steps of: obtaining a dynamic capacitance simulation curve of a SF6 circuit breaker contact fracture through a preset two-dimensional axisymmetric simulation calculation model; calculating a dynamic capacitance measurement curve of the SF6 circuit breaker contact fracture through a capacitance measurement circuit; determining whether the curve trend of the capacitance measurement curve and the capacitance simulation curve is consistent; if yes, inputting a to-be-tested capacitance curve into a preset BP neural network to obtain an ablation state of the SF6 circuit breaker contact; if no, recalculating the dynamic capacitance measurement curve of the SF6 circuit breaker contact fracture; before the step of inputting the to-be-tested capacitance curve into the preset BP neural network to obtain the ablation state of the SF6 circuit breaker contact, the method further comprises the steps of: taking the capacitance measurement curve as a test sample set, and dividing the test sample set into a training set and a verification set; inputting the training set into an initial BP neural network to obtain a trained BP neural network; inputting the verification set into the trained BP neural network to obtain a preset BP neural network; the step of inputting the training set into the initial BP neural network to obtain the trained BP neural network comprises the steps of: extracting a maximum capacitance value at a contact separation moment, a stroke position at which the maximum capacitance value appears, an average capacitance value, and a capacitance and stroke surrounding area from the capacitance measurement curves under different ablation states; inputting the maximum capacitance value at the contact separation moment, the stroke position at which the maximum capacitance value appears, and the average capacitance value of the training sample set into the initial BP neural network to obtain an evaluation result of the SF6 contact state; determining whether the evaluation result meets a preset result, if yes, determining that the trained BP neural network tends to be stable, and performing the next step; if no, adjusting a parameter of the trained BP neural network, and inputting the training sample set into the adjusted BP neural network again.

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