CN114460423A - Method and device for correcting frequency domain dielectric spectrum curve and computer equipment - Google Patents
Method and device for correcting frequency domain dielectric spectrum curve and computer equipment Download PDFInfo
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Abstract
The application relates to a method, an apparatus, a computer device, a storage medium and a computer program product for correcting frequency domain dielectric spectrum curves. The method for correcting the frequency domain dielectric spectrum curve comprises the following steps: respectively acquiring first test data of dielectric loss curves of sleeves at different constant temperatures; acquiring nonlinear relations between a plurality of characteristic parameter values and temperature in a preset dielectric relaxation model according to the first test data; obtaining the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing under the time-varying temperature according to the dielectric relaxation model and the nonlinear relation; and according to an Arrhenius formula and the corresponding relation between the test frequency point and the equivalent temperature, performing translational correction on the frequency point of the frequency domain dielectric spectrum curve at the time-varying temperature.
Description
Technical Field
The application relates to the technical field of oil paper insulation, in particular to a method and a device for correcting a frequency domain dielectric spectrum curve and computer equipment.
Background
Frequency Domain Spectroscopy (FDS) technology is widely used in the state diagnosis of oil-paper insulated power equipment. However, since the frequency domain dielectric spectrum curve is tested in a low frequency band for a long time, the temperature of the device is often in dynamic change during the test process, and the existing evaluation database is established based on the constant temperature frequency domain dielectric spectrum curve, and a result of using the time-varying temperature frequency domain dielectric spectrum curve to evaluate the insulation state has certain errors.
Disclosure of Invention
In view of the above, it is necessary to provide a correction method, an apparatus, a computer device, a computer readable storage medium, and a computer program product capable of correcting a time-varying temperature frequency-domain dielectric spectral curve to a frequency-domain dielectric spectral curve under a constant temperature condition, in view of the above technical problems.
A method of correcting a frequency domain dielectric spectral curve, comprising:
respectively acquiring first test data of medium loss curves of sleeves at different constant temperatures;
acquiring nonlinear relations between a plurality of characteristic parameter values and temperature in a preset dielectric relaxation model according to the first test data;
obtaining equivalent temperature corresponding to each test frequency point of a medium loss curve of a sleeve at a time-varying temperature according to the dielectric relaxation model and the nonlinear relation;
and according to an Arrhenius formula and the corresponding relation between the test frequency point and the equivalent temperature, performing translational correction on the frequency point of the frequency domain dielectric spectrum curve at the time-varying temperature.
In one embodiment, the obtaining, according to the dielectric relaxation model and the nonlinear relationship, an equivalent temperature corresponding to each test frequency point of a dielectric loss curve of a casing at a time-varying temperature includes:
respectively acquiring expressions of a real part and an imaginary part of a complex dielectric constant according to the dielectric relaxation model;
and solving the real part and the imaginary part of the complex dielectric constant by a least square method according to the nonlinear relation so as to obtain the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing at the time-varying temperature.
In one embodiment, before solving the real part and the imaginary part of the complex permittivity by a least square method according to the nonlinear relationship, the method further includes:
constructing an equivalent scaling model of the casing;
and carrying out heat conduction analysis according to the equivalent scaling model to obtain a heat dissipation equation of the sleeve, wherein the heat dissipation equation is used for representing the relation between the heat dissipation time and the insulation temperature inside the sleeve.
In one embodiment, the solving the real part and the imaginary part of the complex permittivity by a least squares method according to the nonlinear relationship comprises:
acquiring the simulation temperature of a target moment according to the heat dissipation equation;
and taking the simulation temperature as an initial value of a least square method, and solving a real part and an imaginary part of the complex dielectric constant through the least square method based on the initial value.
In one embodiment, the obtaining a nonlinear relationship between a plurality of characteristic parameter values in a preset dielectric relaxation model and temperature according to the first test data includes:
obtaining a plurality of characteristic parameter values in a dielectric relaxation model through a heuristic algorithm according to the first test data;
and acquiring a plurality of nonlinear relations between the characteristic parameters and the temperature by adopting a cubic spline interpolation function.
In one embodiment, the method further comprises the following steps:
acquiring second test data of a medium loss curve of the sleeve at the time-varying temperature;
and comparing the second test data with the frequency domain dielectric spectrum curve after the translation correction so as to verify the accuracy of the correction method.
A device for correcting a frequency domain dielectric spectrum curve, comprising:
the data acquisition module is used for respectively acquiring first test data of medium loss curves of the sleeves at different constant temperatures;
the nonlinear relation operation module is used for acquiring nonlinear relations between a plurality of characteristic parameter values and temperatures in a preset dielectric relaxation model according to the first test data;
the equivalent temperature acquisition module is used for acquiring equivalent temperature corresponding to each test frequency point of a medium loss curve of the casing at the time-varying temperature according to the dielectric relaxation model and the nonlinear relation;
and the translation correction module is used for performing translation correction on the frequency points of the frequency domain dielectric spectrum curve at the time-varying temperature according to the Arrhenius formula and the corresponding relation between the test frequency points and the equivalent temperature.
A computer device comprising a memory storing a computer program and a processor implementing the steps of the method described above when executing the computer program.
A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the above-mentioned method.
A computer program product comprising a computer program which, when executed by a processor, carries out the steps of the method described above.
According to the frequency domain dielectric spectrum curve correction method, the frequency domain dielectric spectrum curve correction device, the computer equipment, the storage medium and the computer program product, the preset dielectric relaxation model can be trained by providing a constant temperature environment and respectively acquiring the first test data at each constant temperature, so that specific values of a plurality of characteristic parameters in the preset dielectric relaxation model are acquired, and the accurate dielectric relaxation model is further acquired. The equivalent temperature corresponding to each test frequency point can be obtained based on the dielectric relaxation model and the nonlinear relation, and the test frequency points of the data obtained under the time-varying temperature condition can be translated by obtaining the equivalent temperature, so that an accurate frequency domain dielectric spectrum curve under the constant temperature condition is provided.
Drawings
FIG. 1 is a tan delta-f plot under constant temperature versus time varying temperature conditions for one embodiment;
FIG. 2 is a flowchart illustrating a method for calibrating a frequency-domain dielectric spectrum according to an embodiment;
FIG. 3 is a schematic illustration of an exemplary experimental platform;
FIG. 4 is a tan delta-f curve at different constant temperatures for one embodiment;
FIG. 5 is a C' -f curve at different constant temperatures for one embodiment;
FIG. 6 is a C "-f curve at different constant temperatures for one embodiment;
FIG. 7 is a diagram illustrating particle movement rules of the PSO algorithm;
FIG. 8 is a cloud of temperature profiles of the bushing at 180 minutes of heat dissipation according to one embodiment;
FIG. 9 is a graph of bushing capacitor core temperature as a function of time for one embodiment;
FIG. 10 is a graph comparing casing temperature versus time to a simulated curve for one embodiment;
FIG. 11 is a plot of frequency domain dielectric spectrum under time varying temperature conditions in accordance with an embodiment;
FIG. 12 is a graph illustrating the calibration results for an embodiment with a reference temperature of 30 ℃;
FIG. 13 is a graph illustrating the calibration results for an exemplary base temperature of 60 ℃;
FIG. 14 is a graph illustrating the calibration results for an embodiment with a reference temperature of 90 ℃;
FIG. 15 is an internal block diagram of a computer device according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
In the related art, in order to obtain an accurate frequency domain dielectric spectrum curve, the insulation characteristics of different insulating oils at different constant temperatures can be researched by adopting a frequency domain dielectric spectroscopy, and the frequency dependence of the dielectric response of the insulating oils can be characterized based on the activation energy. The influence of temperature on the nonlinear conductivity loss characteristic of the low-frequency band of the oil paper insulation can be researched by preparing samples with different moisture degrees and aging degrees. The effect of water and temperature in the casing on the frequency domain dielectric spectral curve can also be discussed, and a curve correction method based on a compensation factor is proposed to calibrate the frequency domain dielectric spectral curve at other steady-state temperatures to the reference temperature condition.
However, the above studies are all based on the evaluation method of the frequency domain dielectric spectrum curve at the steady state temperature. Under actual conditions, the field environment is complex, and is particularly affected by external environments such as regions, climate and the like. Therefore, when the dielectric response data is acquired during shutdown and maintenance, the equipment is often in a dynamic cooling process, the test period of the low-frequency band is long, and the complete test flow usually takes about 1 hour. Furthermore, because the "time window" for field service is short and the time for performing the dielectric response test is limited, it is not possible to perform the dielectric response evaluation after the temperature of the casing has stabilized. For the reasons, when the dielectric response test is performed under the working condition, the difference between the initial temperature and the ending temperature is large, and the frequency domain dielectric spectrum curve under the test curve and the steady-state temperature has large deviation.
Specifically, fig. 1 is a tan δ -f curve under the conditions of constant temperature and time-varying temperature according to an embodiment, referring to fig. 1, the frequency domain dielectric spectrum curve has fewer test frequency points in the high frequency band, and accordingly, the test time is shorter, and the temperature is basically unchanged. Therefore, the time-varying temperature profile is less different from the constant temperature profile in the high frequency band. As the test frequency decreases, the temperature begins to decrease, and the time-varying temperature profile has a tendency to move to the left, with increasing difference from the constant temperature profile. This is because the carrier mobility in the oil paper insulation is greatly reduced in the heat dissipation process, which results in the low-frequency band conductance loss being reduced and the curve being shifted to the left. The low-frequency band of the frequency domain dielectric spectrum curve is closely related to the damp aging state of the oil paper insulation, so that the accuracy of the insulation state evaluation result is reduced by the difference of the low-frequency band of the curve. In addition, because the traditional evaluation database of the frequency domain dielectric spectrum curve is often constructed based on a constant temperature curve, the time-varying temperature curve needs to be corrected to the constant temperature curve under the working condition, and the insulation state of the power equipment can be accurately evaluated. Meanwhile, since the conventional evaluation database is established based on a constant temperature profile, the time-varying temperature profile needs to be corrected to a constant temperature condition for effective insulation evaluation.
Therefore, an embodiment of the present application provides a method for correcting a frequency-domain dielectric spectrum curve, fig. 2 is a flowchart illustrating a method for correcting a frequency-domain dielectric spectrum curve according to an embodiment, and referring to fig. 2, in the embodiment, the method for correcting a frequency-domain dielectric spectrum curve includes steps S100 to S400.
S100, first test data of dielectric loss curves of the sleeves at different constant temperatures are respectively obtained.
Fig. 3 is a schematic diagram of an experimental platform according to an embodiment, and referring to fig. 3, the casing may be subjected to frequency domain dielectric spectrum curve tests at different constant temperatures through the experimental platform to obtain first test data of dielectric loss curves of the casing at different constant temperatures. The water content of the sleeve may be 0.56%, for example. Specifically, the bushing may be vertically placed in an oven with a constant temperature and humidity, and connected to a frequency domain dielectric spectroscopy (FDS) tester and a PC controller through an interface provided in an outer shell of the oven, and a high-voltage end and a testing end are respectively connected to a guide rod and a tail screen of the bushing through electrodes embedded in the oven for testing. Based on the experiment platform, the temperature in the oven can be controlled through the PC controller, and the data output by the frequency domain dielectric spectrum tester is analyzed, so that the first test data of the sleeve can be obtained.
Exemplary assay temperatures may include, but are not limited to, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃. Specifically, the temperature was adjusted by means of a gradient temperature rise, and the measurement was performed after 5 hours of stabilization at each temperature. FIG. 4 is a tan delta-f curve at different constant temperatures of an embodiment, FIG. 5 is a C' -f curve at different constant temperatures of an embodiment, and FIG. 6 is a C "-f curve at different constant temperatures of an embodiment. Referring to fig. 4, tan δ -f curves at different temperatures have significant intersections in the middle and high frequency bands. the low frequency portion of the tan delta-f curve, where the frequency is less than the intersection point, increases dielectric loss with increasing temperature. the high frequency portion of the tan delta-f curve, where the frequency is greater than the intersection point, decreases in dielectric loss with increasing temperature. the tan delta-f curve as a whole follows a translational trend. Referring to fig. 5, for the C' -f curve, as the temperature increases, the curve shows a significant upwarp in the low frequency part. There are two main reasons for this upwarping, one of which is that the temperature increase reduces the time constant for interfacial polarization between the oiled papers, which is accomplished in a shorter time. Secondly, according to the low-frequency dispersion theory, the recombination and dissociation of ions in the high-frequency band tend to be balanced in the oscillation process, and a part of ions are blocked and bound due to the increase of the stroke along with the reduction of the frequency, so that the real part of the complex capacitance is increased. And the temperature aggravates the recombination and dissociation of ions, so that the low-frequency dispersion is more obvious. Referring to FIG. 6, the C "-f curve reflects the conductance loss and polarization loss of the oiled paper insulation, and has the same trend as the tan delta-f curve. The low frequency portion of the C "-f curve reflects mainly the conduction losses, which greatly increases the mobility of the carriers in the oilpaper insulation due to the increase in temperature. Polarization loss is mainly reflected in the high-frequency part of the C' -f curve, the molecular thermal motion is intensified due to the increase of temperature, the molecular steering polarization difficulty is increased, and the polarization loss is reduced.
S200, acquiring nonlinear relations between a plurality of characteristic parameter values and temperature in a preset dielectric relaxation model according to the first test data.
Wherein, the plurality of characteristic parameter values corresponding to different temperatures are different. Therefore, the accuracy of the subsequent calculation process can be effectively improved by respectively obtaining a plurality of characteristic parameter values corresponding to the temperatures. Specifically, the values of ε s, τ, α, β all differ for the frequency domain dielectric spectral curves at different temperatures. Where ε s may be expressed as a function of the microscopic polarizabilities of electron polarization ae and dipole polarization a 0. Ae is not affected by temperature because the electronic structure in the atom is independent of temperature. However, the molecules have different energies at different temperatures, and their degree of orientation polarization differs, so a0 is temperature dependent. Furthermore, relaxation of the medium is caused by energy transfer between particles within the system. That is, the higher the temperature, the faster the speed of energy transfer, and the smaller the relaxation time τ. The energy of the particles is distributed according to Boltzmann, so that the relaxation time tau has an exponential relationship with the temperature. Wherein, alpha and beta are shape parameters and have no physical significance. From this, it is possible to derive the functional relationship of the dielectric loss value and the temperature T as shown in equations (14) and (15). Wherein N is the number of independent permanent dipoles, R is the relevant atomic radius, epsilon 0 is the vacuum dielectric constant, A is the constant coefficient, U is the molecular activation energy, K is the Boltzmann constant, and K is 1.38 multiplied by 10-23J/K.
tanδ＝f(εs(T)，ε∞，τ(T)，α(T)，β(T)) (14)
S300, obtaining the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing at the time-varying temperature according to the dielectric relaxation model and the nonlinear relation.
Under the condition of time-varying temperature, the temperature of the corresponding test frequency point is not a fixed value because the time for testing the dielectric spectrum curve of the low-frequency range (0.1 Hz-1 mHz) frequency domain is long. Therefore, by obtaining the equivalent temperature in this step, the curve can be accurately temperature-corrected in the subsequent steps.
S400, according to the Arrhenius formula and the corresponding relation between the test frequency point and the equivalent temperature, the frequency point of the frequency domain dielectric spectrum curve at the time-varying temperature is subjected to translation correction.
Wherein, the Arrhenius equation (Arrhenius equation) is shown as formula (17), and the Arrhenius equation is used for translating the frequency point under the time-varying temperature to the required constant temperature condition. Wherein Ts is the corrected target temperature; f0 is the frequency corresponding to the frequency before the translation of a certain point of the frequency domain dielectric spectrum curve under the equivalent temperature Tequal; f is the frequency corresponding to the point at the temperature Ts after translation; ea is the activation energy of the insulating paper; k is the Boltzmann constant.
In this embodiment, in the above multiple steps, by providing an environment with a constant temperature and respectively obtaining first test data at each constant temperature, the preset dielectric relaxation model may be trained, so as to obtain specific values of multiple characteristic parameters in the preset dielectric relaxation model, and further obtain an accurate dielectric relaxation model. The equivalent temperature corresponding to each test frequency point can be obtained based on the dielectric relaxation model and the nonlinear relation, and the test frequency points of the data obtained under the time-varying temperature condition can be translated by obtaining the equivalent temperature, so that an accurate frequency domain dielectric spectrum curve under the constant temperature condition is provided.
In one embodiment, step S200 obtains a nonlinear relationship between a plurality of characteristic parameter values in a preset dielectric relaxation model and a temperature according to the first test data, including steps S210 to S220.
S210, obtaining a plurality of characteristic parameter values in the dielectric relaxation model through a heuristic algorithm according to the first test data.
Among them, in the classical theory of dielectrics, the dielectric process is described by using a Dybe model of a single relaxation time. But in most cases the relaxation times are distributed with the greatest probability. For this reason, in this embodiment, the dielectric relaxation model may be an H-N (Havriliak-Negami) model, which is a combination of Cole-Cole equation and Cole-Davidson function, and provides a more general function for explaining the dielectric relaxation and mechanical relaxation processes of some polymer systems. The expression of the H-N model is as shown in formula (9). Wherein j is a unit imaginary number; τ is the relaxation time constant; ε s and ε ∞ respectively represent the static permittivity and the optical frequency permittivity, α and β are shape parameters related to the relaxation time distribution, α is 0-1, and β is 0-1.
However, on one hand, an expression of the H-N model is complex, the problem that the relation between the parameters and the temperature is difficult to solve by using a traditional method belongs to NP (Non-deterministic polymeric) is solved, the solving process has the characteristics of discretization, multiple indexes, nonlinearity, uncertainty and the like, and the time cost and the space cost for simultaneously solving the multiple parameters are huge. On the other hand, the traditional method has high requirement on initial values of parameter fitting, and initial values far away from the optimal solution cause model performance degradation, so that the error of the solution result is increased.
Therefore, in the present embodiment, a heuristic PSO (Particle Swarm Optimization) algorithm is used to solve the parameters of the H-N model at different constant temperatures. The PSO algorithm has the advantages of simple algorithm flow, easy realization and less parameters to be adjusted. In the particle swarm optimization process, good development capacity can be obtained in the early stage of optimization through adjusting the relation weight coefficient, the self-learning factor and the social learning factor, the global search is favored, the good search capacity is obtained, and the local search is favored in the later stage, so that the solution precision is improved. In order to ensure the accuracy of the result, in this embodiment, the minimum mean square error between the calculated complex permittivity and the actually measured complex permittivity is used as an objective function, and the H-N model parameters are used as a solution to transform the problem into an optimization problem.
Wherein, the parameter setting of the algorithm can be as shown in table 2 in consideration of the H-N model characteristics.
TABLE 2PSO Algorithm parameters
Specifically, the PSO algorithm process is as follows. And (3) forming a particle group by n particles in the feasible region, wherein the position of each particle represents a feasible solution, and the position of the ith particle after the (k + 1) th iteration can be represented as the formula (18). The selection of parameters such as the particle self-learning factor c1, the social learning factor c2, and the maximum iteration number ngen affects the convergence speed of the PSO algorithm.
The update of the feasible solution is completed by the movement of the particle, and then the position of the ith particle after the (k + 1) th iteration under the dimension d is as shown in equation (19). Wherein x is a parameter of the H-N model, and v is the velocity of the particle swarm. The velocity of the particle population may be expressed as equation (20). Wherein ω is the inertial weight; c1 is a self-learning factor, c2 is a social learning factor; r1 and r2 are random numbers on [0,1] to increase the randomness of the search; pb is the historical best position of particle i; gb is the historical best position for the entire population of particles. Fig. 7 is a schematic diagram of a particle movement rule of the PSO algorithm, and referring to fig. 7, a movement vector of a particle is composed of an original movement direction of an individual particle, a difference value between a current position of the individual particle and a historical optimal position, and a difference value between the current position of the individual particle and a population optimal position. In the PSO algorithm, the quality of a solution is measured through the particle fitness, and a particle fitness function is defined as the formula (21). The subscript pso represents a calculated value obtained by substituting the optimal result of the particle swarm optimization into the formula (10) and the formula (11), test represents an actually measured value of the frequency domain dielectric spectrum curve, and s represents a test frequency point of the frequency domain dielectric spectrum curve.
Based on the equations (14) and (15), the corresponding 5 parameter values in the H-N model can be inverted by using the frequency domain dielectric spectrum curve data at different constant temperatures, specifically as shown in table 3, where table 3 shows a plurality of characteristic parameter values corresponding to the respective temperatures of 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃ and 90 ℃.
TABLE 3H-N model parameters at different temperatures
And S220, acquiring a nonlinear relation between a plurality of characteristic parameters and the temperature by adopting a cubic spline interpolation function. As a plurality of time-varying temperatures between 30 ℃ and 90 ℃ need to be corrected, the cubic spline interpolation can pass through a smooth curve of a series of shape-value points, and mathematically obtain a curve function group by solving a three-bending-moment equation group. Therefore, the accurate relation between each parameter of the H-N model and the temperature is constructed by adopting a cubic spline interpolation function.
In the embodiment, the PSO algorithm is used for solving the relation between the H-N model parameters and the temperature, so that the problems of discretization, nonlinearity, uncertainty and the like of the solving process caused by the complex model expression can be solved, the time cost and the space cost of calculation are reduced, and the solving precision is improved.
In one embodiment, step S300 obtains an equivalent temperature corresponding to each test frequency point of a dielectric loss curve of a casing at a time-varying temperature according to a dielectric relaxation model and a nonlinear relationship, and includes steps S310 to S320.
Step S310, respectively obtaining expressions of a real part and an imaginary part of the complex dielectric constant according to the dielectric relaxation model. According to the complex analysis theory, the expressions of the real part and the imaginary part of the complex dielectric constant are respectively expressed as an expression (10) and an expression (11) according to the expression (9).
And S320, solving the real part and the imaginary part of the complex dielectric constant through a least square method according to the nonlinear relation so as to obtain the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing at the time-varying temperature.
Specifically, from the expressions (10) and (11), an expression of the dielectric loss can be obtained as in the expression (12), in which the expression of θ is shown as in the expression (13). Further, by combining the reference equations (14) and (15), when the frequency and the dielectric loss value of a certain point of the dielectric spectrum are known, the corresponding equivalent temperature can be obtained as shown in equation (16). However, as can be seen from the reference, the equation (16) is complicated and an explicit expression thereof cannot be obtained, so in this embodiment, a Least square method (LS) is adopted for solving. The least squares method is a mathematical optimization technique. It finds the best functional match of the data by minimizing the sum of the squares of the errors. The unknown parameters of the H-N model can be easily obtained by the least square method, and the sum of squares of errors between the parameters and actual data is minimized.
Tequal＝f-1(tanδ,ω) (16)
In one embodiment, step S320 further includes steps S330 to S340 before solving the real part and the imaginary part of the complex permittivity by a least square method according to the nonlinear relationship.
And S330, constructing an equivalent scaling model of the casing.
The structure and the material of the simulation model are the same as those of the actual casing. The structure of the simulation model is determined according to a central current-carrying conductor, insulating paper, aluminum foil, transformer oil, an outer sheath, an air gap and the like. The main insulation can be equivalent to a coaxial series capacitor formed by a plurality of layers of aluminum foil electrodes, the central current-carrying conductor adopts a copper conductor with high thermal conductivity, and the shell is made of polymethyl methacrylate organic glass. The casing model parameters are shown in table 4.
TABLE 4 casing model parameters
| Number of layers of polar plate | Thickness (mm) | Upper extreme difference (mm) | Lower extreme difference (mm) | Polar plate length (mm) |
| 0 | / | / | / | 260 |
| 1 | 1.6 | 24 | 6 | 220 |
| 2 | 1.6 | 29 | 8 | 180 |
| 3 | 1.6 | 34 | 8 | 140 |
| 4 | 1.6 | 57 | 16 | 65 |
The method specifically comprises the following steps of constructing an equivalent scaling model of the casing. Constructing a two-dimensional axisymmetric model of the sleeve, carrying out model mesh subdivision, setting parameters such as constant-pressure heat capacity, heat conductivity coefficient and density aiming at materials such as guide rods, transformer oil, insulating paper and aluminum foil, designing a transient solver and simulation time, and setting a domain probe to obtain two-dimensional and three-dimensional temperature distribution cloud pictures of the sleeve. Wherein, the radius R0 of the zero screen is 16.5mm, and the length L0 is 260 mm. Meanwhile, the capacitance type oiled paper sleeve model structure comprises three substance forms of solid, liquid and gas, according to the actual sleeve operation condition, the initial oil temperature of the model is set to be 70 ℃, the initial temperature of the capacitor core is 85 ℃, and the initial temperature of the air gap and the initial temperature of the outer sheath are the same as the ambient temperature. By constructing an equivalent scaling model of the sleeve, temperature field simulation can be performed, so that an accurate temperature analysis result is obtained.
And S330, performing heat conduction analysis according to the equivalent scaling model to obtain a heat dissipation equation of the sleeve, wherein the heat dissipation equation is used for representing the relation between heat dissipation time and insulation temperature inside the sleeve.
Specifically, the casing is always subjected to power frequency alternating voltage during operation, and the overall temperature of the casing is kept constant. When the power failure is maintained, the temperature of the sleeve can be changed due to heat conduction among media, heat convection between air and the sleeve and heat radiation of the sleeve. However, the temperature obtained under the working condition is always the temperature of the sleeve oil, and the insulation temperature of the sleeve cannot be truly reflected. That is, the temperature correction can be performed by selecting the internal insulation temperature of the electrical equipment instead of the oil temperature, so that a more accurate result can be obtained. Therefore, the COMSOL finite element simulation can be applied to analyze the heat dissipation process inside the sleeve. In combination with the casing heat dissipation environment, the present embodiment mainly considers three heat dissipation processes, i.e., conduction heat dissipation, convection heat dissipation, and radiation heat dissipation.
The heat conduction and dissipation refers to a heat transfer phenomenon when molecules in a medium do not move macroscopically in a solid state, a liquid state and a gas state, and differential equations of the heat conduction and dissipation are shown in a formula (1) and a formula (2). Where T is temperature in K. x, y, z are coordinate values in m. K is a thermal conductivity coefficient in W.m < -1 > K < -1 >. Cp is constant pressure heat capacity, and the unit is J.kg-1. K-1. Rho is density and has the unit of kg.m < -3 >. t is time in units of s. Q is the heating power per unit volume, and the unit is W.m < -3 >. The parameters of each material during the simulation are shown in table 5.
TABLE 5 Heat dissipation parameters of materials
Convective heat dissipation refers to the convective heat transfer that occurs between the surface of a medium and a fluid. For the capacitance type oil paper sleeve, the outmost layer is in contact with air, and due to the fact that temperature difference exists in the vertical direction, convection heat transfer occurs due to the fact that gas flows under the action of air buoyancy, and the capacitance type oil paper sleeve belongs to natural convection heat transfer. The transformer oil is sealed in the sleeve and generates natural convection heat exchange with the sealed cavity of the sleeve. The basic equations for thermal convection are as follows mass conservation equation (3), momentum conservation equation (4), and energy conservation equation (5). Wherein nu is the speed and the unit is m/s. F is the gravitational force to which the fluid is subjected, in units of N. p is the fluid pressure in Pa. Eta is dynamic viscosity in kg.m-1.
The loss characteristic of the outer surface when dissipating heat through natural convection is generally characterized by a convection heat transfer coefficient h, which is specifically represented by formula (6). Wherein L is the object size in m. RaL and Pr are dimensionless Rayleigh and Prandtl numbers.
Radiation heat dissipation means that the surface of the sleeve also dissipates heat by radiating electromagnetic energy outwards, the heat is radiated from the heating element to the surrounding medium with lower temperature in the form of wave, and the magnitude of the heat radiation energy is related to the temperature of the sleeve and the physical property of the surface of the sleeve. The maximum radiation flux density of the surface of the object in the heat radiation process is as shown in the formula (7). Wherein Ts is the absolute temperature of the surface of the object and has a unit of K. σ is the stefan-boltzmann constant (σ ═ 5.67 × 10-8).
In this embodiment, the simulation model considers the conductive heat dissipation inside the capacitor core, the natural convection heat dissipation outside the vertical wall and the horizontal wall, and the radiation heat dissipation of the outer sheath surface to the environment, so as to obtain the temperature distribution cloud charts of the sleeve under different heat dissipation times. FIG. 8 is a cloud of temperature profiles of the bushing at 180 minutes of heat dissipation according to one embodiment, and referring to FIG. 8, the highest temperature of the bushing is present at the capacitive core and the lowest temperature is present at the apex of the outer jacket of the bushing. Along with the increase of the heat dissipation time, the temperature in the sleeve pipe is gradually reduced, and the radial temperature and the axial temperature of the capacitor core are uniformly distributed all the time in the heat dissipation process.
Fig. 9 is a graph showing a relationship between a temperature of the capacitor core of the bushing and a time, in which the relationship between a temperature of the insulation inside the bushing and a time of heat dissipation is more intuitively understood as shown in fig. 9, and the capacitor core of the bushing is selected as a research object to obtain a heat dissipation curve. As can be seen from fig. 9, as the heat dissipation time increases, the temperature of the insulation inside the bushing does not decrease at a constant rate, but rather, it shows an exponential decrease trend, with the highest temperature being the starting temperature and the lowest temperature being the ambient temperature, and the heat dissipation rate is changed from fast to slow. The heat dissipation equation of the casing can be obtained by fitting as shown in formula (8). Therefore, the insulation temperature at any time in the heat dissipation process of the sleeve can be obtained. The time-varying temperature frequency domain dielectric spectrum curve correction based on this temperature is more accurate than using oil temperature.
T＝57.42e-0.00884t+25.82 (8)
In one embodiment, the step S320 of solving the real part and the imaginary part of the complex permittivity by the least square method according to the nonlinear relationship includes steps S321 to S322.
And S321, acquiring the simulation temperature of the target moment according to the heat dissipation equation. That is, the simulated temperature at the target time is obtained by the heat dissipation equation of equation (8).
And S322, taking the simulation temperature as an initial value of a least square method, and solving a real part and an imaginary part of the complex dielectric constant through the least square method based on the initial value.
Specifically, based on the foregoing steps, the five characteristic parameter values may be replaced with a function of temperature in equations (10) - (11) to solve for the equivalent temperature. Since equation (16) cannot be expressed as an explicit expression, and the known data is more than the number of parameters to be solved. It is understood that the least squares method depends heavily on the initial value, and the selection of the initial value has a great influence on the final result. Therefore, the accuracy of the calculation result can be ensured by taking the insulation internal temperature obtained by simulation as an initial value of the least square method through the formula (8).
In one embodiment, the method for correcting the frequency-domain dielectric spectrum curve further includes steps S510 to S520.
And S510, acquiring second test data of the dielectric loss curve of the casing at the time-varying temperature.
Specifically, frequency domain dielectric spectrum curve measurement under time-varying temperature is carried out on the equivalent scaling model of the sleeve in a laboratory. In the experiment, the cannula was first placed in a constant oven, warmed to 85 ℃ and stabilized for 5 hours. And then taking out the sleeve immediately to perform frequency domain dielectric spectrum curve test, arranging two groups of T-shaped thermocouples at the guide rod of the capacitor core and in the surrounding transformer oil respectively, and monitoring the temperature change of the sleeve in the heat dissipation process. From the second test data, a time-varying profile of the casing temperature may be obtained.
S520, the second test data is compared with the frequency domain dielectric spectrum curve after the translation correction, so that the accuracy of the correction method is verified.
Specifically, fig. 10 is a comparison graph of the temperature of the casing tube varying with time and a simulation curve according to an embodiment, and referring to fig. 10, it can be seen that the shapes and corresponding values of the two curves are substantially the same, but the experimental temperature is higher than the simulation temperature. The simulation result is the temperature of the bushing capacitor core, and the insulation internal temperature cannot be tested during the experiment, so the average value of the temperature of the guide rod and the temperature of the oil is used for substitution, and the overall temperature is slightly higher than the internal insulation temperature. In addition, with the increase of the heat dissipation time, the temperature obtained by the experiment and the simulation does not decrease at a constant rate, but shows an exponential decrease trend, the highest temperature is the initial temperature, the lowest temperature is the environment temperature, and the heat dissipation rate shows a trend of changing from fast to slow. The similarity of the two curves is calculated to be 2.8909 based on the root mean square error, so that the accuracy of the simulation model and the heat dissipation characteristic of the sleeve can be verified.
In the experimental process of the present embodiment, time-varying temperature frequency domain dielectric spectrum curves of the sleeve under the heat-dissipated conditions of 25min (Case1), 84min (Case2) and 143min (Case3) are respectively tested, fig. 11 is a frequency domain dielectric spectrum curve under the time-varying temperature condition of the embodiment, and referring to fig. 11, the test result of the middle-high frequency part (5kHz to 0.1Hz) is substantially consistent with the constant temperature curve. With the reduction of the test temperature, the frequency domain dielectric spectrum curve of less than 0.1Hz in three cases has the tendency of leftward shift, and the data difference is larger compared with the constant temperature curve. The reason is that the frequency point frequency domain dielectric spectrum curve corresponding to the higher frequency has shorter test period and small temperature difference change, and the tan delta value is close to the measured value at constant temperature. Along with the reduction of the test frequency, the electric field change period under the corresponding frequency point is gradually increased, the insulation temperature of the sleeve pipe is exponentially reduced in the low-frequency band of the frequency domain dielectric spectrum curve, and the tan delta value is shifted to the left.
It can be understood that the dielectric loss in the low frequency band is mainly composed of two parts, namely, a conduction loss and a polarization loss. On one hand, the dielectric conductance current caused by the mobility of the carrier in the oil paper insulation is reduced due to the fact that the conductivity is reduced along with the temperature, and the corresponding conductance loss is in a descending trend. On the other hand, as can be seen from equation (8), the polar molecule is weak in thermal motion at a lower temperature, the relaxation time τ of the insulating medium is increased, the contribution of the relaxation polarization to the total loss is gradually reduced, and the frequency domain dielectric spectrum curve shows a left-shift trend. Therefore, in order to calibrate the time-varying temperature curve to any constant reference temperature in the three cases, the equivalent temperature of each frequency point in the low frequency band (0.1Hz to 1mHz) can be calculated by using the least square method based on the formula (16), wherein the initial temperature used in the calculation by the least square method can be obtained by simulation in the manner shown in fig. 8. The equivalent temperature (. degree. C.) at each frequency point is shown in Table 5.
TABLE 1 equivalent temperature per frequency point under time-varying temperature conditions
| (f/Hz) | 0.001 | 0.002 | 0.005 | 0.01 | 0.022 | 0.046 | 0.1 |
| Case1 | 66.184 | 68.417 | 70.514 | 71.853 | 75.842 | 78.382 | 80.195 |
| Case2 | 50.811 | 52.568 | 54.004 | 54.708 | 57.052 | 58.317 | 59.019 |
| Case3 | 37.672 | 38.243 | 40.601 | 42.212 | 43.992 | 44.45 | 44.491 |
In the present example, the time-varying temperature curves in the three cases were corrected based on the formula (17) with the reference temperatures of 30 ℃, 60 ℃ and 90 ℃, with the empirical value of 0.98eV being used for the activation energy. The calibration results are shown in fig. 12 to 14 in comparison with the frequency domain dielectric spectrum curve test results. Fig. 12 is a correction result of the reference temperature of 30 ℃ according to an embodiment, fig. 13 is a correction result of the reference temperature of 60 ℃ according to an embodiment, and fig. 14 is a correction result of the reference temperature of 90 ℃ according to an embodiment, and it can be seen from fig. 12 to fig. 14 that, compared with the test results under the reference temperature conditions of 30 ℃, 60 ℃ and 90 ℃, the test result under the time-varying temperature condition is distorted in the low frequency part, and the curve shows a left-shift trend; the correction results under the three conditions are basically consistent with the test results at the reference temperature of 30 ℃, 60 ℃ and 90 ℃, the curve coincidence degree is better, and the accuracy of the correction model is verified.
Therefore, the testing result under the time-varying temperature condition can be effectively corrected according to the proposed correction method based on the H-N model, and therefore accurate evaluation of the insulation state of the power equipment under the time-varying temperature condition is achieved. The result shows that the similarity between the temperature curve of the sleeve changing along with the time and the simulation curve is 2.8909, and the simulation accuracy is verified. Moreover, under the condition of time-varying temperature, the test result of a high-frequency band (5 kHz-0.1 Hz) in the frequency domain dielectric spectrum curve is consistent with the reference temperature curve. With the reduction of the test temperature, the low-frequency band (0.1 Hz-1 mHz) curve of the frequency domain dielectric spectrum curve has the tendency of leftward translation, and the data difference is increased compared with the constant temperature curve. Namely, the time-varying temperature curve correction method based on the H-N model can effectively correct the test result under the time-varying temperature condition.
It should be understood that, although the steps in the flowcharts related to the embodiments are shown in sequence as indicated by the arrows, the steps are not necessarily executed in sequence as indicated by the arrows. The steps are not performed in a strict order unless explicitly stated in the present embodiment, and may be performed in other orders. Moreover, at least a part of the steps in the flowcharts related to the above embodiments may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least a part of the steps or stages in other steps.
Based on the same inventive concept, the embodiment of the present application further provides a device for correcting the frequency domain dielectric spectrum curve, which is used for implementing the method for correcting the frequency domain dielectric spectrum curve. The implementation scheme for solving the problem provided by the apparatus is similar to the implementation scheme described in the above method, so specific limitations in the following embodiments of the apparatus for correcting one or more frequency-domain dielectric spectral curves can be referred to the limitations on the method for correcting the frequency-domain dielectric spectral curves, and are not described herein again. Specifically, the device for correcting the frequency domain dielectric spectrum curve comprises a data acquisition module, a nonlinear relation operation module, an equivalent temperature acquisition module and a translation correction module.
The data acquisition module is used for respectively acquiring first test data of medium loss curves of the casings at different constant temperatures. The nonlinear relation operation module is used for acquiring nonlinear relations between a plurality of characteristic parameter values in a preset dielectric relaxation model and the temperature according to the first test data. The equivalent temperature acquisition module is used for acquiring the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing under the time-varying temperature according to the dielectric relaxation model and the nonlinear relation. And the translation correction module is used for performing translation correction on the frequency points of the frequency domain dielectric spectrum curve at the time-varying temperature according to the Arrhenius formula and the corresponding relation between the test frequency points and the equivalent temperature.
The modules in the device for correcting the dielectric spectrum curve of the frequency domain can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, and the computer device may be a terminal, and the internal structure diagram thereof may be as shown in fig. 15. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless communication can be realized through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. The computer program is executed by a processor to implement a method of correcting a frequency domain dielectric spectral curve. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 15 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, a computer device is provided, comprising a memory in which a computer program is stored and a processor, which when executing the computer program, implements the method in the preceding embodiments.
In one of the embodiments, a computer-readable storage medium is provided, on which a computer program is stored, which, when being executed by a processor, carries out the method of the preceding embodiment.
In one of the embodiments, a computer program product is provided, comprising a computer program which, when executed by a processor, implements the method of the preceding embodiment.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware related to instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, database, or other medium used in the embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, high-density embedded nonvolatile Memory, resistive Random Access Memory (ReRAM), Magnetic Random Access Memory (MRAM), Ferroelectric Random Access Memory (FRAM), Phase Change Memory (PCM), graphene Memory, and the like. Volatile Memory can include Random Access Memory (RAM), external cache Memory, and the like. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others. The databases referred to in various embodiments provided herein may include at least one of relational and non-relational databases. The non-relational database may include, but is not limited to, a block chain based distributed database, and the like. The processors referred to in the embodiments provided herein may be general purpose processors, central processing units, graphics processors, digital signal processors, programmable logic devices, quantum computing based data processing logic devices, etc., without limitation.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.
Claims (10)
1. A method for correcting a frequency domain dielectric spectrum curve, comprising:
respectively acquiring first test data of medium loss curves of sleeves at different constant temperatures;
acquiring nonlinear relations between a plurality of characteristic parameter values and temperature in a preset dielectric relaxation model according to the first test data;
obtaining equivalent temperature corresponding to each test frequency point of a medium loss curve of a sleeve at a time-varying temperature according to the dielectric relaxation model and the nonlinear relation;
and according to an Arrhenius formula and the corresponding relation between the test frequency point and the equivalent temperature, performing translational correction on the frequency point of the frequency domain dielectric spectrum curve at the time-varying temperature.
2. The method for correcting a frequency-domain dielectric spectrum curve according to claim 1, wherein the obtaining an equivalent temperature corresponding to each test frequency point of a dielectric loss curve of a casing at a time-varying temperature according to the dielectric relaxation model and the nonlinear relationship comprises:
respectively acquiring expressions of a real part and an imaginary part of a complex dielectric constant according to the dielectric relaxation model;
and solving the real part and the imaginary part of the complex dielectric constant by a least square method according to the nonlinear relation so as to obtain the equivalent temperature corresponding to each test frequency point of the dielectric loss curve of the casing at the time-varying temperature.
3. The method for correcting dielectric spectrum curve of frequency domain according to claim 2, wherein before solving the real part and the imaginary part of the complex dielectric constant by the least square method according to the nonlinear relationship, the method further comprises:
constructing an equivalent scaling model of the casing;
and carrying out heat conduction analysis according to the equivalent scaling model to obtain a heat dissipation equation of the sleeve, wherein the heat dissipation equation is used for representing the relation between heat dissipation time and insulation temperature inside the sleeve.
4. The method for correcting dielectric spectrum curves of frequency domain according to claim 3, wherein said solving the real and imaginary parts of the complex permittivity by least squares based on the nonlinear relationship comprises:
acquiring the simulation temperature of a target moment according to the heat dissipation equation;
and taking the simulation temperature as an initial value of a least square method, and solving a real part and an imaginary part of the complex dielectric constant through the least square method based on the initial value.
5. The method for correcting frequency-domain dielectric spectrum curve of claim 1, wherein the obtaining the non-linear relationship between the plurality of characteristic parameter values and the temperature in the preset dielectric relaxation model according to the first test data comprises:
obtaining a plurality of characteristic parameter values in a dielectric relaxation model through a heuristic algorithm according to the first test data;
and acquiring a plurality of nonlinear relations between the characteristic parameters and the temperature by adopting a cubic spline interpolation function.
6. The method for correcting a frequency-domain dielectric spectrum curve of claim 1, further comprising:
acquiring second test data of a medium loss curve of the sleeve at the time-varying temperature;
and comparing the second test data with the frequency domain dielectric spectrum curve after the translation correction so as to verify the accuracy of the correction method.
7. An apparatus for correcting a frequency domain dielectric spectrum curve, comprising:
the data acquisition module is used for respectively acquiring first test data of medium loss curves of the sleeves at different constant temperatures;
the nonlinear relation operation module is used for acquiring nonlinear relations between a plurality of characteristic parameter values and temperatures in a preset dielectric relaxation model according to the first test data;
the equivalent temperature acquisition module is used for acquiring equivalent temperature corresponding to each test frequency point of a medium loss curve of the casing at the time-varying temperature according to the dielectric relaxation model and the nonlinear relation;
and the translation correction module is used for performing translation correction on the frequency points of the frequency domain dielectric spectrum curve at the time-varying temperature according to the Arrhenius formula and the corresponding relation between the test frequency points and the equivalent temperature.
8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 6.
9. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.
10. A computer program product comprising a computer program, characterized in that the computer program realizes the steps of the method of any one of claims 1 to 6 when executed by a processor.
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| CN117112971B (en) * | 2023-10-25 | 2024-03-29 | 宁德时代新能源科技股份有限公司 | Temperature curve generation method and device, electronic equipment and storage medium |
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