Reclosing locking method and system based on winding hot-spot temperature fitting

Abstract

The invention discloses a reclosing locking method and system based on winding hot-spot temperature fitting, and relates to the technical field of power transformer dynamic stability assessment, and the method comprises the steps: determining a target transformer, collecting parameters, building a winding current calculation model, calculating steady-state and short-circuit current waveforms, and carrying out the winding temperature rise test of the transformer, the method comprises the following steps: measuring a steady-state temperature rise value, constructing and correcting an electromagnetic heat flow coupling model, generating steady-state and transient-state temperature field data of a winding, constructing a target function of a winding hot-spot temperature, fitting simulation data by utilizing an optimization algorithm, obtaining a fitting function, calculating a winding stress value under a short-circuit working condition in real time, and comparing the winding stress value with a dynamically adjusted stress limit value, so as to obtain a winding stress value. Alarm and locking reclosing are triggered according to the result, and intelligent protection of the transformer is achieved. According to the invention, through accurate parameter acquisition, model establishment, temperature field simulation, hot-spot temperature fitting and stress calculation, real-time monitoring and intelligent protection of the transformer winding under the short-circuit working condition are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of dynamic stability assessment of power transformers, and in particular to a reclosing locking method and system based on winding hot spot temperature fitting. Background Art

[0002] When a fault occurs in the current power system, the relay protection system usually cuts off the faulty line. However, due to the existence of the reclosing system, the circuit breaker will be reclosed after a certain setting time to improve the reliability of the power supply of the power grid. However, if the fault is a permanent fault, the power system will suffer two short-circuit shocks in a short period of time.

[0003] Traditional reclosing setting strategies generally do not use the dynamic stability of the transformer as a basis for setting, do not distinguish between non-permanent faults and permanent faults, and do not consider the current operating conditions of the transformer and the current setting status. However, due to different operating conditions of the transformer, the state of the transformer winding is also different, especially the temperature state of the transformer, which varies greatly. Coupled with the influence of the short-circuit current itself, the dynamic stability of the transformer winding may be greatly reduced.

[0004] Therefore, in order to reduce the possibility of serious mechanical failure of the transformer, it is of great significance to consider the actual operating conditions of the transformer, calculate the possible hot spot temperature of the transformer winding under permanent fault of reclosing, correct the stress limit value of the dynamic stability of the transformer winding, and take the dynamic stability of the transformer winding into consideration when formulating the transformer reclosing locking strategy. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by the present invention is that the setting of the reclosing circuit breaker of the traditional relay protection system does not take into account the influence of the hot spot temperature of the transformer on the dynamic stability, resulting in the problem that the reclosing circuit breaker impact damages the transformer.

[0007] In order to solve the above technical problems, a reclosing locking method based on winding hot spot temperature fitting is proposed, including:

[0008] Determine the target transformer, collect the target transformer parameters, establish the transformer winding current calculation model, calculate the steady-state winding current waveform and short-circuit current waveform; perform a winding temperature rise test on the target transformer, measure the winding steady-state temperature rise value, construct a transformer electromagnetic thermal flow coupling model, and calibrate the model parameters. Use the calibrated model to generate the steady-state and transient temperature field data of the transformer winding; construct the target function of the transformer winding hot spot temperature, fit the simulation data through the optimization algorithm, obtain the fitting function, calculate the winding stress value under the short-circuit condition in real time, and compare it with the stress limit value. Trigger the alarm and lock the reclosing switch based on the comparison results.

[0009] As a preferred solution of the reclosing locking method based on winding hot spot temperature fitting described in the present invention, wherein: said collecting target transformer parameters includes collecting geometric parameters, structural parameters and line parameters of the target transformer;

[0010] The transformer winding current calculation model is established by adjusting the circuit breaker opening and closing time to simulate the maximum short-circuit impact current, and outputting the steady-state current waveform under different load rates and the short-circuit current waveform corresponding to the short-circuit time;

[0011] The calculation of the steady-state winding current waveform and the short-circuit current waveform includes selecting different load rates and simulating the winding current waveform under steady-state conditions; adjusting the circuit breaker opening and closing time in a three-phase short-circuit grounding condition so that the power supply potential crosses zero to trigger a short circuit; setting the short-circuit time; and obtaining waveform data of the maximum short-circuit impact current.

[0012] As a preferred embodiment of the reclosing lockout method based on winding hotspot temperature fitting described in the present invention, the winding temperature rise test includes measuring the winding hotspot temperature using an optical fiber temperature measuring device, and adjusting the excitation and boundary conditions of the electromagnetic heat flow coupling model according to the measured data until the deviation between the model calculated value and the test value is less than a preset error threshold;

[0013] The correction model parameters are constructed based on the finite element method to construct a transformer electromagnetic heat-fluid coupling model, and the steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model. When the deviation between the hot spot temperature output by the electromagnetic heat-fluid coupling model and the experimental measurement value is greater than or equal to 5 Kelvin, the excitation parameters and boundary conditions of the electromagnetic heat-fluid coupling model are adjusted until the deviation is less than 5 Kelvin.

[0014] As a preferred embodiment of the reclosing lockout method based on winding hotspot temperature fitting described in the present invention, the generating of the steady-state and transient temperature field data of the transformer winding includes generating the steady-state and transient temperature field data of the transformer winding by using a calibrated electromagnetic heat flow coupling model in combination with multiple sets of load factors, ambient temperatures, and short-circuit time conditions;

[0015] The generation of steady-state and transient temperature field data of the transformer winding also includes inputting the steady-state current waveform under different load rates into the corrected model, combining it with different preset ambient temperature conditions, calculating the steady-state temperature field distribution, using the steady-state temperature field as the initial condition, and inputting the short-circuit current waveform as the transient excitation into the corrected electromagnetic heat-flow coupling model to simulate the transient temperature rise process during the short-circuit time, and extracting the hot spot temperature data of the winding.

[0016] As a preferred solution of the reclosing locking method based on winding hot spot temperature fitting described in the present invention, wherein: the objective function of constructing the transformer winding hot spot temperature includes defining it through multicollinearity theory and fitting the temperature field data using a particle swarm optimization algorithm;

[0017] Obtaining the fitting function includes defining a nonlinear functional relationship between the hot spot temperature of the winding and the load rate, the ambient temperature, and the short-circuit time based on the multicollinearity theory, iteratively optimizing the simulation data set using a particle swarm optimization algorithm, selecting the optimal fitting parameters by minimizing the root mean square error, and determining the objective function as the final fitting function when the root mean square error is less than 5 Kelvin;

[0018] The objective function of the transformer winding hot spot temperature is expressed as:

[0019] T h =(a1·L r 2 +a2·L r +a3)×(a4·T amb +a5)×(a6·t s +a7)+a8

[0020] Among them, a1, a2, a3, a4, a5, a6, a7 and a8 are fitting coefficients, T h is the hot spot temperature of the transformer winding, L r is the load rate, T amb is the ambient temperature, t s is the short circuit time.

[0021] As a preferred embodiment of the reclosing lockout method based on winding hotspot temperature fitting described in the present invention, the real-time calculation of the winding stress value under the short-circuit condition includes calculating the radial force and axial force of the winding under the short-circuit condition using an electromagnetic heat-flow coupling model, and converting the electrodynamic force into average annular stress, radial bending stress, axial compressive stress, and axial bending stress;

[0022] The average annular stress is determined by the ratio of the radial force per unit length of the winding to the cross-sectional area of ​​the conductor. The radial bending stress is calculated by the radial displacement of the coil and the geometric parameters. The axial compressive stress is derived based on the ratio of the effective area of ​​the pad to the axial force. The axial bending stress is calculated by the axial displacement of the conductor and the moment of inertia parameters.

[0023] The dynamic adjustment of the stress limit value includes calculating the actual hot spot temperature of the winding after short circuit based on the fitting function, combining the characteristics of the winding material yield strength changing with temperature, correcting the static stress limit value specified in the national standard, and obtaining the dynamic stress limit value that matches the current temperature.

[0024] As a preferred embodiment of the reclosing lockout method based on winding hotspot temperature fitting described in the present invention, the triggering of the alarm and the locking of the reclosing comprises: calculating the winding stress value under the short-circuit condition in real time, comparing it with the stress limit value, and triggering the alarm and locking the reclosing according to the comparison result;

[0025] Comparison with the stress limit value includes: when the calculated stress value reaches 90% to 100% of the dynamic stress limit value, an alarm signal is triggered, prompting to adjust the load factor or shorten the setting time; when the calculated stress value exceeds the dynamic stress limit value, the reclosing operation is immediately locked, prohibiting the circuit breaker from closing;

[0026] The execution process of the alarm or lockout instruction includes real-time collection of the load rate, ambient temperature and short-circuit time parameters during transformer operation, using the parameters for data fitting and stress calculation, generating dynamic stress assessment results, outputting the alarm or lockout instruction through the relay protection system interface, and linking the control of the circuit breaker's action logic.

[0027] As a preferred solution of the reclosing lockout system based on winding hot spot temperature fitting described in the present invention, it is characterized by including a transformer parameter acquisition and current calculation module, a winding temperature rise test and electromagnetic heat flow coupling model correction module, a temperature field data generation and fitting function construction module, and a real-time stress calculation and alarm lockout control module.

[0028] The transformer parameter acquisition and current calculation module is used to acquire target transformer parameters, establish a transformer winding current calculation model, simulate the maximum short-circuit impact current by adjusting the circuit breaker opening and closing time, and output steady-state current waveforms and short-circuit current waveforms under different load rates.

[0029] The winding temperature rise test and electromagnetic heat-flux coupling model correction module includes a winding temperature rise test unit and an electromagnetic heat-flux coupling model correction unit, which are used to measure the winding hotspot temperature, adjust the excitation and boundary conditions of the electromagnetic heat-flux coupling model according to the measured data, and construct the transformer electromagnetic heat-flux coupling model based on the finite element method. The steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model to adjust the model parameters.

[0030] The temperature field data generation and fitting function construction module includes a temperature field data generation unit and a fitting function construction unit, which is used to use the corrected electromagnetic heat flow coupling model, combined with multiple sets of load rate, ambient temperature and short-circuit time conditions, to generate steady-state and transient temperature field data of the transformer winding, and calculate the steady-state temperature field distribution. Using the steady-state temperature field as the initial condition, the transient temperature rise process during the short-circuit time is simulated, and the hot spot temperature data of the winding is extracted. The objective function of the hot spot temperature of the winding is defined by the multicollinearity theory, and the temperature field data is fitted using the particle swarm optimization algorithm to obtain the fitting function.

[0031] The real-time stress calculation and alarm lockout control module includes a real-time stress calculation unit and an alarm lockout control unit, which are used to calculate the winding stress value under short-circuit conditions in real time and correct the dynamic stress limit value based on the actual hot spot temperature calculated by the fitting function and the temperature-dependent characteristic of the winding material yield strength. When the calculated stress value reaches 90% to 100% of the dynamic stress limit value, an alarm is triggered. When the dynamic stress limit value is exceeded, the reclosing operation is immediately locked, and the circuit breaker operation logic is controlled in a linkage manner through the output command of the relay protection system interface.

[0032] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of a method for reclosing lockout based on winding hot spot temperature fitting are implemented.

[0033] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for reclosing lockout based on winding hot spot temperature fitting.

[0034] Beneficial effects of the present invention: The present invention establishes an accurate transformer winding current calculation model by determining the target transformer and collecting parameters, realizes the accurate calculation of steady-state and short-circuit current waveforms, provides a reliable data basis for subsequent temperature field simulation and stress analysis, and improves the accuracy and effectiveness of the entire locking method; by performing a winding temperature rise test on the target transformer and correcting the electromagnetic heat flow coupling model, the high accuracy of the model is ensured, and the steady-state and transient temperature field data generated by the model are closer to reality, providing accurate data support for hot spot temperature fitting and stress calculation, and enhancing the practicality and reliability of the method; by constructing a multivariate-based The objective function of the collinearity theory was fitted using the particle swarm optimization algorithm to obtain an accurate fitting function, which realized the real-time calculation of the winding stress value under short-circuit conditions and the accurate comparison with the stress limit value, providing a scientific basis for triggering alarms and locking reclosing, and improving the system's response speed and decision-making accuracy. By calculating the winding stress value under short-circuit conditions in real time and comparing it with the dynamically adjusted stress limit value, real-time monitoring and early warning of the transformer's operating status were achieved. When the stress value reached or exceeded the limit value, the alarm was triggered in time and the reclosing operation was locked, effectively preventing overheating and damage of the transformer and ensuring the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 An overall flow chart of a reclosing lockout method based on winding hotspot temperature fitting is provided in accordance with an embodiment of the present invention.

[0037] Figure 2 A schematic diagram of a MATLAB Simulink current calculation model for a reclosing lockout method based on winding hotspot temperature fitting provided by one embodiment of the present invention.

[0038] Figure 3 A schematic diagram of a MATLAB Simulink current calculation model for a reclosing lockout method based on winding hotspot temperature fitting provided by one embodiment of the present invention.

[0039] Figure 4 A schematic diagram of a transformer electromagnetic force heat flow finite element model for a reclosing lockout method based on winding hot spot temperature fitting provided by one embodiment of the present invention.

[0040] Figure 5A flow chart of a system solution for a reclosing lockout system based on winding hotspot temperature fitting is provided in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0041] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in this field without creative work should fall within the scope of protection of the present invention.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it individually or selectively refer to an embodiment that is mutually exclusive of other embodiments.

[0044] The present invention is described in detail with reference to schematic diagrams. For ease of illustration, cross-sectional views of device structures may be partially enlarged and not to scale when describing embodiments of the present invention. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of the present invention. Furthermore, in actual production, the three-dimensional dimensions of length, width, and depth should be included.

[0045] In the description of the present invention, it should be noted that the terms "upper, lower, inner, and outer" and other references to orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first, second, or third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In this disclosure, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they may refer to fixed, removable, or integral connections. They may also refer to mechanical, electrical, or direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this disclosure.

[0047] Example 1, reference Figure 1 , which is the first embodiment of the present invention, provides a reclosing locking method based on winding hot spot temperature fitting, comprising:

[0048] S1: Determine the target transformer, collect the target transformer parameters, establish the transformer winding current calculation model, and calculate the steady-state winding current waveform and short-circuit current waveform.

[0049] The target transformer is determined, and the transformer geometric parameters, structural parameters, and line parameters are collected. A transformer winding current calculation model is established using MATLAB Simulink. On the one hand, the winding current calculation model is used to calculate the winding current waveforms of n groups of steady-state working conditions with different load rates. On the other hand, the short-circuit current calculation model is used to calculate the short-circuit current waveform when coinciding with a permanent fault under a three-phase short-circuit grounding condition. The circuit breaker opening and closing time is set based on the maximum short-circuit impact current, and the short-circuit current waveform is obtained.

[0050] The short-circuit current calculation model includes establishing a short-circuit current calculation model for the power system including the transformer based on the collected electrical parameters, structural parameters and line parameters of the transformer. Based on the user's consideration of data accuracy and on-site conditions, n groups of different load rates are selected, and the winding current is calculated and current waveform data is obtained under steady-state conditions. The short-circuit current calculation model is used to simulate the conditions of coincidence with permanent faults under three-phase short-circuit grounding conditions, and the circuit breaker opening and closing times are set so that the power supply potential just passes through the zero value. The short-circuit time is also set to obtain the maximum short-circuit impact current.

[0051] S2: Perform a winding temperature rise test on the target transformer, measure the steady-state temperature rise of the winding, construct an electromagnetic heat-flow coupling model of the transformer, calibrate the model parameters, and use the calibrated model to generate steady-state and transient temperature field data of the transformer winding.

[0052] Furthermore, the winding temperature rise test includes measuring the hot spot temperature of the winding using an optical fiber temperature measuring device, and adjusting the excitation and boundary conditions of the electromagnetic heat flow coupling model according to the measured data until the deviation between the model calculated value and the test value is less than a preset error threshold;

[0053] In an embodiment of the present application, the correction model parameters are constructed based on the finite element method to construct a transformer electromagnetic heat-flow coupling model, and the steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model. When the hot spot temperature output by the electromagnetic heat-flow coupling model deviates from the experimental measurement value by greater than or equal to 5 Kelvin, the excitation parameters and boundary conditions of the electromagnetic heat-flow coupling model are adjusted until the deviation is less than 5 Kelvin.

[0054] In an optional embodiment, the correction model parameters are arranged by arranging thermistors on the surface of the transformer windings, collecting the winding temperature distribution data under different load rates through the thermistors, and constructing a simplified two-dimensional heat conduction model. The test data is compared with the model calculation results, and the model thermal conductivity parameters are manually adjusted so that the error is less than 10 Kelvin.

[0055] In another optional embodiment, the correction model parameters use an infrared thermal imager to measure the surface temperature of the winding, estimate the hotspot temperature, directly calculate the winding temperature rise based on the national standard empirical formula, compare the formula calculation results with the infrared temperature measurement data, and manually adjust the formula coefficients so that the error is less than 15 Kelvin.

[0056] Furthermore, generating the steady-state and transient temperature field data of the transformer winding includes using the calibrated electromagnetic heat flow coupling model and combining multiple sets of load factors, ambient temperatures, and short-circuit time conditions to generate the steady-state and transient temperature field data of the transformer winding;

[0057] In an embodiment of the present application, the generation of steady-state and transient temperature field data of the transformer winding also includes inputting the steady-state current waveform under different load rates into the corrected model, combining it with different preset ambient temperature conditions, calculating the steady-state temperature field distribution, using the steady-state temperature field as the initial condition, and inputting the short-circuit current waveform as the transient excitation into the corrected electromagnetic heat-flow coupling model to simulate the transient temperature rise process during the short-circuit time, and extracting the hot spot temperature data of the winding.

[0058] In an optional embodiment, generating transient temperature field data includes calculating the steady-state temperature field under different load rates and ambient temperatures, assuming that the temperature instantaneously jumps to a steady-state value during a short circuit, and using the steady-state temperature as the hot spot temperature after the short circuit to input into the stress calculation module.

[0059] In another optional embodiment, generating transient temperature field data includes establishing a one-dimensional heat conduction equation, inputting steady-state current and short-circuit current as heat sources, calculating the axial temperature distribution, and taking the highest temperature point as the hotspot temperature.

[0060] S3: Construct the objective function of the transformer winding hot spot temperature, fit the simulation data through the optimization algorithm, obtain the fitting function, calculate the winding stress value under the short-circuit condition in real time, and compare it with the stress limit value. According to the comparison result, trigger the alarm and lock the reclosing switch.

[0061] Furthermore, the objective function of constructing the hot spot temperature of the transformer winding includes defining it through multicollinearity theory and fitting the temperature field data using a particle swarm optimization algorithm;

[0062] Obtaining the fitting function includes defining a nonlinear functional relationship between the hot spot temperature of the winding and the load rate, the ambient temperature, and the short-circuit time based on the multicollinearity theory, iteratively optimizing the simulation data set using a particle swarm optimization algorithm, selecting the optimal fitting parameters by minimizing the root mean square error, and determining the objective function as the final fitting function when the root mean square error is less than 5 Kelvin;

[0063] The objective function of the transformer winding hot spot temperature is expressed as:

[0064] T h =(a1·L r 2 +a2·L r +a3)×(a4·T amb +a5)×(a6·t s +a7)+a8

[0065] Among them, a1, a2, a3, a4, a5, a6, a7 and a8 are fitting coefficients, T h is the hot spot temperature of the transformer winding, L r is the load rate, T amb is the ambient temperature, t s is the short circuit time.

[0066] Furthermore, the real-time calculation of the winding stress value under the short-circuit condition includes calculating the radial force and axial force of the winding under the short-circuit condition using an electromagnetic heat-flux coupling model, and converting the electrodynamic force into average annular stress, radial bending stress, axial compressive stress, and axial bending stress;

[0067] According to the national standard GB1094.5, the average annular stress is determined by the ratio of the radial force per unit length of the winding to the cross-sectional area of ​​the conductor. The radial bending stress is calculated by the radial displacement of the coil and the geometric parameters. The axial compressive stress is derived based on the ratio of the effective area of ​​the pad to the axial force. The axial bending stress is calculated by the axial displacement of the conductor and the moment of inertia parameters.

[0068] The formula for calculating the average annular stress is:

[0069]

[0070] The calculation formula for radial bending stress is:

[0071]

[0072] The calculation formula for axial compressive stress is:

[0073]

[0074] The calculation formula for axial bending stress is:

[0075]

[0076] Among them, σ t1 is the average annular stress, F c A is the average radial force per unit length of the winding, cu is the cross-sectional area of ​​the winding wire, π is the circumference of the circle, F r is the radial force on the coil conductor, σ br is the radial bending stress, I0 is the polar moment of inertia, n b is the number of radially parallel windings, n d is the number of windings connected in parallel axially, t ν is the radial thickness of the winding, w ν is the axial height of the coil, σ act is the axial compressive stress, F a is the inter-segment axial force, A z is the effective area of ​​the spacer, paper insulation, end ring or pressure plate, σ ba is the axial bending stress, is the maximum allowable radial displacement of the conductor, Δ is the axial displacement of the conductor, F g is the winding axial force.

[0077] The dynamic adjustment of the stress limit value includes calculating the actual hot spot temperature of the winding after short circuit based on the fitting function, and correcting the static stress limit value specified in the national standard in combination with the characteristics of the winding material yield strength changing with temperature to obtain the dynamic stress limit value that matches the current temperature. The specific limit values ​​are shown in the following table:

[0078]

[0079]

[0080] It should be noted that the relationship between the yield strength of the transformer winding material and temperature is:

[0081] R p0.2 =-0.187T+174.42

[0082] Among them, R p0.2 is the yield strength, T is the temperature;

[0083] The triggering of the alarm and locking of the reclosing switch includes calculating the winding stress value under the short-circuit working condition in real time, comparing it with the stress limit value, and triggering the alarm and locking of the reclosing switch according to the comparison result;

[0084] Comparison with the stress limit value includes: when the calculated stress value reaches 90% to 100% of the dynamic stress limit value, an alarm signal is triggered, prompting to adjust the load factor or shorten the setting time; when the calculated stress value exceeds the dynamic stress limit value, the reclosing operation is immediately locked, prohibiting the circuit breaker from closing;

[0085] The execution process of the alarm or lockout instruction includes real-time collection of the load rate, ambient temperature and short-circuit time parameters during transformer operation, using the parameters for data fitting and stress calculation, generating dynamic stress assessment results, outputting the alarm or lockout instruction through the relay protection system interface, and linking the control of the circuit breaker's action logic.

[0086] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0087] Example 2, reference Figure 5 , which is the second embodiment of the present invention, provides a reclosing lockout system based on winding hotspot temperature fitting, including a transformer parameter acquisition and current calculation module, a winding temperature rise test and electromagnetic heat flow coupling model correction module, a temperature field data generation and fitting function construction module, and a real-time stress calculation and alarm lockout control module.

[0088] The transformer parameter acquisition and current calculation module is used to acquire target transformer parameters, establish a transformer winding current calculation model, simulate the maximum short-circuit impact current by adjusting the circuit breaker opening and closing time, and output steady-state current waveforms and short-circuit current waveforms under different load rates.

[0089] The winding temperature rise test and electromagnetic heat-flux coupling model correction module includes a winding temperature rise test unit and an electromagnetic heat-flux coupling model correction unit, which are used to measure the winding hotspot temperature, adjust the excitation and boundary conditions of the electromagnetic heat-flux coupling model according to the measured data, and construct the transformer electromagnetic heat-flux coupling model based on the finite element method. The steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model to adjust the model parameters.

[0090] The temperature field data generation and fitting function construction module includes a temperature field data generation unit and a fitting function construction unit, which is used to use the corrected electromagnetic heat flow coupling model, combined with multiple sets of load rate, ambient temperature and short-circuit time conditions, to generate steady-state and transient temperature field data of the transformer winding, and calculate the steady-state temperature field distribution. Using the steady-state temperature field as the initial condition, the transient temperature rise process during the short-circuit time is simulated, and the hot spot temperature data of the winding is extracted. The objective function of the hot spot temperature of the winding is defined by the multicollinearity theory, and the temperature field data is fitted using the particle swarm optimization algorithm to obtain the fitting function.

[0091] The real-time stress calculation and alarm lockout control module includes a real-time stress calculation unit and an alarm lockout control unit, which are used to calculate the winding stress value under short-circuit conditions in real time and correct the dynamic stress limit value based on the actual hot spot temperature calculated by the fitting function and the temperature-dependent characteristic of the winding material yield strength. When the calculated stress value reaches 90% to 100% of the dynamic stress limit value, an alarm is triggered. When the dynamic stress limit value is exceeded, the reclosing operation is immediately locked, and the circuit breaker operation logic is controlled in a linkage manner through the output command of the relay protection system interface.

[0092] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0093] Example 3, reference Figure 2-Figure 4 , which is an embodiment of the present invention, provides a reclosing locking method based on winding hot spot temperature fitting. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0094] Collect the geometric parameters, structural parameters and line parameters of the transformer and establish the MATLAB Simulink short-circuit current calculation model as follows Figure 2 shown.

[0095] Furthermore, based on the user's considerations for data accuracy and on-site conditions, n groups of different load rates are selected, and their winding currents are calculated and current waveform data is obtained under steady-state conditions. In this example, four groups of different load rates are selected, namely 25%, 50%, 75%, and 100%. Thereafter, the model is used to simulate the condition of a three-phase short-circuit grounding condition with a coincidence of a permanent fault. The circuit breaker opening and closing times are set so that the power supply potential just crosses the zero value, and the short-circuit time is set to 4 seconds to obtain the maximum short-circuit impact current.

[0096] The test site layout is as follows: Figure 3As shown in the figure, this test adopts the method of embedding optical fibers in the slots of the support bars to install the temperature probe. The test process is divided into two stages. The first stage is the preheating stage: in order to quickly increase the temperature of the transformer and shorten the total test time, preheating is performed before starting the formal test to heat the transformer temperature to a higher level; the second stage is the loading stage, in which 50%, 75%, and 100% load rates are applied to the transformer respectively. The temperature of the optical fiber measuring point at 90% of the A-phase winding is approximately the hotspot temperature. When the temperature rise rate of each temperature measuring point and the top oil is less than 1 Kelvin per hour, it is maintained for 1 hour. During this period, the temperature values ​​of all optical fiber points and the top oil layer are recorded every 10 minutes. Finally, the steady-state value of the hotspot temperature within this 1 hour is used as the test result.

[0097] Furthermore, the transformer electromagnetic force and heat flow finite element model is constructed based on the transformer geometric parameters and structural parameters. Figure 4 As shown in the figure, the excitation and boundary conditions are set to be consistent with the experimental conditions, and the model is corrected by comparing the hot spot temperature data in the experimental data. The experimentally measured hot spot temperature data of the transformer winding at 50%, 75%, and 100% load rates are 318.75 Kelvin, 334.35 Kelvin, and 362.45 Kelvin, respectively. Compared with the simulation calculation values ​​of 315.28 Kelvin, 334.11 Kelvin, and 360.44 Kelvin, the errors are all within 5 Kelvin, thus verifying the simulation accuracy of the transformer electromagnetic force thermal flow field simulation model.

[0098] The winding current waveforms obtained under four sets of steady-state working conditions with different load rates are used as the steady-state temperature field excitation of the transformer winding. Four different ambient temperatures are set, namely 273.15 Kelvin, 293.15 Kelvin, 313.15 Kelvin, and 333.15 Kelvin, to calculate the temperature field of the transformer winding under steady-state working conditions. The calculated steady-state temperature field is used as the initial condition, and the transformer short-circuit current under a short-circuit time of 4 seconds is used as the excitation. The transient temperature rise of the transformer winding during the short-circuit process is calculated, and the hotspot temperature data of each phase winding are extracted to form a data set.

[0099] The fitting function can be obtained by fitting using the PSO method:

[0100] T h =(0.0031·L r 2 +0.0863·L r +632.47)×(0.1673·T amb +144.06)×(6.92×10 -6 ·t s +0.009)+812.018

[0101] Among them, T his the hot spot temperature of the transformer winding, L r is the load rate, T amb is the ambient temperature, t s is the short circuit time.

[0102] Based on existing experimental data, the relationship between the yield strength of transformer winding materials and temperature is:

[0103] R p0.2 =-0.187T+174.42

[0104] Among them, R p0.2 is the yield strength, T is the temperature;

[0105] According to the national standard GB1094.5, the average annular stress σ is selected t1 , radial bending stress σ br , axial compressive stress σ act , axial bending stress σ ba , assuming that the actual operating condition of the current transformer is 90% load rate, the ambient temperature is 30℃, and a sudden three-phase short circuit and grounding permanent fault occurs, and the short circuit lasts for 2 seconds, determine whether it will alarm or lock out the reclosing.

[0106] The calculated stress values ​​at the design temperature (75°C) and the stress limit values ​​at the actual winding hot spot temperature are shown in the following table:

[0107]

[0108] It can be seen that the average annular stress with the minimum margin is σ t1 The percentage of the distance from the actual stress limit value is 61.15%, so the transformer design margin is large and there is no need for alarm or lockout. The fault is cut off by the relay protection action.

[0109] Example 4, the fourth embodiment of the present invention, is different from the first three embodiments in that:

[0110] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0111] The logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0112] More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk cartridge (magnetic devices), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disc read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0113] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

Claims

1. A reclosing locking method based on winding hot spot temperature fitting, characterized by: include, Determine the target transformer, collect the target transformer parameters, establish the transformer winding current calculation model, and calculate the steady-state winding current waveform and short-circuit current waveform; Conduct a winding temperature rise test on the target transformer, measure the winding steady-state temperature rise value, build a transformer electromagnetic heat-flow coupling model, calibrate the model parameters, and use the calibrated model to generate the steady-state and transient temperature field data of the transformer winding; The objective function of the transformer winding hot spot temperature is constructed, and the simulation data is fitted through the optimization algorithm to obtain the fitting function. The winding stress value under the short-circuit condition is calculated in real time and compared with the stress limit value. The alarm and reclosing lock are triggered according to the comparison result.

2. The reclosing locking method based on winding hot spot temperature fitting according to claim 1, characterized in that: The collecting of target transformer parameters includes collecting geometric parameters, structural parameters and line parameters of the target transformer; The transformer winding current calculation model is established by adjusting the circuit breaker opening and closing time to simulate the maximum short-circuit impact current, and outputting the steady-state current waveform under different load rates and the short-circuit current waveform corresponding to the short-circuit time; The calculation of the steady-state winding current waveform and the short-circuit current waveform includes selecting different load rates and simulating the winding current waveform under steady-state conditions; adjusting the circuit breaker opening and closing time in a three-phase short-circuit grounding condition so that the power supply potential crosses zero to trigger a short circuit; setting the short-circuit time; and obtaining waveform data of the maximum short-circuit impact current.

3. The reclosing locking method based on winding hot spot temperature fitting according to claim 2, characterized in that: The winding temperature rise test includes measuring the hot spot temperature of the winding using an optical fiber temperature measuring device, and adjusting the excitation and boundary conditions of the electromagnetic heat flow coupling model according to the measured data until the deviation between the model calculated value and the test value is less than a preset error threshold; The correction model parameters are constructed based on the finite element method to construct a transformer electromagnetic heat-fluid coupling model, and the steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model. When the deviation between the hot spot temperature output by the electromagnetic heat-fluid coupling model and the experimental measurement value is greater than or equal to 5 Kelvin, the excitation parameters and boundary conditions of the electromagnetic heat-fluid coupling model are adjusted until the deviation is less than 5 Kelvin.

4. The reclosing locking method based on winding hot spot temperature fitting according to claim 3, characterized in that: Generating the steady-state and transient temperature field data of the transformer winding includes using the calibrated electromagnetic heat flow coupling model and combining multiple sets of load factors, ambient temperatures, and short-circuit time conditions to generate the steady-state and transient temperature field data of the transformer winding; The generation of steady-state and transient temperature field data of the transformer winding also includes inputting the steady-state current waveform under different load rates into the corrected model, combining it with different preset ambient temperature conditions, calculating the steady-state temperature field distribution, using the steady-state temperature field as the initial condition, and inputting the short-circuit current waveform as the transient excitation into the corrected electromagnetic heat-flow coupling model to simulate the transient temperature rise process during the short-circuit time, and extracting the hot spot temperature data of the winding.

5. The reclosing locking method based on winding hot spot temperature fitting according to claim 4, characterized in that: The objective function of constructing the hot spot temperature of the transformer winding includes defining it through multicollinearity theory and fitting the temperature field data using a particle swarm optimization algorithm; Obtaining the fitting function includes defining a nonlinear functional relationship between the hot spot temperature of the winding and the load rate, the ambient temperature, and the short-circuit time based on the multicollinearity theory, iteratively optimizing the simulation data set using a particle swarm optimization algorithm, selecting the optimal fitting parameters by minimizing the root mean square error, and determining the objective function as the final fitting function when the root mean square error is less than 5 Kelvin; The objective function of the transformer winding hot spot temperature is expressed as: <h2 style=";text-align:left;direction:ltr">T<h2 style=";text-align:left;direction:ltr"> h <h2 style=";text-align:left;direction:ltr"> =(a1·L<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +a2·L<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> +a3)×(a4·T<h2 style=";text-align:left;direction:ltr"> amb <h2 style=";text-align:left;direction:ltr"> +a5)×(a6·t<h2 style=";text-align:left;direction:ltr"> s <h2 style=";text-align:left;direction:ltr"> +a7)+a8 Among them, a1, a2, a3, a4, a5, a6, a7 and a8 are fitting coefficients, T h is the hot spot temperature of the transformer winding, L r is the load rate, T amb is the ambient temperature, t s is the short circuit time.

6. The reclosing locking method based on winding hot spot temperature fitting according to claim 5, characterized in that: The real-time calculation of the winding stress value under the short-circuit working condition includes calculating the radial force and axial force of the winding under the short-circuit working condition using an electromagnetic heat-flow coupling model, and converting the electrodynamic force into average annular stress, radial bending stress, axial compressive stress and axial bending stress; The average annular stress is determined by the ratio of the radial force per unit length of the winding to the cross-sectional area of ​​the conductor. The radial bending stress is calculated by the radial displacement of the coil and the geometric parameters. The axial compressive stress is derived based on the ratio of the effective area of ​​the pad to the axial force. The axial bending stress is calculated by the axial displacement of the conductor and the moment of inertia parameters. The dynamic adjustment of the stress limit value includes calculating the actual hot spot temperature of the winding after short circuit based on the fitting function, combining the characteristics of the winding material yield strength changing with temperature, correcting the static stress limit value specified in the national standard, and obtaining the dynamic stress limit value that matches the current temperature.

7. The reclosing locking method based on winding hot spot temperature fitting according to claim 6, characterized in that: The triggering of the alarm and locking of the reclosing switch includes calculating the winding stress value under the short-circuit working condition in real time, comparing it with the stress limit value, and triggering the alarm and locking of the reclosing switch according to the comparison result; Comparison with the stress limit value includes triggering an alarm signal when the calculated stress value reaches 90% to 100% of the dynamic stress limit value, prompting adjustment of the load rate or shortening of the setting time; When the calculated stress value exceeds the dynamic stress limit value, the reclosing operation is immediately blocked and the circuit breaker is prohibited from closing; The execution process of the alarm or lockout instruction includes real-time collection of the load rate, ambient temperature and short-circuit time parameters during transformer operation, using the parameters for data fitting and stress calculation, generating dynamic stress assessment results, outputting the alarm or lockout instruction through the relay protection system interface, and linking the control of the circuit breaker's action logic.

8. A system using the reclosing locking method based on winding hot spot temperature fitting according to any one of claims 1 to 7, characterized in that: It includes transformer parameter acquisition and current calculation module, winding temperature rise test and electromagnetic heat flow coupling model correction module, temperature field data generation and fitting function construction module, and real-time stress calculation and alarm locking control module; The transformer parameter acquisition and current calculation module is used to acquire target transformer parameters, establish a transformer winding current calculation model, simulate the maximum short-circuit impact current by adjusting the circuit breaker opening and closing time, and output the steady-state current waveform and short-circuit current waveform under different load rates; The winding temperature rise test and electromagnetic heat-flux coupling model correction module includes a winding temperature rise test unit and an electromagnetic heat-flux coupling model correction unit, which are used to measure the winding hotspot temperature, adjust the excitation and boundary conditions of the electromagnetic heat-flux coupling model according to the measured data, and construct the transformer electromagnetic heat-flux coupling model based on the finite element method. The steady-state temperature rise data measured in the test is compared with the calculation results of the finite element model to adjust the model parameters; The temperature field data generation and fitting function construction module includes a temperature field data generation unit and a fitting function construction unit, which is used to use the corrected electromagnetic heat flow coupling model, combined with multiple sets of load rate, ambient temperature and short-circuit time conditions, to generate steady-state and transient temperature field data of the transformer winding, and calculate the steady-state temperature field distribution. Using the steady-state temperature field as the initial condition, the transient temperature rise process during the short-circuit time is simulated, and the hot spot temperature data of the winding is extracted. The objective function of the hot spot temperature of the winding is defined by the multicollinearity theory, and the temperature field data is fitted using the particle swarm optimization algorithm to obtain the fitting function. The real-time stress calculation and alarm lockout control module includes a real-time stress calculation unit and an alarm lockout control unit, which are used to calculate the winding stress value under short-circuit conditions in real time and correct the dynamic stress limit value based on the actual hot spot temperature calculated by the fitting function and the temperature-dependent characteristic of the winding material yield strength. When the calculated stress value reaches 90% to 100% of the dynamic stress limit value, an alarm is triggered. When the dynamic stress limit value is exceeded, the reclosing operation is immediately locked, and the circuit breaker operation logic is controlled in a linkage manner through the output command of the relay protection system interface.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of a reclosing locking method based on winding hot spot temperature fitting according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a reclosing locking method based on winding hot spot temperature fitting according to any one of claims 1 to 7 are implemented.

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