An on-line monitoring and evaluation device and method for series compensation capacitor

Abstract

This invention relates to the field of power equipment condition monitoring technology, and discloses an online monitoring and evaluation device and method for series compensation capacitors. The method includes: acquiring operating signals and extracting steady-state operating characteristics and transient characteristic parameters; combining historical cumulative fatigue damage, calculating the dynamic frequency-varying equivalent series resistance modulated by the damage positive feedback effect, and substituting it into the thermal differential equation to iteratively calculate the dynamic hot spot temperature sequence; for transient events, constructing a cross-coupling term characterizing the synergistic effect of electrodynamics and thermomechanical softening, and calculating the high-frequency equivalent partial discharge; performing thermomechanical softening correction on the transient overvoltage peak to obtain the thermomechanical equivalent transient stress, and dynamically updating the electro-thermal-mechanical coupled cumulative fatigue damage by combining real-time dynamic hot spot temperature and high-frequency equivalent partial discharge; finally outputting a health status index. This invention integrates the time-varying evolution of thermal stress and the multi-physics field transient synergistic damage mechanism, significantly improving the accuracy of equipment damage quantification.

Description

Technical Field

[0001] This invention belongs to the field of power equipment condition monitoring technology, and particularly relates to an online monitoring and evaluation device and method for series compensation capacitors. Background Technology

[0002] Series-compensated capacitors play a crucial role in enhancing the transmission capacity and stability of ultra-high voltage and extra-high voltage power grids. Their operating environment is extremely harsh, enduring continuous thermal effects from power frequency voltage and harmonic currents, while repeatedly experiencing overvoltage and inrush current surges caused by transient events such as system short circuits and line switching. This complex stress condition involving multiple coupled physical fields easily triggers irreversible aging and fatigue damage accumulation in the capacitor's internal insulating medium. Current mainstream online monitoring and life assessment technologies have fundamental flaws, relying primarily on idealized steady-state thermodynamic models for analysis. These models use static thermal resistance parameters for temperature prediction, completely ignoring the dynamic impact of environmental wind speed changes and equipment aging processes on thermal boundary conditions during actual operation, leading to significant discrepancies between calculated hotspot temperatures and actual operating conditions. More critically, in the transient event assessment stage, existing methods treat electrical, thermal, and mechanical stresses in isolation, using only whether the voltage peak exceeds the limit as a single criterion. This linear, fragmented analytical model fails to capture the nonlinear synergistic damage mechanism resulting from the interaction of transient high currents, localized abnormal temperature rises, and extreme electric field strengths. Consequently, the cumulative damage to equipment caused by severe transient events is systematically underestimated. These technical limitations make it difficult for existing monitoring systems to accurately quantify the fatigue damage evolution process of the insulating medium, failing to provide a reliable basis for equipment health status assessment and significantly increasing the risks to power grid operation. Summary of the Invention

[0003] The purpose of this invention is to provide an online monitoring and evaluation device and method for series compensation capacitors, aiming to solve the above-mentioned problems.

[0004] This invention is implemented as follows: an online monitoring and evaluation method for a series compensation capacitor, comprising the following steps: Step S10: acquiring the operating signal of the series compensation capacitor, extracting the effective voltage value sequence, the effective harmonic current value sequence, the peak value of transient overvoltage, the peak value of transient overcurrent, the maximum rate of change of transient voltage, and the charge quantity of synchronous partial discharge; Step S20: combining the historical cumulative fatigue damage degree and the effective harmonic current value sequence of the previous evaluation cycle, calculating the dynamic frequency-varying equivalent series resistance; substituting it and the effective voltage value sequence into the thermal differential equation, calculating the dynamic hotspot including the damage positive feedback effect. Temperature sequence; Step S30: For transient events, construct a cross-coupling term of electrodynamic and thermomechanical softening, and calculate the high-frequency equivalent partial discharge quantity by combining the synchronous partial discharge television charge quantity and the maximum rate of change of the transient voltage; Step S40: Perform thermomechanical softening correction on the transient overvoltage peak to obtain the thermomechanical equivalent transient stress, and calculate the damage amplification index by combining the dynamic hot spot temperature sequence and the high-frequency equivalent partial discharge quantity, and then accumulate and update the electro-thermal-mechanical coupling cumulative fatigue damage degree; Step S50: Calculate the health status index of the series compensation capacitor based on the updated electro-thermal-mechanical coupling cumulative fatigue damage degree.

[0005] A further technical solution, in step S20, the specific logic for calculating the dynamic hotspot temperature sequence includes: constructing a negative correlation mapping relationship between ambient wind speed and dynamic equivalent thermal resistance to characterize the improvement of heat dissipation efficiency by forced convection; constructing a positive nonlinear modulation function of historical cumulative fatigue damage, hotspot temperature at the previous moment, and fundamental equivalent series resistance, and calculating the dynamic frequency-varying equivalent series resistance to characterize the reduction of conductive area caused by the self-healing inside the capacitor and the resulting positive feedback effect of heat generation surge; based on the sum of the current dielectric heat loss and the Joule heat loss considering the dynamic frequency-varying equivalent series resistance, subtracting the heat dissipation modulated by the dynamic equivalent thermal resistance, and iteratively calculating the dynamic hotspot temperature sequence through discrete time steps.

[0006] A further technical solution, in step S30, the specific logic for calculating the high-frequency equivalent partial discharge quantity includes: extracting the charge quantity of the synchronous partial discharge television synchronized with the transient event as a reference base; setting a thermo-mechanical coupling amplification factor with the glass transition temperature of the insulating medium as the trigger boundary; when the transient hot spot temperature exceeds the glass transition temperature, constructing a mechanical stress characterization term using the square term of the transient overcurrent peak value, and performing nonlinear surge amplification in the process of approaching the absolute temperature of the physical melting point to characterize the severe deformation of the internal micropores caused by the electrodynamic force under the high elastic state; introducing a nonlinear acceleration term of the maximum rate of change of transient voltage relative to the rated rate of change; and performing synergistic multiplication or exponentialization processing on the reference base, the thermo-mechanical coupling amplification factor, and the nonlinear acceleration term to output the high-frequency equivalent partial discharge quantity.

[0007] A further technical solution, in step S40, includes the following specific logic for thermomechanical softening correction of the transient overvoltage peak: using the transient overvoltage peak as the basic electrical stress; constructing a thermomechanical softening correction coefficient that is positively correlated with the transient overcurrent peak and whose absolute temperature of the transient hot spot is close to the physical melting point as the limiting divergence boundary; setting an anti-overflow safety margin temperature parameter at the limiting divergence boundary to limit the calculation upper limit; and using the thermomechanical softening correction coefficient to perform nonlinear amplification mapping on the basic electrical stress to output the event-level thermomechanical equivalent transient stress.

[0008] A further technical solution, in step S40, includes the following specific logic for calculating the event-level damage amplification index and updating the electrothermal-mechanical coupling cumulative fatigue damage: extracting the inherent reference fatigue index of the insulating material, and using the thermal aging temperature rise ratio of the transient hot spot temperature compared to the rated reference temperature, and the degradation ratio of the high-frequency equivalent partial discharge quantity relative to the critical discharge threshold, respectively, to positively modulate and amplify the reference fatigue index to obtain the event-level damage amplification index of a single event; after normalizing the thermo-mechanical equivalent transient stress of each transient event, performing nonlinear calculation with the corresponding event-level damage amplification index as the power exponent, and accumulating it over the entire monitoring period to obtain the electrothermal-mechanical coupling cumulative fatigue damage.

[0009] A further technical solution, in step S50, the specific logic for calculating the health status index includes: setting an initial health baseline value under full score conditions, constructing a monotonically decreasing decay function with the cumulative fatigue damage degree of the electrothermal coupling as an independent variable; as the cumulative fatigue damage degree of the electrothermal coupling increases, the health status index shows a non-linear decrease from the initial health baseline value until it reaches the failure and scrapping threshold.

[0010] An online monitoring and evaluation device for series compensation capacitors includes: a memory for storing computer programs; and a processor communicatively connected to the memory for executing the computer programs to implement the various steps of the online monitoring and evaluation method for series compensation capacitors described above.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. This invention breaks through the limitations of traditional thermal models that use static resistance and static thermal resistance. It not only corrects the heat dissipation boundary in real time by using ambient wind speed, but also introduces for the first time the historical cumulative fatigue damage degree of the previous evaluation cycle to dynamically modulate the current high-frequency equivalent series resistance. It accurately restores the microscopic vicious positive feedback process inside the capacitor, which is "damage leads to a surge in resistance, the surge in resistance causes a surge in heat generation, and high temperature further accelerates damage". It completely solves the technical pain point of serious distortion in hot spot temperature tracking in traditional methods.

[0013] 2. This invention overcomes the linear drawbacks of existing technologies that isolate and analyze electrical, thermal, and mechanical stresses in a linear fashion. It innovatively constructs a deep cross-coupling function of transient inrush current electrodynamics, high-temperature thermomechanical softening threshold boundary, and high-frequency electric field distortion slope. It corrects the transient overvoltage and partial discharge measured by conventional methods into thermomechanical equivalent transient stress and high-frequency equivalent partial discharge that truly conform to the physical nature of thin film micropore deformation failure. This effectively solves the long-term systematic underestimation of the true cumulative damage caused by severe transient events to the insulating medium. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of an online monitoring and evaluation method for series compensation capacitors provided by the present invention;

[0015] Figure 2 This invention provides a structural block diagram of an online monitoring and evaluation device for series compensation capacitors.

[0016] Figure 3 The block diagram of multi-physics coupling and historical damage closed-loop logic provided by the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0019] like Figure 1 and Figure 3 As shown, an embodiment of the present invention provides an online monitoring and evaluation method for series compensation capacitors, comprising the following steps:

[0020] Step S10: Acquire the operating signals of the series compensation capacitor, and extract the voltage RMS value sequence, harmonic current RMS value sequence, transient overvoltage peak value, transient overcurrent peak value, maximum transient voltage change rate, and synchronous partial discharge charge. The series compensation capacitor is a core power device used in ultra-high voltage and extra-high voltage power grids to improve transmission capacity and system stability. During long-term operation, it is subjected to continuous power frequency voltage, harmonic current, and transient events. Operating signals refer to various electrical and physical quantity data collected by sensors during the operation of the series compensation capacitor, such as voltage, current, temperature, and partial discharge. The voltage RMS value sequence is a continuous data set showing the root mean square value of the terminal voltage of the series compensation capacitor changing over time, reflecting the continuous electrical stress borne by the capacitor. The harmonic current RMS value sequence is a continuous data set showing the root mean square value of each harmonic current flowing through the series compensation capacitor changing over time; these harmonic currents are a significant factor causing internal heating of the capacitor. The peak transient overvoltage refers to the instantaneous maximum voltage reached at the terminals of the series compensation capacitor during transient events such as system short circuits and switching, which impacts the capacitor's insulation structure. The peak transient overcurrent refers to the instantaneous maximum current flowing through the series compensation capacitor during a transient event; the resulting electrodynamic force may damage the capacitor's internal structure. The maximum rate of change of transient voltage refers to the maximum speed at which the voltage at the terminals of the series compensation capacitor changes within a very short time during a transient event, reflecting the severity of the transient impact. The apparent charge of synchronous partial discharge refers to the amount of apparent charge of partial discharge simultaneously measured by partial discharge detection equipment during a transient event; it is a key indicator for assessing the degree of insulation degradation.

[0021] Step S20: Combining the historical cumulative fatigue damage degree and harmonic current RMS value sequence from the previous evaluation cycle, calculate the dynamic frequency-varying equivalent series resistance; substitute it and the voltage RMS value sequence into the thermal differential equation to calculate the dynamic hot spot temperature sequence including the damage positive feedback effect; the historical cumulative fatigue damage degree from the previous evaluation cycle refers to the degree of fatigue damage accumulated by the series compensation capacitor before the current evaluation cycle, reflecting the aging state of the equipment. The dynamic frequency-varying equivalent series resistance refers to the equivalent series resistance of the series compensation capacitor, the value of which changes dynamically with factors such as operating frequency, temperature, and the aging degree of the capacitor itself. The thermal differential equation is a mathematical model describing the temperature distribution and change law inside an object, and the hot spot temperature inside the capacitor can be calculated through this equation. The damage positive feedback effect refers to the phenomenon that damage inside the capacitor (such as insulation aging) will cause changes in its electrical and thermal properties, thereby accelerating heating or stress concentration, further aggravating the damage. The dynamic hot spot temperature sequence refers to the continuous data set of the value of the highest temperature inside the series compensation capacitor changing over time, which takes into account the dynamic influence of operating conditions, environmental conditions, and changes in the characteristics of the equipment itself.

[0022] Step S30: For transient events, construct a cross-coupling term of electrodynamics and thermomechanical softening. Combine this with the synchronous partial discharge television at the maximum rate of change of charge and transient voltage to calculate the high-frequency equivalent partial discharge quantity. A transient event refers to an abnormal operating condition in a power system that is short-duration, high-amplitude, and drastically changing, such as a short-circuit fault or switching operation. The cross-coupling term of electrodynamics and thermomechanical softening refers to the mathematical characterization term representing the mutual influence and interaction between the electrodynamics generated by the large current and the decrease in material mechanical strength (thermal softening) caused by high temperature during a transient event. The high-frequency equivalent partial discharge quantity is an equivalent quantitative index of the partial discharge phenomenon under transient high-frequency impact, which comprehensively considers the amplitude, frequency characteristics, and transient stress of the partial discharge.

[0023] Step S40: The transient overvoltage peak value is corrected using thermomechanical softening to obtain the thermomechanical equivalent transient stress. The damage amplification index is calculated by combining the dynamic hotspot temperature sequence and the high-frequency equivalent partial discharge quantity, and then the electro-thermal-mechanical coupled cumulative fatigue damage degree is accumulated and updated. Thermomechanical softening correction refers to adjusting the transient overvoltage peak value to reflect the impact of the decrease in the mechanical strength of the capacitor insulation material on the electrical stress bearing capacity under high temperature. The thermomechanical equivalent transient stress refers to the transient stress after thermomechanical softening correction, which more realistically reflects the actual stress level borne by the capacitor under the combined action of transient high temperature and electrical stress. The damage amplification index refers to the factor that accelerates the accumulation of capacitor fatigue damage under specific operating conditions, such as high temperature or increased partial discharge. The electro-thermal-mechanical coupled cumulative fatigue damage degree refers to the total degree of fatigue damage accumulated by the series-compensated capacitor after comprehensively considering electrical stress, thermal stress, mechanical stress, and their mutual coupling effects.

[0024] Step S50: Calculate the health status index of the series compensation capacitor based on the updated cumulative fatigue damage degree of the thermoelectric coupling. The health status index is a quantitative indicator for assessing the current operating condition and remaining life potential of the series compensation capacitor, usually expressed as a percentage or grade.

[0025] This embodiment provides an online monitoring and evaluation method for series compensation capacitors, aiming to solve the problems of hot spot temperature tracking distortion and insufficient characterization of multi-stress nonlinear synergistic damage effects in existing methods.

[0026] Specifically, various methods can be used to acquire the operating signals of series-compensated capacitors and extract multiple characteristic parameters. For example, current and voltage transformers can be installed at the capacitor's input and output terminals to acquire analog current and voltage signals in real time. These analog signals are then sent to a data acquisition unit and converted into digital signals. For the extraction of the voltage RMS sequence and harmonic current RMS sequence, a digital signal processor can be used to perform a Fourier transform on the acquired digital signals to separate the fundamental and harmonic components and calculate their RMS values. For the extraction of transient overvoltage and transient overcurrent peak values, fixed amplitude and duration thresholds can be set, and the maximum value of the signal exceeding these thresholds can be recorded. The maximum rate of change of transient voltage can be obtained by performing differential operations on the voltage signal and finding its maximum slope. The charge quantity of synchronous partial discharge can be obtained by installing a high-frequency partial discharge sensor near the capacitor and using time synchronization technology to match the partial discharge signal with the occurrence time of the transient event.

[0027] The calculation of the dynamic frequency-varying equivalent series resistance, which combines the historical cumulative fatigue damage degree and the effective value sequence of harmonic current from the previous evaluation cycle, and then substitutes this resistance, along with the effective value sequence of voltage, into the thermal differential equation to calculate the dynamic hot spot temperature sequence including the damage positive feedback effect, can be achieved as follows: The calculation of the dynamic frequency-varying equivalent series resistance can be based on a preset empirical model that takes the frequency and amplitude of the harmonic current as input and corrects it according to a coarse level of historical cumulative fatigue damage degree. For example, a simple linear relationship can be set such that the equivalent series resistance increases by a fixed proportion as the historical damage degree increases. Subsequently, the calculated dynamic frequency-varying equivalent series resistance and the effective value sequence of voltage are substituted into a simplified lumped-parameter thermal differential equation. This equation can be solved iteratively using fixed thermal resistance and thermal capacity parameters. During the iteration process, the damage positive feedback effect can be achieved by adjusting the heating power term inside the capacitor by a preset proportion based on the current temperature value after each temperature calculation, to simulate the accelerating effect of damage on heating.

[0028] For transient events, the following approach can be used to construct a cross-coupling term for electrodynamic and thermomechanical softening effects, and to calculate the high-frequency equivalent partial discharge quantity by combining the synchronous partial discharge television's charge quantity with the maximum rate of change of transient voltage. The construction of the cross-coupling term for electrodynamic and thermomechanical softening effects can be achieved by independently evaluating the electrodynamic effect generated by transient overcurrent and the thermomechanical softening effect caused by transient high temperature leading to a decrease in material strength, and then combining the two through a simple weighted summation. For example, two fixed weighting factors can be set, multiplied by the intensity index of the electrodynamic effect and the intensity index of the thermomechanical softening effect respectively, and then the results are added together. The calculation of the high-frequency equivalent partial discharge quantity can be based on the product of the synchronous partial discharge television's charge quantity and the maximum rate of change of transient voltage, with a fixed correction coefficient introduced. For example, when the maximum rate of change of transient voltage exceeds a certain preset threshold, the synchronous partial discharge television's charge quantity is multiplied by a preset amplification factor to reflect the enhancing effect of high-frequency transient impact on partial discharge.

[0029] The following approach can be used to calculate the thermomechanical equivalent transient stress by applying thermomechanical softening correction to the peak value of transient overvoltage, and then calculating the damage amplification index by combining the dynamic hotspot temperature sequence and the high-frequency equivalent partial discharge quantity, thereby accumulating and updating the electrothermal-mechanical coupled cumulative fatigue damage. The thermomechanical softening correction can be achieved by consulting a preset temperature-material strength relationship curve. Based on the dynamic hotspot temperature at the moment of the transient event, the corresponding material strength reduction coefficient is obtained from the curve, and then the peak value of the transient overvoltage is multiplied by this coefficient to obtain the thermomechanical equivalent transient stress. The calculation of the damage amplification index can be based on a preset lookup table, which takes the current value of the dynamic hotspot temperature sequence and the level of the high-frequency equivalent partial discharge quantity as input, and outputs a fixed damage amplification coefficient. For example, when both the temperature and the partial discharge quantity are at a high level, the lookup table will return a larger fixed damage amplification index. The cumulative update of the electrothermal-mechanical coupled cumulative fatigue damage can use a simple linear accumulation model, directly adding the damage value calculated for each transient event to the historical cumulative damage.

[0030] The following approach can be used to calculate the health status index of the series compensation capacitor based on the updated cumulative fatigue damage degree of the thermoelectric coupling. The health status index can be calculated by comparing the updated cumulative fatigue damage degree of the thermoelectric coupling with a preset health status threshold and using a simple piecewise function or linear mapping relationship. For example, a linearly decreasing function can be set to map the cumulative damage degree to a health status index range of 0 to 100; the higher the damage degree, the lower the health status index.

[0031] This application further proposes that the specific logic for calculating the dynamic hotspot temperature sequence in step S20 includes: constructing a negative correlation mapping relationship between ambient wind speed and dynamic equivalent thermal resistance to characterize the improvement of heat dissipation efficiency by forced convection; constructing a positive nonlinear modulation function of historical cumulative fatigue damage, hotspot temperature at the previous moment, and fundamental equivalent series resistance, and calculating the dynamic frequency-varying equivalent series resistance to characterize the reduction of conductive area caused by the self-healing of the capacitor and the resulting positive feedback effect of heat generation surge; based on the sum of dielectric heat loss at the current moment and Joule heat loss considering the dynamic frequency-varying equivalent series resistance, subtracting the heat dissipation modulated by the dynamic equivalent thermal resistance, and iteratively calculating the dynamic hotspot temperature sequence through discrete time step; the mathematical formula for calculating the dynamic frequency-varying equivalent series resistance and the dynamic hotspot temperature sequence is:

[0032]

[0033]

[0034]

[0035] in: Indicates dynamic equivalent thermal resistance; This represents the equivalent thermal resistance of static natural convection. Indicates the wind speed convection cooling coefficient; Indicates real-time ambient wind speed; This represents the dynamic frequency-varying equivalent series resistance. Indicates the fundamental equivalent series resistance; Indicates the harmonic order; Indicates the damage-resistance coupling coefficient; This indicates the historical cumulative fatigue damage level from the previous assessment period; This represents the dynamic hotspot temperature at the previous sampling time; This represents the dynamic hotspot temperature at the current k-th sampling time, i.e., the dynamic hotspot temperature sequence. Indicates the rated reference thermodynamic temperature; This represents the activation energy temperature constant; Indicates the sampling time interval; Indicates equivalent heat capacity; Indicates the highest harmonic order; This represents the effective value of the h-th harmonic current at time k. This represents the effective voltage value at time k. Indicates the power frequency angular frequency; Indicates capacitance; This represents the tangent of the loss angle of the insulating medium; Indicates ambient temperature.

[0036] The dynamic equivalent thermal resistance is calculated using an empirical formula for wind speed convection. This dynamic equivalent thermal resistance is a dynamic parameter characterizing the heat dissipation capacity of a series-compensated capacitor, and its value changes with the real-time ambient wind speed. Its purpose is to address the problem that traditional static thermal resistance cannot reflect the dynamic changes in actual heat dissipation conditions. This calculation can be performed using an empirical formula for wind speed convection. To achieve this, in which The equivalent thermal resistance is static natural convection. The wind speed convective cooling coefficient is determined by real-time monitoring of ambient wind speed. Dynamic calculations are performed. In addition, other environmental factors, such as ambient temperature and humidity, can be considered. The dynamic equivalent thermal resistance can be determined by establishing a multivariate empirical model or a lookup table fitted based on computational fluid dynamics (CFD) simulation results. The calculation includes a dynamic hotspot temperature sequence incorporating damage positive feedback effects. This dynamic hotspot temperature sequence refers to continuous data showing the temperature change of the hottest spot inside the series-compensated capacitor over time. It considers not only changes in the external environment but also the impact of the capacitor's own aging damage on its heating characteristics. Its purpose is to provide more accurate internal temperature information of the capacitor, providing a reliable basis for subsequent calculations of cumulative fatigue damage. This calculation can be performed using thermal differential equations. Iterative calculations are performed. This includes the dynamically varying equivalent series resistance. This includes the positive feedback effect of damage. Alternatively, a finite element analysis (FEA) model can be used, in which the geometry, material properties, heat source distribution, and dynamic boundary conditions (such as thermal resistance affected by wind speed) of the capacitor are input into the model. The internal temperature field distribution can be obtained through numerical solution, and then the hot spot temperature sequence can be extracted.

[0037] This solution addresses the issue of distortion in dynamic hotspot temperature calculations by optimizing the calculation process of the dynamic hotspot temperature sequence from three aspects: dynamic correction of heat dissipation boundaries, positive feedback correction of equivalent resistance damage, and recursive calculation of hotspot temperatures. This approach better reflects the complex operating conditions of capacitors in actual service, yielding more realistic dynamic hotspot temperature results. Firstly, it calculates the dynamic equivalent thermal resistance based on real-time ambient wind speed. Using the static natural convection equivalent thermal resistance as a foundation, it combines the wind speed convection cooling coefficient and real-time ambient wind speed to obtain the dynamic thermal resistance that changes with the environment. This solves the problem that the original static thermal resistance cannot adapt to the dynamic changes in actual environmental heat dissipation conditions, accurately reflecting the actual heat dissipation capacity of the capacitor under different wind speed conditions. Secondly, when calculating the dynamic frequency-varying equivalent series resistance, a basic resistance matching the frequency characteristics is first obtained by combining the fundamental equivalent series resistance with the square root of the harmonic order. Then, a correction term is constructed by introducing the historical cumulative fatigue damage degree of the previous evaluation cycle and the dynamic hot spot temperature of the previous sampling time. This not only reflects the frequency characteristics of the equivalent series resistance under different harmonic orders, but also shows that cumulative damage increases the equivalent resistance, thereby further increasing the positive feedback effect of heat generation. It also adapts to the influence of temperature on the accelerated damage effect, solving the problem that the original static resistance could not reflect the changes in heat generation characteristics after capacitor aging and degradation, and can more accurately calculate the heat generation power corresponding to each harmonic of the capacitor. Finally, the dynamic hot spot temperature at the current sampling time is calculated by successive recursion based on the thermal differential equation. The calculation process integrates the heat generation power of each harmonic and the heat generation power of the insulation medium itself, while subtracting the heat dissipation power calculated based on the current dynamic thermal resistance. This allows for the successive updating of the dynamic hot spot temperature at each sampling time, taking into account the dynamic changes in heat dissipation boundary and the positive feedback of heat generation from damage throughout the process. This provides accurate and reliable basic temperature data for subsequent cumulative fatigue damage calculation and health status assessment. By providing a more accurate and dynamically responsive hotspot temperature sequence, this scheme directly enhances the reliability of subsequent calculations of cumulative fatigue damage caused by electrothermal coupling and assessment of health status indices. The improved temperature data, by considering dynamic environmental changes and internal damage evolution, ensures that fatigue damage accumulation is based on more realistic temperature stress, thereby making the health status assessment of the series compensation capacitor more accurate and reliable.

[0038] As a specific implementation method, real-time environmental wind speed This can be obtained from a weather sensor (e.g., an anemometer) installed near the series compensation capacitor. Voltage RMS value sequence. Harmonic Current RMS Value Sequence The parameters can be obtained through sampling and calculation using voltage and current transformers connected to the capacitor circuit, in conjunction with a data acquisition unit. Regarding parameter determination... (Static natural convection equivalent thermal resistance) and The (wind speed convection cooling coefficient) can be calibrated by conducting thermal tests on typical capacitor cells under different wind speed conditions in the laboratory, or by fitting the results with reference to the thermal characteristic data and computational fluid dynamics (CFD) simulation results provided by the manufacturer. The fundamental equivalent series resistance can be obtained by impedance measurement at the rated frequency and temperature. The damage-resistance coupling coefficient can be determined by analyzing the trend of resistance change with cumulative damage through accelerated aging tests. (Rated reference thermodynamic temperature) and The activation energy temperature constant is usually an inherent property of insulating materials and can be obtained from the material supplier or determined through thermal degradation experiments. (Equivalent heat capacity) can be estimated based on the material composition and mass of the capacitor, or determined experimentally. The dielectric loss tangent (or dielectric loss angle tangent) is a parameter representing the dielectric loss characteristic of an insulating material, which can be obtained through dielectric loss testing. In computational implementation, the above mathematical formula can be programmed into an embedded processor (e.g., a digital signal processor (DSP) or a field-programmable gate array (FPGA)) or an industrial control computer. The system samples at a preset time interval. (For example, perform iterative calculations every 1 second or every 1 minute): First, read the current real-time environmental wind speed. Harmonic current RMS value sequence Voltage RMS value sequence and ambient temperature Secondly, utilize Calculate dynamic equivalent thermal resistance Secondly, the historical cumulative fatigue damage level from the previous assessment period was considered. Dynamic hotspot temperature at the previous sampling time Calculate the dynamic frequency-varying equivalent series resistance corresponding to each harmonic. Finally, these parameters are substituted into the thermal differential equation to calculate and update the dynamic hotspot temperature at the current sampling time k. This value is stored to form a dynamic hotspot temperature sequence, and also serves as the reference for the next sampling time. .

[0039] By introducing the damage positive feedback effect through the above technical solution, the calculation of the dynamically frequency-varying equivalent series resistance can reflect the degradation of the capacitor's inherent characteristics caused by cumulative fatigue damage during long-term operation. Specifically, damage increases the equivalent resistance, thereby increasing heat generation, making the hotspot temperature calculation more realistic. Ultimately, this iteratively calculated dynamic hotspot temperature sequence integrates the effects of dynamic heat dissipation boundaries and damage-induced heat generation positive feedback, providing a highly accurate and reliable characterization of the capacitor's internal thermal state. This effectively solves the problem of hotspot temperature tracking distortion in traditional methods, providing solid and accurate foundational data for subsequent cumulative fatigue damage calculations and health status assessments.

[0040] This application further proposes that the specific logic for calculating the high-frequency equivalent partial discharge quantity in step S30 includes: extracting the charge quantity of the synchronous partial discharge television synchronized with the transient event as a reference base; setting a thermo-mechanical coupling amplification factor with the glass transition temperature of the insulating medium as the trigger boundary; when the transient hot spot temperature exceeds the glass transition temperature, constructing a mechanical stress characterization term using the square term of the transient overcurrent peak value, and performing nonlinear surge amplification in the process of approaching the absolute temperature of the physical melting point to characterize the severe deformation of the internal micropores caused by electrodynamic force under high elasticity; introducing a nonlinear acceleration term of the maximum rate of change of transient voltage relative to the rated rate of change; performing synergistic multiplication or exponentialization processing on the reference base, the thermo-mechanical coupling amplification factor, and the nonlinear acceleration term to output the high-frequency equivalent partial discharge quantity; the specific mathematical formula for calculating the high-frequency equivalent partial discharge quantity is:

[0041]

[0042] in: This represents the high-frequency equivalent partial discharge quantity corresponding to the i-th transient event; This indicates the amount of charge in the synchronous partial discharge television; Indicates the electrodynamic-micropore deformation coupling coefficient; Indicates the peak value of transient overcurrent; Indicates the rated current; The real-time dynamic hotspot temperature at the moment of occurrence of the i-th transient event is obtained by aligning the event trigger times and extracting the values ​​at the corresponding sampling moments in the dynamic hotspot temperature sequence. Indicates the glass transition temperature; Represents the physical melting point, or absolute temperature. This represents a very small positive number that prevents the denominator from being zero; Indicates the maximum rate of change of transient voltage; Indicates the rate of change of the rated power frequency reference voltage; This represents the nonlinear acceleration index.

[0043] In the above technical solution, extracting the synchronization parameters at the time of the transient event is a fundamental step in calculating the high-frequency equivalent partial discharge quantity. Its purpose is to obtain key data on the capacitor's operating state during the transient event. These parameters can be synchronously acquired by a high-precision, high-sampling-rate data acquisition system, for example, by configuring multiple sensors (such as current sensors, voltage sensors, partial discharge sensors, temperature sensors, etc.) and synchronizing them in time to ensure that all relevant data points are recorded at the same timestamp. Calculating the high-frequency equivalent partial discharge quantity is the core of this solution. It aims to correct the originally measured partial discharge quantity by introducing multi-physics coupling effects to more accurately reflect its damage to the insulating material. This is typically accomplished by implementing the aforementioned mathematical model in an embedded processor or host computer software. Synchronous partial discharge measurement is related to charge quantity. This is the raw data directly measured by partial discharge monitoring equipment, which can be acquired by ultra-high frequency (UHF) sensors, acoustic sensors, or traditional partial discharge detectors. Electrodynamic-micropore deformation coupling coefficient. This is a parameter characterizing the degree of microstructural deformation of an insulating material under the action of an electric field. Its value can be obtained through materials mechanics experiments, finite element simulation analysis, or empirical calibration based on historical operating data. (Transient overcurrent peak value) This is the maximum current flowing through the capacitor during a transient event, which can be measured using sensors such as high-bandwidth current transformers or Rogowski coils. Rated current. This is the nominal operating current of the capacitor, which can usually be found on the equipment nameplate or in the design specifications. Real-time dynamic hotspot temperature. This is the temperature of the hottest spot inside the capacitor at the moment the transient event occurs. It can be measured directly by a fiber optic temperature sensor or estimated using a thermal model (such as the dynamic hot spot temperature sequence calculation method mentioned above) combined with the event trigger time. Glass transition temperature. and physical melting point absolute temperature These are key thermodynamic properties of insulating materials, reflecting changes in the material's mechanical behavior at different temperatures. These parameters are typically obtained from datasheets provided by material suppliers or through experimental methods such as differential scanning calorimetry (DSC). Minimum normal values... It is a numerical stability parameter used to avoid zero denominators in mathematical calculations, and is usually taken as a very small positive number, such as 10. -9 or 10- 12 Maximum rate of change of transient voltage This is the maximum slope of the voltage waveform during a transient event. It can be measured using a high-voltage divider and a high-speed oscilloscope, or obtained by numerical differentiation of the acquired voltage waveform. Rated power frequency reference voltage change rate. This is the rate of change of voltage of a capacitor under its rated power frequency voltage, which can be calculated based on the rated voltage and the power frequency angular frequency. Nonlinear acceleration index. It is an empirical coefficient that reflects the effect of transient voltage change rate on partial discharge acceleration. Its value can be determined by accelerated aging test or statistical analysis of historical fault data.

[0044] This scheme addresses the inaccuracy of partial discharge assessment in traditional methods by integrating multi-physics coupling effects to correct for partial discharge during transient events. Specifically, based on acquiring the operating signal of the series compensation capacitor and calculating the dynamic hotspot temperature sequence by combining historical cumulative fatigue damage and harmonic current RMS value sequences, this scheme further extracts synchronization parameters at the time of the transient event, including the synchronous partial discharge in charge. Transient overcurrent peak value Real-time dynamic hotspot temperature and the maximum rate of change of transient voltage These parameters, as input, are used in conjunction with the aforementioned mathematical formula to transform the original synchronous local display television into a quantity of charge. Corrected to high-frequency equivalent partial discharge quantity The exponential term in the formula takes into account the electrodynamic-micropore deformation coupling effect, i.e., the peak value of the transient overcurrent. With rated current The square of the ratio term reflects the deformation effect of the electrodynamic force generated by the transient high current on the insulating micropores, thereby accelerating the development of partial discharge. Simultaneously, the formula also incorporates the thermomechanical softening effect, through real-time dynamic hotspot temperature... Glass transition temperature and physical melting point absolute temperature The functional relationship between the two values ​​characterizes the amplification effect of the softening of insulating materials at high temperatures on partial discharge. Furthermore, the maximum rate of change of transient voltage... Rate of change of rated power frequency reference voltage The ratio term, combined with the nonlinear acceleration index This reflects the promoting effect of high voltage change rate on electric field distortion and partial discharge development. Through this multi-factor nonlinear coupling correction, this scheme can more comprehensively and accurately quantify the true damage intensity of partial discharge under transient conditions, providing a more reliable input for subsequent calculation of electrothermal-mechanical coupled cumulative fatigue damage, thereby improving the accuracy of the entire online monitoring and evaluation method.

[0045] As a specific implementation method, an integrated online monitoring system can be used to achieve the above technical solution. This system may include: a high-precision current transformer and a high-voltage divider, used to acquire the current and voltage signals of the series compensation capacitor in real time, and extract the transient overcurrent peak value from them. and maximum rate of change of transient voltage Ultra-high frequency (UHF) partial discharge sensor, used to synchronously monitor and acquire the charge quantity of synchronous partial discharge. ; and fiber optic temperature sensors, used to directly measure or calculate real-time dynamic hotspot temperatures through thermal models. All sensor data is synchronously acquired and timestamped via a high-speed data acquisition unit, and then transmitted to a central processing unit. The central processing unit can be a high-performance industrial control computer or an embedded digital signal processor (DSP), which pre-stores the glass transition temperature of the insulating material. Physical melting point and absolute temperature Electrodynamic-micropore deformation coupling coefficient Nonlinear acceleration index and very small normal numbers Parameters such as synchronization parameters. When the system detects a transient event, the central processing unit immediately extracts the corresponding synchronization parameters from the collected data and calculates the high-frequency equivalent partial discharge quantity in real time according to the above mathematical formula. For example, when a system short-circuit fault occurs, the monitoring system simultaneously records the peak transient overcurrent, the maximum rate of change of transient voltage, the amount of charge in the synchronous partial discharge, and the real-time hotspot temperature at the moment of the fault. The central processing unit substitutes these data into a formula to calculate the high-frequency equivalent partial discharge caused by the transient event.

[0046] Through the above technical solution, this application effectively solves the problem of inaccurate partial discharge assessment under transient conditions using traditional methods. This solution introduces nonlinear coupling corrections of multiple factors, including electrodynamics, thermomechanical softening, and transient voltage change rate, to correct the original monitored synchronous partial discharge charge quantity into a high-frequency equivalent partial discharge quantity that more closely reflects the actual damage effect. This makes the assessment of insulation damage in series-compensated capacitors more accurate, avoiding the assessment bias caused by neglecting the synergistic effects of multiple physical fields in traditional methods. This provides a more accurate and reliable basis for subsequent calculations of cumulative fatigue damage, thereby improving the accuracy and reliability of health status assessment for series-compensated capacitors.

[0047] This application further proposes the following specific logic for thermodynamic softening correction of the transient overvoltage peak value in step S40: using the transient overvoltage peak value as the basic electrical stress; constructing a thermodynamic softening correction coefficient positively correlated with the transient overcurrent peak value, and using the transient hot spot temperature approaching the physical melting point absolute temperature as the limiting divergence boundary; setting an overflow safety margin temperature parameter at the limiting divergence boundary to limit the calculation upper limit; using the thermodynamic softening correction coefficient to perform nonlinear amplification mapping on the basic electrical stress, outputting the event-level thermodynamic equivalent transient stress; the specific mathematical formula for calculating the thermodynamic equivalent transient stress is:

[0048]

[0049] in: This represents the thermomechanical equivalent transient stress corresponding to the i-th event; Indicates the peak value of transient overvoltage; Indicates the peak value of transient overcurrent; Indicates the rated current; Represents the real-time dynamic hotspot temperature at the moment of occurrence of the i-th transient event; Indicates the rated reference thermodynamic temperature; Represents the physical melting point, or absolute temperature. This indicates the temperature at which there is a safety margin to prevent overflow.

[0050] To better understand the above scheme, the key technical features involved are described in detail below. Transient overvoltage peak value. This refers to the maximum instantaneous voltage across the series compensation capacitor during the i-th transient event. This peak value can be monitored and recorded in real time using a high-precision voltage sensor (e.g., a capacitive voltage divider or fiber optic voltage sensor), or predicted using a power grid simulation model. (Transient overcurrent peak value) This refers to the instantaneous maximum value of the current flowing through the series compensation capacitor during the i-th transient event. This peak value can be monitored and recorded in real time by a high-precision current sensor (e.g., a current transformer or Rogowski coil), or predicted by a power grid simulation model. Rated current. This refers to the effective value of the continuously flowing current that the series compensation capacitor is designed to handle under normal operating conditions. This parameter is usually provided by the capacitor manufacturer and can be found on the equipment nameplate or in the technical specifications. Real-time dynamic hotspot temperature at the moment of the i-th transient event. This refers to the actual temperature at the point where the internal insulating medium of the series compensation capacitor reaches its highest temperature during the i-th transient event. This temperature can be directly measured by embedding a fiber optic temperature sensor inside the capacitor, or calculated and tracked in real time using a dynamic thermal model (as described in step S20 above) based on capacitor operating signals (such as the effective voltage value sequence and the effective harmonic current value sequence) and environmental parameters (such as ambient temperature and wind speed). Rated reference thermodynamic temperature This refers to the standard ambient temperature or internal reference temperature used as the basis for designing or testing capacitors. This temperature is usually a fixed value and is used as a benchmark for evaluating the thermal state of the capacitor. Physical melting point (absolute temperature) This refers to the physical melting point of the insulating dielectric material that makes up a capacitor, expressed in an absolute temperature scale. This parameter is an inherent property of the insulating material, reflecting the critical point at which the material undergoes a phase transition or structural softening at high temperatures. Overflow safety margin temperature. This refers to a very small positive temperature value that is artificially set to prevent numerical instability or overflow during calculations due to the denominator approaching zero. This value ensures that the real-time dynamic hotspot temperature... Very close to the physical melting point absolute temperature At this time, the denominator can still maintain a finite non-zero value, thus ensuring the robustness of the calculation.

[0051] The proposed solution corrects the original transient overvoltage peak value by introducing a thermomechanical softening correction, thereby obtaining a thermomechanical equivalent transient stress that accurately reflects the actual operating conditions. This provides a reliable basis for the subsequent accurate calculation of cumulative fatigue damage. The overall transient overvoltage peak value is considered. As a basis for correction, the core influence of overvoltage amplitude on transient stress is retained, ensuring that the stress calculation is based on actual physical laws. This is achieved by adjusting the peak value of the transient overcurrent. With rated current The square of the ratio, with the addition of a correction term, characterizes the promoting effect of the electrodynamic effect generated by the transient high current on the softening of the insulating medium. The larger the transient overcurrent, the stronger the deformation and softening effect on the dielectric structure, and the corresponding equivalent transient stress will also increase accordingly, which is consistent with the law of synergistic destruction by electrodynamic and thermal effects in actual operation. Simultaneously, the current real-time dynamic hotspot temperature is incorporated. With the rated reference thermodynamic temperature The difference is fully utilized to calculate the dynamic hotspot temperature information obtained in step S20 above, reflecting the impact of the capacitor's current actual thermal state on the degree of dielectric softening. The higher the temperature, the worse the mechanical properties of the dielectric itself, and the greater the equivalent stress actually borne under the same original overvoltage. This solves the problem that the original scheme did not consider the impact of actual operating temperature rise on dielectric performance. In addition, the physical melting point absolute temperature is used. With current dynamic hotspot temperature The difference characterizes the extent to which temperature rise affects the degradation of the mechanical properties of the medium, while also introducing a safety margin temperature to prevent overflow. By taking the maximum value, the problem of abnormal overflow of the denominator during the calculation is avoided, ensuring the stability and reliability of the calculation process. The final obtained thermodynamic equivalent transient stress... It can accurately reflect the actual stress magnitude after the coupling of electrical, thermal, and mechanical effects under transient events, providing accurate input parameters for subsequent accurate calculation of cumulative damage and assessment of health status.

[0052] As a specific implementation method, in the online monitoring and evaluation system for series compensation capacitors, after receiving the signal of the i-th transient event, the processor first obtains the peak value of the transient overvoltage corresponding to the event from the data acquisition module. and transient overcurrent peak Simultaneously, the processor extracts the real-time dynamic hotspot temperature aligned with the moment the transient event occurs from the real-time hotspot temperature tracking module (which is based on the calculation results from step S20 above). Rated current Rated reference thermodynamic temperature Physical melting point and absolute temperature and overflow safety margin temperature These parameters are pre-stored in memory. The processor substitutes these parameters into the above formula for calculating the equivalent transient stress of the thermodynamic engine. For example, when the peak value of the transient overcurrent... Much greater than the rated current And real-time dynamic hotspot temperature Significantly higher than the rated reference thermodynamic temperature And close to the physical melting point absolute temperature At that time, the correction term will become very large, thus making the calculated equivalent transient stress of the thermomechanical system... Much higher than the original transient overvoltage peak value Conversely, if both transient overcurrent and hot spot temperature are at relatively low levels, the impact of the correction term is relatively small. In this way, the system can dynamically and accurately assess the actual stress on the capacitor caused by each transient event based on the actual operating conditions.

[0053] Through the above technical solution, this application effectively solves the problem of inaccurate stress assessment caused by the failure of traditional methods to fully consider the thermomechanical softening effect when evaluating the impact of transient events on series compensation capacitors. This solution corrects the transient overvoltage peak value for thermomechanical softening, enabling the calculated thermomechanical equivalent transient stress to more accurately reflect the actual stress on the capacitor under transient high-current impacts and local abnormal temperature rises. This avoids the cumulative fatigue damage calculation bias caused by the underestimation of true stress in traditional methods, significantly improving the accuracy and reliability of online monitoring and evaluation of series compensation capacitors. It provides more precise input parameters for capacitor health status assessment, thereby enabling more accurate prediction of equipment lifespan and guiding operation and maintenance.

[0054] This application further proposes the following specific logic for calculating the event-level damage amplification index and updating the electrothermal-mechanical coupling cumulative fatigue damage degree in step S40: Extracting the inherent reference fatigue index of the insulating material, and using the thermal aging temperature rise ratio of the transient hotspot temperature compared to the rated reference temperature, and the degradation ratio of the high-frequency equivalent partial discharge quantity relative to the critical discharge threshold, respectively, to positively modulate and amplify the reference fatigue index to obtain the event-level damage amplification index for a single event; normalizing the thermo-mechanical equivalent transient stress of each transient event, and performing nonlinear calculations using the corresponding event-level damage amplification index as the power exponent, and accumulating the results over the entire monitoring period to obtain the electrothermal-mechanical coupling cumulative fatigue damage degree; the specific mathematical formulas for calculating the event-level damage amplification index and updating the electrothermal-mechanical coupling cumulative fatigue damage degree are as follows:

[0055]

[0056] in: This represents the event-level damage amplification index corresponding to the i-th event; Indicates the baseline fatigue index; Represents the real-time dynamic hotspot temperature at the moment of occurrence of the i-th transient event; Indicates the rated reference thermodynamic temperature; This represents the high-frequency equivalent partial discharge quantity corresponding to the i-th transient event; This represents the physical threshold of the critical discharge charge. This indicates the cumulative fatigue damage degree of the updated electrothermal coupling; This represents the total number of transient events that have occurred up to the current period. This represents the thermomechanical equivalent transient stress corresponding to the i-th event; This indicates the rated voltage.

[0057] The event-level damage amplification index This parameter is used to quantify the amplification effect of each transient event on the fatigue damage caused to the series-compensated capacitor. It is a dynamically changing parameter that adjusts according to the specific operating state of the capacitor at the time of the transient event, thus more accurately reflecting the severity of damage under different operating conditions. Its calculation can be based on empirical models, physical models, or data-driven models to capture the influence of temperature and partial discharge on the material's fatigue life. (Baseline fatigue index) This represents the inherent fatigue characteristics of the series-compensated capacitor material under standard or rated operating conditions. It is typically obtained through laboratory fatigue testing or material handbooks and serves as a starting point for calculating the damage amplification index. For example, it can be determined based on the slope of the SN curve (stress-cycle count curve) or by fitting fatigue life data of a specific material under conditions of no thermal stress and no partial discharge. The real-time dynamic hotspot temperature at the moment of the i-th transient event. This refers to the actual temperature of the hottest spot inside the series-compensated capacitor during the i-th transient event. Obtaining this parameter is crucial because it directly reflects the thermal stress state of the capacitor, and high temperatures significantly accelerate the aging and fatigue damage of the insulation material. This temperature can be extracted from a dynamic hotspot temperature sequence, which is calculated using thermal differential equations combined with operating signals (such as voltage RMS value sequences and harmonic current RMS value sequences). Rated reference thermodynamic temperature. This is a reference temperature set in the capacitor's design or operating specifications, typically the capacitor's stable operating temperature under rated conditions or the ambient reference temperature. It serves as a reference point to measure the deviation of real-time hotspot temperature from normal conditions, quantifying the impact of temperature on the damage amplification index. The high-frequency equivalent partial discharge quantity corresponding to the i-th transient event. This represents the equivalent intensity of the partial discharge inside the capacitor during the i-th transient event. Partial discharge is a significant indicator of insulation degradation; the higher the intensity, the more destructive the effect on the insulating material. This parameter can be obtained by constructing a cross-coupling term of electrodynamics and thermomechanical softening based on the maximum rate of change of charge and transient voltage during synchronous partial discharge. The physical threshold of the critical discharge charge is also relevant. This is the upper limit of the partial discharge charge that the capacitor insulation material can withstand; exceeding this threshold is considered to lead to a sharp acceleration of insulation damage. It is a material property parameter, typically determined through dielectric strength testing or life testing of the insulation material, and serves as a normalized reference for the effect of partial discharge on the damage amplification index. Updated thermo-mechanical coupling cumulative fatigue damage degree. This represents the total fatigue damage accumulated by the series compensation capacitor up to the current assessment period k, taking into account the coupling effects of electrical, thermal, and mechanical stresses. It is a continuously accumulating quantity, reflecting the overall aging state of the capacitor since it was put into operation. This damage level can serve as a key indicator for assessing the remaining life and health status of the capacitor. The total number of transient events that have occurred up to the current period. The total number of transient events detected from the time the capacitor was put into operation until the current evaluation period k is recorded. Each transient event causes some degree of damage to the capacitor, so the damage from all events needs to be accumulated. The thermomechanical equivalent transient stress corresponding to the i-th event is recorded. This is the comprehensive stress caused to the capacitor by the i-th transient event. It not only considers the peak value of the transient overvoltage but also incorporates the effects of the peak value of the transient overcurrent and the real-time dynamic hot spot temperature through thermomechanical softening correction. This correction makes the stress value more accurately reflect the actual mechanical and electrical stresses caused to the material by the transient event under high temperature and high current impact. This stress can be obtained by thermomechanical softening correction based on the peak value of the transient overvoltage. Rated voltage This is the rated operating voltage specified in the design or operating specifications of the series compensation capacitor. It serves as a benchmark for measuring transient stress levels, used to normalize the equivalent transient stress of the thermodynamic engine for comparison in fatigue damage calculations.

[0058] This application's solution addresses the problem in traditional methods where a fixed damage index cannot accurately reflect the true damage of transient events under different working conditions by introducing a dynamically changing event-level damage amplification index. Specifically, during the update of accumulated fatigue damage, the event-level damage amplification index is first calculated for each transient event. The calculation of this index fully considers the real-time dynamic hotspot temperature of the capacitor at the moment of the transient event. and high-frequency equivalent partial discharge quantity Real-time dynamic hotspot temperature The exponential function reflects the accelerating effect of temperature on the aging damage of insulating materials; that is, the higher the temperature, the more significant the damage amplification effect. Meanwhile, the high-frequency equivalent partial discharge quantity... Then, by comparing with the physical threshold of the critical discharge charge... The ratio was further adjusted to correct the damage amplification index, reflecting the amplification effect of the degree of partial discharge development on damage. This method of dynamically adjusting the damage amplification index based on real-time operating parameters allows the damage assessment of each transient event to accurately adapt to the specific operating conditions at the time of its occurrence, thus overcoming the limitations of a fixed damage index. Based on this, the cumulative fatigue damage degree of the thermo-mechanical coupling was updated. At that time, the total number of transient events that have occurred up to the current period will be counted. The equivalent transient stress of the thermomechanical system corresponding to each event in the process. With rated voltage The ratio, based on the dynamic event-level damage amplification index corresponding to the event. The summation is performed exponentially. This summation method not only conforms to the physical characteristic of irreversible accumulation of fatigue damage, but more importantly, it matches a unique, real-time-condition-corrected damage amplification exponent to each transient event. It can accurately capture the nonlinear damage to capacitors caused by different transient events under various operating conditions. For example, under conditions of high temperature or severe partial discharge, even if the transient stress level is the same, the resulting damage will be greater. The damage amplification index is amplified to more realistically reflect the actual aging process of the capacitor. This scheme is closely integrated with the aforementioned techniques for calculating dynamic hotspot temperature sequences, high-frequency equivalent partial discharge, and thermomechanical equivalent transient stress, forming a complete and interconnected damage assessment system. Accurate calculation of the dynamic hotspot temperature sequence provides precise temperature input for the damage amplification index; the introduction of high-frequency equivalent partial discharge further improves the characterization of insulation damage; and the correction of thermomechanical equivalent transient stress ensures the authenticity of the transient stress input. The precise acquisition and dynamic coupling of these parameters mean that the calculation of cumulative fatigue damage is no longer based on an idealized static model, but can reflect the real damage accumulation process of the capacitor under complex operating conditions in real time, dynamically, and comprehensively. In this way, this application can provide more accurate and reliable basic data for the health status assessment of series-compensated capacitors.

[0059] As a specific implementation method, when the series compensation capacitor encounters a transient event (such as a system short circuit or switching operation) during operation, the real-time dynamic hot spot temperature at the moment the event occurs is first recorded. and high-frequency equivalent partial discharge quantity Assuming the capacitor's internal temperature is high and there is some degree of partial discharge, the system will adjust the parameters based on a preset baseline fatigue index. Rated reference thermodynamic temperature and the physical threshold of critical discharge charge Combined with real-time acquisition and Through formula Calculate the event-level damage amplification index specific to this transient event. .because higher and Existence, calculated The value will be larger than the baseline value under normal temperature and no partial discharge conditions, thus reflecting the accelerating effect of high temperature and partial discharge on damage. Subsequently, for this transient event, the system will calculate its corresponding thermomechanical equivalent transient stress. This stress value has taken into account the combined effects of transient overvoltage peak value, transient overcurrent peak value, and real-time dynamic hotspot temperature. Finally, the event... With the rated voltage of the capacitor The ratio, based on the event-level damage amplification index just calculated. The cumulative fatigue damage degree of the electrothermal coupling is a power-law sum, added to the current value. In the middle. For example, if it has already happened before. If the event is a transient event, then the damage contribution of this event will be... and add it to the front Based on the accumulated damage from each event, the updated value is obtained. In this way, the damage contribution of each transient event can be dynamically adjusted and accurately evaluated according to the specific working conditions at the time of its occurrence, ensuring the accuracy of the calculation of cumulative fatigue damage.

[0060] Through the above technical solution, this application effectively solves the problem of inaccurate calculation of cumulative fatigue damage in traditional methods. By introducing real-time operating parameters (such as real-time dynamic hotspot temperature and high-frequency equivalent partial discharge quantity) to dynamically correct the event-level damage amplification index, and then updating the cumulative damage based on the corrected amplification index, the damage assessment of each transient event can accurately adapt to the specific operating conditions at the time of its occurrence. This dynamic adjustment mechanism can accurately reflect the true damage degree of the capacitor under different transient operating conditions, overcoming the limitation that a fixed damage index cannot reflect the amplification effect of temperature and partial discharge on damage. Furthermore, this solution, combined with the above-mentioned techniques for calculating dynamic hotspot temperature sequences, high-frequency equivalent partial discharge quantities, and thermomechanical equivalent transient stress, forms a more complete damage assessment system. The introduction of dynamic hotspot temperature and high-frequency equivalent partial discharge quantities makes the correction of the damage amplification index more comprehensive and precise, thereby significantly improving the accuracy and reliability of the calculation of electrothermal-mechanical coupled cumulative fatigue damage. Ultimately, this provides more accurate, reliable, and practically engineering-guiding basic data for subsequent health status assessments of series compensation capacitors, which helps to achieve refined management and predictive maintenance of capacitor operating status, thereby extending equipment life and ensuring the safe and stable operation of the power grid.

[0061] This application further proposes that the specific logic for calculating the health status index in step S50 includes: setting an initial health baseline value under full score conditions, constructing a monotonically decreasing decay function with the cumulative fatigue damage degree of the electrothermal engine coupling as an independent variable; as the cumulative fatigue damage degree of the electrothermal engine coupling increases, the health status index shows a non-linear decrease from the initial health baseline value until it reaches the failure and scrapping threshold; the specific mathematical formula for calculating the health status index is:

[0062] in: Indicates a health status index; This represents the baseline full score under perfect condition; This indicates the updated cumulative fatigue damage degree of the electrothermal coupling.

[0063] Calculating the Health Status Index (HSI) involves using a specific mathematical model to transform the cumulative fatigue damage of a capacitor into an easily understood and assessable numerical indicator. This calculation can be performed by a dedicated processing unit integrated into the monitoring system, such as an embedded processor executing a pre-defined algorithm, or by data processing by host computer software. The aim is to abstract complex physical damage information into a unified health score, allowing maintenance personnel to quickly grasp the equipment's status. The HSI is a comprehensive indicator that quantifies the current operating condition of a series compensation capacitor. This index is typically presented as a percentage; a higher value indicates a better health condition, while a lower value indicates varying degrees of deterioration or damage. The HSI serves as an important basis for equipment maintenance, repair, and replacement decisions. For example, when the HSI falls below a certain preset threshold, the system can automatically issue a warning or suggest further inspection. The baseline maximum score of 100 for a healthy state represents the upper limit of the HSI, signifying that the capacitor is in a brand-new, undamaged, and ideal operating condition. This benchmark provides a clear reference point, making any health status index below 100 intuitively reflect the degree of degradation of the capacitor relative to its initial good condition. This value can be set according to industry standards or equipment manufacturer specifications to ensure the universality and comparability of assessment results. Updated thermo-mechanical coupling cumulative fatigue damage. The damage level comprehensively considers the cumulative damage caused by the combined effects of electrical, thermal, and mechanical stresses on the capacitor during operation. This damage level is a dimensionless value that gradually increases with the aging and damage of the capacitor. It serves as a key parameter for assessing the remaining life and reliability of a capacitor, and its calculation results directly reflect the actual fatigue condition of the capacitor's internal insulating dielectric and structural materials.

[0064] The solution of this application accumulates fatigue damage by coupling the updated electrothermal engine obtained in the aforementioned steps. As the core input, it is transformed into a health status index using a negative exponential function model. Specifically, the scheme sets a baseline maximum score of 100 for a capacitor in a completely undamaged state. The result is zero; at this point, the calculated value is zero. A value of 100 visually indicates that the equipment is in optimal health. During long-term operation, the continuous power frequency voltage and harmonic current heating, as well as the overvoltage and inrush current impacts from transient events, cause irreversible aging and fatigue damage to the internal insulating medium of the capacitor, leading to… It gradually accumulates and increases. At this point, the negative exponential function... The value will decrease accordingly, thus affecting the health status index. Starting from 100, the score gradually decreases. This exponential decay conversion effectively reflects the non-linear relationship between the accumulation of capacitor damage and the deterioration of its health status. That is, in the early stages of damage, the decline in health status may be relatively slow, but as damage accumulates further, the rate of decline may accelerate, which aligns with the aging characteristics of actual equipment. Through this conversion, the originally abstract and complex cumulative fatigue damage degree of electrothermal-mechanical coupling is transformed into an intuitive and easy-to-understand percentage-based health score. This allows engineers to quickly and accurately assess the operational health status of series compensation capacitors, thus solving the problem that traditional assessment methods yield unintuitive results and hinder engineers from quickly grasping the equipment's health status.

[0065] The following is a concrete example to illustrate this. Assume that in an online monitoring system for a series-compensated capacitor, the cumulative fatigue damage degree of the thermoelectric coupling has been calculated and updated in real time through the aforementioned steps. In one specific implementation, this calculation process can be implemented in the processor of the monitoring device. For example, the cumulative fatigue damage degree when the system is started up or when the capacitor is first put into operation. The value is 0. At this point, the processor calculates according to the formula. Calculate the health status index This indicates that the capacitor is in good condition. As the capacitor's operating time increases, assuming that at the end of a certain evaluation cycle, the monitoring system calculates the updated cumulative fatigue damage of the thermo-mechanical coupling. The value is 0.1. The processor substitutes this value into the formula and calculates... In subsequent operation, if the capacitor is subjected to multiple transient shocks or prolonged overheating, the cumulative fatigue damage will further increase, for example, reaching [a certain level]. At this point, the processor will calculate... These calculated health status indices It can be displayed in real time on the operator interface or stored in a database for trend analysis. In this way, maintenance personnel can intuitively see the process of the capacitor's health score gradually decreasing from 100, thereby understanding the degree of equipment degradation in a timely manner and formulating corresponding maintenance strategies accordingly.

[0066] Through the above technical solution, this application can directly convert the actual cumulative damage results of the capacitor obtained through multi-parameter coupling analysis in the aforementioned steps into intuitive and readable health indicators, thereby solving the problem that traditional assessment methods are not intuitive and are not conducive to engineers quickly grasping the health status of equipment. This solution uses the updated electrothermal coupling cumulative fatigue damage degree as the calculation basis, ensuring the consistency between the health status assessment results and the actual aging damage degree of the capacitor, and avoiding the disconnect between the health assessment and damage analysis processes. The cumulative damage degree is converted into a health status index using a negative exponential transformation, which converts the continuously increasing damage degree from zero into a health score that gradually decreases from a baseline full score. This aligns with the intuitive understanding of health status assessment in the engineering field and is easy for engineers to understand and grasp. Setting 100 as the baseline full score in a good condition, when the capacitor has no cumulative damage, the calculated health status index is exactly 100, which conforms to the conventional practice in the engineering field for health scoring of brand-new, intact equipment. Engineers can directly judge the health level of the capacitor intuitively based on the obtained index value without additional conversion adjustments, greatly improving the intuitiveness and practicality of online monitoring and assessment.

[0067] As an optional embodiment of the present invention, in order to ensure the universality and high accuracy of the online monitoring and evaluation method in series compensation capacitors of different models and batches, this application uses the empirical parameters of physical mechanism properties (static natural convection equivalent thermal resistance) involved in the formulas mentioned above. Wind speed and convection cooling coefficient Damage-resistance coupling coefficient Electrodynamic-micropore deformation coupling coefficient Nonlinear acceleration index and benchmark fatigue index This provides a standard offline multi-stress calibration procedure. The specific calibration steps are as follows:

[0068] Step 1: Macroscopic thermodynamic parameters ( , ) calibration

[0069] A single series compensation capacitor sample from the same batch as the device under test was selected and placed in an ambient temperature chamber and wind tunnel test channel. A constant fundamental current was injected under zero wind speed conditions. After the temperature rise stabilized, the hot spot temperature was measured using an infrared thermal imager or an embedded fiber optic sensor. The static natural convection equivalent thermal resistance was calculated based on Newton's law of cooling and the heat balance equation. Subsequently, the wind speed in the wind tunnel was adjusted in stages. Record the equivalent thermal resistance values ​​after stabilization under different wind speed gradients, and use a univariate nonlinear formula. As the objective regression function, the least squares method was used for curve fitting, and the wind speed convection cooling coefficient was calibrated to obtain the coefficient. In the typical model corresponding to this embodiment, the calibration results are as follows: Typical value , Typical value .

[0070] Step 2: Damage to metallization film - resistive coupling coefficient ( ) and activation energy temperature constant ( ) calibration

[0071] Samples of biaxially oriented polypropylene (BOPP) metallized film monomers from the same batch as the capacitors were taken and placed in a multi-stress electromagnetic heating test bench. The test bench was controlled at the rated reference thermodynamic temperature. The film was operated under different constant temperature gradients, including high-elasticity state and near-melting point, and high-frequency pulsed current was applied to the film to simulate its long-term service and self-healing process; under different historical cumulative fatigue damage degrees During this phase, a high-precision LCR digital bridge was used for online frequency sweep measurement of its high-frequency equivalent series resistance. The dynamic frequency-varying equivalent series resistance calculation formula was used as described in the instruction manual:

[0072] As the objective function for multidimensional optimization, the measured high-frequency resistance, damage degree, and real-time temperature under each experimental gradient are substituted into it, and the Levenberg-Marquardt nonlinear surface fitting algorithm is used for joint solution, thereby calibrating and outputting a unique damage-resistance coupling coefficient. and activation energy temperature constant In this embodiment, the thin film of this type... The calibration mean is 0.042. Typical value .

[0073] Step 3: Microscopic electrodynamic and acceleration effect parameters ( , ) calibration

[0074] Maintaining the temperature gradient of the thin film sample, a high-voltage transient pulse generator was used to apply different maximum rates of change of transient voltage to both ends of the thin film. The impact stress, while adjusting the circuit impedance to excite the transient overcurrent peak required for electrodynamics. The amount of charge in synchronous partial discharge was collected using an ultra-high frequency (UHF) partial discharge sensor. And construct the high-frequency equivalent partial discharge quantity by combining the sample breakdown threshold. Matrix. Using the high-frequency equivalent partial discharge quantity formula mentioned earlier in the specification:

[0075] As a nonlinear regression model, it is applicable beyond the glass transition temperature of the material. Within the defined region, the amplification increment of micropore distortion discharge caused by the high-current Lorentz force was quantitatively analyzed. The electrodynamic-micropore deformation coupling coefficient was calibrated by performing surface convergence fitting on multiple sets of orthogonal experimental data using a multivariate nonlinear regression algorithm. and nonlinear acceleration index In this embodiment, the calibration results The typical value is 0.115. The typical value is 2.64.

[0076] Step 4: Inherent reference fatigue index of insulating materials ( The calibration process involves applying constant rated electrical and thermal stress to a large sample size of thin-film monomers until insulation breakdown occurs, recording the cumulative charge degradation and failure time for each sample. Following the statistical analysis method for electrical insulation data specified in IEEE Std 930, the breakdown time data is mapped to a two-parameter Weibull distribution model to extract characteristic lifetimes. Furthermore, by combining the slope of the classic SN fatigue curve of the material, an inverse fitting is used to derive the intrinsic reference fatigue index of the insulating material under conditions of no temperature rise distortion and no strong partial discharge effect. In this embodiment, the polypropylene film material The calibration benchmark value is 4.85. In summary, by using the offline multi-stress calibration program, the constant parameters obtained from calibration optimization are pre-stored in the memory of the online monitoring and evaluation device. The processor can then call and execute high-precision online damage closed-loop dynamic calculations without requiring secondary manual intervention during operation, thus meeting the requirements for high automation and robustness in engineering field implementation.

[0077] like Figure 2 As shown in the figure, this application provides an online monitoring and evaluation device for series compensation capacitors, including: a memory for storing a computer program, which converts a monitoring and evaluation method containing accurate damage calculation logic into storable code. The memory enables stable storage of the program and running data, providing a foundation for subsequent operation and ensuring that the logic and data of the evaluation process can be stably called; and a processor, which is communicatively connected to the memory to ensure that the processor can smoothly obtain the computer program and related data stored in the memory, avoiding communication blockage that would affect the normal operation of the evaluation process. When the processor executes the computer program, it can completely run all steps of the improved online monitoring and evaluation method for series compensation capacitors, thus implementing the accurate evaluation logic that considers the positive feedback effect of damage and the synergistic damage effect of electrothermal coupling.

[0078] The core innovation of this embodiment lies in achieving accurate calculation of the actual cumulative fatigue damage and health status of the series compensation capacitor by combining the memory and processor through a communication connection. Specifically, when the processor executes the computer program, it first acquires the capacitor's operating signal and extracts multiple characteristic parameters, including the effective voltage value sequence, the effective harmonic current value sequence, the peak value of transient overvoltage, the peak value of transient overcurrent, the maximum rate of change of transient voltage, and the charge on synchronous partial discharge. Subsequently, combining the historical cumulative fatigue damage degree and the effective harmonic current value sequence from the previous evaluation cycle, it calculates the dynamic frequency-varying equivalent series resistance and substitutes it and the effective voltage value sequence into the thermal differential equation to calculate the dynamic hot spot temperature sequence containing the damage positive feedback effect. For transient events, the processor constructs a cross-coupling term of electrodynamics and thermomechanical softening, calculates the high-frequency equivalent partial discharge quantity by combining the charge on synchronous partial discharge and the maximum rate of change of transient voltage; it performs thermomechanical softening correction on the peak value of transient overvoltage to obtain the thermomechanical equivalent transient stress, calculates the damage amplification index by combining the dynamic hot spot temperature sequence and the high-frequency equivalent partial discharge quantity, and then accumulates and updates the electro-thermal-mechanical coupled cumulative fatigue damage degree. Finally, the health status index of the series compensation capacitor is calculated based on the updated cumulative fatigue damage degree of the electrothermal coupling.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for online monitoring and evaluation of series compensation capacitors, characterized in that, Includes the following steps: Step S10: Obtain the operating signal of the series compensation capacitor, and extract the effective voltage value sequence, the effective harmonic current value sequence, the peak value of transient overvoltage, the peak value of transient overcurrent, the maximum rate of change of transient voltage, and the charge of synchronous partial discharge. Step S20: Combine the historical cumulative fatigue damage degree and harmonic current effective value sequence of the previous evaluation cycle to calculate the dynamic frequency-varying equivalent series resistance; substitute it and the voltage effective value sequence into the thermal differential equation to calculate the dynamic hot spot temperature sequence containing the damage positive feedback effect. Step S30: For transient events, construct a cross-coupling term of electrodynamic and thermomechanical softening, and calculate the high-frequency equivalent partial discharge quantity by combining the synchronous partial discharge television at the maximum rate of change of charge and transient voltage; Step S40: Perform thermomechanical softening correction on the transient overvoltage peak to obtain the thermomechanical equivalent transient stress, and calculate the damage amplification index by combining the dynamic hot spot temperature sequence and the high-frequency equivalent partial discharge quantity, and then accumulate and update the electrothermal-mechanical coupling cumulative fatigue damage degree. Step S50: Calculate the health status index of the series compensation capacitor based on the updated cumulative fatigue damage degree of the electrothermal coupling.

2. The online monitoring and evaluation method for series compensation capacitors according to claim 1, characterized in that, In step S20, the specific logic for calculating the dynamic hotspot temperature sequence includes: A negative correlation mapping relationship between ambient wind speed and dynamic equivalent thermal resistance is constructed to characterize the improvement of heat dissipation efficiency by forced convection. A positive nonlinear modulation function is constructed to integrate historical cumulative fatigue damage, previous hot spot temperature and fundamental equivalent series resistance. The dynamic frequency-varying equivalent series resistance is calculated to characterize the reduction in conductive area caused by the self-healing inside the capacitor and the resulting surge in heat generation positive feedback effect. Based on the sum of the current dielectric heat loss and the Joule heat loss considering the dynamic frequency-varying equivalent series resistance, and subtracting the heat dissipation modulated by the dynamic equivalent thermal resistance, the dynamic hot spot temperature sequence is calculated iteratively through discrete time steps.

3. The online monitoring and evaluation method for series compensation capacitors according to claim 2, characterized in that, In step S30, the specific logic for calculating the high-frequency equivalent partial discharge quantity includes: The charge quantity of the synchronous partial discharge television synchronized with the transient event is used as the reference base. A thermomechanical coupling amplification factor is set with the glass transition temperature of the insulating medium as the trigger boundary. When the transient hot spot temperature exceeds the glass transition temperature, a mechanical stress characterization term is constructed using the square term of the transient overcurrent peak value. Nonlinear surge amplification is performed in the process of approaching the absolute temperature of the physical melting point to characterize the severe deformation of the internal micropores caused by the electrodynamic force under the high elastic state. A nonlinear acceleration term is introduced for the maximum rate of change of transient voltage relative to the rated rate of change; The reference base, the thermo-mechanical coupling amplification factor, and the nonlinear acceleration term are synergistically multiplied or exponentialized to output the high-frequency equivalent partial discharge quantity.

4. The online monitoring and evaluation method for series compensation capacitors according to claim 3, characterized in that, In step S40, the specific logic for thermomechanical softening correction of the transient overvoltage peak includes: The peak value of transient overvoltage is used as the basic electrical stress; A thermomechanical softening correction coefficient is constructed that is positively correlated with the peak value of transient overcurrent and takes the absolute temperature of the transient hot spot temperature approaching the physical melting point as the limit of divergence; and an overflow safety margin temperature parameter is set at the limit of divergence boundary to limit the upper limit of calculation. The basic electrical stress is nonlinearly amplified and mapped using the aforementioned thermomechanical softening correction coefficient to output the event-level thermomechanical equivalent transient stress.

5. The online monitoring and evaluation method for series compensation capacitors according to claim 4, characterized in that, In step S40, the specific logic for calculating the event-level damage amplification index and updating the cumulative fatigue damage degree of the thermoelectric coupling includes: The inherent baseline fatigue index of the insulating material is extracted. The thermal aging temperature rise ratio of the transient hot spot temperature compared to the rated reference temperature and the degradation ratio of the high-frequency equivalent partial discharge quantity relative to the critical discharge threshold are used to positively modulate and amplify the baseline fatigue index to obtain the event-level damage amplification index of a single event. After normalizing the thermo-mechanical equivalent transient stress of each transient event, nonlinear calculations are performed using the corresponding event-level damage amplification index as the power exponent, and the results are accumulated over the entire monitoring period to obtain the electro-thermal-mechanical coupled cumulative fatigue damage degree.

6. The online monitoring and evaluation method for series compensation capacitors according to claim 5, characterized in that, In step S50, the specific logic for calculating the health status index includes: Set a health initial baseline value under full score condition, and construct a monotonically decreasing decay function with the cumulative fatigue damage degree of the electrothermal engine coupling as an independent variable; As the cumulative fatigue damage of the electrothermal engine coupler increases, the health status index decreases non-linearly from the initial health baseline value until it reaches the failure and scrapping threshold.

7. An online monitoring and evaluation device for series compensation capacitors, characterized in that, include: Memory, used to store computer programs; The processor, communicatively connected to the memory, is used to execute the computer program to implement the various steps of the online monitoring and evaluation method for a series compensation capacitor as described in any one of claims 1 to 6.

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