Online monitoring system and method for dissolved gas in transformer oil
By constructing a closed trajectory model of the differential parameters of the electron paramagnetic resonance signal and combining it with the dynamic temperature rise and fall cycle driven by oil temperature, viscosity interference and chemical reaction components are separated in real time. This solves the problem of misjudgment in the monitoring of dissolved gases in transformer oil under dynamic temperature conditions and realizes early identification and accurate monitoring of partial discharge.
Patent Information
- Application Number
- CN202511125349.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-12
- Publication Date
- 2025-11-07
AI Technical Summary
Existing technologies for monitoring dissolved gases in transformer oil are unable to accurately identify gas evolution signals under dynamic temperature conditions, leading to false alarms or missed fault conditions. This is mainly because the changes in oil properties caused by oil temperature fluctuations create continuous disturbances in the EPR signal that are highly similar to the actual changes in free radical generation, and there is a lack of effective spectral drift modeling and correction methods.
By constructing a closed trajectory model based on differential parameters of electron paramagnetic resonance signals, and combining the dynamics of heating and cooling cycles driven by oil temperature, viscosity interference components and chemical reaction components are separated in real time. The net rate of free radical generation is calculated, and the early evolution process and development trend of partial discharge are determined by the loop area and rate as dual indicators.
It significantly improves the response sensitivity and accuracy of dissolved gas monitoring in transformer oil, enabling timely identification of the early evolution process and development trend of partial discharge, and overcoming the problems of misjudgment and delayed response of traditional methods under dynamic thermal environments.
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Figure CN120908239A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of power equipment monitoring, more particularly, it relates to a transformer oil dissolved gas online monitoring system and method. BACKGROUND
[0002] At present, for the state monitoring of dissolved gas in oil-immersed power transformers, gas chromatography is widely used as the mainstream technical means. However, the generation, dissolution, transfer and accumulation of gas in oil often have hysteresis, which is difficult to reflect the instantaneous electrochemical change process. In recent years, electron paramagnetic resonance (EPR) has been studied for monitoring short-lived free radical species in oil, because it can directly respond to the molecular fission process caused by partial discharge, thermal cracking or radioactive effect. EPR technology relies on parameters in the spectrum to determine the type and concentration change of free radicals, and has potential advantages for early response to faults.
[0003] However, in actual operation, especially for oil-immersed transformers of 110 kV and above, the oil temperature fluctuates dynamically in the range of 40 to 90 degrees throughout the year with load changes, and the temperature may rise or drop by 15 to 30 degrees in a short time. Such rapid changes in oil temperature can significantly change the physical state of the oil, most directly affecting the thermal physical parameters such as the viscosity and density of the oil.
[0004] In EPR measurement, the rotation correlation time of free radicals is closely related to the viscosity of the oil. An increase in oil temperature will cause a rapid decrease in viscosity, thereby accelerating the relaxation process of molecular spin, making the EPR signal linewidth narrower, and also affecting the stability of the g value. These signal shifts caused by changes in physical environment are highly similar to the signal changes caused by chemical reactions (such as free radicals released by partial discharge), and cannot be directly distinguished from the surface of the spectrum.
[0005] More complexly, the free radicals themselves often increase during the temperature rise, so that the temperature rise is accompanied by signal disturbance from physical changes and real free radical concentration increase; similarly, during the temperature drop process, the increase in oil viscosity leads to an increase in linewidth, but the free radicals do not necessarily decrease simultaneously, and even persist under certain hysteresis conditions. This overlap and misplacement in characterization makes it difficult for EPR monitoring to determine the true cause of the spectrum line change.
[0006] In addition, the EPR calibration data obtained under the conditions of conventional laboratory static oil samples cannot cover the signal drift effect under dynamic oil temperature and continuous flow environment. Therefore, the g value standard reference and linewidth threshold obtained based on the traditional method are difficult to be directly applied to actual operation monitoring, which is easy to cause false alarm or missed alarm of fault state.
[0007] In summary, the root cause of the existing technical problems is:
[0008] The oil temperature fluctuation in operation causes the change of oil physical properties, which continuously disturbs the EPR signal.
[0009] The continuous disturbance is highly similar to the real free radical generation change in spectrum performance, so that the EPR monitoring is difficult to accurately identify the gas evolution signal without a separation mechanism.
[0010] Therefore, the existing scheme lacks a modeling and correction method for the spectral line shift in a dynamic temperature environment, so that the fault diagnosis judgment cannot accurately correspond to the real electrical change process. SUMMARY
[0011] The present application provides an online monitoring system and method for dissolved gases in transformer oil, which solves the technical problems raised in the background art.
[0012] In a first aspect, the present application provides an online monitoring method for dissolved gases in transformer oil, comprising:
[0013] S1, obtaining reference parameters, including g value reference and line width reference;
[0014] S2, collecting real-time parameters at fixed time intervals, including real-time g value and real-time line width;
[0015] S3, determining the temperature rise and fall cycle time period, and constructing a closed trajectory based on the reference parameters and real-time parameters;
[0016] S4, determining the empty area of the closed trajectory, and accumulating the empty area to obtain the loop area;
[0017] S5, determining the viscosity interference component corresponding to the real-time parameters, and further excluding the viscosity interference component to obtain the chemical reaction component;
[0018] S6, determining the free radical instantaneous generation rate based on the chemical reaction component, and calculating the average free radical net generation rate in the temperature rise and fall cycle time period;
[0019] S7, generating a monitoring and warning signal according to the loop area and the average free radical net generation rate.
[0020] Further, the reference parameters are obtained, including:
[0021] The static oil sample of the same batch as the running transformer oil is kept at a constant temperature of 35 to 45 degrees for a predetermined time, and is simultaneously placed in a manganese divalent standard sample for magnetic field calibration;
[0022] The static oil sample and the manganese divalent standard sample are scanned respectively, and the g value reference is calculated based on the resonance magnetic field of the manganese divalent standard sample;
[0023] The static oil sample is scanned K times to obtain K sets of line width data, and the average value of the K sets of line width data is taken as the line width reference.
[0024] Further, the real-time parameters are collected at fixed time intervals, including:
[0025] The transformer oil is continuously scanned at fixed time intervals to collect electron paramagnetic resonance spectrum at each time;
[0026] The electron paramagnetic resonance spectrum is fitted to obtain real-time g value and real-time line width.
[0027] Further, the temperature rise and fall cycle time period is determined, and a closed trajectory is constructed based on the reference parameters and real-time parameters, including:
[0028] The temperature of the transformer oil is synchronously collected at fixed time intervals to obtain a time-temperature sequence;
[0029] The first-order difference of the time-temperature sequence is calculated, and the temperature rise peak and temperature drop valley are identified according to the sign change of the first-order difference, so as to divide the temperature rise and fall cycle time period by the adjacent temperature rise peaks;
[0030] In the temperature rise and fall cycle time period, the real-time g value and real-time line width are subtracted from the g value reference and line width reference to obtain difference coordinate points;
[0031] The difference coordinate points are connected in time sequence to form a closed trajectory corresponding to the temperature rise and fall cycle time period; wherein the difference coordinate point at the i-th time in the closed trajectory is (x i ,y i ), x i is the difference between the real-time g value at the i-th time and the g value reference, and y i is the difference between the real-time line width at the i-th time and the line width reference.
[0032] Further, the enclosed area of the closed trajectory is determined, and the loop area is accumulated by accumulating the enclosed area, including:
[0033] Each difference coordinate point in the closed trajectory is extracted in time sequence to obtain a difference coordinate sequence;
[0034] The first difference coordinate point in the difference coordinate sequence is repeatedly added to the end of the difference coordinate sequence to obtain a closed coordinate sequence;
[0035] The closed coordinate sequence is sequentially subjected to trapezoidal method to calculate microelement area and accumulate to obtain signed area;
[0036] The absolute value of the signed area is taken as the loop area, and the sign is recorded as the loop direction marker.
[0037] Further, the viscosity interference component corresponding to the real-time parameter is determined, and the chemical reaction component is further excluded by excluding the viscosity interference component, including:
[0038] Reading the temperature of the transformer oil at the i th moment as an input variable of the Andrade model to calculate the corresponding viscosity;
[0039] Based on the viscosity, the rotation-related time is calculated and the motion broadening is obtained, so as to determine the viscosity interference component;
[0040] Subtract the viscosity interference component from y i To obtain the chemical reaction component at the i th moment.
[0041] Further, based on the chemical reaction component, the instantaneous radical generation rate is determined, and the average radical net generation rate in the temperature rise and fall cycle period is calculated, including:
[0042] The chemical reaction component is converted into the instantaneous radical concentration at the i th moment according to a preset conversion coefficient;
[0043] The difference between the instantaneous radical concentrations at adjacent moments is divided by a fixed time interval to obtain the instantaneous radical generation rate;
[0044] The average value of all the instantaneous radical generation rates in the temperature rise and fall cycle period is obtained to obtain the average radical net generation rate in the temperature rise and fall cycle period.
[0045] Further, according to the loop area and the average radical net generation rate, a monitoring and early warning signal is generated, including:
[0046] Reading the loop area, loop direction and average radical net generation rate corresponding to the temperature rise and fall cycle period to generate a monitoring and early warning signal, specifically as follows:
[0047] When the loop area is not counterclockwise, a device failure early warning signal is generated;
[0048] Comparing the loop area with a preset area threshold value, and comparing the average radical net generation rate with a preset rate threshold value, when both exceed the threshold value, an early partial discharge early warning signal is generated;
[0049] If at least three temperature rise and fall cycle periods successively generate an early partial discharge early warning signal, the early partial discharge early warning signal is upgraded to a partial discharge development early warning signal.
[0050] The second aspect is an online monitoring system for dissolved gases in transformer oil, which is applied to any one of the online monitoring methods for dissolved gases in transformer oil, including:
[0051] The baseline establishment module is used to obtain baseline parameters, including g value baseline and line width baseline;
[0052] The data acquisition module is used to acquire real-time parameters at a fixed time interval, including real-time g value and real-time line width;
[0053] a trajectory construction module configured to determine a temperature rise and fall cycle period and construct a closed trajectory based on a benchmark parameter and a real-time parameter;
[0054] a trajectory analysis module configured to determine an enclosed area of the closed trajectory and accumulate the enclosed area to obtain a loop area;
[0055] an interference elimination module configured to determine a viscosity interference component corresponding to the real-time parameter and further eliminate the viscosity interference component to obtain a chemical reaction component;
[0056] a free radical calculation module configured to determine a free radical instantaneous generation rate based on the chemical reaction component and calculate an average free radical net generation rate of the temperature rise and fall cycle period;
[0057] a monitoring and early warning module configured to generate a monitoring and early warning signal according to the loop area and the average free radical net generation rate.
[0058] The present application has the beneficial effect that by constructing a closed trajectory model based on the difference parameter of the electron paramagnetic resonance signal, combined with the temperature rise and fall cycle dynamics under the driving of oil temperature, the interference component caused by the change of physical properties in the spectrum line change and the chemical reaction component caused by partial discharge are separated in real time, so that the net generation rate of free radicals is accurately extracted, and the early evolution process and development trend of partial discharge are judged by the loop area and the rate double indicators, which significantly improves the response sensitivity, monitoring accuracy and early warning foresight of the evolution of dissolved gas in the running transformer oil, and overcomes the technical bottleneck that the traditional method is easy to misjudge or delayed response in the dynamic thermal environment. BRIEF DESCRIPTION OF DRAWINGS
[0059] Fig. 1 is a flowchart of the present application;
[0060] Fig. 2 is a module diagram of the present application;
[0061] Fig. 3 is a monitoring and early warning schematic diagram of the present application. DETAILED DESCRIPTION
[0062] The subject matter described herein will now be discussed with reference to example implementations. It should be understood that the discussion of these implementations is merely meant to provide a better understanding of the subject matter described herein and can be changed in function and arrangement without departing from the scope of the present description. Each of the various examples can omit, substitute or add various procedures or components as desired. In addition, features described in relation to some examples can also be combined in other examples.
[0063] Example One:
[0064] AsFigs. 1-3 The transformer oil dissolved gas online monitoring method shown in the embodiment comprises the following steps:
[0065] S1, acquiring reference parameters, including: g value reference and line width reference;
[0066] S2, collecting real-time parameters at fixed time intervals, including: real-time g value and real-time line width;
[0067] S3, determining a temperature rise and fall cycle time period, and constructing a closed trajectory based on the reference parameters and the real-time parameters;
[0068] S4, determining the empty area of the closed trajectory, and accumulating the empty area to obtain a loop area;
[0069] S5, determining a viscosity interference component corresponding to the real-time parameters, and further excluding the viscosity interference component to obtain a chemical reaction component;
[0070] S6, determining a free radical instantaneous generation rate based on the chemical reaction component, and calculating an average free radical net generation rate of the temperature rise and fall cycle time period;
[0071] S7, generating a monitoring and early warning signal according to the loop area and the average free radical net generation rate.
[0072] In an embodiment of the present application, the reference parameters are acquired, including:
[0073] The static oil sample of the same batch as the running transformer oil is kept at a constant temperature of 35 to 45 degrees for a preset time period, and a manganese divalent standard sample is simultaneously placed therein for magnetic field calibration;
[0074] The static oil sample and the manganese divalent standard sample are scanned respectively, and the g value reference is calculated based on the resonance magnetic field of the manganese divalent standard sample;
[0075] The static oil sample is scanned K times to obtain K sets of line width data, and the average value of the K sets of line width data is taken as the line width reference.
[0076] It should be noted that the static oil sample of the same batch as the running transformer oil is selected because the transformer oils of different batches may differ in composition, antioxidant content, etc., and the static oil sample of the same batch can ensure the consistency of the reference and the actual monitoring object to the greatest extent. The static oil sample is placed in a constant temperature environment of 35 to 45 degrees for a preset time period, and the temperature interval is in the lower range of the normal operating oil temperature of the transformer, and the oil properties are relatively stable; the constant temperature treatment can eliminate the influence of temperature fluctuations on the viscosity and molecular motion state of the oil, and avoid the initial signal deviation caused by temperature changes. At the same time, the manganese divalent standard sample is simultaneously placed therein, and the nominal g value of the manganese divalent standard sample is 2.0014, which is taken as the reference for magnetic field calibration. Mn
[0077] Since the g-value of the divalent manganese standard sample is known, the magnetic field strength corresponding to its resonance (resonance magnetic field) can be obtained through scanning. Based on this resonance magnetic field, combined with physical constants (Planck's constant, microwave frequency, Bohr magneton), the g-value reference can be calculated, specifically including:
[0078] The resonance condition for electron paramagnetic resonance is that the energy of the electron spin level transition is equal to the energy of the incident microwave, i.e.: hv = gβB res Where h is Planck's constant, v is the microwave frequency, g is the value of g, β is the Bohr magneton, and B... res The intensity of the resonant magnetic field.
[0079] For the divalent manganese standard sample, its resonant magnetic field B was obtained by scanning. res,Mn Then, with the resonant magnetic field B res,Mn First, verify the accuracy of the magnetic field calibration; then, based on the same microwave and magnetic field environment, when scanning a static oil sample, use the above resonance condition formula to derive: Among them, B res,oil The resonant magnetic field of the static oil sample is given. In actual operation, since the divalent manganese standard sample and the oil sample are calibrated synchronously in the same resonant cavity, the magnetic field consistency has been calibrated through the standard sample. Therefore, the final calculated g-value of the oil sample is the reference g. ref .
[0080] A static oil sample is scanned K times, with each scan providing linewidth data. Linewidth measurement is susceptible to random noise during the scanning process; multiple scans and averaging effectively reduce random errors, making the linewidth baseline closer to the true value. The linewidth baseline reflects the linewidth of the oil sample when there are no significant chemical changes.
[0081] In detail, scanning refers to the acquisition of EPR spectra from static oil samples using an electron paramagnetic resonance spectrometer. The linewidth of the EPR spectra is a key parameter characterizing the spectral morphology, reflecting the spin-spin interactions of free radicals and the molecular motion state. It can be extracted by Lorentz fitting or Gaussian fitting of the acquired EPR spectra.
[0082] In one embodiment of the present invention, real-time parameters are collected at fixed time intervals, including:
[0083] The transformer oil is continuously scanned at fixed time intervals to collect electron paramagnetic resonance spectra at each moment;
[0084] The electron paramagnetic resonance spectral lines were fitted to obtain the real-time g value and real-time linewidth.
[0085] It should be noted that the continuously scanned object is the running transformer oil sample. Unlike the static oil sample in the laboratory, the state of the running oil sample dynamically fluctuates with the load change, and the continuous scanning can completely capture the EPR signal change in this dynamic process. Each scan generates an electron paramagnetic resonance spectrum line, which takes the magnetic field strength as the horizontal axis and the signal strength as the vertical axis, directly reflecting the spin resonance characteristics of the free radicals in the oil, i.e., the changes in the type, concentration and physical environment (viscosity) of the free radicals will be reflected in the change in the spectrum line form (peak position, width).
[0086] The original form of the electron paramagnetic resonance spectrum line is a continuous curve, which cannot be directly used for calculation or comparison and needs to be fitted. The fitting process usually uses the Lorentz model to obtain the real-time g value and real-time line width. The real-time g value is a parameter calculated by the magnetic field strength corresponding to the resonance peak of the spectrum line, and its value is determined by the electron spin-orbit coupling characteristics of the free radicals. Different types of free radicals (such as peroxide radicals generated by partial discharge) have a characteristic g value range, and are also affected by the local magnetic field environment in the oil (such as the distribution of dissolved gas), so the change in the g value can reflect the changes in the type and physical environment of the free radicals.
[0087] The real-time line width is the magnetic field difference between two adjacent peaks of the spectrum line, and its size is related to the rotation rate of the free radicals: when the oil viscosity decreases, the rotation of the free radicals speeds up, and the line width becomes narrower; when the free radical concentration increases or chemical exchange occurs, the line width will widen. Therefore, the change in the line width can indirectly reflect the combined influence of the oil viscosity and the activity of the free radicals.
[0088] In an embodiment of the present application, the temperature rise and fall cycle time period is determined, and a closed trajectory is constructed based on the reference parameters and real-time parameters, including:
[0089] The temperature of the transformer oil is synchronously collected at fixed time intervals to obtain a time-temperature sequence;
[0090] The first-order difference of the time-temperature sequence is calculated, and the temperature rise peaks and temperature drop valleys are identified according to the sign change of the first-order difference, and the temperature rise and fall cycle time period is divided by the adjacent temperature rise peaks;
[0091] In the temperature rise and fall cycle time period, the real-time g value and real-time line width are subtracted from the g value reference and line width reference to obtain the difference coordinate points;
[0092] The difference coordinate points are connected in time sequence to form a closed trajectory corresponding to the temperature rise and fall cycle time period; wherein the difference coordinate point at the i th time in the closed trajectory is (x i ,y i ), x i is the difference between the real-time g value at the i th time and the g value reference, and y i is the difference between the real-time line width at the i th time and the line width reference.
[0093] It should be noted that the calculation method of the first-order difference is to subtract the temperature at the previous moment from the temperature at the current moment and then divide by the fixed time interval, and the result reflects the temperature change rate per unit time. Symbol change refers to the conversion of the positive and negative values of the first-order difference. When the first-order difference changes from positive to negative, it indicates that the temperature changes from rising to falling, and the corresponding moment is defined as the temperature rising peak. When the first-order difference changes from negative to positive, it indicates that the temperature changes from falling to rising, and the corresponding moment is defined as the temperature falling valley. Taking two adjacent temperature rising peaks as boundaries, the time period between the two boundaries is a complete temperature rising and falling cycle period.
[0094] It should be noted that the real-time g value and the real-time line width are EPR spectral line parameters obtained in real time in online monitoring, and the g value reference and the line width reference are reference values obtained by static oil sample calibration. The real-time g value at the same time is subtracted from the g value reference to obtain the g value difference at the time, and the real-time line width at the same time is subtracted from the line width reference to obtain the line width difference at the time. The g value difference and the line width difference at each time jointly constitute a difference coordinate point, which eliminates the influence of the initial reference state and only reflects the parameter change amount in the dynamic monitoring process.
[0095] The time sequence connection ensures that the trajectory can accurately reflect the dynamic correlation between the g value and the line width during the temperature rising and falling process. Since a complete temperature rising and falling cycle ends, the temperature returns to a state similar to the initial stage, and the corresponding g value and line width change also form a closed loop, so that the connection forms a closed trajectory. The difference coordinate point at the i th moment is composed of the g value difference and the line width difference at the moment, and the deviation from the reference at the i th moment is fully presented.
[0096] In an embodiment of the present application, the enclosed area of the closed trajectory is determined, and the cumulative enclosed area is obtained as a loop area, comprising:
[0097] The time sequence of each difference coordinate point in the closed trajectory is extracted to obtain a difference coordinate sequence;
[0098] The first difference coordinate point in the difference coordinate sequence is repeatedly added to the end of the difference coordinate sequence to obtain a closed coordinate sequence;
[0099] The closed coordinate sequence is sequentially calculated by the trapezoidal method to obtain a signed area;
[0100] The absolute value of the signed area is taken as the loop area, and the sign is recorded as a loop direction marker.
[0101] It should be noted that the differential coordinate point is composed of the difference between the real-time parameter and the reference parameter, wherein the horizontal axis is the difference between the real-time g value and the g value reference, and the vertical axis is the difference between the real-time line width and the line width reference. Since the closed trajectory is formed by the dynamic change of the transformer oil in one temperature rise and fall cycle over time, the time sequence of the coordinate point directly reflects the evolution process of the trajectory.
[0102] It should be noted that the area calculation of the closed trajectory needs to be based on the closed geometric boundary. Since the starting point and the ending point of the original differential coordinate sequence are continuous in time but not directly connected, by supplementing the first point to the end of the sequence, the coordinate sequence can form a complete closed loop, simulating the actual closed state of the trajectory.
[0103] It should be noted that the signed area is obtained by calculating the microelement area of the closed coordinate sequence in turn using the trapezoidal method and accumulating it. The trapezoidal method is an integral method suitable for discrete coordinate sequences, and its principle is to approximate the area formed by the adjacent two coordinate points and the horizontal axis as a trapezoid, and to obtain the overall area by calculating the area (microelement area) of each trapezoid and accumulating it. Specifically, for two adjacent points (x i ,y i ) and (x i+1 ,y i+1 ) in the sequence, the microelement area is one half of the product of y i +y i+1 and x i+1 -x i . By accumulating all the microelement areas, the signed area obtained contains not only the numerical value of the area enclosed by the trajectory, but also reflects the direction of the trajectory through the sign: positive value corresponds to clockwise direction, and negative value corresponds to counterclockwise direction.
[0104] The loop area needs to be represented in the form of non-negative value, so as to determine whether the state of the transformer oil is abnormal. Taking the absolute value can unify the numerical representation form of the area, and ensure the comparability of the areas of trajectories in different directions. At the same time, the sign of the signed area is retained as a direction marker, which can be used to identify whether the direction of the trajectory is in line with the normal law.
[0105] In an embodiment of the present application, the viscosity disturbance component corresponding to the real-time parameter is determined, and the chemical reaction component is further obtained by excluding the viscosity disturbance component, comprising:
[0106] The temperature of the transformer oil at the i th moment is read as an input variable of the Andrade model to calculate the corresponding viscosity;
[0107] The rotation correlation time is calculated based on the viscosity, and the motion broadening is obtained, so as to determine the viscosity disturbance component;
[0108] The viscosity disturbance component is deducted from y i to obtain the chemical reaction component at the i th moment.
[0109] It should be noted that when the transformer is running, the oil temperature changes dynamically with the load, and the oil temperature directly affects the viscosity of the oil, that is, the viscosity decreases as the temperature rises, and the viscosity increases as the temperature decreases. The change in viscosity will indirectly interfere with the linewidth of the EPR signal through molecular motion, which is a physical interference. In order to quantify this interference, the oil temperature needs to be converted into viscosity. The Andrade model is a classic empirical model for describing the relationship between liquid viscosity and temperature, and its core is to calculate the viscosity at the corresponding time by taking the oil temperature as the input and combining the specific constant of the oil product (obtained by calibrating the static oil sample).
[0110] It should be noted that the change in viscosity will affect the motion state of the free radical molecules in the oil, which is specifically manifested as a change in the rotation correlation time, that is, the higher the viscosity, the slower the molecular rotation, and the longer the rotation correlation time; on the contrary, the faster the rotation, and the shorter the rotation correlation time. The rotation correlation time directly determines the motion broadening of the EPR signal, that is, the linewidth change caused by the change in the motion state of the molecules, and this part of the linewidth change is completely caused by the viscosity and belongs to the interference component that needs to be removed. In the calculation, the rotation correlation time is first obtained from the Stokes-Einstein relationship (which describes the relationship between molecular motion and viscosity) according to the viscosity, and then the rotation correlation time is converted into motion broadening, so as to determine the specific interference of the viscosity on the linewidth (viscosity interference component).
[0111] It should be noted that the linewidth change of the EPR signal contains two parts: one is the above-mentioned physical interference caused by viscosity (viscosity interference component), and the other is the real change caused by chemical processes (such as the generation of free radicals by partial discharge, the reaction between free radicals, etc.). In order to obtain the linewidth change caused only by chemical processes, the viscosity interference component needs to be deducted from the linewidth difference, and the result obtained after deduction is the chemical reaction component. The chemical reaction component only reflects the influence of chemical reactions in the oil on the EPR linewidth.
[0112] In an embodiment of the present application, the average free radical net generation rate of the temperature rising and falling cycle time period is determined based on the chemical reaction component, and the average free radical net generation rate of the temperature rising and falling cycle time period is calculated, including:
[0113] The chemical reaction component is converted into the instantaneous free radical concentration at the ith time according to a preset conversion coefficient;
[0114] The difference between the instantaneous free radical concentrations at adjacent times is divided by a fixed time interval to obtain the instantaneous free radical generation rate;
[0115] The average value of all the instantaneous free radical generation rates in the temperature rising and falling cycle time period is obtained to obtain the average free radical net generation rate of the temperature rising and falling cycle time period.
[0116] It should be noted that the chemical reaction component is the change amount of the spectral line width caused by free radicals and other chemical substances after excluding the interference of physical factors such as oil viscosity. The preset conversion coefficient is a fixed proportional relationship obtained by offline experiment calibration, and its role is to establish a quantitative corresponding relationship between the change amount of the line width and the free radical concentration. By converting the chemical reaction component through the coefficient, the instantaneous free radical concentration at the i th moment can be obtained, that is, the chemical reaction component is converted into a concentration index directly reflecting the number of chemical substances.
[0117] It should be noted that the difference between the instantaneous free radical concentrations of adjacent moments reflects the change amount of the number of free radicals between the two moments. The fixed time interval refers to the time interval for continuous data acquisition, and provides a unified time reference for rate calculation. The concentration difference is divided by the fixed time interval, and the result obtained is the instantaneous generation rate of free radicals. The instantaneous generation rate of free radicals can reflect the speed of generation or consumption of free radicals at each moment, and a positive number indicates that the generation rate is greater than the consumption rate, and a negative number indicates that the consumption rate is dominant.
[0118] It should be noted that the average value of all instantaneous generation rates of free radicals in the temperature rise and fall cycle period can eliminate the random fluctuations of the instantaneous rate, and obtain an average index (average free radical net generation rate) that can represent the overall balance state of free radical generation and consumption in the whole cycle. The average free radical net generation rate comprehensively reflects the strength of the chemical process in a complete temperature cycle, and is the core quantitative basis for judging whether abnormal chemical activity such as partial discharge occurs and the degree.
[0119] In an embodiment of the present application, the monitoring and early warning signal is generated according to the loop area and the average free radical net generation rate, comprising:
[0120] The loop area, loop direction and average free radical net generation rate corresponding to the temperature rise and fall cycle period are read, and the monitoring and early warning signal is generated, specifically as follows:
[0121] When the loop area is not counterclockwise, a device failure early warning signal is generated;
[0122] The loop area is compared with the preset area threshold value, and the average free radical net generation rate is compared with the preset rate threshold value, and when both exceed the limit, an early partial discharge early warning signal is generated;
[0123] If the early partial discharge early warning signal is generated continuously for at least three temperature rise and fall cycle periods, the early partial discharge early warning signal is upgraded to a partial discharge development early warning signal.
[0124] It should be noted that when the loop direction is not counterclockwise, the device failure warning signal is generated. Because in the normal operation of the transformer, the oil temperature rise and fall leads to the dynamic change of oil viscosity, accompanied by the generation and recombination of free radicals, the coupling of the two will make the closed trajectory of the EPR signal difference parameter present a stable counterclockwise direction. If the direction deviates from counterclockwise, it means that the monitoring system may have abnormalities, such as magnetic field calibration deviation, sensor connection failure or signal acquisition error, etc.
[0125] It should be noted that the loop area is compared with the preset area threshold, and the average free radical net generation rate is compared with the preset rate threshold, and when both exceed their respective thresholds, the early partial discharge warning signal is generated. The preset area threshold is determined based on a large number of experiments and field data, reflecting the upper limit of the loop area under normal working conditions; the preset rate threshold corresponds to the critical value of the free radical net generation rate under normal state. The loop area exceeds the limit, indicating that the coupling strength of viscosity change and chemical reaction is abnormally enhanced, and the average free radical net generation rate exceeds the limit, indicating that the free radical generation activity is abnormally active. When both conditions are met, short-term disturbances can be ruled out, and the characteristics of the early stage of partial discharge can be accurately identified. At this time, the early partial discharge warning signal is generated, indicating that there may be initial partial discharge phenomenon.
[0126] It should be noted that if the early partial discharge warning signal is generated in at least three consecutive temperature rise and fall cycle time periods, it is upgraded to a partial discharge development warning signal. Since a single early warning may be caused by occasional factors, and three or more consecutive cycles meet the early warning conditions, it indicates that the partial discharge is not a transient disturbance, but a continuous development trend, and the free radical generation activity in the oil is increasing, and the fault state is deteriorating. By upgrading the warning signal, the development trend of the fault can be more timely reflected, providing more urgent disposal basis for the operation and maintenance personnel, and avoiding further expansion of the fault.
[0127] Embodiment two:
[0128] An online monitoring system for dissolved gases in transformer oil is applied in any one of the online monitoring methods for dissolved gases in transformer oil, comprising:
[0129] A baseline establishment module for obtaining baseline parameters, including g-value baseline and linewidth baseline;
[0130] A data acquisition module for acquiring real-time parameters at fixed time intervals, including real-time g-value and real-time linewidth;
[0131] A trajectory construction module for determining temperature rise and fall cycle time periods, and constructing a closed trajectory based on baseline parameters and real-time parameters;
[0132] A trajectory analysis module for determining the surrounding area of the closed trajectory, and accumulating the surrounding area to obtain the loop area;
[0133] The interference elimination module is used for determining a viscosity interference component corresponding to the real-time parameter, and further eliminating the viscosity interference component to obtain a chemical reaction component;
[0134] The radical calculation module is used for determining a radical instantaneous generation rate based on the chemical reaction component, and calculating an average radical net generation rate in the temperature rising and falling cycle period;
[0135] The monitoring and early warning module is used for generating a monitoring and early warning signal according to the loop area and the average radical net generation rate.
[0136] The above describes the embodiments of the embodiments, but the embodiments are not limited to the specific embodiments described above, and the specific embodiments described above are only illustrative but not restrictive, and those skilled in the art can make many forms under the inspiration of the embodiments, which all belong to the protection of the embodiments.
Claims
1. An on-line monitoring method of dissolved gases in transformer oil, characterized in that, The method comprises the following steps: S1, obtaining reference parameters, including: g value reference and line width reference; S2, collecting real-time parameters at fixed time intervals, including: real-time g value and real-time line width; S3, determining the temperature rise and fall cycle time period, and constructing a closed trajectory based on the reference parameters and real-time parameters; S4, determining the enclosed area of the closed trajectory, and accumulating the enclosed area to obtain the loop area; S5, determining the viscosity interference component corresponding to the real-time parameters, and further excluding the viscosity interference component to obtain the chemical reaction component; S6, determining the instantaneous generation rate of free radicals based on the chemical reaction component, and calculating the average net generation rate of free radicals in the temperature rise and fall cycle time period; S7, generating a monitoring and warning signal according to the loop area and the average net generation rate of free radicals.
2. The method of claim 1, wherein the transformer oil is a mineral oil. Obtaining reference parameters, including: Keeping the static oil sample of the same batch as the running transformer oil at a constant temperature of 35-45 degrees for a predetermined time, and synchronously placing a manganese divalent standard sample to calibrate the magnetic field; Respectively scanning the static oil sample and the manganese divalent standard sample, and calculating the g value reference based on the resonance magnetic field of the manganese divalent standard sample; Scanning the static oil sample K times to obtain K sets of line width data, and taking the average of the K sets of line width data as the line width reference.
3. The method of claim 2, wherein the transformer oil is a mineral oil. Collecting real-time parameters at fixed time intervals, including: Continuously scanning the transformer oil at fixed time intervals to collect electron paramagnetic resonance spectrum at each time; Fitting the electron paramagnetic resonance spectrum to obtain real-time g value and real-time line width.
4. The method of claim 3, wherein the transformer oil is a mineral oil. Determining the temperature rise and fall cycle time period, and constructing a closed trajectory based on the reference parameters and real-time parameters, including: Synchronously collecting the temperature of the transformer oil at fixed time intervals to obtain a time-temperature sequence; Calculating the first-order difference of the time-temperature sequence, and identifying the temperature rise peak and the temperature drop valley according to the sign change of the first-order difference, and dividing the temperature rise and fall cycle time period according to the adjacent temperature rise peaks; In the temperature rise and fall cycle time period, the real-time g value and the real-time line width are subtracted from the g value reference and the line width reference to obtain difference coordinate points; The differential coordinate points are connected in time sequence to form a closed trajectory corresponding to a temperature rise and fall cycle time period; wherein the differential coordinate point at the i th moment in the closed trajectory is , is a difference between the real-time g value at the i th moment and the g value reference, is a difference between the real-time line width at the i th moment and the line width reference.
5. The method of claim 4, wherein the transformer oil is a mineral oil. Determining the enclosed area of the closed trajectory, and accumulating the enclosed area to obtain the loop area, including: Extracting each difference coordinate point in the closed trajectory in time sequence to obtain a difference coordinate sequence; Repeating the first difference coordinate point in the difference coordinate sequence and adding it to the end of the difference coordinate sequence to obtain a closed coordinate sequence; Using the trapezoidal method to calculate the microelement area of the closed coordinate sequence in turn and accumulating to obtain a signed area; Taking the absolute value of the signed area as the loop area, and recording the sign as a loop direction marker.
6. The method of claim 5, wherein the transformer oil is a mineral oil. Determining the viscosity interference component corresponding to the real-time parameters, and further excluding the viscosity interference component to obtain the chemical reaction component, including: Reading the temperature of the transformer oil at the i th moment as the input variable of the Andrade model to calculate the corresponding viscosity; Calculating the rotational correlation time and obtaining the motion broadening based on the viscosity, so as to determine the viscosity interference component; The viscosity disturbance component is deducted from the viscosity signal to obtain the chemical reaction component at the i-th time point. The viscosity disturbance component is deducted from the viscosity signal to obtain the chemical reaction component at the i-th time point.
7. The method of claim 6, wherein the transformer oil is a mineral oil. Determining the instantaneous generation rate of free radicals based on the chemical reaction component, and calculating the average net generation rate of free radicals in the temperature rise and fall cycle time period, including: Converting the chemical reaction component into the instantaneous free radical concentration at the i th moment according to a predetermined conversion coefficient; The difference of the instantaneous free radical concentration of adjacent time is divided by the fixed time interval to obtain the instantaneous generation rate of free radical; The average value of the instantaneous generation rate of free radical in the whole temperature rising and falling cycle period is obtained to obtain the average net generation rate of free radical in the temperature rising and falling cycle period.
8. The method of claim 7, wherein the transformer oil is a mineral oil. The monitoring and early warning signal is generated according to the loop area and the average net generation rate of free radical, including: The loop area, the loop direction and the average net generation rate of free radical corresponding to the temperature rising and falling cycle period are read to generate the monitoring and early warning signal, specifically as follows: The device failure early warning signal is generated when the loop area is not counterclockwise; The loop area is compared with the preset area threshold value, and the average net generation rate of free radical is compared with the preset rate threshold value, and the early local discharge early warning signal is generated when both are over limit; If the early local discharge early warning signal is generated in at least three temperature rising and falling cycle periods continuously, the early local discharge early warning signal is upgraded to the local discharge development early warning signal.
9. A transformer oil dissolved gas online monitoring system, applied to the transformer oil dissolved gas online monitoring method of any one of claims 1-8, characterized in that, Including: The baseline establishment module is used for acquiring reference parameters, including: g value reference and line width reference; The data acquisition module is used for acquiring real-time parameters at fixed time intervals, including: real-time g value and real-time line width; The trajectory construction module is used for determining the temperature rising and falling cycle period, and constructing a closed trajectory based on the reference parameters and the real-time parameters; The trajectory analysis module is used for determining the loop area of the closed trajectory, and accumulating the loop area to obtain the loop area; The interference exclusion module is used for determining the viscosity interference component corresponding to the real-time parameters, and further excluding the viscosity interference component to obtain the chemical reaction component; The free radical calculation module is used for determining the instantaneous generation rate of free radical based on the chemical reaction component, and calculating the average net generation rate of free radical in the temperature rising and falling cycle period; The monitoring and early warning module is used for generating the monitoring and early warning signal according to the loop area and the average net generation rate of free radical.