Method and device for calculating life loss rate of insulation paper

Abstract

This invention belongs to the field of oil-paper insulation technology, and relates to a method and apparatus for calculating the life loss rate of insulating paper. The calculation method, by considering the limiting degree of polymerization and time-varying load of the insulating paper, calculates the life loss rate of the insulating paper in oil-immersed power transformers, including: measuring the DP of the insulating paper at different aging times t under a pre-set constant temperature. t Value; plot the curve of DP value as a function of aging time t at this constant temperature. t‑t According to at least three sets of parameters k obtained at different temperatures from the fitting, 10 Using k2, the LODP values ​​at different thermal aging test temperatures were calculated; taking the hottest spot inside the transformer as the calculation object, the DP of this hot spot under time-varying temperatures was calculated. t The curve of DP value changing with aging time t t‑t This invention calculates and predicts the lifespan loss rate of the insulating paper in transformer oil-paper insulation. A computing device is used to implement the above calculation method. This invention reduces the error in predicting the lifespan loss rate of the insulating paper.

Description

Technical Field

[0001] This invention belongs to the field of oil-paper insulation technology and relates to a method and device for calculating the life loss rate of insulating paper. By considering the limiting degree of polymerization of the insulating paper in transformer oil-paper insulation and the time-varying load method, the life loss rate of the insulating paper in oil-immersed power transformer oil-paper insulation is calculated. Background Technology

[0002] Oil-paper insulation, composed of mineral oil and insulating paper, is the main insulating material for large oil-immersed power transformers. The insulating paper is generally made of fiber insulating paper. During equipment operation, the insulating paper will gradually age due to the influence of electrical, thermal, and mechanical factors.

[0003] The lifespan of insulating paper determines the technical lifespan of power transformers, and the degree of polymerization is usually used as a direct indicator of the degree of insulation paper degradation. The initial degree of polymerization of new insulating paper is approximately 1200, and it is considered to have reached the end of its lifespan when the limiting degree of polymerization drops to around 200. Studies have shown that equipment operating temperature and thermal aging play a decisive role in the lifespan of insulating paper. Thermal life models for oil-paper insulation are commonly used in research to describe the change in the degree of polymerization of insulating paper over time at different temperatures. Therefore, the determination of the thermal life model for oil-paper insulation and its parameters plays a crucial role in equipment insulation design and the assessment of the remaining lifespan of insulating paper.

[0004] In the existing technology, there are three commonly used thermal life models for oil-paper insulation:

[0005] Model 1: Using the aging rate at 98℃ as a reference value, assuming the aging rate at this temperature is 1, and employing the 6℃ half-life criterion given in the mineral oil transformer guideline IEEE Std C57.91-1995, the thermal aging rate of oil-paper insulation is given. It is assumed that for every 6℃ increase in temperature, the life of the insulating paper is halved and the aging rate doubles. Limitations of this model: It can only roughly describe the relative aging rate relative to the 98℃ reference temperature, does not consider the difference in aging rate of insulating paper cellulose at different degrees of polymerization, and cannot describe the time-varying law of the absolute value of the degree of polymerization of the insulating paper.

[0006] Model 2: A zero-order kinetic equation for fiber thermal degradation is proposed, assuming the fiber chain breaking rate of insulating paper at a given temperature is a constant, which is then used to fit aging data. Limitations of this model: It shows good agreement in the early stages of insulating paper aging, but under long-term aging conditions, especially in the later stages, the fitted data does not match the actual experimental data.

[0007] Model 3: A second-order kinetic equation is proposed to address the time-varying nature of the degree of polymerization of oil-paper insulation, assuming that the rate of fiber degradation in the insulation paper is a value that varies with time. Limitations of this model: To date, the quantitative relationship between some model parameters and temperature remains unknown, preventing this model from being used to calculate the variation characteristics of the degree of polymerization of insulation paper under time-varying temperatures. Summary of the Invention

[0008] To address the limitations of existing technologies, this invention provides a method for calculating the DP value of oil-paper insulation paper over time during thermal aging. By studying key parameters related to the aging temperature of the insulation paper and the relationship between the LODP value and temperature, the DP value of the insulation paper under time-varying temperatures is calculated. t-t The curve is used to calculate and predict the life loss rate of the insulating paper in transformer oil-paper insulation.

[0009] In this invention, for the sake of convenience in textual description, the following technical terms are defined: First, DP value, where DP is an abbreviation for Degree of Polymerization, referring to the degree of polymerization of the insulating paper; second, LODP value, where LODP is Levelling-Off Degree of Polymerization, referring to the limiting degree of polymerization of the insulating paper; third, DP... t The first value refers to the degree of polymerization of the insulating paper at aging time t; the second value is the DP0 value, which refers to the initial degree of polymerization of the insulating paper; the third value is the DP... t-t The curve represents the change of DP value with aging time t, with the horizontal axis representing aging time t and the vertical axis representing DP value.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] Methods for calculating the life loss rate of insulating paper include:

[0012] DP of insulating paper at different aging times t under a pre-set constant temperature was measured. t Value, wherein the DP t The value refers to the degree of polymerization of the insulating paper at aging time t;

[0013] Based on the obtained DP of the insulating paper t Plot the curve of DP value as a function of aging time t at a preset constant temperature. t-t The DP value refers to the degree of polymerization of the insulating paper.

[0014] For the change curve DP t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2;

[0015] By changing the preset constant temperature and repeating the process, the parameter k corresponding to different constant temperatures can be obtained. 10 And k2, to obtain at least three sets of parameters k at a pre-set constant temperature. 10 and k2;

[0016] Obtain at least three sets of parameters k 10 The relationship between k2 and the corresponding preset constant temperature;

[0017] According to at least three pre-set parameters k at constant temperature obtained by fitting. 10 k2 and k2 are used to calculate the LODP value at different constant temperatures during thermal aging tests, where the LODP value refers to the limiting degree of polymerization of the insulating paper.

[0018] Taking the hottest spot inside the transformer as the calculation object, calculate the DP of the hottest spot inside the transformer under time-varying temperature. t The curve of DP value changing with aging time t t-t The hottest spot inside the transformer is the place with the highest temperature inside the transformer.

[0019] According to the change curve DP t-t Predict the life loss rate of insulating paper.

[0020] Preferably, formula (1) is used to analyze the variation curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2, parameter k 10 k2 only represents the fitting result and has no actual technical meaning. Other letters can be used instead.

[0021]

[0022] In Formula 1, e is the base of the natural logarithm, which is approximately 2.718.

[0023] Fit the data according to formulas (2), (3), and (4) and obtain at least three sets of parameters k. 10 The relationship between k2 and the corresponding preset constant temperature;

[0024]

[0025] A1 and E a1 These refer to the pre-exponential factor and activation energy of a chemical reaction, respectively. R is the Boltzmann constant, T is the absolute temperature of the experiment, and exp is the base of the natural logarithm.

[0026]

[0027]

[0028] Preferably, the LODP values ​​at different preset constant temperatures are calculated using formula (5):

[0029]

[0030] The device for calculating the life loss rate of insulating paper includes:

[0031] Change curve DP t-t The plotting module is used to measure the DP of insulating paper at different aging times t under a pre-set constant temperature. t Value, wherein the DP t The value refers to the degree of polymerization of the insulating paper at aging time t; based on the obtained DP of the insulating paper t Plot the curve of DP value as a function of aging time t at a constant temperature. t-t The DP value refers to the degree of polymerization of the insulating paper.

[0032] Change curve DP t-t The fitting module is used to fit the changing curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 And k2; change the preset constant temperature, and repeat the process to obtain the corresponding parameter k at different constant temperatures. 10 Following steps k2, parameters k are obtained at at least three pre-set temperatures. 10 and k2;

[0033] The LODP value calculation module is used to obtain at least three sets of parameters k. 10 The relationship between k2 and the corresponding preset constant temperature; according to at least three sets of parameters k at different temperatures obtained by fitting. 10 Using k2, the LODP value at different thermal aging test temperatures is calculated, where the LODP value refers to the limiting degree of polymerization of the insulating paper;

[0034] Transformer internal hot spot variation curve DP t-t The calculation module is used to calculate the dynamic range (DP) of the hottest spot inside the transformer under time-varying temperatures, taking the hottest spot inside the transformer as the calculation object. t The curve of DP value changing with aging time t t-t The hottest spot inside the transformer is the place with the highest temperature inside the transformer.

[0035] The insulation paper life loss rate calculation and prediction module is used to calculate and predict the life loss rate based on the change curve DP. t-t Predict the life loss rate of insulating paper.

[0036] The above functional modules can be installed and run on a computer, and used in conjunction with temperature control and timing devices to conduct predictive experiments.

[0037] Preferably, the change curve DP t-t The fitting module uses formula (1) to fit the change curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2:

[0038]

[0039] In Formula 1, e is the base of the natural logarithm, which is approximately 2.718.

[0040] By fitting according to formulas (2), (3), and (4), at least three sets of parameters k are obtained. 10 The relationship between k2 and the corresponding preset constant temperature;

[0041]

[0042] A1 and E a1 These refer to the pre-exponential factor and activation energy of a chemical reaction, respectively; R is the Boltzmann constant; T is the absolute temperature of the experiment; and exp is the base of the natural logarithm.

[0043]

[0044]

[0045] Preferably, the LODP value calculation module calculates the LODP value at different preset constant temperatures using formula (5);

[0046]

[0047] In this invention, time-varying temperature means that the temperature changes with the aging process and is not a constant value.

[0048] Compared with the prior art, the beneficial effects of this invention are as follows:

[0049] 1. This invention enables multi-parameter non-destructive evaluation of the life loss rate of insulating paper in transformer oil-paper insulation, and improves the accuracy and practicality of polymerization degree evaluation;

[0050] 2. This invention can determine the relationship between the key parameters of transformer insulation paper and the LODP value and temperature, and also the curve of the DP value of transformer hot spots changing over time under time-varying temperatures. t-t The calculation incorporates the LODP value and time-varying temperature factor into the transformer oil-paper insulation life loss rate calculation model, which reduces the error in the prediction of insulation paper life loss rate and improves the reliability of the prediction results. Attached Figure Description

[0051] Figure 1 This is 1 / DP of Embodiment 1 of the present invention. t A schematic diagram showing the correspondence between -1 / DP0 and time t;

[0052] Figure 2 The hotspot temperature and DP under normal load rate in Embodiment 1 of the present invention t-t Schematic diagram of the curve;

[0053] Figure 3 This is the simulated hotspot temperature and DP under three emergency overload conditions in Embodiment 1 of the present invention. t-t Schematic diagram of the curve. Detailed Implementation

[0054] The specific embodiments of the present invention will be described below through practical examples.

[0055] Example 1

[0056] The method for calculating the life loss rate of insulating paper includes the following steps:

[0057] 1. Conduct accelerated thermal aging tests on the insulating paper of the oil-paper insulation at at least three temperatures, and take samples at regular intervals to measure the DP value of the insulating paper until the DP value reaches the LODP value or the DP value is <200 at each temperature;

[0058] The principle for selecting the temperature is to balance the "aging efficiency" and the "unchanged aging mechanism". Too low a temperature will take too long, and too high a temperature will not have an equivalent aging mechanism. It is generally recommended to select within the range of 90 to 130°C, with at least three temperatures and the intervals should be as even as possible.

[0059] The sampling interval depends on the aging temperature and the required number of sampling points. For example, at 130 degrees Celsius, the lifespan of the insulating paper is 30 days, and if 10 data points are sampled, the sampling time is once every 3 days. At 90 degrees Celsius, the lifespan of the insulating paper is 90 days, and if 10 data points are sampled, the sampling time is once every 9 days.

[0060] The sampling and measurement methods for the DP and LODP values ​​of insulating paper are existing technologies. Specific measurement methods should be performed according to standards GB / T29305-2012 or IEC60450:2007. The LODP value of the insulating paper varies with different test temperatures and different combinations of oil-paper insulation, thus requiring measurement.

[0061] DP is typically obtained from three consecutive sampling intervals. t If the value change is less than 5%, the sample insulation paper is considered to have reached the LODP value.

[0062] 2. Plot the curves of DP as a function of aging time t (days or hours) at various temperatures. t-t Formula (1) is used to apply DPt-t By performing a fitting, the parameter k is obtained. 10 and k2 value;

[0063] 3. Calculate k 10 The ratio of k to k2, and the parameter k at different temperatures is calculated using formula (2). 10 By fitting k2, we obtain A1 and E. a1 value;

[0064] 4. Using formula (3) to calculate k at different temperatures 10 By fitting the data, we obtain A2 and E. a2 value;

[0065] 5. The value of k2 is obtained using formula (4):

[0066] 6. Further, the LODP values ​​at different temperatures can be obtained, as shown in formula (5):

[0067] By doing so, the key parameter k of the insulating paper material was obtained. 10 The relationship between k2 and LODP values ​​and temperature is then established. Next, the DP value of the transformer hotspot under time-varying temperature is calculated as a function of aging time t. t-t curve.

[0068] 7. Let y = 1 / DP t -1 / DP0, where y represents the insulation level decreasing from DP0 to the current DP. t The average number of chain breaks during the value process. The relationship curve between y and t is as follows: Figure 1 As shown, a cellulose chain breaks at the 1-4-β glycosidic bond, decomposing into two shorter cellulose chains; this is called a primary chain breakage. y represents the degree of polymerization (DP) of the insulating paper as the fiber decreases from its initial degree of polymerization (DP0) at aging time t. t The average number of broken links experienced during the value process.

[0069] 8. For any aging time t a The corresponding number of chain breaks is denoted as y. a For any point (t) a ,y a Taking the derivative with respect to y, we can obtain the chain breaking rate k at any time, as shown in formula (6):

[0070] k = dy / dt = k 10 exp(-k2t) (6)

[0071] That is to say Figure 1 The slope at that point.

[0072] 9. Consider a unit time d t The aging temperature of the inner insulating paper is T, and the state of the insulating paper fibers changes from ya Change to y b The average number of chain breaks increased by d y , then y b This can be expressed as formula (7):

[0073]

[0074] Therefore, if the insulating paper is known at a certain time t a DP a The value can be used to calculate the d-days it undergoes at aging temperature T. t DP after b Value, when d t When the temperature is sufficiently low, the DP of the insulating paper material under time-varying temperatures can be obtained. t-t curve.

[0075] The curve of DP changing with aging time has been calculated, meaning the DP value at each moment is known. Therefore, the insulation paper life loss rate can be calculated using the formula: Insulation Paper Life Loss Rate = (DP...) t The life loss rate of the insulation paper can be obtained by dividing the value of DP0 by the value of DP0.

[0076] The following data is based on the measured load of a 330kV oil-immersed power transformer from January to December of a certain year, with the load recorded hourly. The hot spot temperature Th is estimated according to the model in IEC 60076-7, and the results are as follows. Figure 2 and Figure 3 As shown. Over these 12 months, the average hot spot temperature of the transformer was approximately 42.3℃, and the maximum hot spot temperature was less than 90℃.

[0077] Since this transformer uses mineral insulating oil-impregnated kraft paper as insulation, by conducting experiments according to the steps described in this invention, the key parameters required for calculation can be obtained. The values ​​are as follows:

[0078]

[0079] Assuming the transformer is newly put into operation and the DP0 value is set to 1162, the curve showing the change of the DP value over one year is as follows. Figure 2 As shown in the upper middle curve, it can be seen that due to the lower average hot spot temperature, the DP value is close to the LODP value at that temperature for most of the time, and is considered to be the aging rate of 0, so the decrease is not obvious; the degree of polymerization decreases significantly from October to December, during which the hot spot temperature also increases significantly due to the increase in electricity load.

[0080] in addition, Figure 3Three scenarios of hotspot temperature rise caused by emergency overload were simulated, lasting for 2 hours, 8 hours and 4 hours respectively, with the hotspot temperature reaching 120℃ in all three scenarios.

[0081] Figure 2 In the absence of an emergency overload, the insulation paper life loss rate = (DP t Value - DP0 value) / DP0 value = (1162 - 1042) / 1162 = 10.33%. Figure 3 In the event of an emergency overload, the insulation paper life loss rate is (1162-1007) / 1162 = 13.34%. It can be seen that a mere 14 hours of emergency overload resulted in a 3% increase in the insulation paper life loss rate compared to the case without an emergency overload.

[0082] Appendix Figure 2 and attached Figure 3 In this context, "Operating" means the transformer is in operation, and "Emergency load" means an emergency overload.

[0083] Example 2

[0084] The device for calculating the life loss rate of insulating paper includes: a variation curve DP. t-t Drawing module, change curve DP t-t Fitting module, LODP value calculation module, transformer internal hotspot variation curve DP t-t Calculation module and insulation paper life loss rate calculation and prediction module.

[0085] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0086] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0087] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0088] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0089] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0090] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0091] In the embodiments of the present invention, all technical features not described in detail are existing technologies or conventional technical means, and will not be repeated here.

[0092] Finally, it should be noted that the above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the life loss rate of insulating paper, characterized in that, include: DP of insulating paper at different aging times t under a pre-set constant temperature was measured. t Value, wherein the DP t The value refers to the degree of polymerization of the insulating paper at aging time t; Based on the obtained DP of the insulating paper t Plot the curve of DP value as a function of aging time t at a preset constant temperature. t-t The DP value refers to the degree of polymerization of the insulating paper. For the change curve DP t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2; By changing the preset constant temperature and repeating the process, the parameter k corresponding to different constant temperatures can be obtained. 10 And k2, to obtain at least three sets of parameters k at a pre-set constant temperature. 10 and k2; Obtain at least three sets of parameters k 10 The relationship between k2 and the corresponding preset constant temperature; According to at least three pre-set parameters k at constant temperature obtained by fitting. 10 k2 and k2 are used to calculate the LODP value at different constant temperatures during thermal aging tests, where the LODP value refers to the limiting degree of polymerization of the insulating paper. Taking the hottest spot inside the transformer as the calculation object, calculate the DP of the hottest spot inside the transformer under time-varying temperature. t The curve of DP value changing with aging time t t-t The hottest spot inside the transformer is the place with the highest temperature inside the transformer. According to the change curve DP t-t Predict the life loss rate of insulating paper; Formula (1) is used to analyze the variation curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2: （1）； In Formula 1, e is the base of the natural logarithm; By fitting according to formulas (2), (3), and (4), at least three sets of parameters k are obtained. 10 The relationship between k2 and the corresponding preset constant temperature; （2）； A1 and E a1 These refer to the pre-exponential factor and activation energy of a chemical reaction, respectively; R is the Boltzmann constant; T is the absolute temperature of the experiment; and exp is the base of the natural logarithm. （3）； （4）； The LODP values ​​at different preset constant temperatures were calculated using formula (5): （5）。 2. A device for calculating the life loss rate of insulating paper, characterized in that, include: Change curve DP t-t The plotting module is used to measure the DP of insulating paper at different aging times t under a pre-set constant temperature. t Value, wherein the DP t The value refers to the degree of polymerization of the insulating paper at aging time t; based on the obtained DP of the insulating paper t Plot the curve of DP value as a function of aging time t at a constant temperature. t-t The DP value refers to the degree of polymerization of the insulating paper. Change curve DP t-t The fitting module is used to fit the changing curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 And k2; change the preset constant temperature, and repeat the process to obtain the corresponding parameter k at different constant temperatures. 10 Following steps k2, parameters k are obtained at at least three pre-set temperatures. 10 and k2; The LODP value calculation module is used to obtain at least three sets of parameters k. 10 The relationship between k2 and the corresponding preset constant temperature; according to at least three sets of parameters k at different temperatures obtained by fitting. 10 Using k2, the LODP value at different thermal aging test temperatures is calculated, where the LODP value refers to the limiting degree of polymerization of the insulating paper; Transformer internal hot spot variation curve DP t-t The calculation module is used to calculate the dynamic range (DP) of the hottest spot inside the transformer under time-varying temperatures, taking the hottest spot inside the transformer as the calculation object. t The curve of DP value changing with aging time t t-t The hottest spot inside the transformer is the place with the highest temperature inside the transformer. The insulation paper life loss rate calculation and prediction module is used to calculate and predict the life loss rate based on the change curve DP. t-t Predict the life loss rate of insulating paper; The change curve DP t-t The fitting module uses formula (1) to fit the change curve DP. t-t By performing a fitting, the corresponding parameter k is obtained. 10 and k2: （1）； In Formula 1, e is the base of the natural logarithm; By fitting according to formulas (2), (3), and (4), at least three sets of parameters k are obtained. 10 The relationship between k2 and the corresponding preset constant temperature; （2）； A1 and E a1 These refer to the pre-exponential factor and activation energy of a chemical reaction, respectively; R is the Boltzmann constant; T is the absolute temperature of the experiment; and exp is the base of the natural logarithm. （3）； （4）； The LODP value calculation module calculates the LODP value at different preset constant temperatures using formula (5); （5）。

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