Method for obtaining inverse power model parameters of solid insulating material by considering pressurization history

Abstract

The invention discloses a method for obtaining parameters of an inverse power model of a solid insulation material by considering pressurization history, and belongs to the technical field of solid insulation electrical life. Carrying out a life pressurization experiment on the experiment sample; carrying out life curve fitting, and drawing a characteristic attenuation curve; acquiring a pressure resistance index of the experimental sample; based on the withstand voltage index, according to an inverse power formula, obtaining a breakdown voltage passing through a pressurization history; and obtaining a withstand voltage index of the pressurized history based on the obtained breakdown voltage data. According to the method disclosed by the invention, the brand new crosslinked polyethylene sample is subjected to constant pressurization treatment to be equivalent to the crosslinked polyethylene with the pressurization history, so that the pressure resistance index of the crosslinked polyethylene with the pressurization history is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of solid insulation electrical life, and in particular to a method for obtaining inverse power model parameters of solid insulation materials by considering pressurization history. Background Art

[0002] When the cross-linked polyethylene cable is in operation, the withstand voltage index changes with time, and the overall trend is that it increases with time. However, the existing experiments and methods all conduct accelerated life tests on cross-linked polyethylene samples, and obtain the withstand voltage index of the experimental samples by fitting the obtained data. Traditional experiments do not take into account the changes in the withstand voltage index of cross-linked polyethylene that has a pressurized history, that is, after aging simulation or use, and usually require destructive tests. It is very difficult to obtain the withstand voltage index of cross-linked polyethylene in operation. Summary of the invention

[0003] The purpose of the present invention is to provide a method for obtaining inverse power model parameters of solid insulating materials taking into account the pressurization history. By subjecting a new cross-linked polyethylene sample to a constant pressurization treatment and making it equivalent to a cross-linked polyethylene with a pressurization history, the pressure resistance index of the cross-linked polyethylene with a pressurization history can be obtained.

[0004] To achieve the above object, the present invention provides a method for obtaining inverse power model parameters of solid insulating materials taking into account pressurization history, the steps comprising:

[0005] S1. preparing a plurality of identical cross-linked polyethylene sheets as samples to be tested;

[0006] S2. Conducting accelerated life test on the sample under the same external applied field strength;

[0007] S3, obtaining the failure time of insulation breakdown of the sample to be tested during the accelerated life test, and calculating the average value of the failure time;

[0008] S4. Fitting the life curve of the sample to be tested according to the inverse power model to obtain the initial breakdown voltage E0 and the pressurization time t0 of the sample to be tested, obtaining the breakdown damage amount and the initial withstand voltage index of the sample to be tested according to the life curve, and drawing the characteristic attenuation curve according to the accelerated life experiment;

[0009] S5. Set the simulated aging test data, and calculate the breakdown voltage E after the simulated aging test, i.e., the pressure history, based on the data obtained in S4 according to the inverse power model. F ;;

[0010] S6, preparing cross-linked polyethylene sheets for simulated aging experiments, and based on the obtained E F The pressure was applied until breakdown occurred, and the pressure resistance index of the cross-linked polyethylene sheet after the simulated aging experiment was calculated according to the inverse power model.

[0011] Preferably, the constant voltage in the accelerated life test in step S2 is 38KV, 40KV and 42KV.

[0012] Preferably, the method for fitting the life curve of the sample to be tested according to the inverse power model in step S4 is:

[0013] Inverse Power Model Transformed into lnt = -n0lnE + lnD0;

[0014] Where n0 represents the voltage tolerance index of the non-aged insulating material, D0 represents the threshold of the dielectric of the non-aged insulating material to withstand electrical damage, and t is the electrical life of the non-aged insulating material under the field strength E.

[0015] Preferably, the characteristic attenuation curve and the life curve of the cross-linked polyethylene in step S4 have the same abscissa t and ordinate E, and are combined in the same coordinate system Et, but need to be shifted by t0.

[0016] Preferably, in step S5, E is calculated according to the inverse power model. F include:

[0017] The pressure value and pressure time of the simulated aging test were set to construct a damage model of the cross-linked polyethylene sheet after the simulated aging test. The formula is:

[0018]

[0019] The damage model is constructed based on the accelerated life test data of the sample to be tested. The formula is:

[0020]

[0021] The two cross-linked polyethylene sheets were pressed in different ways, but the damage amount of samples of the same material was the same, and the formula was obtained:

[0022]

[0023] In the formula, It indicates the amount of damage that occurs when a breakdown occurs under constant pressure at the voltage of E0. represents the damage amount obtained by the simulated aging experiment, Indicates that in E F The damage amount of breakdown caused by constant pressure under a voltage of , E0 represents the initial breakdown voltage, which is 42KV, t0 is the breakdown time, which is 1064s, n0 is the initial withstand voltage index, E1 represents the constant voltage applied in the simulated aging experiment, which is 36kv, t1 is the duration of E1, which is 7200s, E F Indicates the breakdown voltage after a voltage-applied history.

[0024] Preferably, in step S6, calculating the pressure resistance index of the cross-linked polyethylene sheet after the simulated aging test according to the inverse power model includes:

[0025] Obtain the life model expression of the sample to be tested considering the aging accumulation process, and substitute the (t0, E0) coordinates on the life curve into the formula:

[0026]

[0027] Set the ratio of the aging amount in the characteristic attenuation curve to the total aging amount as x, and construct the formula:

[0028]

[0029] The remaining life is expressed as:

[0030]

[0031] The end point on the characteristic attenuation curve (L-t0, E F ) into the remaining life formula, and then the proportion of the aging amount in the characteristic curve to the total aging amount is obtained:

[0032]

[0033] The pressure resistance index formula is derived as follows:

[0034]

[0035] Where, E0 represents the initial breakdown voltage, t0 is the breakdown time, n0 is the initial withstand voltage index, E1 is the voltage corresponding to the breakdown time of the simulated aging experiment, t1 is the duration of E1, and E F It represents the breakdown voltage after a history of pressure application, n represents the withstand voltage index of the cross-linked polyethylene sheet with a history of pressure application, L represents the life of the insulating material under the field strength E1, and K1 represents the characteristic constant of the material.

[0036] Therefore, the present invention adopts the above-mentioned method of obtaining the inverse power model parameters of solid insulating materials taking into account the pressurization history. By subjecting a new cross-linked polyethylene sample to a constant pressurization treatment and making it equivalent to the cross-linked polyethylene with a pressurization history, the characteristic attenuation curve is combined with the life curve to obtain the pressure resistance index of the cross-linked polyethylene with a pressurization history, which has a strong practical application value.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0039] Figure 2 It is a combined graph of the characteristic attenuation curve and the life curve of the cross-linked polyethylene according to an embodiment of the present invention;

[0040] Figure 3 It is a schematic diagram of the damage amount of cross-linked polyethylene under different pressurization methods according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Reference Figure 1 The present invention provides a method for obtaining inverse power model parameters of solid insulating materials taking into account pressurization history, the steps comprising:

[0043] S1. Prepare a plurality of identical cross-linked polyethylene sheets as samples to be tested.

[0044] S2. Perform accelerated life test on the sample under the same external applied field strength, and constantly apply pressure at 38KV, 40KV and 42KV until the sample breaks down.

[0045] S3. Obtain the failure time of insulation breakdown of the sample to be tested during the accelerated life test, and calculate the average value of the failure time.

[0046] S4. Fit the life curve of the sample to be tested according to the inverse power model to obtain the initial breakdown voltage E0 and the pressurization time t0 of the sample to be tested, obtain the breakdown damage amount and the initial withstand voltage index of the sample to be tested according to the life curve, and draw the characteristic attenuation curve according to the accelerated life experiment.

[0047] Characteristic degradation curve

[0048] When the samples are subjected to pressure test, the electrical strength of the samples is tested at different times. It is found that the electrical strength of each sample decreases as the pressure time increases. When the number of samples is large enough, a curve showing the change of the sample's pressure resistance characteristics over time can be drawn. This is the characteristic attenuation curve. If the sample's pressure resistance characteristics decay to the voltage gradient it is subjected to, a breakdown will occur. Until the breakdown occurs, the pressure resistance characteristics are higher than the voltage that Yangping is subjected to. The initial point of the characteristic curve is the initial value E0. This value is the same as the voltage corresponding to the life curve t0, so the time starting point of the characteristic curve must be shifted by t0, such as Figure 2 shown.

[0049] The method for fitting the life curve of the sample to be tested according to the inverse power model is:

[0050] Inverse Power Model Transformed into lnt = -n0lnE + lnD0;

[0051] Where n0 represents the voltage tolerance index of the non-aged insulating material, D0 represents the threshold of the dielectric of the non-aged insulating material to withstand electrical damage, and t is the electrical life of the non-aged insulating material under the field strength E.

[0052] S5. Set the simulated aging test data, and calculate the breakdown voltage E after the simulated aging test, i.e., the pressure history, based on the data obtained in S4 according to the inverse power model. F . Specifically include:

[0053] The pressure value and pressure time of the simulated aging test were set to construct a damage model of the cross-linked polyethylene sheet after the simulated aging test. The formula is:

[0054]

[0055] The damage model is constructed based on the accelerated life test data of the sample to be tested. The formula is:

[0056]

[0057] The two cross-linked polyethylene sheets were pressed in different ways, but the damage amount of samples with the same material was the same, e.g. Figure 3 As shown, the formula is obtained according to the damage amount:

[0058]

[0059] In the formula, It indicates the amount of damage that occurs when a breakdown occurs under constant pressure at the voltage of E0. represents the damage amount obtained by the simulated aging experiment, Indicates that in E FThe damage amount of breakdown caused by constant pressure under a voltage of , E0 represents the initial breakdown voltage, which is 42KV, t0 is the breakdown time, which is 1064s, n0 is the initial withstand voltage index, E1 represents the constant voltage applied in the simulated aging experiment, which is 36kv, t1 is the duration of E1, which is 7200s, E F Indicates the breakdown voltage after a voltage-applied history.

[0060] In this step, we first use the theory to find an E F , and then verify whether it is correct based on the actual situation.

[0061] S6, preparing cross-linked polyethylene sheets for simulated aging experiments, and based on the obtained E F The pressure was applied until breakdown occurred, and the pressure resistance index of the cross-linked polyethylene sheet after the simulated aging experiment was calculated according to the inverse power model.

[0062] The compressive strength index of the cross-linked polyethylene sheet after the simulated aging test calculated according to the inverse power model includes:

[0063] Obtain the life model expression of the sample to be tested considering the aging accumulation process, and substitute the (t0, E0) coordinates on the life curve into the formula:

[0064]

[0065] Set the ratio of the aging amount in the characteristic attenuation curve to the total aging amount as x, and construct the formula:

[0066]

[0067] The remaining life is expressed as:

[0068]

[0069] The end point on the characteristic attenuation curve (L-t0, E F ) into the remaining life formula, and then the proportion of the aging amount in the characteristic curve to the total aging amount is obtained:

[0070]

[0071] The pressure resistance index formula is derived as follows:

[0072]

[0073]

[0074] Where, E0 represents the initial breakdown voltage, t0 is the breakdown time, n0 is the initial withstand voltage index, E1 is the voltage corresponding to the breakdown time of the simulated aging experiment, t1 is the duration of E1, and E FIt represents the breakdown voltage after a history of pressure application, n represents the withstand voltage index of the cross-linked polyethylene sheet with a history of pressure application, L represents the life of the insulating material under the field strength E1, and K1 represents the characteristic constant of the material.

[0075] In this embodiment, a plurality of identical cross-linked polyethylene sheets are prepared as test samples, and constant pressure is applied at 38KV, 40KV and 42KV until the test samples break down. The time when the breakdown occurs is recorded and the average value is calculated. Some experimental data are shown in Table 1.

[0076] Table 1 Experimental data

[0077]

[0078] The life curve was fitted according to the inverse power model, and the breakdown damage amount and initial withstand voltage index of the tested sample were obtained, which were 87.396 and 21.57, respectively.

[0079] Calculation of E based on two pressurization methods F :

[0080] Pressurization method 1: Constantly pressurize at 42KV voltage for 1064s until breakdown occurs, that is, accelerated life test;

[0081] Pressurization method 2: Constant pressurization for 7200s at 36KV voltage, and then constant pressurization for 1064s at 42KV voltage until breakdown occurs, that is, first simulated aging (pressurization history) and then accelerated life test.

[0082] E is calculated based on the set value F The theoretical value is 41.38KV.

[0083] Calculate the pressure resistance index of cross-linked polyethylene with a history of pressure. Since the pressure resistance index is increasing, E F The actual value of E is smaller than the theoretical value. F Set to 39KV, as shown in Table 2, for E F =Partial experimental data at 39KV, t F is the breakdown time obtained by constant voltage at 39KV. From the table, we can see that its data is close to 1064 under ideal conditions. Therefore, it can be concluded that when E F =39KV, the amount of damage obtained is the same as that without pressure history. Based on these data, the pressure resistance index of cross-linked polyethylene with pressure history is 21.93, which is more accurate than the initial pressure resistance index of 21.57.

[0084] Table 2E F Experimental data at 39KV

[0085] E(KV) t(s) <![CDATA[E F (KV)]]> <![CDATA[t F (s)]]> 36 7200 39 1939.7 36 7200 39 943

[0086] Therefore, the present invention adopts the above-mentioned method of obtaining the inverse power model parameters of solid insulating materials taking into account the pressurization history. By subjecting a new cross-linked polyethylene sample to a constant pressurization treatment and making it equivalent to the cross-linked polyethylene with a pressurization history, the pressure resistance index of the cross-linked polyethylene with a pressurization history is obtained.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for obtaining inverse power model parameters of solid insulating materials considering pressurization history, characterized in that the steps include: S1. preparing a plurality of identical cross-linked polyethylene sheets as samples to be tested; S2. Conducting accelerated life test on the sample under the same external applied field strength; S3, obtaining the failure time of insulation breakdown of the sample to be tested during the accelerated life test, and calculating the average value of the failure time; S4. Fitting the life curve of the sample to be tested according to the inverse power model to obtain the initial breakdown voltage E0 and the pressurization time t0 of the sample to be tested, obtaining the breakdown damage amount and the initial withstand voltage index of the sample to be tested according to the life curve, and drawing the characteristic attenuation curve according to the accelerated life experiment; S5. Set the simulated aging test data, and calculate the breakdown voltage E after the pressure history according to the inverse power model based on the data obtained in S4. F ; S6, preparing cross-linked polyethylene sheets for simulated aging experiments, and based on the obtained E F The pressure was applied until breakdown occurred, and the pressure resistance index of the cross-linked polyethylene sheet after the simulated aging experiment was calculated according to the inverse power model.

2. The method for obtaining inverse power model parameters of solid insulating materials considering pressurization history according to claim 1, characterized in that: The constant voltages in the accelerated life test in step S2 are 38 KV, 40 KV and 42 KV.

3. The method for obtaining inverse power model parameters of solid insulating materials considering pressurization history according to claim 2, characterized in that: The method for fitting the life curve of the sample to be tested according to the inverse power model in step S4 is: The inverse power model D0 = tE n0 Transformed into lnt = -n0lnE + lnD0; Where n0 represents the voltage tolerance index of the non-aged insulating material, D0 represents the threshold of the dielectric of the non-aged insulating material to withstand electrical damage, and t is the electrical life of the non-aged insulating material under the field strength E.

4. The method for obtaining inverse power model parameters of solid insulating materials considering pressurization history according to claim 3, characterized in that: In step S4, the characteristic attenuation curve and the life curve of the cross-linked polyethylene have the same abscissa t and ordinate E, and are combined in the same coordinate system Et, but need to be shifted by t0.

5. The method for obtaining inverse power model parameters of solid insulating materials considering pressurization history according to claim 4, characterized in that: In step S5, E is calculated according to the inverse power model. F include: The pressure value and pressure time of the simulated aging test were set to construct a damage model of the cross-linked polyethylene sheet after the simulated aging test. The formula is: The damage model is constructed based on the accelerated life test data of the sample to be tested. The formula is: The two cross-linked polyethylene sheets were pressed in different ways, but the damage amount of samples of the same material was the same, and the formula was obtained: In the formula, It indicates the amount of damage that occurs when a breakdown occurs under constant pressure at the voltage of E0. represents the damage amount obtained by the simulated aging experiment, Indicates that in E F The damage amount of breakdown caused by constant pressure under a voltage of , E0 represents the initial breakdown voltage, which is 42KV, t0 is the breakdown time, which is 1064s, n0 is the initial withstand voltage index, E1 represents the constant voltage applied in the simulated aging experiment, which is 36kv, t1 is the duration of E1, which is 7200s, E F Indicates the breakdown voltage after a voltage-applied history.

6. The method for obtaining inverse power model parameters of solid insulating materials considering pressurization history according to claim 5, characterized in that: In step S6, the pressure resistance index of the cross-linked polyethylene sheet after the simulated aging test is calculated according to the inverse power model, including: Obtain the life model expression of the sample to be tested considering the aging accumulation process, and substitute the (t0, E0) coordinates on the life curve into the formula: Set the ratio of the aging amount in the characteristic attenuation curve to the total aging amount as x, and construct the formula: The remaining life is expressed as: The end point on the characteristic attenuation curve (L-t0, E F ) into the remaining life formula, and then the proportion of the aging amount in the characteristic curve to the total aging amount is obtained: The pressure resistance index formula is derived as follows: Where, E0 represents the initial breakdown voltage, t0 is the breakdown time, n0 is the initial withstand voltage index, E1 is the voltage corresponding to the breakdown time of the simulated aging experiment, t1 is the duration of E1, and E F It represents the breakdown voltage after a history of pressure application, n represents the withstand voltage index of the cross-linked polyethylene sheet with a history of pressure application, L represents the life of the insulating material under the field strength E1, and K1 represents the characteristic constant of the material.

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