Insulation material aging assessment method and system based on polarization integral current and IRC

Abstract

A method and system for evaluating aging of insulating materials based on polarization integral current and IRC, the method comprising: measuring polarization current under applied DC voltage, integrating and calculating the polarization current to obtain the equivalent resistance and equivalent capacitance of the test sample, thereby obtaining a first time constant reflecting the polarization state of the test sample; after short circuit, measuring the isothermal relaxation current of the test sample, and fitting the isothermal relaxation current with a third-order exponential decay function when the first time constant is known; calculating the aging factor A according to the fitting result, and the aging state of the insulating material is positively correlated with the value of the aging factor A. It is noted that the polarization current of the IRC test contains information that can reflect the polarization characteristics of the material, which is often ignored in previous experiments; at the same time, obtaining an accurate first time constant as a prerequisite for three-exponential fitting can reduce the error of the aging factor introduced in the fitting process and more accurately evaluate the aging state of the insulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulation status assessment of electrical equipment, and more specifically, relates to an insulation material aging status assessment method based on polarization integral current and isothermal relaxation current. Background Art

[0002] As a non-destructive test method, the IRC method (Isothermal Relaxation Current) can effectively evaluate the aging state of insulation by using the characteristics of the current during the depolarization process. This method is currently used in aging evaluation of cables, generator stator bar insulation, etc. Due to the characteristics of the insulation material of the cable, its IRC curve uses a third-order exponential decay function to fit the three different polarization types in the material.

[0003] The fitting result of the third-order exponential decay function directly affects the calculation of the aging factor and determines the evaluation of the cable aging state. In the fitting process, it is difficult to accurately fit the first time constant, which reflects the body polarization state of the test sample in the measurement system, because it is much smaller than the second and third time constants; and its deviation will greatly affect the calculation of the aging factor. Therefore, obtaining an accurate first time constant is very important for the aging evaluation model based on the IRC method.

[0004] The existing technology generally aims at the overall optimal fitting effect and uses software to obtain three time constants within the empirical range. However, the first time constant obtained cannot accurately reflect the body polarization state of the test sample in the test system, resulting in deviations in the aging factor calculation results and the aging state evaluation.

[0005] Prior art document 1 (CN113777138A) uses the current results of linear boosting at different boosting rates to obtain equivalent resistance and equivalent capacitance, but repeated linear boosting processes may damage the sample, and the linear boosting process is difficult to control.

[0006] In addition, the IRC-based insulation material aging assessment method uses the time integration method of the depolarization current to obtain the aging factor. The actual IRC test process includes the polarization stage and the depolarization stage, and there is a corresponding relationship between the polarization and depolarization processes. The traditional IRC-based aging assessment test focuses more on the information related to the trap density distribution reflected by the relaxation current in the depolarization process. In fact, the current in the polarization process of the IRC test contains information that can reflect the polarization characteristics of the material, which is often ignored in previous experiments. Summary of the invention

[0007] In order to solve the problem of inaccurate first time constant in the IRC fitting process in the prior art, the present invention provides an insulation material aging state assessment method based on polarization integral current and IRC. By integrating the polarization current in the polarization process, an accurate first time constant is obtained; when the first time constant is determined, the IRC in the depolarization process is fitted, so that the calculated aging factor more accurately reflects the actual aging state of the cable.

[0008] The present invention adopts the following technical solutions. The first invention of the present invention provides an insulation material aging assessment method based on polarization integral current and IRC, the method comprising:

[0009] The polarization current is measured under the application of DC voltage, and the equivalent resistance and equivalent capacitance of the test sample are obtained by integrating the polarization current, thereby obtaining the first time constant reflecting the polarization state of the test sample body; after short circuit, the isothermal relaxation current of the test sample is measured, and when the first time constant is known, the isothermal relaxation current is fitted with a third-order exponential decay function; the aging factor A is calculated based on the fitting results, and the aging state of the insulating material is positively correlated with the aging factor A value.

[0010] Preferably, in a closed environment at room temperature 298K, a DC voltage U is applied during the polarization stage. p =1kV, voltage application time is 1800s, polarization current I is measured p (t); In the depolarization stage, the short circuit duration is 1800s, and the depolarization current I is measured. d (t).

[0011] Preferably, the current sampling rate in the polarization and depolarization stages is set to 50 sampling points / second.

[0012] Preferably, the polarization current I p (t) is decomposed into a constant resistive current component I R and the capacitive current component I that varies with time t C (t), using the capacitive current component I C (t) The integration result is used to calculate the equivalent capacitance C of the insulating material, using the resistive current component I R Calculate the equivalent resistance R.

[0013] Preferably, the polarization current I p (t) The quasi-steady-state current value tending to steady state represents the resistive current component I R .

[0014] Preferably, the equivalent resistance R of the insulating material is expressed by the following formula:

[0015]

[0016] Where:

[0017] U p Indicates the DC voltage applied to the insulating material.

[0018] I p0 Represents the polarization current I p (t) Quasi-steady-state current value tending to steady state.

[0019] Preferably, the capacitive current component I is used C (t) The calculation of the equivalent capacitance C of the insulating material by integration results includes the following steps:

[0020] Polarization current I p (t) capacitive current component I C (t) is expressed as follows:

[0021] I C (t) = I p (t)-I R

[0022] Where:

[0023] I C (t) represents the polarization current I p (t) capacitive current component;

[0024] For capacitive current component I C (t) Take time t in [0,t p ] is expressed as follows:

[0025]

[0026] Where:

[0027] Q C Represents the polarization integrated current result;

[0028] By applying voltage U p With the capacitive current component I C The integral of (t) is used to calculate the equivalent capacitance, which is expressed as follows:

[0029]

[0030] Where:

[0031] C represents the equivalent capacitance of the insulating material.

[0032] Preferably, the first time constant is calculated using the equivalent capacitance C and the equivalent resistance R obtained through the polarization process, and is expressed as follows:

[0033] τ1=RC

[0034] Where:

[0035] τ1 represents a first time constant.

[0036] Preferably, the third-order exponential decay function is expressed by the following formula:

[0037]

[0038] Where:

[0039] I0 represents the depolarization current I d (t) is the quasi-steady-state current,

[0040] α1 represents the first fitting coefficient, α2 represents the second fitting coefficient, and α3 represents the third fitting coefficient.

[0041] τ1 represents the first time constant, τ2 represents the second time constant, and τ3 represents the third time constant;

[0042] The aging factor is calculated using the following formula:

[0043]

[0044] in:

[0045] Q2(τ2) is calculated as follows:

[0046]

[0047] Q3(τ3) is calculated as follows:

[0048]

[0049] A represents the aging factor.

[0050] The second invention of the present invention provides an insulation material aging assessment system based on polarization integral current and IRC, and runs the insulation material aging assessment method based on polarization integral current and IRC, including: a switch, a DC high voltage source, a protection resistor, an ammeter, a ground side resistor and a data processing module;

[0051] The switch is a single-pole double-throw switch, which is used to switch the connection between the DC high-voltage source, the grounding side resistor and the insulating material to be tested. The third end of the switch is connected to the insulating material to be tested through a conductor.

[0052] A DC high voltage source is connected in series with a protective resistor and then connected to a first end of the switch to apply a DC voltage to the insulating material;

[0053] A ground side resistor is connected to the second end of the switch and is used for depolarizing the insulating material;

[0054] The ammeter is used to collect the current flowing through the insulating material during the polarization stage and the depolarization stage;

[0055] The data processing module is used for first time constant calculation, third-order exponential decay function fitting and aging factor A evaluation.

[0056] Compared with the prior art, the beneficial effects of the present invention include at least:

[0057] The present invention obtains the equivalent resistance and equivalent capacitance of the test sample by integrating the polarization current in the polarization stage of the IRC test, and obtains an accurate first time constant. On the basis of the known first time constant, the relaxation current in the depolarization stage is fitted with a third-order exponential decay function to obtain the second and third time constants, so as to obtain a more accurate aging factor to evaluate the aging state of the insulation.

[0058] The polarization phase of the IRC measurement contains information about the bulk polarization process of the sample. The equivalent resistance of the test sample is determined by the steady-state value and voltage value of the polarization current; the equivalent capacitance of the test sample is determined by the integral value of the polarization current after removing the resistive component; the first time constant is calculated by the product of the equivalent capacitance and the equivalent resistance. When the first time constant is determined, the IRC is fitted with a three-exponential decay function, the remaining fitting parameters are determined, and the aging factor is calculated to evaluate the aging state of the test sample.

[0059] Compared with the prior art, the present invention focuses on the fact that the polarization current of the IRC test contains information that can reflect the polarization characteristics of the material, which is often ignored in previous experiments; at the same time, obtaining an accurate first time constant as a prerequisite for three-exponential fitting can reduce the error of the aging factor introduced in the fitting process and more accurately evaluate the aging state of the insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A flowchart of a method for evaluating the aging state of an insulating material based on polarization integral current and IRC according to an embodiment of the present invention;

[0061] Figure 2 A schematic diagram of a test system device provided according to an embodiment of the present invention;

[0062] Figure 3 is the polarization current test result;

[0063] Figure 4 This is the result of fitting a three-exponential decay function based on the polarization integrated current;

[0064] Figure 5 This is a comparison chart of the fitting results of the three-exponential decay function based on the traditional method;

[0065] In the picture;

[0066] 1- Switch;

[0067] 2- DC high voltage source;

[0068] 3-Protective resistor;

[0069] 4- Coaxial cable connection line;

[0070] 5- Cable;

[0071] 6- Ammeter;

[0072] 7- Ground side resistance;

[0073] 8- Conductor;

[0074] 9-semiconductive layer;

[0075] 10-Insulation layer. DETAILED DESCRIPTION

[0076] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0077] like Figure 1 As shown, embodiment 1 of the present invention provides an insulation material aging state assessment method based on polarization integral current and IRC, comprising the following steps:

[0078] Step 1: Perform IRC test on the cable to be tested, including polarization stage and depolarization stage. In the polarization stage, a DC voltage is applied to the insulation material to obtain the polarization current I p (t); In the depolarization stage, the insulating material is short-circuited to obtain the depolarization current I d (t).

[0079] In an exemplary but non-limiting embodiment, step 1 specifically includes: in the polarization stage, a DC voltage of a set magnitude is applied to the insulating material to be tested, the insulating material is polarized for a set time, and a polarization current I is collected during the polarization period. p (t); In the depolarization phase, the insulating material to be tested is short-circuited and depolarized for the same set time. During the depolarization period, the depolarization current I is collected. d (t).

[0080] In a further preferred but non-limiting embodiment, the IRC test environment is to apply a DC voltage U in a closed environment at room temperature 298K during the polarization phase. p=1kV, the voltage application time is 1800s, and the measured current is the polarization current I p (t); In the depolarization stage, the short circuit duration is 1800s, and the measured current is the depolarization current I d (t); The sampling rate of the current in the polarization and depolarization stages was set to 50 sampling points / s.

[0081] In an exemplary but non-limiting embodiment, taking an unaged cable as an example, an IRC test system such as Figure 2 As shown, when the switch 1 is placed in the DC high voltage source 2 loop, the DC high voltage source 2 provides a high voltage to the conductor of the cable 5 through the protective resistor 3 and the coaxial cable connecting line 4, and the polarization voltage is 1 kV.

[0082] It is worth noting that the magnitude of the applied voltage is related to the insulating material and its thickness. In general tests, the value is taken to make the electric field strength around 2 to 5 kV / mm.

[0083] After pressurization for 1800s, the switch 1 is switched to the ground side resistor 7 to short-circuit the cable 5, and the short-circuit duration is also 1800s. The current during pressurization and short-circuiting is collected by the ammeter 6, stored and calculated, and the polarization current I is obtained. p (t) and the depolarization current I d (t). The sampling rate is 50 sampling points / second. The test process is in an isothermal and closed environment.

[0084] It is worth noting that the non-aged cable is only an example, and those skilled in the art can implement the present invention in any insulation material status assessment activities, which all fall within the scope of the present invention.

[0085] Step 2: Use the polarization current I obtained in step 1 p (t), the equivalent resistance R and equivalent capacitance C of the insulating material to be tested are obtained by integral calculation.

[0086] In a preferred but non-limiting embodiment of the present invention, the collected polarization current I p (t) is processed, specifically, the polarization current I p (t) contains capacitive current component and resistive current component, which can be expressed as follows:

[0087] I p (t) = I C (t)+I R

[0088] Where:

[0089] I C (t) represents the capacitive current component, I R Represents the resistive current component.

[0090] Since the polarization current contains a capacitive current component I that decreases with time t C (t) and the stable resistive current component I R , so the polarization current I p (t) Quasi-steady-state current value I tending to steady state p0 As the resistive current component I R .

[0091] According to Ohm's law, the equivalent resistance R of the insulating material is calculated and expressed as follows:

[0092]

[0093] Where:

[0094] U p Indicates the DC voltage applied to the insulating material.

[0095] For example, in the non-aged cable example mentioned above, the equivalent resistance value in the test is R = 5.36 × 10 12 Ω.

[0096] Correspondingly, the polarization current I p (t) capacitive current component I C (t) is expressed as follows:

[0097] I C (t) = I p (t)-I R

[0098] Where:

[0099] I C (t) represents the polarization current I p (t) is the capacitive current component.

[0100] For capacitive current component I C (t) Take time t in [0,t p ] is expressed as follows:

[0101]

[0102] Where:

[0103] Q C It represents the polarization integrated current result. The integral of the capacitive current component over time can reflect the amount of charge accumulation.

[0104] When the applied voltage is low, the complex charge transport processes such as charge trapping and recombination are not considered. p With the capacitive current component I CThe integral of determines the equivalent capacitance as follows:

[0105]

[0106] Where:

[0107] Q(t) represents the charge accumulated by the charging current during the polarization process to form the capacitor.

[0108] For example, in the unaged cable example mentioned above, the equivalent capacitance value in the test is C = 1.23 × 10 -12 F.

[0109] Step 3: The first time constant is characterized by reflecting the body polarization state of the test sample in the test system, which is determined by the equivalent capacitance C and the equivalent resistance R obtained during the polarization process. The first time constant is calculated using the equivalent capacitance C and the equivalent resistance R obtained through the polarization process, and is expressed as follows:

[0110] τ1=RC

[0111] Where:

[0112] τ1 represents a first time constant.

[0113] For example, in the non-aged cable example mentioned above, the first time constant τ1 is calculated by the equivalent capacitance C and the equivalent resistance R, where τ1=RC=6.59s.

[0114] Step 4: Perform a third-order exponential fitting on the IRC based on the known first time constant. The third-order exponential decay function is expressed by the following formula:

[0115]

[0116] Where:

[0117] I0 represents the depolarization current I d (t) is the quasi-steady-state current,

[0118] α1 represents the first fitting coefficient, α2 represents the second fitting coefficient, and α3 represents the third fitting coefficient.

[0119] τ1 represents the first time constant, which is related to the bulk polarization of the sample, τ2 represents the second time constant, which is related to the interface polarization between the crystalline region and the amorphous region in the sample, and τ3 represents the third time constant, which is related to the polarization caused by aging in the sample.

[0120] For example, in the example of the non-aged cable mentioned above, the first time constant τ1 is 6.59s according to step 3, and the empirical ranges of the second time constant τ2 and the third time constant τ3 are set to 10-100s and 50-500s respectively. The optimal fitting parameters τ2=34.3s, τ3=146.59s, α1=6.459, α2=3.016, α3=0.79, and I0=0.049 are determined based on the goodness of fit R2 using the software's three-exponential decay model. The fitting results are shown in Figure 2. Figure 4 As shown, the depolarizing current I d (t) is basically consistent with the fitting curve, and its goodness of fit is R2=0.99724, indicating that the fitting effect is good.

[0121] Step 5: Use the IRC third-order exponential fitting result obtained in step 4 to calculate the aging factor A and evaluate the insulation aging status. The aging status of the insulation material is positively correlated with the aging factor A value.

[0122] In a preferred but non-limiting embodiment of the present invention, step 5 specifically comprises:

[0123] Q2(τ2) is calculated as follows:

[0124]

[0125] Where:

[0126] Q3(τ3) is calculated as follows:

[0127]

[0128] The aging factor is calculated using the following formula:

[0129]

[0130] Where:

[0131] A represents the calculated aging factor.

[0132] The larger the aging factor A is, the more serious the material aging state is. For example, in the non-aged cable example mentioned above, according to the fitting results in step 5, Q2(τ2)=132.1176, Q3(τ3)=217.7764 are obtained, so the aging factor A is 1.648. A is less than 1.75, indicating that the test sample is in an unaged state.

[0133] In order to compare the difference between the results of this method and the traditional fitting method, the relaxation current was fitted under the condition of limiting the time constant according to the empirical range, and the results were as follows: Figure 5 As shown, the corresponding aging factor A is calculated according to the formula in step 5. The comparison of specific fitting parameter results is shown in Table 1.

[0134] Table 1 Comparison of IRC third-order fitting results

[0135]

[0136]

[0137] Goodness of fit R of the two methods 2 All of them are greater than 0.99, and the fitting degree of the results is good. However, the existing technology will cause the calculation result of the aging factor to be too low, which will lead to a large aging factor and affect the aging assessment.

[0138] Compared with the prior art, this method integrates the polarization current of the IRC test, calculates the equivalent capacitance and equivalent resistance of the test sample to obtain the first time parameter τ1 that can accurately reflect the body polarization state. On the basis of the known first time constant, the IRC is fitted with a three-exponential decay function to determine the remaining fitting parameters. The method based on the polarization integrated current can obtain an accurate first time constant τ1, thereby obtaining an accurate three-exponential fitting result of the IRC based on the determination of the first time parameter, which helps to reflect the true aging state of the sample.

[0139] like Figure 2 As shown, Example 2 of the present invention provides an insulating material aging assessment system based on polarization integral current and IRC, which runs the insulating material aging assessment method based on polarization integral current and IRC described in Example 1, including: a switch 1, a DC high voltage source 2, a protective resistor 3, an ammeter 6, a ground side resistor 7 and a data processing module.

[0140] The object to be tested is the aging state of the insulation material of the cable 5 , including: a coaxial cable connecting line 4 , a conductor 8 , a semiconductive layer 9 and an insulating layer 10 .

[0141] The switch 1 is a single-pole double-throw switch, which is used to switch the connection between the DC high-voltage source 2, the grounding side resistor 7 and the insulating material to be tested. The third end of the switch 1 is connected to the insulating material to be tested via a conductor.

[0142] A DC high voltage source 2 is connected in series with a protective resistor 3 and then connected to a first end of a switch 1 to apply a DC voltage to the insulating material;

[0143] The grounding side resistor 7 is connected to the second end of the switch 2 and is used for depolarizing the insulating material;

[0144] The ammeter 6 is used to collect the current flowing through the insulating material during the polarization stage and the depolarization stage.

[0145] The data processing module is used for calculating the first time constant, fitting the third-order exponential decay function, and evaluating the aging factor A.

[0146] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating insulation material aging based on polarization integral current and IRC, characterized in that: The method comprises: The polarization current is measured under the application of DC voltage, and the equivalent resistance and equivalent capacitance of the test sample are obtained by integrating the polarization current, including: p (t) is decomposed into a constant resistive current component I R and the capacitive current component I that varies with time t C (t), using the capacitive current component I C (t) The integration result is used to calculate the equivalent capacitance C of the insulating material, using the resistive current component I R The equivalent resistance R is calculated to obtain the first time constant reflecting the polarization state of the test sample. After short circuit, the isothermal relaxation current of the test sample is measured. When the first time constant is known, the isothermal relaxation current is fitted with a third-order exponential decay function. The aging factor A is calculated based on the fitting results. The aging state of the insulating material is positively correlated with the aging factor A value.

2. The insulating material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: In a closed environment at room temperature 298K, a DC voltage U is applied during the polarization stage. p =1kV, voltage application time is 1800s, polarization current I is measured p (t); In the depolarization stage, the short circuit duration is 1800s, and the depolarization current I is measured. d (t).

3. The insulating material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: The current sampling rate during the polarization and depolarization phases was set to 50 samples / s.

4. The insulating material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: With polarization current I p (t) The quasi-steady-state current value tending to steady state represents the resistive current component I R .

5. The insulating material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: The equivalent resistance R of the insulating material is expressed as follows: Where: U p It represents the DC voltage applied to the insulating material; I p0 Represents the polarization current I p (t) Quasi-steady-state current value tending to steady state.

6. The insulation material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: Using the capacitive current component I C (t) The calculation of the equivalent capacitance C of the insulating material by integration results includes the following steps: Polarization current I p (t) capacitive current component I C (t) is expressed as follows: I C (t)=I p (t)-I R Where: I C (t) represents the polarization current I p (t) capacitive current component; For capacitive current component I C (t) Take time t in [0,t p ] is expressed as follows: Where: Q C Represents the polarization integrated current result; By applying voltage U p With the capacitive current component I C The integral of (t) is used to calculate the equivalent capacitance, which is expressed as follows: Where: C represents the equivalent capacitance of the insulating material.

7. The insulation material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: The first time constant is calculated using the equivalent capacitance C and equivalent resistance R obtained through the polarization process, expressed as follows: τ1=RC Where: τ1 represents a first time constant.

8. The insulation material aging assessment method based on polarization integral current and IRC according to claim 1, characterized in that: The third-order exponential decay function is expressed as follows: Where: I0 represents the depolarization current I d (t) is the quasi-steady-state current, α1 represents the first fitting coefficient, α2 represents the second fitting coefficient, and α3 represents the third fitting coefficient. τ1 represents the first time constant, τ2 represents the second time constant, and τ3 represents the third time constant; The aging factor is calculated using the following formula: in: Q2(τ2) is calculated as follows: Q3(τ3) is calculated as follows: A represents the aging factor.

9. An insulation material aging assessment system based on polarization integral current and IRC, running the insulation material aging assessment method based on polarization integral current and IRC as described in any one of claims 1 to 8, comprising: A switch (1), a DC high voltage source (2), a protective resistor (3), an ammeter (6), a grounding resistor (7) and a data processing module; characterized in that: The switch (1) is a single-pole double-throw switch, used for switching the connection between the DC high-voltage source (2), the grounding side resistor (7) and the insulating material to be tested. The third end of the switch (1) is connected to the insulating material to be tested via a conductor. A DC high voltage source (2) is connected in series with a protective resistor (3) and then connected to a first end of a switch (1) for applying a DC voltage to an insulating material; A grounding side resistor (7) is connected to the second end of the switch (1) and is used for depolarizing the insulating material; The ammeter (6) is used to collect the current flowing through the insulating material during the polarization stage and the depolarization stage; The data processing module is used for first time constant calculation, third-order exponential decay function fitting and aging factor A evaluation.

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