Method for evaluating aging degree of high-voltage oil-immersed capacitor

Abstract

The invention provides an aging degree evaluation method for a high-voltage oil-immersed capacitor, and relates to the technical field of capacitor detection, and the method comprises the steps: carrying out the capacitor loss measurement of each new high-voltage oil-immersed capacitor when the capacitor enters a factory, and obtaining a first loss voltage curve corresponding to each new high-voltage oil-immersed capacitor; performing capacitor loss measurement on the to-be-measured high-voltage oil-immersed capacitor to obtain a second loss voltage curve; according to the second loss voltage curve and the first loss voltage curve when the high-voltage oil-immersed capacitor to be measured enters the factory, determining the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be measured or the decrease degree of the packaging pressure of the capacitor core; and evaluating the aging degree of the high-voltage oil-immersed capacitor to be tested according to the increase rate of the carrier concentration or the decrease degree of the packaging pressure of the capacitor core. According to the scheme, the accuracy of capacitor aging degree detection and evaluation can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitor detection, and in particular to an aging degree assessment method for a high-voltage oil-immersed capacitor. Background Art

[0002] High-voltage direct current transmission has occupied an important position in the transmission network due to its advantages such as large capacity, low loss and long-distance power transmission. As a key equipment in high-voltage direct current transmission projects, high-voltage oil-immersed capacitors play the role of absorbing neutral bus current or other grounding current, and are widely used in the field of reactive power compensation and harmonic control in power systems. However, long-term operation under the action of heat and electricity can easily lead to aging of high-voltage capacitors, thereby affecting their actual role in engineering operation and threatening the stability of the power system. Therefore, it is of great significance to evaluate the aging degree of high-voltage capacitors.

[0003] At present, when evaluating the aging degree of capacitors in the industry, the state of the capacitor is usually judged by the change of capacitance. However, this method can only reflect the failure of the capacitor when the internal components of the capacitor fail, and cannot judge the aging degree of the capacitor. For example, as the capacitor runs, the packing pressure of the capacitor core will gradually release, the distance between the plates will increase, the impurity particles in the impregnant will gradually increase, and the loss will increase. However, these changes in capacitance in the early stage are very small, and it is difficult to accurately reflect the aging degree of the capacitor. Summary of the invention

[0004] In view of this, in order to address the above shortcomings, it is necessary to propose an aging degree assessment method for high-voltage oil-immersed capacitors to improve the accuracy of capacitor aging degree detection and assessment.

[0005] In a first aspect, the present invention provides a method for evaluating the aging degree of a high-voltage oil-immersed capacitor, comprising:

[0006] When the capacitors enter the factory, the capacitor loss is measured for each new high-voltage oil-immersed capacitor to obtain the first loss voltage curve corresponding to each new high-voltage oil-immersed capacitor;

[0007] Conduct capacitor loss measurement on the high-voltage oil-immersed capacitor to be tested to obtain a second loss voltage curve;

[0008] Determine the rate of increase of carrier concentration of the high-voltage oil-immersed capacitor to be tested or the degree of reduction of packaging pressure of the capacitor core according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory;

[0009] The aging degree of the high-voltage oil-immersed capacitor to be tested is evaluated according to the increase rate of the carrier concentration or the reduction degree of the packaging pressure of the capacitor core.

[0010] Preferably, the determining the rate of increase of the carrier concentration of the high-voltage oil-immersed capacitor to be tested according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory comprises:

[0011] Calculating the height difference between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the height of the loss platform is used to characterize the capacitor loss value before the capacitor loss decreases significantly with the voltage change;

[0012] The ratio of the height difference to the height of the loss platform in the first loss voltage curve is calculated to obtain the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be tested.

[0013] Preferably, in the evaluation of the aging degree of the high-voltage oil-immersed capacitor to be tested according to the increase rate of the carrier concentration, the larger the value of the increase rate of the carrier concentration, the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested.

[0014] Preferably, the step of determining the reduction degree of the capacitor core packing pressure of the high-voltage oil-immersed capacitor to be tested according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory comprises:

[0015] Calculating the difference in width between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the width of the loss platform is used to characterize the voltage interval before the capacitor loss significantly decreases with voltage change;

[0016] The ratio of the width difference to the width of the loss platform in the first loss voltage curve is calculated to obtain the degree of reduction of the core packing pressure of the high-voltage oil-immersed capacitor to be tested.

[0017] Preferably, in evaluating the aging degree of the high-voltage oil-immersed capacitor to be tested according to the degree of reduction of the packing pressure of the capacitor core, the more serious the reduction of the packing pressure of the capacitor core, the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested.

[0018] Preferably, the first loss voltage curve and the second loss voltage curve are both average values ​​of several capacitor loss measurement results.

[0019] Preferably, a high voltage bridge tester is used to measure the loss of the high voltage oil-immersed capacitor.

[0020] Preferably, the test frequency for capacitor loss measurement is any value between 500 Hz and 1500 Hz.

[0021] In a second aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to execute the data calculation and processing process as in the first aspect.

[0022] In a third aspect, the present invention provides a computing device including a memory and a processor, wherein the memory stores executable code, and when the processor executes the executable code, the data calculation and processing process in the first aspect is implemented.

[0023] It can be seen from the above technical solution that when evaluating the aging degree of high-voltage oil-immersed capacitors, first, when the capacitors enter the factory, the loss of each capacitor is measured to obtain the first loss voltage curve of each capacitor. Then, when it is necessary to evaluate the aging degree of a certain capacitor, the loss of the high-voltage oil-immersed capacitor to be tested is first measured to obtain the second loss voltage curve; further, according to the first loss voltage curve and the second loss voltage curve of the high-voltage oil-immersed capacitor to be tested, the increase in the carrier concentration of the high-voltage oil-immersed capacitor to be tested or the decrease in the packaging pressure of the capacitor core can be determined, and then according to the increase in the carrier concentration or the decrease in the packaging pressure of the capacitor core, the aging degree of the high-voltage oil-immersed capacitor to be tested can be determined. As the capacitor operates, the carriers in the capacitor impregnant will gradually increase under the action of thermoelectric combined aging; and as the capacitor operates, the capacitor core packing pressure will gradually decrease under the action of vibration and thermal stress. Therefore, this embodiment considers evaluating the aging degree of the capacitor by using the increase in carrier concentration or the decrease in core packing pressure as indicators, so that the aging degree of the capacitor can be more accurately evaluated in advance before the capacitor element fails and the capacitor fault is exposed, so that the impact of capacitor aging on the power system can be greatly reduced by taking corresponding measures in time. Moreover, compared with the traditional method of directly judging by the change in capacitance, this scheme has higher evaluation accuracy by using carrier concentration and core packing pressure as judgment indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a method for evaluating the aging degree of a high-voltage oil-immersed capacitor provided in an embodiment of the present invention.

[0025] Figure 2 It is a curve showing the change of capacitor loss with voltage under low voltage.

[0026] Figure 3 The loss voltage curve before and after the carrier concentration in an impregnant is increased.

[0027] Figure 4 It is a loss voltage curve before and after the packaging pressure is released. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] High-voltage oil-immersed capacitors are widely used in the field of reactive power compensation and harmonic control in power systems. Currently, the state of capacitors can only be judged by the change in capacitance. This method can only reflect capacitor failure when components fail inside the capacitor, but cannot accurately assess the aging of the capacitor. In order to measure the aging of the capacitor, it is often necessary to measure partial discharge or use a high-voltage bridge to measure the loss of the capacitor, so as to assess the aging of the capacitor to a certain extent.

[0030] However, partial discharge can reflect defects inside the capacitor. Although there is a certain probability that defects such as bubbles and solid impurities will occur when the capacitor ages more seriously, the aging of the capacitor can be reflected by changes in partial discharge. However, since defects are not an inevitable phenomenon of capacitor aging, it is not generally accepted to use partial discharge to characterize the degree of capacitor aging. In the method of measuring the change in capacitance to evaluate the degree of capacitor aging, as the capacitor runs, the packing pressure of the capacitor core is gradually released, the distance between the plates increases, the capacitance value decreases, the impurity particles in the impregnant gradually increase, and the loss increases. However, the changes reflected in the capacitance in the early stage are very small, and it is difficult to directly use the capacitance of the capacitor to reflect the degree of capacitor aging. In most cases, it is impossible to obtain a more accurate evaluation result. Based on this, if Figure 1 As shown, the present invention provides a method for evaluating the aging degree of a high-voltage oil-immersed capacitor, which may include the following steps:

[0031] Step 101: When the capacitors enter the factory, capacitor loss is measured for each new high-voltage oil-immersed capacitor to obtain a first loss voltage curve corresponding to each new high-voltage oil-immersed capacitor;

[0032] Step 102: measuring capacitor loss on the high-voltage oil-immersed capacitor to be tested, and obtaining a second loss voltage curve;

[0033] Step 103: determining the rate of increase of carrier concentration of the high-voltage oil-immersed capacitor to be tested or the degree of reduction of packaging pressure of the capacitor core according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory;

[0034] Step 104: Evaluate the aging degree of the high-voltage oil-immersed capacitor to be tested according to the increase rate of the carrier concentration or the reduction degree of the packaging pressure of the capacitor core.

[0035] In this embodiment, considering that as the capacitor operates, the carriers in the capacitor impregnant will gradually increase under the action of thermoelectric combined aging; and as the capacitor operates, the capacitor core packing pressure will gradually decrease under the action of vibration and thermal stress, so this embodiment evaluates the aging degree of the capacitor by using the increase in carrier concentration or the decrease in core packing pressure as indicators, and can make a relatively accurate assessment of the aging degree of the capacitor in advance before the capacitor element fails and the capacitor fault is exposed, so that the impact of capacitor aging on the power system can be greatly reduced by taking corresponding measures in time. Moreover, compared with the traditional method of directly judging by the change in capacitance, this scheme has higher evaluation accuracy by using carrier concentration and core packing pressure as judgment indicators.

[0036] Moreover, compared with the method of training an evaluation model based on partial discharge data and then using the trained evaluation model to evaluate the degree of capacitor aging, the evaluation method of this solution is simpler and does not require a large amount of equipment resources.

[0037] For step 101, when the capacitors enter the factory, capacitor loss is measured for each new high-voltage oil-immersed capacitor to obtain a first loss voltage curve corresponding to each new high-voltage oil-immersed capacitor;

[0038] In this step, when the capacitors enter the factory, the loss of each capacitor is measured first, and the first loss voltage curve of each new high-voltage oil-immersed capacitor is obtained and stored. Of course, it should be pointed out that when storing the first loss voltage curve, each first loss voltage curve and the corresponding high-voltage oil-immersed capacitor number should be bound and stored to ensure the consistency of the data correspondence during subsequent use.

[0039] In order to further improve the accuracy of capacitor loss measurement, several loss measurements can be performed on each new high-voltage oil-immersed capacitor, and then the measured data are averaged to obtain a first loss voltage curve with the horizontal axis being voltage and the vertical axis being the loss tangent value.

[0040] In step 102, capacitor loss is measured on the high-voltage oil-immersed capacitor to be tested to obtain a second loss voltage curve;

[0041] In this step, when a high-voltage oil-immersed capacitor needs to be evaluated for aging, its loss can be measured to obtain a second loss voltage curve. As the capacitor runs, the stability of the capacitor loss during measurement will decrease. In order to further improve the accuracy of capacitor loss measurement, several loss measurements can be performed on the high-voltage oil-immersed capacitor to be tested, and then the measured data can be averaged to obtain a second loss voltage curve with the horizontal axis being voltage and the vertical axis being the loss tangent value.

[0042] For step 103, the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be tested or the degree of reduction in the packaging pressure of the capacitor core is determined based on the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory; and, in step 104, the aging degree of the high-voltage oil-immersed capacitor to be tested is evaluated based on the increase rate of the carrier concentration or the degree of reduction in the packaging pressure of the capacitor core.

[0043] When evaluating the aging degree of the capacitor, step 103 and step 104 can be implemented in two ways.

[0044] Method 1: Aging evaluation based on carrier concentration

[0045] As the capacitor operates, the carriers in the capacitor impregnant will gradually increase under the effect of thermal and electrical aging. Therefore, in this method, the aging degree of the capacitor can be evaluated by the carrier concentration. Specifically, step 103 can determine the increase rate of the carrier concentration by the following method:

[0046] Calculating the height difference between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the height of the loss platform is used to characterize the capacitor loss value before the capacitor loss decreases significantly with the voltage change;

[0047] The ratio of the height difference to the height of the loss platform in the first loss voltage curve is calculated to obtain the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be tested.

[0048] like Figure 2 The measurement results show that as the voltage increases, there is a platform area in the loss curve. After passing the platform area, the loss will drop rapidly and then tend to a stable value. Therefore, the height of the platform area is defined as the height difference between the loss value of the platform area and the stable value, which is tanδ G0 The width of the platform is defined as the voltage value when the loss starts to decrease, recorded as V G So, if Figure 3 As shown, the loss platform height of the new capacitor and the loss platform height of the old capacitor are Δtanδ, and its ratio to the platform height of the new capacitor is k is the increase multiple of the carrier concentration in the liquid medium after the capacitor is operated.

[0049] It is easy to understand that in evaluating the aging degree of the high-voltage oil-immersed capacitor to be tested based on the increase rate of carrier concentration, the larger the value of the increase rate of carrier concentration, that is, the larger the increase multiple k of carrier concentration, the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested.

[0050] It should be pointed out that the new capacitor curve in the figure is the first loss voltage curve measured when entering the factory, and the aged capacitor curve is the second loss voltage curve of the high-voltage oil-immersed capacitor to be tested after the capacitor has been running for a period of time.

[0051] Method 2: Evaluate the aging degree of capacitors based on the packing pressure of capacitor cores

[0052] As the capacitor operates, the core packing pressure used to press and fix the stacked components in the core will gradually decrease under the action of vibration and thermal stress. For example, as the capacitor ages, the elasticity of the packing tape in the capacitor will decrease, thereby reducing the packing pressure. Therefore, in this method, the core packing pressure is considered as an indicator for evaluating the degree of capacitor aging, and the degree of capacitor aging is evaluated. Specifically, step 103 can determine the degree of reduction of the core packing pressure of the high-voltage oil-immersed capacitor to be tested in the following manner:

[0053] Calculating the difference in width between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the width of the loss platform is used to characterize the voltage interval before the capacitor loss significantly decreases with voltage change;

[0054] The ratio of the width difference to the width of the loss platform in the first loss voltage curve is calculated to obtain the degree of reduction of the core packing pressure of the high-voltage oil-immersed capacitor to be tested.

[0055] like Figure 4 As shown, the difference between the loss platform width of the new capacitor and the loss platform width of the old capacitor is ΔV, and its ratio to the platform width of the new capacitor is p represents the rate of change of the thickness of the oil gap in the capacitor. The larger the p value is, the more serious the reduction in the packing pressure of the capacitor core is, and the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested is.

[0056] In addition, it should be pointed out that when measuring capacitor loss, a high-voltage bridge tester can be used to measure the loss of high-voltage oil-immersed capacitors. The voltage for capacitor loss measurement can be 0.1V-20V, and the test frequency can be any value from 500Hz-1500Hz. If the frequency is too low, the width of the loss platform may be too small, and if the frequency is too high, the platform height may be too small. Using any value from 500Hz-1500Hz can meet the needs of most capacitors. Of course, in the actual measurement process, the measurement frequency can be appropriately adjusted according to the width and height of the loss platform.

[0057] Of course, in some embodiments, the aging degree of the capacitor can be evaluated by using both the rate of increase of the carrier concentration and the degree of reduction of the packaging pressure of the capacitor core.

[0058] In one embodiment, the present invention also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed in a computer, the computer is caused to perform data calculation and processing processes as in the first aspect, such as processing the first loss voltage curve and the second loss voltage curve, calculating the increase multiple of the carrier concentration and the rate of change of the oil gap thickness, etc.

[0059] In one embodiment, the present invention also provides a computing device, including a memory and a processor, wherein executable code is stored in the memory. When the processor executes the executable code, the data calculation and processing process in the first aspect is implemented, such as processing the first loss voltage curve and the second loss voltage curve, calculating the increase multiple of the carrier concentration and the rate of change of the oil gap thickness, etc.

[0060] The modules or units in the device of the embodiment of the present invention can be combined, divided and deleted according to actual needs. The above disclosure is only the preferred embodiment of the present invention, and of course it cannot be used to limit the scope of the rights of the present invention. Those skilled in the art can understand that all or part of the processes of the above embodiment are implemented, and the equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for evaluating the aging degree of a high-voltage oil-immersed capacitor, characterized in that: include: When the capacitors enter the factory, the capacitor loss is measured for each new high-voltage oil-immersed capacitor to obtain the first loss voltage curve corresponding to each new high-voltage oil-immersed capacitor; Conduct capacitor loss measurement on the high-voltage oil-immersed capacitor to be tested to obtain a second loss voltage curve; Determine the rate of increase of carrier concentration of the high-voltage oil-immersed capacitor to be tested or the degree of reduction of packaging pressure of the capacitor core according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory; The aging degree of the high-voltage oil-immersed capacitor to be tested is evaluated according to the increase rate of the carrier concentration or the reduction degree of the packaging pressure of the capacitor core.

2. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 1 is characterized in that: The method of determining the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be tested according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory comprises: Calculating the height difference between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the height of the loss platform is used to characterize the capacitor loss value before the capacitor loss decreases significantly with the voltage change; The ratio of the height difference to the height of the loss platform in the first loss voltage curve is calculated to obtain the increase rate of the carrier concentration of the high-voltage oil-immersed capacitor to be tested.

3. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 2 is characterized in that: In the evaluation of the aging degree of the high-voltage oil-immersed capacitor to be tested according to the increase rate of the carrier concentration, the larger the value of the increase rate of the carrier concentration is, the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested is.

4. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 1, characterized in that: Determining the reduction degree of the capacitor core packaging pressure of the high-voltage oil-immersed capacitor to be tested according to the second loss voltage curve and the first loss voltage curve of the high-voltage oil-immersed capacitor to be tested when it enters the factory includes: Calculating the difference in width between the loss platform in the second loss voltage curve and the first loss voltage curve; wherein the width of the loss platform is used to characterize the voltage interval before the capacitor loss significantly decreases with voltage change; The ratio of the width difference to the width of the loss platform in the first loss voltage curve is calculated to obtain the degree of reduction of the core packing pressure of the high-voltage oil-immersed capacitor to be tested.

5. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 4, characterized in that: In evaluating the aging degree of the high-voltage oil-immersed capacitor to be tested according to the reduction degree of the packing pressure of the capacitor core, the more serious the reduction of the packing pressure of the capacitor core, the more serious the aging degree of the high-voltage oil-immersed capacitor to be tested.

6. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 1, characterized in that: The first loss voltage curve and the second loss voltage curve are both average values ​​of several capacitor loss measurement results.

7. The aging degree assessment method of a high-voltage oil-immersed capacitor according to claim 1, characterized in that: The loss of high voltage oil-immersed capacitors is measured using a high voltage bridge tester.

8. The aging degree assessment method of high-voltage oil-immersed capacitor according to claim 7, characterized in that: The test frequency for capacitor loss measurement is any value between 500Hz-1500Hz.

9. A computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to execute the data calculation and processing process as claimed in claims 1 to 8.

10. A computing device comprising a memory and a processor, wherein the memory stores executable codes, and when the processor executes the executable codes, the data computing and processing processes in claims 1-8 are implemented.

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