Metallized film capacitor service life prediction system and method

Abstract

The invention discloses a metallized film capacitor service life prediction system and method. The system comprises a model building module which is used for building a life prediction model according to the relation between the temperature rise of a capacitor shell and capacitance data; and the prediction output module is used for predicting the end-of-life state of the capacitor to be detected based on the life prediction model. When the system predicts the end-of-life time of the capacitor to be detected, the capacity attenuation condition of the capacitor can be quickly identified and analyzed based on the life prediction model by monitoring the temperature of the capacitor in real time, the detection efficiency is improved, and the detection period is shortened; and guarantees are provided for finding operation faults of the capacitor in real time and ensuring safe and reliable operation of the capacitor.

Description

Technical Field

[0001] The invention belongs to the field of power capacitors and relates to a life prediction system and method for metallized film capacitors. Background Art

[0002] With the development of flexible DC transmission systems, metallized film capacitors are widely used as DC support capacitors in converter valves due to their high reliability, high power density and good self-healing properties. They play the role of voltage support, harmonic suppression and reactive power compensation. However, in actual operating conditions, metallized film capacitors are subjected to complex conditions of DC voltage superimposed on AC harmonics for a long time. Their failure rate is much higher than that of traditional capacitors, and their service life is only 1 / 3 of that of traditional capacitors. Usually, the failure sign of a capacitor is when the capacity loss reaches 5% of the initial capacity.

[0003] The capacity of metallized film capacitors is mainly affected by dielectric constant, plate area and plate spacing, but these three are difficult to monitor during operation. Nowadays, the monitoring of capacity attenuation mainly focuses on the measurement of electrical parameters, including monitoring current signals, voltage signals, etc., and lacks the measurement of other parameters to ensure the accuracy of the measurement.

[0004] Therefore, there is an urgent need to study a metallized film capacitor life prediction system and method to monitor capacitor operation failures in real time and provide protection for the safe and reliable operation of the capacitor. Summary of the invention

[0005] In order to overcome the above problems, the present invention proposes a life prediction system and method for metallized film capacitors. The system includes: a model building module, which is used to build a life prediction model based on the relationship between the temperature rise of the capacitor shell and the capacitance data; a prediction output module, which is used to predict the end-of-life state of the capacitor to be detected based on the life prediction model. When predicting the end-of-life state of the capacitor to be detected, the system only monitors the temperature of the capacitor in real time, improves the detection efficiency based on the life prediction model, shortens the detection cycle, and reduces the detection cost, thereby providing a guarantee for real-time discovery of capacitor operation failures and ensuring the safe and reliable operation of the capacitor, thereby completing the present invention.

[0006] Specifically, the purpose of the present invention is to provide the following aspects:

[0007] In one aspect, a metallized film capacitor life prediction system is provided, the system comprising:

[0008] A model building module, which is used to build a life prediction model based on the relationship between the capacitor housing temperature rise and the capacitance data;

[0009] The prediction output module is used to predict the end-of-life state of the capacitor to be detected based on the life prediction model.

[0010] Wherein, the model building module includes:

[0011] The power-on aging unit is used to perform a power-on aging test on the pre-treated capacitor.

[0012] Wherein, the model building module also includes:

[0013] A data acquisition unit, which is used to obtain the shell temperature rise and capacitance data of the capacitor during the power-on aging test of the capacitor;

[0014] The data processing unit is used to construct a life prediction model according to the relationship between the acquired shell temperature rise and capacitance data.

[0015] The pretreatment includes: subjecting the capacitor to a preset field strength at 10-30°C, and then leaving it in a power-off environment for 12-48 hours.

[0016] Wherein, the data acquisition unit includes a shell temperature data acquisition component.

[0017] Wherein, the shell temperature data acquisition component includes a thermocouple, and the thermocouple is used to monitor the capacitor shell temperature in real time.

[0018] In a second aspect, a method for predicting the life of a metallized film capacitor is provided, the method comprising:

[0019] Constructing a life prediction model based on the relationship between the capacitor shell temperature rise and the capacitance data;

[0020] The end-of-life state of the capacitor to be inspected is predicted based on the life prediction model.

[0021] Among them, building a life prediction model based on the relationship between capacitor shell temperature rise and capacitance attenuation includes the following steps:

[0022] Conducting power-on aging test on the pre-treated capacitors;

[0023] During the capacitor power-on aging test, the capacitor case temperature rise and capacitance data are obtained;

[0024] Based on the relationship between the shell temperature rise and the capacitance data obtained, a life prediction model is constructed.

[0025] The pretreatment includes: subjecting the capacitor to a preset field strength at 10-30° C., and then leaving it in a power-off environment for 12-48 hours.

[0026] The shell temperature is obtained through a thermocouple.

[0027] The beneficial effects of the present invention include:

[0028] (1) The metallized film capacitor life prediction system provided by the present invention can quickly identify and analyze the capacity attenuation of the capacitor based on the life prediction model by only monitoring the temperature of the capacitor in real time, thereby improving the detection efficiency and shortening the detection cycle, thereby providing a guarantee for real-time detection of capacitor operation faults and ensuring the safe and reliable operation of the capacitor.

[0029] (2) The metallized film capacitor life prediction system provided by the present invention monitors the temperature of the capacitor in real time through a thermocouple. The temperature rise measurement method is simple, the detection efficiency is high, and the detection cycle is short.

[0030] (3) The life prediction method of the metallized film capacitor provided by the present invention constructs a life prediction model through the relationship between the temperature rise of the capacitor shell and the capacitance data, so as to more accurately predict the end-of-life state of the capacitor, thereby shortening the aging test cost and providing a reliable basis for the maintenance and replacement of the capacitor.

[0031] (4) The life prediction method of the metallized film capacitor provided by the present invention is used to evaluate the performance and reliability of the capacitor under different working conditions, which helps to screen out potential faulty capacitors and improve the reliability of the entire capacitor batch; and through accurate life prediction and timely maintenance and replacement, the service life of the capacitor is extended, and the power outage accidents and maintenance costs caused by capacitor failure are reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only used for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0033] In the attached picture:

[0034] Figure 1 A graph showing the relationship between the temperature rise of the capacitor housing and the aging time in Example 1 is shown;

[0035] Figure 2 A graph showing the relationship between capacitor capacitance decay and aging time in Example 1;

[0036] Figure 3 The shell temperature and capacitance attenuation fitting diagram in Example 1 is shown;

[0037] Figure 4 The graph showing the relationship between the capacitance attenuation rate, the measured value of the shell temperature rise and the aging time during power-on aging of the capacitors of the 250Hz group in Example 1 is shown. DETAILED DESCRIPTION

[0038] The following will refer to the attached Figures 1 to 4 Specific embodiments of the present invention are described in more detail. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0039] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0040] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", etc. indicate positions or positional relationships based on the working state of the present invention, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0041] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0042] On the one hand, according to a method for predicting the life of a metallized film capacitor provided by the present invention, the method comprises:

[0043] Step 1, constructing a life prediction model according to the relationship between the temperature rise of the capacitor shell and the capacitance data;

[0044] Step 2: predicting the end-of-life state of the capacitor to be detected based on the life prediction model.

[0045] The above capacitor life prediction method is described in detail below.

[0046] Step 1: construct a life prediction model based on the relationship between the capacitor shell temperature rise and the capacitance data.

[0047] In step 1, the constructed prediction model has the following representation:

[0048]

[0049] Where y represents the capacitance loss rate, in %, and represents the ratio of the capacitance value at this moment to the initial capacitance value; k1 and k2 are both fitting parameters; E represents the electric field strength; E N is the rated electric field strength, E and E N The unit is kV / mm; f is the frequency of the AC voltage component, in Hz; f0 represents the power frequency of 50Hz; T represents the actual shell temperature at this moment, T0 represents the shell temperature value measured in the first 24-hour period, T N Indicates the ambient temperature. The unit of temperature is ℃.

[0050] According to a preferred embodiment, constructing a life prediction model based on the relationship between capacitor housing temperature rise and capacitance attenuation includes the following steps:

[0051] Step 1-1, performing a power-on aging test on the pretreated capacitor;

[0052] Step 1-2, during the power-on aging test of the capacitor, obtaining the shell temperature rise and capacitance data of the capacitor;

[0053] Step 1-3, constructing a life prediction model based on the relationship between the shell temperature rise and the capacitance data obtained.

[0054] In step 1-1, the pretreatment is beneficial to making the aging capacity decay more stable.

[0055] Furthermore, the pretreatment includes: subjecting the capacitor to a preset field strength at 10-30°C, and then leaving it in a power-off environment for 12-48 hours. If there are multiple capacitors, they must be from the same batch.

[0056] In step 1-1, the electric field when tolerating the preset field strength is (1.1~1.2)E N , E N is the rated electric field strength, the E N The range is usually 200~250 kV / mm; for example, the electric field at the preset field strength is 1.1E N , E N It is 235kV / mm.

[0057] Among them, through (1.1~1.2)E NSlightly higher than the rated electric field strength of the capacitor, it is the maximum electric field stress that the capacitor may encounter in actual work. Under this condition, tolerating the preset field strength makes the shell temperature and capacitance data collected subsequently more truly reflect the performance degradation of the capacitor in actual use.

[0058] In step 1-1, the time for tolerating the preset field strength is 18 to 36 hours, preferably 24 to 28 hours, for example 24 hours.

[0059] Among them, in actual applications, capacitors may need to work continuously for several hours or even days. The 18-36h preset field strength tolerance time is closer to the working cycle of the capacitor under actual working conditions, so its performance in actual use can be more accurately predicted.

[0060] In step 1-1, when the power is turned off, the capacitor is left to stand for a certain period of time to ensure that the capacitor reaches thermal equilibrium and stable performance in the simulated actual use environment. The standing time is preferably 12 to 24 hours, for example 12 hours.

[0061] Furthermore, in order to keep the pretreatment conditions simple and mild, the standing temperature is 26-35°C, preferably 28-32°C, for example 30°C.

[0062] In step 1-1, the pre-processing is completed, and the capacitance of the capacitor is measured as the aging initial capacitance value.

[0063] In step 1-1, after pretreatment, a thermocouple is installed in the middle of the capacitor housing, and the thermocouple is used to monitor the housing temperature in real time.

[0064] Among them, a thermocouple is installed in the middle of the capacitor casing to avoid the influence of local hot spots on temperature measurement, so as to improve the reliability and practicality of the test results.

[0065] In step 1-1, an insulating tape with good heat dissipation is used at the fixed connection between the thermocouple and the capacitor housing to ensure that the capacitor housing has good heat dissipation. The insulating tape is preferably a polyimide insulating tape.

[0066] In step 1-1, the power-on aging test is performed at 50-70° C., such as 60° C., to better evaluate the reliability and life of the capacitor in an actual use environment.

[0067] In step 1-1, the voltage applied in the power-on aging test is a combined voltage stress, that is, it contains a DC component and an AC component. The DC component is used to accelerate the aging of the dielectric inside the capacitor, and the AC component is used to simulate the influence of the AC voltage in actual use. The voltage applied in the power-on aging test is usually (1.2~1.3)E N_DC + (0.1~0.2) E N_AC , EN_DC is the rated DC voltage, E N_AC Rated AC voltage; for example, the voltage applied in the power-on aging test is 1.25E N_DC +0.15E N_AC .

[0068] In step 1-1, the frequency applied in the power-on aging test is 50-250 Hz. The higher the applied frequency, the more obvious the temperature rise of the capacitor and the faster the capacitance decays.

[0069] In step 1-1, the power-on aging test lasts for 20 to 30 days, for example, 22 days.

[0070] In step 1-2, the capacitance change and the corresponding shell temperature are observed every 24 hours. The shell temperature is obtained by thermocouple, and the capacitance is obtained by LCR tester. The capacitance at this time is compared with the initial capacitance value to obtain the current capacitance loss rate.

[0071] In step 1-2, the capacitor case temperature can also be monitored in real time, which is conducive to obtaining complete case temperature evolution data.

[0072] In step 1-3, as the power-on aging test proceeds, the capacitance gradually decays, and a life prediction model is established by fitting the shell temperature and capacitance data; or it can be understood that a life prediction model is established by fitting the shell temperature and capacitance decay, and the life prediction model has the following expression:

[0073] .

[0074] According to the current shell temperature T and the capacitance loss rate y, the fitting parameters k1 and k2 are obtained.

[0075] Furthermore, to obtain the fitting parameters k1 and k2, data analysis software such as Origin can be used to directly solve them; or the terms in the above equation can be shifted, combined, and logarithmic, and k1 and k2 can be directly solved according to the slope and intercept of the linear equation. The above equation can be shifted, combined, and logarithmic, and the following expression can be obtained:

[0076]

[0077] The intercept and slope in the above formula can be used to obtain the values ​​of the fitting parameters k1 and k2.

[0078] Step 2: predicting the end of life of the capacitor to be tested based on the life prediction model.

[0079] In step 2, based on the life prediction model, the capacitor case temperature T is obtained when the capacity decays to 95% of the initial value (y=0.95), and this temperature is used as the end-of-life state of the capacitor to be detected.

[0080] On the other hand, according to a metallized film capacitor life prediction system provided by the present invention, the system comprises:

[0081] A model building module, which is used to build a life prediction model based on the relationship between the capacitor housing temperature rise and the capacitance data;

[0082] A prediction output module is used to predict the end-of-life state of the capacitor to be detected based on the life prediction model. According to a preferred embodiment, the model building module includes:

[0083] A powered aging unit, which is used to perform a powered aging test on the pre-treated capacitor;

[0084] A data acquisition unit, which is used to obtain the shell temperature rise and capacitance data of the capacitor during the power-on aging test of the capacitor;

[0085] The data processing unit is used to construct a life prediction model according to the relationship between the acquired shell temperature rise and capacitance data.

[0086] The data acquisition unit includes a shell temperature data acquisition component and a capacitance data acquisition component. The shell temperature data acquisition component includes a thermocouple and an insulating tape. The thermocouple is arranged in the middle of the capacitor shell and is used to monitor the shell temperature in real time. The insulating tape is used to fix the thermocouple and the capacitor.

[0087] The present invention is further described below through specific examples, but these examples are merely exemplary and do not constitute any limitation to the scope of protection of the present invention.

[0088] Example 1

[0089] (1) Constructing a lifespan prediction model

[0090] Select three new metallized film capacitors from the same batch and pre-treat them according to the following steps: N Withstand 24h under DC voltage, where E N The voltage is 235 kV / mm, and then the power is turned off and the capacitor is placed in an oven at 30°C for 12 hours. The capacitance of each capacitor is measured as the initial value.

[0091] A thermocouple was installed in the middle of each capacitor housing, and the thermocouple and the capacitor housing were fixedly connected with polyimide insulating tape. Afterwards, the power-on aging test was carried out according to the following steps: the three capacitors were placed in a constant temperature oven at 60°C, and 1.25E N_DC +0.15E N_AC The voltage, frequency are 50Hz, 150Hz, 250Hz, and the power-on aging time is 528h. During the power-on aging process, the temperature change of each capacitor shell is monitored in real time by thermocouples, and the capacitance change and the corresponding shell temperature are observed every 24h.

[0092] Next, by fitting the shell temperature and capacitance attenuation, the established life prediction model is as follows:

[0093]

[0094] Where E is the electric field strength, here E / E N is 1.4; f is the applied frequency, where the f / f0 of the three capacitors are 1, 1 / 3, and 1 / 5 respectively; T represents the measured value of the shell temperature at this moment, T0 is the measured temperature in the first 24 hours; T N is the ambient temperature, which is 60°C here, and k1 and k2 are fitting parameters.

[0095] By shifting terms, combining, and taking logarithms, the above formula can be expressed as follows:

[0096]

[0097] Through the corresponding calculation of the intercept and the slope, the fitting parameters k1 under the aging conditions of 50Hz, 150Hz, and 250Hz are 0.00195, 0.0019, and 0.0023 respectively; k2 are 0.71, 2.1, and 3.6 respectively.

[0098] (2) Based on the life prediction model in step (1), the casing temperature rise of the capacitor to be tested at the end of its life is predicted.

[0099] In order to shorten the experimental cost and cycle, the 250Hz group with the fastest decay was used for prediction and verification. According to the life prediction model, when the capacity decays to 95% of the initial value (y=0.95), the temperature rise of the capacitor case is 5.8℃.

[0100] (3) Verify the accuracy of the life prediction model

[0101] For the capacitors aged in the 250Hz group in step (1), continue to age at 1.25E N_DC +0.15E N_ACAging under voltage conditions. During the power-on aging process, the temperature change of each capacitor shell is monitored in real time by thermocouples, and the capacitance change and the shell temperature corresponding to this time are observed every 24 hours. Aging to the end of life. Compare whether the shell temperature at the end of life (capacitance decays to 95%) is the predicted temperature in the above step (2).

[0102] Figure 1 The graph showing the relationship between the temperature rise of the capacitor shells and the aging time of the three capacitors pretreated in step (1) shows that as the aging time increases, the capacitor shells all show obvious temperature rise, especially the temperature rise of the capacitors aged at a frequency of 250 Hz is more obvious.

[0103] Figure 2 The graph showing the relationship between the capacitance attenuation and aging time of the above three capacitors shows that with the increase of aging time, the capacitance of the pre-treated capacitors all shows obvious attenuation, especially the capacitance attenuation of the capacitors aged at a frequency of 250Hz is more obvious.

[0104] Figure 3 The figure shows the fitting diagram of shell temperature and capacitance decay, with the horizontal axis being the difference between the shell temperature rise and the initial value, and the vertical axis being the capacitance loss rate. The scattered points are the measured data, and the dotted line is the fitting result of the life prediction model. Taking 250Hz as an example, when the measured shell temperature rise reaches 5.8℃, the capacitor basically reaches the end of its life (that is, the capacitance decays to 95% of the initial value).

[0105] Figure 4 The graph shows the relationship between the capacitance decay rate, the measured value of the shell temperature rise and the aging time when the capacitors in the 250Hz group are powered on and aged. It can be seen that when the capacitance decays to 95%, the measured shell temperature rise is 5.8~6.0℃, which is consistent with the predicted shell temperature rise value mentioned above.

[0106] The present invention is described in detail above in combination with preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are only illustrative explanations of the present invention and do not constitute any limitation on the protection scope of the present invention. Without exceeding the spirit and protection scope of the present invention, various improvements, equivalent substitutions or modifications may be made to the technical content of the present invention and its embodiments, which all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. A metallized film capacitor life prediction system, characterized in that: The system comprises: A model building module, which is used to build a life prediction model based on the relationship between the capacitor housing temperature rise and the capacitance data; The prediction output module is used to predict the end-of-life state of the capacitor to be detected based on the life prediction model.

2. The system according to claim 1, characterized in that Preferably, the model building module includes: The power-on aging unit is used to perform a power-on aging test on the pre-treated capacitor.

3. The system according to claim 1, characterized in that The model building module also includes: A data acquisition unit, which is used to obtain the shell temperature rise and capacitance data of the capacitor during the power-on aging test of the capacitor; The data processing unit is used to construct a life prediction model according to the relationship between the acquired shell temperature rise and capacitance data.

4. The system according to claim 2, characterized in that The pretreatment includes: subjecting the capacitor to a preset field strength at 10-30°C, and then leaving it in a power-off environment for 12-48 hours.

5. The system according to claim 4, characterized in that The data acquisition unit includes a housing temperature data acquisition component.

6. The system according to claim 5, characterized in that The shell temperature data acquisition component includes a thermocouple, and the thermocouple is used to monitor the capacitor shell temperature in real time.

7. A method for predicting the life of a metallized film capacitor, characterized in that: The method comprises: Constructing a life prediction model based on the relationship between the capacitor shell temperature rise and the capacitance data; The end-of-life state of the capacitor to be inspected is predicted based on the life prediction model.

8. The method according to claim 7, characterized in that The life prediction model is constructed based on the relationship between the capacitor case temperature rise and the capacitance data, which includes the following steps: Conducting power-on aging test on the pre-treated capacitors; During the capacitor power-on aging test, the capacitor case temperature rise and capacitance data are obtained; Based on the relationship between the shell temperature rise and the capacitance data obtained, a life prediction model is constructed.

9. The method according to claim 8, characterized in that The pretreatment includes: subjecting the capacitor to a preset field strength at 10-30° C., and then allowing the capacitor to stand in a power-off environment for 12-48 hours.

10. The method according to claim 8, characterized in that The case temperature is obtained via a thermocouple.

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