A method for evaluating the state of a capacitor-type device based on the dielectric loss factor tgδ

Abstract

The application relates to a capacitor type equipment state evaluation method based on a dielectric loss factor tgdelta, which comprises the following steps: (1) forming a vector form of A, B and C three-phase equipment dielectric loss factor tgdelta historical data; (2) calculating a dielectric loss factor correlation coefficient r AB between A and B phases, a dielectric loss factor correlation coefficient r BC between B and C phases and a dielectric loss factor correlation coefficient r CA between A and C phases; (3) judging whether A, B and C phases are in normal state, attention state or abnormal state by comparing the values of r AB , r BC and r CA . The capacitor type equipment state evaluation method based on the dielectric loss factor tgdelta forms a vector form of tgdelta historical data obtained by a capacitor type equipment on-line monitoring device, calculates the correlation coefficients of tgdelta historical data of three-phase equipment of the same line, and takes the correlation coefficients as evaluation basis, so that capacitor type equipment state evaluation is more quantitative, and the accuracy is improved.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment condition assessment technology, and particularly relates to a method for condition assessment of capacitive equipment based on the dielectric loss factor tgδ. Background Technology

[0002] Online measurement of the dielectric loss factor (tgδ) of capacitive equipment such as current transformers and high-voltage bushings can effectively assess the equipment's operating status. Currently, online monitoring of the dielectric loss factor (tgδ) typically employs a detection method that extracts a standard voltage signal from a capacitive voltage transformer (CVT). However, because the phase difference of a capacitive voltage transformer is related to many factors, the voltage signal obtained from its low-voltage side cannot completely and accurately reflect the phase of the high-voltage side. This leads to problems such as low accuracy, large dispersion, and poor stability in the tgδ measurement results. Furthermore, electromagnetic interference and environmental changes in the field also significantly affect the measurement results, causing large fluctuations in the tgδ measurement value of the same normally operating equipment.

[0003] Long Feng and Wang Furong et al. from Southwest Jiaotong University analyzed the error sources and methods to improve the measurement accuracy of online measurement of dielectric loss factor tgδ. Sun Heyi and Pu Shaobang et al. from Harbin Institute of Technology proposed a harmonic interference suppression method based on a comb-shaped notch filter, eliminating the error caused by harmonic interference when measuring dielectric loss factor tgδ online. The key to assessing the condition of capacitive equipment using dielectric loss factor tgδ lies in obtaining real and accurate experimental data, followed by scientific analysis and judgment of the data. Currently, the condition assessment method for capacitive equipment based on the dielectric loss tangent tgδ relies primarily on the subjective judgment of the testing personnel. This involves comparing the current value with historical data or data from the same batch of products. If a significant change in the dielectric loss factor tgδ is found, the equipment is considered to have an insulation defect. The above assessment methods have several shortcomings: firstly, judging the operating status of equipment through data comparison is subjective and lacks scientific criteria; secondly, the boundaries for appropriate actions (such as enhanced monitoring or power outage maintenance) after obtaining the assessment results are unclear, requiring precise judgment of the results to guide the next steps on-site. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, provide more effective judgment criteria, and improve the accuracy of assessment, this invention provides a method for assessing the condition of capacitive equipment based on the dielectric loss factor tgδ. The method organizes the historical tgδ data obtained from online monitoring of the capacitive equipment into a vector form, calculates the correlation coefficient of the historical tgδ data of the three-phase equipment on the same line, and uses it as the assessment basis, making the condition assessment of capacitive equipment more quantitative and improving the accuracy of the assessment.

[0005] The technical solution adopted in this invention is:

[0006] It includes the following steps,

[0007] (1) The historical data of the dielectric loss factor tgδ of the three-phase equipment A, B, and C are arranged into a vector form, which are tgδ A ,tgδ B and tgδ C ;

[0008] (2) Calculate the correlation coefficient r of the dielectric loss factor between phases A and B. AB The correlation coefficient r of the dielectric loss factor between phases B and C BC And the correlation coefficient r of the dielectric loss factor between phases A and C CA ;

[0009] (3) Compare r by calculation AB r BC and r CA The numerical values ​​are used to determine whether phases A, B, and C are in a normal, attentive, or abnormal state, respectively.

[0010] Furthermore, in step (1),

[0011] tgδ A =[tgδ A1 ,tgδ A2 ,tgδ A3 ...tgδ An ];

[0012] tgδ B =[tgδ B1 ,tgδ B2 ,tgδ B3 ...tgδ Bn ];

[0013] tgδ C =[tgδ C1 ,tgδ C2 ,tgδ C3 ...tgδ Cn ];

[0014] Formula tgδ A ,tgδ B and tgδ C In the middle, tgδ A1 ,tgδ A2 ,tgδ A3 …tgδ An These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth devices in phase A; tgδ B1 ,tgδ B2 ,tgδ B3 …tgδBn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth device in phase B; tgδ C1 ,tgδ C2 ,tgδ C3 …tgδ Cn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth devices in phase C, respectively; n represents the number of historical data points for tgδ.

[0015] Further, in step (2), the correlation coefficient r of the dielectric loss factor between phases A and B is calculated. AB ,

[0016] in,

[0017]

[0018]

[0019] In step (2), the dielectric loss correlation coefficient r between phases B and C is calculated. BC ,

[0020]

[0021] in,

[0022]

[0023]

[0024] In step (2), the dielectric loss correlation coefficient r between phases A and C is calculated. CA ,

[0025]

[0026] in,

[0027]

[0028]

[0029] n represents the number of historical data points for tgδ.

[0030] Furthermore, in step (3), the device status is normal, alert, or abnormal.

[0031] Furthermore, in step (3), if r AB r BC and r CA If all values ​​are between 0.85 and 1, then the three-phase equipment A, B, and C are in normal condition.

[0032] Furthermore, in step (3), if r AB and r CA Between 0.75 and 0.85, r BC If the value is between 0.85 and 1, then phase B and C equipment are in normal condition, while phase A equipment is in a state of alert, and phase A should be monitored more closely; when r AB and r CA All are less than 0.75, r BC If the value is between 0.85 and 1, then the equipment in phases B and C is in normal condition, while the equipment in phase A is in abnormal condition. Phase A should be shut down for maintenance in a timely manner.

[0033] Furthermore, in step (3), if r AB and r BC Between 0.75 and 0.85, r CA If the value is between 0.85 and 1, then phases A and C are in normal condition, while phase B is in a state of alert, and phase B should be monitored more closely; when r AB and r BC All are less than 0.75, r CA If the value is between 0.85 and 1, then the equipment in phases A and C is in normal condition, while the equipment in phase B is in abnormal condition. Phase B should be shut down for maintenance in a timely manner.

[0034] Furthermore, in step (3), if r CA and r BC Between 0.75 and 0.85, r AB If the value is between 0.85 and 1, then phases A and B are in normal condition, while phase C is in a state of alert, and monitoring of phase C should be strengthened; when r CA and r BC All are less than 0.75, r AB If the value is between 0.85 and 1, then the equipment in phases A and B is in normal condition, while the equipment in phase C is in abnormal condition. Phase C should be shut down for maintenance in a timely manner.

[0035] Furthermore, in step (3), if r CA r AB and r BC All are between 0.75 and 0.85, and r AB Greater than r BC and r CA If any one of the following conditions is met, then the C-phase equipment is in normal condition, while the A and B-phase equipment are in a state of alert, and monitoring of the A and B phases should be strengthened.

[0036] Furthermore, in step (3), if r CA r AB and r BC All are between 0.75 and 0.85, and r BC Greater than rAB and r CA If any one of the following is true, then the A-phase equipment is in normal condition, and the B and C-phase equipment is in a state of alert, requiring enhanced monitoring of the B and C phases; if r CA r AB and r BC All are between 0.75 and 0.85, and r CA Greater than r AB and r BC If any one of the following conditions is met, then the B-phase equipment is in normal condition, while the A and C-phase equipment are in a state of alert, and monitoring of the A and C phases should be strengthened.

[0037] The beneficial effects of this invention are: by calculating the correlation of historical tgδ data between every two phases of equipment, this invention determines whether the equipment is in a normal, alert, or abnormal state based on the magnitude of the correlation coefficient. Equipment in a normal state can continue to operate, equipment in an alert state should be monitored more closely, and equipment in an abnormal state should be promptly scheduled for power outage and maintenance. Attached Figure Description

[0038] Figure 1 This is a vector diagram of the medium loss factor.

[0039] Figure 2 This is a schematic diagram of a commonly used online monitoring device for dielectric loss factor.

[0040] Figure 3 This is a schematic diagram of data extraction.

[0041] Figure 4 The dismantling of phase B equipment in Example 3;

[0042] Figure 5 The dismantling of the C-phase equipment in Example 3;

[0043] Figure 6 The dismantling of the A-phase equipment in Example 3. Detailed Implementation

[0044] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following description, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation methods, structures, and effects of the present invention.

[0045] Its characteristics and effects are detailed below.

[0046] Example 1

[0047] The technical concept of this invention is as follows: The operating environment of three-phase equipment on the same line is basically the same. When the state of one or two phases of the equipment changes, the changing trend of the historical tgδ data of the three-phase equipment will differ. By comparing the correlation of the historical tgδ data of the three-phase equipment, the influence of errors caused by testing methods and electromagnetic interference can be eliminated.

[0048] The energy loss within an insulating material under the influence of an electric field, due to the hysteresis effects of dielectric conductivity and polarization, is called dielectric loss, or simply dielectric loss. Under an alternating electric field, the complementary angle δ of the angle (power factor angle Φ) between the current phasor and voltage phasor flowing through the dielectric is called the dielectric loss angle, and the tangent of the dielectric loss angle is called the dielectric loss factor. Figure 1 A vector diagram of the medium factor is given.

[0049] Example 2

[0050] This invention provides a method for assessing the condition of capacitive devices based on the dielectric loss factor tgδ. In existing technologies, such as... Figure 2 The schematic diagram of a commonly used online monitoring device for dielectric loss factor is shown. The device detects the leakage current signal from the end screen of the equipment through a current transformer and obtains the voltage signal from the secondary side of a voltage transformer. After amplification, filtering, and A / D conversion, the signal is converted into a digital signal. The built-in program performs a fast Fourier transform on the two digital signals of voltage and current to obtain the fundamental Fourier coefficients of the two signals. The phase difference between the two fundamental waves is then calculated to obtain the loss factor tgδ of the equipment.

[0051] The present invention includes the following steps:

[0052] (1) The historical data of the dielectric loss tangent tgδ of the three-phase equipment A, B, and C are combined to form a system.

[0053] Vector form, respectively tgδ A ,tgδ B and tgδ C ;

[0054] tgδ A =[tgδ A1 ,tgδ A2 ,tgδ A3 ...tgδ An ];

[0055] tgδ B =[tgδ B1 ,tgδ B2 ,tgδ B3 ...tgδ Bn ];

[0056] tgδ C =[tgδ C1 ,tgδ C2 ,tgδ C3 ...tgδ Cn ];

[0057] Formula tgδ A ,tgδB and tgδ C In the middle, tgδ A1 ,tgδ A2 ,tgδ A3 …tgδ An These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth devices in phase A; tgδ B1 ,tgδ B2 ,tgδ B3 …tgδ Bn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth device in phase B; tgδ C1 ,tgδ C2 ,tgδ C3 …tgδ Cn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth devices in phase C, respectively; n represents the number of historical data points for tgδ.

[0058] (2) Calculate the correlation coefficient r of the dielectric loss factor between phases A and B. AB ,

[0059]

[0060] in,

[0061]

[0062]

[0063] Calculate the dielectric loss correlation coefficient r between phases B and C. BC ,

[0064]

[0065] in,

[0066]

[0067]

[0068] Calculate the correlation coefficient r of dielectric loss between phases A and C. CA ,

[0069]

[0070]

[0071]

[0072] Where, r AB rBC and r CA In this context, n represents the number of historical data points for tgδ.

[0073] (3) By judging r AB r BC and r CA The numerical value is used to determine the state of phases A, B, and C. The state can be classified as normal, abnormal, or alert.

[0074] The judgment method is shown in Table 1. Table 1: State Assessment Criteria

[0075]

[0076] The explanation of Table 1 is as follows.

[0077] In step (3):

[0078] If r AB r BC and r CA If all values ​​are between 0.85 and 1, then the three-phase equipment A, B, and C are in normal condition.

[0079] If r AB and r CA Between 0.75 and 0.85, r BC If the value is between 0.85 and 1, then the equipment in phases B and C is in normal condition, while the equipment in phase A is in a state of alert, and phase A should be monitored more closely.

[0080] If r AB and r CA All are less than 0.75, r BC If the value is between 0.85 and 1, then the equipment in phases B and C is in normal condition, while the equipment in phase A is in abnormal condition. Phase A should be shut down for maintenance in a timely manner.

[0081] If r AB and r BC Between 0.75 and 0.85, r CA If the value is between 0.85 and 1, then the equipment in phases A and C is in normal condition, while the equipment in phase B is in a state of alert, and phase B should be monitored more closely.

[0082] If r AB and r BC All are less than 0.75, r CA If the value is between 0.85 and 1, then the equipment in phases A and C is in normal condition, while the equipment in phase B is in abnormal condition. Phase B should be shut down for maintenance in a timely manner.

[0083] If r CA and r BC Between 0.75 and 0.85, r ABIf the value is between 0.85 and 1, then the equipment in phases A and B is in normal condition, while the equipment in phase C is in a state of alert, and phase C should be monitored more closely.

[0084] If r CA and r BC All are less than 0.75, r AB If the value is between 0.85 and 1, then the equipment in phases A and B is in normal condition, while the equipment in phase C is in abnormal condition. Phase C should be shut down for maintenance in a timely manner.

[0085] If r CA r AB and r BC All are between 0.75 and 0.85, and r AB Greater than r BC and r CA If any one of the following conditions is met, then the C-phase equipment is in normal condition, while the A and B-phase equipment are in a state of alert, and monitoring of the A and B phases should be strengthened.

[0086] If r CA r AB and r BC All are between 0.75 and 0.85, and r BC Greater than r AB and r CA If any one of the following conditions is met, then the A-phase equipment is in normal condition, while the B and C-phase equipment are in a state of alert, and monitoring of the B and C phases should be strengthened.

[0087] If r CA r AB and r BC All are between 0.75 and 0.85, and r CA Greater than r AB and r BC If any one of the following conditions is met, then the B-phase equipment is in normal condition, while the A and C-phase equipment are in a state of alert, and monitoring of the A and C phases should be strengthened.

[0088] like Figure 3 As shown, the judgment method of the present invention can be set in the evaluation system, and the input is tgδ obtained through an online monitoring device. A ,tgδ B and tgδ C r is calculated through the evaluation system's internal program. AB r BC and r CA And determine r AB r BC and r CA The numerical relationship is used to output the device status, i.e., normal, abnormal, or alert status.

[0089] Example 3

[0090] This invention takes the actual measurement process of a current transformer in a 500kV substation as an example. The specific test process is as follows:

[0091] (1) The current transformer model is LVB-220W3, which was put into operation in 2012.

[0092] (2) Connect the evaluation system to the online monitoring device via an RS-485 cable and retrieve the historical dielectric loss factor tgδ values ​​for phases A, B, and C. The data retrieval rule is one set of data per month, for a total of 24 sets of data, as shown in Table 2. In order to achieve accurate comparison of dielectric loss factor tgδ values, the historical dielectric loss factor tgδ data are arranged into a vector form, as shown in Equation (1).

[0093] tgδ=[tgδ1, tgδ2, tgδ3...tgδ n (1)

[0094] Historical data on the dielectric loss factor tgδ of three-phase equipment are represented by equations (2)-(4).

[0095] tgδ A =[tgδ A1 ,tgδ A2 ,tgδ A3 ...tgδ An (2)

[0096] tgδ B =[tgδ B1 ,tgδ B2 ,tgδ B3 ...tgδ Bn (3)

[0097] tgδ C =[tgδ C1 ,tgδ C2 ,tgδ C3 ...tgδ Cn (4)

[0098] The specific data is shown in Table 2.

[0099]

[0100] The correlation coefficient can describe the linear correlation between different variables, thus accurately determining the similarity between variables. The calculation method of the correlation coefficient is shown in equations (5)-(7).

[0101]

[0102]

[0103]

[0104] r is obtained by formulas (5) to (7). AB =0.493,r BC =0.857,r AC =0.690.

[0105] The condition assessment criteria are shown in Table 1, indicating that the A-phase equipment is abnormal, while the B and C-phase equipment are normal.

[0106] For capacitor-type equipment, the operating environment of the three-phase equipment on the same line is basically the same, and the probability of insulation defects in all three phases is almost zero. When the insulation condition of all three phases is normal, the trend of the dielectric loss factor tgδ is consistent. At this time, the correlation of historical data of dielectric loss factor tgδ between any two phases should be greater than threshold 1. When the insulation condition of one phase changes slightly but it can still continue to operate, the correlation of historical data of dielectric loss factor tgδ between it and the normal phase should be less than threshold 1. When the insulation condition continues to deteriorate and a power outage for maintenance should be arranged as soon as possible, the correlation of historical data of dielectric loss factor tgδ between it and the normal phase should be less than threshold 2. When the insulation condition of two phases changes simultaneously, this situation objectively exists. To avoid omissions and misjudgments, additional criteria should be added. In order to solve the problems of the prior art and avoid evaluation failure caused by improper threshold setting, this invention creatively determines threshold 1 as 0.85 and threshold 2 as 0.75.

[0107] To verify the accuracy of the present invention, the test device of the above embodiments was disassembled for verification.

[0108] The disintegration process is as follows Figure 4-6 As shown, Figure 4 The equipment in phase B was disassembled. After inspection and testing, the insulation structure of the equipment was found to be in good condition and the equipment was in normal condition. Figure 5 The equipment in phase C was disassembled. After inspection and testing, the insulation structure of the equipment was found to be in good condition, and the equipment was in normal condition. Figure 6 After disassembling and inspecting the A-phase equipment, it was found that the contact between the cap and the through-core rod was poor. After long-term operation, the equipment overheated severely and gradually showed creepage marks. After a long period of operation, the insulation gradually deteriorated, causing the dielectric loss factor tgδ of the A-phase equipment to gradually change compared to the other two phases.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A condition assessment method for capacitive equipment based on the dielectric loss factor tgδ, characterized by... It lies in, It includes the following steps, (1) The historical data of the dielectric loss factor tgδ of the three-phase equipment A, B, and C are arranged into a vector form, which are tgδ A ,tgδ B and tgδ C ; (2) Calculate the correlation coefficient r of the dielectric loss factor between phases A and B. AB The correlation coefficient r of the dielectric loss factor between phases B and C BC And the correlation coefficient r of the dielectric loss factor between phases A and C CA ; (3) Compare r by calculation AB r BC and r CA The numerical values ​​are used to determine whether phases A, B, and C are in a normal, attentive, or abnormal state, respectively. In step (1), ； ； ； Formula tgδ A ,tgδ B and tgδ C In the middle, tgδ A1 ,tgδ A2 ,tgδ A3 ...tgδ An They represent the A phase number 1 and 2 respectively. Historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth device; tgδ B1 ,tgδ B2 ,tgδ B3 ...tgδ Bn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth device in phase B; tgδ C1 ,tgδ C2 ,tgδ C3 ...tgδ Cn These represent the historical data of the dielectric loss factor tgδ for the 1st, 2nd, 3rd, and up to the nth devices in phase C, respectively; n represents the number of historical data points for tgδ. In step (2), the correlation coefficient r of the dielectric loss factor between phases A and B is calculated. AB , ； in, ; ; In step (2), the dielectric loss correlation coefficient r between phases B and C is calculated. BC , in, ; ; In step (2), the dielectric loss correlation coefficient r between phases A and C is calculated. CA , in, ; ； n represents the number of historical data points for tgδ; In step (3), the device status is normal, alert, or abnormal. In step (3), if r AB r BC and r CA If all values ​​are between 0.85 and 1, then the three-phase equipment A, B, and C are in normal condition.

2. A capacitive device based on dielectric loss factor tgδ according to claim 1 The condition assessment method is characterized by, In step (3), if r AB and r CA Between 0.75 and 0.85, r BC If the value is between 0.85 and 1, then phase B and C equipment are in normal condition, while phase A equipment is in a state of alert, and phase A should be monitored more closely; when r AB and r CA All are less than 0.75, r BC If the value is between 0.85 and 1, then the equipment in phases B and C is in normal condition, while the equipment in phase A is in abnormal condition. Phase A should be shut down for maintenance in a timely manner.

3. A capacitor-type device based on dielectric loss factor tgδ according to claim 2 The condition assessment method is characterized by, In step (3), if r AB and r BC Between 0.75 and 0.85, r CA If the value is between 0.85 and 1, then phases A and C are in normal condition, while phase B is in a state of alert, and phase B should be monitored more closely; when r AB and r BC All are less than 0.75, r CA If the value is between 0.85 and 1, then the equipment in phases A and C is in normal condition, while the equipment in phase B is in abnormal condition. Phase B should be shut down for maintenance in a timely manner.

4. A capacitor-type device based on dielectric loss factor tgδ according to claim 3. The condition assessment method is characterized by, In step (3), if r CA and r BC Between 0.75 and 0.85, r AB If the value is between 0.85 and 1, then phases A and B are in normal condition, while phase C is in a state of alert, and monitoring of phase C should be strengthened; when r CA and r BC Less than 0.75, r AB If the value is between 0.85 and 1, then the equipment in phases A and B is in normal condition, while the equipment in phase C is in abnormal condition. Phase C should be shut down for maintenance in a timely manner.

5. The method for assessing the condition of capacitive equipment based on the dielectric loss factor tgδ according to claim 4, characterized in that, In step (3), if r CA r AB and r BC All are between 0.75 and 0.85, and r AB Greater than r BC and r CA If any one of the following conditions is met, then the C-phase equipment is in normal condition, while the A and B-phase equipment are in a state of alert, and monitoring of the A and B phases should be strengthened.

6. The method for assessing the condition of capacitive equipment based on the dielectric loss factor tgδ according to claim 5, characterized in that, In step (3), if r CA r AB and r BC All are between 0.75 and 0.85, and r BC Greater than r AB and r CA If any one of the following is true, then phase A equipment is in normal condition, and phases B and C equipment are in a state of alert, requiring enhanced monitoring of phases B and C; if r CA r AB and r BC All are between 0.75 and 0.85, and r CA Greater than r AB and r BC If any one of the following conditions is met, then the B-phase equipment is in normal condition, while the A and C-phase equipment are in a state of alert, and monitoring of the A and C phases should be strengthened.

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