A method for experimental evaluation of the influence of temperature on the cumulative effect of dielectric

Abstract

The invention discloses an experimental evaluation method for the influence of temperature on dielectric cumulative effect, and relates to the technical field of insulation test. The main points of the technical scheme are: building a dielectric cumulative effect equivalent experimental model with ambient temperature as a variable; obtaining a maximum value Tmax and a minimum value Tmin of the operating temperature of electrical equipment corresponding to the insulating dielectric, and setting the initial temperature of the experimental environment as Tmin; under the condition of constant temperature of the initial temperature Tmin, using an impulse voltage generator to obtain a dielectric cumulative effect U-N characteristic curve of the corresponding temperature; increasing the temperature with ΔT as a step length to obtain the dielectric cumulative effect U-N characteristic curve at different temperatures; obtaining an evaluation standard for the influence of temperature on the insulating dielectric cumulative effect according to the dielectric cumulative effect U-N characteristic curve at different temperatures, testing the cumulative characteristics of the insulating dielectric at different temperatures, obtaining the influence law of temperature on the insulating dielectric cumulative effect, and thus accurately evaluating the insulation characteristics at the actual operating temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation testing, and more particularly to a test and evaluation method for the cumulative effect of temperature on dielectrics. Background Art

[0002] During operation, power equipment will be subjected to multiple impulse voltages. Studies have shown that the insulation level of power equipment will decrease after being subjected to multiple impulse voltages, that is, there is a "cumulative effect".

[0003] At present, there are literatures that have studied and explained the test methods for the cumulative effect of dielectrics. However, the current tests on the cumulative effect of dielectrics are mostly conducted at room temperature. However, during the operation of power equipment, the internal temperature is affected by many factors such as ambient temperature and operating status, and the range of variation is large. Therefore, it is difficult to accurately evaluate the insulation characteristics of dielectrics at actual operating temperatures by simply considering the cumulative effect of dielectrics at a single temperature.

[0004] Therefore, how to study and design an experimental evaluation method for the cumulative effect of temperature on dielectrics is an issue that we urgently need to solve, in order to provide an accurate and reliable basis for the evaluation of the insulation properties of insulating dielectrics. Summary of the invention

[0005] The purpose of the present invention is to provide a test evaluation method for the influence of temperature on the cumulative effect of dielectrics, to test the cumulative characteristics of insulating dielectrics at different temperatures, to obtain the influence law of temperature on the cumulative effect of insulating dielectrics, and thus to accurately evaluate the insulation characteristics at the actual operating temperature.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: A test evaluation method for the influence of temperature on the cumulative effect of dielectrics, comprising the following steps:

[0007] S1: Build an equivalent experimental model of dielectric cumulative effect with ambient temperature as a variable;

[0008] S2: Obtain the maximum value Tmax and the minimum value Tmin of the operating temperature of the electrical equipment corresponding to the insulating dielectric, and set the initial temperature of the experimental environment to Tmin;

[0009] S3: Under the constant temperature condition of initial temperature Tmin, the characteristic curve of dielectric cumulative effect UN corresponding to the temperature is obtained by using impulse voltage generator;

[0010] S4: increasing the temperature with a step length of ΔT, and repeating step S3 to obtain a characteristic curve of dielectric cumulative effect UN at different temperatures until the temperature increases to Tmax;

[0011] S5: Based on the statistical analysis of the dielectric cumulative effect UN characteristic curve at different temperatures, the evaluation standard of the influence of temperature on the cumulative effect of insulating dielectric is obtained.

[0012] Preferably, the equivalent experimental model includes an impulse voltage generator, a voltage divider, a temperature control box and a test oil cup, the voltage divider is composed of two capacitors connected in series; the high-voltage end of the impulse voltage generator and the voltage divider connected in parallel is connected to the high-voltage electrode of the test oil cup, and the other end is grounded; the test oil cup is placed in the temperature control box, and the low-voltage electrode of the test oil cup is grounded; the insulating dielectric is located between the high-voltage electrode and the low-voltage electrode of the test oil cup, and is immersed in a liquid insulating impregnant.

[0013] Preferably, the ΔT temperature value is 5-15°C.

[0014] Preferably, the test is started after the experimental environment temperature is adjusted and preheated at a constant temperature for 40-60 minutes.

[0015] Preferably, in step S3, the specific steps of the dielectric cumulative effect test are:

[0016] S31: Test the 50% breakdown voltage of the insulating dielectric under impulse voltage, use the step-up and step-down method to test the 50% impulse breakdown voltage of the insulating dielectric, and record the impulse voltage peak value Um;

[0017] S32: Take Um as the reference voltage, and reduce the output voltage of the impulse voltage generator with a step length of ΔU, ΔU is 5%-15% Um, and under the output voltage U1=Um-ΔU of the impulse voltage generator, repeatedly apply the impulse voltage to the test oil cup until the insulating dielectric breaks down, and record the number of impulse voltage applications n1 at this time, repeat this step 10 times, and obtain a series of impulse voltage application times n1, n2, ..., n10, and take the average value thereof as N1; wherein the time interval between each impulse voltage is greater than 60s;

[0018] S33: Continue to reduce the output voltage of the impulse voltage generator to U2=Um-2ΔU, repeat step S32, and obtain the average value N2 of the number of breakdowns at this time;

[0019] S34: if the average value of the breakdown times is less than 1000, repeat step S33; if the average value of the breakdown times is greater than 1000, stop the test;

[0020] S35: According to the obtained series of impulse voltage amplitudes (U1, U2, ..., Un) and their corresponding breakdown times (N1, N2, ..., Nn), a UN characteristic curve is obtained with voltage as the ordinate and the times as the abscissa.

[0021] Preferably, the evaluation criteria are as follows: U = A × N B+C*(T-Tmin); where A, B, and C are constants, U is the peak value of the impulse voltage to which the dielectric is subjected, N is the number of impulse voltages that the dielectric can withstand, T is the dielectric temperature, and Tmin is the minimum dielectric temperature; the values ​​of A, B, and C are determined by the dielectric's own characteristics, the thickness of the test object, and the number of layers of the test object.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Compared with the traditional cumulative effect test at a single temperature, the present invention takes into account the influence of the actual operating temperature of the dielectric during operation on the cumulative effect characteristics, so the results obtained are more comprehensive.

[0024] (2) The dielectric cumulative effect curves at different temperatures obtained by the present invention can be used to more accurately evaluate the insulation status using the cumulative effect curves. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0026] Figure 1 is a flow chart in an embodiment of the present invention;

[0027] Figure 2 is a structural schematic diagram of an equivalent experimental model in an embodiment of the present invention;

[0028] Figure 3 2 is a schematic diagram of the structure of the test oil cup in an embodiment of the present invention;

[0029] Figure 4 is a UN characteristic curve diagram at a temperature in an embodiment of the present invention;

[0030] Figure 5 2 is a graph showing UN characteristic curves at various temperatures in an embodiment of the present invention.

[0031] Marks and corresponding parts names in the attached drawings:

[0032] 1. Impulse voltage generator; 2. Test oil cup; 21. Container tube; 22. Insulation cover; 23. High voltage electrode; 24. High voltage end; 25. Low voltage electrode; 26. Low voltage end; 27. Liquid insulating impregnant; 28. Insulating dielectric; 3. Temperature control box; 4. Voltage divider. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the following is a summary of the present invention with reference to the embodiments and the accompanying drawings. Figure 1-5, the present invention is further described in detail. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0034] Example: A test method for evaluating the cumulative effect of temperature on dielectrics, such as Figure 1-3 As shown, the following steps are included:

[0035] Step 1, build an equivalent experimental model of dielectric cumulative effect with ambient temperature as a variable. The equivalent experimental model includes an impulse voltage generator 1, a voltage divider 4, a temperature control box 3 and a test oil cup 2, and the voltage divider 4 is composed of two capacitors in series. The test oil cup 2 includes a container tube 21, an insulating cover 22, a high-voltage electrode 23, a low-voltage electrode 25 and an insulating dielectric 28. The high-voltage end 24 of the impulse voltage generator 1 and the voltage divider 4 after being connected in parallel is connected to the high-voltage electrode 23 of the test oil cup 2, and the other end is grounded. The test oil cup 2 is placed in the temperature control box 3, which can control the temperature of the test oil cup 2, and the low-voltage electrode 25 of the test oil cup 2 is grounded. The insulating dielectric 28 is located between the high-voltage electrode 23 and the low-voltage electrode 25 of the test oil cup 2, and is immersed in the liquid insulating impregnant 27.

[0036] Step 2: Obtain the maximum value Tmax and the minimum value Tmin of the operating temperature of the electrical equipment corresponding to the insulating dielectric 28, and set the initial temperature of the experimental environment to Tmin.

[0037] Step 3: Under the condition of constant temperature of initial temperature Tmin, the characteristic curve of dielectric cumulative effect UN corresponding to the temperature is obtained by using impulse voltage generator 1. After adjusting the experimental environment temperature, the constant temperature preheating is carried out for 40-60 minutes before starting the test.

[0038] The specific steps of the dielectric cumulative effect test are as follows:

[0039] (1) Testing the 50% breakdown voltage of the insulating dielectric 28 under impulse voltage: Using the voltage step-up and voltage step-down method, testing the 50% impulse breakdown voltage of the insulating dielectric 28, and recording the impulse voltage peak value Um.

[0040] (2) Take Um as the reference voltage and reduce the output voltage of the impulse voltage generator 1 with a step size of ΔU, where ΔU is 5%-15% of Um. When the output voltage of the impulse voltage generator 1 is U1=Um-ΔU, the impulse voltage is repeatedly applied to the test oil cup 2 until the insulating dielectric 28 breaks down. The number of impulse voltage applications n1 is recorded. Repeat this step 10 times to obtain a series of impulse voltage application times n1, n2, ..., n10, and take the average value thereof as N1; wherein the time interval between each impulse voltage application is greater than 60s.

[0041] (3) Continue to reduce the output voltage of the impulse voltage generator 1 to U2 = Um-2ΔU, repeat step S32, and obtain the average value N2 of the number of breakdowns at this time.

[0042] (4) If the average value of the breakdown times is less than 1000, repeat step S33; if the average value of the breakdown times is greater than 1000, stop the test.

[0043] (5) Based on the obtained series of impulse voltage amplitudes (U1, U2, ..., Un) and their corresponding breakdown times (N1, N2, ..., Nn), a UN characteristic curve is obtained with voltage as the ordinate and the number of times as the abscissa.

[0044] Step 4: Increase the temperature with a step length of ΔT, and repeat step S3 to obtain the dielectric cumulative effect UN characteristic curve at different temperatures until the temperature rises to Tmax, and the ΔT temperature value is 5-15°C.

[0045] Step 5: Statistically analyzing characteristic curves of dielectric cumulative effect UN at different temperatures to obtain an evaluation standard for the influence of temperature on the cumulative effect of the insulating dielectric 28 .

[0046] The specific evaluation criteria are: U = A × N B +C*(T-Tmin); where A, B, and C are constants, U is the peak value of the impulse voltage to which the dielectric is subjected, N is the number of impulse voltages that the dielectric can withstand, T is the dielectric temperature, and Tmin is the minimum dielectric temperature; the values ​​of A, B, and C are determined by the dielectric's own characteristics, the thickness of the test object, and the number of layers of the test object.

[0047] Capacitors are common equipment in power systems, and they play a role in reactive power compensation and filtering. The switching on and off of capacitor banks and external intrusion waves will cause the capacitor to be repeatedly subjected to multiple impulse voltages during operation. Therefore, it is necessary to obtain the cumulative effect of the capacitor oil film medium under impulse voltage to evaluate the insulation life of the capacitor. First, the operating temperature test is carried out on the test object. The test results show that the maximum operating temperature of the test object is 50°C and the minimum temperature is 30°C. The temperature step size is selected as 10°C. First, the dielectric cumulative effect at 30°C is tested to obtain a series of impulse voltage amplitudes and corresponding breakdown times, as shown in Table 1. The test results are as follows Figure 4 shown.

[0048] Table 1 Impulse voltage amplitude and breakdown times

[0049] Breakdown voltage amplitude 16kV 15.5kV 15kV 14.5kV 14kV 13.5kV 13kV 12.5kV Number of breakdowns 1 12 35 60 90 165 320 605

[0050] By increasing the temperature of the temperature control box 3 in steps of 10°C, the UN characteristic curves at different temperatures can be obtained, such as Figure 4 As shown. Figure 5 The cumulative effect characteristic curves at different temperatures shown can be used to evaluate the insulation life of the capacitor in combination with the operating temperature of the capacitor and the number of impulse voltages received.

[0051] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A test method for evaluating the influence of temperature on dielectric cumulative effect, characterized in that: The following steps are involved: S1: Build an equivalent experimental model of dielectric cumulative effect with ambient temperature as a variable; S2: Obtain the maximum value Tmax and the minimum value Tmin of the operating temperature of the electrical equipment corresponding to the insulating dielectric, and set the initial temperature of the experimental environment to Tmin; S3: Under the constant temperature condition of initial temperature Tmin, the characteristic curve of dielectric cumulative effect UN corresponding to the temperature is obtained by using impulse voltage generator; S4: increasing the temperature with a step length of ΔT, and repeating step S3 to obtain a characteristic curve of dielectric cumulative effect UN at different temperatures until the temperature increases to Tmax; S5: Based on the statistical analysis of the dielectric cumulative effect UN characteristic curve at different temperatures, the evaluation criteria for the influence of temperature on the cumulative effect of insulating dielectrics are obtained; In step S3, the specific steps of the dielectric cumulative effect test are: S31: Test the 50% breakdown voltage of the insulating dielectric under impulse voltage, use the step-up and step-down method to test the 50% impulse breakdown voltage of the insulating dielectric, and record the impulse voltage peak value Um; S32: Take Um as the reference voltage, and reduce the output voltage of the impulse voltage generator with a step length of ΔU, ΔU is 5%-15% Um, and under the output voltage U1=Um-ΔU of the impulse voltage generator, repeatedly apply the impulse voltage to the test oil cup until the insulating dielectric breaks down, and record the number of impulse voltage applications n1 at this time, repeat this step 10 times, and obtain a series of impulse voltage application times n1, n2, ..., n10, and take the average value thereof as N1; wherein the time interval between each impulse voltage is greater than 60s; S33: Continue to reduce the output voltage of the impulse voltage generator to U2=Um-2ΔU, repeat step S32, and obtain the average value N2 of the number of breakdowns at this time; S34: if the average value of the breakdown times is less than 1000, repeat step S33; if the average value of the breakdown times is greater than 1000, stop the test; S35: According to the obtained series of impulse voltage amplitudes (U1, U2, ..., Un) and their corresponding breakdown times (N1, N2, ..., Nn), a UN characteristic curve is obtained with voltage as the ordinate and the times as the abscissa; The evaluation criteria are specifically: U = A × N B +C*(T-Tmin); where A, B, and C are constants, U is the peak value of the impulse voltage to which the dielectric is subjected, N is the number of impulse voltages that the dielectric can withstand, T is the dielectric temperature, and Tmin is the minimum dielectric temperature; the values ​​of A, B, and C are determined by the dielectric's own characteristics, the thickness of the test object, and the number of layers of the test object.

2. The test and evaluation method for the influence of temperature on the cumulative effect of dielectric according to claim 1, characterized in that: The equivalent experimental model includes an impulse voltage generator, a voltage divider, a temperature control box and a test oil cup, wherein the voltage divider is composed of two capacitors connected in series; the high-voltage end of the impulse voltage generator and the voltage divider connected in parallel is connected to the high-voltage electrode of the test oil cup, and the other end is grounded; the test oil cup is placed in the temperature control box, and the low-voltage electrode of the test oil cup is grounded; the insulating dielectric is located between the high-voltage electrode and the low-voltage electrode of the test oil cup, and is immersed in a liquid insulating impregnant.

3. The test and evaluation method for the influence of temperature on the cumulative effect of dielectric according to claim 1, characterized in that: The ΔT temperature value is 5-15°C.

4. The test and evaluation method for the influence of temperature on the cumulative effect of dielectrics according to claim 1, characterized in that: The test was started after the experimental environment temperature was adjusted and preheated at a constant temperature for 40-60 minutes.

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