A method for evaluating aging of oil-paper insulation based on moisture migration

Abstract

The application discloses an oil-paper insulation aging evaluation method based on moisture migration, and relates to the technical field of transformer performance evaluation.The method comprises the following steps: constructing an oil-paper insulation moisture balance curve under different oil temperatures and different aging degrees; constructing a relationship curve between the change value of the water content in oil and the aging degree by using the oil-paper insulation moisture balance curve; detecting the water content in the oil of the transformer in real time, taking the difference between the measured water content in the oil and a base value as the change value of the water content in the oil, and obtaining the corresponding aging degree of the oil-paper insulation from the relationship curve.The application utilizes the moisture migration in the oil, does not need to calculate the moisture content in the insulation paper, and can also realize the evaluation of the aging degree of the oil-paper insulation in the transformer under the actual operation condition.

Description

Technical Field

[0001] This invention relates to the field of transformer performance evaluation technology, and in particular to a method for evaluating the aging of oil-paper insulation based on moisture migration. Background Technology

[0002] Oil-paper insulation is a crucial insulation combination in transformers. Under the influence of electric fields, temperature, mechanical vibration, moisture, and oxygen, its electrical and mechanical properties gradually decline, leading to a reduction in insulation life and ultimately increasing the operational risks of the transformer, which is detrimental to its safe operation. Currently, methods for determining the aging degree of oil-paper insulation mainly include: dielectric response method, furfural content, degree of polymerization measurement, and dissolved gas method. Although there are methods that utilize moisture in the oil to assess the aging of oil-paper insulation, these methods primarily combine moisture with other factors for judgment, or calculate the moisture content in the paper after determining the moisture content in the oil, ultimately obtaining the total moisture content in the insulation. There is a lack of methods that utilize moisture migration between the oil and paper layers to assess aging. Summary of the Invention

[0003] To address the aforementioned problems and technical needs, the inventors have proposed a method for assessing the aging state of oil-paper insulation based on moisture migration, which can effectively evaluate the aging condition of transformer oil-paper insulation. The technical solution of this invention is as follows: An aging assessment method for oil-paper insulation based on moisture migration includes the following steps: Construct multiple moisture balance curves for oil-paper insulation with different aging degrees at constant oil temperature; A curve relating the change in water content in oil to the degree of aging was constructed using the moisture balance curves of oil-paper insulation at different aging degrees under unaged and constant oil temperatures. The water content in the transformer oil is detected in real time, and the difference between the measured water content and the baseline value is used as the change value of water content in the oil. The corresponding aging degree of the oil-paper insulation is obtained from the relationship curve. The baseline value is the initial water content in the oil measured under the condition that the oil-paper insulation has not aged.

[0004] A further technical solution involves constructing moisture balance curves for oil-paper insulation at different aging levels, both unaged and at constant oil temperature, including: Oil-paper insulation samples were placed in an aging chamber for thermal aging tests of different degrees. Then, the thermally aged oil-paper insulation samples and the unaged oil-paper insulation samples were placed in a constant temperature and humidity chamber, with different temperatures and humidity levels set at each temperature. When the moisture in the oil-paper insulation samples reached equilibrium, the moisture balance curves of oil-paper insulation with different aging degrees and the moisture balance curves of unaged oil-paper insulation were plotted at a constant temperature.

[0005] A further technical solution involves placing the oil-paper insulation sample in an aging chamber for thermal aging tests of varying degrees, including: Based on the life loss of the oil-paper insulation sample, the 6-degree rule was used to estimate the aging time of the oil-paper insulation. Various aging times for the oil-paper insulation were designed at a set temperature. Moisture balance curves of the oil-paper insulation were obtained at both the unaged oil-paper insulation and each designed aging time, so as to correlate the aging time with the temperature.

[0006] A further technical solution involves designing formulas for various oil-paper insulation aging times: ; in, D i The design of the first i The aging time of the oil paper insulation. Y i This indicates that the transformer is at the set operating temperature. T i The specified number of years of operation under the given conditions T 0 indicates the set temperature for the aging test of the oil paper insulation sample.

[0007] A further technical solution involves constructing a curve showing the relationship between the change in water content in the oil and the degree of aging using the moisture balance curve of the oil-paper insulation, including: The oil temperature and water content in the transformer are obtained during operation. Based on the measured oil temperature, the moisture balance curves of the oil-paper insulation with different aging degrees corresponding to that temperature are selected. From the moisture balance curves of the oil-paper insulation with different aging degrees, the aging degree of the moisture balance curve corresponding to the change of the oil water content from the baseline value to the measured oil water content is determined, thereby establishing the relationship curve between the difference between the measured oil water content and the baseline value and the aging degree.

[0008] A further technical solution involves obtaining the oil temperature and water content in the transformer during operation, including: Temperature sensors and micro-water sensors are used to detect the oil temperature and water content in the transformer, respectively.

[0009] The further technical solution is to set up two sets of temperature sensors and micro-water sensors. One set is used to monitor the water content and oil temperature in the oil outlet pipe of the transformer oil tank in real time, and the other set is used to monitor the water content and oil temperature in the oil return pipe of the transformer oil tank in real time. The oil temperature and water content measured by the same type of sensors in the two sets within the set error range are selected, and the average value is taken to construct the relationship curve.

[0010] A further technical solution is that the method also includes: When the real-time measured water content in the oil exceeds the standard value, it is considered that the oil-paper insulation of the transformer has begun to age, and the corresponding degree of aging of the oil-paper insulation is obtained from the relationship curve based on the difference between the measured water content in the oil and the baseline value.

[0011] The beneficial technical effects of this invention are: This invention is an aging assessment method for oil-paper insulation based on moisture migration. It fully considers the moisture migration between oil and paper, and only requires real-time monitoring of the moisture content in the oil. It does not require using the moisture in the oil to calculate the moisture in the paper and thus obtain the total moisture content of the oil-paper insulation. This method is consistent with the actual operating conditions of transformers. This method not only provides a new approach to assessing the aging degree of oil-paper insulation, but also has the potential to provide good application prospects for fault diagnosis of power equipment such as oil-paper insulation in transformers. Attached Figure Description

[0012] Figure 1 This is a flowchart of the aging assessment method for oil-paper insulation based on moisture migration provided in this application.

[0013] Figure 2 These are the moisture balance curves of oil-paper insulation under different oil temperatures and different aging degrees provided in this application. Among them: (a) represents the moisture balance curves of oil-paper insulation at different temperatures, and (b) represents the moisture balance curves of oil-paper insulation at different aging degrees at a constant temperature.

[0014] Figure 3 This is a schematic diagram of the installation of the micro water sensor and oil temperature sensor provided in this application.

[0015] Figure 4 This is a curve showing the relationship between the difference in water content in the oil and the degree of aging, as provided in this application. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0017] like Figure 1 As shown, this application provides a method for evaluating the aging of oil-paper insulation based on moisture migration, which includes the following steps: Step 1: Construct moisture balance curves for oil-paper insulation at different aging levels, both before and at a constant oil temperature. This includes the following sub-steps: Step 1-1: Place the oil-paper insulation sample in a constant temperature and humidity chamber, set different temperatures, and set different humidity levels at each temperature.

[0018] In this embodiment, the temperatures in the constant temperature and humidity chamber are set to 35℃, 50℃, 70℃, and 85℃, respectively, and four humidity values ​​are set for each constant temperature: 20%RH, 40%RH, 60%RH, and 80%RH. Figure 2As shown in (a), the moisture balance curve of the unaged transformer oil paper insulation is as follows: (1) In equation (1), This refers to the moisture content in the cardboard. This refers to the water content in the oil. T This refers to the oil temperature.

[0019] Step 1-2: Then take a new oil paper insulation sample and place it in an aging chamber to conduct thermal aging tests of different degrees. Perform the same operation on the oil paper insulation samples with different aging degrees as in Step 1-1. When the moisture in the oil paper insulation sample reaches equilibrium, plot the moisture balance curves of the oil paper insulation with different aging degrees at a constant temperature.

[0020] Specifically, according to the IEEE standard, 130℃ was selected as the aging test temperature for the oil-paper insulation samples. Based on GBT15164-1994, the load guideline for oil-immersed power transformers, the operating temperature of oil-immersed transformers in my country varies within the range of 80℃ to 140℃. The life loss of the oil-paper insulation samples is estimated according to the 6-degree rule. Therefore, based on the 6-degree rule, various aging times for oil-paper insulation were designed at the set transformer operating temperature. Moisture balance curves of the oil-paper insulation were obtained for both unaged and designed aging times to correlate aging time with temperature. Taking the oil-paper insulation sample at 85℃ placed in the aging chamber in step 1-1 as an example, the resulting moisture balance curve is as follows: Figure 2 As shown in (b), the remaining temperatures are operated in the same manner as steps 1-2, and the resulting equilibrium curves are similar, so they will not be listed and shown again.

[0021] The formulas for designing various aging times for oil-paper insulation are as follows: (2) in, D i The design of the first i The aging time of the oil-paper insulation is expressed in days. Y i This indicates that the transformer is at the set operating temperature. T i The specified number of years of operation under the given conditions, in years. T 0 represents the set temperature for the aging test of the oil-paper insulation sample, which is taken as 0 in this example. T 0 = 130℃.

[0022] In this embodiment, considering only thermal aging factors, the transformer in T i Operating at 80℃ Y i=After 20 years, the degree of aging of its oil paper insulation is similar to T Accelerated thermal aging at 0=130℃ D i =The aging degree is the same at 22.6 days, and the calculation method according to formula (2) is as follows:

[0023] therefore, Figure 2 The other three aging times illustrated in (b) are for transformers at... T i Operating at 80℃ respectively Y i =The degree of aging of the oil paper insulation after 5 years, 10 years, and 15 years, and T Accelerated thermal aging at 0=130℃ D i =The aging levels were the same at 5.65 days, 11.3 days, and 16.95 days.

[0024] Step 2: Construct a curve showing the relationship between the change in water content in the oil and the degree of aging using the moisture balance curves of oil-paper insulation at different aging degrees under both unaged and constant oil temperatures. This includes the following sub-steps: Step 2-1: Obtain the oil temperature and water content in the transformer during operation.

[0025] In this embodiment, a temperature sensor and a micro-water sensor are used to detect the transformer oil temperature and the water content in the oil, respectively. Figure 3 As shown, it mainly includes: a transformer oil tank, an oil outlet pipe and an oil outlet valve, an oil return pipe and an oil return valve, an oil pump and an oil pump valve, a micro-water sensor 1 and an oil temperature sensor 1, a micro-water sensor 2 and an oil temperature sensor 2, and a data storage module. Specifically, micro-water sensor 1 and oil temperature sensor 1 are used to monitor the water content M1 and oil temperature T1 in the oil outlet pipe of the transformer oil tank in real time, while micro-water sensor 2 and oil temperature sensor 2 are used to monitor the water content M2 and oil temperature T2 in the oil return pipe of the transformer oil tank in real time, and the collected data is saved to the data storage module.

[0026] When selecting measurement data from the data storage module in subsequent steps, the water content value M and oil temperature value T should be selected when the errors of M1 and M2, and T1 and T2 are simultaneously controlled within 0.5%. This minimizes the measurement error caused by instability on the oil outlet and return sides, and the average values ​​are taken respectively. Used to construct relationship curves.

[0027] Step 2-2: Based on the measured oil temperature Select the moisture balance curves of the oil-paper insulation at different aging degrees corresponding to this temperature. Optionally, if the balance curve does not include this oil temperature... Step 1 can be used to obtain the moisture balance curves of oil paper insulation with different aging degrees at the corresponding temperature.

[0028] Steps 2-3: Due to the aging of the oil-paper insulation, moisture in the paperboard migrates into the oil, causing changes in the trace moisture content of the oil. From the moisture balance curves of oil-paper insulation at different aging degrees, the change in oil moisture content from the baseline value M0 to the measured oil moisture content is determined. The degree of aging of the oil-paper insulation moisture balance curve at a certain point in time corresponds to the actual operating process of the transformer. t The difference in water content in the oil is ΔM= -M0, thus establishing a curve showing the relationship between the difference in water content ΔM in the oil and the degree of aging, such as Figure 4 As shown. Wherein, the base value M0 is the measured oil temperature. The initial water content in the oil was measured under the condition that the oil-paper insulation was not aged.

[0029] Step 3: Real-time detection of water content in transformer oil, and use the difference ΔM between the measured water content in oil and the baseline value as the change value of water content in oil, and obtain the corresponding aging degree of oil-paper insulation from the relationship curve.

[0030] Optionally, according to GB / T14542-2017 Transformer Oil Maintenance and Management Guidelines, for voltage levels between 330kV and 1000kV, the moisture content of the operating oil should be ≤15mg / L. When the detected water content in the oil is >15mg / L, the transformer's oil-paper insulation has begun to age. Therefore, when the real-time measured water content in the oil is greater than the standard value of 15mg / L, step 3 is executed to obtain the time. t The corresponding degree of aging of the paper insulation.

[0031] Based on the above method steps, it can be seen that this application only requires measuring the moisture content in the transformer oil. It creatively proposes a method to assess the aging of transformer oil paper by utilizing the moisture migration between oil and paper, without using the moisture in the oil to calculate the moisture in the paper and thus obtain the total moisture content of the oil-paper insulation. This method is consistent with the actual operating conditions of transformers. This method not only provides a new approach to assessing the aging degree of oil-paper insulation, but also has the potential to provide a good application prospect for fault diagnosis of power equipment such as oil-paper insulation in transformers.

[0032] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for assessing the aging of oil-paper insulation based on moisture migration, characterized in that, The method includes: Unaged oil-paper insulation samples were placed in a constant temperature and humidity chamber. Different temperatures and humidity levels were set at each temperature to obtain the moisture balance curve of the unaged oil-paper insulation. New oil-paper insulation samples were then subjected to thermal aging tests of different degrees. The constant temperature and humidity chamber tests were repeated for oil-paper insulation samples with different aging degrees. When the moisture in the samples reached equilibrium, multiple moisture balance curves of oil-paper insulation with different aging degrees at constant oil temperature were constructed. The oil temperature and water content in the transformer during operation are obtained. Based on the measured oil temperature, the moisture balance curves of the oil-paper insulation with different aging degrees at the corresponding temperature are selected. The aging degree corresponding to the change of the water content in the oil from the unaged baseline value to the measured water content in the oil is determined. Thus, the relationship curve between the change value of water content in the oil and the aging degree is constructed by using the moisture balance curves of the oil-paper insulation with different aging degrees under unaged and constant oil temperature. The water content in the transformer oil is detected in real time, and the difference between the measured water content in the oil and the baseline value is used as the change value of the water content in the oil. The corresponding aging degree of the oil-paper insulation is obtained from the relationship curve. The base value is the initial water content in the oil measured at the corresponding oil temperature under the condition that the oil-paper insulation has not aged.

2. The method for evaluating the aging of oil-paper insulation based on moisture migration according to claim 1, characterized in that, The oil-paper insulation samples were placed in an aging chamber for thermal aging tests of varying degrees, including: Based on the life loss of the oil-paper insulation sample, the 6-degree rule was used to estimate the aging time of the oil-paper insulation. Various aging times for the oil-paper insulation were designed at a set temperature. Moisture balance curves of the oil-paper insulation were obtained at both the unaged oil-paper insulation and each designed aging time, so as to correlate the aging time with the temperature.

3. The method for evaluating the aging of oil-paper insulation based on moisture migration according to claim 2, characterized in that, The formulas for designing the aging time of various types of oil-paper insulation are as follows: ； in, D i The design of the first i The aging time of the oil paper insulation. Y i This indicates that the transformer is at the set operating temperature. T i The specified number of years of operation under the given conditions T 0 indicates the set temperature for the aging test of the oil paper insulation sample.

4. The method for assessing the aging of oil-paper insulation based on moisture migration according to claim 1, characterized in that, Obtaining the oil temperature and water content in the transformer during operation includes: Temperature sensors and micro-water sensors are used to detect the oil temperature and water content in the transformer, respectively.

5. The method for assessing the aging of oil-paper insulation based on moisture migration according to claim 4, characterized in that, Two sets of temperature sensors and micro-water sensors are set up. One set is used to monitor the water content and oil temperature in the oil outlet pipe of the transformer tank in real time, and the other set is used to monitor the water content and oil temperature in the oil return pipe of the transformer tank in real time. The oil temperature and water content measured by the same type of sensors in the two sets within the set error range are selected, and the average value is taken to construct the relationship curve.

6. The method for assessing the aging of oil-paper insulation based on moisture migration according to any one of claims 1-5, characterized in that, The method further includes: When the real-time measured water content in the oil is greater than the standard value, it is considered that the oil-paper insulation of the transformer has begun to age, and the process of obtaining the corresponding degree of aging of the oil-paper insulation from the relationship curve based on the difference between the measured water content in the oil and the baseline value is initiated.

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