A method and system for evaluating the moisture content state of oil-paper insulated power equipment

Abstract

The embodiment of the present application provides a method and system for evaluating the moisture state of oil-paper insulated power equipment, aiming to solve the technical problems of low accuracy, difficult implementation on site and slow evaluation speed of the existing methods for evaluating the moisture state of oil-paper insulated power equipment. The method includes: grounding the high-voltage end of the oil-paper insulated power equipment for a preset duration, after dissipating the residual charges in the oil-paper insulated power equipment, connecting the high-voltage end of the dielectric loss meter to the high-voltage end of the oil-paper insulated power equipment; connecting the low-voltage end of the dielectric loss meter to the low-voltage end of the oil-paper insulated power equipment; adjusting the output voltage of the dielectric loss meter based on a preset step field strength value to determine the variable-voltage dielectric loss loop curve; determining the moisture state of the oil-paper insulated power equipment based on the slope information of the variable-voltage dielectric loss loop curve and the opening state in the low-voltage part. The present application realizes the accurate evaluation of the moisture state of the oil-paper insulated power equipment through the above method.

Description

Technical Field

[0001] The present application relates to the technical field of electrical equipment performance evaluation, and in particular, to a method and system for evaluating the moisture state of oil-paper insulated power equipment. Background Art

[0002] Oil-paper composite insulation is a classic insulation combination method and is widely used in power equipment. However, due to the loose and porous structure of insulating paper, it has strong water absorption. Moisture generated due to factors such as internal residue, external intrusion, and insulation aging significantly accelerates the deterioration process of insulating paper, greatly reducing the electrical performance of oil-paper insulation, thereby reducing the reliability of power equipment and threatening the safe operation of the power grid. Therefore, moisture evaluation of power equipment has important practical significance.

[0003] The on-site environment of substations is complex, and the power outage time window of power equipment is small, which limits the on-site application of existing moisture evaluation methods. Moisture is mainly distributed in insulating paper. The method of inferring the moisture condition of insulating paper by obtaining the water content in oil through oil chromatographic analysis has poor accuracy. Methods such as Karl Fischer titration method and near-infrared spectroscopy have high accuracy, but they require destructive sampling of power equipment and cannot be applied on-site. The power frequency dielectric loss data is small, and there are many influencing factors, so the effectiveness of moisture evaluation is poor. The frequency domain dielectric spectroscopy method takes a long time, the test voltage is low, and the high price also limits its wide application.

[0004] Considering the requirements for evaluating the moisture state of power equipment and on-site conditions, there is an urgent need for a method for evaluating the moisture state of oil-paper insulated power equipment at substations that is highly accurate, easy to implement on-site, and fast. Summary of the Invention

[0005] The embodiments of the present application provide a method and system for evaluating the moisture state of oil-paper insulated power equipment, which are used to solve the technical problems that the existing evaluation methods for the moisture state of oil-paper insulated power equipment have low accuracy, are not easy to implement on-site, and have a slow evaluation speed.

[0006] On the one hand, the embodiments of the present application provide a method for evaluating the moisture state of oil-paper insulated power equipment, which is characterized in that the high-voltage end of the oil-paper insulated power equipment is grounded for a preset duration. After the residual charges in the oil-paper insulated power equipment are dissipated, the high-voltage end of the dielectric loss tester is connected to the high-voltage end of the oil-paper insulated power equipment; the low-voltage end of the dielectric loss tester is connected to the low-voltage end of the oil-paper insulated power equipment; the output voltage of the dielectric loss tester is adjusted based on a preset step field strength value to determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment; the variable-voltage dielectric loss loop curve includes a dielectric loss rising curve and a dielectric loss falling curve; the moisture state of the oil-paper insulated power equipment is determined based on the slope information of the variable-voltage dielectric loss loop curve and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part.

[0007] In the embodiment of the present application, by using a dielectric loss instrument to measure the variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment, after the measurement of the variable-voltage dielectric loss loop curve is completed, according to the principle that moisture can change the charge injection barrier of the oil-paper insulated power equipment under high field strength, thereby changing the characteristics of the variable-voltage dielectric loss loop curve, the moisture condition of the oil-paper insulated power equipment is judged. By using the above method provided by the embodiment of the present application to judge the moisture state of the oil-paper insulated power equipment, not only can an accurate evaluation result be obtained for the evaluation of the moisture state of the oil-paper insulated power equipment, but also because the operation process is simple, it is easy to implement on-site and the evaluation is fast.

[0008] In one implementation manner of the present application, based on a preset step field strength value and the size of the oil-paper insulated power equipment, the output voltage of the dielectric loss instrument is adjusted to determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment, which specifically includes: determining the step voltage value of the dielectric loss instrument based on the preset step field strength value and the size of the oil-paper insulated power equipment; adjusting the output voltage of the dielectric loss instrument based on the step voltage value of the dielectric loss instrument, so that the dielectric loss instrument obtains the dielectric loss values corresponding to the oil-paper insulated power equipment at different field strength values; determining the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment based on the dielectric loss values corresponding to the oil-paper insulated power equipment at different field strength values.

[0009] In one implementation manner of the present application, the method further includes: determining that the starting output voltage value of the dielectric loss instrument is greater than a preset threshold based on a preset starting field strength value and the size of the oil-paper insulated power equipment, so as to determine that when the output voltage of the dielectric loss instrument is the starting voltage value, there are carriers injected from the electrode into the dielectric body of the oil-paper insulated power equipment.

[0010] In one implementation manner of the present application, the formation of the variable-voltage dielectric loss loop curve is because when the oil-paper insulated power equipment is under high voltage, the carriers injected from the electrode cannot dissipate directly, resulting in the dielectric loss value corresponding to the voltage-drop dielectric loss curve being higher than the dielectric loss value corresponding to the voltage-rise dielectric loss curve at the same field strength value.

[0011] In one implementation manner of the present application, determining the step voltage value of the dielectric loss instrument based on a preset step field strength value and the size of the oil-paper insulated power equipment specifically includes: substituting the preset step field strength value into the following linear relational expression to determine the step voltage value of the dielectric loss instrument;

[0012] y = a * x + b

[0013] where y is the step voltage value of the dielectric loss instrument, x is the preset step field strength value, and a and b are fixed parameters; among them, the fixed parameters a and b are determined by the size of the oil-paper insulated power equipment.

[0014] In one implementation of the present application, after adjusting the output voltage of the dielectric loss instrument based on the step voltage value of the dielectric loss instrument, the method further includes: determining the dielectric loss curve of the oil-paper insulated power equipment within a second preset duration at the field strength value corresponding to the output voltage based on the output voltage of the dielectric loss instrument; and determining the dielectric loss value of the oil-paper insulated power equipment at the field strength value corresponding to the output voltage based on the dielectric loss curve within the second preset duration.

[0015] In one implementation of the present application, the dielectric loss value is determined by the following formula:

[0016]

[0017] where q is the charge amount of the carrier, N is the total number of carriers, C p is the equivalent capacitance value of the cellulose pores, d is the pore diameter of the cellulose pores, ω is the angular frequency of the excitation voltage, m is a constant determined by the carrier properties, U c is the saturation voltage of the carrier movement, and U is the output voltage of the dielectric loss instrument.

[0018] In one implementation of the present application, based on the overall slope of the variable-voltage dielectric loss loop curve and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part, the moisture state of the oil-paper insulated power equipment is determined, which specifically includes: when the slope information of the variable-voltage dielectric loss loop curve is less than the preset threshold and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part is closed, it is determined that the oil-paper insulated power equipment is in an unmoistened state; when the slope information of the variable-voltage dielectric loss loop curve is less than the preset threshold and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part is open, it is determined that the oil-paper insulated power equipment is in a generally moistened state; when the slope information of the variable-voltage dielectric loss loop curve is greater than the preset threshold and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part is open, it is determined that the oil-paper insulated power equipment is in a severely moistened state.

[0019] In one implementation of the present application, the slope information of the variable-voltage dielectric loss loop curve is the slope of the line segment between the dielectric loss value corresponding to the first preset field strength value and the dielectric loss value corresponding to the second preset field strength value in the dielectric loss rising voltage curve; where the first preset field strength value is the field strength value generated by the oil-paper insulated power equipment at the initial output voltage of the dielectric loss instrument plus a step voltage value, and the second preset field strength value is the field strength value generated by the oil-paper insulated power equipment at the highest output voltage of the dielectric loss instrument minus a step voltage value.

[0020] On the other hand, the embodiment of the present application also provides a moisture ingress state evaluation system for an oil-paper insulated power equipment, which is characterized in that the equipment includes: a dielectric loss tester and a processor; the high-voltage end of the dielectric loss tester is connected to the high-voltage end of the oil-paper insulated power equipment; the low-voltage end of the dielectric loss tester is connected to the low-voltage end of the oil-paper insulated power equipment; the dielectric loss tester is configured to adjust the output voltage based on a preset step field strength value to determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment; the variable-voltage dielectric loss loop curve includes a dielectric loss step-up curve and a dielectric loss step-down curve; the processor is configured to determine the moisture ingress state of the oil-paper insulated power equipment based on the slope information of the variable-voltage dielectric loss loop curve and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0022] Figure 1 is a flowchart of a method for evaluating the moisture ingress state of an oil-paper insulated power equipment provided by an embodiment of the present application;

[0023] Figure 2 is a variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in an unmoistened state provided by an embodiment of the present application;

[0024] Figure 3 is a variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in a moistened state provided by an embodiment of the present application;

[0025] Figure 4 is a variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in a severely moistened state provided by an embodiment of the present application;

[0026] Figure 5 is a schematic structural diagram of a moisture ingress state evaluation system for an oil-paper insulated power equipment provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments in the present application belong to the scope of protection of the present application.

[0028] During the manufacturing process and operation of oil-paper insulated power equipment, due to defects in the manufacturing process or the influence of the environment on the equipment, the water content inside the equipment may be higher than the normal level. Especially when the equipment is in a humid environment with high humidity for a long time, the equipment is prone to moisture absorption, resulting in an increase in internal moisture, which endangers the operation of the equipment and even causes economic losses to the power grid operation, leading to safety accidents. Therefore, it is essential to evaluate the moisture state of oil-paper insulated power equipment.

[0029] Existing methods for judging the moisture state of oil-paper insulated equipment based on dielectric response have problems such as long test time, low test voltage, strict requirements for the equipment under test, and low test accuracy. For example, in the invention patent application with the application number CN109030954A, although it uses a method of analyzing the loop curve and has increased the output voltage range of the test power supply compared to ordinary dielectric responses, it still belongs to low-voltage testing. Therefore, there are still large errors in analyzing the water content through the obtained dielectric loss curve. In addition, the test method in CN109030954A is only applicable to oil-paper insulated equipment with only the defect of excessive water content and no aging or partial discharge defects, making the test range extremely narrow and the applicability rate low.

[0030] The embodiments of the present application provide a method and device for evaluating the moisture state of oil-paper insulated power equipment, aiming to solve the technical problems of low accuracy, difficulty in on-site implementation, and slow evaluation speed of the existing methods for evaluating the moisture state of oil-paper insulated power equipment.

[0031] The technical solutions proposed in the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0032] Figure 1 It is a flowchart of a method for evaluating the moisture state of an oil-paper insulated power equipment provided by an embodiment of the present application. As Figure 1 shown, a method for evaluating the moisture state of an oil-paper insulated power equipment provided by an embodiment of the present application specifically includes the following steps:

[0033] Step 101: Ground the high-voltage end of the oil-paper insulated power equipment for a preset duration. After the residual charges in the oil-paper insulated power equipment dissipate, connect the high-voltage end of the dielectric loss tester to the high-voltage end of the oil-paper insulated power equipment; connect the low-voltage end of the dielectric loss tester to the low-voltage end of the oil-paper insulated power equipment.

[0034] Since oil-paper insulated power equipment may be affected singly or interactively by various factors such as magnetic field, static electricity, air humidity, and usage conditions in normal placement or working environments, residual charges exist in the oil-paper insulation within the oil-paper insulated power equipment. A method for evaluating the moisture state of an oil-paper insulated power equipment provided by an embodiment of this application is based on the principle that moisture changes the charge injection barrier, with a high test voltage, so that more injected carriers are generated, thereby amplifying the way the medium changes the characteristics of the dielectric loss loop curve. Therefore, before testing the oil-paper insulated power equipment, the high-voltage end of the oil-paper insulated power equipment needs to be grounded to dissipate the residual charges in the oil-paper insulated power equipment, ensuring the accuracy of the results of the measured dielectric loss loop curve.

[0035] To ensure complete dissipation of the residual charges in the oil-paper insulated power equipment, the grounding time of the high-voltage end of the oil-paper insulated power equipment should be greater than a preset duration. In an embodiment of this application, the preset duration can be set to ten minutes. It should be noted that the preset duration set by the embodiments of this application does not constitute a limitation on the preset duration, and the preset duration can be determined according to specific usage scenarios.

[0036] After determining that the grounding time of the high-voltage end of the oil-paper insulated power equipment should be greater than the preset duration, disconnect the grounding. Then connect the high-voltage end of the dielectric loss tester to the high-voltage end of the oil-paper insulated power equipment, and connect the low-voltage end of the dielectric loss tester to the low-voltage end of the oil-paper insulated power equipment.

[0037] Step 102: The dielectric loss tester adjusts the output voltage based on a preset step field strength value to determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment.

[0038] In an embodiment of this application, the variable-voltage dielectric loss loop curve includes a dielectric loss rising curve and a dielectric loss falling curve. The formation of the dielectric loss rising curve and the dielectric loss falling curve is because in the case of high voltage in the oil-paper insulated power equipment, the carriers injected by the electrodes cannot dissipate directly, resulting in the dielectric loss value corresponding to the falling dielectric loss curve being higher than the dielectric loss value corresponding to the rising dielectric loss curve at the same field strength value.

[0039] Since the electric field formed in the oil-paper insulated power equipment will cause the carriers to be injected from the electrode into the insulating dielectric body in the form of Schottky injection only after the output voltage of the dielectric loss meter is greater than a certain preset threshold, therefore, before measuring the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment, the starting voltage value should first be determined according to the preset starting field strength value. In addition, when measuring the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment, the electric field formed in the oil-paper insulated power equipment should also be changed according to a fixed step value. Therefore, before measuring the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment, the step voltage value of the dielectric loss meter corresponding to the preset step field strength value should also be determined.

[0040] In one embodiment of the present application, it is experimentally verified that when the electric field strength formed by the AC voltage output by the dielectric loss meter is greater than 0.5 kV / mm, there are carriers injected from the electrode into the dielectric body of the oil-paper insulated power equipment. Therefore, the preset starting field strength value can be set to 0.5 kV / mm. It should be noted that the preset starting field strength value of the embodiment of the present application does not constitute a limitation on the preset starting field strength value. The preset starting field strength value can be greater than 0.5 kV / mm, which is specifically determined according to the voltage range of the dielectric loss meter used.

[0041] It can be understood that the test field strength formed in the oil-paper insulated power equipment is determined by the output voltage of the dielectric loss meter and the size of the oil-paper insulated power equipment. Therefore, after determining the preset starting field strength value and the preset step field strength value, the preset step field strength value can be brought into the following linear relationship to determine the starting voltage value and step voltage value of the dielectric loss meter;

[0042] y=a*x+b

[0043] Where y is the step voltage value of the dielectric loss meter, x is the preset step field strength value, and a and b are fixed parameters; where fixed parameters a and b are determined by the size of the oil-paper insulated power equipment. For example, if the oil-paper insulation thickness of the power equipment to be tested is 10mm, the preset starting field strength value is 0.5kV / mm, the preset step field strength value is 0.5kV / mm, and the field strength range to be tested is 0.5kV / mm~5kV / mm, then the output AC voltage range of the dielectric loss meter is 100V~1000V.

[0044] In one embodiment of the present application, after determining the starting voltage value and the step voltage value, the dielectric loss meter is run, and the voltage is output according to the starting voltage value and the step voltage value, so that the dielectric loss meter obtains the dielectric loss value corresponding to the oil-paper insulated power equipment under different field strength values.

[0045] It should be noted that the measurement process should be carried out in the way of first boosting the voltage and then reducing the voltage according to the step voltage value. In addition, to avoid the interference of the power frequency electric field generated by the oil-paper insulated power equipment to be measured, the output voltage frequency of the dielectric loss tester can be selected as 45Hz or 55Hz.

[0046] It should also be noted that after each adjustment of the output voltage of the dielectric loss tester, in order to avoid the influence of the instantaneous voltage boost or instantaneous voltage reduction of the dielectric loss tester on the measurement result of the dielectric loss value of the oil-paper insulated power equipment at the adjusted output voltage, the dielectric loss curve within the second preset duration after applying the voltage for a period of time should be selected as the curve for analyzing the dielectric loss value at the current output voltage. For example, select the dielectric loss curve from the second second to the thirty-first second after the adjustment of the output voltage is completed as the analysis curve of the dielectric loss value at the current output voltage.

[0047] In an embodiment of the present application, the method for determining the dielectric loss value of the oil-paper insulated power equipment based on the dielectric loss curve within the second preset duration can be to select the dielectric loss value at the last moment within the second preset duration as the dielectric loss value of the oil-paper insulated power equipment at the current output voltage, or to take the average value of the amplitude of the dielectric loss curve within the second preset duration as the dielectric loss value of the oil-paper insulated power equipment at the current output voltage. The present application does not make a limit here, and different methods for determining the dielectric loss value from the dielectric loss curve within the second preset duration can be selected according to the specific measurement environment.

[0048] In an embodiment of the present application, the basic principle for the dielectric loss tester to determine the dielectric loss value is as follows:

[0049] Under an alternating current voltage, the dielectric loss includes polarization loss and conductance loss. The polarization loss caused by dipoles is independent of the voltage, while the conductance loss is greatly affected by the voltage. When the output voltage makes the formed electric field strength reach the critical value, carriers are injected into the insulating medium from the electrode in the form of Schottky injection, and the relationship between the current density and the electric field strength is shown by the following formula:

[0050] j = AT 2 exp[(β sc hE 1 / 2 -φ) / kT]

[0051] β sc h = (e 3 / 4πε0ε r ) 1 / 2

[0052] where j is the current density, A is the emission constant, T is the Kelvin temperature, E is the electric field, where φ is the barrier height, β sch is the Schottky coefficient, k is the Boltzmann constant, ε0 is the vacuum permittivity, and ε r is the relative permittivity.

[0053] From the perspective of the microscopic mechanism of current, the current density can be expressed as follows:

[0054] j = nqv

[0055] where n is the number of carriers per unit volume in the medium, q is the electric charge carried by the carrier, and v is the movement speed of the carrier.

[0056] Therefore, the expression for the dielectric loss value based on the microscopic mechanism of carrier movement is as follows:

[0057]

[0058] where q is the electric charge of the carrier, N is the total number of carriers, C p is the equivalent capacitance value of the cellulose pores, d is the pore diameter of the cellulose pores, ω is the angular frequency of the excitation voltage, m is a constant determined by the carrier properties, U c is the saturation voltage of the carrier movement, and U is the output voltage of the dielectric loss instrument.

[0059] After determining the dielectric loss values corresponding to different field strength values of the oil-paper insulated power equipment, based on the dielectric loss values corresponding to different field strength values, determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment, as Figure 2 , Figure 3 , Figure 4 shown.

[0060] Step 103: The processor determines the moisture state of the oil-paper insulated power equipment based on the slope information of the variable-voltage dielectric loss loop curve and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part.

[0061] In an embodiment of the present application, to ensure the accuracy of the moisture state assessment, the slope information of the variable-voltage dielectric loss loop curve is calculated by taking the average. Specifically, first calculate the slope between all adjacent two points in the variable-voltage dielectric loss loop curve. Taking the Figure 4 shown variable-voltage dielectric loss loop curve as an example, calculate the slopes between 18 adjacent two points in the Figure 4 step-up curve and the step-down curve, and obtain 18 slope values with a calculation interval of 0.5 kV / mm. Figure 4 Taking the variable-voltage dielectric loss loop curve shown in Figure 4 as an example, after calculating the slopes between 18 adjacent two points in the variable-voltage dielectric loss loop curve, average the 18 slope values and determine that the average value is the Figure 4 slope information of the variable-voltage dielectric loss loop curve shown in

[0062] When the slope information of the variable-voltage dielectric loss loop curve is less than the preset threshold and the opening state in the low-voltage part is closed, it is determined that the oil-paper insulated power equipment is not damp. Figure 2 The variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in the non-damp state provided by an embodiment of the present application is as Figure 2 shown. The water content in the oil-paper insulated power equipment sample is 0.74%, the sample is in a dry state, the rising and falling dielectric loss curves are relatively flat as a whole, the two curves coincide at low voltage, and the overall shape is a closed loop. When the slope information of the variable-voltage dielectric loss loop curve is less than the preset threshold and the opening state in the low-voltage part is open, it is determined that the oil-paper insulated power equipment is generally damp. Figure 3 The variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in the generally damp state provided by an embodiment of the present application is shown in Figure 3. When the moisture content in the oil-paper insulated power equipment sample increases to 2.97%, the rising and falling dielectric loss curves are still relatively flat as a whole, the rising and falling curves do not coincide in the low-voltage part, and the overall shape is an open loop. When the slope information of the variable-voltage dielectric loss loop curve is greater than the preset threshold and the opening state in the low-voltage part is open, it is determined that the oil-paper insulated power equipment is severely damp. Figure 4 The variable-voltage dielectric loss loop curve of an oil-paper insulated power equipment in the severely damp state provided by an embodiment of the present application is as Figure 4 shown. When the water content in the oil-paper insulated power equipment sample is 5.62%, the slopes of the rising and falling dielectric loss curves increase significantly, the area between the rising and falling curves is larger, and the overall open-loop shape feature is more prominent. In an embodiment of the present application, the preset threshold can be set to 1 / 32.

[0063] Based on the same inventive concept, an embodiment of the present application also provides a damp state evaluation system for an oil-paper insulated power equipment, and its structural schematic diagram is as Figure 5 shown.

[0064] Figure 5 The structural schematic diagram of a damp state evaluation system for an oil-paper insulated power equipment provided by an embodiment of the present application. As Figure 5 shown, a damp state evaluation system 500 for an oil-paper insulated power equipment provided by an embodiment of the present application includes: a dielectric loss meter 501 and a processor 502.

[0065] Those skilled in the art can understand that Figure 5 the structural schematic diagram of the damp state evaluation system of the oil-paper insulated power equipment shown does not constitute a limitation on the damp state evaluation system of the oil-paper insulated power equipment. In fact, the damp state evaluation system of the oil-paper insulated power equipment can include more than Figure 5More or fewer components as shown, or combining certain components, or arranging different components.

[0066] In one embodiment of the present application, the high-voltage end of the dielectric loss meter 501 is connected to the high-voltage end of the oil-paper insulated power equipment; the low-voltage end of the dielectric loss meter 501 is connected to the low-voltage end of the oil-paper insulated power equipment; the dielectric loss meter 501 is used to adjust the output voltage based on a preset step field strength value to determine the variable-voltage dielectric loss loop curve of the oil-paper insulated power equipment; the variable-voltage dielectric loss loop curve includes a dielectric loss boost curve and a dielectric loss step-down curve; the processor 502 is used to determine the moisture ingress state of the oil-paper insulated power equipment based on the slope information of the variable-voltage dielectric loss loop curve and the opening state of the variable-voltage dielectric loss loop curve in the low-voltage part.

[0067] Each embodiment in the present application is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the key points of each embodiment are the differences from other embodiments. In particular, for the device embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiments.

[0068] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, commodity or device. Without further limitation, the element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, commodity or device including the said element.

[0069] The above description is only for the embodiments of the present application and is not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for evaluating the moisture content state of an oil-paper insulated power equipment, characterized in that the high voltage end of the oil-paper insulated power equipment is grounded for a preset duration. After the residual charges in the oil-paper insulated power equipment are dissipated, the high voltage end of the dielectric loss tester is connected to the high voltage end of the oil-paper insulated power equipment; the low voltage end of the dielectric loss tester is connected to the low voltage end of the oil-paper insulated power equipment; adjust the output voltage of the dielectric loss tester based on a preset step field strength value to determine the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment; the variable voltage dielectric loss loop curve includes a dielectric loss rising curve and a dielectric loss falling curve; determine the moisture content state of the oil-paper insulated power equipment based on the slope information of the variable voltage dielectric loss loop curve and the opening state of the variable voltage dielectric loss loop curve in the low voltage part.

2. The moisture state evaluation method of an oil-paper insulated power equipment according to claim 1, wherein, Adjust the output voltage of the dielectric loss tester based on a preset step field strength value to determine the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment, specifically including: determine the step voltage value of the dielectric loss tester based on the preset step field strength value and the size of the oil-paper insulated power equipment; adjust the output voltage of the dielectric loss tester based on the step voltage value of the dielectric loss tester, so that the dielectric loss tester obtains the dielectric loss values corresponding to different field strength values of the oil-paper insulated power equipment; determine the variable voltage dielectric loss loop curve of the oil-paper insulated power equipment based on the dielectric loss values corresponding to different field strength values of the oil-paper insulated power equipment.

3. A method for evaluating the moisture state of an oil-paper insulated power equipment according to claim 2, characterized in that, The method further includes: determine that the starting output voltage value of the dielectric loss tester is greater than a preset threshold based on a preset starting field strength value and the size of the oil-paper insulated power equipment, so as to determine that when the output voltage of the dielectric loss tester is the starting voltage value, there are carriers injected from the electrode into the dielectric body of the oil-paper insulated power equipment.

4. The method for evaluating the moisture content state of an oil-paper insulated power equipment according to claim 2, characterized in that the formation of the variable voltage dielectric loss loop curve is due to the fact that when the oil-paper insulated power equipment is under high voltage, the carriers injected from the electrode cannot be directly dissipated, resulting in the dielectric loss value corresponding to the dielectric loss falling curve being higher than the dielectric loss value corresponding to the dielectric loss rising curve at the same field strength value.

5. The moisture state evaluation method of an oil-paper insulated power equipment according to claim 2, characterized in that, Determine the step voltage value of the dielectric loss tester based on the preset step field strength value and the size of the oil-paper insulated power equipment, specifically including: substitute the preset step field strength value into the following linear relationship formula to determine the step voltage value of the dielectric loss tester; y = a * x + b where y is the step voltage value of the dielectric loss tester, x is the preset step field strength value, and a and b are fixed parameters; among them, the fixed parameters a and b are determined by the size of the oil-paper insulated power equipment.

6. The method for evaluating the moisture state of an oil-paper insulated power equipment according to claim 2, wherein, After adjusting the output voltage of the dielectric loss tester based on the step voltage value of the dielectric loss tester, the method further includes: determine the dielectric loss curve of the oil-paper insulated power equipment within a second preset duration at the field strength value corresponding to the output voltage of the dielectric loss tester based on the output voltage of the dielectric loss tester; determine the dielectric loss value of the oil-paper insulated power equipment at the field strength value corresponding to the output voltage of the dielectric loss tester based on the dielectric loss curve within the second preset duration.

7. The moisture state evaluation method of an oil-paper insulated power equipment according to claim 2, characterized in that, The dielectric loss value is determined by the following formula: Among them, q is the charge of the carrier, N is the total number of carriers, and C p is the equivalent capacitance value of the cellulose pores, d is the pore diameter of the cellulose pores, ω is the angular frequency of the excitation voltage, m is a constant determined by the carrier properties, and I c is the saturation voltage of the carrier movement, and U is the output voltage of the dielectric loss meter.

8. A method for evaluating the moisture state of an oil-paper insulated power equipment according to claim 1, characterized in that, Determine the moisture content state of the oil-paper insulated power equipment based on the overall slope of the variable-voltage dissipation factor loop curve and the opening state of the variable-voltage dissipation factor loop curve in the low-voltage part, specifically including: When the slope information of the variable-voltage dissipation factor loop curve is less than a preset threshold and the opening state of the variable-voltage dissipation factor loop curve in the low-voltage part is closed, determine that the oil-paper insulated power equipment is in an unmoistened state; When the slope information of the variable-voltage dissipation factor loop curve is less than a preset threshold and the opening state of the variable-voltage dissipation factor loop curve in the low-voltage part is open, determine that the oil-paper insulated power equipment is in a general moisture content state; When the slope information of the variable-voltage dissipation factor loop curve is greater than a preset threshold and the opening state of the variable-voltage dissipation factor loop curve in the low-voltage part is open, determine that the oil-paper insulated power equipment is in a severely moistened state.

9. The method for evaluating the moisture content state of an oil-paper insulated power equipment according to claim 8, wherein the slope information of the variable-voltage dissipation factor loop curve is the slope of the line segment between the dissipation factor value corresponding to the first preset field strength value and the dissipation factor value corresponding to the second preset field strength value in the dissipation factor boosting curve; wherein, the first preset field strength value is the field strength value generated by the oil-paper insulated power equipment when the starting output voltage of the dissipation factor measuring instrument is added with a step voltage value, and the second preset field strength value is the field strength value generated by the oil-paper insulated power equipment when the highest output voltage of the dissipation factor measuring instrument is subtracted by a step voltage value.

10. A moisture state evaluation system for oil-paper insulated power equipment, characterized in that, The system includes: a dissipation factor measuring instrument, a processor; The high-voltage end of the dissipation factor measuring instrument is connected to the high-voltage end of the oil-paper insulated power equipment; the low-voltage end of the dissipation factor measuring instrument is connected to the low-voltage end of the oil-paper insulated power equipment; The dissipation factor measuring instrument is used to adjust the output voltage based on a preset step field strength value to determine the variable-voltage dissipation factor loop curve of the oil-paper insulated power equipment; the variable-voltage dissipation factor loop curve includes a dissipation factor boosting curve and a dissipation factor lowering curve; The processor is used to determine the moisture content state of the oil-paper insulated power equipment based on the slope information of the variable-voltage dissipation factor loop curve and the opening state of the variable-voltage dissipation factor loop curve in the low-voltage part.

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