Insulation resistance estimation method for power apparatus

Abstract

To provide a method for estimating insulation resistance of a power apparatus in an uninterruptible state without using a sound wave signal.SOLUTION: According to the present invention, an insulation resistance estimation method for a power apparatus includes a step (a) for acquiring actual measurement target data being an actual measurement value of target data of either a ground current value under a live-line state of a target power apparatus being an epoxy molded power apparatus of a measurement target or electromagnetic wave intensity radiated from the target power apparatus in a live-line state, a step (b) for calculating an actual measurement steepness value corresponding to rising steepness of the actual measurement target data, a step (c) for reading correlation information between steepness of target data recorded in advance and a surface insulation resistance value of the epoxy molded power apparatus, a step (d) for deriving a surface insulation resistance value corresponding to the actual measurement steepness value on the basis of the correlation information, and a step (e) for determining an estimation value of surface insulation resistance of the target power apparatus on the basis of the surface insulation resistance value derived in the step (d).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the insulation resistance of electric power equipment, and more particularly to a method for estimating the insulation resistance of epoxy-molded electric power equipment. [Background technology]

[0002] For substation equipment such as transformers and high-voltage panels, it is important to predict the end of their service life and prevent accidents before they occur. For this reason, preventive maintenance has been proposed, which focuses on precursory phenomena that lead to deterioration and accidents in substation equipment and takes measures in advance.

[0003] One known method for determining the progression of deterioration of electric power equipment is to measure insulation resistance. When dust or ions adhere to the surface of electric power equipment, the resistance decreases, making it more susceptible to creeping discharge. In addition, when defects such as voids exist in the insulation of electric power equipment, partial discharge occurs, and as this partial discharge progresses, the insulation resistance decreases.

[0004] The most common method for measuring the insulation resistance of electric power equipment is to use an insulation resistance tester, also known as a megger, while the equipment is in a power outage state. An insulation resistance tester generates a high voltage internally, applies this voltage to the equipment being measured, detects the current flowing, and calculates the resistance value based on Ohm's law.

[0005] However, putting the target device into a power outage state in order to measure the insulation resistance of the target device is a cumbersome procedure.

[0006] For example, Patent Document 1 below proposes a method for estimating the insulation resistance of a power device in an uninterruptible state. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5802991 Summary of the Invention [Problem to be solved by the invention]

[0008] The method described in Patent Document 1 involves detecting the discharge sound of an insulator using a microphone or the like, subjecting the discharge sound to a fast Fourier transform to extract frequency components with high discharge sound intensity, and estimating the surface insulation resistance based on information related to the extracted frequencies.

[0009] However, because the above method is based on sound wave signals detected by a microphone, it is prone to picking up noise caused by noise, especially in areas with heavy traffic near the power equipment. In particular, the document estimates insulation resistance based on the intensity of sound signals in the 10-15 kHz frequency band, but signals in this frequency band can also be included in ambient noise. It is also known that power conditioners installed in solar power generation systems tend to emit signals in the same frequency band when in operation. Therefore, even when estimating the insulation resistance of power equipment installed near a solar power generation system, the accuracy of the estimation may be extremely low.

[0010] In view of the above-mentioned problems, an object of the present invention is to provide a method for estimating the insulation resistance of a power device in an uninterruptible state without using a sound wave signal. [Means for solving the problem]

[0011] The insulation resistance estimation method for electric power equipment according to the present invention includes: A step (a) of obtaining measured target data, which is a measured value of either a ground current value in a live-line state of a target electric power device that is an epoxy-molded electric power device to be measured, or an electromagnetic wave intensity radiated from the target electric power device in a live-line state; (b) analyzing the change in the actual measurement data to calculate an actual measurement gradient value corresponding to the gradient of the rise of the actual measurement data; a step (c) of reading out pre-recorded correlation information between the steepness of the target data and the surface insulation resistance value of a sample whose main material is epoxy resin; (d) deriving the surface insulation resistance value corresponding to the measured gradient value based on the correlation information and the measured gradient value; and (e) determining an estimated value of the surface insulation resistance of the target electric power device based on the surface insulation resistance value derived in (d).

[0012] As a result of extensive research, the present inventors have newly discovered that there is a high correlation between the rising edge of the ground current generated in an epoxy resin component (hereinafter referred to as a "sample") when a high voltage is applied and the surface insulation resistance of the sample, and between the rising edge of the electromagnetic wave intensity radiated from the sample when a high voltage is applied and the surface insulation resistance of the sample. This fact was previously unknown and is a new discovery by the present inventors. Note that "a sample whose main material is epoxy resin" means that 80% or more of the material constituting the sample is epoxy resin, but typically 95% or more of the material is epoxy resin.

[0013] For example, by measuring the surface insulation resistance of multiple samples made primarily of epoxy resin and having different surface insulation resistances, and measuring the rising steepness of the ground current or the rising steepness of the electromagnetic wave intensity for each sample, the correlation between the two can be recorded. In the actual estimation process, an operator visits the installation location of the actual electric power equipment to be measured (target electric power equipment) and measures the ground current or the electromagnetic wave intensity for the live target electric power equipment. Based on the temporal changes in the measured data (target electric power data), the rising steepness of the target electric power data (measured steepness value) is derived, and the surface insulation resistance of the target electric power equipment is estimated based on the derived measured steepness value and the previously recorded correlation.

[0014] Epoxy resin is a material with extremely high insulating properties. Deterioration of epoxy-molded power equipment occurs from the surface of the equipment, so the surface resistance of epoxy-molded power equipment decreases, while the internal resistance of the equipment often remains relatively high. Therefore, by obtaining an estimate of the surface resistance (surface insulation resistance) of epoxy-molded power equipment, the degree of deterioration of the epoxy-molded power equipment can be understood.

[0015] Steps (b), (c), and (d) can all be performed by computer-based computation. In other words, the minimum required work for an operator is to install a current sensor for measuring the ground current of the epoxy-molded power equipment or an antenna for receiving electromagnetic waves emitted from the epoxy-molded power equipment in a predetermined location and connect the current sensor or antenna to a computer. This simple procedure allows for the estimation of the insulation resistance of the epoxy-molded power equipment, more specifically, the estimated surface insulation resistance. Furthermore, because this method does not use acoustic signals, the estimated surface insulation resistance can be derived with relatively high accuracy regardless of the location of the epoxy-molded power equipment.

[0016] When receiving electromagnetic waves emitted from an epoxy-molded power device, an antenna is installed near the epoxy-molded power device, preferably within 3 m, more preferably within 2 m, and most preferably within 1 m from the outer surface of the epoxy-molded power device.

[0017] In step (e), the surface insulation resistance value corresponding to the measured gradient value derived in step (d) may itself be used as the estimated value of the surface insulation resistance of the target electric power equipment. However, the present invention does not exclude the case where an approximation value of the surface insulation resistance value corresponding to the measured gradient value derived in step (d) is used as the estimated value of the surface insulation resistance of the target electric power equipment. The "approximation value" here means a value within an error range of ±10% of the surface insulation resistance value corresponding to the measured gradient value derived in step (d).

[0018] As an example of the current sensor, a clamp-type current sensor can be used.

[0019] The step (b) a step (b1) of extracting a plurality of maximum values ​​that satisfy a predetermined extraction condition from the time-varying actual measurement target data obtained in the step (a); a step (b2) of determining a reference maximum value that appears earliest among the plurality of maximum values ​​obtained in the step (b1); (b3) extracting, immediately before the occurrence timing of the reference maximum value, a first reference time when the measured object data indicates a first reference value, which is a value of a first predetermined ratio set to any ratio within a range of 5% to 15% of the reference maximum value, and a second reference time when the measured object data indicates a second reference value, which is a second predetermined ratio set to any ratio within a range of 85% to 95% of the reference maximum value; The method may further include a step (b4) of calculating the measured gradient value based on the elapsed time from the first reference timing to the second reference timing and the difference between the first reference value and the second reference value.

[0020] The target electric power equipment may be, for example, a transformer, a switch, a circuit breaker, or a bushing. [Effects of the Invention]

[0021] According to the method of the present invention, it is possible to estimate the insulation resistance of a power device in an uninterruptible state without using a sound wave signal. [Brief explanation of the drawings]

[0022] [Figure 1] 3 is a flowchart schematically illustrating an example of a procedure of an insulation resistance estimation method according to the first embodiment. [Figure 2] 1 is a diagram schematically illustrating an implementation of an insulation resistance estimation method according to a first embodiment. [Figure 3]3 is a functional block diagram schematically showing the configuration of a processing unit 20 in FIG. 2. FIG. [Figure 4] 3 is a diagram showing an example of data measured by a current sensor 12 in FIG. 2. [Figure 5] This graph clearly shows the maximum points P1 to P6 in comparison with the graph in FIG. [Figure 6] 6 is a graph in which the maximum point P1 corresponding to the reference maximum value is clearly indicated from the graph of FIG. 5. [Figure 7] 7 is a diagram showing an example of a method for extracting a first reference timing T1 and a second reference timing T2 using a graph in which the vicinity of a maximum point P1 in the graph of FIG. 6 is enlarged. [Figure 8] 10 is a graph showing an example of the correlation between the steepness of the ground current value and the surface insulation resistance value of a sample made of epoxy resin. [Figure 9] 1 is a diagram schematically illustrating the configuration of an experimental system. [Figure 10] 10 is an enlarged schematic view of a portion of FIG. 9. [Figure 11] 1 is a diagram for explaining a method for measuring the surface insulation resistance of sample 35. [Figure 12] 1 is a diagram for explaining a method for measuring the surface insulation resistance of sample 35. [Figure 13] 10 is a flowchart schematically illustrating an example of a procedure of an insulation resistance estimation method according to a second embodiment. [Figure 14] 10 is a diagram schematically illustrating an example of an insulation resistance estimation method according to a second embodiment. [Figure 15] 1 is a graph showing an example of the correlation between the steepness of electromagnetic wave intensity and the surface insulation resistance value of a sample made of epoxy resin. [Figure 16] 1 is a diagram schematically illustrating the configuration of an experimental system. DETAILED DESCRIPTION OF THE INVENTION

[0023] An embodiment of a method for estimating insulation resistance of electric power equipment (hereinafter abbreviated as "insulation resistance estimation method") according to the present invention will be described with reference to the drawings as appropriate. Note that the dimensional ratios in the drawings do not necessarily coincide with the actual dimensional ratios.

[0024] The electric power equipment to which the insulation resistance estimation method of the present invention is applicable is epoxy-molded electric power equipment. Epoxy-molded electric power equipment refers to electric power equipment containing an insulator whose main component is epoxy resin. Epoxy resin has a dielectric breakdown voltage approximately 10 times that of air and exhibits high withstand voltage even at high voltages. Furthermore, since epoxy-molded electric power equipment does not use insulating oil, it has the property of extremely low risk of fire and other hazards. Examples of such electric power equipment include transformers, switches, circuit breakers, and bushings.

[0025] [First embodiment] A first embodiment of an insulation resistance estimation method according to the present invention will be described with reference to the drawings. Fig. 1 is a flowchart schematically showing an example of the procedure of the insulation resistance estimation method of this embodiment. In the following description, reference will be made to the symbols in the flowchart shown in Fig. 1 as appropriate.

[0026] Fig. 2 is a diagram schematically illustrating an example of an embodiment of the insulation resistance estimation method of the present embodiment. In the example shown in Fig. 2, the target electric power device for which insulation resistance is to be estimated is a transformer 5 in a cubicle 3.

[0027] (Step #1) Under a live line condition (uninterruptible power condition), the ground current of the target electric power equipment, a transformer 5, is measured. In the example of FIG. 2, a current sensor 12 is attached to a ground wire 10. The current sensor 12 is connected to a processing unit 20 via a signal line 14, and data measured by the current sensor 12 is input to the processing unit 20. The signal line 14 is, for example, a coaxial cable.

[0028] In the example of Figure 2, for ease of understanding, the current sensor 12 is shown attached to the ground wire 10 outside the cubicle 3, but the current sensor 12 may also be attached to the ground wire 10 inside the cubicle 3. As the current sensor 12, for example, a general-purpose current sensor such as a CT clamp type sensor can be used.

[0029] 3 is a functional block diagram schematically illustrating the configuration of the arithmetic processing device 20. The arithmetic processing device 20 is, for example, a notebook computer. As another example, the arithmetic processing device 20 can be realized as a general-purpose device such as a tablet computer or a smartphone, or as a dedicated device.

[0030] The arithmetic processing device 20 includes an input unit 21, an arithmetic processing unit 22, a memory unit 23, and an output unit 24. The input unit 21 is an input interface that makes the measurement data sent from the current sensor 12 via the signal line 14 available within the arithmetic processing device 20. The arithmetic processing unit 22 is functional means that performs arithmetic processing based on the input data accepted by the input unit 21, and is configured with software or dedicated hardware. The memory unit 23 is a storage area for temporarily storing information (described later) and data generated when the arithmetic processing unit 22 performs arithmetic processing, and is configured with a flash memory or the like. The output unit 24 is an output interface that outputs data obtained by the arithmetic processing performed by the arithmetic processing unit 22 to the outside. The output unit 24 can be realized with a known configuration such as a screen display means or a data transmission means.

[0031] In step #1, data relating to the ground current value measured by current sensor 12 is continuously sent to calculation processing device 20. FIG. 4 is a diagram showing an example of the ground current value measured by current sensor 12. Continuous data relating to the ground current value, as shown in FIG. 4, is sent to calculation processing device 20.

[0032] In this embodiment, the ground current value corresponds to the “target data,” and the ground current value measured by the current sensor 12 corresponds to the “actually measured target data.” This step #1 corresponds to process (a).

[0033] (Step #2) The calculation processing device 20 performs calculation processing using the information on the ground current value sent in step #1 to derive the rising steepness of the waveform (corresponding to the "measured steepness value"). An example of a specific method will be described below.

[0034] The data processing unit 27 of the arithmetic processing device 20 extracts maximum values ​​that satisfy predetermined extraction conditions based on information on the ground current values ​​that change over time sent via the input unit 21. Figure 5 is a graph in which maximum points P1 to P6 are clearly indicated in addition to the graph in Figure 4. In this embodiment, the maximum values ​​refer to the current values ​​corresponding to maximum points P1 to P6.

[0035] Here, the extraction conditions for extracting the maximum values ​​are conditions for recognizing a maximum value when a fluctuation exceeding a minimum threshold is observed within a reference time, so that not all extremely small fluctuations are recognized as maximum values. An example of such extraction conditions is a reference time set to 6 ns and a minimum threshold set to 1 mA. Information regarding the extraction conditions is recorded in the memory unit 23, and the data processing unit 27 may read the extraction conditions from the memory unit 23 and extract multiple maximum values ​​from data related to the actually measured ground current values. This extraction process corresponds to step (b1).

[0036] Next, the data processing unit 27 determines the maximum value that appears earliest from among the extracted multiple maximum values ​​(here, the current values ​​corresponding to maximum points P1 to P6). The maximum value determined here is hereinafter referred to as the "reference maximum value." In the example of FIG. 5, the current value i1 corresponding to maximum point P1 is determined as the reference maximum value (see FIG. 6). This process corresponds to step (b2).

[0037] Next, the data processing unit 27 calculates the gradient of the change in the ground current value immediately before the occurrence timing of the maximum point P1 corresponding to the reference maximum value i1. More specifically, this is done as follows.

[0038] First, the data processing unit 27 extracts the appearance timing (first reference timing T1) of a first reference value, which is a value of a first predetermined ratio set to any ratio within a range of 5% to 15% relative to the reference maximum value i1, and the appearance timing (second reference timing T2) of a second reference value, which is a value of a second predetermined ratio set to any ratio within a range of 85% to 95%, immediately before the appearance timing of the reference maximum value i1 (the appearance timing of the maximum point P1).

[0039] Fig. 7 is a diagram showing an example of a method for extracting the first reference timing T1 and the second reference timing T2, and shows an enlarged view of the vicinity of the maximum point P1 from the graph of Fig. 6. In the example of Fig. 7, the first predetermined ratio is set to 10%, and the second predetermined ratio is set to 90%. Note that information regarding the values ​​of the first predetermined ratio and the second predetermined ratio may be stored in advance in the storage unit 23.

[0040] 7, the data processing unit 27 recognizes, based on the information on the ground current value, the occurrence timing of a reference value (first reference value) corresponding to 10% of the reference maximum value i1, i.e., the first reference timing T1, and the occurrence timing of a reference value (second reference value) corresponding to 90% of the reference maximum value i1, i.e., the second reference timing T2. This process corresponds to step (b3).

[0041] Next, the data processing unit 27 calculates a gradient α1 of the change in the ground current value over the time elapsed from the first reference time T1 to the second reference time T2 based on the information on the ground current value (see FIG. 7). Then, this gradient α1 is used to obtain the measured gradient value for the ground current value sent in step #1. This process corresponds to step (b4).

[0042] (Step #3) Next, based on the measured gradient value derived by the data processing unit 27, the estimation processing unit 28 derives an estimated value of the surface insulation resistance of the transformer 5.

[0043] Information indicating the correlation between the steepness of the target data (here, ground current value) and the surface insulation resistance value of a sample whose main material is epoxy resin is stored in advance in storage unit 23. Fig. 8 is a graph showing an example of this correlation. In Fig. 8, the horizontal axis corresponds to the surface insulation resistance value, and the vertical axis corresponds to the steepness of the ground current value.

[0044] 9 to 12 are diagrams schematically showing an example of a method for measuring information relating to the correlation in advance. This method was also adopted when acquiring the information relating to the correlation shown in FIG.

[0045] Fig. 9 is a diagram showing a schematic configuration of an experimental system. The experimental system shown in Fig. 9 includes a transformer 32, a sample 35 made of epoxy resin, and an oscilloscope 46. Fig. 10 is a side view showing an enlarged schematic view of the vicinity of sample 35 in Fig. 9.

[0046] As shown in Figures 9 and 10, an insulating sheet 36, a ground plate 37, and an acrylic plate 38 were placed in this order in a predetermined area on the surface of workbench 30, and sample 35 was placed on the upper surface of acrylic plate 38. Sample 35 had dimensions of 0.6 cm length x width x height, 10 cm length x width x height, and was supported by a support member 39 so that it could be stably placed on acrylic plate 38. The bottom surface of support member 39 was in contact with the surface of acrylic plate 38, and the side surface was in contact with the surface of sample 35. Support member 39 was an acrylic plate.

[0047] The insulating sheet 36 is an acrylic resin sheet material. The ground plate 37 is a stainless steel plate material and is electrically connected to the ground wire 31 via the measurement resistor 34R. The acrylic plate 38 is an acrylic resin plate material and is provided for the purpose of ensuring an electrical distance between the ground plate 37 and the sample 35. The measurement resistor 34R was set to 50 Ω. The voltage across the measurement resistor 34R was measured by a voltage probe 45, and its output terminal was connected to an oscilloscope 46.

[0048] The transformer 32 is provided for the purpose of boosting the commercial power supply, with the ground terminal 32a electrically connected to the ground wire 31 and the boost terminal 32b electrically connected to a voltage application wire 41. The voltage application wire 41 is in contact with the surface of the sample 35, and is configured to be able to apply a high voltage to the sample 35. A gap Dg between the position where the voltage application wire 41 contacts the sample 35 and the upper surface of the acrylic plate 38 was set to 5 cm. The thickness of the acrylic plate 38 was 3 mm.

[0049] As sample 35, a plurality of samples with different surface conditions were prepared by applying water containing different concentrations of nitrate ions to an epoxy resin plate and then drying it.

[0050] (Calculation of ground current steepness) 9 and 10, a voltage of 2.5 kV was applied to sample 35 from voltage application line 41, and the voltage waveform input to oscilloscope 46 from voltage probe 45 during voltage application was divided by the resistance value of measurement resistor 34R to obtain a ground current waveform. Then, in step #2, the steepness of the ground current in sample 35 was calculated using a method similar to that described above.

[0051] (Measurement of surface insulation resistance) The surface insulation resistance of Sample 35 was measured using a method based on the double ring electrode method specified in JIS K 6271-1. Figures 11 and 12 are diagrams for explaining the method used to measure the surface insulation resistance of Sample 35.

[0052] As shown in Fig. 11, a main electrode 51 and a ring electrode 52 were arranged on one principal surface of a sample 35, and a counter electrode 53 was arranged on the other principal surface. The main electrode 51 and the ring electrode 52 were arranged with a gap of 13 mm between them. A test voltage Va was applied between the main electrode 51 and the ring electrode 52, and a current ib flowing between the electrodes was measured with an ammeter 55. The surface insulation resistance Ri [Ω] was calculated using the following equation (1), where the outer diameter of the main electrode 51 is D1 [m] and the inner diameter of the ring electrode 52 is D2 [m]. Ri[Ω]=π(D1+D2)Va / [(D2-D1)×ib] ……(1)

[0053] By carrying out the above-mentioned processes while changing the sample 35 to have different surface conditions, the relationship between the surface insulation resistance Ri of the sample 35 and the steepness of the ground current of the sample 35 was plotted, and the results shown in Figure 8 were obtained.

[0054] Information regarding the correlation between the surface insulation resistance Ri of the sample 35 and the steepness of the ground current of the sample 35, which is obtained by previously conducting the above-mentioned experiment in a test room or the like, is recorded in the storage unit 23.

[0055] 8, a high correlation is observed between the surface insulation resistance Ri of sample 35 and the steepness of the ground current of sample 35. Because sample 35 is a plate material made of epoxy resin, it is thought that a similar trend will be observed between the surface insulation resistance and the steepness of the ground current in power equipment molded with epoxy resin.

[0056] In step #3, the estimation processing unit 28 reads out the information relating to the correlation stored in the storage unit 23 and determines the surface insulation resistance Ri corresponding to the measured gradient value derived in step #2. The determined value of the surface insulation resistance Ri can be used as an estimate of the surface insulation resistance of the transformer 5 corresponding to the measured gradient value derived in step #2.

[0057] The estimated value of the surface insulation resistance of the transformer 5 may be a value derived by performing a correction process on the determined value of the surface insulation resistance Ri taking into account a predetermined error.

[0058] This step #3 corresponds to steps (d) and (e).

[0059] 11 and 12, the method for measuring surface insulation resistance using the double ring electrode method can be used when the measurement object is a plate-like resin, but cannot be performed on a live transformer 5. In other words, in the method according to the present invention, the method for measuring surface insulation resistance using the double ring electrode method is used for the purpose of obtaining information on the correlation in advance.

[0060] [Second embodiment] A second embodiment of the insulation resistance estimation method according to the present invention will be described, focusing on differences from the first embodiment.

[0061] In the first embodiment, the ground current value of the target power equipment (here, transformer 5) was measured, and an estimated value of the surface insulation resistance of transformer 5 was derived by utilizing the correlation between the steepness of the ground current value and the surface insulation resistance.

[0062] Here, when a discharge occurs in an insulator, it is expected that there is a high correlation between the current generated during the discharge and the electromagnetic wave intensity. In other words, it is thought that it is possible to derive an estimated value of the surface insulation resistance of the transformer 5 by using the steepness based on the electromagnetic wave intensity radiated from the transformer 5 instead of the steepness of the ground current value of the transformer 5.

[0063] Fig. 13 is a flow chart showing an example of the procedure of the insulation resistance estimation method of this embodiment, and Fig. 14 is a diagram showing an example of the insulation resistance estimation method of this embodiment.

[0064] In this embodiment, step #1A is executed instead of step #1, as compared with the first embodiment.

[0065] (Step #1A) Under a live line condition (uninterruptible power condition), an electromagnetic wave signal emitted from the target power equipment, transformer 5, is received to measure the electromagnetic wave intensity. Specifically, as shown in FIG. 14, antenna 13 is placed near transformer 5. If transformer 5 is deteriorated, it will emit an electromagnetic wave signal resulting from discharge. Antenna 13 is placed in a position where it can receive this electromagnetic wave signal. Specifically, antenna 13 is preferably placed within 3 m, and more preferably within 2 m, of the outer surface of transformer 5. In this case, antenna 13 may be fixed in place by a magnet or the like.

[0066] The data on the electromagnetic wave intensity measured in this step # 1 A is continuously sent to the processor 20 via the signal line 14 .

[0067] In this embodiment, the electromagnetic wave intensity corresponds to the “target data,” and the electromagnetic wave intensity measured by the antenna 13 corresponds to the “actually measured target data.” This step #1A corresponds to the process (a).

[0068] (Step #2) The calculation processing device 20 performs calculation processing using information about the electromagnetic wave intensity transmitted from the antenna 13 during execution of step #1A, and derives the rising steepness (measured steepness value) of the electromagnetic wave intensity waveform. A method similar to the method described above in the first embodiment is used for the derivation. Note that, in the method of this embodiment, extraction conditions may be appropriately set to recognize a maximum value when a fluctuation exceeding a minimum threshold value is recognized within a reference time, so that not all extremely minute fluctuations are recognized as maximum values. In this embodiment, an example of extraction conditions for extracting maximum values ​​is to set the reference time to 6 ns and the minimum threshold to 50 mV.

[0069] (Step #3) The estimation processing unit 28 derives an estimated value of the surface insulation resistance of the transformer 5 based on the measured steepness value derived in step #2.

[0070] In this embodiment, information indicating the correlation between the gradient of target data (here, electromagnetic wave intensity) and the surface insulation resistance value of a sample whose main material is epoxy resin is stored in advance in the storage unit 23. Fig. 15 is a graph showing an example of this correlation. In Fig. 15, the horizontal axis corresponds to the surface insulation resistance value, and the vertical axis corresponds to the gradient of electromagnetic wave intensity.

[0071] The method for measuring the surface insulation resistance value, which corresponds to the horizontal axis of the graph shown in FIG. 15, is the same as in the first embodiment, and therefore description thereof will be omitted.

[0072] The steepness of the electromagnetic wave intensity, which corresponds to the vertical axis of the graph shown in Fig. 15, is calculated using, for example, the experimental system shown in Fig. 16. Compared to the experimental system shown in Fig. 9, the experimental system shown in Fig. 16 does not include measurement resistor 34R and voltage probe 45, but instead includes antenna 47.

[0073] Antenna 47 was installed on the surface of workbench 30 at a position 1 m away from sample 35. Then, using the experimental system shown in FIG. 16 , a voltage of 2.5 kV was applied to sample 35 from voltage application line 41, and an electromagnetic wave signal was received by antenna 47 while the voltage was being applied. A voltage signal derived from the intensity of the electromagnetic wave signal received by antenna 47 was input to oscilloscope 46 via signal line 48, and a voltage waveform derived from the electromagnetic wave intensity was obtained by oscilloscope 46. Then, the steepness of the electromagnetic wave intensity in sample 35 was calculated using a method similar to the method described above in step #2 of the first embodiment.

[0074] The surface insulation resistance of sample 35 was measured and the steepness of the electromagnetic wave intensity received by antenna 47 was calculated while changing sample 35 to one with a different surface condition, and the results shown in Figure 15 were obtained by plotting each of these.

[0075] The results shown in Figure 15 show a slightly lower correlation than those shown in Figure 8. However, it is possible to improve this correlation by adjusting the sensitivity of antenna 47. Furthermore, considering that a high correlation was observed between the steepness of the ground current value of sample 35 and the surface insulation resistance of sample 35 during uninterruptible power supply, theoretically, a high correlation should also be observed between the steepness of the electromagnetic wave intensity radiated from sample 35 during uninterruptible power supply and the surface insulation resistance of sample 35. Therefore, by measuring the electromagnetic wave intensity radiated from the target electric power equipment and applying this to previously obtained correlation information between the steepness of the electromagnetic wave intensity and the surface insulation resistance value of a sample whose main material is epoxy resin, the surface insulation resistance value of the target electric power equipment can be estimated.

[0076] [Another embodiment] Another embodiment will be described below.

[0077] <1> The arithmetic processing device 20 may be configured to be capable of communicating, and may receive data from a server (not shown) to update the information regarding correlations recorded in the memory unit 23 as appropriate.

[0078] <2> The first and second embodiments may be combined. That is, both step #1 and step #1A may be performed, and an estimated value of the surface insulation resistance of the transformer 5 may be derived based on both the measured gradient value corresponding to the ground current value and the measured gradient value corresponding to the electromagnetic wave intensity.

[0079] <3> The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to provide a better understanding of the present invention, and the present invention is not necessarily limited to those having all of the configurations described. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0080] 3: Cubicle 5: Transformer 10: Ground wire 12: Current sensor 13: Antenna 14: Signal line 20: Processing unit 21: Input section 22: Processing unit 23: Storage section 24: Output section 27: Data processing section 28: Estimation processing unit 30: Workbench 31: Ground wire 32: Transformer 32a: Transformer ground terminal 32b: Step-up terminal of the transformer 34R:Measurement resistance 35: Sample 36: Insulation sheet 37: Ground plate 38: Acrylic plate 39: Support member 41: Voltage application line 45: Voltage probe 46: Oscilloscope 47: Antenna 48: Signal line 51: Main electrode 52: Ring electrode 53: Counter electrode 55: Ammeter

Claims

1. A method for estimating insulation resistance of electric power equipment, comprising: A step (a) of obtaining actual measurement target data, which is an actual measurement value of target data of either a ground current value in a live-line state of a target electric power device that is an epoxy-molded electric power device to be measured, or an electromagnetic wave intensity radiated from the target electric power device in a live-line state; (b) analyzing the change in the actual measurement target data to calculate an actual measurement gradient value corresponding to the gradient of the rising edge of the actual measurement target data; a step (c) of reading out pre-recorded correlation information between the steepness of the target data and the surface insulation resistance value of the sample containing the epoxy resin; (d) deriving the surface insulation resistance value corresponding to the measured gradient value based on the correlation information and the measured gradient value; and (e) determining an estimated value of the surface insulation resistance of the target electric power equipment based on the surface insulation resistance value derived in (d).

2. The step (b) a step (b1) of extracting a plurality of maximum values ​​that satisfy predetermined extraction conditions from the time-varying actual measurement target data obtained in the step (a); a step (b2) of determining a reference maximum value that appears earliest among the plurality of maximum values ​​obtained in the step (b1); (b3) extracting, immediately before the occurrence timing of the reference maximum value, a first reference time when the measured object data indicates a first reference value, which is a value of a first predetermined ratio set to any ratio within a range of 5% to 15% with respect to the reference maximum value, and a second reference time when the measured object data indicates a second reference value, which is a second predetermined ratio set to any ratio within a range of 85% to 95% with respect to the reference maximum value; 2. The insulation resistance estimation method for electric power equipment according to claim 1, further comprising: a step (b4) of calculating the actually measured gradient value based on an elapsed time from the first reference timing to the second reference timing and a difference value between the first reference value and the second reference value.

3. the target data is a ground current value of the target electric power device, 3. The method for estimating insulation resistance of electric power equipment according to claim 1, wherein step (a) is a step of obtaining the actually measured target data by attaching a current sensor to the ground wire of the target electric power equipment in a live state and measuring changes over time in the ground current value of the target electric power equipment.

4. the target data is the intensity of electromagnetic waves radiated from the target electric power device, 3. The method for estimating insulation resistance of electric power equipment according to claim 1, wherein the step (a) is a step of obtaining the actual measurement target data by installing an antenna in the vicinity of the target electric power equipment and measuring a change over time in the intensity of an electromagnetic wave signal radiated from the target electric power equipment and received by the antenna.

5. 3. The method for estimating insulation resistance of electric power equipment according to claim 1, wherein the target electric power equipment is a transformer, a switchgear, a circuit breaker, or a bushing.

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