Method for measuring partial discharge inception voltage

Abstract

To provide a technique effective for improving the reliability of partial discharge inception voltage (PDIV) measurement result of an enamel wire.SOLUTION: The method for measuring partial discharge inception voltage is used, the method measuring the partial discharge inception voltage of an enamel wire with two enamel wires having coating around a conductor being in contact with each other and stacked over a prescribed area of the enamel wire in a longitudinal direction. The method includes: detecting a discharge signal indicating time change of discharge current generated in the enamel wire while measuring the partial discharge inception voltage, defining a section where a current value is convex to a positive side and a section where the current value is convex to a negative side respectively as one section in a curve indicating time change of the discharge current based on the detected discharge signal, and deriving a section discharge charge amount which is a charge amount for each one section; and creating information indicating a frequency distribution of the section discharge charge amount corresponding to the measured partial discharge inception voltage on the basis of the derived section discharge charge amount. A state of the frequency distribution of section discharge charge amount is in strong correlation with degree of suppressed variations of the PDIV measurement result.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the partial discharge inception voltage of an enameled wire. [Background technology]

[0002] It is known that for an enameled wire having a coating around a conductor with a substantially rectangular cross section, the partial discharge inception voltage can be measured using a predetermined method (see, for example, Non-Patent Document 1). The partial discharge inception voltage is also called PDIV (Partial Discharge Inception Voltage). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Denso Technical Review, Vol. 16, 2011, P. 68-76 Summary of the Invention [Problem to be solved by the invention]

[0004] In measuring the PDIV of enameled wire, it is desirable to improve the reliability of the PDIV measurement results by suppressing the variability in the PDIV measurement results. Therefore, there is room for improvement in terms of being able to determine whether the variability in the PDIV measurement results has been suppressed.

[0005] Due to the above circumstances, there is a need for an effective technique for improving the reliability of PDIV measurement results for enameled wires. [Means for solving the problem]

[0006] A representative embodiment of the present application is a method for measuring the partial discharge inception voltage of two enameled wires, each having a coating around its conductor, stacked together in contact over a predetermined region in the longitudinal direction of the enameled wire. The method includes the steps of: detecting a discharge signal that indicates a time change in a discharge current generated in the enameled wire while measuring the partial discharge inception voltage; determining, as a section in a curve that indicates the time change in the discharge current based on the detected discharge signal, a section in which the current value is convex on the positive side and a section in which the amount of charge is convex on the negative side, respectively; deriving an sectional discharge charge amount, which is the amount of charge for each of the sections; and generating information that indicates a frequency distribution of the sectional discharge charge amount corresponding to the measured partial discharge inception voltage, based on the derived sectional discharge charge amount. [Effects of the Invention]

[0007] According to a representative embodiment of the present application, it is possible to provide a technique that is effective in improving the reliability of PDIV measurement results of enameled wires. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram showing an example of the configuration of a measurement sample. [Figure 2] FIG. 10 is a diagram illustrating a Y-shaped gap portion of a measurement sample. [Figure 3] FIG. 10 is a diagram for explaining a corner R gap portion of a measurement sample. [Figure 4] 1 is a flowchart showing a PDIV measurement method according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing an example of a change over time in a voltage applied to a measurement sample. [Figure 6] FIG. 1 is a diagram for explaining the contact angle of a liquid, which is an index of hydrophilicity. [Figure 7] 1 is a table showing conditions for preliminary discharge and PDIV measurement using a PDIV measurement device. [Figure 8] FIG. 10 is a diagram showing a model of the electrical characteristics of a measurement sample when the coating surface is not sufficiently hydrophilized. [Figure 9]FIG. 10 is a diagram showing a model of the electrical properties of a measurement sample when the coating surface is sufficiently hydrophilic. [Figure 10] FIG. 10 is a diagram showing a comparative example of the amount of charge discharged when the coating is insufficiently and sufficiently hydrophilized. [Figure 11] FIG. 10 is a diagram showing an example of a graph showing the relationship between the voltage applied to the measurement sample and the amount of charge discharged. [Figure 12] FIG. 10 is a diagram for explaining a method for deriving an interval discharge charge amount. [Figure 13] FIG. 10 is a diagram showing an example of a histogram illustrating the relationship between the interval discharge charge amount of partial discharge and its occurrence frequency when the coating surface is not sufficiently hydrophilized. [Figure 14] FIG. 10 is a diagram showing an example of a discharge emission image when a partial discharge occurs in a case where the hydrophilization of the coating surface is insufficient. [Figure 15] FIG. 10 is a diagram showing an example of a histogram illustrating the relationship between the interval discharge charge amount of partial discharge and its occurrence frequency when the coating surface is sufficiently hydrophilized. [Figure 16] FIG. 10 is a diagram showing an example of a discharge emission image when a partial discharge occurs in a case where the coating surface is sufficiently hydrophilic. [Figure 17] FIG. 1 is a diagram illustrating an example of the configuration of a PDIV measurement system according to a first embodiment. [Figure 18] FIG. 1 illustrates an example of the configuration of a computer. [Figure 19] 10 is a flowchart showing an example of a process flow for generating frequency distribution information of sectional discharge charge amounts. DETAILED DESCRIPTION OF THE INVENTION

[0009] Now, embodiments will be described. Note that each embodiment described below is an example for carrying out the present invention, and does not limit the technical scope of the present invention. Furthermore, in each embodiment below, components having the same function are denoted by the same reference numerals, and repeated description thereof will be omitted unless particularly necessary.

[0010] <Background of the study by the inventor> The present inventors have been studying ways to reduce variance in partial discharge inception voltage (hereinafter also referred to as PDIV) measurement results and improve the reliability of the measurement results when measuring the partial discharge inception voltage (hereinafter also referred to as PDIV) of a measurement sample using two enameled wires. Through these studies, the present inventors have found a strong correlation between the degree to which variance in the PDIV measurement results of the measurement sample is reduced and the frequency distribution of the amount of charge that flows through the measurement sample for each partial discharge that occurs in the measurement sample (the interval discharge charge amount, described below). This correlation will be explained in more detail as follows.

[0011] First, the inventors discovered that there is a strong correlation between the degree of suppression of variation in PDIV measurement results and the location of partial discharge occurrence in the measurement sample. Specifically, when variation in PDIV measurement results is suppressed, most partial discharges occur at predetermined locations that are expected in advance. On the other hand, when variation in PDIV measurement results is not suppressed, partial discharges often occur in locations other than the predetermined locations.

[0012] The inventors also found that there is a strong correlation between the location of partial discharges in the measurement sample and the frequency distribution of the amount of charge flowing through the measurement sample for each partial discharge. Specifically, when most of the partial discharges in the measurement sample occur at predetermined locations, the amount of charge for each partial discharge tends to be biased toward a relatively small predetermined amount of charge. On the other hand, when many partial discharges in the measurement sample occur at locations other than the predetermined locations, the amount of charge for each partial discharge tends to vary more toward a relatively large amount of charge.

[0013] That is, there is a strong correlation between the degree of suppression of variation in PDIV measurement results and the location of partial discharge occurrence in the measurement sample, and there is also a strong correlation between the location of partial discharge occurrence in the measurement sample and the frequency distribution of the amount of charge per partial discharge. From these findings, it was found that there is a strong correlation between the degree of suppression of variation in PDIV measurement results and the distribution of the amount of charge per partial discharge.

[0014] Therefore, the present inventors have devised a method for objectively evaluating and determining whether or not the variation in PDIV measurement results is suppressed based on the frequency distribution of the amount of charge per partial discharge. The embodiment described below is an example of the embodiment of the method.

[0015] <Configuration of measurement sample> First, the configuration of the measurement sample to be used for measuring PDIV will be described.

[0016] Fig. 1 shows an example of the configuration of a measurement sample 2. As shown in Fig. 1, the measurement sample 2 has two rectangular enameled wires 1, each having a conductor 1a made of a metal wire with a substantially rectangular cross section and a coating 1b around the conductor 1a. The rectangular enameled wire 1 is an example of the "enameled wire" of the present application.

[0017] Each of the two rectangular enameled wires 1 has a back-to-back portion 1c. The back-to-back portion 1c extends over a predetermined region D1, for example, 120 mm long along the longitudinal direction of the rectangular enameled wire 1. The back-to-back portion 1c has a mating surface 11. The two rectangular enameled wires 1 are fixed with the mating surfaces 11 of the back-to-back portions 1c in contact with each other. That is, the two rectangular enameled wires 1 are fixed back-to-back. In other words, when measuring PDIV, the measurement sample 2 is constructed by stacking two rectangular enameled wires 1, each with a conductor 1a coated with an insulating coating 1b, in the thickness direction C1. In the measurement sample 2, the two rectangular enameled wires 1 are fixed at five locations in the predetermined region D1 using fixtures 12, such as wires or clips.

[0018] The cross section of the conductor 1a of the rectangular enameled wire 1 is, for example, 1.900 mm wide and 3.450 mm thick. The thickness of the coating 1b of the rectangular enameled wire 1 is, for example, 0.150 to 1.162 mm.

[0019] The coating 1b at the end 1d of the measurement specimen 2 (see the right side in Figure 1) has been peeled off, exposing the copper conductor 1a. In the example shown in Figure 1, the conductor 1a is also exposed at the other end, i.e., the left side, of the measurement specimen 2 (reference numeral 1d is omitted). The PDIV can be measured by electrically connecting this conductor 1a to the high-voltage and ground wires of the measurement equipment. The end 1d at both ends of the measurement specimen 2 are curved at a predetermined bending angle θ so that the end 1d of the rectangular enameled wire 1 is spaced apart. Specifically, the end 1d is curved so that it is warped at a predetermined bending angle θ relative to the mating surface 11. The bending angle θ is, for example, θ = 20°.

[0020] Next, we will explain the area in which partial discharges are particularly likely to occur in the measurement sample 2. The area where partial discharges are particularly likely to occur is the surface portion of the coating 1b that forms the boundary between the areas where the two rectangular enameled wires 1 are in contact with each other, and this is called the gap portion.

[0021] Figure 2 is a diagram illustrating the Y-gap of the measurement sample. As shown in Figure 2, the terminal ends 1d of the two rectangular enameled wires 1 constituting the measurement sample 2 are curved so as to separate from each other, forming a Y-shape overall. The part where the terminal ends 1d begin to separate is called the Y-gap Y. The Y-gap Y is one of the parts of the measurement sample 2 where partial discharges are likely to occur. The Y-gap Y is also the "predetermined location" mentioned above where partial discharges occur.

[0022] Figure 3 is a diagram illustrating the corner R gap of the measurement sample. Figure 3 is a cross-sectional view of the measurement sample 2 shown in Figure 2 taken along line AA. As shown in Figure 3, the corner R gap R is the portion at each end in the width direction B1 of the mating surface 11 of the two rectangular enameled wires 1 that make up the measurement sample 2. The corner R gap R is also one of the areas in the measurement sample 2 where partial discharge is likely to occur.

[0023] To reduce the variation in PDIV measurements for the measurement sample 2, it is important that the surface contours of the coating 1b at the Y-shaped gap Y and the R-corner gap R are formed symmetrically in the thickness direction C1 with respect to the mating surface 11. Furthermore, to reduce the variation in PDIV measurements due to differences in the measurement sample, it is important that the surface contour shapes of the coating 1b at the Y-shaped gap Y and the R-corner gap R are stably formed to be substantially the same shape.

[0024] Furthermore, in order to reduce the variation in the PDIV measurement values ​​of the measurement sample 2, it is also important to remove foreign matter, charges, etc. remaining on the surface of the coating 1b of the rectangular enameled wire 1.

[0025] (Embodiment 1) Hereinafter, a PDIV measurement method (partial discharge inception voltage measurement method) according to the first embodiment will be described with reference to the drawings.

[0026] <Flow of PDIV measurement method according to embodiment 1> FIG. 4 is a flowchart showing a PDIV measurement method according to the first embodiment.

[0027] As shown in Figure 4, in step (process) S1, rectangular enameled wire 1 is taken to serve as measurement sample 2. Specifically, two rectangular enameled wires 1 each 320 mm long are taken from a bobbin around which rectangular enameled wire 1 is wound or from a coil incorporated in a drive motor mounted on an electric vehicle.

[0028] In step S2, the rectangular enameled wire is shaped. Specifically, the two rectangular enameled wires 1 are stretched by 2% along their longitudinal direction to remove any bending tendencies. Then, using a bending tool or fixture, both ends 1d of the rectangular enameled wire 1 in the extending direction F1 are bent at a bending angle θ in the same direction in the thickness direction C1 of the rectangular enameled wire 1. The bending angle θ is, for example, 20°, and the curvature of the bent portion is a predetermined value, for example, R30 to R50 mm.

[0029] In step S3, a measurement sample is manually formed. Specifically, a measurement sample 2 as shown in Fig. 1 is formed without using a bending tool or fixture. For example, as shown in Figs. 2 and 3, two rectangular enameled wires 1 are bent to a predetermined bending angle θ and placed back-to-back with their mating surfaces 11 facing each other. Then, as shown in Fig. 1, the two back-to-back rectangular enameled wires 1 are fixed in a predetermined region D1 with a fixture 12 such as a wire, thereby forming the measurement sample 2.

[0030] In step S4, lubricating oil and other substances adhering to the surface of the coating 1b of the rectangular enameled wire 1 are removed (oil removal). Specifically, the rectangular enameled wire 1 is immersed in an organic solvent containing hexane for, for example, 24 hours or more. After that, the rectangular enameled wire 1 is removed from the organic solvent and allowed to air dry.

[0031] The organic solvent in which the rectangular enameled wire 1 is immersed can be, for example, a hydrocarbon organic solvent such as normal hexane. Note that the organic solvent is not limited to hydrocarbon organic solvents, and may be an alcohol organic solvent, an ester organic solvent, or a ketone organic solvent.

[0032] In the oil removal process, ultrasonic cleaning may be performed on the surface of the coating 1b of the rectangular enameled wire 1. In this case, the rectangular enameled wire 1 is immersed in a solvent contained in a container such as a measuring cylinder. The container is then immersed in a liquid (e.g., water) in a liquid tank of an ultrasonic cleaner, and the rectangular enameled wire 1 is ultrasonically cleaned.

[0033] In step S5, moisture is removed from the coating of the rectangular enameled wire. Specifically, the rectangular enameled wire 1, which serves as the measurement sample 2, is left in an environment at a temperature of 150°C for about an hour to remove moisture from the coating 1b of the rectangular enameled wire 1. The sample is then left for about an hour in the same environment as when the PDIV is measured (for example, a temperature of 23°C and a humidity of 35%). The temperature and humidity can be controlled, for example, by placing the rectangular enameled wire 1 in a constant temperature and humidity chamber.

[0034] In step S6, the charge on the surface of the coating of the rectangular enameled wire is removed. Specifically, the charge stored on the surface of the coating 1b of the rectangular enameled wire 1, which serves as the measurement sample 2, is removed by a static eliminator such as an ionizer.

[0035] In step S7, the sensitivity of the voltage / charge measurement circuit, which will be described later, is calibrated. The applied voltage during calibration is AC, its frequency is 1 kHz, and the discharge charge amount is 100 pC.

[0036] In step S8, the surface of the coating 1b is hydrophilized. Specifically, the surfaces of the coatings 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 are hydrophilized. In this example, one method for hydrophilizing the surfaces of the coatings 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 is to perform preliminary discharges multiple times using a PDIV measurement device (described later) to apply a preset fixed voltage (effective voltage) to the measurement sample 2 for a fixed period of time and discharge the wires for a fixed period of time. In other words, the fixed voltage is applied to the measurement sample 2 multiple times for a fixed period of time.

[0037] Here, preliminary discharge refers to a partial discharge that occurs before starting PDIV measurement, and is also called pre-discharge. Specifically, an AC voltage (e.g., a high-frequency voltage with a frequency of 1 kHz) is applied between one end and the other end of each of the two rectangular enameled wires 1 that make up the measurement sample 2. The applied voltage (hereinafter, unless otherwise specified, "voltage" means AC voltage, and "voltage (value)" means effective voltage) is gradually increased until a partial discharge occurs in the measurement sample 2. The applied voltage is maintained for a certain period of time, e.g., about 20 seconds, to allow the partial discharge to continue. After that, the application of voltage to the measurement sample 2 is stopped.

[0038] The hydrophilization of the surface of the coating of the enameled wire in step S8, i.e., the preliminary discharge, will be described in detail later in the explanation of <Changes in voltage applied to the measurement sample over time>.

[0039] In step S9, PDIV measurement and discharge signal detection are performed. Specifically, using a PDIV measurement device (described later), a voltage (e.g., a high-frequency voltage with a frequency of 1 kHz) is applied between one end and the other end of each of the two rectangular enameled wires 1 constituting the measurement sample 2 using a voltage generation circuit (described later). The applied voltage is gradually increased, and when the occurrence of partial discharge in the measurement sample 2 is detected by the voltage / charge measurement circuit (described later), the applied voltage at that point is recorded as the PDIV, and the application of voltage to the measurement sample 2 is stopped. This series of voltage application operations is repeated multiple times, for example, about five times, to measure the PDIV for multiple times. The average or minimum PDIV value for the multiple times is then identified as the measured PDIV for the measurement sample 2.

[0040] In addition, in parallel with the PDIV measurement, that is, while the PDIV is being measured, a discharge signal is detected. Specifically, the discharge signal is detected using a discharge signal detection device, which will be described later. The discharge signal is a signal that represents the change over time in the value of the discharge current that accompanies a discharge that occurs between the two rectangular enameled wires 1 that make up the measurement sample 2. The discharge current is the current that flows through the measurement sample 2 when a discharge occurs in the measurement sample 2. The PDIV measurement in step S9 will be described in detail later in the explanation of <Change over time of voltage applied to the measurement sample>. The detection of the discharge signal in step S9 will be described in detail separately later.

[0041] In step S10, the interval discharge charge amount is derived. Specifically, a computer described later determines the time change of the discharge current based on the discharge signal acquired from the discharge signal detection device, and derives the interval discharge charge amount from the determined time change of the discharge current.

[0042] The interval discharge charge amount refers to the amount of charge flowing through the measurement specimen 2 in a time interval corresponding to one partial discharge that occurred in the measurement specimen 2. More specifically, the interval discharge charge amount is the amount of charge calculated by integrating the current value over time in a curve (waveform) representing the time change of the discharge current, where each interval is convex on the positive side and each interval is convex on the negative side. As described above, the frequency distribution of the interval discharge charge amount for each partial discharge, for example, the magnitude or stability of the interval discharge charge amount, is strongly correlated with the degree of suppression of variation in the PDIV measurement results. Therefore, the interval discharge charge amount is one of the indicators suitable for evaluating and judging the degree of suppression of variation in the PDIV measurement results, and is an indicator discovered by the present inventor.

[0043] The derivation of the interval discharge charge amount in step S10 will be described in detail later. Also, the reason why the interval discharge charge amount can be used as the above index and an example of a method for evaluating and determining the degree of suppression of the variation in the PDIV measurement results using the interval discharge charge amount will be described in detail later.

[0044] In step S11, frequency distribution information of the sectional discharge charge amount is generated. Specifically, the computer generates frequency distribution information representing the distribution of the occurrence frequency of the sectional discharge charge amount for each PDIV measurement based on the derived sectional discharge charge amount. The frequency distribution information is, for example, a histogram. The generation of the frequency distribution information of the sectional discharge charge amount in step S11 will be described in detail later.

[0045] In step S12, frequency distribution information of the sectional discharge charge amount is output. Specifically, the computer outputs the generated frequency distribution information of the sectional discharge charge amount. For example, the computer controls a display device (described later) so that a histogram as the frequency distribution information is displayed for each PDIV measurement.

[0046] <Temporal change of voltage applied to the measurement sample> Fig. 5 is a diagram showing an example of the change over time of the voltage applied to the measurement sample 2. Fig. 5 shows the change over time of the voltage V applied to the measurement sample 2 when preliminary discharge for hydrophilizing the measurement sample 2 (particularly, for hydrophilizing the surface of the coating 1b) and PDIV measurement are performed consecutively.

[0047] As shown in Fig. 5, when the PDIV measurement process using the PDIV measurement device is started, a preliminary discharge is first performed. Specifically, the applied voltage V to the measurement sample 2 gradually increases from 0. When the applied voltage V reaches a voltage V20a, which is a fixed value (a value that does not vary for each measurement sample) that is preset to hydrophilize the surface of the coating 1b, the applied voltage V is fixed at voltage V20a and maintained for approximately 20 seconds. During this time, partial discharge is maintained in the measurement sample 2. After that, the applied voltage V returns to 0.

[0048] Then, voltage is applied to the measurement sample 2 again, and a second preliminary discharge is performed. In this case, too, when the applied voltage V reaches a fixed value, voltage V20a, the applied voltage V is fixed at voltage V20a and maintained for approximately 20 seconds. Thereafter, the applied voltage V returns to 0 again. The preliminary discharge is performed a predetermined number of times (for example, 10 times). The number of times the preliminary discharge is performed is determined based on, for example, the degree of variation in the measured value in the PDIV measurement or the degree of variation in the interval discharge charge amount in the PDIV measurement.

[0049] Next, the PDIV measurement is performed. Specifically, the applied voltage V to the measurement sample 2 gradually increases from 0. When the applied voltage V reaches the voltage V21 at which partial discharge starts, the voltage V21 at that time is stored as the first PDIV measurement value, and the applied voltage V returns to 0.

[0050] The applied voltage V changes in the same way in the second to fifth PDIV measurements, and rises and falls repeatedly from peaks at voltages V22 to V25 at which partial discharges start. The voltages V22 to V25 are stored as the second to fifth PDIV measurement values.

[0051] <Making the coating surface of rectangular enameled wire hydrophilic> Here, the process of making the surface of the coating 1b of the rectangular enameled wire 1 hydrophilic, which is carried out in step S8, will be described in detail.

[0052] After extensive investigation, the inventors discovered that making the surface of the coating 1b of the rectangular enameled wire 1 hydrophilic, particularly the surface of the coating 1b that forms the boundary between the areas where two rectangular enameled wires 1 come into contact with each other, is extremely effective in suppressing the variation in PDIV measurements.

[0053] The surface of the coating 1b that forms the boundary of the area where two rectangular enameled wires 1 contact each other is, for example, the surface of the coating 1b at the Y-shaped gap Y and the R-corner gap R as shown in Figures 2 and 3.

[0054] Therefore, the hydrophilization of the surface of the coating 1b performed in step S8 is a process of hydrophilizing at least the surface of the coating 1b that forms the boundary of the contact area between the two rectangular enameled wires 1. The surface of the coating 1b that forms the boundary is, for example, the surface of the coating 1b at the Y-shaped gap Y and the R-corner gap R shown in Figures 2 and 3.

[0055] Whether the surface of the coating 1b has been hydrophilized can be determined by checking whether an index indicating the degree of hydrophilicity (wettability) of the surface of the coating 1b exceeds a preset standard. For example, the "contact angle" of a liquid can be used as an index indicating the degree of hydrophilicity.

[0056] FIG. 6 is a diagram illustrating the contact angle of a liquid, which is an index of hydrophilicity. According to the Physics and Chemistry Dictionary (Iwanami Shoten, 4th Edition), "contact angle" is defined as "the angle between the liquid surface and the solid surface where the free surface of a stationary liquid comes into contact with a solid wall (the angle is taken as an angle inside the liquid)." That is, as shown in FIG. 6, for example, the "contact angle" can be expressed as the angle α between the solid surface 91 and a tangent line L that passes through the boundary between the solid surface 91 and a droplet 92 formed by dropping a liquid on the solid surface 91. In this embodiment, the solid surface 91 is the surface of the coating 1b of the rectangular enameled wire 1.

[0057] As a result of investigations by the present inventors, the hydrophilization of the surface of the coating 1b can be defined as modification (activation) of the surface of the coating 1b such that the contact angle α between the surface of the coating 1b and the droplet 92 becomes 20° (degrees) or less. More preferably, the hydrophilization of the surface of the coating 1b is modification (activation) of the surface of the coating 1b such that the contact angle α between the surface of the coating 1b and the droplet 92 becomes 10° (degrees) or less. Note that the "contact angle" can be calculated using, for example, the width-height method (θ / 2 method), the perfect circle method, the tangent method, the ellipse method, the Young-Laplace method, or the like.

[0058] The inventors have also found that one effective method for making the surface of the coating 1b hydrophilic is to apply a fixed voltage higher than the partial discharge inception voltage to the measurement sample 2 and perform preliminary discharge multiple times.

[0059] Therefore, in this embodiment, in order to make the surface of the coating 1b hydrophilic, a method is adopted in which preliminary discharge is performed multiple times on the measurement sample 2 at a preset fixed voltage higher than the partial discharge inception voltage. The preliminary discharge method for making the surface of the coating 1b hydrophilic according to the proposed method can be determined, for example, as follows.

[0060] The measurement sample is connected to the PDIV measurement device, and an AC voltage is applied between one end and the other end of each of the two rectangular enameled wires 1 that make up the measurement sample 2. The applied voltage V is gradually increased until it reaches a fixed voltage value preset to hydrophilize the surface of the coating 1b. From that point on, the voltage is maintained for a certain period of time, e.g., about 20 seconds, to maintain partial discharge. The application of voltage to the measurement sample 2 is then stopped. Similarly, the process of increasing the applied voltage V, maintaining it at the fixed voltage value for a certain period of time (e.g., about 20 seconds), and then stopping the voltage application is repeated multiple times (e.g., 10 times).

[0061] The fixed voltage is the voltage required to hydrophilize at least the surface of coating 1b at Y-shaped gap Y and R-corner gap R of rectangular enameled wire 1 constituting measurement sample 2, and is higher than the average PDIV measured for measurement samples of the same type. For example, the PDIV can be measured multiple times, for example, five times or more, in advance for multiple measurement samples of the same type, and the fixed voltage can be the maximum voltage value among the measured PDIVs.

[0062] In this embodiment, the control circuit in the PDIV measurement device may be configured to store multiple PDIVs measured in advance and set the maximum voltage value among the multiple PDIVs as the fixed voltage value used for preliminary discharge. That is, the program executed by the processor in the PDIV measurement device may be configured to enable such setting.

[0063] As mentioned above, in step S4, the rectangular enameled wire 1 is immersed in an organic solvent, and in step S8, preliminary discharge is performed multiple times to remove the lubricating oil adhering to the coating of the rectangular enameled wire 1. These steps can reduce the variation in the PDIV measurement values ​​of the measurement sample 2.

[0064] <Conditions for preliminary discharge and PDIV measurement> Figure 7 is a table showing the conditions for preliminary discharge and PDIV measurement using a PDIV measurement device. As shown in Figure 7, the applied voltage frequency is 1 kHz. The conditions for determining that a partial discharge has started during preliminary discharge (the partial discharge determination threshold shown in Figure 7) are that the discharge charge is 100 pC or more and that the occurrence frequency is 1000 pps or more. During preliminary discharge, the voltage application time when a partial discharge occurs is approximately 20 s, the applied voltage increase step (voltage increase rate) is 200 V / s, and the applied voltage decrease step (voltage decrease rate) is output off after 0 V command control.

[0065] In addition, in the PDIV measurement, the conditions for determining that a partial discharge has started (partial discharge determination threshold shown in Figure 7) are that the discharge charge is 100 pC or more and the occurrence frequency is 1000 pps or more. In this PDIV measurement, the applied voltage increase step (voltage increase rate) is 30 V / s for the primary (up to 200 V) and 10 V / s for the secondary (after 200 V), and the applied voltage decrease step (voltage decrease rate) is output off after 0 V instruction control. The measurement environment is a temperature of 23°C and humidity of 35%.

[0066] Under the above conditions, the preliminary discharge is carried out, for example, from 1 to 10 times.

[0067] <Why interval discharge charge is suitable as an evaluation index for PDIV measurement results> Next, the reason why the interval discharge charge amount is suitable as an evaluation index for the PDIV measurement results will be explained.

[0068] Fig. 8 is a diagram showing a model of the electrical properties of a measurement sample when the coating surface is insufficiently hydrophilized, and Fig. 9 is a diagram showing a model of the electrical properties of a measurement sample when the coating surface is sufficiently hydrophilized.

[0069] 8 and 9, it is believed that capacitance occurs between the coatings 1b in the Y-shaped gap of measurement sample 2. Here, it is assumed that the distances between the coating 1b of one rectangular enameled wire and the coating 1b of the other rectangular enameled wire that make up measurement sample 2 are, in order from shortest to longest, d1, d2, d3, and d4.

[0070] If the surface of the coating 1b covering the conductor 1a of each of the two rectangular enameled wires constituting the measurement sample 2 is not sufficiently hydrophilic, it is likely that the entire surface of the coating 1b is not electrically connected smoothly. In this case, the capacitance is assumed to consist of three independent and unstable capacitance components: a capacitance component corresponding to distance d1, a capacitance component corresponding to distance d2, a capacitance component corresponding to distance d3, and a capacitance component corresponding to distance d4. Therefore, in this case, as shown in Figure 8, it can be assumed that each capacitance component from distance d1 to distance d4 is independently connected to the voltage generating circuit, and each closed circuit exists independently and unstable.

[0071] On the other hand, if the surface of the coating 1b covering the conductor 1a of each of the two rectangular enameled wires constituting the measurement sample 2 is sufficiently hydrophilic, the entire surface of the coating 1b is considered to be electrically smooth and connected. In this case, the capacitance is assumed to exist stably in a parallel configuration, with the capacitance components corresponding to distances d1, d2, d3, and d4 connected in parallel, as shown in Figure 9. Therefore, in this case, it can be assumed that the capacitance components from distances d1 to d4 are connected in parallel, forming a stable single closed circuit in which the voltage generating circuit and the parallel-connected capacitance C0 are connected.

[0072] Fig. 10 shows a comparative example of the amount of discharge charge when the coating is insufficiently and sufficiently hydrophilized, and Fig. 11 shows an example of a graph showing the relationship between the voltage V applied to the measurement sample and the amount of discharge charge Qi.

[0073] As described above, when the hydrophilicity of the coating is insufficient, when considering the capacitance components at each point from distance d1 to distance d4, it is assumed that there exists a closed circuit in which each capacitance component is independently connected to the voltage generating circuit. Therefore, the amount of discharge charge in this case, i.e., the amount of charge that flows when a discharge occurs in the Y-shaped gap of the measurement sample, is one of the charge amounts Q1, Q2, Q3, and Q4 corresponding to the capacitance components at each point from distance d1 to distance d4, or a combination of several of them.

[0074] Furthermore, as described above, if the coating is sufficiently hydrophilic, when considering the capacitance components at each point from distance d1 to distance d4, it is assumed that there exists a single closed circuit in which each capacitance component is connected in parallel to a voltage generating circuit. Therefore, the amount of discharge charge in this case, i.e., the amount of charge flowing through the measurement sample when a discharge occurs in the Y-shaped gap of the measurement sample, is the amount of charge Q0 corresponding to the electrostatic capacitance C0 obtained by connecting the capacitance components at each point from distance d1 to distance d4 in parallel.

[0075] Therefore, when comparing the charge amount of partial discharge in the Y-shaped gap when the coating is sufficiently and insufficiently hydrophilized, the charge amount Q1, Q2, Q3, or Q4 is less than the charge amount Q0, as shown in Figure 10. In other words, when the coating is sufficiently hydrophilized, the charge amount of partial discharge occurring in the Y-shaped gap is relatively larger but more stable than when the coating is not sufficiently hydrophilized.

[0076] In the relationship between the applied voltage V and the discharge charge Qi, when the charge amounts Q1, Q2, Q3, Q4, and Q0 are compared with one another, the following relationship holds, as shown in FIG. 11: slope of charge Q1<slope of charge Q2<slope of charge Q3<slope of charge Q4<slope of charge Q0.

[0077] The above explanation of the magnitude and stability of the partial discharge charge is for the partial discharge in the Y-shaped gap of the measurement sample. Partial discharges in the corner R gap, back-to-back parts, etc. of the measurement sample must be considered separately.

[0078] <Method of deriving interval discharge charge amount> Fig. 12 is a diagram for explaining a method for deriving the interval discharge charge amount. As shown in Fig. 12, the interval discharge charge amount Q is obtained by integrating the discharge current I over time t for a time width Δt corresponding to each interval, where the current value is convex on the positive side and the current value is convex on the negative side in a curve (waveform) representing the time change of the discharge current I. In other words, the area of ​​the region of the peak that is convex on the positive side or the region of the peak that is convex on the negative side in the curve of the discharge current I is obtained as the interval discharge charge amount Q. The calculation formula for deriving the interval discharge charge amount Q is expressed by the following equation (1).

[0079] Q = I × Δt …(1) Q: Discharge charge [C], I: Current [A], Δt: Time width (time difference) [s]

[0080] In the computer, the numerical algorithm for integrating the discharge current I over time t to derive the interval discharge charge amount Q is, for example, the Simpson method or a method similar thereto.

[0081] <Discharge behavior when the coating surface is not sufficiently hydrophilic> Fig. 13 is a diagram showing an example of a histogram illustrating the relationship between the interval discharge charge amount of partial discharge and its occurrence frequency when the coating surface is insufficiently hydrophilized. Fig. 14 is a diagram showing an example of a discharge light emission image when partial discharge occurs when the coating surface is insufficiently hydrophilized. Note that the examples shown in Figs. 13 and 14 are examples when no preliminary discharge is performed (0 times).

[0082] If the coating surface is not sufficiently hydrophilic, the capacitance of each circuit in the Y-gap of the measurement sample is small, and the interval discharge charge of partial discharges that occur in the Y-gap of the measurement sample is often less than 100 pC, as shown on the left side of Figure 10. On the other hand, at the back-to-back or corner R gap of the two rectangular enameled wires that make up the measurement sample, partial discharges are likely to occur between one coating and the other.

[0083] Therefore, if the coating surface is not sufficiently hydrophilic, as can be seen from the histogram in Figure 13, the voltage applied to the measurement sample when partial discharge occurs increases, and the partial discharge occurs in areas including the back-to-back portion of the measurement sample or the R-corner gap. As a result, the interval discharge charge varies on the side greater than 100 pC (right side), and the frequency of occurrence of interval discharge charge amounts above a certain level increases dramatically due to partial discharges in the back-to-back portion of the measurement sample or the R-corner gap. As can be seen from the discharge light emission image in Figure 14, the partial discharge occurs in areas throughout the entire measurement sample, including the back-to-back portion, and it can be confirmed that discharge light is emitted from almost the entire measurement sample.

[0084] <Discharge behavior when the coating surface is sufficiently hydrophilic> Fig. 15 is a diagram showing an example of a histogram illustrating the relationship between the interval discharge charge amount of partial discharge and its occurrence frequency when the coating surface is sufficiently hydrophilized. Fig. 16 is a diagram showing an example of a discharge light emission image when partial discharge occurs when the coating surface is sufficiently hydrophilized. The examples shown in Figs. 15 and 16 are examples when preliminary discharges were performed (10 times).

[0085] When the coating surface is sufficiently hydrophilic, the capacitance of the circuit is large in the Y-gap of the measurement sample, and the interval discharge charge that occurs in the Y-gap of the measurement sample often exceeds 100 pC, as shown on the right side of Figure 10. On the other hand, at the back-to-back part of the two rectangular enameled wires that make up the measurement sample or at the R-corner gap, discharge between one coating and the other is unlikely to occur.

[0086] Therefore, when the coating surface is sufficiently hydrophilic, the voltage applied to the measurement sample when partial discharge occurs is lower than when the coating surface is not sufficiently hydrophilic, as can be seen from the histogram in Figure 15. The locations where partial discharges occur on the measurement sample are concentrated near the back-to-back portion of the measurement sample or near the base of the Y-shaped gap, not including the R-corner gap. The interval discharge charge peaks around 100 pC and spreads throughout, but tends to stabilize. As can be seen from the discharge light emission image in Figure 16, it can be confirmed that the discharge light emission occurs near the base of the Y-shaped gap, not including the back-to-back portion or the R-corner gap.

[0087] The partial discharges and their interval discharge charge can be summarized as follows. When the coating is insufficiently hydrophilic, discharges are likely to occur not only in the Y-shaped gap of the measurement sample but also in the back-to-back or rounded corner gap between two rectangular enameled wires. On the other hand, when the coating is sufficiently hydrophilic, discharges are likely to occur in the Y-shaped gap of the measurement sample, but are unlikely to occur in the back-to-back or rounded corner gap between two rectangular enameled wires. Based on these findings, when the coating is properly hydrophilized, i.e., when treatment to reduce variability in PDIV measurement results is performed, the interval discharge charge per partial discharge tends to be relatively small and biased toward a predetermined value. On the other hand, when the coating is not properly hydrophilized, i.e., when treatment to reduce variability in PDIV measurement results is not performed, the interval discharge charge per partial discharge tends to be relatively large and more variable.

[0088] From the above, by referring to the magnitude and variation of the interval discharge charge amount in multiple partial discharges, it is possible to evaluate whether the coating surface has been sufficiently hydrophilized and modified, resulting in suppression of variation in PDIV measurement results. In other words, if variation in PDIV measurement results is suppressed, the basis for this can be found from the magnitude of the interval discharge charge amount or the degree of variation in the interval discharge charge amount. Therefore, the interval discharge charge amount in multiple partial discharges is suitable as an index for evaluating (determining) the degree of suppression of variation in PDIV measurement results. Displaying the interval discharge charge amount in multiple partial discharges, and further displaying a histogram showing the occurrence frequency for each range of the interval discharge charge amount, leads to an evaluation of the degree of suppression of variation in PDIV measurement results.

[0089] <Configuration of PDIV measurement system according to embodiment 1> Hereinafter, a PDIV measurement system according to the first embodiment will be described with reference to the drawings.

[0090] Fig. 17 is a diagram showing an example of the configuration of a PDIV measurement system according to embodiment 1. As shown in Fig. 17, a PDIV measurement system 40 includes a PDIV measurement device 50, a discharge signal detection device 60, a computer 70, an operation device 81, and a display device 82. The PDIV measurement device 50, the discharge signal detection device 60, the operation device 81, and the display device 82 are connected to the computer 70 in a communicable manner. Note that a printer, a data transmitter to an external device, etc. may be connected to the computer 70.

[0091] The operation device 81 is configured with, for example, a keyboard, a mouse, etc. The display device 82 is, for example, a liquid crystal display monitor, an organic EL display monitor, etc. The operation device 81 and the display device 82 may be integrated into one device such as a touch panel.

[0092] The PDIV measurement device 50 includes, for example, a voltage generation circuit, a voltage / charge measurement circuit, and a control circuit.

[0093] The voltage generation circuit has a high-voltage line terminal and a ground line terminal, each of which is connected to the measurement sample 2. A high AC voltage (for example, with a frequency of several kHz and an effective voltage of up to several kV) is generated between these two terminals by the voltage generation circuit, thereby applying a voltage to the measurement sample 2.

[0094] The voltage and charge measurement circuit measures the voltage between the high-voltage line terminal and the ground line terminal and the amount of charge flowing between these terminals, thereby measuring the voltage applied between one end and the other end of each of the two rectangular enameled wires 1 that make up the measurement sample 2 and the amount of charge generated in the measurement sample 2. However, the amount of charge measured here is used for processing within the PDIV measurement device 50 and is not output to the outside of the PDIV measurement device 50.

[0095] The control circuit controls the voltage generation circuit and the voltage / charge measurement circuit. For example, the control circuit sends a control signal to the voltage generation circuit to control the effective voltage value, frequency, etc. of the voltage generated by the voltage generation circuit between the high-voltage line terminal and the ground line terminal. Furthermore, for example, the control circuit measures the voltage between the terminals of the voltage generation circuit or the amount of charge flowing between the terminals based on the output signal from the voltage / charge measurement circuit. In response to user operation and based on set conditions, the control circuit automatically performs a preliminary discharge and PDIV measurement on the measurement sample 2 connected to both of the above terminals.

[0096] The PDIV measurement device 50 does not necessarily have to include a control circuit. In this case, the computer 70 controls the voltage generation circuit and the voltage / charge measurement circuit in place of the control circuit.

[0097] The discharge signal detection device 60 includes, for example, an oscilloscope and a current transformer. The current transformer converts the discharge current flowing through the wiring connecting the PDIV measurement device 50 and the measurement sample 2 into a voltage signal and outputs the voltage signal. The current transformer may be a board-mounted type or a clamp type. The oscilloscope is, for example, a digital oscilloscope. The oscilloscope is connected to the current transformer and converts the waveform of the voltage signal input from the current transformer, i.e., the discharge signal representing the time change of the discharge current, into data, stores it, and outputs it. Note that the configuration of the discharge signal detection device 60 is not limited to the above configuration and may be other configurations.

[0098] Fig. 18 is a diagram showing an example of the configuration of a computer. As shown in Fig. 18, a computer 70 includes a processor 71, a memory 72, a storage 73, an interface 74, and a communication bus 75. The processor 71, the memory 72, the storage 73, and the interface 74 are connected via the communication bus 75 so as to be able to communicate with each other.

[0099] The processor 71 is, for example, a CPU (Central Processing Unit), an MPU (Micro Processor Unit), or an MCU (Micro Controller Unit). The memory 72 is, for example, a semiconductor storage circuit, such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The storage 73 is, for example, an SSD (Solid State Drive) or an HDD (Hard Disk Drive). The interface 74 is connected to an external device and performs data transmission and reception.

[0100] A program P7 is stored in the storage 73. The processor 71 reads the program P7 from the storage 73, loads it into the memory 72, and executes it to perform various processes.

[0101] The computer 70 performs various processes, such as the following. Based on the detected discharge signal, the computer 70 references the output voltage characteristics of the current transformer in the discharge signal detection device 60 and performs a process of generating a curve representing the time change of the discharge current, i.e., waveform data of the discharge current. The computer 70 performs a process of deriving the amount of charge for each section, with each section being convex on the positive side and each section being convex on the negative side in the curve representing the time change of the discharge current. The computer 70 performs a process of controlling the display device 82 so that the derived amount of charge for each section is displayed. The computer 70 also controls the display device 82 so that a histogram representing the frequency of occurrence in each range of the amount of charge is displayed.

[0102] <Processing flow for generating frequency distribution information of section discharge charge amount> 19 is a flowchart showing an example of the process flow for generating frequency distribution information of sectional discharge charge amounts. This flowchart describes in detail the process from the detection of a discharge signal in step S9 to the generation of frequency distribution information of sectional discharge charge amounts in step S11 in the flowchart of FIG.

[0103] In step S101, a process is performed to detect the discharge current flowing between the PDIV measurement device and the measurement sample as a voltage signal. Specifically, while the PDIV measurement device 50 is measuring the PDIV, the discharge signal detection device 60 converts the discharge current flowing between the PDIV measurement device 50 and the measurement sample 2 into a voltage signal and detects the converted voltage signal as a discharge signal. The computer 70 acquires the detected discharge signal from the discharge signal detection device 60.

[0104] In step S102, a process is performed to determine whether one PDIV measurement has been completed. Specifically, for example, the computer 70 determines whether one PDIV measurement has been completed based on whether a preset predetermined time (a time corresponding to one PDIV measurement) has elapsed since the start of the PDIV measurement or discharge signal detection. Alternatively, the computer 70 determines whether one PDIV measurement has been completed based on an output signal from the PDIV measurement device 50. Here, if it is determined that one PDIV measurement has been completed (S102: YES), the process proceeds to step S103. On the other hand, if it is determined that one PDIV measurement has not been completed (S102: NO), the process returns to step S101, and the detection of the discharge signal continues.

[0105] In step S103, a process is performed to determine whether all PDIV measurements (here, five measurements) have been completed. Specifically, the computer 70 determines whether the PDIV measurements have been completed based on the output signal from the PDIV measurement device 50, or based on whether a preset time has elapsed, or based on the number of YES determinations in S102. Here, if it is determined that the PDIV measurements have been completed (S103: YES), the process proceeds to step S104. On the other hand, if it is determined that the PDIV measurements have not been completed (S103: NO), the process returns to step S101, and detection of the discharge signal continues.

[0106] In step S104, a process is performed to extract a time change in the discharge current (for example, a time change in the discharge current as shown in Fig. 12) based on a discharge signal obtained at each predetermined time. Specifically, the computer 70 extracts data representing a time change in the discharge current (hereinafter also referred to as discharge current waveform data) for each of the PDIV measurements from the first to the Nth (fifth in this embodiment), which are all of the PDIV measurements, based on a discharge signal obtained for each PDIV measurement.

[0107] In step S105, a process is performed to extract sections that are convex on both the positive and negative sides of the current value in a curve that represents the time change of the discharge current based on the discharge signal detected in the PDIV measurement. Specifically, the computer 70 extracts sections that are convex on both the positive and negative sides of the current value in a curve that represents the time change of the discharge current for one PDIV measurement, based on the discharge current waveform data extracted in step S104.

[0108] In step S106, the current value is integrated over time for each interval to derive the interval discharge charge amount for each interval. Specifically, the computer 70 performs a calculation to integrate the current value for each interval extracted in step S105 over time to derive the interval discharge charge amount, which is the discharge charge amount for that interval.

[0109] In step S107, a process is performed to generate information representing a frequency distribution of the sectional discharge charge amounts corresponding to one PDIV measurement based on the derived sectional discharge charge amounts. Specifically, the computer 70 generates information representing a frequency distribution of the sectional discharge charge amounts corresponding to one PDIV measurement based on the sectional discharge charge amounts for each sectional calculated in step S106. Here, the computer 70 generates a histogram in which one axis represents each range of the sectional discharge charge amount and the other axis represents the occurrence frequency of the sectional discharge charge amount within that range. This generates a histogram representing the occurrence frequency of each range of the sectional discharge charge amount in one PDIV measurement. The bin width of the histogram can be, for example, approximately 10 pC to 50 pC, and is 40 pC in this embodiment.

[0110] In this embodiment, the process of step S107 is repeatedly executed to generate information (five pieces of information in total) representing the frequency distribution of the section discharge charge amount corresponding to each of the five PDIV measurements as shown in Fig. 5. That is, taking Fig. 5 as an example, for measured PDIVs V21 to V25, information corresponding to the PDIV measurement of V21, information corresponding to the PDIV measurement of V22, information corresponding to the PDIV measurement of V23, information corresponding to the PDIV measurement of V24, and information corresponding to the PDIV measurement of V25 are generated.

[0111] In step S108, a process is performed to determine whether information (histograms) for all PDIV measurements have been generated. Specifically, the computer 70 determines whether histograms for all PDIV measurements have been generated based on the histogram generation history. In this embodiment, it is determined whether histograms representing the frequency distribution of section discharge charge amounts corresponding to all five PDIV measurements, as shown in FIG. 5, have been generated. Taking FIG. 5 as an example, it is determined whether histograms corresponding to the PDIV measurements V21 to V25, i.e., a total of five histograms, have been generated. Here, if it is determined that histograms for all PDIV measurements have been generated (S108: YES), the process ends. On the other hand, if it is determined that histograms for all PDIV measurements have not been generated (S108: NO), the process returns to step S105, and the process continues to generate a histogram for another PDIV measurement.

[0112] The above process generates histograms for all PDIV measurements (five in this example). When the peak of each generated histogram is near 100 pC, as shown in Fig. 15, it is inferred that the effects of the preliminary discharge, such as hydrophilizing the coating surface, are realized, and partial discharge measurement at the Y-shaped gap is performed with high accuracy. On the other hand, when the peak of each generated histogram is near a charge amount relatively larger than 100 pC, such as 700 pC to 900 pC, as shown in Fig. 13, it is inferred that the effects of the preliminary discharge, such as hydrophilizing the coating surface, are not realized sufficiently, and partial discharge measurement is performed not only at the Y-shaped gap but also at the back-to-back portion.

[0113] 19 is merely an example, and the present invention is not limited to this example. The process flow for generating information representing the frequency distribution of the interval discharge charge amount may be a modified example of the process flow or another process flow.

[0114] For example, in the example of the processing flow described above, in the processing of step S102, it is determined sequentially whether one PDIV measurement has been completed. However, the processing of step S102 may be omitted. Furthermore, the processing of step S104 may be started when it is determined in step S102 that one PDIV measurement or a predetermined number of PDIV measurements have been completed, without waiting for the completion of all PDIV measurements.

[0115] Also, for example, in the example of the processing flow described above, in the processing of S104, data representing the time change of the discharge current is extracted for each PDIV measurement. However, data representing the time change of the discharge current for all N PDIV measurements (from the first to the Nth measurements: N is a natural number of 2 or more) may be extracted all at once, and then the extracted data may be separated for each PDIV measurement.

[0116] Furthermore, for example, in the example of the processing flow described above, the PDIV is measured N times (N is a natural number of 2 or more), and information representing the frequency distribution of the sectional discharge charge amount is generated by dividing the PDIV into individual measurements (a total of N pieces of information are generated). However, the PDIV may be measured N times (N is a natural number of 2 or more), and the curve representing the time change of the discharge current for the N measurements may not be divided into individual measurements of the PDIV, but information representing the frequency distribution of the sectional discharge charge amount may be generated based on the sectional discharge charge amount included in the entire curve representing the time change of the discharge current over all N measurements of the PDIV. In other words, information representing the frequency distribution of the sectional discharge charge amount corresponding to all N measurements of the PDIV may be generated (a total of one piece of information is generated).

[0117] Furthermore, for example, the PDIV may be measured N times (N is a natural number of 2 or more) and information representing the frequency distribution of the sectional discharge charge amount corresponding to the entirety of at least one of the N PDIV measurements may be generated (a total of one piece of information is generated). When it is possible to determine a measurement that is preferable to adopt from all N PDIV measurements, this process can be applied to generate information representing the frequency distribution of the sectional discharge charge amount with higher accuracy or higher reliability.

[0118] Furthermore, for example, the PDIV may be measured N times (N is an even number equal to or greater than 4), and the N PDIV measurements may be divided equally into L (L is a natural number smaller than N) measurements to generate information representing the frequency distribution of the sectional discharge charge amount (a total of M / L pieces of information may be generated). When the number of PDIV measurements N is very large, application of this process can reduce the amount of information representing the frequency distribution of the sectional discharge charge amount to be generated, making the information easier for the user to understand or handle.

[0119] In addition, for example, in the example of the processing flow described above, it is assumed that the PDIV measurement is performed multiple times. However, if the PDIV measurement is performed only once, the processes of S102, S103, and S108 may be omitted.

[0120] In the above example of the processing flow, the information representing the frequency distribution of the sectional discharge charge amount is a histogram. However, the information may be in any form as long as it visualizes the frequency distribution of the sectional discharge charge amount. For example, it may be a line graph, a curve graph, a frequency distribution table, or the like. Furthermore, multiple pieces of this information in different forms may be generated, and the multiple pieces of generated information may be output together.

[0121] As described above, according to the first embodiment, the magnitude of the interval discharge charge amount corresponding to each partial discharge in the measurement specimen 2 is displayed, so that the user can confirm whether the interval discharge charge amount is biased toward a relatively large predetermined value or toward a relatively small predetermined value. As a result, based on the interval discharge charge amount in the measurement specimen 2, the user can determine whether the partial discharge occurrence locations are concentrated in the ideal Y-shaped gap portion or extend to the non-ideal back-to-back portion, thereby enabling a more reliable evaluation of the variation in the PDIV measurement results.

[0122] For example, even if the variation in the PDIV measurement results appears to be suppressed, if the interval discharge charge amount is biased toward a relatively large predetermined value, the hydrophilization and modification of the coating surface may be insufficient, and remeasurement may be considered. Conversely, even if the variation in the PDIV measurement results is somewhat observed, if the discharge charge amount is biased toward a relatively small predetermined value, the hydrophilization and modification of the coating surface may be sufficient, and the PDIV measurement may have been performed accurately and satisfactorily.

[0123] First Modification of First Embodiment In the PDIV measurement method according to the first embodiment, a process may be added to determine whether a peak in the frequency distribution of the sectional discharge charge amount is within a predetermined range or whether it is equal to or greater than a predetermined threshold or equal to or less than a predetermined threshold.

[0124] For example, a process is performed to determine whether a peak in the frequency distribution of the interval discharge charge amount is within a range of 100 pC ± 50 pC. If it is determined that the peak is within the range of 100 pC ± 50 pC (50 pC or more and 150 pC or less), it can be determined that the PDIV measurement was performed satisfactorily. On the other hand, if it is determined that the peak is not within the range of 100 pC ± 50 pC, it can be determined that the PDIV measurement was not performed satisfactorily.

[0125] Further, for example, a process is performed to determine whether the peak in the frequency distribution of the sectional discharge charge amount is 150 pC or less. If it is determined that the peak is 150 pC or less, it can be determined that the PDIV measurement was performed satisfactorily. On the other hand, if it is determined that the peak is not 150 pC or less (is greater than 150 pC), it can be determined that the PDIV measurement was not performed satisfactorily.

[0126] Further, for example, a process is performed to determine whether or not the peak in the frequency distribution of the sectional discharge charge amount is 200 pC or more. If it is determined that the peak is 200 pC or more, it can be determined that the PDIV measurement was not performed properly. On the other hand, if it is determined that the peak is not 200 pC or more (is smaller than 200 pC), it can be determined that the PDIV measurement was performed properly.

[0127] When outputting the frequency distribution of the sectional discharge charge amount, information indicating a preset range or threshold may be superimposed on the frequency distribution and output. Also, the above-mentioned determination result may be output together.

[0128] <Modification 2 of Embodiment 1> In the first embodiment, the measurement object is a measurement sample made of two rectangular enameled wires, but the measurement object may be a measurement sample made of two enameled wires whose cross-sectional shape is different from a substantially rectangular shape.

[0129] Although various embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and includes various modifications. Furthermore, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. All of these fall within the scope of the present invention. Furthermore, numerical values ​​and the like included in the text and figures are merely examples, and the use of different values ​​does not impair the effects of the present invention.

[0130] For example, in the above-described embodiment, a rectangular enameled wire, in which a conductor such as copper is covered with an enamel coating, is used as the electric wire constituting the measurement sample, but the present invention is not limited to this. That is, the present invention can also be applied to, for example, an enameled wire whose conductor is a metal other than copper, or an electric wire whose coating is an insulating film other than enamel. [Explanation of symbols]

[0131] 1 Flat enameled wire, 1a conductor, 1b coating, 1c back-to-back portion, 1d terminal portion, 2 Measurement sample, 11 Mating surface, 12 Fixture, 50 PDIV measurement device, 60 Discharge signal detection device, 70 Computer, 71 Processor, 72 Memory, 73 Storage, 74 Interface, 75 Communication bus, 81 Operation device, 82 Display device, 91 Solid surface, 92 Droplet, L Tangent, P7 Program, α Contact angle, θ Bending angle

Claims

1. A method for measuring the partial discharge inception voltage of two enameled wires, each having a coating around a conductor, in a state where the enameled wires are stacked together in contact with each other over a predetermined region in the longitudinal direction of the enameled wires, comprising the steps of: detecting a discharge signal representing a time change in a discharge current generated in the enameled wire while measuring the partial discharge inception voltage; In a curve representing a time change of the discharge current based on the detected discharge signal, a section in which the current value is convex on the positive side and a section in which the current value is convex on the negative side are defined as one section, and an interval discharge charge amount, which is the charge amount for each of the sections, is derived; generating information representing a frequency distribution of the section discharge charge amounts corresponding to the measured partial discharge inception voltages based on the derived section discharge charge amounts; Method for measuring partial discharge inception voltage.

2. 2. The method for measuring a partial discharge inception voltage according to claim 1, Before measuring the partial discharge inception voltage, a preliminary discharge is performed multiple times by applying an AC voltage having a preset effective voltage between one end and the other end of each of the two enameled wires for a certain period of time, thereby making the surfaces of the coatings of the two enameled wires hydrophilic; Method for measuring partial discharge inception voltage.

3. The method for measuring a partial discharge inception voltage according to claim 1, A histogram of the interval discharge charge amount is generated as the information. Method for measuring partial discharge inception voltage.

4. 2. The method for measuring a partial discharge inception voltage according to claim 1, The partial discharge inception voltage of the two enameled wires is measured N times (N is a natural number of 2 or more), generating the information corresponding to at least one entire measurement of the N measurements of the partial discharge inception voltage; Method for measuring partial discharge inception voltage.

5. 5. The method for measuring a partial discharge inception voltage according to claim 4, generating the information for each measurement of the partial discharge inception voltage; Method for measuring partial discharge inception voltage.

6. 5. The method for measuring a partial discharge inception voltage according to claim 4, generating the information corresponding to all of the N measurements of the partial discharge inception voltage; Method for measuring partial discharge inception voltage.

7. 2. The method for measuring a partial discharge inception voltage according to claim 1, determining whether a peak in the frequency distribution of the section discharge charge amount represented by the generated information is within a predetermined range or is equal to or greater than a predetermined threshold or equal to or less than a predetermined threshold; Method for measuring partial discharge inception voltage.

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