Method and device for measuring partial discharge inception voltage of enameled wire

Abstract

To suppress variations in PDIV (partial discharge inception voltage) measurements of an enameled wire.SOLUTION: A partial discharge inception voltage measurement method is provided, for measuring the partial discharge inception voltage of enameled wires while two enameled wires with coatings are brought into contact and laminated together over a given range in a longitudinal direction of the enameled wires, the method comprising a hydrophilization step (S7) of hydrophilizing surfaces of the coatings of the two enameled wires before measuring the partial discharge inception voltage.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] A method for measuring the partial discharge inception voltage of an enameled wire, which has a coating around a conductor with a substantially rectangular cross section, is known to evaluate the electrical characteristics of the wire (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] When evaluating the electrical properties of enameled wires using PDIV measurements, it is necessary to suppress the variability in the PDIV measurement results in order to improve the reliability of the evaluation.

[0005] Due to the above circumstances, there is a need for a technology that can suppress the variation in the PDIV measurement results of 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 a measurement sample in which two enameled wires with coatings are laminated together, the method comprising a hydrophilization step of hydrophilizing the surfaces of the coatings of the two enameled wires before measuring the partial discharge inception voltage. [Effects of the Invention]

[0007] According to a representative embodiment of the present application, it is possible to suppress variations in PDIV measurement results. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram showing an example of the configuration of a measurement sample. [Figure 2A] FIG. 10 is a diagram illustrating a Y-shaped gap portion of a measurement sample. [Figure 2B] FIG. 10 is a diagram for explaining a corner R gap portion of a measurement sample. [Figure 3] 1 is a flowchart illustrating a reference PDIV measurement method. [Figure 4] 1 is a flowchart showing a PDIV measurement method according to the first embodiment. [Figure 5] FIG. 1 is a diagram illustrating an example of a hardware configuration of a PDIV measurement device. [Figure 6] FIG. 10 is a diagram showing an example of the time change of the voltage applied to the measurement sample by the standard method. [Figure 7] FIG. 10 is a diagram showing an example of the time change of the voltage applied to the measurement sample according to the proposed method. [Figure 8A] FIG. 2 is a front view showing an example of a widthwise structure of a bending tool. [Figure 8B] FIG. 2 is a side view showing an example of the longitudinal structure of a bending tool. [Figure 9] 1A and 1B are diagrams showing how the surface of the coating of an enameled wire is ultrasonically cleaned. [Figure 10A] 10A and 10B are diagrams illustrating an example of the widthwise structure of a fixing jig. [Figure 10B] 10A and 10B are diagrams illustrating an example of the structure of a fixing jig in the longitudinal direction. [Figure 11] FIG. 1 is a diagram for explaining the contact angle of a liquid, which is an index of hydrophilicity. [Figure 12] 1 is a table showing conditions for preliminary discharge and PDIV measurement. [Figure 13] 1 is a histogram of PDIV measurement values ​​of measurement samples according to a standard method. [Figure 14] 1 is a histogram of the PDIV measurement values ​​of the sample measured by the proposed method. 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] First, the configuration of a measurement sample to be used for measuring the partial discharge inception voltage (PDIV) will be described.

[0011] FIG. 1 shows an example of the structure of a measurement sample. As shown in FIG. 1, the measurement sample 2 includes two enameled wires 1 (hereinafter also referred to as flat enameled wires 1) each having a conductor 1a composed of a metal wire with a substantially rectangular cross-section and a coating 1b surrounding the conductor 1a. The two enameled wires 1 are fixed in a back-to-back state, with the back-to-back portions 1c of the two enameled wires 1 in contact with each other at mating surfaces 11, over a predetermined region D1, e.g., 120 mm long, along the longitudinal direction of the flat enameled wires 1. In other words, when measuring PDIV, the measurement sample 2 is configured such that two enameled wires 1, each having a conductor 1a coated with an insulating coating 1b, are stacked in the thickness direction C1. The measurement sample 2 includes two enameled wires 1 fixed at five locations within the predetermined region D1 using fixtures 12, such as wires or clips.

[0012] 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.

[0013] 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°.

[0014] 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.

[0015] 2A is a diagram illustrating the Y-shaped gap of the measurement sample. As shown in Fig. 2A, 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-shaped gap Y. The Y-shaped gap Y is one of the parts of the measurement sample 2 where partial discharge is likely to occur.

[0016] Figure 2B is a diagram illustrating the corner R gap of the measurement sample. Figure 2B is a cross-sectional view of measurement sample 2 taken along line AA in Figure 2A. As shown in Figure 2B, the corner R gap R is the portion at each end of mating surface 11 of two rectangular enameled wires 1 constituting measurement sample 2 in the width direction B1. The corner R gap R is also one of the areas in measurement sample 2 where partial discharge is likely to occur.

[0017] 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.

[0018] 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.

[0019] (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.

[0020] Fig. 3 is a flowchart showing a reference PDIV measurement method. Fig. 4 is a flowchart showing a PDIV measurement method according to the first embodiment.

[0021] The reference PDIV measurement method shown in Fig. 3 is an example of a PDIV measurement method previously devised by the present inventors, and is intended for comparison with the PDIV measurement method of embodiment 1 shown in Fig. 4. Hereinafter, the reference PDIV measurement method will also be referred to as the "reference method," and the PDIV measurement method according to embodiment 1 will also be referred to as the "proposed method."

[0022] <Flow of the standard PDIV measurement method> First, we will explain the standard method for measuring PDIV. The flow of the standard method is as follows:

[0023] As shown in Figure 3, in step (process) J1, 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.

[0024] In step J2, the rectangular enameled wires are straightened. Specifically, the lengths of the two rectangular enameled wires 1 are elongated by 2% along their longitudinal directions to remove any bending tendency in the rectangular enameled wires 1.

[0025] In step J3, foreign matter on the surface of the coating of the rectangular enameled wire is removed using an adhesive. Specifically, an adhesive roller (a rotating body with adhesive properties) is rolled over the entire surface of the coating 1b of the rectangular enameled wire 1, which serves as the measurement sample 2, to remove foreign matter such as dust adhering to the surface of the coating 1b.

[0026] In step J4, a measurement sample is manually formed. Specifically, measurement sample 2 as shown in Figure 1 is formed without using a bending tool or fixture, which will be described later. For example, measurement sample 2 is formed by placing two rectangular enameled wires 1 back to back with their mating surfaces 11 facing each other and fixing them with fixture 12 such as a wire, and bending both ends 1d of the two rectangular enameled wires 1 in the extending direction F1 so that they are separated from each other.

[0027] In step J5, moisture is removed from the coating of the rectangular enameled wire. Specifically, the rectangular enameled wire 1, which will serve 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 wire is then left for about an hour in the same environment as when the PDIV measurement is performed (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.

[0028] In step J6, 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.

[0029] In step J7, the sensitivity of the voltage / charge measuring device 52, which will be described later, is calibrated. The voltage applied during calibration is AC, its frequency is 1 kHz, and the discharge charge amount is 100 pC.

[0030] In step J8, a preliminary discharge is performed using the partial discharge inception voltage. A preliminary discharge, also known as a pre-discharge, is a partial discharge that occurs before the PDIV measurement begins. Specifically, an AC voltage (e.g., a high-frequency voltage with a frequency of 1 kHz) is applied between one and the other of the two rectangular enameled wires 1 that make up the measurement specimen 2. The applied voltage (hereinafter, unless otherwise specified, "voltage" refers to AC voltage, and "voltage (value)" refers to effective voltage) is gradually increased until a partial discharge occurs in the measurement specimen 2. The applied voltage is maintained for a certain period of time, e.g., approximately 20 seconds, to allow the partial discharge to continue. Then, the application of voltage to the measurement specimen 2 is stopped.

[0031] In step J9, PDIV measurements are performed multiple times consecutively. Specifically, a voltage (e.g., a high-frequency voltage with a frequency of 1 kHz) is applied between one and the other of the two rectangular enameled wires 1 constituting the measurement sample 2 using a voltage generator 51 (described later). The applied voltage is gradually increased, and when a partial discharge is detected in the measurement sample 2 using a voltage / charge measuring device 52 (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.

[0032] The preliminary discharge in step J8 and the PDIV measurement in step J9 are carried out using, for example, a PDIV measurement device. Here, the PDIV measurement device will be described.

[0033] 5 is a functional block diagram showing a schematic configuration of a PDIV measurement device 50. As shown in FIG. 5, the PDIV measurement device 50 includes at least a voltage generator 51, a voltage / charge measurement device 52, and a computer 60 as a control device.

[0034] Voltage generator 51 has a high-voltage line terminal and a ground line terminal, each of which is connected to measurement sample 2. Voltage generator 51 generates a high AC voltage (e.g., a frequency of several kHz and an effective voltage of up to several kV) between these terminals, thereby applying a voltage to measurement sample 2. Voltage and charge measuring device 52 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 and the other of two rectangular enameled wires 1 that make up measurement sample 2 and the amount of charge generated in measurement sample 2. Computer 60, which serves as a control device, is connected to voltage generator 51 and voltage and charge measuring device 52 via interface 66.

[0035] The computer 60, which is a control device, sends a control signal to the voltage generator 51 to control the effective voltage value, frequency, etc. of the voltage that the voltage generator 51 generates between the high-voltage line terminal and the ground line terminal, and measures the voltage between the terminals of the voltage generator 51 or the amount of charge flowing between the terminals based on an output signal from the voltage / charge measuring device 52. The control device 53 is also configured to automatically perform the above-mentioned preliminary discharge and PDIV measurement on the measurement sample 2 connected to both of the above-mentioned terminals in response to a user's operation.

[0036] As shown in FIG. 5, the computer 60 includes a processor 61 , a memory 62 , a storage 63 , an operation unit 64 , a display unit 65 , an interface 66 , and a bus 67 .

[0037] The processor 61 is configured, for example, by an MCU (Micro-Control Unit) or an MPU (Micro-Processing Unit). The memory 62 is configured, for example, by a RAM (Random Access Memory). The storage 63 is configured, for example, by an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The operation unit 64 is configured, for example, by a keyboard, a mouse, etc. The display unit 65 is configured, for example, by a liquid crystal display, a 7-segment display, etc.

[0038] The processor 61, memory 62, storage 63, operation unit 64, display unit 65, and interface 66 are connected to a bus 67. The voltage generator 51 and voltage / charge measuring device 52 are connected to the interface 66.

[0039] A program P for measuring the PDIV is stored in the storage 63. The processor 61 reads the program P from the storage 63, expands the read program P in the memory 62, and executes the program P, thereby functioning as the above-mentioned control device and executing processing for automatically performing preliminary discharge and PDIV measurement.

[0040] The storage 63 also functions as a memory unit, and stores various data such as the PDIV measurement value, the voltage applied to the sample, the charge amount as a partial discharge determination condition, the set pre-discharge voltage, the dispersion of the measurement value, σ (standard deviation), the average value of the measurement value, the number of samples, etc.

[0041] FIG. 6 is a diagram showing an example of the change over time in the voltage applied to the measurement sample using the standard method. In FIG. 6, the horizontal axis represents time t, and the vertical axis represents the applied voltage V. As shown in FIG. 6, 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. Then, when a partial discharge starts, the applied voltage V is fixed to voltage V10, which is the applied voltage when the partial discharge started, and maintained for a certain period of time, for example, approximately 20 seconds. After that, the applied voltage V is temporarily returned to 0.

[0042] Next, PDIV measurement is performed. Specifically, the applied voltage V to the measurement specimen 2 is gradually increased from 0. When partial discharge starts in the measurement specimen 2, the applied voltage at that time, V11, is stored in the storage 63 as the first PDIV measurement value, and the applied voltage V is immediately returned to 0.

[0043] Next, the applied voltage V to the measurement specimen 2 is gradually increased again from 0. When a partial discharge starts in the measurement specimen 2, the applied voltage at that time, V12, is stored in the storage 63 as the second PDIV measurement value, and the applied voltage V is immediately returned to 0.

[0044] The applied voltage V changes in the same way in the third to fifth PDIV measurements, and rises and falls repeatedly from peaks at voltages V13 to V15 at which partial discharges start. The voltages V13 to V15 are stored in storage 63 as the third to fifth PDIV measurement values.

[0045] <Proposed PDIV measurement method flow> Next, a description will be given of the proposed PDIV measurement method according to embodiment 1. The flow of the proposed method is as follows.

[0046] As shown in Figure 4, in step S1, the rectangular enameled wire 1 is shaped using a bending tool. Specifically, the bending tool is used to bend both end portions 1d of the rectangular enameled wire 1 in the extending direction F1 to the same direction in the thickness direction C1 of the rectangular enameled wire 1 at a bending angle θ. 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. Details of shaping the rectangular enameled wire 1 using the bending tool will be described later.

[0047] In step S2, moisture is removed from the coating of the rectangular enameled wire. Step S2 is the same process as step J5 in the standard method, so a detailed explanation will be omitted here.

[0048] In step S3, the surface charge of the coating of the rectangular enameled wire is removed. Step S3 is the same process as step J6 in the standard method, so a detailed explanation will be omitted here.

[0049] In step S4, the rectangular enameled wire is ultrasonically cleaned. Specifically, the rectangular enameled wire is cleaned with a solvent in an ultrasonic cleaner to remove foreign matter, oils, and other components adhering to the surface of the coating. Details of ultrasonic cleaning of rectangular enameled wire will be described later.

[0050] In step S5, a measurement sample is formed using a fixing jig. Specifically, two rectangular enameled wires 1, each having bent terminal portions 1d on both sides, are stacked and fixed using the fixing jig to form measurement sample 2. Details of forming the measurement sample using the fixing jig will be described later.

[0051] In step S6, the sensitivity of the voltage / charge measuring device 52 is calibrated. Step S6 is the same process as step J6 in the reference method. The applied voltage during calibration is AC, its frequency is 1 kHz, and the discharge charge amount is 100 pC.

[0052] In step S7, the surface of the coating is made hydrophilic. Specifically, the surface of the coating 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 is made hydrophilic. In addition, in the proposed method, one method for making the surface of the coating 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 hydrophilic is to perform a preliminary discharge on the measurement sample 2 at a preset fixed voltage (first effective voltage) for a certain period of time (first period). Details of making the surface of the coating 1b hydrophilic will be described later.

[0053] In step S8, the PDIV measurement is performed multiple times consecutively on the rectangular enameled wire 1 whose surface of the coating 1b has been made hydrophilic. In step S8, the PDIV measurement is performed using the same measurement method as in step J9 of the standard method. Therefore, a detailed description of this method will be omitted here.

[0054] The preliminary discharge in step S7 and the PDIV measurement in step S8 are performed, for example, as in the reference method, using the PDIV measurement device 50. The configuration and function of the PDIV measurement device 50 are basically the same as those described in the reference method, but the control of the voltage V applied to the measurement sample 2, i.e., the content of the program P to be executed, differs from that of the reference method.

[0055] Specifically, in the preliminary discharge of the measurement sample 2 performed in step S7, the control device 53 of the PDIV measurement device 50 accepts the setting of the fixed voltage value so that the voltage applied to and maintained at the measurement sample 2 can be set to a preset fixed voltage value. That is, the program P is configured to be able to accept the setting of the fixed voltage value.

[0056] Fig. 7 shows an example of the time change of the voltage applied to the measurement specimen 2 using the proposed method. Note that Fig. 7 shows the time change of the voltage V applied to the measurement specimen 2 when preliminary discharge and PDIV measurement of the measurement specimen 2 are performed consecutively.

[0057] 7, when the PDIV measurement process by the PDIV measurement device 50 starts, 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 V20, which is a preset fixed value (a value that does not vary for each measurement sample), the applied voltage V is fixed at voltage V20 and maintained for approximately 20 seconds. During this time, partial discharge is maintained in the measurement sample 2. Thereafter, the applied voltage V returns to 0.

[0058] 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.

[0059] 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.

[0060] <Shaping rectangular enameled wire using a bending tool> Here, the shaping of the rectangular enameled wire by the bending tool performed in step S1 will be described in detail with reference to the drawings.

[0061] Fig. 8A is a front view showing an example of the structure of the bending tool in the width direction, and Fig. 8B is a side view showing an example of the structure of the bending tool in the length direction.

[0062] The bending tool 3 is a tool for bending the terminal portion 1d of the rectangular enameled single wire in the measurement sample 2, which is composed of two rectangular enameled wires 1 stacked together, and has a bending mechanism 4 for bending the terminal portion 1d in the extension direction F1 of the measurement sample 2, i.e., in the longitudinal direction A1 of the bending tool 3.

[0063] The bending mechanism 4 includes a base 5 that supports the rectangular enameled wire 1, a guide plate 6 that regulates the position of the rectangular enameled wire 1 in the width direction B1, a presser plate 7 that regulates and presses the rectangular enameled wire 1 in the thickness direction C1 of the rectangular enameled wire, and a presser plate 8 that applies a load to the end portion 1d of the rectangular enameled wire 1 to bend it. Four support columns 10 are provided on the top surface 5a of the base 5 to guide the upward and downward movement of the presser plate 8.

[0064] In the bending mechanism 4, guide plates 6 are arranged on both the left and right sides of the rectangular enameled wire 1 placed on the top surface 5a of the base 5, and the sides of each guide plate 6 are pressed against the sides of the rectangular enameled wire 1 from both sides to regulate the position of the rectangular enameled wire 1 in the width direction B1 on the base 5. In other words, misalignment of the rectangular enameled wire 1 in the width direction B1 on the base 5 is suppressed.

[0065] Furthermore, in the bending mechanism 4, the flat enameled wire 1, whose position in the width direction B1 is restricted by the guide plate 6 on the upper surface 5a of the base 5, is pressed from above by the lower surface 7a of the pressing plate 7, thereby restricting the position of the flat enameled wire 1 in the thickness direction C1 on the base 5.

[0066] That is, in the bending mechanism 4, the position of the flat enameled wire 1 in the width direction B1 on the base 5 is restricted by the guide plate 6, and the position of the flat enameled wire 1 in the thickness direction C1 is restricted by the presser plate 7. Then, with the position of the flat enameled wire 1 restricted in the width direction B1 and the thickness direction C1 on the top surface 5a of the base 5, the presser plate 8 is lowered under the guidance of the support 10, and a load is applied by the presser plate 8 to the end portion 1d of the flat enameled wire 1. This operation allows the end portion 1d of the flat enameled wire 1 to be bent accurately and stably to the specified bend angle θ.

[0067] The presser plate 7 and the guide plate 6 have through holes 7b and 6a, respectively, and bolts 9 are threaded through the through holes 7b and 6a of the presser plate 7 and the guide plate 6 to connect the base 5 to the bolts. The threaded connection between the bolts 9 and the base 5 firmly presses the presser plate 7 and the guide plate 6 against the top surface 5a of the base 5, so that even when a load is applied to the end 1d of the flat enameled wire 1 by the presser plate 8, the flat enameled wire 1 can be firmly fixed to the top surface 5a of the base 5.

[0068] 8B, the base 5 has an upper surface (support surface) 5a capable of supporting the rectangular enameled wire 1, and this upper surface 5a includes a flat portion 5c having a flat surface 5b and a first curved portion 5e having a curved surface 5d. However, the upper surface 5a may include portions other than the flat portion 5c and the first curved portion 5e.

[0069] Meanwhile, the pressing plate 8 has a pressing surface 8a that presses the terminal end 1d of the rectangular enameled wire 1 from above, and the pressing surface 8a includes a second curved surface portion 8c having a curved surface 8b. The curved surface 5d of the first curved surface portion 5e and the curved surface 8b of the second curved surface portion 8c are curved surfaces that can fit together. In other words, the pressing surface 8a has a second curved surface portion 8c with a curved surface 8b having the same curvature as the curved surface 5d of the first curved surface portion 5e.

[0070] Thus, the end portion 1d of the rectangular enameled wire 1 is bent by the curved surface 5d of the first curved surface 5e on the upper surface 5a of the base 5 and the curved surface 8b of the second curved surface 8c on the pressing surface 8a of the pressing plate 8. That is, the predetermined area D1 of the rectangular enameled wire 1 is placed on the flat portion 5c on the upper surface 5a of the base 5, and the end portion 1d is placed on the first curved surface 5e. In this state, the curved surface 8b of the second curved surface 8c on the pressing surface 8a of the pressing plate 8 is pressed against the end portion 1d, bending the end portion 1d of the rectangular enameled wire 1 to the predetermined bending angle θ.

[0071] The curved surface 5d of the first curved surface portion 5e of the upper surface 5a of the base 5 is a curved surface with a curvature of R50, for example.

[0072] In the case of a rectangular enameled wire 1 whose end 1d is bent by such a bending tool 3, the bending angle θ and curvature of the end 1d are accurately fixed, and the surface contour of the coating 1b at the Y-shaped gap Y in the resulting measurement sample 2 is stably formed. On the other hand, in the standard method, the end 1d of the rectangular enameled wire 1 is shaped manually, so the surface contour of the coating 1b at the Y-shaped gap Y in the resulting measurement sample 2 is not stably formed.

[0073] <Ultrasonic cleaning of rectangular enameled wire> Here, the ultrasonic cleaning of the rectangular enameled wire carried out in step S4 will be described in detail with reference to the drawings.

[0074] Fig. 9 shows how the surface of the coating of a rectangular enameled wire is ultrasonically cleaned. As shown in Fig. 9, the rectangular enameled wire 1 is immersed in a solvent 71 contained in a container 70 such as a measuring cylinder, and the container 70 is then immersed in a liquid (e.g., water) 81 in a liquid tank of an ultrasonic cleaner 80 to perform the ultrasonic cleaning. This ultrasonic cleaning not only removes foreign matter adhering to the surface of the coating 1b of the rectangular enameled wire 1, but also removes oils and fats present on the surface of the coating 1b.

[0075] After extensive investigation, the inventors have found that removing the oily components present on the surface of the coating 1b of the rectangular enameled wire 1 is effective in suppressing the variation in PDIV measurements. Furthermore, the inventors have also found that ultrasonic cleaning using a solvent 71 is an effective method for removing the oily components from the surface of the coating 1b. The standard method uses an adhesive roller, which can remove some of the foreign matter adhering to the surface of the coating 1b, but it is difficult to remove the oily components present on the surface of the coating 1b.

[0076] The inventors have found that hexane is an effective solvent for ultrasonic cleaning, but the solvent is not limited to this. The solvent 71 may be any solvent that can remove oil and fat components, such as alcohol, dichloromethane, carbon tetrachloride, benzene, toluene, or acetone.

[0077] <Forming the measurement sample using a fixture> Here, the molding of the measurement sample by the fixture performed in step S5 will be described in detail with reference to the drawings.

[0078] Fig. 10A is a diagram showing an example of the structure of a fixing jig in the width direction, and Fig. 10B is a diagram showing an example of the structure of a fixing jig in the length direction.

[0079] The fixing jig 33 is a jig capable of fixing the measurement sample 2, which is made up of two laminated rectangular enameled wires 1, and is provided with a fixing mechanism part 34 that fixes a predetermined region D1 in the extension direction F1 (which is also the longitudinal direction A1) of the measurement sample 2 shown in FIG. 2A.

[0080] The fixing mechanism 34 includes a pressure plate 35 that regulates the position of the two rectangular enameled wires 1 in a width direction B1 perpendicular to the thickness direction (stacking direction) C1 of the two rectangular enameled wires 1 in a specified region D1 of the measurement sample 2, and a pair of clamping plates 36 that are arranged on either side of the pressure plate 35 in the thickness direction (stacking direction) C1 of the two rectangular enameled wires 1 and that clamp the specified region D1 of the measurement sample 2 from both sides.

[0081] Furthermore, the fixing mechanism 34 includes a pressure plate 38 that applies a load to the measurement sample 2 in a direction along the thickness direction (stacking direction) C1 via a pair of clamping plates 36. The upper clamping plate 36 has a two-layer structure consisting of an upper insulating plate 36a and an upper metal plate 36c provided thereon. Similarly, the lower clamping plate 36 has a two-layer structure consisting of a lower insulating plate 36b and a lower metal plate 36d provided thereunder.

[0082] Additionally, a pressure plate 38 is provided above the clamping plate 36 via a coil spring 37. When measuring the PDIV, a load is applied to the pressure plate 38 so that it is pressed downward. That is, the coil spring 37, located between the clamping plate 36 and the pressure plate 38, applies a load to the two stacked rectangular enameled wires 1 in the stacking direction, i.e., the thickness direction C1. This operation restricts the positions of the two rectangular enameled wires 1 in the thickness direction C1 and prevents lifting that occurs at the mating surface 11 of the two rectangular enameled wires 1.

[0083] On the other hand, in the predetermined region D1 of the measurement sample 2 shown in FIG. 2A, the fixing mechanism 34 shown in FIG. 10A has a pressure plate 35 between the upper and lower clamping plates 36 of a pair of clamping plates 36, which restricts the positions of the two rectangular enameled wires 1 in the width direction B1.

[0084] The presser plates 35 are provided on both the left and right sides of the two rectangular enameled wires 1 in the width direction B1 of the rectangular enameled wires 1. The flat surfaces 35a of each presser plate 35 are pressed against the sides of the two rectangular enameled wires 1 from both sides, thereby regulating the positions of the two rectangular enameled wires 1 in the width direction B1. This operation prevents the two stacked rectangular enameled wires 1 from misaligning in the width direction B1.

[0085] The bolt 39 is inserted into the spiral of the coil spring 37, and a spacer 40 is disposed between the pressure plate 38 and the upper metal plate 36c. Therefore, by changing the thickness of the spacer 40, the magnitude of the load applied to the measurement sample 2 by the coil spring 37 can be controlled.

[0086] The pressing plate 38, the upper metal plate 36c, the upper insulating plate 36a, and the lower insulating plate 36b each have a plurality of through holes 38a, 36i, 36g, and 36h formed along the extension direction F1 (longitudinal direction A1) of the measurement sample 2. In this embodiment, the pressing plate 38, the upper metal plate 36c, the upper insulating plate 36a, and the lower insulating plate 36b each have two through holes 38a, 36i, 36g, and 36h formed along the extension direction (longitudinal direction A1) of the measurement sample 2.

[0087] Bolts 39 are threaded through two through-holes 38a, 36i, 36g, and 36h in each of pressure plate 38, upper metal plate 36c, upper insulating plate 36a, and lower insulating plate 36b, and are connected to lower metal plate 36d. At this time, coil spring 37 is sandwiched between pressure plate 38 and upper metal plate 36c in the thickness direction (stacking direction) C1, and measurement sample 2 is sandwiched between upper insulating plate 36a and lower insulating plate 36b. Therefore, a load is applied by coil spring 37 to the two stacked rectangular enameled wires 1 along the stacking direction, i.e., the thickness direction C1.

[0088] The upper insulating plate 36a and the lower insulating plate 36b preferably have the same length (120 mm) as the length of the mating surface 11 (the length of the predetermined region D1) of the measurement sample 2, so that they can be sandwiched in the extension direction (longitudinal direction A1) of the measurement sample 2. Furthermore, the curvature of the end of the lower surface 36e of the upper insulating plate 36a and the end of the upper surface 36f of the lower insulating plate 36b is preferably the same as the curvature (R30 or R50) of the terminal portion 1d of the measurement sample 2.

[0089] In the measurement sample 2 held by this fixture 33, the clamping pressure of the two rectangular enameled wires 1 is evenly applied in the specified region D1 in the extension direction F1, resulting in uniform contact and adhesion between the rectangular enameled wires 1. Positional deviation of the rectangular enameled wire 1 in the width direction B1 is also suppressed, resulting in a stable surface contour of the coating 1b in the corner R gap R. In contrast, with the standard method, the clamping pressure of the rectangular enameled wire 1 is relatively strong only in the area held by the fixture 12, such as a clip. This results in unstable contact and adhesion between the rectangular enameled wires 1, and they are prone to lifting in areas other than those held by the fixture 12.

[0090] <Making the surface of the coating of rectangular enameled wire hydrophilic> Here, the hydrophilization of the surface of the coating of the rectangular enameled wire carried out in step S7 will be described in detail.

[0091] 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.

[0092] 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 FIGS. 2A and 2B.

[0093] Therefore, the hydrophilization of the surface of the coating 1b performed in step S7 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 2A and 2B.

[0094] 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.

[0095] FIG. 11 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), the term "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. 11, 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.

[0096] In the proposed method, the hydrophilization of the surface of the coating 1b can be defined as a 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, as a result of investigations by the inventors. More preferably, the hydrophilization of the surface of the coating 1b is a 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). 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.

[0097] The present inventors have also found that one effective method for making the surface of the coating 1b hydrophilic is to subject the measurement sample 2 to preliminary discharge at a relatively high fixed voltage.

[0098] Therefore, in the proposed method, in order to make the surface of the coating 1b hydrophilic, a method is adopted in which a preliminary discharge is performed at a preset fixed voltage on the measurement sample 2. 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.

[0099] The measurement sample is connected to the PDIV measurement device 50, and an AC voltage is applied between one and the other 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 preset fixed voltage value, at which point the voltage is maintained for a certain period of time, for example, about 20 seconds, to maintain partial discharge. After that, the application of voltage to the measurement sample 2 is stopped.

[0100] 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.

[0101] In the proposed method, the control device 53 of the PDIV measurement device 50 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 P executed by the processor 61 of the computer 60 may be configured to enable such setting.

[0102] As mentioned above, the proposed method differs from the reference method in steps S1, S4 to S5, and S7, but it is also possible to simply replace at least one of steps J3 to J5 in the reference method with the corresponding step in the proposed method. Even with this change in at least one step, it is possible to suppress the variation in the PDIV measurement values ​​of the measurement sample 2.

[0103] <verification> The inventors have verified that the proposed method is effective in suppressing the variation in PDIV measurement values. The verification method and verification results are described below.

[0104] The verification method involves preparing nine measurement samples 2 each for the standard method and the proposed method using the same type of rectangular enameled wire 1. Then, using the standard method and the proposed method, PDIV measurements are performed five times consecutively for each measurement sample 2, and the minimum value of the five measurements is taken as the measured PDIV value for that measurement sample 2.

[0105] Figure 12 is a table showing the conditions for preliminary discharge and PDIV measurement. As shown in Figure 12, the applied voltage frequency is 1 kHz. The conditions for determining partial discharge in preliminary discharge according to the standard method are that the discharge charge is 100 pC or more and the occurrence frequency is 1000 pps or more. In preliminary discharge, the voltage application time when partial discharge occurs is approximately 20 seconds, the applied voltage increase step (voltage increase rate) is 200 V / s, and the applied voltage high-voltage step (voltage decrease rate) is output off after 0 V instruction control.

[0106] In addition, the partial discharge judgment conditions for PDIV measurement are that the discharge charge is 100pC or more and the occurrence frequency is 1000pps or more. In PDIV measurement, the applied voltage increase step (increase rate) is primary (up to 200V): 30V / s, secondary (200V or more): 10V / s, and the applied voltage high voltage step (decrease rate) is output off after 0V indication control. The measurement environment is a temperature of 23°C and humidity of 35%.

[0107] Figure 13 is a histogram of PDIV measurements of samples measured using the standard method. Figure 14 is a histogram of PDIV measurements of samples measured using the proposed method. In the PDIV measurement test using the standard method, the preliminary discharge voltage was 2076 to 2617 Vp, the average PDIV measurement was 2069 Vp, and the standard deviation σ was 102.8. In the PDIV measurement test using the proposed method, the preliminary discharge voltage was 2617 Vp, the average PDIV measurement was 1992 Vp, and the standard deviation σ was 38.2. Comparing these test results, it can be seen that the proposed method has smaller variance in PDIV measurements than the standard method.

[0108] The PDIV measurement method according to the first embodiment includes a step of hydrophilizing the surface of the coating 1b of the rectangular enameled wire 1 constituting the measurement sample 2, particularly the coating 1b at the Y-shaped gap Y and the R-corner gap R, where partial discharges are likely to occur. The inventors' research has confirmed that hydrophilizing the surface of the coating 1b of the rectangular enameled wire 1 is very effective in suppressing variation in PDIV measurements. Therefore, the PDIV measurement method according to the first embodiment can suppress variation in PDIV measurements of the rectangular enameled wire 1.

[0109] Furthermore, the inventors have confirmed through their research that ultrasonic cleaning of rectangular enameled wire 1 with solvent 71 is effective in suppressing the variation in PDIV measurements. Therefore, if the PDIV measurement method further includes a step of immersing rectangular enameled wire 1 constituting measurement sample 2 in solvent 71 and performing ultrasonic cleaning, the variation in PDIV measurements of rectangular enameled wire 1 can be further suppressed.

[0110] Furthermore, the inventors have confirmed through their studies that shaping rectangular enameled wire 1 with bending tool 3 and fixing it with fixture 33 to form measurement sample 2 is effective in suppressing variability in PDIV measurements. Therefore, if the PDIV measurement method further includes the step of shaping rectangular enameled wire 1 with bending tool 3 and fixing it with fixture 33 to form measurement sample 2, variability in PDIV measurements of rectangular enameled wire 1 can be further suppressed.

[0111] (Embodiment 2) A PDIV measurement device 50 that measures the PDIV after performing a preliminary discharge of the measurement sample 2 and is configured to include a control device according to the proposed method is also an embodiment of the present application. Specifically, the control device according to the proposed method accepts the setting of a fixed voltage value as the applied voltage V used for the preliminary discharge so that the surface of the coating 1b of the rectangular enameled wire 1 that constitutes the measurement sample 2 can be made hydrophilic.

[0112] Such a PDIV measurement device 50 can easily make the surface of the coating 1b of the rectangular enameled wire 1 constituting the measurement sample 2 hydrophilic, and can also suppress variations in PDIV measurement values.

[0113] In addition, in such a PDIV measurement device 50, a configuration in which the control device stores a plurality of measurement values ​​obtained by PDIV measurements performed in advance and sets the maximum voltage value among the measurement values ​​as the fixed voltage value is also one embodiment of the present application.

[0114] According to the PDIV measurement device 50, the process of setting a fixed voltage value as the applied voltage used for preliminary discharge can be automatically performed, thereby reducing the need for complicated operations by the user. Note that the process of setting the fixed voltage value described above may also be performed manually in response to an operation by the user.

[0115] (Embodiment 3) Furthermore, a program P for causing the computer 60 provided in the PDIV measurement device 50 to function as a control device according to the proposed method, and a computer-readable storage medium storing the program P, are also embodiments of the present application.

[0116] When the program according to the third embodiment is executed by a processor, the same effects as those of the second embodiment can be obtained.

[0117] 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.

[0118] For example, in the above-described embodiment, a rectangular enameled wire made of a conductor such as copper covered with an enamel coating is used as the enameled wire constituting the measurement sample, but the present invention is not limited to this. That is, the present invention can also be applied to enameled wires whose conductor is made of a metal other than copper. [Explanation of symbols]

[0119] 1. Flat enameled wire 1a conductor 1b Coating 1c Back-to-back section 1d Terminal part 2. Measurement sample 3 Bending tools 4 Bending mechanism 5. Foundation 5a Top side 5b flat surface 5c flat area 5d curved surface 5e 1st curved surface part 6 Guide plate 6a Through hole 7 Retaining plate 7a Bottom side 7b Through hole 8 Pressure plate 8a Pressing surface 8b curved surface 8c 2nd curved surface part 9 volts 10 Support section 11 Mating surface 12 Fixtures 33 Fixture 34 Fixing mechanism section 35 Retaining plate 35a flat surface 36 Clamping plate 36a Upper insulating plate 36b Lower insulation board 36c Upper metal plate 36d lower metal plate 36e Bottom 36f top surface 36g,36h,36i through hole 37 Coil spring 38 Pressure plate 38a through hole 39 volts 40 spacer 50 PDIV measurement device 51 Voltage generator 52 Voltage and charge measuring device 60 Computer 61 processors 62 memory 63 Storage 64 Operation section 65 Display section 66 Interface Bus 67 70 containers 71 Solvent 80 Ultrasonic Cleaner 81 liquid 91 Solid Surface 92 droplets A1 Longitudinal direction B1 width direction C1 Thickness direction D1 Predetermined area F1 Extending direction L tangent P Program α contact angle θ bending angle

Claims

1. A partial discharge inception voltage measuring method for measuring the partial discharge inception voltage of two rectangular enameled wires having coatings, in which the rectangular enameled wires are stacked together in contact with each other over a predetermined region in the longitudinal direction of the rectangular enameled wires, and the partial discharge inception voltage of the rectangular enameled wires is measured, a hydrophilization step of hydrophilizing the surfaces of the coatings of the two rectangular enameled wires before measuring the partial discharge inception voltage, the hydrophilization step is a step of applying an AC voltage having a preset first effective voltage between one and the other of the two rectangular enameled wires for a first period of time to perform preliminary discharge; the first effective voltage is a voltage higher than the average value of a plurality of measured partial discharge inception voltages obtained by measuring a plurality of times the partial discharge inception voltages of rectangular enameled wires of the same type as the rectangular enameled wire being measured, or a maximum voltage of the plurality of measured values; the hydrophilization step is a step of hydrophilizing the surface of the coating so that the contact angle between the surface of the coating and a liquid droplet is 20 degrees or less; The preliminary discharge is a discharge that maintains partial discharge of the rectangular enameled wire for a certain period of time. Partial discharge inception voltage measurement method.

2. In the partial discharge inception voltage measuring method according to claim 1, the first effective voltage is a fixed value according to the type of the rectangular enameled wire; Partial discharge inception voltage measurement method.

3. In the partial discharge inception voltage measuring method according to claim 2, the surfaces of the coating are the surfaces of the coating at the Y-shaped gap portion and the R-shaped gap portion of the two rectangular enameled wires; Partial discharge inception voltage measurement method.

4. In the partial discharge inception voltage measuring method according to claim 3, The hydrophilization step is a step of hydrophilizing the surface of the coating so that the contact angle between the surface of the coating and a liquid droplet is 10 degrees or less. Partial discharge inception voltage measurement method.

5. 2. The partial discharge inception voltage measuring method according to claim 1, The first time period is 20 seconds. Partial discharge inception voltage measurement method.

6. 6. The partial discharge inception voltage measuring method according to claim 5, Before measuring the partial discharge inception voltage, a cleaning step of ultrasonically cleaning the two rectangular enameled wires using a solvent. Partial discharge inception voltage measurement method.

7. 7. The partial discharge inception voltage measuring method according to claim 6, The solvent is hexane, alcohol, dichloromethane, carbon tetrachloride, benzene, toluene, or acetone; Partial discharge inception voltage measurement method.

8. 7. The partial discharge inception voltage measuring method according to claim 6, Before measuring the partial discharge inception voltage, a molding step of fixing the two rectangular enameled wires using a fixing jig that regulates the positions of the rectangular enameled wires in the width direction and thickness direction to form a measurement sample; Partial discharge inception voltage measurement method.

9. 9. The partial discharge inception voltage measuring method according to claim 8, Before the molding step, a shaping step of shaping each of the two rectangular enameled wires using a bending tool that bends an end portion of the rectangular enameled wire in the extending direction into a specific shape; Partial discharge inception voltage measurement method.

10. A partial discharge inception voltage measuring method for measuring the partial discharge inception voltage of two rectangular enameled wires having coatings, in which the rectangular enameled wires are stacked together in contact with each other over a predetermined region in the longitudinal direction of the rectangular enameled wires, and the partial discharge inception voltage of the rectangular enameled wires is measured, Before measuring the partial discharge inception voltage, a cleaning step of ultrasonically cleaning the two rectangular enameled wires using a solvent; a molding step of fixing the two rectangular enameled wires using a fixing jig that regulates the positions of the rectangular enameled wires in the width direction and thickness direction to form a measurement sample; a hydrophilization step of hydrophilizing the surfaces of the coatings of the two rectangular enameled wires; Equipped with the hydrophilization step is a step of applying an AC voltage having a preset first effective voltage between one and the other of the two rectangular enameled wires for a first period of time to perform preliminary discharge; the first effective voltage is a voltage higher than the average value of a plurality of measured partial discharge inception voltages obtained by measuring a plurality of times the partial discharge inception voltages of rectangular enameled wires of the same type as the rectangular enameled wire being measured, or a maximum voltage of the plurality of measured values; the hydrophilization step is a step of hydrophilizing the surface of the coating so that the contact angle between the surface of the coating and a liquid droplet is 20 degrees or less; The preliminary discharge is a discharge that maintains partial discharge of the rectangular enameled wire for a certain period of time. Partial discharge inception voltage measurement method.

11. A partial discharge inception voltage measuring device for measuring the partial discharge inception voltage of two rectangular enameled wires having coatings, in a state where the rectangular enameled wires are stacked together in contact with each other over a predetermined region in the longitudinal direction of the rectangular enameled wires, comprising: a voltage generator; a control device that receives a setting of a first effective voltage and controls the voltage generator to apply an AC voltage of the first effective voltage between one and the other of the two rectangular enameled wires for a first period of time to perform a preliminary discharge; the first effective voltage is a voltage higher than the average value of a plurality of measured partial discharge inception voltages obtained by measuring a plurality of times the partial discharge inception voltages of rectangular enameled wires of the same type as the rectangular enameled wire being measured, or a maximum voltage of the plurality of measured values; The preliminary discharge is a hydrophilization step, the hydrophilization step is a step of hydrophilizing the surface of the coating so that the contact angle between the surface of the coating and a liquid droplet is 20 degrees or less; The preliminary discharge is a discharge that maintains partial discharge of the rectangular enameled wire for a certain period of time. Partial discharge inception voltage measuring device.

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