Method for measuring partial discharge initiation voltage of enameled wire

Abstract

To reduce variations in measurement results of a partial discharge initiation voltage (PDIV) of enameled wires.SOLUTION: A partial discharge initiation voltage measurement method is to measure a partial discharge initiation voltage of enameled wires in a state in which two enameled wires each having a coating are brought into contact with each other and laminated over a predetermined area in the longitudinal direction of the enameled wires, and the method includes an oil content removal step (S4) of removing oil content attached to the surfaces of the coatings of the two enameled wires by using an organic solvent including hexane before measuring the partial discharge initiation voltage.SELECTED DRAWING: Figure 4

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] In order to evaluate the electrical characteristics of an enameled wire having a coating around a conductor with a substantially rectangular cross section, a method of measuring the partial discharge inception voltage of the enameled wire is known (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 characteristics of enameled wires using PDIV measurements, it is necessary to suppress the variance in the PDIV measurement results in order to improve the reliability of the evaluation.

[0005] Due to the above circumstances, a technique capable of suppressing the variation in the PDIV measurement results of an enameled wire is desired. [Means for solving the problem]

[0006] A representative embodiment of the present application is a partial discharge inception voltage measuring method for measuring the partial discharge inception voltage of two enameled wires having coatings in a state in which the enameled wires are stacked in contact with each other over a predetermined region in the longitudinal direction of the enameled wires, and the method includes an oil removal step of removing oil adhering to the surfaces of the coatings of the two enameled wires by using an organic solvent containing hexane before measuring the partial discharge inception voltage. Effect of the Invention

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

[0008] [Figure 1] FIG. 2 is a diagram showing an example of a configuration of a measurement sample. [Figure 2A] FIG. 2 is a diagram for explaining a Y-shaped gap portion of a measurement sample. [Figure 2B] FIG. 13 is a diagram for explaining a corner R gap portion of a measurement sample. [Diagram 3] 1 is a flowchart illustrating a reference PDIV measurement method. [Figure 4] 1 is a flowchart illustrating a PDIV measurement method according to an embodiment. [Diagram 5] FIG. 1 is a diagram illustrating an example of a hardware configuration of a PDIV measurement device. [Figure 6] FIG. 13 is a diagram showing an example of the change over time of the voltage applied to a measurement sample by the standard method. [Figure 7] FIG. 13 is a diagram showing an example of the time change of the voltage applied to a measurement sample according to the proposed method. [Figure 8] FIG. 2 is a diagram for explaining the contact angle of a liquid, which is an index of hydrophilicity. [Figure 9] This shows the results of measuring the oil concentration adhering to the coating of a measurement sample immersed in an organic solvent and a measurement sample not immersed in the organic solvent. [Figure 10] 1 is a table showing conditions for preliminary discharge and PDIV measurement. [Figure 11]1 is a histogram of PDIV measurement values ​​of a measurement sample that is not immersed in an organic solvent. [Figure 12] 1 is a histogram of PDIV measurement values ​​of a measurement sample immersed in an organic solvent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] From now on, the 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. In addition, in each embodiment described below, components having the same function are given 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 partial discharge inception voltage (PDIV) will be described.

[0011] FIG. 1 is a diagram showing an example of the configuration of a measurement sample. As shown in FIG. 1, the measurement sample 2 has two enameled wires 1 (hereinafter also referred to as rectangular enameled wires 1) each having a conductor 1a made of a metal wire having a substantially rectangular cross-sectional shape and a coating 1b around the conductor 1a. 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 having a length of, for example, 120 mm in 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 in a state in which the mating surfaces 11 of the back-to-back portions 1c are in contact with each other. That is, the two rectangular enameled wires 1 are fixed in a back-to-back state. In other words, when measuring the PDIV, the measurement sample 2 has a structure in which two rectangular enameled wires 1, each of which has a conductor 1a coated with a coating 1b, which is an insulating material, are stacked in the thickness direction C1. In the measurement sample 2, for example, two rectangular enameled wires 1 are fixed at five points in the predetermined region D1 by fasteners 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 in width and 3.450 mm in thickness. The coating 1b of the rectangular enameled wire 1 has a thickness of, for example, 0.150 to 1.162 mm.

[0013] The coating 1b of the end 1d of the measurement sample 2 (see the right side in FIG. 1) is peeled off, and the conductor 1a made of copper is exposed. In the example shown in FIG. 1, the conductor 1a is also exposed at the other end, i.e., the left side, of the measurement sample 2 (reference numeral 1d is omitted). The conductor 1a is electrically connected to the high-voltage line and ground line of the measurement device, and the PDIV can be measured. Here, the end 1d at both ends of the measurement sample 2 is curved at a predetermined bending angle θ so that the end 1d of the rectangular enameled wire 1 is spaced apart from each other. In detail, the end 1d is curved so that it is warped at a predetermined bending angle θ with respect to the mating surface 11. The bending angle θ is, for example, θ=20°.

[0014] Next, we will explain the part of the measurement sample 2 where partial discharges are particularly likely to occur. The part where partial discharges are particularly likely to occur is the surface part 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 part is called the gap part.

[0015] Fig. 2A is a diagram for explaining the Y-gap of the measurement sample. As shown in Fig. 2A, the terminals 1d at both ends of the two rectangular enameled wires 1 constituting the measurement sample 2 are curved so as to separate from each other to form a Y-shape as a whole, and the portion where the terminals 1d start to separate is called the Y-gap Y. The Y-gap Y is one of the portions of the measurement sample 2 where partial discharge is likely to occur.

[0016] Fig. 2B is a diagram for explaining the corner R gap of the measurement sample. Fig. 2B is a cross-sectional view of the measurement sample 2 shown in Fig. 2A along the line AA. As shown in Fig. 2B, the portions at both ends in the width direction B1 of the mating surface 11 of the two rectangular enameled wires 1 constituting the measurement sample 2 are called the corner R gap R. The corner R gap R is also one of the portions of the measurement sample 2 where partial discharge is likely to occur.

[0017] In order to reduce the variation in the PDIV measurement value in the measurement sample 2, it is important that the contours of the surfaces 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. Also, in order to reduce the variation in the PDIV measurement value due to differences in the measurement sample, it is important that the contour shapes of the surfaces 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 value 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) Hereinafter, a PDIV measuring method (partial discharge inception voltage measuring method) according to an 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 is also referred to as the "reference method", and the PDIV measurement method according to the embodiment is also 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 be measurement sample 2. Specifically, two rectangular enameled wires 1 each having a length of 320 mm are taken from a bobbin around which rectangular enameled wire 1 is wound or from a coil built into a drive motor mounted on an electric vehicle.

[0024] In step J2, the rectangular enameled wire is shaped. Specifically, the two rectangular enameled wires 1 are shaped by elongating the length of the rectangular enameled wire 1 by 2% along their longitudinal direction to eliminate any bending tendency of the rectangular enameled wire 1. Then, using a bending tool or a 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 on one side in the thickness direction C 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.

[0025] In step J3, foreign matter on the surface of the coating of the rectangular enameled wire is removed with an adhesive. Specifically, an adhesive roller (a rotating body having adhesiveness) is rolled over the entire surface of the coating 1b of the rectangular enameled wire 1, which is 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 formed manually. Specifically, a measurement sample 2 as shown in Fig. 1 is formed without using a bending tool or a fixing jig. For example, as shown in Figs. 2A and 2B, two rectangular enameled wires 1 bent and shaped at a predetermined bending angle θ are 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 fixing tool 12 such as a wire, thereby forming the measurement sample 2.

[0027] In step J5, the moisture in the coating of the rectangular enameled wire is removed. Specifically, the rectangular enameled wire 1 that serves as the measurement sample 2 is left in an environment with a temperature of 150°C for about one hour to remove the moisture contained in the coating 1b of the rectangular enameled wire 1. After that, it is left in the same environment as when the PDIV measurement is performed (for example, a temperature of 23°C and a humidity of 35%) for about one hour. The temperature and humidity are 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 serving 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 applied voltage during the calibration is an AC voltage, the frequency of which 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 is a partial discharge that is generated in advance before starting the PDIV measurement, and is also called a pre-discharge. Specifically, an AC voltage (for example, 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 constitute the measurement sample 2. The applied voltage (hereinafter, unless otherwise specified, "voltage" means AC voltage, and "voltage (value)" means effective voltage value) is gradually increased, and when a partial discharge occurs in the measurement sample 2, the applied voltage at that point is maintained for a certain period of time, for example, about 20 seconds, to continue the partial discharge. After that, the application of the voltage to the measurement sample 2 is stopped.

[0031] In step J9, PDIV measurement is continuously performed multiple times. Specifically, a voltage (for example, 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 using a voltage generator 51 described later. The applied voltage is gradually increased, and when partial discharge occurs in the measurement sample 2 and is detected by a voltage / charge measurement device 52 described later, the applied voltage at that time is recorded as PDIV, and the application of voltage to the measurement sample 2 is stopped. Such a series of voltage application operations is repeated multiple times, for example, about 5 times, to measure PDIV for multiple times. Then, the average value or the minimum value of the PDIV for multiple times is specified as the PDIV measurement value for the measurement sample 2.

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

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

[0034] The voltage generator 51 has a high-voltage line terminal and a ground line terminal, and each of the high-voltage line terminal and the ground line terminal is connected to the measurement sample 2. By generating an alternating high voltage (for example, a frequency of several kHz and an effective voltage of up to several kV) between these two terminals by the voltage generator 51, a voltage is applied to the measurement sample 2. The voltage / charge measurement device 52 measures 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 charge amount generated in the measurement sample 2 by measuring the voltage between the above-mentioned high-voltage line terminal and the ground line terminal and the charge amount flowing between these two terminals. The computer 60, which is the control device, is connected to the voltage generator 51 and the voltage / charge measurement device 52 via an interface 66.

[0035] The computer 60, which is a control device, transmits a control signal to the voltage generator 51 to control the effective voltage value, frequency, etc. of the voltage generated by the voltage generator 51 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 computer 60, which is a control device, 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, a 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) and 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) and an SSD (Solid State Drive). The operation unit 64 is configured, for example, by a keyboard and a mouse. The display unit 65 is configured, for example, by a liquid crystal display and a 7-segment display.

[0038] The processor 61, the memory 62, the storage 63, the operation unit 64, the display unit 65, and the interface 66 are connected to a bus 67. The voltage generator 51 and the 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, and expands and executes the read program P in the memory 62, thereby functioning as the above-mentioned control device and executing processes for automatically performing the preliminary discharge and the 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 variation of the measurement values, σ (standard deviation), the average value of the measurement values, the number of samples, and the like.

[0041] FIG. 6 is a diagram showing an example of the change over time of the voltage applied to the measurement sample by 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 by 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 a voltage V10, which is the applied voltage when the partial discharge starts, and is maintained for a certain time, for example, about 20 seconds. After that, the applied voltage V is temporarily returned to 0.

[0042] Next, the PDIV measurement is performed. Specifically, the applied voltage V to the measurement specimen 2 gradually increases from 0. When partial discharge starts in the measurement specimen 2, the applied voltage V11 at that time 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 partial discharge starts in the measurement specimen 2, the applied voltage at that time, that is, voltage 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 manner in the third to fifth PDIV measurements, and repeatedly rises and falls from the peaks at voltages V13 to V15 at which partial discharges start. The voltages V13 to V15 are stored in the 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] 4, in step S1, a rectangular enameled wire 1 is taken as a measurement sample 2. Step S1 is the same process as step J1 in the standard method, so a description thereof will be omitted here.

[0047] In step S2, the rectangular enameled wire 1 is shaped. Step S2 is the same process as step J2 in the standard method, so a description thereof will be omitted here.

[0048] In step S3, a measurement sample is manually molded. Step S3 is the same process as step J4 in the standard method, so a description of it will be omitted here.

[0049] In step S4, lubricating oil and the like adhering to the surface of the coating 1b of the rectangular enameled wire 1 are removed (oil removal step). 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 taken out of the organic solvent, and the organic solvent remaining on the surface of the coating 1b of the rectangular enameled wire 1 is removed using, for example, a wiper soaked in acetone.

[0050] The organic solvent in which the rectangular enameled wire 1 is immersed can be, for example, a hydrocarbon organic solvent such as toluene, methylcyclohexane, ethylhexane, gasoline (naphtha, benzine), etc. The organic solvent is not limited to a hydrocarbon organic solvent, and may be an alcohol organic solvent, an ester organic solvent, or a ketone organic solvent.

[0051] In step S5, moisture is removed from the coating 1b of the rectangular enameled wire 1. Step S5 is the same process as step J5 in the standard method, so a description of it will be omitted here.

[0052] In step S6, the charge on the surface of the coating 1b of the rectangular enameled wire 1 is removed. Step S6 is the same process as step J6 in the standard method, so a description of it will be omitted here.

[0053] In step S7, the sensitivity of the voltage / charge measuring device 52 is calibrated. Step S7 is the same process as step J7 in the reference method. The applied voltage during calibration is AC, its frequency is 1 kHz, and the discharge charge amount is 100 pC.

[0054] In step S8, the surface of the coating 1b is made hydrophilic (hydrophilization step). Specifically, the surfaces of the coating 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 are made hydrophilic. In the proposed method, one method for making the surfaces of the coating 1b of the two rectangular enameled wires 1 constituting the measurement sample 2 hydrophilic is to perform preliminary discharge on the measurement sample 2 at a preset fixed voltage (effective voltage) for a certain period of time. Details of the hydrophilization of the surface of the coating 1b will be described later.

[0055] In step S9, the PDIV measurement is continuously performed multiple times on the rectangular enameled wire 1 whose surface of the coating 1b has been made hydrophilic. In step S9, the PDIV measurement is performed by the same measurement method as in step J9 of the standard method. Therefore, a description thereof will be omitted here.

[0056] The preliminary discharge in step S8 and the PDIV measurement in step S9 are performed, for example, in the same manner 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 applied voltage V to the measurement sample 2, i.e., the contents of the program P to be executed, differs from that of the reference method.

[0057] Specifically, in the preliminary discharge of the measurement sample 2 performed in step S8, the computer 60, which is a control device of the PDIV measurement device 50, accepts the setting of the fixed voltage value so that the voltage applied to and maintained on the measurement sample 2 can be set to a fixed voltage value previously set for hydrophilizing the surface of the coating 1b, which will be described later. That is, the program P is configured to be able to accept the setting of the fixed voltage value.

[0058] Fig. 7 is a diagram showing an example of the time change of the voltage applied to the measurement sample by the proposed method. Fig. 7 shows the time change of the voltage V applied to the measurement sample 2 when preliminary discharge for hydrophilizing the measurement sample 2 (particularly, hydrophilizing the surface of the coating 1b) and PDIV measurement are performed consecutively.

[0059] 7, when the PDIV measurement process by the PDIV measurement device 50 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 V20, which is a fixed value (a value that does not vary for each measurement sample) that is preset for hydrophilizing the surface of the coating 1b, the applied voltage V is fixed at voltage V20 and maintained for about 20 seconds. During this time, partial discharge is maintained in the measurement sample 2. After that, the applied voltage V returns to 0 once.

[0060] 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 point is stored as the first PDIV measurement value, and the applied voltage V returns to 0.

[0061] The applied voltage V changes in the same way in the second to fifth PDIV measurements, and repeatedly rises and falls from the 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.

[0062] <Making the surface of the coating 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.

[0063] After much 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 of the area where two rectangular enameled wires 1 come into contact with each other, is extremely effective in suppressing the variation in PDIV measurement values.

[0064] The surface of the coating 1b that forms the boundary of the area where the 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 2A and 2B.

[0065] 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 region where the two rectangular enameled wires 1 contact each other. 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.

[0066] Whether the surface of the coating 1b has been hydrophilized can be determined based on whether an index indicating the degree of hydrophilicity (wettability) of the surface of the coating 1b exceeds a preset standard. As an index indicating the degree of hydrophilicity, for example, the "contact angle" of a liquid can be used.

[0067] FIG. 8 is a diagram for explaining the contact angle of a liquid, which is an index of hydrophilicity. According to the Dictionary of Physics and Chemistry (Iwanami Shoten, 4th Edition), the term "contact angle" is defined as "the angle between the liquid surface and the solid surface at the place 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)." In other words, as shown in FIG. 8, for example, the "contact angle" can be expressed by an angle α between the solid surface 91 and a tangent L that passes through the boundary between a droplet 92 formed by dropping a liquid on a solid surface 91 and the solid surface 91 and touches the droplet 92. In this embodiment, the solid surface 91 is the surface of the coating 1b of the rectangular enameled wire 1.

[0068] In the present 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° or less, as a result of investigations by the present 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° or less. Note that the calculation method of this "contact angle" can be, 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.

[0069] 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 fixed voltage higher than the partial discharge inception voltage.

[0070] Therefore, in the present proposed method, in order to make the surface of the coating 1b hydrophilic, a method is adopted in which preliminary discharge is performed 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 present proposed method can be determined, for example, as follows.

[0071] The measurement sample is connected to the PDIV measurement device 50, and an AC voltage is applied between one end and the other end of each of the two rectangular enameled wires 1 constituting 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, at which point the voltage is maintained for a certain period of time, for example, about 20 seconds, to maintain partial discharge. Thereafter, the application of voltage to the measurement sample 2 is stopped.

[0072] The above-mentioned fixed voltage is a voltage required to hydrophilize at least the surface of the coating 1b at the Y-shaped gap Y and the R-corner gap R of the rectangular enameled wire 1 constituting the measurement sample 2, and is a voltage higher than the average PDIV measurement value for the same type of measurement samples. The above-mentioned fixed voltage can be determined, for example, by measuring the PDIV multiple times or more, for example five times or more, in advance for multiple measurement samples of the same type, and setting the maximum voltage value among the measured PDIVs.

[0073] In the proposed method, the computer 60, which is a control device of the PDIV measurement device 50, may be configured to store a plurality of PDIVs measured in advance and set the maximum voltage value among the plurality of PDIVs as a fixed voltage value to be 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.

[0074] As mentioned above, the proposed method differs from the reference method in steps S4 and S8. In particular, in step S4, the rectangular enameled wire 1 is immersed in an organic solvent to remove the lubricating oil adhering to the coating of the rectangular enameled wire 1. This change in step S4 can reduce the variability in the PDIV measurement values ​​of the measurement sample 2. In addition, in the proposed method, the surface of the coating 1b is made hydrophilic in step S8, which can reduce the variability in the PDIV measurement values ​​of the measurement sample 2 compared to the reference method.

[0075] <verification> The inventors have verified that immersing the rectangular enameled wire 1 in an organic solvent is effective in suppressing the variation in PDIV measurement values ​​in the proposed method. The verification method and verification results are described below.

[0076] First, two measurement samples, one immersed in an organic solvent and one not immersed, are prepared using the same type of rectangular enameled wire 1. Then, the concentration of oil adhering to the surface of the coating 1b of each measurement sample is measured.

[0077] Figure 9 shows the results of measuring the oil concentration on the surface of the coating 1b of each measurement sample. In Figure 9, the vertical axis shows the oil concentration [mg / g] on the surface of the coating 1b of the rectangular enameled wire 1.

[0078] For measurement sample P1, the coating 1b of the rectangular enameled wire 1 has not been cleaned by immersing it in an organic solvent or by making the surface of the coating 1b hydrophilic. For measurement samples P2 and P3, the rectangular enameled wire 1 has been immersed for 24 hours in gasoline (naphtha, benzine), an organic solvent containing hexane, to remove the oil from the coating 1b. Note that the octane numbers of the gasoline used as the organic solvent for measurement samples P2 and P3 are different, with the gasoline in which measurement sample P3 was immersed having a higher octane number. That is, so-called regular gasoline was used for measurement sample P2, and so-called premium gasoline with a higher octane number was used for measurement sample P3.

[0079] For measurement sample P4, the hydrophilization in step S8 was performed without immersing the rectangular enameled wire 1 in an organic solvent. For measurement sample P5, the surface of the coating 1b of the rectangular enameled wire 1 was ultrasonically cleaned without immersing the rectangular enameled wire 1 in an organic solvent. When ultrasonically cleaning the surface of the coating 1b of the rectangular enameled wire 1, the rectangular enameled wire 1 is immersed in a solvent contained in a container such as a graduated cylinder. Then, the container is immersed in a liquid (e.g., water) in a liquid tank of an ultrasonic cleaner to ultrasonically clean the rectangular enameled wire 1.

[0080] As shown in Figure 9, the oil concentration in the coating of rectangular enameled wire 1 of measurement sample P1 is about 0.01450 [mg / g]. The oil concentrations of measurement samples P2 and P3 are both about 0.00260 [mg / g], which is about 1 / 6 of the oil concentration of measurement sample P1. The oil concentrations of measurement samples P4 and P5 are about 0.00700 [mg / g] and 0.00600 [mg / g], respectively, which are lower than that of measurement sample P1. However, the oil concentrations of measurement samples P2 and P3 are less than half of the oil concentrations of measurement samples P4 and P5. This shows that if rectangular enameled wire 1 is immersed in gasoline for more than 24 hours, the oil attached to the coating is largely removed.

[0081] Next, the PDIV measurement in step S7 (or J9) is performed five times consecutively for the measurement samples P1 and P2, and the minimum value of the five measured values ​​is determined as the measured PDIV value of the measurement sample P2.

[0082] Fig. 10 is a table showing the conditions for preliminary discharge and PDIV measurement. As shown in Fig. 10, the applied voltage frequency is 1 kHz. In preliminary discharge in the standard method, the conditions for determining that partial discharge has started (partial discharge determination threshold shown in Fig. 10) are that the discharge charge amount 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 about 20 s, the applied voltage increase step (increase rate) is 200 V / s, and the applied voltage high voltage step (decrease rate) is output off after 0 V instruction control.

[0083] In addition, in PDIV measurements using the standard method and the proposed method, the conditions for determining that a partial discharge has started (partial discharge determination threshold shown in Figure 10) are that the discharge charge is 100pC or more and the occurrence frequency is 1000pps or more. In this PDIV measurement, the boost step (boost rate) of the applied voltage is 30V / s for the primary (up to 200V), 10V / s for the secondary (after 200V), and the high voltage step (drop rate) of the applied voltage is output off after 0V indication control. The measurement environment is 23°C in temperature and 35% in humidity.

[0084] FIG. 11 is a histogram of PDIV measurements of a measurement sample P1 that is not immersed in an organic solvent (i.e., PDIV measurements of a measurement sample according to the flow of the reference method). FIG. 12 is a histogram of PDIV measurements of a measurement sample P2 that is immersed in an organic solvent (regular gasoline) (i.e., PDIV measurements of a measurement sample according to the flow of the proposed method). In FIG. 11 and FIG. 12, the horizontal axis indicates the PDIV measurements, and the vertical axis indicates the frequency [%]. Here, the frequency is the percentage of times that the measurement value obtained in each measurement was a specified value out of 46 measurements performed PDIV measurements.

[0085] As shown in Fig. 11, the PDIV measurement values ​​of the measurement sample P1 that was not immersed in an organic solvent ranged from 1760 Vp to 2460 Vp. On the other hand, as shown in Fig. 12, the PDIV measurement values ​​of the measurement sample P2 that was immersed in an organic solvent ranged from 1900 Vp to 2400 Vp. Comparing these test results, it can be seen that the PDIV measurement values ​​of the measurement sample P2 that was immersed in an organic solvent have smaller variations than the measurement sample P1 that was not immersed in an organic solvent.

[0086] By immersing the rectangular enameled wire 1 in an organic solvent, oil such as lubricating oil that inhibits the modification (activation) of the coating 1b of the rectangular enameled wire 1 by hydrophilization is removed. In particular, as shown in Figure 9, the concentration of oil adhering to the surface of the coating 1b of the rectangular enameled wire 1 is significantly reduced by immersing the wire in gasoline. This is presumably because, in the proposed method, immersion in an organic solvent containing hexane such as gasoline suppresses the emission of primary electrons from the surface of the coating 1b, which is the source of partial discharge. More specifically, it is presumed that the oil present on the surface of the coating 1b dissolves in an organic solvent containing hexane such as gasoline, suppressing the emission of the above-mentioned primary electrons, thereby reducing the variation in PDIV measurement values. In addition, it is considered that the electric field at the Y-shaped gap Y shown in Figure 2A is concentrated or relaxed depending on the state of distribution of oil at the Y-shaped gap Y. In contrast, in the proposed method, it is estimated that the distortion of the electric field in the Y-gap Y can be suppressed by removing the oil distributed in the Y-gap Y using an organic solvent containing hexane, such as gasoline. As a result, the variation in the PDIV measurement value is reduced for the rectangular enameled wire 1 immersed in the organic solvent.

[0087] (Embodiment 2) A PDIV measurement device 50 that measures the PDIV after performing a preliminary discharge of the measurement sample 2 is also an embodiment of the present application, configured to have a control device according to the present proposed method. Specifically, the control device according to the present proposed method accepts the setting of a fixed voltage value as the applied voltage V used for preliminary discharge so that the surface of the coating 1b of the rectangular enameled wire 1 constituting the measurement sample 2 can be made hydrophilic.

[0088] 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 the variation in the PDIV measurement values.

[0089] 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 above-mentioned fixed voltage value is also an embodiment of the present application.

[0090] According to such a PDIV measurement device 50, the process of setting a fixed voltage value as the applied voltage used for preliminary discharge can be automatically performed, and the troublesome operation by the user can be reduced. Note that the process of setting the fixed voltage value described above may be performed manually in response to an operation by the user.

[0091] (Embodiment 3) In addition, a program P for causing the computer 60 included in the PDIV measurement device 50 to function as a control device according to the proposed method, and a computer-readable storage medium for storing the program P are also embodiments of the present application.

[0092] 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.

[0093] Although various embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modified examples are included. Furthermore, the above-mentioned embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. Furthermore, it is possible to replace a 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 belong to the scope of the present invention. Furthermore, the numerical values ​​and the like included in the text and figures are merely examples, and the effect of the present invention is not impaired even if different ones are used.

[0094] For example, in the above 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 is also applicable to enameled wires whose conductor is made of a metal other than copper. [Explanation of symbols]

[0095] 1 rectangular enameled wire (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, 51 voltage generator, 52 voltage / charge measurement device, 60 computer, 61 processor, 62 memory, 63 storage, 64 operation unit, 65 display unit, 66 interface, 67 bus, 91 solid surface, 92 droplet, 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 enameled wires having coatings, 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: the partial discharge inception voltage measuring method, comprising an oil removal step of removing oil adhering to the surfaces of the coatings of the two enameled wires with a hydrocarbon organic solvent before measuring the partial discharge inception voltage.

2. 2. The partial discharge inception voltage measuring method according to claim 1, the oil removal step is a step of immersing the enameled wire in the organic solvent for 24 hours or more.

3. 2. The partial discharge inception voltage measuring method according to claim 1, The partial discharge inception voltage measuring method, wherein the hydrocarbon organic solvent is an organic solvent containing hexane.

4. 4. The partial discharge inception voltage measuring method according to claim 3, The hydrocarbon organic solvent is gasoline.

5. 2. The partial discharge inception voltage measuring method according to claim 1, the partial discharge inception voltage measuring method further comprising, after the oil removing step, a hydrophilizing step of hydrophilizing the surfaces of the two enameled wires.

6. 6. The partial discharge inception voltage measuring method according to claim 5, the hydrophilization step comprises applying a voltage higher than the partial discharge inception voltage between one end and the other end of each of the two enameled wires to hydrophilize the surface of the coating of the enameled wire.

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