Method for measuring the partial discharge initiation voltage of enameled wire.

Abstract

This reduces variability in PDIV (Partial Discharge Initiation Voltage) measurement results for enameled wires and shortens the time required for PDIV measurement. [Solution] A method for measuring the partial discharge initiation voltage of enameled wires, in which two enameled wires having a coating are stacked over a predetermined area in the longitudinal direction of the enameled wires, includes a hydrophilization step (S8) in which, before measuring the partial discharge initiation voltage, a preliminary discharge is performed multiple times by applying an AC voltage at a preset effective voltage value to one end of each of the two enameled wires for a certain period of time, thereby hydrophilizing the surface of the coating of the two enameled wires. The certain period of time is 15 seconds or less.

Description

Technical Field

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

Background Art

[0002] In order to evaluate the electrical characteristics of enameled wire having an insulating coating around a conductor, the partial discharge inception voltage of enameled wire is measured. Partial discharge inception voltage refers to the voltage applied to an enameled wire when partial discharge begins to occur. Partial discharge occurs when ions ionized by charged charges on the surface of the insulating coating and space radiation are accelerated by a high electric field in space and repeatedly collide with gas molecules. In addition, partial discharge inception voltage is also referred to as PDIV (Partial Discharge Inception Voltage).

[0003] Patent Document 1 discloses a method for measuring partial discharge inception voltage, in which preliminary discharge is performed to cause the enameled wire to discharge a certain amount before measuring PDIV. By performing preliminary discharge, the amount of charge on the surface of the insulating coating is controlled before PDIV measurement, and variation in PDIV measurement results is reduced.

Prior Art Literature

Patent Literature

[0004]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] In order to improve the reliability of evaluation on the electrical characteristics of enameled wire, a technology that can further suppress variation in PDIV measurement results of enameled wire is desired. In addition, it is desired to reduce the time required for PDIV measurement.

Means for Solving the Problem

[0006] A typical embodiment of the method for measuring the partial discharge initiation voltage of an enameled wire involves stacking two enameled wires having a coating over a predetermined region in the longitudinal direction of the enameled wires, and measuring the partial discharge initiation voltage of the enameled wires. The method for measuring the partial discharge initiation voltage of an enameled wire includes a hydrophilization step, in which a preliminary discharge is performed multiple times by applying an AC voltage at a preset effective voltage value to one end of each of the two enameled wires for a certain period of time, thereby hydrophilizing the surface of the coating of the two enameled wires. The certain period of time is 15 seconds or less. [Effects of the Invention]

[0007] According to a typical embodiment, variations in the measurement results of the partial discharge initiation voltage of the enameled wire can be suppressed. Furthermore, the time required for measurement can be shortened. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the composition of a measurement sample. [Figure 2A] This is a diagram illustrating the Y-shaped gap portion of the measurement sample. [Figure 2B] This is a diagram illustrating the corner radius gap of the measurement sample. [Figure 3] This is a flowchart showing the standard PDIV measurement method. [Figure 4] This is a flowchart showing the PDIV measurement method according to Embodiment 1. [Figure 5] This figure shows an example of the hardware configuration of a PDIV measurement device. [Figure 6] This figure shows an example of the time variation of the voltage applied to a measurement sample using the reference method. [Figure 7] This figure shows an example of the time variation of the voltage applied to a sample using the proposed method. [Figure 8] This diagram illustrates the contact angle of a liquid, which is an indicator of hydrophilicity. [Figure 9]This table shows the conditions for preliminary discharge and PDIV measurement. [Figure 10] This figure shows the relationship between the number of preliminary discharges and the PDIV measurement results when the holding time is set to 5 seconds. [Figure 11] This figure shows the relationship between the number of preliminary discharges and the coefficient of variation obtained by PDIV measurement for each holding time of 5[s], 10[s], 15[s], and 20[s]. [Figure 12] This graph shows the relationship between the number of preliminary discharges and the coefficient of variation. [Figure 13] This graph shows the relationship between the total time required for preliminary discharge and the coefficient of variation. [Figure 14] This graph shows the relationship between the cumulative number of partial discharges that occurred during preliminary discharge and the coefficient of variation. [Modes for carrying out the invention]

[0009] The embodiments described below will now be explained. Note that the embodiments described below are merely examples for carrying out the present invention and do not limit the technical scope of the present invention. Furthermore, in the following embodiments, components having the same function are denoted by the same reference numerals, and repeated descriptions thereof are omitted unless particularly necessary.

[0010] The following describes the method for measuring the partial discharge initiation voltage (PDIV), which is an electrical characteristic of enameled wire with a coating, according to this embodiment. First, the configuration of the sample to be measured for partial discharge initiation voltage (PDIV) will be described.

[0011] Figure 1 shows an example of the configuration of a measurement sample. As shown in Figure 1, the measurement sample 2 has two enameled wires 1. Each enameled wire 1 has a conductor 1a made of metal wires with a roughly rectangular cross-sectional shape, and a coating 1b surrounding the conductor 1a. In the following description, enameled wire 1 will also be referred to as rectangular enameled wire 1.

[0012] Each of the two rectangular enameled wires 1 has a back-to-back portion 1c. The back-to-back portion 1c is, for example, a predetermined region D1 with a length of 120 [mm] in the longitudinal direction (extending direction) F1 of the rectangular enameled wire 1. The back-to-back portion 1c has a mating surface 11.

[0013] The two rectangular enameled wires 1 are fixed in a state where the mating surfaces 11 of the respective 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 PDIV, the measurement sample 2 has a structure formed by laminating two rectangular enameled wires 1, each of which has a conductor 1a covered with an insulating coating film 1b, in the thickness direction C1. Note that the thickness direction C1 is a direction intersecting (orthogonal or substantially orthogonal to) the extending direction F1 of the rectangular enameled wire 1. In the measurement sample 2, for example, at five positions in the predetermined region D1, the two rectangular enameled wires 1 are fixed by a fixing member 12 such as a wire or a clip. Here, the predetermined region D1 is a region where the two rectangular enameled wires 1 are in contact with each other. Further, at each of one end and the other end of the rectangular enameled wire 1, the two rectangular enameled wires 1 have a region separated from each other such that the separation distance gradually increases toward the tip. If this region is defined as a separation region, the predetermined region D1 is a region excluding the separation region in the entire length region of the rectangular enameled wire 1.

[0014] 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 thickness of the coating film 1b of the rectangular enameled wire 1 is, for example, 0.150 to 1.162 [mm].

[0015] At the terminal portion 1d (see the right side in FIG. 1) of the measurement sample 2, the coating film 1b at the tip portion including the tip thereof is peeled off, so that the conductor 1a made of copper is exposed. In the example shown in FIG. 1, the conductor 1a is similarly exposed at the other end, that is, the left side of the measurement sample 2 (the reference numeral 1d is omitted). PDIV measurement can be performed by electrically connecting this conductor 1a to the high-voltage line and grounding line of the measurement instrument.

[0016] Here, the terminal portions 1d of the two flat enameled wires 1 that make up the measurement sample 2 are spaced apart from each other by being bent into a curved shape at a predetermined bending angle θ. In detail, the terminal portions 1d are bent into a curved shape so as to curve back at a predetermined bending angle θ with respect to the mating surface 11. The bending angle θ is, for example, θ = 20 [°].

[0017] Next, we will describe the areas in the measurement sample 2 where partial discharge is particularly likely to occur. The areas where partial discharge is particularly likely to occur are the surface portions of the coating 1b that form the boundary between the regions where the two flat rectangular enameled wires 1 are in contact with each other. In the following description, the areas where partial discharge is likely to occur may be referred to as gap portions. The two flat rectangular enameled wires 1 have a Y-shaped gap portion and a corner radius gap portion as gap portions.

[0018] Figure 2A is a diagram illustrating the Y-shaped gap Y of the measurement sample 2. As shown in Figure 2A, the terminal portions 1d at both ends of the two flat enameled wires 1 that make up the measurement sample 2 are bent in a curved shape so that they are spaced apart from each other. As a result, the terminal portions 1d are formed in a Y shape as a whole. The gap portion where the terminal portions 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.

[0019] Figure 2B is a diagram illustrating the corner radius gap R of the measurement sample 2. Figure 2B is a cross-sectional view of the measurement sample 2 shown in Figure 2A along line AA. As shown in Figure 2B, the gaps at both ends in the width direction B1 of the mating surface 11 of the two flat rectangular enameled wires 1 that constitute the measurement sample 2 are called the corner radius gap R. The corner radius gap R is also one of the parts of the measurement sample 2 where partial discharge is likely to occur.

[0020] To minimize variations in PDIV measurements in sample 2, the following points should be considered: Firstly, the surface contours of the coating 1b in the Y-shaped gap Y and the corner R gap R should be formed symmetrically with respect to the mating surface 11 in the thickness direction C1. Secondly, in order to minimize variations in PDIV measurements due to differences in sample 2, the surface contour shapes of the coating 1b in the Y-shaped gap Y and the corner R gap R should be stably formed to substantially the same shape in various sample 2s. Thirdly, any foreign matter, electric charge, etc. remaining on the surface of the coating 1b of the flat rectangular enamel wire 1 should be removed.

[0021] (Embodiment 1) Next, the PDIV measurement method (method for measuring partial discharge initiation voltage) according to Embodiment 1 will be described with reference to the drawings.

[0022] Figure 3 is a flowchart showing a standard PDIV measurement method. Figure 4 is a flowchart showing a PDIV measurement method according to Embodiment 1.

[0023] The standard PDIV measurement method shown in Figure 3 is an example of a PDIV measurement method devised by the present inventors to date, and is intended for comparison with the PDIV measurement method of Embodiment 1 shown in Figure 4. Hereafter, the standard PDIV measurement method will also be referred to as the "standard method," and the PDIV measurement method of Embodiment 1 will also be referred to as the "proposed method."

[0024] <Flowchart based on the PDIV measurement method, which is the standard method> First, let's explain the PDIV measurement method, which is the standard method. The flow of the standard method is as follows:

[0025] As shown in Figure 3, in step J1, the flat enameled wire 1, which will be the measurement sample 2, is collected. Specifically, two 320 mm long pieces of flat enameled wire 1 are collected from the bobbin on which the flat enameled wire 1 is wound, or from a coil incorporated into a drive motor mounted on an electric vehicle.

[0026] In step J2, the rectangular enameled wire is shaped. Specifically, the two selected rectangular enameled wires 1 are stretched by 2% of their length along their extending direction F1. This shapes the selected rectangular enameled wires 1 so that they are free from any bending tendencies. Subsequently, using a bending tool or fixing jig, 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 along the thickness direction C1 of the rectangular enameled wire 1. The bending angle θ is, for example, 20[°], and the curvature of the bent portion is a predetermined value, for example, R30~R50[mm].

[0027] In step J3, foreign matter on the surface of the coating of the rectangular enameled wire is removed by an adhesive. Specifically, by rolling an adhesive roller (a rotating body with adhesive properties) over the entire surface of the coating 1b of the rectangular enameled wire 1, which will be the measurement sample 2, foreign matter such as dust adhering to the surface of the coating 1b is removed.

[0028] In step J4, the measurement sample 2 is formed manually. Specifically, the measurement sample 2 shown in Figure 1 is formed without the use of bending tools or fixing jigs. For example, as shown in Figures 2A and 2B, the mating surfaces 11 of two flat enameled wires 1, which have been bent to a predetermined bending angle θ, are placed back to back. Then, as shown in Figure 1, the two back-to-back flat enameled wires 1 are fixed in a predetermined region D1 with a fixing device 12 such as a wire. As a result, the measurement sample 2 is formed.

[0029] In step J5, moisture is removed from the coating of the rectangular enamel wire 1. Specifically, the rectangular enamel wire 1, which will be the measurement sample 2, is left in an environment with a temperature of 150°C for about 1 hour. As a result, the moisture contained in the coating 1b of the rectangular enamel wire 1 is removed. After that, the rectangular enamel wire 1 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 1 hour. Temperature and humidity are controlled, for example, by placing the rectangular enamel wire 1 in a constant temperature and humidity chamber.

[0030] 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 will be the measurement sample 2, is removed by a static eliminator such as an ionizer.

[0031] In step J7, the sensitivity of the voltage / charge measuring device 52, described later, is calibrated. The applied voltage during calibration is AC, with a frequency of 1 kHz, and the discharge charge is 100 pC.

[0032] In step J8, a preliminary discharge is performed using a partial discharge initiation voltage. A preliminary discharge is a partial discharge that is generated in advance before the start of the PDIV measurement, and is also called a pre-discharge. Specifically, an AC voltage (for example, a high-frequency voltage of 1 kHz) is applied between one end and the other end of each of the two flat enameled wires 1 that make up the measurement sample 2. The applied voltage (hereafter, unless otherwise specified, "voltage" means AC voltage, and "voltage (value)" means effective voltage value) is gradually increased. Once a partial discharge occurs in the measurement sample 2, the applied voltage at that time is maintained for a certain period of time, for example, about 20 seconds, and the partial discharge continues. After that, the application of voltage to the measurement sample 2 is stopped.

[0033] In step J9, PDIV measurements are performed multiple times in succession. Specifically, the partial discharge initiation voltage is measured as follows: A voltage (for example, a high-frequency voltage of 1 kHz) is applied between one end and the other end of each of the two flat enameled wires 1 that make up the measurement sample 2 using a voltage generator 51, which will be described later. The applied voltage is gradually increased, and when the voltage / charge measuring device 52, which will be described later, detects that a partial discharge has occurred in the measurement sample 2, the applied voltage at that point is recorded as the PDIV. The value of the applied voltage at this time is the value of the measured partial discharge initiation voltage. After that, the application of voltage to the measurement sample 2 is stopped. This series of voltage application operations is repeated multiple times, for example, about 5 times, and multiple PDIVs are measured. The average or minimum value of these multiple PDIVs is then identified as the PDIV measurement value for the measurement sample 2.

[0034] The preliminary discharge in step J8 and the PDIV measurement in step J9 described above are performed using, for example, a PDIV measuring apparatus. Here, the PDIV measuring apparatus will be described.

[0035] <PDIV測定装置> FIG. 5 is a functional block diagram schematically showing the configuration of a PDIV measuring apparatus 50. As shown in FIG. 5, the PDIV measuring apparatus 50 includes at least a voltage generator 51, a voltage-charge measuring device 52, and a computer 60 serving as a control device.

[0036] The voltage generator 51 has a high-voltage line terminal and a ground line terminal. Each of the high-voltage line terminal and the ground line terminal is connected to a measurement sample 2. The voltage generator 51 applies a voltage to the measurement sample 2 by generating an AC high voltage (for example, a frequency of several kHz and an effective voltage of several kV at maximum) between these two terminals.

[0037] The voltage-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 two terminals. Thereby, the voltage-charge measuring device 52 acquires the voltage applied between one end and the other end of each of the two rectangular enameled wires 1 constituting the measurement sample 2 and the amount of charge generated in the measurement sample 2, and measures said values. The computer 60 serving as the control device is connected to the voltage generator 51 and the voltage-charge measuring device 52 via an interface 66.

[0038] The computer 60 serving as the control device transmits a control signal to the voltage generator 51 to control the effective voltage value, frequency and the like of the voltage that the voltage generator 51 generates between the high-voltage line terminal and the ground line terminal. Further, the computer 60 serving as the control device 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. Furthermore, the computer 60 serving as the control device is configured to automatically perform the above-described preliminary discharge and PDIV measurement on the measurement sample 2 connected to the two terminals in accordance with a user's operation.

[0039] As shown in Figure 5, the computer 60 includes a processor 61, memory 62, storage 63, an operating unit 64, a display unit 65, an interface 66, and a bus 67.

[0040] The processor 61 is composed of, for example, an MCU (Micro-Control Unit) or an MPU (Micro-Processing Unit). The memory 62 is composed of, for example, RAM (Random Access Memory). The storage 63 is composed of, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The operating unit 64 is composed of, for example, a keyboard or a mouse. The display unit 65 is composed of, for example, a liquid crystal display or a 7-segment display.

[0041] The processor 61, memory 62, storage 63, operation unit 64, display unit 65, and interface 66 are connected to the bus 67. The voltage generator 51 and voltage / charge measuring device 52 are connected to the interface 66.

[0042] The storage 63 stores the program P for PDIV measurement. The processor 61 reads the program P from the storage 63, loads the read program P into the memory 62, and executes it, thereby functioning as the control device described above and performing the processes necessary to automatically carry out preliminary discharge and PDIV measurement.

[0043] Furthermore, storage 63 also functions as a memory unit. Storage 63 stores various data such as PDIV measurement values, applied voltage to the sample, charge amount as a partial discharge determination condition, set preliminary discharge voltage, measurement value variability, σ (standard deviation), average value of measurement values, and number of samples.

[0044] Figure 6 shows an example of the time variation of the voltage applied to the measurement sample 2 according to the reference method. In Figure 6, the horizontal axis represents time t, and the vertical axis represents the applied voltage V. As shown in Figure 6, when the PDIV measurement process by the PDIV measuring device is started, a preliminary discharge is performed first. Specifically, the voltage V applied to the measurement sample 2 gradually increases from 0. Then, when partial discharge starts, the applied voltage V is fixed at the voltage V10 that was applied when the partial discharge started, and is maintained for a certain period of time, for example, about 20 seconds. After that, the applied voltage V is returned to 0. In the following explanation, the certain period of time during which the applied voltage V is fixed at voltage V10 may be referred to as the holding time.

[0045] Next, PDIV measurement is performed. Specifically, the voltage V applied to the sample 2 is gradually increased from 0. When partial discharge begins in the sample 2, the applied voltage V11 at that time is stored in storage 63 as the first PDIV measurement value, and the applied voltage V is immediately returned to 0.

[0046] Next, the voltage V applied to the measurement sample 2 gradually increases again from 0. When partial discharge begins in the measurement sample 2, the applied voltage V12 at that time is stored in storage 63 as the second PDIV measurement value, and the applied voltage V is immediately returned to 0.

[0047] The applied voltage V changes similarly during the third to fifth PDIV measurements, repeatedly rising and falling with each voltage V13 to V15, where partial discharge begins, as its peak. Voltages V13 to V15 are stored in storage 63 as the PDIV measurements from the third to the fifth time.

[0048] <Flowchart of the proposed PDIV measurement method> Next, we will describe the PDIV measurement method according to Embodiment 1 of the proposed method. The flow of the proposed method is as follows.

[0049] As shown in Figure 4, in step S1, a flat enameled wire 1, which will become the measurement sample 2, is taken. Step S1 is the same process as step J1 of the reference method. Therefore, the explanation is omitted here.

[0050] In step S2, the rectangular enameled wire 1 is shaped. Step S2 is the same process as step J2 of the standard method. Therefore, the explanation is omitted here.

[0051] In step S3, the measurement sample 2 is formed manually. Step S3 is the same process as step J4 of the reference method. Therefore, the explanation is omitted here.

[0052] In step S4, lubricating oil and other substances adhering to the surface of the coating 1b of the rectangular enamel wire 1 are removed (oil removal step). Specifically, the rectangular enamel wire 1 is immersed in an organic solvent containing hexane for, for example, 24 hours or more. After that, the rectangular enamel wire 1 is removed from the organic solvent and allowed to air dry.

[0053] As the organic solvent into which the rectangular enameled wire 1 is immersed, for example, a hydrocarbon-based organic solvent such as n-hexane is used. However, the organic solvent is not limited to hydrocarbon-based organic solvents, and may also be an alcohol-based organic solvent, an ester-based organic solvent, or a ketone-based organic solvent.

[0054] Furthermore, in the oil removal process, ultrasonic cleaning may be performed on the surface of the coating 1b of the rectangular enamel wire 1. In this case, the rectangular enamel wire 1 is immersed in a solvent contained in a container such as a graduated cylinder. The container is then immersed in a liquid (such as water) in the liquid tank of an ultrasonic cleaner, thereby ultrasonically cleaning the rectangular enamel wire 1.

[0055] In step S5, moisture is removed from the coating 1b of the rectangular enamel wire 1. Step S5 is the same process as step J5 of the standard method. Therefore, the explanation is omitted here.

[0056] 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 of the standard method. Therefore, the explanation is omitted here.

[0057] In step S7, the sensitivity of the voltage / charge measuring device 52 is calibrated. Step S7 is the same process as step J7 of the reference method. The applied voltage during calibration is AC, with a frequency of 1 kHz, and the discharge charge is 100 pC.

[0058] In step S8, the surface of the coating 1b is made hydrophilic (hydrophilization step). Specifically, the surfaces of the coating 1b of the two flat rectangular enameled wires 1 that make up the measurement sample 2 are made hydrophilic. In addition, in this proposed method, as one method of making the surface of the coating 1b of the two flat rectangular enameled wires 1 that make up the measurement sample 2 hydrophilic, a preliminary discharge is performed multiple times by applying an AC voltage at a predetermined effective voltage value for a certain period of time to the measurement sample 2. That is, the measurement sample 2 is subjected to the application of an AC voltage for a certain period of time multiple times. Here, the certain period is 15 seconds or less. Preferably, the certain period is 10 seconds or less, and more preferably 5 seconds or less. Details of the hydrophilization of the surface of the coating 1b will be described later.

[0059] In step S9, PDIV measurements are performed multiple times consecutively on the flat enamel wire 1 whose surface of the coating 1b has been hydrophilized. In step S9, the PDIV measurement is performed using the same measurement method as in step J9 of the standard method. Therefore, the explanation is omitted here.

[0060] The preliminary discharge in step S8 and the PDIV measurement in step S9 are performed using a PDIV measuring device 50, similar to the reference method. The configuration and function of the PDIV measuring 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 executed, differs from the reference method.

[0061] Specifically, in step S8, during the preliminary discharge of the measurement sample 2, the computer 60, which is the control device of the PDIV measuring device 50, accepts the setting of the effective voltage value. The effective voltage value is the value of the effective voltage applied to and maintained on the measurement sample 2 for hydrophilization of the surface of the coating 1b, which will be described later, and is a preset value. In other words, program P is configured to accept the setting of this effective voltage value.

[0062] Figure 7 shows an example of the time change of the voltage applied to the measurement sample 2 by the proposed method. Figure 7 shows the time change of the voltage V applied to the measurement sample 2 when preliminary discharge for hydrophilization of the measurement sample 2 (particularly hydrophilization of the surface of coating 1b) and PDIV measurement are performed continuously.

[0063] As shown in Figure 7, when the PDIV measurement process by the PDIV measuring device 50 is started, a preliminary discharge is performed first. Specifically, the voltage V applied to the measurement sample 2 gradually increases from 0. When the applied voltage V reaches voltage V20a, which is a preset effective voltage value (a value that does not vary for each measurement sample) for hydrophilization of the surface of the coating 1b, the applied voltage V is fixed at voltage V20a and maintained for a predetermined holding time. During this time, partial discharge is maintained in the measurement sample 2. After that, the applied voltage V returns to 0.

[0064] Then, voltage is applied to the measurement sample 2 again, and a second preliminary discharge is performed. In this case as well, when the applied voltage V reaches the effective voltage value V20a, the applied voltage V is fixed at V20a and maintained for a predetermined holding time. After that, the applied voltage V returns to 0 again. The above preliminary discharge is performed a predetermined number of times. The holding time and the number of preliminary discharges are determined based on the degree of variation of the measurement results of the PDIV measurement, which will be described later.

[0065] Next, PDIV measurement is performed. Specifically, the voltage V applied to the sample 2 gradually increases from 0 until it reaches the voltage V21 at which partial discharge begins. At that point, the voltage V21 is stored as the first PDIV measurement, and the applied voltage V returns to 0.

[0066] The applied voltage V changes similarly during the second to fifth PDIV measurements, repeatedly rising and falling with peaks at voltages V22 to V25, where partial discharge begins. Voltages V22 to V25 are stored as the PDIV measurement values ​​from the second to the fifth measurement.

[0067] <Hydrophilicization of the surface coating of flat enamel wire> Here, we will explain in detail the hydrophilization of the surface of the coating 1b of the rectangular enameled wire 1, which is carried out in step S8. Hydrophilization is the process in which the molecular chains on the surface of the coating 1b are broken by the discharge, oxygen molecules from the air bond to the surface of the coating 1b, and active groups such as hydroxyl groups, carboxylic acids, and amines are formed, causing the coating 1b to become hydrophilic.

[0068] As a result of repeated studies, the inventors have found that hydrophilizing the surface of the coating 1b on the rectangular enameled wire 1 is effective in suppressing variations in PDIV measurement values. In particular, hydrophilizing the surface of the coating 1b that forms the boundary of the region where two rectangular enameled wires 1 come into contact with each other is extremely effective in suppressing variations in PDIV measurement values. The surface of the coating 1b that forms the boundary of the region where two rectangular enameled wires 1 come into contact with each other is, for example, the surface of the coating 1b in the Y-shaped gap Y and the R-shaped gap R as shown in Figures 2A and 2B.

[0069] Therefore, the hydrophilization of the surface of the coating 1b performed in step S8 is a step of hydrophilizing at least the surface of the coating 1b that forms the boundary of the region where the two flat rectangular enamel wires 1 come into contact with each other. The surface of the coating 1b that forms the boundary is, for example, the surface of the coating 1b of the Y-shaped gap Y and the R-shaped gap R shown in Figures 2A and 2B.

[0070] Whether or not the surface of coating 1b has become hydrophilic can be determined by whether or not an index indicating the degree of hydrophilicity (wettability) of the surface of coating 1b exceeds a predetermined standard. For example, the "contact angle" of a liquid can be used as an index indicating the degree of hydrophilicity.

[0071] Figure 8 is a diagram illustrating the contact angle of a liquid, which serves as an indicator of hydrophilicity. According to the Dictionary of Physics and Chemistry (Iwanami Shoten, 4th edition), the "contact angle" is defined as "the angle between the liquid surface and the solid surface at the point where the free surface of a stationary liquid touches a solid wall (taking the angle within the liquid)." In other words, the "contact angle" can be expressed as the angle α between the solid surface 91 and the tangent line L that passes through the boundary between the solid surface 91 and the droplet 92 formed by dropping liquid onto the solid surface 91, as shown in Figure 8. In this embodiment, the solid surface 91 is the surface of the coating 1b of the rectangular enameled wire 1.

[0072] In the proposed method, hydrophilization of the surface of the coating 1b can be defined, based on the inventors' studies, as modification (activation) of the surface of the coating 1b such that the contact angle α between the surface of the coating 1b and the droplet 92 becomes 20° or less. More preferably, hydrophilization of the surface of the coating 1b is modification (activation) of the surface of the coating 1b such that the contact angle α between the surface of the coating 1b and the droplet 92 becomes 10° or less. The "contact angle" can be calculated using methods such as the width-to-height method (θ / 2 method), the circle method, the tangent method, the ellipse method, or the Young-Laplace method.

[0073] Furthermore, the inventors have also found that one effective method for hydrophilizing the surface of the coating 1b is to perform multiple preliminary discharges on the measurement sample 2 by applying an effective voltage value higher than the partial discharge initiation voltage.

[0074] Therefore, in this proposed method, in order to make the surface of the coating 1b hydrophilic, the measurement sample 2 is subjected to multiple preliminary discharges at a preset effective voltage value higher than the partial discharge initiation voltage. The preliminary discharge method for making the surface of the coating 1b hydrophilic in this proposed method can be defined, for example, as follows.

[0075] The measurement sample 2 is connected to the PDIV measuring device 50. An AC voltage is applied between one end and the other end of each of the two flat rectangular enameled wires 1 that make up the measurement sample 2. The applied voltage V is gradually increased. When the applied voltage V reaches a preset effective voltage value for hydrophilizing the surface of the coating 1b, the voltage is maintained for a certain period of time from that point, and partial discharge is maintained. After that, the application of voltage to the measurement sample 2 is stopped. The process of increasing the applied voltage V, maintaining it at the effective voltage value for a certain period of time, and stopping the application of voltage is repeated several times. In the following explanation, the certain period of time during which the applied voltage V that has reached the effective voltage value during preliminary discharge is maintained is called the holding time. The holding time and the number of preliminary discharges will be explained in detail later.

[0076] The above effective voltage value is the voltage required to hydrophilize the surface of the coating 1b of the flat rectangular enameled wire 1 that constitutes the measurement sample 2, specifically the Y-shaped gap Y and the R-shaped gap R of the coating 1b. This effective voltage value is higher than the average PDIV measurement value for similar measurement samples. The above effective voltage value can be determined, for example, by measuring PDIV multiple times, for example five times or more, on the measurement sample 2 beforehand and using the highest voltage value among the measured PDIVs.

[0077] In this proposed method, the computer 60, which is the control device for the PDIV measuring device 50, may be configured to store a plurality of previously measured PDIVs and set the maximum voltage value among these PDIVs as the effective 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 a setting.

[0078] As mentioned above, the proposed method differs from the standard method in steps S4 and S8. In step S4, the rectangular enameled wire 1 is immersed in an organic solvent, and in step S8, multiple preliminary discharges are performed to remove the lubricating oil adhering to the coating of the rectangular enameled wire 1. These changes in steps can suppress variations in the PDIV measurement values ​​of the measurement sample 2. Furthermore, in the proposed method, the surface of the coating 1b is hydrophilized in step S8, which can suppress variations in the PDIV measurement values ​​of the measurement sample 2 compared to the standard method.

[0079] In particular, multiple preliminary discharges are performed, causing the surface of the coating 1b to become hydrophilic. This leads to modification of the surface of the coating 1b in the Y-shaped gap Y shown in Figure 2A, thereby mitigating the charge in the Y-shaped gap Y. Therefore, it is estimated that the variability in PDIV measurements caused by the concentration and relaxation of the electric field in the Y-shaped gap Y can be reduced.

[0080] <Holding time and number of preliminary discharges> The inventors have derived suitable values ​​for the number of preliminary discharges and the holding time during each preliminary discharge in the hydrophilization step of the proposed method. The method is described below.

[0081] First, multiple flat enameled wires 1 of the same type as the flat enameled wire 1 used for the measurement sample 2 are prepared. These multiple flat enameled wires 1 are used for verification to determine the holding time and the number of preliminary discharges. The multiple verification flat enameled wires 1 are subjected to the processes shown in steps S4 to S7 in Figure 4. Then, PDIV measurements are performed on the multiple verification flat enameled wires 1 with different numbers of preliminary discharges and different holding times for the preliminary discharges.

[0082] Figure 9 is a table showing the conditions for preliminary discharge and PDIV measurement. As shown in Figure 9, the applied voltage frequency is 1 kHz. In the preliminary discharge under the reference method, the conditions for determining that partial discharge has started (partial discharge determination threshold shown in Figure 9) are that the discharge charge amount is 100 pC or more and the occurrence frequency is 1000 pps or more. In the preliminary discharge, the voltage application time (i.e., holding time) when partial discharge occurs is one of 5 s, 10 s, 15 s, or 20 s. The voltage boost step (boost rate) is 200 V / s, and the voltage buck step (buck rate) is output off after 0 V instruction control.

[0083] Furthermore, in PDIV measurements using the standard method and the proposed method, the conditions for determining that partial discharge has started (partial discharge determination threshold shown in Figure 9) are that the discharge charge amount is 100 [pC] or more and the occurrence frequency is 1000 [pps] or more. In the PDIV measurement, the applied voltage boost step (boost rate) is 30 [V / s] for the primary (up to 200 [V]) and 10 [V / s] for the secondary (after 200 [V]), and the applied voltage buck step (buck rate) is output off after 0 [V] instruction control. The measurement environment is 23 [°C] ambient temperature and 35 [%] humidity.

[0084] Under the above conditions, preliminary discharges are performed with holding times set to 5, 10, 15, and 20 seconds, ranging from 1 to 10 times for each holding time. Specifically, when the holding time is set to 5 seconds, one preliminary discharge is performed for 5 seconds, after which PDIV is measured 5 times. Then, a second preliminary discharge is performed for 5 seconds, after which PDIV is measured 5 times again. In this case, the measured value of the second PDIV is equivalent to the value obtained when two preliminary discharges with a holding time of 5 seconds are performed. The above measurements are repeated until the number of preliminary discharges reaches 10.

[0085] This measurement is performed on five different test rectangular enameled wires 1. This yields five PDIV measurements for each of the five test rectangular enameled wires 1 during each of the 1 to 10 preliminary discharges, with a holding time of 5 [s]. In other words, a total of 25 PDIV measurements are obtained from the five test rectangular enameled wires 1 during each of the 1 to 10 preliminary discharges.

[0086] Figure 10 shows the measured values ​​of PDIV when the holding time is 5 [s]. In Figure 10, the measured values ​​of PDIV obtained from two different verification flat enameled wires 1 (Sample No. 1 and Sample No. 5) are shown as representative values ​​out of the measured values ​​of PDIV obtained from five different verification flat enameled wires 1.

[0087] Based on the 25 PDIV measurements obtained, the coefficient of variation (CV), which indicates the degree of variability in PDIV measurements for each number of preliminary discharges, is calculated. The coefficient of variation (CV) is calculated using the following equation (1).

[0088] Coefficient of variation (CV) = Standard deviation (σ) / Mean (AVE) × 100 ... (1) The same process is performed when the holding time is 10 [s], 15 [s], and 20 [s]. That is, for each of the holding times of 10 [s], 15 [s], and 20 [s], 25 PDIV measurements are obtained for each of the 1 to 10 preliminary discharges. Then, the coefficient of variation (CV) is calculated based on the above equation (1).

[0089] Figure 11 is a table showing the coefficient of variation (CV) for each number of preliminary discharges, when the holding time is 5 [s], 10 [s], 15 [s], and 20 [s]. Figure 12 is a graph showing the relationship between the number of preliminary discharges and the coefficient of variation (CV) shown in Figure 11. Figure 13 is a graph showing the relationship between the total time required for preliminary discharge and the coefficient of variation (CV).

[0090] In Figure 12, the horizontal axis represents the number of preliminary discharges, and the vertical axis represents the coefficient of variation (CV). In Figure 13, the horizontal axis represents the total time required for preliminary discharge, and the vertical axis represents the coefficient of variation (CV). In Figures 12 and 13, the coefficient of variation (CV) for a holding time of 5 [s] is represented by an X (×), the coefficient of variation (CV) for a holding time of 10 [s] is represented by a triangle (▲), the coefficient of variation (CV) for a holding time of 15 [s] is represented by a square (◆), and the coefficient of variation (CV) for a holding time of 20 [s] is represented by a circle (●).

[0091] When the coefficient of variation (CV) is close to 1%, the variability of the PDIV measurements can be considered to be suppressed. In the following explanation, a value where the coefficient of variation (CV) is close to 1% will be referred to as the evaluation value. In other words, the evaluation value is a value that indicates that the variability of the PDIV measurements is suppressed. The evaluation value may be exactly 1%, or it may be a value obtained by adding or multiplying a predetermined coefficient to 1%. The predetermined coefficient should be set to a suitable value based on the results of simulations and various tests.

[0092] As shown in Figure 12, when the holding time is 5 [s], after 9 preliminary discharges, the coefficient of variation (CV) becomes approximately 1 [%], which is the evaluation value, and the variability of the PDIV measurement is suppressed. That is, as shown in Figure 13, when the total time during which 9 preliminary discharges are performed is 45 [s], the variability of the PDIV measurement is suppressed. In other words, the total time during which the AC voltage is applied to the verification flat enameled wire 1 is 45 [s], and 9 preliminary discharges are performed on the verification flat enameled wire 1, until the coefficient of variation (CV) reaches the evaluation value.

[0093] Furthermore, when the holding time is 10 [s], as shown in Figure 12, after 6 preliminary discharges, the coefficient of variation (CV) becomes the evaluation value, and the variability of the PDIV measurement is suppressed. That is, as shown in Figure 13, after 6 preliminary discharges have been performed and the total time is 60 [s], the variability of the PDIV measurement is suppressed. In other words, the total time during which the AC voltage is applied to the verification flat enameled wire 1 is 60 [s], and 6 preliminary discharges have been performed on the verification flat enameled wire 1, until the coefficient of variation (CV) becomes the evaluation value.

[0094] Similarly, when the holding time is 15 seconds, as shown in Figure 12, the coefficient of variation (CV) becomes the evaluation value after four preliminary discharges, and the variability of the PDIV measurement is suppressed. When the holding time is 15 seconds, as shown in Figure 13, the variability of the PDIV measurement is suppressed when the total time of preliminary discharges reaches 90 seconds. In other words, the total time that the AC voltage is applied to the verification flat enameled wire 1 is 90 seconds, and four preliminary discharges are performed on the verification flat enameled wire 1, before the coefficient of variation (CV) becomes the evaluation value.

[0095] When the holding time is 20 seconds, as shown in Figure 12, the coefficient of variation (CV) becomes the evaluation value after four preliminary discharges, and the variability of the PDIV measurement is suppressed. When the holding time is 20 seconds, as shown in Figure 13, the variability of the PDIV measurement is suppressed when the total time of preliminary discharges reaches 100 seconds. In other words, the total time that the AC voltage is applied to the verification flat enameled wire 1 is 100 seconds, and four preliminary discharges are performed on the verification flat enameled wire 1, before the coefficient of variation (CV) becomes the evaluation value.

[0096] Thus, as the holding time increases, the number of preliminary discharges decreases, but the total duration of preliminary discharges increases, before the variability of PDIV measurements is suppressed. Conversely, as the holding time decreases, the number of preliminary discharges increases, but the total duration of preliminary discharges decreases.

[0097] Considering the above points, in this embodiment, the holding time and the number of preliminary discharges are determined based on the coefficient of variation (CV), which is a value representing the degree of variation in the PVDI measurement. Specifically, the holding time and the number of preliminary discharges are determined by the time the AC voltage was applied to the verification rectangular enameled wire 1 and the number of preliminary discharges performed until the value of the coefficient of variation (CV) reached the evaluation value. The holding time is set to 15 [s] or less. As a result, if the holding time is 5 [s], multiple preliminary discharges (9 times) are performed so that the total preliminary discharge time is 45 [s]. If the holding time is 10 [s], multiple preliminary discharges (6 times) are performed so that the total preliminary discharge time is 60 [s]. If the holding time is 15 [s], multiple preliminary discharges (5 times) are performed so that the total preliminary discharge time is 90 [s]. Thus, when the holding time is 15 [s] or less, the number of preliminary discharges increases as the holding time becomes shorter than 15 [s].

[0098] However, by setting the holding time to 15 seconds or less, it becomes possible to shorten the total time of preliminary discharge compared to performing multiple preliminary discharges with the same 20-second holding time as the standard method, resulting in a total time of 100 seconds. As a result, it becomes possible to shorten the time required for the hydrophilization process during PDIV measurement of sample 2.

[0099] Figure 14 is a graph showing the relationship between the cumulative number of partial discharges generated from the surface of coating 1b during preliminary discharge and the coefficient of variation (CV). The condition for determining that a partial discharge has started is the partial discharge threshold shown in Figure 9, as described above, which is a discharge charge amount of 100 [pC] or more. The cumulative number of partial discharges is the value obtained by accumulating the number of partial discharges generated in each of the multiple preliminary discharges that occurred.

[0100] In Figure 14, the horizontal axis represents the cumulative number of partial discharges, and the vertical axis represents the coefficient of variation (CV). Also in Figure 14, the coefficient of variation (CV) for a holding time of 5 [s] is represented by an X (×), for a holding time of 10 [s] by a triangle (▲), for a holding time of 15 [s] by a square (◆), and for a holding time of 20 [s] by a circle (●).

[0101] As shown in Figure 14, the coefficient of variation (CV) decreases as the number of preliminary discharges increases (i.e., the total time increases), but the cumulative number of partial discharges increases. An increase in the cumulative number of partial discharges indicates an increase in the number of collisions of accelerated electrons with the coating 1b of the rectangular enamel wire 1. In this case, there is a higher probability that the coating 1b of the rectangular enamel wire 1 is being physically eroded. Therefore, a lower cumulative number of partial discharges is desirable.

[0102] Here, we set the baseline value of the cumulative number of partial discharges at 1 million cycles and focus on the coefficient of variation (CV) at this point. In this case, when the holding time is 5[s] and 10[s], the coefficient of variation (CV) is 2[%] or less. In contrast, when the holding time is 15[s] and 20[s], the coefficient of variation (CV) is 4[%] or more. In other words, when the cumulative number of partial discharges reaches the baseline value, there is variation in the coefficient of variation (CV) depending on the holding time.

[0103] As mentioned above, considering the physical effects on the coating 1b, it is desirable to have a small cumulative number of partial discharges. Therefore, in this embodiment, the holding time is set so that the coefficient of variation (CV) is less than or equal to a threshold when the cumulative number of partial discharges reaches the reference value of 1 million. Here, the threshold is, for example, 2%. However, the threshold is not limited to this value, and it is preferable that it be close to the evaluation value of the coefficient of variation (CV), which is 1%.

[0104] As mentioned above, the coefficient of variation (CV) becomes 2% or less of the threshold when the cumulative number of partial discharges reaches the reference value when the holding time is 5 seconds and 10 seconds. Therefore, in this embodiment, the holding time can be set to 5 seconds or 10 seconds based on the cumulative number of partial discharges during preliminary discharge and the coefficient of variation (CV), which is the degree of variation of the PVDI measurement values. In other words, the holding time is determined by the time an alternating current is applied to the verification rectangular enameled wire 1 when the coefficient of variation (CV) of the PVDI measurement values ​​becomes 2% or less of the threshold when the coefficient of variation (CV) reaches the reference value.

[0105] Based on the results obtained using the flat enameled wire 1 for verification as described above, in this embodiment, the holding time for the preliminary discharge is set to 15 [s] or less. More preferably, the holding time is set to 5 [s] or 10 [s].

[0106] By setting the holding time to 15 seconds or less, the total time can be shortened, although the number of preliminary discharges increases compared to the standard method where the holding time is 20 seconds and multiple preliminary discharges are performed. This reduces the time required for the hydrophilization process of sample 2, and thus shortens the time required for PDIV measurement of sample 2.

[0107] More preferably, the holding time is set to 5 seconds or 10 seconds. By setting the holding time to 5 seconds or 10 seconds, it is possible to reduce the number of partial discharges that occur during preliminary discharge. As a result, physical erosion of the coating 1b of the rectangular enamel wire 1 is suppressed.

[0108] Furthermore, in this embodiment, an oil removal step is performed in which the flat enameled wire 1 is immersed in an organic solvent before the hydrophilization step. It is presumed that immersing the flat enameled wire 1 in an organic solvent can suppress 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 such as n-hexane, and the emission of primary electrons as described above can be suppressed, thereby reducing the variability of the PDIV measurement values. Also, it is thought that the electric field in the Y-shaped gap Y is concentrated or relaxed depending on the state of oil distribution in the Y-shaped gap Y shown in Figure 2A. In contrast, it is presumed that the distortion of the electric field in the Y-shaped gap Y is suppressed by removing the oil distributed in the Y-shaped gap Y with an organic solvent such as n-hexane. In addition, immersing the flat enameled wire 1 in an organic solvent removes oils such as lubricating oil that inhibit the modification (activation) of the coating of the flat enameled wire 1 by hydrophilization. As a result, it becomes possible to reduce the number of preliminary discharges required to reduce the variability in PDIV measurements. In other words, it becomes possible to shorten the time required to obtain stable PDIV measurements with less variability.

[0109] (Embodiment 2) An embodiment of this application is a PDIV measuring device 50 that performs PDIV measurement after performing a preliminary discharge on the measurement sample 2, and is configured to have a control device according to the proposed method. Specifically, the control device according to the proposed method accepts the setting of an effective voltage value as the applied voltage V used for the preliminary discharge, so as to enable hydrophilization of the surface of the coating 1b of the flat rectangular enameled wire 1 that constitutes the measurement sample 2.

[0110] With such a PDIV measuring device 50, the surface of the coating 1b of the flat enamel wire 1 constituting the measurement sample 2 can be easily made hydrophilic, and furthermore, variations in PDIV measurement values ​​can be suppressed.

[0111] Furthermore, in a PDIV measuring device 50, one embodiment of the present invention is one in which the control device is configured to store multiple measured values ​​obtained from a PDIV measurement performed in advance and to set the maximum voltage value among those measured values ​​as the effective voltage value.

[0112] With such a PDIV measuring device 50, the process of setting the effective voltage value as the applied voltage used for preliminary discharge can be performed automatically, reducing the complicated operations required by the user. However, the process of setting the effective voltage value as described above may also be performed manually in response to user input.

[0113] (Embodiment 3) Furthermore, a program P for causing the computer 60 provided in the PDIV measuring 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 this invention.

[0114] Even when the program according to this embodiment 3 is executed by the processor, the same effects as in embodiment 2 can be obtained.

[0115] Although various embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are included. Furthermore, the embodiments described above are described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. In addition, 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 are within the scope of the present invention. Furthermore, the numerical values ​​and other figures included in the text and figures are merely examples, and using different ones will not impair the effects of the present invention.

[0116] For example, in the above-described embodiment, a flat enameled wire in which a conductor such as copper is 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 in which the conductor is a metal other than copper, for example. [Explanation of Symbols]

[0117] 1 Flat enameled wire (enameled wire), 1a Conductor, 1b Coating, 1c Back-to-back joint, 1d Terminal, 2 Measurement sample, 11 Matting surface, 12 Fixing device, 50 PDIV measuring device, 51 Voltage generator, 52 Voltage / charge measuring 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 method for measuring the partial discharge initiation voltage of enameled wires, wherein two enameled wires having a coating are stacked together over a predetermined region in the longitudinal direction of the enameled wires, and the partial discharge initiation voltage of the enameled wires is measured. The process includes a hydrophilization step in which, before measuring the partial discharge initiation voltage, a preliminary discharge is performed multiple times in which an AC voltage at a predetermined effective voltage value is applied for a certain period of time between one end and the other end of each of the two enameled wires, thereby hydrophilizing the surface of the coating on the two enameled wires. A method for measuring the partial discharge initiation voltage, wherein the aforementioned fixed time is 15 seconds or less.

2. In the method for measuring the partial discharge initiation voltage according to claim 1, A method for measuring the partial discharge initiation voltage, wherein the number of times the preliminary discharge is performed increases as the aforementioned fixed time becomes shorter than 15 seconds.

3. In the method for measuring the partial discharge initiation voltage according to claim 2, A method for measuring partial discharge initiation voltage, comprising, prior to the hydrophilization step, an oil removal step of removing oil adhering to the surface of the coating of the two enameled wires using an organic solvent containing hexane.

4. In the method for measuring the partial discharge initiation voltage according to claim 3, A method for measuring partial discharge initiation voltage, wherein the oil removal step is a step of immersing the enameled wire in the organic solvent for 24 hours or more.

5. In the method for measuring the partial discharge initiation voltage according to claim 4, A method for measuring partial discharge initiation voltage, wherein the organic solvent containing hexane is a hydrocarbon-based organic solvent.

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