Rotor short-circuit detection method, rotor manufacturing method, and rotor short-circuit detection device

Abstract

To obtain a rotor short-circuit detection method that can determine whether the cause of a decrease in the motor output and torque of an induction motor is electrical conductivity between the iron core and the rotor bars, or electrical conductivity between adjacent rotor bars due to aluminum foil. [Solution] The rotor short-circuit detection method includes a measurement step, a plotting step, and a determination step. In the measurement step, the real part of the impedance and the parallel resistance are measured for each of the multiple rotors. In the plotting step, the points consisting of the values ​​of the real part of the impedance and the parallel resistance for each of the multiple rotors are plotted on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes. In the determination step, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be the set of rotors where an iron core short-circuit has occurred, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be the set of rotors where an aluminum short-circuit has occurred.

Description

[Technical Field]

[0001] This disclosure relates to a rotor short-circuit detection method, a rotor manufacturing method, and a rotor short-circuit detection device for detecting a short circuit in the rotor of an induction motor. [Background technology]

[0002] The rotor of an induction motor comprises an iron core made of multiple laminated electromagnetic steel sheets, multiple rotor bars housed in multiple slots provided in the iron core, an end ring connecting the multiple rotor bars at both ends of the iron core, and a rotating shaft for rotating these components together. In small motors, aluminum, which has high conductivity, is generally used for the secondary conductor consisting of the rotor bars and end ring. In this way, in an induction motor, a secondary current flows through the secondary conductor with low electrical resistance, generating torque. In induction motors, it is desirable to have high torque for a given motor input power, that is, high motor output and high efficiency. Therefore, it is necessary to reduce losses such as copper loss, iron loss, mechanical loss, and stray load loss that reduce motor output. Hereafter, aluminum may also be referred to as aluminum.

[0003] One type of stray load loss is the heat loss generated in the conductive core of an induction motor's rotor when the rotor core and rotor bars become conductive, causing a current called "cross-current" or "lateral current" to flow.

[0004] Patent Document 1 discloses a measuring device for measuring the conductivity between the inner circumference of the iron core slots and the rotor bars in the rotor of an induction motor. The measuring device described in Patent Document 1 discloses that an alternating magnetic field is applied from the winding of the measuring device to the rotor, and the phase difference between the current flowing through the winding and the voltage applied to the winding, or the real and imaginary parts of the impedance, is measured. Patent Document 2 also discloses a measuring device that measures impedance by applying an alternating magnetic field to the rotor in the same manner as in Patent Document 1, and measures the resistance between the rotor bars with the iron core in between. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2018 / 173211 [Patent Document 2] Japanese Patent Application Publication No. 59-041162 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Electrical conductivity between the iron core and the secondary conductor can occur in two processing steps: the die-casting of aluminum into the iron core's slots, and the subsequent machining of the iron core's outer surface. In the former step, since the press-punched iron core cross-section lacks an insulating coating, electrical conductivity may occur when the inner circumference of the iron core's slots comes into contact with the rotor bars. In addition, on the outer surface of the rotor, a thin layer of aluminum may penetrate into the gaps between the laminated iron cores, causing electrical conductivity between adjacent rotor bars via a thin layer of aluminum foil. In the latter step, since the machined outer surface of the rotor lacks an insulating coating, electrical conductivity may occur when the iron core and rotor bars come into contact on the outer surface of the rotor.

[0007] Ideally, the iron core and the secondary conductor should be electrically insulated from each other. However, in reality, the iron core and the secondary conductor conduct electricity, and a current called "cross-current" or "cross-current" flows. In a short circuit with high electrical resistance, this causes heat loss, reducing motor output and torque. Therefore, when conduction occurs between the iron core and the secondary conductor, it is necessary to know the cause of the conduction. The technology described in Patent Document 1 can detect the occurrence of conduction between the iron core and the secondary conductor, and the technology described in Patent Document 2 can detect conduction between rotor bars with the iron core in between. However, determining whether the conduction is between the iron core and the secondary conductor or between rotor bars separated by aluminum foil with the iron core in between requires measurements using both the technology described in Patent Document 1 and Patent Document 2, which is time-consuming. In other words, there was a need for a technology that could determine whether the electrical conduction is between the iron core and the rotor bars or between adjacent rotor bars separated by aluminum foil in a single measurement.

[0008] This disclosure has been made in view of the above, and aims to provide a rotor short-circuit detection method that can determine whether the cause of a decrease in the motor output and torque of an induction motor is electrical conductivity between the iron core and the rotor bars, or electrical conductivity between adjacent rotor bars due to aluminum foil. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the rotor short-circuit detection method according to this disclosure includes a measurement step, a plotting step, and a determination step. In the measurement step, the real part of the impedance and the parallel resistance are measured for each of a plurality of rotors, each having an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core. In the plotting step, points consisting of pairs of the real part of the impedance and the parallel resistance of each of the plurality of rotors are plotted on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes. In the determination step, among the sets of points plotted on the Cartesian coordinate system, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be a set of rotors where an iron core short circuit has occurred, in which the iron core and the secondary conductor of the rotor conduct to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be a set of rotors where an aluminum short circuit has occurred, in which the short-circuit current flows through something other than the iron core of the rotor. [Effects of the Invention]

[0010] This disclosure provides the effect of being able to determine whether the cause of the decrease in the motor output and torque of an induction motor is electrical conductivity between the iron core and the rotor bar, or electrical conductivity between adjacent rotor bars due to aluminum foil. [Brief explanation of the drawing]

[0011] [Figure 1] A perspective view showing an example of the configuration of the rotor to be detected by the rotor short-circuit detection device according to Embodiment 1. [Figure 2] Cross-sectional view showing an example of the rotor core structure. [Figure 3] A partially enlarged cross-sectional view showing an example of the configuration of the outer surface of the rotor. [Figure 4] A partially enlarged front view showing an example of the configuration of the outer surface of the rotor. [Figure 5] This figure shows an example of the configuration of the rotor short-circuit detection device according to Embodiment 1. [Figure 6] This diagram schematically shows an example of a state in which a rotor is inserted into the sensor unit of the rotor short-circuit detection device according to Embodiment 1. [Figure 7] FIG. 1 is a diagram showing an example of measurement results of impedances of a plurality of rotors in the rotor short - circuit detection device according to Embodiment 1. [Figure 8] FIG. 2 is a flowchart showing an example of a processing procedure of the rotor short - circuit detection method according to Embodiment 1. [Figure 9] FIG. 3 is a flowchart showing an example of a processing procedure of the rotor short - circuit detection method according to Embodiment 1. [Figure 10] FIG. 4 is a cross - sectional view for explaining a state of cutting of the outer peripheral surface of the rotor. [Figure 11] FIG. 5 is a cross - sectional view for explaining a state of dissolving the outer peripheral surface of the rotor with an alkaline aqueous solution. [Figure 12] FIG. 6 is a cross - sectional view for explaining another example of retracting the outer peripheral surface of the rotor bar. [Figure 13] FIG. 7 is a cross - sectional view schematically showing an example of the configuration of a sensor unit of the rotor short - circuit detection device according to Embodiment 4. [Figure 14] FIG. 8 is a block diagram showing an example of the configuration of a computer system that realizes a determination device of the rotor short - circuit detection device according to Embodiments 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a rotor short - circuit detection method, a rotor manufacturing method, and a rotor short - circuit detection device according to an embodiment of the present disclosure will be described in detail based on the drawings.

[0013] Embodiment 1. FIG. 1 is a perspective view showing an example of the configuration of a rotor to be detected by the rotor short - circuit detection device according to Embodiment 1. The rotor 10 includes an iron core 11, rotor bars 12, end rings 13, and a rotating shaft 14.

[0014] The iron core 11 is a cylindrical member formed by stacking annular-shaped plates. The annular-shaped plates are obtained by punching out electrical steel sheets using press processing or the like. Multiple annular-shaped plates are stacked axially around a central hole into which the rotating shaft 14 is inserted. At this time, the annular-shaped plates are positioned rotated by a predetermined angle relative to the annular-shaped plate placed below them. Figure 2 is a cross-sectional view showing an example of the configuration of the rotor's iron core. In Figure 2, the cross-section is shown in a direction perpendicular to the rotating shaft 14. As shown in Figure 2, the iron core 11 has multiple teeth 11t protruding toward the outer circumference, multiple slots 11s sandwiched between two adjacent teeth 11t and opening on the outer circumference, and an opening 11o provided in the center. The teeth 11t and slots 11s are arranged alternately and continuously in the circumferential direction of the iron core 11. The opening 11o is an axially extending opening formed by the central hole of the annular-shaped plate.

[0015] Returning to Figure 1, the rotor bars 12 are made of aluminum, which is considered a highly conductive material. The rotor bars 12 are die-cast and fitted into the slots 11s of the iron core 11. The end rings 13 are provided at both ends of the iron core 11 in the axial direction. The end rings 13 are integrally formed with the multiple rotor bars 12 fitted into the multiple slots 11s and at both ends of the iron core 11 in the axial direction. The rotor bars 12 and the end rings 13 correspond to secondary conductors. The rotating shaft 14 is press-fitted into an opening 11o provided in the center of the iron core 11. In this way, the iron core 11, rotor bars 12 and end rings 13 are held by the rotating shaft 14 and form a single unit that constitutes the rotor 10.

[0016] Figure 3 is a partially enlarged cross-sectional view showing an example of the configuration of the outer surface of the rotor. Figure 3 shows a cross-section of the outer surface of the rotor 10 perpendicular to the rotation axis 14, with the rotor bar 12 housed between the two teeth 11t of the iron core 11. The iron core 11 and the rotor bar 12 of the rotor 10 have different coefficients of thermal expansion. Therefore, when the rotor bar 12 is sufficiently cooled after die casting, the iron core 11 and the rotor bar 12 separate from each other. A thin insulating layer 15, consisting of an air layer or an aluminum oxide film, is then formed between the iron core 11 and the rotor bar 12. Ideally, this insulating layer 15 electrically insulates the iron core 11 and the rotor bar 12.

[0017] However, in reality, a core short circuit 20 is formed in the insulating layer 15 between the iron core 11 and the rotor bar 12, electrically connecting the iron core 11 and the rotor bar 12. After the formation of the iron core 11 by laminating annular plate material and the aluminum die casting of the rotor bar 12, the outer peripheral surface of the side of the rotor 10 is machined to improve its roundness or cylindricity. At this time, the machined surface of the relatively soft rotor bar 12 stretches, and a part of the rotor bar 12 comes into contact with the machined surface or punched cross section of the relatively hard iron core 11, thereby forming a core short circuit 20. As a result, two adjacent rotor bars 12 become electrically connected through the outer peripheral surface or punched cross section of the iron core 11. Multiple such core short circuits 20 exist inside the rotor 10.

[0018] When the rotor 10 is used as an induction motor, ideally, secondary current flows only through the highly conductive rotor bars 12, generating torque that rotates the rotor 10. However, in reality, a current called "lateral current" or "cross-current" flows through the short-circuited core 20, causing significant heat loss in the less conductive core 11, and reducing motor output. It is also known that the torque decreases or varies from rotor 10 to rotor. Hereafter, "lateral current" or "cross-current" will be referred to simply as "lateral current".

[0019] Next, we will explain how losses due to "crossflow" occur even in cases other than core short circuits 20. Figure 4 is a partially enlarged front view showing an example of the configuration of the outer surface of the rotor. The iron core 11 has a structure in which annular-shaped plate materials 111 are stacked in the axial direction, and generally, gaps of several tens of micrometers, called inter-laminated gaps 16, are formed between the stacked annular-shaped plate materials 111. When aluminum is die-cast into the rotor 10, aluminum may unintentionally penetrate into the inter-laminated gaps 16 and remain as broadly defined inter-laminated aluminum 17. Among the inter-laminated aluminum 17, there are narrowly defined inter-laminated aluminum 18 in which aluminum has only penetrated to a part of the inter-laminated gap 16, and there are also cases where aluminum has penetrated the entire inter-laminated gap 16 between adjacent rotor bars 12, resulting in an aluminum short circuit 30. The aluminum short circuit 30 is formed by aluminum foil made of thin aluminum that has penetrated into the inter-laminated gap 16, connecting adjacent rotor bars 12. Although aluminum has high conductivity, the aluminum short circuit 30 has high electrical resistance because the cross-sectional area of ​​the gap 16 between the laminates is small. Therefore, if an aluminum short circuit 30 is present and current flows through it due to "cross-current", a large heat loss occurs, and similar to the iron core short circuit 20, the torque decreases or the torque varies from rotor 10 to rotor.

[0020] The following describes a rotor short-circuit detection device for distinguishing between an iron core short-circuit 20 and an aluminum short-circuit 30 in the rotor 10 of an induction motor. Figure 5 shows an example of the configuration of a rotor short-circuit detection device according to Embodiment 1. The rotor short-circuit detection device 40 includes a sensor unit 50 that measures the impedance Z of the rotor 10, and a determination device 60 that determines the type of short-circuit in the rotor 10 from the impedance Z of the rotor 10 measured by the sensor unit 50.

[0021] The sensor unit 50 comprises a sensor core 51, a sensor winding 52, and an LCR meter 53. The sensor core 51 is a cylindrical member having an opening 51o in its center through which the rotor 10 to be inspected can be inserted and removed. The sensor core 51 has a plurality of teeth 51t protruding toward the inner circumference. The opening 51o is formed by the inner surfaces of the plurality of teeth 51t. The sensor winding 52 is wound around each of the plurality of teeth 51t. The number of turns of the sensor winding 52 wound around each tooth 51t is the same. In addition, the sensor windings 52 are wound such that the winding direction is opposite for adjacent teeth 51t, and the sensor windings 52 wound around each tooth 51t are connected in series. Both terminals of the sensor winding 52 are connected to the LCR meter 53. The LCR meter 53 is connected to both ends of the sensor winding 52 and measures the impedance Z of the rotor 10 inserted into the opening 51o of the sensor core 51. Specifically, the LCR meter 53 applies an AC voltage to both ends of the sensor winding 52 connected in series, measures the magnitude and phase difference of the current flowing through the sensor winding 52 with respect to the applied voltage, and converts it to an equivalent impedance. The LCR meter 53 corresponds to an impedance measuring device.

[0022] Figure 6 is a schematic diagram showing an example of a rotor inserted into the sensor unit of the rotor short-circuit detection device according to Embodiment 1. In Figure 6, only the sensor unit 50 of the rotor short-circuit detection device 40 is shown. The rotor 10 to be inspected is inserted into and removed from the axial direction through the opening 51o inside the sensor core 51 of the sensor unit 50. The rotor 10 before impedance measurement is inserted into the opening 51o inside the sensor core 51 from the axial direction, and after the impedance Z is measured with the LCR meter 53, the rotor 10 is removed from the opening 51o inside the sensor core 51. Subsequently, another rotor 10 before impedance measurement is similarly inserted into the opening 51o inside the sensor core 51 and the impedance Z is measured. In this way, the sensor unit 50 is configured to measure the impedance Z of multiple rotors 10 one by one in sequence.

[0023] Before describing the configuration of the determination device 60, we will briefly explain the method for distinguishing between a core short circuit 20 and an aluminum short circuit 30 by measuring the impedance Z of the rotor 10 of the induction motor with the rotor short circuit detection device 40. In the sensor unit 50 of Figure 6, when an AC voltage is applied to the sensor winding 52 with the LCR meter 53, magnetic flux is linked from the sensor unit 50 to the secondary conductor composed of the rotor bar 12 and end ring 13. This induces a secondary current in the secondary conductor, and a reaction magnetic flux is generated from the rotor 10 to the sensor unit 50. Therefore, the LCR meter 53 of the sensor unit 50 measures the impedance Z corresponding to the magnitude of the resistance and inductance of the secondary conductor of the rotor 10. Here, if there are varying degrees of core short circuits 20 or aluminum short circuits 30 in each of the multiple rotors 10, the magnitude of the short-circuit current flowing through the core short circuit 20 or aluminum short circuit 30 will change. As a result, the sensor unit 50 detects that the impedance value measured by the LCR meter 53 fluctuates across the multiple rotors 10 due to the increase or decrease in resistance of the iron core short circuit 20 or aluminum short circuit 30, and the reaction magnetic flux due to the short circuit current. In this way, the difference in impedance Z among the multiple rotors 10 is measured.

[0024] Figure 7 shows an example of the measurement results of the impedance of multiple rotors in the rotor short-circuit detection device according to Embodiment 1. In Figure 7, the horizontal axis is the real part Re[Z] of impedance Z and the vertical axis is the parallel resistance Rp of impedance Z, and the pairs of the values ​​of the real part Re[Z] of impedance Z and the parallel resistance Rp of multiple rotors 10 are plotted on a Cartesian coordinate system.

[0025] The measurement is performed by modeling the rotor short-circuit detection device 40 and the rotor 10 using electromagnetic field analysis. In Embodiment 1, a typical ventilation fan rotor 10 with 14 slots is used, along with a sensor unit 50 having a sensor core 51 with 8 slots. In addition, to simulate multiple rotors 10, the number of core short circuits 20 and aluminum short circuits 30 in the model is varied.

[0026] Figure 7 shows a plot of multiple points in a Cartesian coordinate system for several rotors 10, each with a different degree of iron core short circuit 20 or aluminum short circuit 30. The pair of the real part value Re[Z] of the impedance Z and the parallel resistance Rp of the impedance Z is used as the plot point for one rotor 10. Note that the value of the parallel resistance Rp is the value of the resistance component in the parallel equivalent circuit mode of the LCR meter 53.

[0027] First, in Figure 7, each of the four circular plot points 21 represents a measured value of the impedance Z of a rotor 10 with different degrees of core short-circuiting 20 on its outer surface. The single square plot point 31 represents a measured value of the impedance Z when the entire outer surface of the rotor 10 is short-circuited with aluminum 30. The solid line 22 connecting the circular plot points 21 of the core short-circuiting 20 represents an interpolation function when the circular plot points 21 are considered to be inversely proportional to the real part Re[Z] of the impedance Z and the parallel resistance Rp. Note that the circular plot point 21a, which has the smallest parallel resistance Rp value, represents a measured value of the impedance Z when the entire outer surface of the rotor 10 is short-circuited with iron core 20.

[0028] The impedance Z is given by equation (1) below, where Re[Z] is the real part and Im[Z] is the imaginary part, and j is the imaginary unit.

[0029] Z = Re[Z] + j·Im[Z] ···(1)

[0030] If the real part of the parallel equivalent circuit mode is G and the imaginary part is B, the reciprocal of the impedance Z is given by equation (2). Also, the parallel resistance Rp is given by equation (3).

[0031] 1 / Z = G + j·B ···(2) Rp = 1 / G ... (3)

[0032] Therefore, if a short circuit occurs in a secondary conductor other than the rotor bar 12 and end ring 13, such as a core short circuit 20 or aluminum short circuit 30 of the rotor 10, the reaction magnetic flux due to the short circuit current increases. This causes a decrease in the magnitude of the impedance Z. When the impedance Z decreases, according to equation (2), the admittance and conductance G, which are the reciprocals of the impedance Z, increase. Also, when the admittance and conductance G increase, according to equation (3), the parallel resistance Rp decreases. In other words, when the magnitude of the impedance Z decreases, the admittance and conductance G increase, and the parallel resistance Rp decreases, as measured by the LCR meter 53. To put it another way, a large parallel resistance Rp occurs when there are few core short circuits 20 or aluminum short circuits 30 on the outer surface of the rotor 10, and conversely, a small parallel resistance Rp occurs when there are many core short circuits 20 or aluminum short circuits 30.

[0033] Therefore, if the impedance Z of multiple rotors 10 varies due to differences in the degree of iron core short circuits 20, plotting the measured impedance Z of multiple rotors 10 will show that the multiple plot points are distributed in an inverse relationship between the real part Re[Z] of the impedance Z and the parallel resistance Rp, as shown by the interpolation function solid line 22 in Figure 7. On the other hand, if the impedance Z of multiple rotors 10 varies due to differences in the degree of aluminum short circuits 30 for a given rotor 10, the plot points will be distributed far apart from the above inverse relationship, as shown by the plot point 31 of the aluminum short circuit 30 relative to the plot point 21a of the iron core short circuit 20 in Figure 7.

[0034] The inverse relationship between the real part Re[Z] of the impedance Z and the parallel resistance Rp is expressed by the following equation (4).

[0035] Rp∝1 / Re[Z] ···(4)

[0036] For example, if we represent the inverse proportion curve with three coefficients a, b, and c using the following equation (5), we can draw the solid line 22 in Figure 7.

[0037] Rp = 1 / (a × Re[Z] + b) + c ... (5)

[0038] The coefficients a, b, and c can be uniquely determined by the least squares method for a set of values ​​of the real part Re[Z] of the impedance Z of multiple rotors 10 and the parallel resistance Rp.

[0039] Here, the annular plate material 111 that constitutes the iron core 11 is made of electrical steel sheet. Generally, several grades of electrical steel sheet with the same thickness but different conductivity are supplied by steel manufacturers. In one example, the conductivity differs by more than 1.1 times between electrical steel sheets of different grades. Therefore, if the conductivity of one adjacent grade differs by k times, it is obvious that the variation in conductivity of the same grade is at least less than k / 2 times. Thus, considering the case where k = 1.05 and the conductivity of the electrical steel sheet can vary to the maximum extent possible, we can determine that a short circuit 20 in the iron core falls within the range of two inverse proportion curves obtained by varying the value of coefficient a in equation (5) by 5%. The inverse proportion curves obtained by varying the value of coefficient a by 5% are the two dashed lines 23a and 23b in Figure 7. Furthermore, a short circuit 30 in the aluminum can be determined that does not fall within the range of the two dashed lines 23a and 23b.

[0040] Thus, in Embodiment 1, if the set of impedance Z values ​​of multiple rotors 10 measured by the sensor unit 50 is distributed in an inverse relationship between the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp, it is determined that the impedance Z of the rotors 10 is varying due to a short circuit 20 in the iron core. On the other hand, if the distribution is divergent from the inverse relationship, it is determined that the impedance Z of the rotors 10 is varying due to a short circuit 30 in the aluminum.

[0041] The determination device 60 determines, according to the principle described above, whether the cause of the variation in the impedance Z of each rotor 10 is a core short circuit 20 or an aluminum short circuit 30, based on the measurement results from the LCR meter 53. Returning to Figure 5, the determination device 60 includes a measurement result acquisition unit 61, a rotor information storage unit 62, a measurement result plotting unit 63, an approximation curve calculation unit 64, and a short circuit determination unit 65.

[0042] The measurement result acquisition unit 61 acquires the impedance Z measurement result for each of the multiple rotors 10 from the LCR meter 53. The measurement result acquisition unit 61 associates the impedance Z measurement result with identification information that identifies the rotor 10 that was measured. The measurement result acquisition unit 61 stores the impedance Z measurement result associated with the rotor 10 identification information in the rotor information storage unit 62. In one example, the measurement result includes a pair of the real part Re[Z] value of the impedance Z and the parallel resistance Rp value. This is just an example; the measurement result only needs to be able to derive the real part Re[Z] value of the impedance Z and the parallel resistance Rp value.

[0043] The rotor information storage unit 62 stores rotor information, which includes the measurement results for each rotor 10 and the determination results for the type of short circuit. The rotor information is information that associates the identification information of the rotor 10 with the measurement results of the impedance Z and the determination results for the type of short circuit. When measurement results are acquired by the measurement result acquisition unit 61, the rotor information stores the identification information of the rotor 10 and the measurement results of the impedance Z. In other words, the rotor information storage unit 62 stores rotor information that associates the value of the real part Re[Z] and the value of the parallel resistance Rp, which are the measurement results of the impedance Z acquired by the measurement result acquisition unit 61, with the identification information of the rotor 10. Furthermore, after the type of short circuit is determined by the short circuit determination unit 65, which will be described later, the determination results are further stored in the rotor information, associated with the identification information of the rotor 10 that was the subject of the determination.

[0044] The measurement result plotting unit 63 plots points representing pairs of the real part Re[Z] value of impedance Z and the parallel resistance Rp value for each of the multiple rotors 10 on a Cartesian coordinate system with the real part Re[Z] of impedance Z and the parallel resistance Rp as two axes, forming a set of plotted points for the multiple rotors 10. In one example, the measurement result plotting unit 63 obtains the pairs of the real part Re[Z] value of impedance Z and the parallel resistance Rp value from the rotor information storage unit 62. In this specification, the points plotted on the Cartesian coordinate system for each identification information pair of the real part Re[Z] value of impedance Z and the parallel resistance Rp value are also referred to as plotted points.

[0045] As shown in the example in Figure 7, it is common for all plotted points 21 and 31 to have a set where the value of the parallel resistance Rp is inversely proportional to the value of the real part Re[Z] of the impedance Z, and a set where the relationship deviates from this inverse proportionality.

[0046] Returning to Figure 5, the approximation curve calculation unit 64 calculates an inverse proportion approximation curve for the set of all plotted points in the Cartesian coordinate system. The approximation curve calculation unit 64 also calculates two inverse proportion curves from the calculated approximation curve that define the range of the set of points where the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inverse proportion relationship. Specifically, the approximation curve calculation unit 64 calculates the coefficients of the inverse proportion equation for the set of points plotted in the Cartesian coordinate system using the least squares method, calculates the maximum and minimum values ​​of the coefficients corresponding to the fluctuations in the conductivity of the iron core 11 of the rotor 10, and defines the two inverse proportion curves as those expressed by the inverse proportion equation using the coefficients of the maximum and minimum values.

[0047] As described above, in the case of a short circuit in the iron core 20, it is known that the parallel resistance Rp is inversely proportional to the real part Re[Z] of the impedance Z. Therefore, the approximation curve calculation unit 64 calculates the coefficients a, b, and c of equation (5) using the least squares method for all plotted points. Substituting the coefficients a, b, and c calculated here into equation (5) gives an approximation equation that represents the inversely proportional approximation curve shown by the solid line 22 in Figure 7.

[0048] The width of coefficient a, that is, the maximum value a max and the minimum value a min are determined in consideration of the range in which the conductivity of the electromagnetic steel sheet constituting the iron core 11 can vary. In one example, when the conductivity of the electromagnetic steel sheet varies, coefficient a will vary by the amount of the conductivity. As described above, in adjacent grades of electromagnetic steel sheets, in one example, the conductivity differs by about 1.1 times or more and 1.2 times or less, so within the same grade, the conductivity can vary within 0.5 times of that, which is half. That is, in this case, the minimum value a min can be set to 0.95 times, and the maximum value a max can be set to 1.05 times. In one example, the approximate curve calculation unit 64 pre-holds a calculation formula for calculating the maximum value a max and the minimum value a min , and calculates the maximum value a max and the minimum value a min using this calculation formula. The approximate curve calculation unit 64 obtains an inverse proportional curve obtained by substituting the minimum value a min into the calculated coefficient a of the inverse proportional approximate curve, and an inverse proportional curve obtained by substituting the maximum value a max into it, and plots them in the rectangular coordinate system. In this example, since coefficients b and c are assumed to be hardly affected by the variation in the conductivity of the electromagnetic steel sheet, the coefficients b and c obtained by calculating the inverse proportional approximate curve are used.

[0049] The short-circuit determination unit 65 determines, for each of all the plotted points plotted in the rectangular coordinate system, the type of short circuit in the rotor 10, that is, whether it is a core short circuit 20 or an aluminum short circuit 30, using two inverse proportional curves. Specifically, the short-circuit determination unit 65 determines that the set of points where the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inverse proportional relationship among the set of all the plotted points plotted in the rectangular coordinate system is the set of rotors 10 in which a core short circuit 20 has occurred where the iron core 11 of the rotor 10 and the secondary conductor are electrically connected to each other. Also, the short-circuit determination unit 65 determines that the set of points that deviate from the inverse proportional relationship and are distributed is the set of rotors 10 in which an aluminum short circuit 30 has occurred where the short-circuit current flows through other than the iron core 11 of the rotor 10.

[0050] To explain in more detail, the short-circuit detection unit 65 determines that a core short circuit 20 exists for rotors 10 corresponding to plot points located in the region between the two inverse proportion curves among all plot points plotted in the Cartesian coordinate system. In this case, if the proportion of plot points in the region between the inverse proportion curves that have a value smaller than a predetermined parallel resistance Rp (for example, 8 kΩ) is greater than a predetermined determination value, the unit determines that there are many core short circuits 20 in the inspected rotors 10. Alternatively, the short-circuit detection unit 65 determines that rotors 10 corresponding to plot points with a value smaller than a predetermined parallel resistance Rp require further processing to resolve the core short circuit 20. Here, the predetermined determination value can be a resistance value at which no loss occurs even if a core short circuit 20 occurs. Furthermore, the short-circuit detection unit 65 determines that an aluminum short circuit 30 exists for rotors 10 corresponding to plot points that do not exist in the region between the two inverse proportion curves among all plot points plotted in the Cartesian coordinate system. Furthermore, if the plotted points lie on two inverse proportion curves, it may be determined that there is a short circuit in the iron core 20, or that there is a short circuit in the aluminum 30.

[0051] The short-circuit determination unit 65 stores the determination result for each plotted point of the rotor 10, namely whether it is an iron core short circuit 20 or an aluminum short circuit 30, in the rotor information, associating it with the identification information of the rotor 10.

[0052] Next, a method for manufacturing a rotor 10, including a rotor short-circuit detection method for distinguishing between an iron core short-circuit 20 and an aluminum short-circuit 30 in an induction motor, will be described. The method for manufacturing the rotor 10 includes a plate material forming step, an iron core forming step, a rotor forming step, a cooling step, a cutting step, and a short-circuit detection step.

[0053] First, in the sheet metal forming process, an electrical steel sheet is punched out to form an annular sheet metal having multiple teeth that protrude toward the outer periphery, multiple slots sandwiched between two adjacent teeth and open on the outer periphery, and a central hole provided in the center.

[0054] Next, in the core formation process, annular plate materials are stacked to form an iron core 11 having a plurality of teeth 11t protruding toward the outer circumference, a plurality of slots 11s sandwiched between two adjacent teeth 11t and opening on the outer circumference, and an opening 11o provided in the center.

[0055] Subsequently, in the rotor forming process, rotor bars 12 are filled into the slots 11s of the iron core 11 by aluminum die casting, thereby forming the rotor 10. In addition, in the rotor forming process, end rings 13 are also formed integrally with the rotor bars 12 at both axial ends of the iron core 11.

[0056] Next, in the cooling process, the rotor 10 is cooled. That is, the iron core 11 and the rotor bars 12 formed inside the slots 11s of the iron core 11 by aluminum die casting are cooled. After that, in the cutting process, the surface of the rotor 10 is machined.

[0057] Then, in the short-circuit detection process, the machined rotor 10 is inspected for short circuits. Multiple rotors 10 are manufactured through the above process. This completes the manufacturing method of the rotor 10.

[0058] Here, we will explain the details of the short-circuit detection process. Figures 8 and 9 are flowcharts showing an example of the processing procedure for the rotor short-circuit detection method according to Embodiment 1. Figures 8 and 9 show an example of the procedure in the short-circuit detection process. Figures 8 and 9 are flowcharts showing a method for determining whether the rotor 10 has a core short circuit 20 or an aluminum short circuit 30.

[0059] The impedance measurement of the rotor 10 using the rotor short-circuit detection device 40 is performed by inserting one rotor 10 into the rotor short-circuit detection device 40, performing the measurement, and then removing the rotor 10 after the measurement. This process is carried out for each of the multiple rotors 10 being inspected.

[0060] First, one rotor 10 is inserted into the sensor core 51 of the sensor unit 50 before measuring the impedance Z (step S11). Next, the LCR meter 53 of the sensor unit 50 measures the impedance Z of the rotor 10 (step S12). Specifically, the LCR meter 53 applies an alternating voltage to the series-connected sensor windings 52 and measures the impedance Z from the magnitude of the current flowing and the phase difference between the voltage and the current. In Embodiment 1, the impedance Z is measured in parallel equivalent circuit mode, and the LCR meter 53 calculates the value of the impedance Z as the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp in parallel equivalent circuit mode (step S13). Note that this is just an example, and the measurement does not have to be in parallel equivalent circuit mode, and the values ​​to be measured do not have to be the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp. In other examples, two independent measurements obtained in series equivalent circuit mode and parallel equivalent circuit mode may be used as long as they can be converted and calculated as the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp. The processes in steps S12 and S13 correspond to measurement steps in which the real part Re[Z] of the impedance Z and the parallel resistance Rp are measured for each of a plurality of rotors 10, each having an iron core 11 and a secondary conductor including a rotor bar 12 formed inside the slots 11s of the iron core 11.

[0061] Next, the measurement result acquisition unit 61 of the determination device 60 acquires the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp calculated from the LCR meter 53 as measurement results (step S14). The measurement result acquisition unit 61 also associates the acquired measurement results with the identification information of the rotor 10 to be inspected and stores them in the rotor information of the rotor information storage unit 62 (step S15). Subsequently, the measurement result plotting unit 63 plots the point consisting of the pair of the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp on a Cartesian coordinate system with the real part Re[Z] of the impedance Z and the parallel resistance Rp as two axes (step S16). At this time, only one point is plotted on the Cartesian coordinate system. Furthermore, since the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp are associated with the identification information of the rotor 10 in the rotor information, it is possible to identify which rotor 10 the plotted point on the Cartesian coordinate system belongs to. The processing in step S16 corresponds to the plotting process.

[0062] The rotor 10 whose impedance Z has been measured is removed from the sensor unit 50 (step S17). Then, the measurement result acquisition unit 61 determines whether there are any rotors 10 that have not been measured (step S18). If there are any rotors 10 that have not been measured (if Yes in step S18), the process returns to step S11, and the processes from step S11 to step S17 are repeatedly executed. In other words, another rotor 10 whose impedance Z has not been measured is inserted into the sensor core 51 of the sensor unit 50, the impedance is measured, and the process of plotting the point represented by the pair of the measured impedance Z real part Re[Z] value and the parallel resistance Rp value in a Cartesian coordinate system is repeatedly executed. As a result, multiple points corresponding one-to-one to the rotor 10 are plotted in the Cartesian coordinate system.

[0063] If there are no unmeasured rotors 10 (the answer is No in step S18), then measurements have been taken for all rotors 10. In this case, the plotted points have different values ​​for the real part Re[Z] of impedance Z and the parallel resistance Rp depending on the degree of iron core short circuit 20 or aluminum short circuit 30, so a set of plotted points is obtained in the orthogonal coordinate system. The approximation curve calculation unit 64 calculates an inversely proportional approximation curve for all plotted points in the orthogonal coordinate system, and calculates two inversely proportional curves from the calculated approximation curve that define the range of the set of points where the real part Re[Z] of impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship (step S19). The process in step S19 corresponds to the approximation curve calculation step of obtaining an inversely proportional approximation curve for the set in the orthogonal coordinate system and calculating two inversely proportional curves that define the range of the set of points where the real part Re[Z] of impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship.

[0064] Specifically, as described above, the approximation curve calculation unit 64 calculates the coefficients a, b, and c of the inverse proportion equation shown in equation (5) using the least squares method for the set of points plotted in the Cartesian coordinate system. This calculates the approximate equation of the inverse proportion approximation curve. The approximation curve calculation unit 64 also calculates the maximum and minimum values ​​of the coefficients to match the variation in conductivity of the iron core 11. Here, the approximation curve calculation unit 64 calculates the maximum value of coefficient a, which varies due to the variation in conductivity of the grade of electrical steel sheet used in the rotor 10. max and minimum value a min The coefficients are calculated according to a predetermined formula. The approximation curve calculation unit 64 then uses the maximum and minimum values ​​of the coefficients to form two inverse proportion curves. Here, the approximation curve calculation unit 64 calculates the maximum value a max and minimum value a min Using coefficients b and c, we calculate two inverse proportion curves.

[0065] The approximation curve calculation unit 64 plots the two calculated inverse proportion curves in a Cartesian coordinate system (step S20). These two inverse proportion curves define the boundary between the iron core short circuit 20 and the aluminum short circuit 30. Subsequently, the short circuit determination unit 65 selects one plot point (step S21) and determines whether the selected plot point lies in the region enclosed by the two inverse proportion curves (step S22).

[0066] If the selected plot point lies within the region enclosed by the two inverse proportion curves (if the answer is Yes in step S22), the short-circuit determination unit 65 determines that the rotor 10 corresponding to the selected plot point has a core short circuit 20 (step S23). In other words, it determines that the measured rotor 10 has a change in impedance Z due to a core short circuit 20. If the selected plot point lies outside the region enclosed by the two inverse proportion curves (if the answer is No in step S22), the short-circuit determination unit 65 determines that the rotor 10 corresponding to the selected plot point has an aluminum short circuit 30 (step S24). In other words, it determines that the measured rotor 10 has a change in impedance Z due to an aluminum short circuit 30. The process from step 22 to step S24 corresponds to a determination step in which, among the sets of points plotted in a Cartesian coordinate system, the set of points where the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship is determined to be the set of rotors 10 in which a core short circuit 20 occurs, in which the iron core 11 of the rotor 10 and the secondary conductor conduct to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be the set of rotors 10 in which an aluminum short circuit 30 occurs, in which a short-circuit current flows through a part other than the iron core 11 of the rotor 10.

[0067] After step S23 or step S24, the short-circuit determination unit 65 stores the determination result in the rotor information, associating it with the identification information of the measured rotor 10 (step 25). Next, it determines whether all plot points have been selected (step S26). If not all plot points have been selected (if No in step S26), the process returns to step S21. If all plot points have been selected (if Yes in step S26), the rotor short-circuit detection method ends.

[0068] In the rotor short-circuit detection method described above, the set of plotted points determined to be a core short circuit 20 is distributed in inverse proportion to the real part of the impedance Z Re[Z] and the parallel resistance Rp. In this case, the set of rotors 10 corresponding to the plotted points is determined to have a change in impedance Z due to the core short circuit 20. On the other hand, the set of plotted points determined to be an aluminum short circuit 30 is distributed far from the curve that is inversely proportional to the real part of the impedance Z Re[Z] and the parallel resistance Rp. In this case, the set of rotors 10 corresponding to the plotted points is determined to have a change in impedance Z due to the aluminum short circuit 30.

[0069] It should be noted that the rotor short-circuit detection method according to Embodiment 1 is not limited to the flowcharts in Figures 8 and 9, and the rotor short-circuit detection method may be implemented by other methods. For example, the impedance Z of multiple rotors 10 may be measured in advance, and the set of values ​​for the impedance Z of multiple rotors 10, i.e., the set of pairs of the real part Re[Z] value of impedance Z and the parallel resistance Rp value, may be stored in the rotor information of the rotor information storage unit 62. Then, after a period of time, the set of values ​​for the real part Re[Z] of impedance Z and the parallel resistance Rp value obtained from the set of impedance Z values ​​stored in the rotor information storage unit 62 may be plotted in a Cartesian coordinate system, and a determination may be made from the plotted result whether the change in impedance Z is caused by a core short circuit 20 or an aluminum short circuit 30. In other words, it is obvious that it is possible to determine whether it is a core short circuit 20 or an aluminum short circuit 30 without simultaneously performing the attachment / detachment of the rotor 10 to and from the rotor short-circuit detection device 40 and the measurement of impedance Z, and the plotting of the impedance Z measurement result in a Cartesian coordinate system and the determination of the type of short circuit of the rotor 10.

[0070] Furthermore, if it is determined in step S23 that the impedance Z has changed due to a core short circuit 20, it may be further determined whether the value of the parallel resistance Rp is lower than a predetermined determination value. The determination value used at this time is a value of the parallel resistance Rp that allows losses due to eddy currents to be ignored even if eddy currents are generated in the core short circuit 20, and is a value set by the user. If the value of the parallel resistance Rp is greater than the determination value, the rotor 10 is one in which losses due to eddy currents can be ignored. On the other hand, if the value of the parallel resistance Rp is less than the determination value, the rotor 10 is one in which losses due to eddy currents cannot be ignored.

[0071] The rotor short-circuit detection device 40 according to Embodiment 1 comprises a sensor unit 50 and a determination device 60 that determines the type of short circuit of the rotor 10 from the impedance Z of the rotor 10 measured by the sensor unit 50. The sensor unit 50 comprises a sensor core 51 having a plurality of teeth 51t protruding inward and an opening 51o in the center from which the rotor 10 to be inspected can be inserted and removed, a sensor winding 52 wound around each of the plurality of teeth 51t, and an impedance measuring device connected to both ends of the sensor winding 52 to measure the impedance Z of the rotor 10 inserted into the opening 51o of the sensor core 51. The sensor unit 50 comprises a core 11 and a secondary conductor including a rotor bar 12 formed inside the slot 11s of the core 11, and measures the real part Re[Z] of the impedance Z and the parallel resistance Rp for each of the plurality of rotors 10 inserted into the opening 51o of the sensor core 51. The determination device 60 includes a measurement result acquisition unit 61, a measurement result plotting unit 63, and a short-circuit determination unit 65. The measurement result acquisition unit 61 acquires the value of the real part Re[Z] of the impedance Z and the value of the parallel resistance Rp for each of the multiple rotors 10. The measurement result plotting unit 63 plots the points consisting of the pairs of the values ​​of the real part Re[Z] of the impedance Z and the parallel resistance Rp for each of the multiple rotors 10 on a Cartesian coordinate system with the real part Re[Z] of the impedance Z and the parallel resistance Rp as two axes, forming a set of plotted points for the multiple rotors 10. The short-circuit determination unit 65 determines that the set of points in the set in which the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship is the set of rotors 10 in which a core short circuit 20 occurs, in which the iron core 11 and the secondary conductor of the rotor 10 are conducting to each other. Furthermore, the short-circuit detection unit 65 determines that a group of points that deviate from the inverse proportional relationship is a group of rotors 10 in which an aluminum short circuit 30 occurs, where a short-circuit current flows through a part of the rotor 10 other than the iron core 11. This has the effect of being able to determine whether the cause of the decrease in motor output and torque is electrical conduction between the iron core 11 and the rotor bars 12, or electrical conduction between adjacent rotor bars 12 due to the aluminum foil.In other words, it is possible to determine whether the cause of the short-circuit current flowing through the rotor 10 that reduces motor torque is a short circuit 20 in the iron core that occurs during the cutting process that cuts the surface of the rotor 10, or an aluminum short circuit 30 that occurs during the aluminum die-casting process.

[0072] The rotor short-circuit detection method according to Embodiment 1 includes a measurement step, a plotting step, and a determination step. In the measurement step, the real part Re[Z] of the impedance Z and the parallel resistance Rp are measured for each of a plurality of rotors 10, each having an iron core 11 and a secondary conductor including a rotor bar 12 formed inside the slot 11s of the iron core 11. In the plotting step, points consisting of the values ​​of the real part Re[Z] of the impedance Z and the parallel resistance Rp for each of the plurality of rotors 10 are plotted on a Cartesian coordinate system with the real part Re[Z] of the impedance Z and the parallel resistance Rp as two axes. In the determination step, among the sets of points plotted on the Cartesian coordinate system, the set of points where the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship is determined to be a set of rotors 10 in which an iron core short circuit 20 occurs, where the iron core 11 and the secondary conductor of the rotor 10 are conducting to each other. Furthermore, in the determination process, a set of points that deviate from the inverse proportional relationship is determined to be a set of rotors 10 where an aluminum short circuit 30 occurs, in which a short-circuit current flows through a part of the rotor 10 other than the iron core 11. This has the effect of being able to determine whether the cause of the decrease in motor output and torque is electrical conduction between the iron core 11 and the rotor bars 12, or electrical conduction between adjacent rotor bars 12 due to the aluminum foil. In other words, it is possible to determine whether the cause of the short-circuit current flowing through the rotor 10 that reduces motor torque is an iron core short circuit 20 that occurs in the cutting process that cuts the surface of the rotor 10, or an aluminum short circuit 30 that occurs in the aluminum die-casting process.

[0073] Embodiment 2. The method for manufacturing the rotor 10 further includes a surface treatment step for processing the surface of the rotor 10 if the short-circuit detection step determines that the impedance Z, i.e., the value of the parallel resistance Rp, of the rotor 10 has decreased due to a short circuit 20 in the iron core. Embodiment 2 describes a case in which the surface treatment step cuts the outer peripheral surface 101 of the rotor 10 again. In other words, in the method for manufacturing the rotor 10 according to Embodiment 2, after the short-circuit detection step described above, a surface treatment step is further performed in which the surface of the rotor 10 is cut again. Figure 10 is a cross-sectional view illustrating the cutting of the outer peripheral surface of the rotor. Figure 10 shows an enlarged cross-sectional view of a part of the outer peripheral surface of the rotor 10. In the surface treatment step, as shown in Figure 10, the rotor 10 is cut so that the outer peripheral surface 101 of the rotor 10 at the time of impedance measurement, i.e., before cutting, becomes the outer peripheral surface 102.

[0074] The outer diameter of the outer surface 102 after machining is smaller than that of the outer surface 101 before machining. Since the core short circuit 20 is removed at the location where the outer surface 101 of the rotor 10 has been machined, the short-circuit current caused by the core short circuit 20 at that location no longer flows.

[0075] The outer diameter of the rotor 10 is finished by machining by several hundred micrometers in the cutting process before impedance measurement to achieve the target dimensions. Therefore, if the outer surface 101 of the rotor 10 is significantly machined again after impedance measurement, the torque will decrease significantly. For this reason, the amount of machining is determined so that the torque decrease due to the reduction in the outer diameter of the rotor 10 is smaller than the torque decrease due to the core short circuit 20. The amount of machining is preferably between several tens of micrometers and 0.1 mm. Within this range of machining, the torque decrease due to the reduction in the outer diameter of the rotor 10 is smaller than the torque decrease due to the core short circuit 20.

[0076] Furthermore, the rotor 10's rotation axis 14 and outer surface 101 have machining errors such as roundness or cylindricity. Therefore, if the outer surface 101 of the rotor 10 is cut again in a suitable manner during the surface treatment process, it will not be possible to cut the entire outer surface of the rotor 10, resulting in a mixture of cut areas (outer surface 102) and uncut areas (outer surface 101). However, in the areas of outer surface 102, the torque will improve and increase by the amount that the core short circuit 20 has been removed.

[0077] The surface treatment process described above may be performed on rotors 10 in which the short-circuit detection process determines that the impedance Z has changed due to a core short circuit 20. Alternatively, it may be performed on rotors 10 in which the short-circuit detection process determines that the impedance Z has changed due to a core short circuit 20, and in which the value of the parallel resistance Rp is smaller than the determination value. Furthermore, the amount of material removed from the rotor 10 in the surface treatment process may be varied according to the value of the parallel resistance Rp. For example, the amount of material removed can be increased as the value of the parallel resistance Rp decreases, and the amount of material removed can be decreased as the value of the parallel resistance Rp increases. In this case as well, the amount of material removed is determined so that the decrease in torque due to the reduction in the outer diameter of the rotor 10 is smaller than the decrease in torque due to the core short circuit 20 described above.

[0078] The method for manufacturing a rotor 10 according to Embodiment 2 includes a measurement step, a plotting step, a determination step, and a surface treatment step. In the measurement step, the real part Re[Z] of the impedance Z and the parallel resistance Rp are measured for each of a plurality of rotors 10, each having an iron core 11 and a secondary conductor including rotor bars 12 formed inside the slots 11s of the iron core 11. In the plotting step, points consisting of the values ​​of the real part Re[Z] of the impedance Z and the parallel resistance Rp for each of the plurality of rotors 10 are plotted on a Cartesian coordinate system with the real part Re[Z] of the impedance Z and the parallel resistance Rp as two axes. In the determination step, among the sets of points plotted on the Cartesian coordinate system, the set of points where the real part Re[Z] of the impedance Z and the parallel resistance Rp are distributed in an inversely proportional relationship is determined to be a set of rotors 10 in which an iron core short circuit 20 occurs, where the iron core 11 and the secondary conductor of the rotor 10 are conductive to each other. Furthermore, in the determination process, a set of points that deviate from the inverse proportional relationship is determined to be a set of rotors 10 where an aluminum short circuit 30 occurs, where a short-circuit current flows through a part of the rotor 10 other than the iron core 11. In the surface treatment process, the surface of the rotors 10 that have been determined to have an iron core short circuit 20 is treated. In this way, by distinguishing between the electrical conductivity between the iron core 11 and the rotor bars 12 and the electrical conductivity between adjacent rotor bars 12 via aluminum foil, it is possible to obtain a highly efficient motor with high motor output and torque.

[0079] Furthermore, in the surface treatment step of the manufacturing method of the rotor 10 according to Embodiment 2, the outer circumferential surface 101 of the rotor 10 that has been determined in the short-circuit detection step to be a collection of rotors 10 where the iron core 11 and the secondary conductor are conducting to each other and a short-circuit current is flowing, i.e., an iron core short circuit 20 has occurred, is cut. As a result, the iron core short circuit 20 is removed by recutting the outer circumferential surface 101 of the rotor 10, and the conduction between the rotor bar 12 and the iron core 11 is eliminated. This has the effect of improving motor output and torque.

[0080] Embodiment 3. Embodiment 3 describes other processes performed in the surface treatment step. In the surface treatment step of the rotor manufacturing method according to Embodiment 3, if the short-circuit detection step determines that the impedance Z, i.e., the value of the parallel resistance Rp, of the rotor 10 has decreased due to a short circuit 20 in the iron core, an alkaline aqueous solution is applied to the outer surface 101 of the rotor 10. This dissolves the outer surface 101 of the rotor bar 12. In other words, the rotor manufacturing method according to Embodiment 3 further includes a surface treatment step of applying an alkaline aqueous solution to the surface of the rotor 10 after the short-circuit detection step described above.

[0081] Figure 11 is a cross-sectional view illustrating the dissolution of the outer surface of the rotor with an alkaline aqueous solution. Figure 11 shows an enlarged cross-sectional view of a portion of the outer surface of the rotor 10. The alkaline aqueous solution is applied to the surfaces of the iron core 11 and the rotor bar 12. Iron is poorly soluble in alkaline aqueous solutions, while aluminum is readily soluble. Therefore, the alkaline aqueous solution applied to the surface of the rotor 10 selectively dissolves the aluminum. As a result, the outer diameter of the outer surface 103 of the rotor bar 12 after application of the alkaline aqueous solution becomes smaller than that of the outer surface 101 of the rotor bar 12 before application. Since the iron core short circuit 20 is removed in the area where the outer surface 101 of the rotor bar 12 is dissolved, the short-circuit current caused by the iron core short circuit 20 in that area no longer flows.

[0082] In the surface treatment step of applying an alkaline aqueous solution to the surface of the rotor 10 in Embodiment 3, the outer diameter of the iron core 11 of the rotor 10 does not change before and after application. Therefore, there is no decrease in torque due to a decrease in the outer diameter of the rotor 10, and the torque increase due to the melting of the iron core short circuit 20 due to application is not offset.

[0083] In the above description, an example of a surface treatment process that does not change the outer diameter of the iron core 11 before and after surface treatment was given in which an alkaline aqueous solution is applied to the outer peripheral surface 101 of the rotor 10. However, as long as the outer diameter of the iron core 11 does not change before and after surface treatment, the surface treatment process may be carried out using other methods. In another example of a surface treatment process, the impedance Z is measured by the sensor unit 50, and if it is determined that the impedance Z, i.e., the value of the parallel resistance Rp, has decreased due to an iron core short circuit 20, a vibrator tool that generates vibration is brought into contact with the outer peripheral surface 101 of the rotor 10. In other words, the method for manufacturing the rotor 10 according to Embodiment 3 further includes a surface treatment process in which a vibrator tool is brought into contact with the outer peripheral surface 101 of the rotor 10 after the short circuit detection process described above.

[0084] Figure 12 is a cross-sectional view illustrating another example of recessing the outer surface of the rotor bar. This process applies vibration to the entire outer surface 101 of the rotor 10. In the vibrated rotor 10, the iron core 11 and the rotor bar 12 vibrate relative to each other, causing the thin core short circuit 20 that connects the iron core 11 and the rotor bar 12 on the outer surface 101 to detach. Furthermore, the relatively soft core short circuit 20 and the outer surface 104 of the rotor bar 12 are crushed, removing the core short circuit 20, so that the short-circuit current caused by the core short circuit 20 in this area no longer flows.

[0085] In other words, similar to the example in Figure 11 where the alkaline aqueous solution is applied, the outer diameter of the iron core 11 of the rotor 10 does not change before and after vibration is applied. Therefore, there is no decrease in torque due to a decrease in the outer diameter of the rotor 10, and the torque increase due to the removal of the iron core short circuit 20 by vibration is not offset.

[0086] The surface treatment process described above may be performed on rotors 10 in which the short-circuit detection process determines that the impedance Z has changed due to a core short circuit 20. Alternatively, it may be performed on rotors 10 in which the short-circuit detection process determines that the impedance Z has changed due to a core short circuit 20, and in which the value of the parallel resistance Rp is smaller than the determination value.

[0087] In Embodiment 3, an alkaline aqueous solution is applied to the outer surface 101 of the rotor 10 where it is determined that the iron core 11 of the rotor 10 and the secondary conductor are conducting to each other, causing a short circuit current to flow, i.e., an iron core short circuit 20 has occurred. As a result, the aluminum in the iron core short circuit 20 is dissolved by the alkaline aqueous solution, and the conduction between the rotor bar 12 and the iron core 11 is eliminated. Furthermore, since the iron core 11, which is mainly composed of iron, does not dissolve in the alkaline aqueous solution, the outer diameter of the iron core 11 hardly changes before and after the application of the alkaline aqueous solution. This has the effect of improving motor output and torque.

[0088] Furthermore, in Embodiment 3, vibration is applied to the outer surface 101 of the rotor 10 using a vibrator tool when it is determined that a short-circuit current is flowing between the iron core 11 and the secondary conductor of the rotor 10, i.e., an iron core short circuit 20 has occurred. As a result, the iron core short circuit 20 is separated from the surface of the iron core 11 by the vibration, and the electrical connection between the rotor bar 12 and the iron core 11 is eliminated. Also, since only vibration is applied with a vibrator tool, the outer diameter of the iron core 11 does not change before and after the vibration. This has the effect of improving motor output and torque.

[0089] Embodiment 4. Figure 13 is a schematic cross-sectional view showing an example of the configuration of a sensor unit of a rotor short-circuit detection device according to Embodiment 4. The rotor short-circuit detection device 40 further comprises a fixed holder 81 that holds the sensor unit 50 and a detachable holder 83 that holds a rotor 10 that is attached to and detached from the sensor unit 50. The sensor unit 50 is fixed to the fixed holder 81. The rotor 10 held by the detachable holder 83 is inserted from directly above the central axis 82 of the sensor unit 50 into the center of the sensor unit 50, i.e., into the opening 51o of the sensor core 51. After the impedance Z is measured, the rotor 10 is pulled up directly above by the detachable holder 83 and removed from the sensor unit 50. After the rotor 10 whose impedance Z has been measured is removed from the detachable holder 83, another rotor 10 whose impedance Z has not been measured is attached to the detachable holder 83, and the measurement of impedance Z is repeated.

[0090] If the iron core 11 of the rotor 10 is mounted to the sensor unit 50 with an axial misalignment from the sensor iron core 51 of the sensor unit 50, impedance measurement cannot be performed correctly. Therefore, the iron core 11 must be positioned in the axial direction of the sensor iron core 51.

[0091] If the axial lengths of the iron core 11 of the rotor 10 mounted on the detachable holder 83 are different, the axial position of the detachable holder 83 is adjustable so that the iron core 11 falls within the range of the axial length of the sensor iron core 51 of the sensor unit 50. In one example, the detachable holder 83 is configured to be movable in the axial direction and in a direction perpendicular to the axis by a drive mechanism (not shown).

[0092] The rotor short-circuit detection device 40 according to Embodiment 4 further includes a removable holder 83 that holds the rotation axis 14 of the rotor 10 and allows the rotor 10 held from above the central axis 82 of the sensor unit 50 to be inserted into and removed from the opening 51o of the sensor core 51, and a fixed holder 81 that holds the sensor unit 50. This has the effect of being able to continuously measure the impedance Z of multiple rotors 10 with different axial lengths without them protruding axially from the sensor core 51 of the sensor unit 50.

[0093] The determination device 60 in the rotor short-circuit detection device 40 according to Embodiments 1 to 4 can be implemented by an information processing device, a display, etc., in one example. The hardware configuration when the determination device 60 is implemented by a computer system, which is an information processing device, will be described below. The determination device 60 functions as the computer system when a program, which is a computer program describing the processing in the determination device 60, is executed on the computer system. Figure 14 is a block diagram showing an example of the configuration of a computer system that implements the determination device of the rotor short-circuit detection device according to Embodiments 1 to 4. As shown in Figure 14, this computer system includes a control unit 901, an input unit 902, a storage unit 903, a display unit 904, a communication unit 905, and an output unit 906, which are connected via a system bus 907.

[0094] In Figure 14, the control unit 901 is, in one example, a processor such as a CPU (Central Processing Unit), which executes a program describing the processing in the determination device 60 of Embodiments 1 to 4. The input unit 902 is, in one example, composed of a keyboard, mouse, etc., and is used by the user of the computer system to input various information. The storage unit 903 includes various types of memory such as RAM (Random Access Memory), ROM (Read Only Memory), and storage devices such as a hard disk, and stores the program to be executed by the control unit 901, necessary data obtained during the processing, etc. The storage unit 903 is also used as a temporary storage area for the program. The display unit 904 is composed of a display, liquid crystal display panel, etc., and displays various screens to the user of the computer system. In one example, the input unit 902 and the display unit 904 may be configured as a touch panel in which the input unit 902 and the display unit 904 are integrally formed. The communication unit 905 is a receiver and transmitter that perform communication processing. The output unit 906 is a printer, speaker, etc. Note that Figure 14 is just one example, and the configuration of the computer system is not limited to the example shown in Figure 14.

[0095] Here, we will describe an example of the operation of the computer system until the program becomes executable. In a computer system with the above configuration, for example, the program is installed in the storage unit 903 from a CD-ROM or DVD-ROM set in a CD (Compact Disc)-ROM drive or DVD (Digital Versatile Disc)-ROM drive (not shown). When the program is executed, the program read from the storage unit 903 is stored in the main memory area of ​​the storage unit 903. In this state, the control unit 901 performs processing as the determination device 60 of Embodiments 1 to 4 according to the program stored in the storage unit 903.

[0096] In the above description, a program describing the processing in the determination device 60 is provided using a CD-ROM or DVD-ROM as the recording medium. However, the system is not limited to this, and depending on the configuration of the computer system, the capacity of the program to be provided, a program provided via a transmission medium such as the Internet via the communication unit 905 may also be used.

[0097] The measurement result acquisition unit 61, measurement result plotting unit 63, approximation curve calculation unit 64, and short-circuit determination unit 65 shown in Figure 5 are realized by the execution of a program stored in the storage unit 903 shown in Figure 14 by the control unit 901 shown in Figure 14. The storage unit 903 shown in Figure 14 is also used to realize the measurement result acquisition unit 61, measurement result plotting unit 63, approximation curve calculation unit 64, and short-circuit determination unit 65. In addition, the communication unit 905 shown in Figure 14 is also used to realize the measurement result acquisition unit 61. The rotor information storage unit 62 is realized by the storage unit 903 shown in Figure 14.

[0098] The configurations shown in the above embodiments are examples only, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention.

[0099] The various aspects of this disclosure are summarized below as an appendix.

[0100] [Note 1] A measurement step of measuring the real part of the impedance and the parallel resistance for each of a plurality of rotors, each having an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, A plotting step of plotting points consisting of pairs of the real part value of the impedance and the parallel resistance value of each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, A determination step in which, among the sets of points plotted in the Cartesian coordinate system, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be a set of rotors in which a core short circuit occurs, in which the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be a set of rotors in which an aluminum short circuit occurs, in which a short-circuit current flows through a part other than the iron core of the rotor, A rotor short-circuit detection method characterized by including the following: [Note 2] The process further includes a step of calculating an approximate curve to find an approximate curve of inverse proportion for the set of Cartesian coordinates, In the approximation curve calculation step, two inverse proportion curves are calculated that define the range of the set of points where the real part of the impedance and the parallel resistance are distributed in an inverse proportion relationship. The rotor short-circuit detection method according to Appendix 1, characterized in that, in the determination step, the rotor corresponding to the point located in the region enclosed by the two inverse proportion curves is determined to be in a core short circuit, and the rotor corresponding to the point not located in the region enclosed by the two inverse proportion curves is determined to be in an aluminum short circuit. [Note 3] The rotor short-circuit detection method according to Appendix 2, characterized in that, in the approximation curve calculation step, the coefficients of the inverse proportion equation are calculated using the least squares method for the set of points plotted in the Cartesian coordinate system, the maximum and minimum values ​​of the coefficients are calculated to match the fluctuations in the conductivity of the iron core, and the two inverse proportion curves are represented by the inverse proportion equation using the maximum and minimum values ​​of the coefficients. [Note 4] A measurement step of measuring the real part of the impedance and the parallel resistance for each of a plurality of rotors, each having an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, A plotting step of plotting points consisting of pairs of the real part value of the impedance and the parallel resistance value of each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, A determination step in which, among the sets of points plotted in the Cartesian coordinate system, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be a set of rotors in which a core short circuit occurs, in which the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be a set of rotors in which an aluminum short circuit occurs, in which a short-circuit current flows through a part other than the iron core of the rotor, A surface treatment step for treating the surface of the rotor which has been determined to have a short circuit in the iron core, A method for manufacturing a rotor, characterized by including the following: [Note 5] The method for manufacturing a rotor according to Appendix 4, characterized in that the surface treatment step involves determining that the rotors are a collection of rotors in which the core short circuit has occurred, and cutting the outer surface of the rotors that have been determined to be in that collection. [Note 6] The method for manufacturing a rotor according to Appendix 4, characterized in that, in the surface treatment step, an alkaline aqueous solution is applied to the outer surface of the rotors that have been determined to be a collection of rotors in which the iron core short circuit has occurred. [Note 7] The method for manufacturing a rotor according to Appendix 4, characterized in that, in the surface treatment step, vibration is applied to the outer surface of the rotors that have been determined to be a collection of rotors in which the iron core short circuit has occurred, using a vibrator tool. [Note 8] A sensor unit comprising: a sensor core having multiple teeth protruding inward and an opening in the center through which a rotor to be inspected can be inserted and removed; sensor windings wound around each of the multiple teeth; and an impedance measuring device connected to both ends of the sensor windings for measuring the impedance of the rotor inserted into the opening of the sensor core; A determination device that determines the type of short circuit in the rotor from the impedance of the rotor measured by the sensor unit, Equipped with, The sensor unit comprises an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, and measures the real part of the impedance and the parallel resistance for each of the plurality of rotors inserted into the openings of the sensor iron core. The determination device is A measurement result acquisition unit that acquires the real part value of the impedance and the parallel resistance value for each of the multiple rotors, A measurement result plotting unit plots points consisting of pairs of the real part value of the impedance and the parallel resistance value for each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, and forms a set of plotted points for the multiple rotors. A short-circuit determination unit determines that, among the aforementioned sets, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is a set of rotors in which a core short circuit occurs, where the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is a set of rotors in which an aluminum short circuit occurs, where a short-circuit current flows through a part other than the iron core of the rotor. A rotor short-circuit detection device characterized by having the following features. [Note 9] The system further comprises an approximation curve calculation unit that finds an approximation curve of inverse proportion for the set of Cartesian coordinates, The approximation curve calculation unit calculates two inverse proportion curves from the calculated approximation curve that define the range of the set of points where the real part of the impedance and the parallel resistance are distributed in an inverse proportion relationship. The rotor short-circuit detection device according to Appendix 8, characterized in that the short-circuit determination unit determines that the rotor corresponding to the point located in the region enclosed by the two inverse proportion curves is in a core short-circuit state, and determines that the rotor corresponding to the point not located in the region enclosed by the two inverse proportion curves is in an aluminum short-circuit state. [Note 10] The system further includes a rotor information storage unit that stores rotor information relating the real value of the impedance and the parallel resistance value acquired by the measurement result acquisition unit to the rotor identification information. The rotor short-circuit detection device according to Appendix 8 or 9, characterized in that the short-circuit determination unit stores the determination result for each rotor in the rotor information in association with the identification information of the rotor. [Note 11] A removable holder that holds the rotation axis of the rotor and allows the rotor, which is held from the central axis of the sensor unit, to be inserted into the opening of the sensor core, A fixed holder for holding the sensor unit, A rotor short-circuit detection device according to any one of appendices 8 to 10, further comprising the above. [Explanation of symbols]

[0101] 10 Rotor, 11 Iron core, 11o, 51o Opening, 11s Slot, 11t, 51t Teeth, 12 Rotor bar, 13 End ring, 14 Rotating shaft, 15 Insulating layer, 17, 18 Interlaminated aluminum, 20 Iron core short circuit, 30 Aluminum short circuit, 40 Rotor short circuit detection device, 50 Sensor unit, 51 Sensor iron core, 52 Sensor winding, 53 LCR meter, 60 Judgment device, 61 Measurement result acquisition unit, 62 Rotor information storage unit, 63 Measurement result plotting unit, 64 Approximation curve calculation unit, 65 Short circuit determination unit, 81 Fixed holder, 82 Central axis, 83 Detachable holder, 101, 102, 103, 104 Outer surface, 111 Plate material, 901 Control unit, 902 Input unit, 903 Storage unit, 904 Display unit, 905 Communications section, 906 output section, 907 system bus.

Claims

1. A measurement step of measuring the real part of the impedance and the parallel resistance for each of a plurality of rotors, each having an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, A plotting step of plotting points consisting of pairs of the real part value of the impedance and the parallel resistance value of each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, A determination step in which, among the sets of points plotted in the Cartesian coordinate system, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be a set of rotors in which a core short circuit occurs, in which the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be a set of rotors in which an aluminum short circuit occurs, in which a short-circuit current flows through a part other than the iron core of the rotor, A rotor short-circuit detection method characterized by including the following:

2. The process further includes an approximation curve calculation step for determining an inverse proportion approximation curve for the set of Cartesian coordinate systems, In the approximation curve calculation step, two inverse proportion curves are calculated that define the range of the set of points where the real part of the impedance and the parallel resistance are distributed in an inverse proportion relationship. The rotor short-circuit detection method according to claim 1, characterized in that, in the determination step, the rotor corresponding to the point located in the region enclosed by the two inverse proportion curves is determined to be in a core short-circuit state, and the rotor corresponding to the point not located in the region enclosed by the two inverse proportion curves is determined to be in an aluminum short-circuit state.

3. The rotor short-circuit detection method according to claim 2, characterized in that, in the approximation curve calculation step, the coefficients of the inverse proportion equation are calculated using the least squares method for the set of points plotted in the Cartesian coordinate system, the maximum and minimum values ​​of the coefficients are calculated to match the fluctuations in the conductivity of the iron core, and the two inverse proportion curves are represented by the inverse proportion equation using the maximum and minimum values ​​of the coefficients.

4. A measurement step of measuring the real part of the impedance and the parallel resistance for each of a plurality of rotors, each having an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, A plotting step of plotting points consisting of pairs of the real part value of the impedance and the parallel resistance value of each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, A determination step in which, among the sets of points plotted in the Cartesian coordinate system, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is determined to be a set of rotors in which a core short circuit occurs, in which the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is determined to be a set of rotors in which an aluminum short circuit occurs, in which a short-circuit current flows through a part other than the iron core of the rotor, A surface treatment step for treating the surface of the rotor which has been determined to have a short circuit in the iron core, A method for manufacturing a rotor, characterized by including the following:

5. The method for manufacturing a rotor according to claim 4, characterized in that the surface treatment step involves determining that the rotors are a collection of rotors in which the core short circuit has occurred, and cutting the outer surface of the rotors that have been determined to be in that collection.

6. The method for manufacturing a rotor according to claim 4, characterized in that the surface treatment step involves applying an alkaline aqueous solution to the outer surface of the rotors that have been determined to be a collection of rotors in which the iron core short circuit has occurred.

7. The method for manufacturing a rotor according to claim 4, characterized in that, in the surface treatment step, vibration is applied to the outer surface of the rotors that have been determined to be a collection of rotors in which the iron core short circuit has occurred, using a vibrator tool.

8. A sensor unit comprising: a sensor core having multiple teeth protruding inward and an opening in the center through which a rotor to be inspected can be inserted and removed; sensor windings wound around each of the multiple teeth; and an impedance measuring device connected to both ends of the sensor windings for measuring the impedance of the rotor inserted into the opening of the sensor core; A determination device that determines the type of short circuit in the rotor from the impedance of the rotor measured by the sensor unit, Equipped with, The sensor unit comprises an iron core and a secondary conductor including rotor bars formed inside the slots of the iron core, and measures the real part of the impedance and the parallel resistance for each of the plurality of rotors inserted into the openings of the sensor iron core. The determination device is A measurement result acquisition unit that acquires the real part value of the impedance and the parallel resistance value for each of the multiple rotors, A measurement result plotting unit plots points consisting of pairs of the real part value of the impedance and the parallel resistance value for each of the multiple rotors on a Cartesian coordinate system with the real part of the impedance and the parallel resistance as two axes, and forms a set of plotted points for the multiple rotors. A short-circuit determination unit determines that, among the aforementioned sets, the set of points where the real part of the impedance and the parallel resistance are distributed in an inversely proportional relationship is a set of rotors in which a core short circuit occurs, where the iron core and the secondary conductor of the rotor are conducting to each other, and the set of points where the distribution deviates from the inversely proportional relationship is a set of rotors in which an aluminum short circuit occurs, where a short-circuit current flows through a part other than the iron core of the rotor. A rotor short-circuit detection device characterized by having the following features.

9. The system further comprises an approximation curve calculation unit that calculates an approximation curve of inverse proportion for the set of Cartesian coordinates, The approximation curve calculation unit calculates two inverse proportion curves from the calculated approximation curve that define the range of the set of points where the real part of the impedance and the parallel resistance are distributed in an inverse proportion relationship. The rotor short-circuit detection device according to claim 8, characterized in that the short-circuit determination unit determines that the rotor corresponding to the point located in the region enclosed by the two inverse proportion curves is in an iron core short-circuit state, and determines that the rotor corresponding to the point not located in the region enclosed by the two inverse proportion curves is in an aluminum short-circuit state.

10. The system further includes a rotor information storage unit that stores rotor information relating the real value of the impedance and the parallel resistance value acquired by the measurement result acquisition unit to the rotor identification information. The rotor short-circuit detection device according to claim 8, characterized in that the short-circuit determination unit stores the determination result for each rotor in the rotor information in association with the identification information of the rotor.

11. A removable holder that holds the rotation axis of the rotor and allows the rotor, which is held from the central axis of the sensor unit, to be inserted into the opening of the sensor core, A fixed holder for holding the sensor unit, A rotor short-circuit detection device according to any one of 8 to 10, further comprising the above.

Images