JP2016065763A - Temperature measurement device of electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measurement device of an electric motor which can highly accurately measure a temperature of a rotor, in the electric motor which in operation.SOLUTION: A temperature measurement device 26 of an electric motor 1 measures a temperature of a rotor in the electric motor having a stator 4, the rotor 8, and a rotating shaft 22 connected to the rotor, and has: an optical fiber 30 which is extended up to a temperature measurement point 32 of the rotor via the inside of the rotating shaft of the electric motor; a light source 34 which makes light incident into the optical fiber; a light detector 36 which detects emission light from the optical fiber; and an optical rotating joint 38 which is arranged at the rotating shaft, and optically connects the optical fiber and the light source. The optical fiber comprises an FBG sensor which reflects only a specified wavelength component of the incident light, and a portion including the FBG sensor in the optical fiber is arranged while extending in parallel with the rotating shaft so as to contactable with the temperature measurement point of the rotor from the rotating shaft side.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric motor temperature measuring device, and more particularly to an electric motor temperature measuring device for measuring the temperature of the rotor in an electric motor having a stator, a rotor, and a rotating shaft connected to the rotor.

  When the electric motor is operated, heat is generated due to copper loss generated by the resistance component of the winding, iron loss generated in the core, eddy current loss generated in the permanent magnet, and the like, and the temperature of each part of the electric motor rises. In order to grasp how the temperature of the electric motor changes due to this temperature rise, or to control the temperature of each part of the electric motor so as not to exceed the maximum allowable temperature, the temperature of the electric motor is measured.

  For example, Patent Document 1 describes that in a three-phase AC synchronous motor, a temperature sensor such as a thermistor is installed in the vicinity of a stator coil of a stator arranged on the outer periphery of the motor, and the temperature of the stator coil is measured. .

JP 2013-223261 A

By the way, during operation of the electric motor, heat is generated not only in the stator but also in the rotor, and the temperature of the rotor rises. Further, the temperature of the rotor also rises due to heat transfer from the stator whose temperature has risen to the rotor. Therefore, in order to accurately grasp the rotor temperature during operation, it is required that the rotor temperature can be directly measured.
However, since the operating rotor rotates at a high speed, it is difficult to measure the temperature by directly attaching an electrical temperature sensor such as a thermocouple having a lead wire or a thermistor to the rotor. By using a mechanism that allows transmission of an electrical signal between a stationary body and a rotating body, such as a slip ring, it is possible to extract a signal from a thermocouple or thermistor attached to the rotor. It is inevitable that contact noise is mixed in the part, and it is difficult to measure temperature with high accuracy. In addition, since a strong electromagnetic field fluctuates inside the electric motor, it is difficult to transmit the temperature sensor signal by radio waves.
In addition, thermography is an example of a non-contact temperature measurement method. In an inner rotor type electric motor in which a rotor rotates inside a stator, the rotor temperature is measured because the rotor is not exposed to the outside. It is not possible.

  The present invention has been made to solve the above-described problems of the prior art, and provides an electric motor temperature measuring device capable of measuring the temperature of a rotor with high accuracy in an operating electric motor. For the purpose.

In order to achieve the above object, an electric motor temperature measurement device according to the present invention includes a stator, a rotor, and a temperature of the electric motor that measures the temperature of the rotor in an electric motor having a rotating shaft connected to the rotor. A measuring device that detects the light emitted from the optical fiber, an optical fiber disposed through the rotating shaft of the electric motor to the temperature measurement point of the rotor, a light source that makes light incident on the optical fiber, and the like. The optical fiber includes a light detector, an optical rotation joint that is provided on the rotation shaft and optically connects the optical fiber to the light source and the light detector, and the optical fiber reflects only a specific wavelength component of incident light. The portion including the Bragg grating portion and including the fiber Bragg grating portion in the optical fiber extends in parallel with the rotation axis and is at a temperature measurement point of the rotor. Characterized in that it is arranged to be contacted from the guinea side.
In the present invention configured as described above, even during operation of the electric motor, the reflected light from the fiber Bragg grating section is not affected by fluctuations in the electromagnetic field inside the electric motor or noise at the electric contacts. A change in wavelength can be detected by a photodetector, and a change in temperature can be measured based on the change in wavelength. The part of the optical fiber that includes the fiber Bragg grating extends parallel to the rotor's rotation axis, so there is no axial distortion in the fiber Bragg grating, and it is specified according to temperature changes. It is possible to detect only a change in wavelength. Since the fiber Bragg grating section is arranged so as to be able to come into contact with the temperature measurement point of the rotor from the rotating shaft side, when the rotor rotates during operation of the electric motor, the fiber Bragg grating section is It is pressed against the temperature measurement point by centrifugal force acting toward the outside in the radial direction. As a result, the fiber Bragg grating portion can be reliably brought into contact with the temperature measurement point, and the temperature of the rotor can be measured with high accuracy in the operating electric motor.

In the present invention, it is preferable that the electric motor includes a stator including armature windings and a rotor including a permanent magnet for field, and the fiber Bragg grating portion of the optical fiber is provided on the rotor. It arrange | positions so that it can contact from the rotating shaft side with respect to the temperature measurement point of the permanent magnet for fields.
In the present invention configured as described above, when the rotor rotates during operation of the electric motor, the fiber Bragg grating section measures the temperature of the field permanent magnet by the centrifugal force acting toward the radially outer side of the rotor. Pressed against a point. As a result, the fiber Bragg grating can be reliably brought into contact with the temperature measurement point of the field permanent magnet, and the temperature of the rotor field permanent magnet can be measured with high accuracy in the electric motor during operation. Can do.

In the present invention, preferably, the rotor of the electric motor includes a columnar rotor core centering on the rotation shaft, and the field permanent magnet is embedded in an embedded hole formed in the rotor core so as to extend in the axial direction. The fiber Bragg grating portion of the optical fiber is formed in the embedded hole from the rotation axis side with respect to the corner formed by the surface of the field permanent magnet and the inner wall surface of the embedded hole at the temperature measurement point. It is arranged so that it can touch.
In the present invention configured as described above, when the rotor rotates during operation of the electric motor, the fiber Bragg grating portion is pressed against the corner by the centrifugal force acting toward the radially outer side of the rotor core. It is reliably pressed against the side surface of the field permanent magnet that forms the corner. As a result, the fiber Bragg grating section can be more reliably brought into contact with the temperature measurement point of the field permanent magnet, and the temperature of the field permanent magnet of the rotor can be measured with high accuracy in the operating electric motor. be able to.

  According to the temperature measuring apparatus for an electric motor according to the present invention, the temperature of the rotor can be measured with high accuracy in the electric motor during operation.

It is sectional drawing which shows the internal structure of the electric motor to which the temperature measuring device by embodiment of this invention is applied. It is the schematic which shows the system configuration | structure of the temperature measuring apparatus of the electric motor by embodiment of this invention. It is sectional drawing of the rotor of the electric motor to which the temperature measuring device by embodiment of this invention is applied. FIG. 4 is an enlarged cross-sectional view showing the periphery of a field permanent magnet in the rotor of the electric motor shown in FIG. 3.

Hereinafter, a temperature measuring apparatus for an electric motor according to an embodiment of the present invention will be described with reference to the accompanying drawings.
First, an electric motor to which a temperature measuring device according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an internal structure of an electric motor to which a temperature measuring device according to an embodiment of the present invention is applied.

  First, in FIG. 1, the code | symbol 1 shows the electric motor to which the temperature measuring device by embodiment of this invention is applied. The electric motor 1 in this embodiment is a permanent magnet embedded three-phase AC synchronous motor, and includes a stator 4 having a coil 2 (armature winding), and a rotor 8 having a field permanent magnet 6. And a housing 10 for housing the stator 4 and the rotor 8.

  The stator 4 includes a stator core 12 formed in a cylindrical shape by stacking annular steel plates. A plurality of (for example, six) teeth 14 are formed at equal intervals in the circumferential direction so as to protrude radially inward from the inner periphery of the stator core 12, and each tooth 14 has a U-phase, V-phase, or W-phase. One of the coils 2 is wound. A three-phase power cable 16 is connected to each coil 2 via a power line.

  The rotor 8 includes a rotor core 18 formed in a cylindrical shape by laminating disc-shaped steel plates. An output shaft 20 and a rotary shaft 22 are inserted through the central portion of the rotor core 18. The output shaft 20 and the rotating shaft 22 protrude in the axial direction from both ends of the rotor core 18 and are rotatably supported by bearings 24 provided in the housing 10. The rotor core 18, the output shaft 20, and the rotation shaft 22 are fixed to each other and rotate integrally. In addition, a plurality of embedded holes extending in the axial direction are arranged in the rotor core 18 in the circumferential direction, and the field permanent magnet 6 is embedded in each embedded hole.

  During operation of the electric motor 1, a rotating magnetic field is generated by supplying an alternating current from the three-phase power cable 16 to the coil 2 of the stator 4, and the field permanent magnet 6 of the rotor 8 is attracted to the rotating magnetic field. As a result, the rotor 8 rotates and is output from the output shaft 20 as power.

  Next, the system configuration of the temperature measuring device for the electric motor 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a schematic diagram showing a system configuration of the temperature measuring device for the electric motor 1 according to the embodiment of the present invention.

First, as shown in FIG. 2, the temperature measurement device 26 according to the embodiment of the present invention includes an optical fiber 30 including an FBG (fiber Bragg grating) sensor 28.
The FBG sensor 28 is formed with a diffraction grating so that the refractive index periodically changes along the axial direction of the optical fiber core. When light enters the FBG sensor 28, diffraction is included in the incident light. Only a specific wavelength (Bragg wavelength) component corresponding to the grating interval and the refractive index of the optical fiber core is reflected by the diffraction grating, and the other wavelength components are transmitted.
When the refractive index of the optical fiber core changes due to the temperature of the FBG sensor 28 changing, the Bragg wavelength changes accordingly, and the wavelength of the light reflected by the diffraction grating of the FBG sensor 28 changes. By detecting this, the temperature of the diffraction grating portion can be measured.
Further, when an external force is applied to the FBG sensor 28 and distortion occurs in the axial direction of the FBG sensor 28, the interval between the diffraction gratings changes, and the Bragg wavelength changes accordingly. Therefore, when the temperature is measured by the FBG sensor 28, it is necessary to prevent external force from being applied in the axial direction of the FBG sensor 28 and to prevent the occurrence of distortion. When the temperature of the FBG sensor 28 changes, thermal distortion occurs in the diffraction grating portion, so the Bragg wavelength also changes due to this thermal strain, but the thermal expansion coefficient of the glass used as the optical fiber core is very small. Regarding the temperature dependence of the Bragg wavelength, the component due to the change of the refractive index is dominant.

  The optical fiber 30 provided with the FBG sensor 28 is disposed up to the temperature measurement point 32 of the rotor 8 via the inside of the rotating shaft 22 of the electric motor 1. The temperature measurement point 32 in the embodiment of the present invention is set on the surface of the field permanent magnet 6 of the rotor 8.

  In addition, the temperature measuring device 26 includes a light source 34 that causes light to enter the optical fiber 30 that includes the FBG sensor 28, and a photodetector 36 that detects light emitted from the optical fiber 30. Since the light source 34 and the light detector 36 are provided outside the electric motor 1, the light source 34 and the light detector 36 are stationary regardless of the operating state of the electric motor 1. On the other hand, since the optical fiber 30 provided with the FBG sensor 28 is attached to the rotating shaft 22 and the rotor 8 of the electric motor 1, it rotates together with the rotating shaft 22 and the rotor 8 when the electric motor 1 is operated. Therefore, an optical rotary joint 38 is provided at the end of the rotary shaft 22 in order to optically connect the stationary light source 34 and photodetector 36 and the rotating optical fiber 30. An end portion of an optical fiber 30 including an FBG sensor 28 is connected to the rotary shaft 22 side of the electric motor 1 in the optical rotary joint 38. An optical fiber 40 for external connection connected to the light source 34 and the photodetector 36 is connected to the outside of the electric motor 1 in the optical rotary joint 38. Thereby, even when the electric motor 1 is in operation, the light source 34, the photodetector 36, and the optical fiber 30 including the FBG sensor 28 are optically connected.

  Next, the detailed arrangement of the FBG sensor 28 will be described with reference to FIGS. 3 is a cross-sectional view of the rotor 8 of the electric motor 1 to which the temperature measuring device 26 according to the embodiment of the present invention is applied. FIG. 4 is a field permanent magnet in the rotor 8 of the electric motor 1 shown in FIG. It is an expanded sectional view showing 6 circumference.

  First, as shown in FIG. 3, embedded holes 42 having a substantially rectangular cross-sectional shape are arranged in the circumferential direction on the outer peripheral portion of the rotor core 18. In the example of FIG. 3, two embedded holes 42 arranged so as to form a V-shape that opens outward in the radial direction of the rotor core 18 are taken as one set, and eight sets of embedded holes 42 are equally spaced in the circumferential direction. It is arranged. A field permanent magnet 6 having a rectangular cross-sectional shape slightly smaller than the buried hole 42 is inserted into each buried hole 42.

  The FBG sensor 28 of the temperature measuring device 26 is disposed inside the embedded hole 42 so as to extend along a direction parallel to the rotation shaft 22 (that is, the axial direction of the rotor core 18). Specifically, as shown in FIG. 4, the inner wall surface of the embedded hole 42 is arranged along the axial direction of the rotor core 18 in the vicinity of the four corners 44 a, 44 b, 44 c, 44 d of the field permanent magnet 6. Grooves 46a, 46b, 46c, and 46d are formed, and the optical fiber 30 including the FBG sensor 28 is disposed so as to extend along the grooves 46a, 46b, 46c, and 46d. The number of the FBG sensors 28 included in the optical fiber 30 disposed in each of the grooves 46a, 46b, 46c, 46d is arbitrary, and is 1 at a position corresponding to the desired temperature measurement point 32 along the axial direction of the optical fiber 30. One or more FBG sensors 28 are arranged in series.

In particular, of the four corners 44 a, 44 b, 44 c, 44 d of the field permanent magnet 6, the vicinity of the three corners 44 b, 44 c, 44 d excluding the corner 44 a located on the outermost side in the radial direction of the rotor core 18. , The groove portions 46 b, 46 c, 46 d of the embedded hole 42 are formed at positions facing each side surface of the field permanent magnet 6 facing the radially inner side of the rotor core 18. Then, corners 48a, 48b, 48c facing radially inward of the rotor core 18 are formed by the side surfaces of the field permanent magnets 6 that are in contact with each other and the wall surfaces of the grooves 46b, 46c, 46d. Accordingly, the FBG sensor 28 disposed in these groove portions 46b, 46c, 46d has a corner portion 48a formed by the wall surface of the groove portions 46b, 46c, 46d and the side surface of the field permanent magnet 6 that is the temperature measurement point 32. 48b and 48c can be contacted from the inside in the radial direction of the rotor core 18 (that is, from the rotating shaft 22 side).
As shown in FIG. 4, since the cross-sectional dimension of the optical fiber 30 is smaller than the cross-sectional dimension of the groove portions 46b, 46c, 46d of the buried hole 42, when the optical fiber 30 is not particularly fixed in the groove portions 46b, 46c, 46d, There is a possibility that the optical fiber 30 moves in a direction perpendicular to the axial direction, and the FBG sensor 28 moves away from the side surface of the field permanent magnet 6 that is the temperature measurement point 32. Therefore, a porous filler 50 having a small thermal expansion coefficient is filled inside the groove portions 46b, 46c, and 46d on the radially inner side of the rotor core 18 with respect to the optical fiber 30. The optical fiber 30 is fixed by the filler 50 so as to contact the side surface of the field permanent magnet 6.

  Of the four corners 44a, 44b, 44c, 44d of the field permanent magnet 6, in the vicinity of the corner 44a located on the outermost side in the radial direction of the rotor core 18, the groove 46a of the buried hole 42 is formed in the rotor core. 18 is formed at a position facing the side surface of the field permanent magnet 6 facing radially outward. Accordingly, the FBG sensor 28 disposed in the groove 46 a can contact the side surface of the field permanent magnet 6, which is the temperature measurement point 32, from the outside in the radial direction of the rotor core 18. In the groove 46a, the optical fiber 30 is filled with a filler 50 on the radially outer side of the rotor core 18, and the optical fiber 30 is fixed by the filler 50 so as to be in contact with the side surface of the field permanent magnet 6. The

  As described above, when an external force is applied to the FBG sensor 28 and distortion occurs in the axial direction of the FBG sensor 28, the Bragg wavelength changes accordingly, so that the Bragg wavelength corresponding to the temperature change cannot be detected. . Therefore, the optical fiber 30 including the FBG sensor 28 is fixed to the grooves 46a, 46b, 46c, and 46d of the embedded hole 42 so that an external force is not applied in the axial direction of the FBG sensor 28. Specifically, the optical fiber 30 is fixed to the grooves 46a, 46b, 46c, and 46d at two points on both sides of the FBG sensor 28 portion in the optical fiber 30. At this time, an extra length portion is provided in the optical fiber 30 between the two fixed points (that is, the length of the optical fiber 30 between the two fixed points is longer than the linear distance between these fixed points. To do). Thereby, even when an external force in the axial direction is applied to the optical fiber 30, the external force is absorbed by the surplus length portion, so that the external force in the axial direction does not reach the FBG sensor 28 portion.

Next, the operation of the temperature measuring device 26 of the electric motor 1 according to the embodiment of the present invention will be described.
As described above, among the four corners 44a, 44b, 44c, 44d of the field permanent magnet 6, the three corners 44b, 44c, excluding the corner 44a located on the outermost side in the radial direction of the rotor core 18, The FBG sensor 28 disposed in the vicinity of 44d is in contrast to the corners 48a, 48b, 48c formed by the wall surfaces of the grooves 46b, 46c, 46d and the side surface of the field permanent magnet 6 that is the temperature measurement point 32. Contact is possible from the inside in the radial direction of the rotor core 18. Therefore, when the rotor 8 rotates during operation of the electric motor 1, these FBG sensors 28 are pressed against the corners 48a, 48b, 48c by the centrifugal force acting toward the radially outer side of the rotor core 18, and the corners 48a. , 48b and 48c are pressed against the side surface (temperature measurement point 32) of the field permanent magnet 6.
The FBG sensor 28 disposed in the vicinity of the corner portion 44a located on the outermost side in the radial direction of the rotor core 18 among the four corner portions 44a, 44b, 44c, 44d of the field permanent magnet 6 The permanent magnet 6 can be brought into contact with the side surface from the radially outer side of the rotor core 18. Therefore, when the rotor 8 rotates during operation of the electric motor 1, centrifugal force acts on the FBG sensor 28 in a direction toward the radially outer side of the rotor core 18 (that is, a direction away from the side surface of the field permanent magnet 6). However, as described above, the optical fiber 30 is fixed so as to be in contact with the side surface of the field permanent magnet 6 by the filler 50 filled in the groove 46 a on the radially outer side of the rotor core 18 with respect to the optical fiber 30. Yes.
At this time, since the centrifugal force acts in a direction perpendicular to the axial direction of the FBG sensor 28, the FBG sensor 28 is not distorted in the axial direction, and only changes in the Bragg wavelength according to temperature changes are detected. Can do.

Next, further modifications of the embodiment of the present invention will be described.
In the above-described embodiment, the electric motor 1 is described as a three-phase AC synchronous motor with a permanent magnet embedded, but the temperature measuring device 26 of the present invention can be applied to other types of electric motors. it can. For example, in a permanent magnet embedded type brushless DC motor, the temperature measuring device 26 of the present invention can be used to measure the surface temperature of a rotor field permanent magnet.

  Next, the effect of the temperature measuring device 26 of the electric motor 1 according to the above-described embodiment of the present invention and the modification of the embodiment of the present invention will be described.

  First, the temperature measurement device 26 includes an optical fiber 30 disposed up to the temperature measurement point 32 of the rotor 8 via the inside of the rotating shaft 22 of the electric motor 1, a light source 34 that makes light incident on the optical fiber 30, The optical fiber 30 includes a light detector 36 that detects light emitted from the optical fiber 30, and an optical rotary joint 38 that optically connects the optical fiber 30, the light source 34, and the light detector 36. Since the FBG sensor 28 that reflects only the Bragg wavelength component is provided, the FBG is not affected by fluctuations in the electromagnetic field inside the electric motor 1 or noise at the electric contacts even during operation of the electric motor 1. A change in wavelength of reflected light from the sensor 28 can be detected by the photodetector 36, and a temperature change can be measured based on the change in wavelength. Since the portion including the FBG sensor 28 in the optical fiber 30 extends in parallel with the rotation axis 22 of the rotor 8, the FBG sensor 28 is not distorted in the axial direction, and changes in Bragg wavelength according to temperature changes. Can only detect. Since the FBG sensor 28 is arranged so as to be able to come into contact with the temperature measurement point 32 of the rotor 8 from the rotating shaft 22 side, when the rotor 8 rotates during operation of the electric motor 1, the FBG sensor 28 It is pressed against the temperature measurement point 32 by the centrifugal force acting toward the outside in the radial direction. Thereby, the FBG sensor 28 can be reliably brought into contact with the temperature measurement point 32, and the temperature of the rotor 8 can be measured with high accuracy in the electric motor 1 during operation.

  In particular, the electric motor 1 has a stator 4 having armature windings and a rotor 8 having a field permanent magnet 6, and the FBG sensor 28 is a temperature of the field permanent magnet 6 of the rotor 8. Since the measurement point 32 is arranged so as to be contactable from the rotary shaft 22 side, when the rotor 8 rotates during operation of the electric motor 1, the FBG sensor 28 acts as a centrifugal force acting toward the radially outer side of the rotor 8. Is pressed against the temperature measurement point 32 of the field permanent magnet 6. As a result, the FBG sensor 28 can be reliably brought into contact with the temperature measurement point 32 of the field permanent magnet 6 and the temperature of the field permanent magnet 6 of the rotor 8 can be measured with high accuracy in the electric motor 1 during operation. can do.

  The field permanent magnet 6 is embedded in a buried hole 42 formed so as to extend in the axial direction in the rotor core 18, and the FBG sensor 28 is field permanent at a temperature measurement point 32 inside the buried hole 42. Since the corners 48a, 48b, and 48c formed by the surface of the magnet 6 and the inner wall surface of the embedded hole 42 are arranged so as to be able to contact from the rotary shaft 22 side, the rotor 8 rotates when the electric motor 1 is operated. Then, since the FBG sensor 28 is pressed against the corners 48a, 48b, 48c by the centrifugal force acting toward the radially outer side of the rotor core 18, the field permanent magnet 6 forming the corners 48a, 48b, 48c. Pressed firmly against the side of the. As a result, the FBG sensor 28 can be more reliably brought into contact with the temperature measurement point 32 of the field permanent magnet 6, and the temperature of the field permanent magnet 6 of the rotor 8 in the electric motor 1 during operation can be increased with high accuracy. It can be measured.

DESCRIPTION OF SYMBOLS 1 Electric motor 2 Coil 4 Stator 6 Field permanent magnet 8 Rotor 18 Rotor core 20 Output shaft 22 Rotating shaft 26 Temperature measuring device 28 FBG sensor 30, 40 Optical fiber 32 Temperature measuring point 34 Light source 36 Photo detector 38 Optical rotary joint 42 buried hole 48a, 48b, 48c corner

Claims (3)

An electric motor temperature measuring device for measuring a temperature of the rotor in an electric motor having a stator, a rotor, and a rotating shaft connected to the rotor,
An optical fiber disposed through the inside of the rotary shaft of the electric motor to the temperature measurement point of the rotor;
A light source for making light incident on the optical fiber;
A photodetector for detecting light emitted from the optical fiber;
An optical rotary joint provided on the rotary shaft and optically connecting the optical fiber to the light source and the photodetector;
The optical fiber includes a fiber Bragg grating portion that reflects only a specific wavelength component of incident light, and a portion including the fiber Bragg grating portion in the optical fiber extends parallel to the rotation axis, And the temperature measuring device of the electric motor, wherein the temperature measuring point of the rotor is arranged so as to be contactable from the rotating shaft side. The electric motor has a stator having armature windings, and a rotor having field permanent magnets,
2. The electric motor according to claim 1, wherein the fiber Bragg grating portion of the optical fiber is disposed so as to be contactable from the rotating shaft side with respect to a temperature measurement point of the field permanent magnet of the rotor. Temperature measuring device. The rotor of the electric motor includes a cylindrical rotor core centered on the rotating shaft, and the field permanent magnet is embedded in a buried hole formed in the rotor core so as to extend in the axial direction.
The fiber Bragg grating portion of the optical fiber is inside the embedded hole with respect to a corner formed by the surface of the field permanent magnet and the inner wall surface of the embedded hole at the temperature measurement point. The temperature measuring device for an electric motor according to claim 2, wherein the temperature measuring device is arranged so as to be contactable from the rotating shaft side.

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