JP2022128155A - Magnetic wedge and rotating electric machine - Google Patents

Abstract

To provide a magnetic wedge capable of improving both the efficiency and torque of a rotating electrical machine to a high level beyond the trade-off relationship in the magnetic wedge.SOLUTION: A magnetic wedge for a rotating electric machine according to the present invention includes a high magnetic permeability portion and a low magnetic permeability portion having relatively different magnetic permeability, the magnetic permeability of the low magnetic permeability portion is lower than the magnetic permeability of the high magnetic permeability portion, the high-permeability portion is positioned at the center of the magnetic wedge in the width direction, and the low-permeability portions are positioned at both ends of the magnetic wedge in the width direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic wedge used in a rotating electrical machine and a rotating electrical machine using the magnetic wedge.

In a typical radial gap type electric rotating machine, a stator (hereafter referred to as stator) and a rotor (hereafter referred to as rotor) are arranged coaxially, and multiple teeth with coils wound around the rotor are arranged in the circumferential direction. arranged at intervals. Also, a magnetic wedge may be arranged at the rotor-side tip of each tooth so as to connect the tips of adjacent teeth. In this case, the magnetic wedge is used without winding a coil around the magnetic wedge itself, unlike the coil component or the like.

By arranging such a magnetic wedge, magnetic flux reaching the coil from the rotor can be magnetically shielded, and eddy current loss in the coil can be suppressed. In addition, by arranging a magnetic wedge, the magnetic flux distribution in the gap between the stator and rotor (especially the magnetic flux distribution in the circumferential direction) is smoothed, not only smoothing the rotation of the rotor, but also reducing the eddy current loss that occurs in the rotor. can also be reduced. Such merits of the magnetic wedge become more conspicuous as the magnetic wedge has a higher magnetic permeability or a thicker magnetic wedge.

Patent Documents 1 and 2 disclose a magnetic wedge made of a laminate of electromagnetic steel sheets or a green compact of ferromagnetic metal powder.

JP 2007-221913 A JP 2019-97258 A

Due to the presence of the magnetic wedges, part of the magnetic flux that should flow from the teeth to the rotor is short-circuited between the teeth via the magnetic wedges. be. Such a side effect becomes more conspicuous as the magnetic permeability of the magnetic wedge is higher or as the magnetic wedge is thicker. In other words, the advantage of the magnetic wedge (lower loss, ie, higher efficiency) and the side effect (lower torque) are in a trade-off relationship with the magnetic permeability or thickness of the magnetic wedge as a parameter. For this reason, the conventional magnetic wedge suppresses the relative magnetic permeability to about 3 to 5 to avoid an excessive decrease in torque, while at the same time being satisfied with improving the efficiency to some extent, and its effect is limited.

Therefore, the present invention provides a magnetic wedge that can improve both the efficiency and the torque of a rotating electric machine to a high level beyond the above trade-off relationship in the magnetic wedge.

A magnetic wedge of the present invention is a magnetic wedge for a rotating electric machine, and has a high magnetic permeability portion and a low magnetic permeability portion having relatively different magnetic permeability, and the magnetic permeability of the low magnetic permeability portion is the high magnetic permeability. The magnetic permeability is lower than that of the magnetic permeability portion, and the high magnetic permeability portion is positioned at the central portion in the width direction of the magnetic wedge, and the low magnetic permeability portion is positioned at both end sides of the magnetic wedge in the width direction. and

In the magnetic wedge, the high magnetic permeability portion preferably includes soft magnetic particles and an electrically insulating substance between the soft magnetic particles.

Further, in the magnetic wedge, the soft magnetic particles are a plurality of Fe-based soft magnetic alloy particles containing an element M that is more easily oxidized than Fe, and the high magnetic permeability portion is the Fe-based soft magnetic alloy particles is preferably bound by an oxide phase containing the element M.

Moreover, in the magnetic wedge, the element M is preferably at least one of Al, Si, Cr, Zr, and Hf.

Also, in the magnetic wedge, the low magnetic permeability portion is preferably non-ferromagnetic.

Further, a rotating electric machine of the present invention uses any one of the magnetic wedges described above.

ADVANTAGE OF THE INVENTION According to this invention, the magnetic wedge which can make the efficiency and torque of a rotary electric machine compatible at a high level can be provided.

1 is a perspective view of a magnetic wedge that is a first embodiment of the present invention; FIG. 1 is an enlarged schematic cross-sectional view of a magnetic wedge that is a first embodiment of the present invention; FIG. FIG. 4 is a perspective view of a magnetic wedge that is a second embodiment of the present invention; FIG. 5 is a schematic diagram of a rotating electric machine according to a third embodiment of the present invention; 4 is a SEM photograph showing a cross-sectional structure of an example of a magnetic wedge; 4 is a graph showing a DC magnetization curve of a high permeability portion; 4 is a graph showing iron loss in a high magnetic permeability portion; 1 is a model diagram of a rotating electric machine used for electromagnetic field analysis; FIG. It is a schematic diagram which shows the cross-section of an Example. It is a schematic diagram which shows the cross-section of a comparative example. It is a graph which shows the electromagnetic field analysis result of a rotary electric machine.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a perspective view of a magnetic wedge 100. As shown in FIG. The magnetic wedge 100 is a magnetic wedge for a rotating electric machine, and has a high magnetic permeability portion and a low magnetic permeability portion whose magnetic permeability is relatively different from each other. The high magnetic permeability portion is positioned at the central portion in the width direction of the magnetic wedge, and the low magnetic permeability portion is positioned at both end sides of the magnetic wedge in the width direction. , in this embodiment, the cross section perpendicular to the longitudinal direction has a convex shape as a whole. Then, from one end of the magnetic wedge 100 in the width direction (the direction of the magnetic path that connects adjacent teeth; the direction of rotation of the rotating electric machine (the circumferential direction of the stator)), the first low magnetic permeability A portion 21, a high magnetic permeability portion 10, and a second low magnetic permeability portion 22 are formed in this order. The terms "high magnetic permeability portion" and "low magnetic permeability portion" indicate the relative relationship between the magnetic permeability of both portions.

The high magnetic permeability portion 10 is positioned substantially in the center of the magnetic wedge 100 in the width direction and within the range of the projecting portion of the convex shape, and is elongated along the longitudinal direction of the magnetic wedge 100 . Further, the high magnetic permeability portion 10 is arranged so as to pass through the magnetic wedge 100 in the thickness direction (the direction perpendicular to the width direction (direction connecting adjacent teeth)). In the magnetic wedge 100 shown in FIG. 1, the cross section of the high magnetic permeability portion is rectangular, but the cross section is not limited to this, and various shapes such as a trapezoid can be applied. The approximate dimensions of the magnetic wedge 100 are, for example, 10 mm to 300 mm in the longitudinal direction, 2 mm to 20 mm in the width direction, and 1 to 5 mm in thickness.

The high magnetic permeability portion 10 can be a composite material made of soft magnetic particles such as iron powder, Fe-based soft magnetic alloy powder, or both, and an electrically insulating substance. The composite material has an electrically insulating substance present between the soft magnetic particles to bind the soft magnetic particles together and electrically isolate the particles, thereby increasing the electrical resistance of the magnetic wedge 100. Thus, eddy current loss occurring in the magnetic wedge 100 can be suppressed.

As for the average particle size of the soft magnetic particles, decreasing the particle size can increase electrical resistance and reduce eddy current loss. It becomes possible to strengthen the effect of the magnetic wedge. From these viewpoints, the average particle size of the soft magnetic particles is preferably 200 µm or less, more preferably 100 µm or less, even more preferably 50 µm or less, preferably 2 µm or more, more preferably 5 µm or more, and even more preferably 10 µm or more.

Both organic and inorganic substances can be used as electrically insulating substances. For example, epoxy resin, phenolic resin, polyimide, polyphenylene sulfide, polyamide, polyamide-imide, silicon resin, colloidal silica, and low-melting-point glass can be used. is. When these are used, they can be produced by transfer molding, injection molding, hot pressing, etc. after mixing the ferromagnetic powder and these electrically insulating substances.

Further, as one form of the high magnetic permeability portion 10, the ferromagnetic particles are an Fe-based alloy containing an element M that is more easily oxidized than Fe, and an oxide phase of the element M is generated between the soft magnetic particles to separate the particles. A bound form is also possible. As a method for producing the high magnetic permeability portion 10 of this form, the oxide phase of the element M can be grown at the grain boundary by heat-treating the soft magnetic particles after press molding in an atmosphere in which oxygen is present. This form is more preferable because the ratio of the electrically insulating material at the grain boundaries can be minimized and the density is increased, resulting in high strength and high magnetic permeability. As the element M, one or more of Al, Si, Cr, Zr, Hf and the like can be used. Here, “the element M that is more easily oxidized than Fe” means an element whose standard Gibbs energy of oxide formation is lower than that of Fe ₂ O ₃ .

The low magnetic permeability portions 21, 22 can be formed using the electrically insulating material described above. A low magnetic permeability portion and a high magnetic permeability portion can be produced separately and integrated by adhesion, welding, or the like so as to form the configuration shown in FIG. It is also possible to integrally mold a low magnetic permeability material and a high magnetic permeability material by a two-color molding method or the like. The electrically insulating material contained in the high magnetic permeability portion 10 and the electrically insulating material forming the low magnetic permeability portion may be the same or may be different materials. Further, in order to improve the strength of the magnetic wedge 100, it is also possible to embed glass fibers or glass cloth inside it.

Further, when Fe-based alloy particles containing an element M, which is more easily oxidized than Fe, are used as the high magnetic permeability portion 10, and an oxide phase of the element M is grown between the particles, the low magnetic permeability portions 21, 22 may be formed as follows. That is, the low magnetic permeability portions 21 and 22 are composed of low magnetic permeability metal particles having a magnetic permeability lower than that of the Fe-based alloy. Here, the low-permeability metal particles contain an element M that is more easily oxidized than Fe. The low-permeability metal particles may be a single element of the element M, an alloy mainly composed of M, or the same alloy system as the Fe-based alloy. In the case of the same alloy system, alloy particles with low magnetic permeability can be obtained by, for example, reducing the Fe composition amount relative to the Fe composition amount of the Fe-based alloy particles constituting the high magnetic permeability portion. So far, the case where the low magnetic permeability portions 21 and 22 are composed of low magnetic permeability metal particles having a magnetic permeability lower than that of the Fe-based alloy has been described, but they may be non-magnetic.
By setting these high magnetic permeability portion and low magnetic permeability portion in a mold and pressing (sizing), an integrated molded body is produced, and by heat-treating this in the presence of oxygen, An oxide phase of the element M can be generated to strongly bond between particles and the boundary between the low magnetic permeability portion and the high magnetic permeability portion.

FIG. 2 is a schematic diagram showing an enlarged boundary between the high magnetic permeability portion 10 and the low magnetic permeability portion 21 (22) in this configuration. The high magnetic permeability portion 10 is composed of a plurality of Fe-based soft magnetic alloy particles, and more specifically, is a compacted body of a plurality of Fe-based soft magnetic alloy particles 1 containing an element M that is more easily oxidized than Fe. . Between the particles of the compacted body, there are voids 2 and surface oxide phases 3 of the Fe-based soft magnetic alloy particles that bind the Fe-based soft magnetic alloy particles 1 together. Such a surface oxide phase is an oxide phase containing the element M.
Also, the low magnetic permeability portion 21 or 22 is composed of a plurality of low magnetic permeability metal particles 4 having a magnetic permeability lower than that of the Fe-based soft magnetic alloy particles 1 . Here, the low magnetic permeability metal particles 4 are characterized by containing an element M which is more easily oxidized than Fe. It has gaps 2 between the low-permeability metal particles 4 and surface oxide phases 5 that bind the low-permeability metal particles 4 together. Such a surface oxide phase is an oxide phase containing the element M.
Furthermore, surface oxide phases 6 are formed at locations where the Fe-based soft magnetic alloy grains 1 and the low-permeability metal grains 4 are adjacent to each other. The surface oxide phase 6 is formed by bonding and integrating the surface oxide phase 3 of the Fe-based soft magnetic alloy particles 1 and the surface oxide phase 5 of the low-permeability metal particles 4. are in different phases. However, by containing the same element M in the Fe-based soft magnetic alloy particles 1 and the low-permeability metal particles 4, the surface oxide phase 6 becomes a more homogeneous surface oxide phase 6 mainly composed of the element M. can do. As a result, the particles of the Fe-based soft magnetic alloy particles 1 and the low-permeability metal particles 4 can be strongly bound together.

(Second embodiment)
Next, a magnetic wedge 200 according to a second embodiment of the invention will be described. The magnetic wedge 200 of the present embodiment and the magnetic wedge 100 of the first embodiment differ only in shape. Moreover, since the same configurations as those of the first embodiment have the same effects, the same reference numerals are used and the descriptions thereof are omitted.

The magnetic wedges are attached by being fitted into projections and grooves formed on the teeth of the stator as described later. Therefore, the cross-section of the magnetic wedge can take various shapes depending on this fitting configuration. In the first embodiment, the magnetic wedge has a stepped shape at both ends, but the magnetic wedge 200 may have a tapered shape at both ends, as shown in FIG. 3, for example. Such a shape is preferable because stress concentration on the corners of the grooves formed in the stator can be alleviated. In the magnetic wedge 200 shown in FIG. 3, the cross section of the high magnetic permeability portion is rectangular, but the cross section is not limited to this, and various shapes such as a trapezoid can be applied.

(Third embodiment)
Next, a rotating electric machine 300, which is a third embodiment of the present invention, will be described.
FIG. 4 is a schematic diagram of the rotating electric machine 300 and shows a cross-sectional structure perpendicular to the rotating shaft of the rotating electric machine 300. As shown in FIG. The rotating electric machine 300 is a radial gap type rotating electric machine, in which a stator 35 and a rotor 32 are arranged coaxially. A plurality of teeth 34 around which coils 33 are wound are arranged on the stator 35 at regular intervals in the circumferential direction.

In the rotary electric machine 300 of the present embodiment, the magnetic wedge 100 of the first embodiment or the magnetic wedge 200 of the second embodiment is arranged at the tip of the teeth 34 on the rotor 32 side so as to connect the tips of the teeth 34 adjacent to each other. is doing.

Here, the relative magnetic permeability and saturation magnetic flux density of the teeth 34 are usually designed to be higher than those of the magnetic wedges 100 or 200 . As a result, the magnetic flux from the rotor 32 that reaches the magnetic wedges 100 or 200 flows into the teeth 34 via the magnetic wedges 100 or 200, and the magnetic flux that reaches the coil is suppressed, thereby reducing eddy current loss occurring in the coil. can do. When the rotating electric machine is driven, most of the magnetic flux in the teeth 34 generated by the coil current flows into the rotor 32 across the gap, but part of it is attracted by the magnetic wedges and spreads in the circumferential direction. Become. As a result, the magnetic flux distribution in the gap between the stator 35 and the rotor 32 is smoothed, and cogging can be suppressed in, for example, a rotating electric machine in which the rotor 32 is provided with permanent magnets. Loss can be reduced. In addition, for example, in an induction-type rotating electrical machine in which cage-shaped conductors are arranged in the rotor 32, secondary copper loss can be reduced. As described above, by disposing the magnetic wedge 100 or 200 according to the present invention in the rotating electrical machine, the loss can be reduced, and the rotating electrical machine 300 with high efficiency and high performance can be obtained.

(Magnetic properties of high permeability part)
Examples of the first embodiment in which Fe--Al--Cr alloy particles containing Al and Cr, which are elements that are more easily oxidized than Fe, are used in the high magnetic permeability portion are shown below.

(Preparation of sample for magnetic property measurement)
An Fe-5%Al-4%Cr (mass %) alloy powder (Fe-based soft magnetic powder) was produced by a high-pressure water atomization method. The average particle diameter (median diameter) of the produced powder was 12 μm. Polyvinyl alcohol (PVA) and ion-exchanged water were added to this alloy powder to prepare slurry, which was spray-dried with a spray dryer to obtain granulated powder. When the raw material powder is 100 parts by mass, the amount of PVA added is 0.75 parts by mass. 0.4 parts by mass of zinc stearate was added to the obtained granulated powder and mixed. The obtained mixed powder was filled in a mold and press-molded at room temperature with a molding pressure of 0.9 GPa. The formed body was subjected to heat treatment at 750° C. for 1 hour in air to obtain a sample for evaluation of magnetic properties. The shape of the prepared magnetic measurement sample was a flat plate shape of 10 mm × 10 mm × 1.5 mm thickness for DC magnetization curve measurement, and an outer diameter 13.4 mm × inner diameter 7.7 mm × thickness for iron loss measurement sample. It has a ring shape of 2.0 mm.

(Cross-sectional structure of high permeability part)
The cross-sectional observation of the high magnetic permeability portion produced as described above was performed using a scanning electron microscope (SEM/EDX), and at the same time, the distribution of each constituent element was examined. The results are shown in FIG. FIG. 5(a) is an SEM image, and FIGS. 5(b) to 5(e) are mapping images showing distributions of Fe (iron), Al (aluminum), Cr (chromium), and O (oxygen), respectively. . Brighter colors indicate more target elements. From FIG. 5, it can be seen that there are many aluminum and oxygen at the grain boundaries between the Fe-based soft magnetic particles, and an oxide phase is formed. Furthermore, it can be seen that the soft magnetic particles are bonded to each other via this oxide phase.

(DC magnetization curve)
The DC magnetization curve (BH curve) of the sample was measured using a DC self-recording magnetometer (TRF-5AH manufactured by Toei Kogyo Co., Ltd.) by sandwiching the above 10 mm square sample between the magnetic poles of an electromagnet and applying a maximum magnetic field of 500 kA/m. FIG. 6 shows the measurement results at room temperature. The magnetic flux density was 1.60 T and the relative magnetic permeability μ was 8.0 at an applied magnetic field of 160 kA/m. In the motor characteristic simulation described later, this measured value was used as the BH curve of the high magnetic permeability portion.

(iron loss)
A primary winding and a secondary winding were applied to the above ring samples using polyurethane-coated copper wire. The number of windings was 50 on both the primary and secondary sides. This sample was connected to a BH analyzer (BH-550 manufactured by IFG) equipped with a large-current bipolar power source to measure iron loss Pcv. The measurement conditions are frequency f=50 Hz to 1 kHz and maximum magnetic flux density Bm=0.05 to 1.55T. In order to prevent the sample temperature from rising due to the Joule heat of the primary winding, the sample was immersed in a cooling bath in which the coolant temperature was kept at 23° C., and the iron loss was measured. Silicone oil was used as the coolant. The measurement results are shown in FIG. White circles in the figure are measured values. As shown in the figure, Pcv tends to gradually saturate in the region where Bm is high because it approaches magnetic saturation. In the evaluation of the motor characteristics described in the next section, this measured value was used as the core loss of the high magnetic permeability portion. It should be noted that although it was possible to actually measure up to Bm=1.55T, there is a possibility that the magnetic wedge inside the motor will be magnetized up to about 2T, which corresponds to the saturation magnetic flux density of the magnetic steel sheet. Therefore, for the Pcv value on the high Bm side exceeding 1.55 T, the measurement results were applied to the following formula by the method of least squares, and the extrapolated value of this formula was used.
Pcv=6.9f/(1+(1.28/Bm) ² )
Here, the unit of Pcv is kW/m ³ , the unit of Bm is T, and the unit of f is Hz. The solid line in FIG. 6 is the calculated value of this formula.

(Rotating electric machine characteristic evaluation)
Characteristics (efficiency and torque) when the magnetic wedges of Examples or Comparative Examples are installed in an induction rotating electric machine were calculated using a two-dimensional electromagnetic field simulation based on the finite element method. At that time, the above-mentioned BH curve and core loss value were incorporated into the calculation as the magnetic properties of the high magnetic permeability portion of each magnetic wedge.
The specifications of the induction type rotary electric machine subjected to the electromagnetic field simulation are as follows.
Stator: diameter 450 mm x height 162 mm
Number of poles: 4
Number of slots: 36
Rotor and stator material: electromagnetic steel plate (50A1000)
Rotating electric machine output: 150 kW
Rotation speed: 1425 rpm

FIG. 8 shows the installation position of the magnetic wedge 100 used in this evaluation. The cross section of the magnetic wedge 100 is T-shaped, and the width of the magnetic wedge 100 (length in the circumferential direction of the rotating electric machine) is 12.0 mm on the coil 33 side and 7.0 mm on the rotor 32 side. The thickness of the magnetic wedge 100 at the center in the width direction (the length in the radial direction of the rotating electric machine) is 3.0 mm, and the thickness of the stepped portion is 1.5 mm.

(Example)
FIG. 9 shows a schematic cross-sectional view of the magnetic wedge 100 of the embodiment. The embodiment consists of a high magnetic permeability portion 10 located in the center in the width direction and low magnetic permeability portions 21 and 22 located on both sides thereof. The magnetic properties of the high permeability portion 10 are as described above, and the width x of the high permeability portion is in the range of 0<x<12 mm. Also, the low magnetic permeability portions 21 and 22 are non-magnetic, and the relative magnetic permeability is fixed at 1.

(Comparative example)
FIG. 10 shows a schematic cross-sectional view of a magnetic wedge 100 of a comparative example. The comparative example consists of a high magnetic permeability portion 10 located on the rotor side and a low magnetic permeability portion 21 located on the coil side. The magnetic properties of the high magnetic permeability portion 10 are as described above, and the thickness y of the high magnetic permeability portion is in the range of 0≤y≤3 mm. Also, the low magnetic permeability portion 21 is non-magnetic, and the relative magnetic permeability is fixed to 1. In this comparative example, the entire magnetic wedge 100 becomes a non-magnetic material when y=0, and the entire magnetic wedge 100 becomes a high magnetic permeability portion when y=3 mm.

(Rotating electric machine characteristic evaluation results)
Table 1 shows the efficiency and torque of the rotating electric machine using the magnetic wedge of the example, and Table 2 shows the efficiency and torque of the rotating electric machine using the magnetic wedge of the comparative example. FIG. 11 shows the results of Tables 1 and 2, with the efficiency of the rotary electric machine on the horizontal axis and the torque on the vertical axis. In FIG. 11, it can be said that the higher the upper right position on the graph, the higher the efficiency and torque, and the better the characteristics.
First, focusing on the results of the magnetic wedges of the comparative examples, the completely non-magnetic comparative example 1 has the highest torque, but the lowest efficiency. As the high permeability portion is increased (Comparative Examples 2 to 4), the efficiency is improved but the torque is decreased. Comparative Example 5, which has a high magnetic permeability portion as a whole, has the highest efficiency among the comparative examples, but the lowest torque. The trade-off relationship as described above in the comparative example is indicated by a dotted line in FIG.
On the other hand, all of the plotted points of the calculation results of the example are located on the upper right side of the above dotted line, showing excellent characteristics of both high torque and high efficiency compared to the comparative example. A magnetic wedge that has been conventionally used is a magnetic wedge as in Comparative Example 5 which is entirely composed of a high magnetic permeability portion. Compared to this comparative example 5, the example is superior in both torque and efficiency, so it is possible to provide a rotating electrical machine with excellent characteristics that could not be achieved with conventional magnetic wedges.

Although the present invention has been described above using the above embodiments, the technical scope of the present invention is not limited to the above embodiments. The contents can be changed within the technical scope described in the claims.

1: Fe-based soft magnetic particles 2: voids 3: surface oxide phase 4: low-permeability metal particles 5: surface oxide phase 6: surface oxide phase 10: high-permeability portions 21, 22: low-permeability portions 31 : Gap 32: Rotor 33: Coil 34: Teeth 35: Stator 100, 200: Magnetic wedge 300: Rotating electric machine

Claims (6)

A magnetic wedge for a rotating electric machine,
Having a high magnetic permeability portion and a low magnetic permeability portion having relatively different magnetic permeability,
the magnetic permeability of the low magnetic permeability portion is lower than the magnetic permeability of the high magnetic permeability portion;
The high magnetic permeability portion is located in the central portion of the magnetic wedge in the width direction,
the low magnetic permeability portions are positioned on both widthwise end sides of the magnetic wedge;
A magnetic wedge characterized by: 2. The magnetic wedge according to claim 1, wherein the high magnetic permeability portion includes soft magnetic particles and an electrically insulating material between the soft magnetic particles. The soft magnetic particles are a plurality of Fe-based soft magnetic alloy particles containing an element M that is more easily oxidized than Fe, and the high magnetic permeability portion includes the Fe-based soft magnetic alloy particles containing the element M. 3. The magnetic wedge of claim 2, wherein the magnetic wedge is bound by an oxide phase. 4. The magnetic wedge according to claim 3, wherein the element M is at least one of Al, Si, Cr, Zr and Hf. 5. A magnetic wedge as claimed in any one of claims 1 to 4, wherein the low permeability portion is non-ferromagnetic. A rotating electrical machine using the magnetic wedge according to any one of claims 1 to 5.

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