FIELD OF INVENTION
[001] The present subject matter described herein, relates to a casting-less skewed caged rotor of a high speed induction motor.
BACKGROUND AND PRIOR ART OF THE INVENTION
[002] The induction motor has always been the most widely used prime-mover in all industrial and utility applications. Among various types and topologies, the squirrel cage type induction motor (wherein the rotor winding is in the form of squirrel cage) is commonly chosen for its well-known robust design and lesser maintenance. For Induction motors, there are two types of rotor configurations, one squirrel cage type and other wound rotor type. The most common configuration is squirrel cage type because of its robust configuration. Usually, the rotor of squirrel cage type induction motor is manufactured using available casting processes.
[003] Conventionally for manufacturing rotor core, the rotor laminations having same size and shape are assembled on a shaft having skewed key so as to achieve desired skew angle.
[004] At high rotational speeds, the complete rotor assembly must have good rotor dynamic design. A good rotor dynamic design helps in upholding better mechanical integrity in the rotor assembly at very high rotational speeds. It also helps in maintaining lower operational vibration levels and achieving larger mean time between failures (MTBF). All these design aspects have been taken care in present invention.
[005] Prior Art Application no. US6777847B1 describes a rotor core utilizing laminations having slots with dual direction skew portions. This patent describes the divided magnet rotors having a stepped skew rather than a helical skew. The stepped skew enables the use of straight magnet

sections that can be inserted into the rotor core notches thereby eliminating the need to produce a helix from the rotor cage. The stepped skew is effective in decoupling stator slot order harmonics. In addition, the stepped skew rotor includes, in some embodiments, open slots so that the rotor is not subject to rotor bridge saturation.
[006] Prior art KR20090007050A describes a rotor structure for line start permanent magnet synchronous motor. This patent explains a rotor structure of single phase induction start type synchronous motor that is provided to reduce slot harmonic generated in starting by forming skew in a squirrel cage conductor bar of a rotor. A rotor structure of single phase induction start type synchronous motor comprises a slot, a permanent magnet, and an aluminum conductor. A skew is formed in a slot in which a squirrel cage conductor bar of a rotor is used, and is not formed in a part in which a permanent magnet is mounted for synchronous operation. A mounting type permanent magnet is coupled with four surfaces of the aluminum conductor inside the slot.
[007] Another Prior art US20120007465A1 explains an electric machine that includes a rotor rotatable about a central axis. The rotor includes at least one rotor element having a first element edge. A stator includes a stator face facing the rotor and a plurality of stator slots. Each stator slot has at least one stator slot edge located at the stator face. A first edge portion of the at least one stator slot edge is oriented nonparallel to the first element edge in a first direction and a second edge portion of the at least one stator slot edge is oriented nonparallel to the first element edge in a second direction.
[008] Yet another prior art JP5518663B2 titled ‘Skew rotor and manufacturing method thereof’ relates to a skew rotor and a manufacturing method thereof. A plurality of rotors each having permanent magnets held in openings formed at substantially equal intervals in the circumferential direction on the outer periphery of a

cylindrical rotor core, and the plurality of rotors are arranged side by side in the axial direction with the central axes aligned. In addition, the adjacent two rotors are arranged with a predetermined angle in the circumferential direction and are arranged integrally with each other. Each rotor has a pair of grooves extending radially inward from the outer peripheral surface of the rotor core between adjacent openings in the outer peripheral portion of the rotor core, and is sandwiched between the pair of grooves. Salient poles that form magnetic flux passages are formed. The salient pole has a protrusion formed by extending the top of the salient pole in the circumferential direction so that the circumferential thickness of the salient pole is greater at the outer peripheral edge than at the radially inner side.
[009] None of the above prior arts can fulfill the requirements of the invention for which it is designed. Hence, the present invention has been introduced.
OBJECTS OF THE INVENTION
[0010] It is therefore the object of the invention to overcome the aforementioned and other drawbacks in prior art.
[0011] The principal objective of the present invention is to provide for a casting-less skewed caged rotor of a high speed induction motor and a method of manufacturing thereof.
[0012] Another object of the present invention is to provide for a casting-less skewed caged rotor having angular displacement in slots of each lamination with respect to its neighborhood lamination so as to achieve required skew angle along the core length.
[0013] Another object of the present invention is to provide for a casting-less skewed caged rotor having rotor core guided on a straight key integrated to the shaft for easier manufacturing and assembly.

[0014] Another object of the present invention is to provide for a casting-less skewed caged rotor having uninsulated bars placed in skewed rotor slots wherein all bars are electrically short-circuited at each end using end rings.
[0015] Another object of the present invention is to provide for a casting-less skewed caged rotor having rotor bars and end rings made of high electrical conductivity based material not limited to aluminium or aluminium alloy or copper or copper alloy or copper-silver or copper-silver alloy or similar materials.
[0016] Another object of the present invention is to provide for a casting-less skewed caged rotor without any conventional casting method to avoid associated defects like pin-holes, blow-holes etc.
[0017] Another object of the present invention is to provide for a casting-less skewed caged rotor having micron sized surface finish so as to achieve 100 to 200 micron size physical airgap between stator and rotor.
[0018] Another object of the present invention is to provide for a casting-less skewed caged rotor which is dynamically balanced to operate at higher rotational speeds upto 12000 RPM.
[0019] Another object of the present invention is to provide for a better inter-lamination insulation in the casting-less skewed caged rotor as compared to conventional casted rotors.
[0020] These and other objects and advantages of the present subject matter would be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION

[0021] One or more drawbacks of the conventional technology based on existing apparatus and processes are overcome, and additional advantages are provided through a novel
[0022] Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0023] In accordance with an embodiment of the present subject matter, a skewed caged rotor for a high speed induction motor a rotor core comprising stack of laminations with a longitudinal skew, a winding with bars and end rings, a rotor shaft having a straight key, a drive end (DE) side bearing and a non-drive end (NDE) side bearing, wherein the rotor core is guided on the key integrated into the rotor shaft. [0024] In another embodiment of the present subject matter, the laminations are made of materials including silicon steel, CRNGO steel, cobalt steel.
[0025] In another embodiment of the present subject matter, the stack of the lamination is formed by wire cut electrical discharge method (EDM) with an angular displacement between two adjacent stacks of lamination. In another embodiment of the present subject matter, the the laminations are in form of a teeth and slot arrangement.
[0026] In another embodiment of the present subject matter, the the winding bars are short –circuited with end rings at each end of the rotor. [0027] In another embodiment of the present subject matter, the the rotor shaft is extended towards the drive end (NE) bearing to connect to a load. [0028] In another embodiment of the present subject matter, the wherein the rotor shaft is extended towards the drive non-drive end (NDE) bearing to connect to sensors.

[0029] In another embodiment of the present subject matter, the rotor bars and end rings are made of materials including aluminium or aluminium alloy or copper or copper alloy or copper-silver or copper-silver alloy. [0030] In another embodiment of the present subject matter, the winding is a squirrel cage rotor winding.
[0031] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0032] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0033] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter, and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0034] Figure 1 illustrates a schematic view of stack of laminations in accordance with an embodiment of the present disclosure;

[0035] Figure 2 illustrates a schematic view of rotor core assembly on dummy shaft in accordance with an embodiment of the present disclosure;
[0036] Figure 3 illustrates a top and side view a single rotor lamination of in accordance with an embodiment of the present disclosure;
[0037] Figure 4 illustrates a top and side view a single rotor bar of in accordance with an embodiment of the present disclosure;
[0038] Figure 5 illustrates a top and side view of a rotor end ring in accordance with an embodiment of the present disclosure;
[0039] Figure 6 illustrates a schematic view of rotor core assembly with end rings and bars in accordance with an embodiment of the present disclosure;
[0040] Figure 7 illustrates a cross –section schematic view of rotor assembly in accordance with an embodiment of the present disclosure;
[0041] Figure 8 illustrates a schematic view of skewed rotor assembly in accordance with an embodiment of the present disclosure;
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0042] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein are not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0043] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein

reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0045] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0046] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0047] The present disclosure discloses a novel a skewed caged rotor for a high speed induction motor. The casting-less skewed caged rotor comprises a rotor core comprising stack of laminations with a longitudinal skew, a winding with bars and end rings, a rotor shaft having a straight key, a drive end (DE) side bearing, and a non-drive end (NDE) side

bearing, wherein the rotor core is guided on the key integrated into the rotor shaft.
[0048] The laminations are made of materials including silicon steel, CRNGO steel, cobalt steel. The stack of the lamination is formed by wire cut electrical discharge method (EDM) with an angular displacement between two adjacent stacks of lamination. The laminations are in form of a teeth and slot arrangement. The winding bars are short –circuited with end rings at each end of the rotor. The rotor shaft is extended towards the drive end (NE) bearing to connect to a load. The rotor shaft is extended towards the drive non-drive end (NDE) bearing to connect to sensors. The rotor bars and end rings are made of materials including aluminium or aluminium alloy or copper or copper alloy or copper-silver or copper-silver alloy. Further, the outer surface of the rotor has a micron sized surface finish with atleast a gap of 100 micron between stator and rotor. The winding is a squirrel cage rotor winding.
[0049] The present rotor also provides for a casting-less skewed caged rotor having rotor core manufactured through wire cut using electrical discharge method from a single stack of laminations made of high electrical resistivity and high magnetic permeability based material which is not limited to silicon steel, CRNGO steel, cobalt steel or similar materials.
[0050] The present squirrel cage type configuration has been achieved with a manufacturing process of assembling the pre-fabricated bars and end rings in the rotor core slots which does not employ any casting. This different manufacturing process has also been adopted to do away with any type of casting defects like pin holes or blow holes etc.
TECHNICAL ADVANTAGES:
[0051] The present skewed caged rotor does not have any casting defects like pin-holes or blow holes.

[0052] The present skewed caged rotor has a robust configuration and required lesser maintenance.
[0053] The rotor outer surface has been grinded to micron-size tolerances to achieve required surface roughness. The super smooth rotor surface thus achieved not only helps in achieving stringent airgap tolerances but also helps in achieving better operational power factor.
[0054] The present skewed caged rotor has lower operational vibration levels and larger mean time between failures (MTBF).
[0055] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0056] With reference to Figure 1 to Figure 8, the present disclosure discloses a casting-less skewed caged rotor 700 of a high speed induction motor.
[0057] With reference to Figure 1 illustrating stack of laminations in the rotor, the present subject matter discloses that a stack is created by pressing the required number of laminations and then welding 102 at all four corners. Later on, this bunch is loaded for wire cutting using electrical discharge method (EDM). The single strand electrical discharge method (EDM) wire 104 is fed in a particular direction 105 to create the rotor profile 103.
[0058] With reference to Figure 2 illustrating the assembly of rotor core on dummy shaft 201. After the wire cutting, the rotor stack is assembled on a dummy shaft 202 with the help of washer 203 and nut 204 on each

end of the shaft. The skewed lamination teeth 205 and slot openings 206 are visible on the stack surface.
[0059] With reference to Figure 3 illustrating a single rotor lamination 301 with top view and side view. The lamination has slots 302 and teeth 303 arrangement. On top of each rotor slot, there is a slot opening 304. Rotor slot has top 305 and bottom 306 profile matching with rotor bar profile with stringent tolerances. The central space 308 of lamination is used for inserting the shaft. The central space has a rectangular key way 307 for guiding the rotor stack on corresponding key on the rotor shaft. The inner surface 310 of the lamination sits on the rotor shaft with stringent tolerance. The outer surface 309 of the lamination is airgap length apart from the stator bore of the motor.
[0060] With reference to Figure 4 illustrating a single rotor lamination 301 with top view and side view. The lamination has slots 302 and teeth 303 arrangement. On top of each rotor slot, there is a slot opening 304. Rotor slot has top 305 and bottom 306 profile which shall match with rotor bar profile with stringent tolerances. The central space 308 of lamination is used for inserting the shaft. The central space also has a rectangular key way 307 for guiding the rotor stack on corresponding key on the rotor shaft. The inner surface 310 of the lamination sits on the rotor shaft with stringent tolerance. The outer surface 309 of the lamination is airgap length apart from the stator bore of the motor.
[0061] With reference to Figure 5 illustrating a rotor end ring 501 with top view and side view. There are two end rings which electrically short circuit each bar of the rotor assembly on each end of the core. This way the squirrel cage rotor winding is realized. The rotor end ring has slots 502 and teeth 503 arrangement similar to lamination. On top of rotor end ring, there is a slot opening 504. The inner surface 506 of the rotor end ring does not touch the shaft. The outer surface 505 of the end ring is airgap length apart from the stator bore of the motor.

[0062] With reference to Figure 6 illustrating the rotor core assembly 601 with end rings and bars. After assembly of the rotor core on dummy shaft 606, rotor bars 605 are inserted inside each slot. Then, end rings 604 are placed on each side of the core. Thereby the end rings electrically short circuit each bar of the rotor assembly on each end of the core. This makes a pre-final assembly of the rotor. At this stage, a visual inspection can be carried out to see the proper assembly of the rotor along with skewed lamination teeth 603 and slot openings 602 on the surface of rotor assembly. Later on, the end rings are brazed using parent material (as that of bars and end rings) as filler material. After completion of brazing, each surface of the rotor is grinded to micron size finish, especially the rotor outer surface.
[0063] With reference to Figure 7 ad 8 illustrating the cross-section of complete rotor assembly. After grinding, the rotor core 701, 801 is guided on the straight key integrated to the rotor shaft 703, 803. The rotor core has skewed teeth and slot openings on the micron size finish outer surface 710, 810. The (3) bars of the rotor are short-circuited at each end of the rotor with end rings 702, 802. The rotor core assembly is guided on the shaft until core assembly touches the step 704, 804 provided on shaft for this purpose. Similarly, (4) drive end (DE) and (5)non-drive end (NDE) side bearings 708,808, 707, 807 are fitted on the shaft till inner race touches their respective steps 706,806 705, 805. On DE side, the shaft is extended 709, 809 for connecting it to the load, whereas on NDE side, it is extended 711, 811 for connecting it to sensors.
[0064] Working of invention
[0065] The present invention relates to a casting-less skewed caged rotor of a high speed induction motor. The rotor has electrically conducting copper bars placed in the rotor slots and short circuited at each end of the rotor core. When the balanced multi-phase stator winding is excited by a balanced muti-phase voltage source, a rotating flux is established in the

machine. This flux, when interacts with the rotor bars, makes the rotor spin on its bearings.
[0066] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the

terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0067] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0068] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations, which fall within the scope of the present subject matter.
REFERENCE NUMERALS:

Reference Numeral Description
101 Stack of laminations
102 Welding joint
103 Rotor outer profile
104 Single strand EDM wire
105 EDM wire feed direction
201 Finished rotor stack
202 Dummy rotor shaft
203 Washer
204 Nut
205 Skewed slot opening
206 Skewed laminations teeth
301 Single rotor lamination
302 Rotor slot
303 Rotor teeth
304 Rotor slot opening
305 Rotor slot top profile
306 Rotor slot bottom profile
307 Keyway
308 Space for rotor shaft
309 Rotor lamination outer surface
310 Rotor lamination inner surface

401 Rotor bar
402 Rotor top profile
403 Rotor bar bottom profile
501 End ring
502 End ring slot
503 End ring teeth
504 End ring slot opening
505 End ring outer surface
506 End ring inner surface
601 Rotor core assembly
602 Skewed slot opening
603 Skewed teeth
604 End ring
605 Rotor bars
606 Dummy shaft
700 Rotor
701 Rotor core
702 winding with bars and end rings
703 Rotor shaft
704 Step for rotor core placement
705 Step for NDE bearing placement
706 Step for DE end bearing placement
707 non-drive end (NDE) side bearing

708 Drive end (DE) bearing
709 Shaft extension for connecting it to load
710 Rotor core outer surface
711 Rotor shaft extension at NDE side
801 Skewed rotor core assembly
802 Skewed rotor teeth
803 Skewed rotor slot openings
804 End ring
805 Rotor shaft
806 NDE bearing
807 DE bearing
808 Shaft extension for connecting it to load
809 Rotor Shaft extension at NDE side
810 Sensors

We Claim:
1. A skewed caged rotor (700, 800) for a high speed induction motor, the
rotor (100) comprises:
a rotor core (701, 801) comprising stack of laminations with a longitudinal skew;
a winding with bars and end rings (702, 802);
a rotor shaft (703, 803) having a straight key;
a non-drive end (NDE) side bearing (707, 807); and
a drive end (DE) side bearing (708, 808),
wherein the rotor core (701, 801) is guided on the key integrated into the rotor shaft (703, 803) and the rotor core (701, 801) comprises a step (704, 804) for rotor core placement.
2. The rotor as claimed in claim 1 , wherein the laminations are made of materials including silicon steel, CRNGO steel, cobalt steel.
3. The rotor as claimed in claims 1 to 2, wherein the stack of the lamination is formed by wire cut electrical discharge method (EDM) with an angular displacement between two adjacent stacks of lamination.
4. The rotor as claimed in claim 1 to 3, wherein the laminations are in form of a teeth and slot arrangement.
5. The rotor as claimed in claims 1 to 4, wherein the winding bars are short –circuited with end rings (702, 802) at each end of the rotor (700, 800).

6. The rotor as claimed in claims 1 to 5,wherein the rotor shaft (703, 803)
is extended towards the drive end (NE) bearing (708, 808) to connect to a
load.
7. The rotor as claimed in claims 1 to 6,wherein the rotor shaft is
extended towards the drive non-drive end (NDE) bearing (707, 807) to
connect to sensors.
8. The rotor as claimed in claims 1 to 7, wherein the rotor bars and end rings (702) are made of materials including aluminium/aluminium/alloy/copper / copper alloy / copper-silver / copper-silver alloy.
9. The rotor as claimed in claims 1 to 8, wherein outer surface of the rotor (700, 800) has a micron sized surface finish with atleast a gap of 100 micron between stator and rotor.
10. The rotor as claimed in claims 1 to 10, wherein the winding is a
squirrel cage rotor winding.