DESC:FIELD OF THE INVENTION

The present disclosure relates generally to permanent magnet synchronous motors for use in submersible pumps systems. More particularly, the present invention disclosure relates to a new and improved rotor assembly for permanent magnet synchronous motors for use in submersible pump-sets having a rotor with one or more inserted permanent magnets and method(s) related thereto. In particularly, the present disclosure relates to an improved rotor assembly that provides improved magnet assembly, magnet protection and easy replacement of magnets against submersible pump use conditions.

BACKGROUND OF THE INVENTION

A permanent magnet synchronous motor uses permanent magnet(s) to provide excitation, so that the structure of motor be simpler, the processing and assembling cost is reduced, a collecting ring and an electric brush which cause a problem are omitted and the running reliability of the motor is improved. For such a design of permanent magnet synchronous motor, excitation current is not needed, excitation loss is avoided, efficiency and power density of the motor are improved.

The permanent magnet synchronous motor usually comprises a stator, a rotor and bearing housings. The rotor of the permanent magnet synchronous motor is divided into surface mounted type and a buried type. For both types of rotor design, the sealing of magnet is very important. As per the design of synchronous permanent magnet motor, rotor is submerged in water and there is a possibility for ingress of water or moisture in the cavity where magnet is inserted or mounted within the rotor. For the efficient working of the motor, it is necessary that all magnets are protected from the ingress of water or moisture to avoid any corrosion during operation.

However, the contemporary permanent magnet synchronous motors are fitted with a rotor having slots wherein magnets are inserted. To avoid ingress of water or moisture both the ends of such a rotor are usually sealed by filling liquid resin which solidify sealing both such ends. In case, if the motor gets burned and due to high temperature, the permanent magnets get damaged or if the performance of the motor gets deteriorated then it becomes necessary to change all such magnets and to refurbish the rotor. However, in such situations, the magnets of such contemporary motors cannot be changed without destroying the rotor or if any attempt is made to change the magnets the same results in damaging the rotor. In such a situation, the user or customer of the motor has no choice but to replace the whole rotor assembly. Moreover, the servicing of such damaged motor is a costly affair.

Further, the existing permanent magnet synchronous motor consists of rotor having cavity for the insertion of magnets in it. Both ends of the rotor are usually sealed or filled with mixtures of resin and hardener in liquid forms which solidify when cured. The curing time for the resin mixture takes a minimum of eight hours at ambient temperature which decreases the overall productivity. In case the motor fails to work or faces any problem during operation due to any reason. In such a situation and in case of servicing or repairing of motor, if one wants to replace the rotor, it is not feasible to remove the solidified resin mixture and to replace the magnet in the rotor. Usually, in such a condition, the motor becomes non-reusable.

If the magnets are not sealed properly and when they get in contact with water during use, the same will get rusted over a period. Day by day the rust will eventually degrade and harm the magnet microstructure and such magnets become powder which results in degradation of magnetic property which in turn affects overall performance of the motors.

Thus, it is intended to provide a new and improved rotor assembly for permanent magnet synchronous motors for underwater use and process(s) relating to same addressing all the foregoing shortcomings.

OBJECTS OF THE INVENTION

It is a primary object of the subject disclosure to provide a new and improved rotor assembly for permanent magnet synchronous motors for use in submersible pump-systems for underwater use, overcoming the shortcomings of the existing motors.

Another object of the present disclosure is high-efficiency permanent magnet synchronous motors for use in a submersible pump system that provides improved protection for the permanent magnets of the motor mounted on the rotor assembly, as well as enhanced durability for the rotor assembly.

Another object of the present disclosure is to provide a new and improved rotor assembly for permanent magnet synchronous motors for submersible pump-sets which operate on solar as well as grid supply via variable frequency drive (VFD’s). With the innovative rotor design, the submersible pump set of the present invention ensures delivery of constant water flow at defined voltage with higher efficiency.

Another object of the present disclosure is to provide a new and improved rotor assembly for permanent magnet synchronous motors having improved means and arrangement of sealing for the protection of permanent magnets from water ingress or moisture during use.

Another object of the present disclosure is to provide a new and improved rotor assembly for permanent magnet synchronous motors wherein the magnets can be replaced easily without any destruction or damaging of the motor. Thus, the improved design and construction of the rotor assembly ensure that the replacement of permanent magnets becomes feasible in the rotor assembly.

Another object of the subject disclosure is to provide a new and improved submersible pump-set having a new rotor design including sealing means and arrangements and slot profile.

A further object of the subject disclosure is to provide a new and improved rotor assembly for permanent magnet synchronous motors for submersible pump-sets which is not only cost effective but also increases overall pump set efficiency as well as saves electrical energy/consumption.

It is another object of the subject disclosure to provide an improved method of construction of an improved rotor assembly for permanent magnet synchronous motors for submersible pump-sets which helps in cost reduction including reduction in the product cost as well as operating cost.

SUMMARY OF THE INVENTION

The subject disclosure, thus, provides a new and improved rotor assembly for permanent magnet synchronous motors for use in submersible pump-sets having a rotor with one or more inserted permanent magnets.

The new and improved rotor assembly for permanent magnet synchronous motors for use in submersible pump-sets of the present disclosure is a rotating equipment vertical in construction. The permanent magnet synchronous motors having the improved rotor assembly of the present disclosure works on the principle of synchronous motor. Variable/constant input power supply is provided to the stator which generates rotating electromagnetic field that will be interlocked with constant magnetic field created by magnetic rotor which results in achieving the synchronous speed.

Accordingly, one aspect of the subject disclosure relates to a submersible pump-set for underwater use for supply of water comprising: a motor including a stator; a rotor assembly; a common casing enclosing the stator and the rotor assembly; a power supply connected to the motor to commutate and control the speed and torque of the motor during operation of the submersible pump-set, wherein the rotor assembly supported by a bearing housing sub-assembly and enclosed by said stator.

Another aspect of the subject disclosure relates to a new and improved rotor assembly for permanent magnet synchronous motors for use in submersible pump-sets, the rotor assembly comprising: a rotor shaft, a rotor stack press fitted on the rotor shaft, one or more permanent magnet bars fixedly inserted within the rotor stack, at least a pair of first and second sealing gaskets each having a central opening to seal and hold the permanent magnet bars within the rotor stack and at least a pair of first and second balancing rings each having a central opening shrink and/or interference fitted to seal and hold the sealing gaskets in place against the rotor stack protecting the permanent magnet bars from water or moisture for a long life ensuring effective working of the rotor assembly.

Another aspect of the subject disclosure relates to a method of construction of an improved rotor assembly for permanent magnet synchronous motors, the method comprising the steps of: inserting a rotor shaft with interference fit within a rotor stack through a bore provided in center of the rotor stack; applying few drops of a retaining adhesive on the outer diameter of the rotor shaft; machining the rotor fitted shaft to maintain outer diameter of rotor stack as per the required dimension to maintain the radial clearance between stator stack and rotor stack for free rotation; cleaning outer surface of the rotor stack with a shot blasting process; painting the rotor stack and keeping the rotor stack for a specified time at a specified temperature in an oven for the baking of paint; arranging the painted rotor shaft vertically on a fixture; inserting magnets in the cavities of the rotor stack in both the upper and lower ends thereof and sealing the magnets inserted in the rotor stack from both the ends.

The step of inserting magnets includes insertion of a plurality of fiber made sunk keys at both sides of the magnet to fill the cavities/slots in the rotor stack.

The step of sealing magnets includes insertion of a first and second sealing gaskets from upper and lower side of the rotor shaft being kept in resting position facing the magnets.

The step of sealing magnets includes insertion of a first and second balancing rings from the upper and lower sides of the rotor shaft such that to rest on the first and second sealing gasket creating a sealed arrangement.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

The foregoing and other objects, features, and advantages of the disclosure will be apparent from the following description taken in conjunction with the accompanying drawing, wherein:

Fig. 1 illustrates a cross-sectional view of a submersible motor of the submersible pump-set of the present disclosure;

Fig. 2A illustrates an exploded view of the rotor assembly of the submersible motor of Fig. 1;

Fig. 2B illustrates the rotor assembly of Fig. 2A in assembled form;

DETAILED DESCRIPTION OF THE INVENTION

Aspects of the presently disclosed disclosure will now be described in detail with reference to the drawings wherein like reference numerals designate identical or corresponding elements. In the drawings and in the description, the term "proximal", "bottom", "down" or "lower" refers to a location on the device that is closest to a user holding the device and/or any part thereof. Conversely, the term "distal", "top", "up" or "upper" refers to a location on the device that is farthest from the user holding the device and/or any part thereof.

As used herein, the terms first, second, third, etc. are understood to describe different structures/elements so as to distinguish one from another. However, the terms are not structurally limiting unless the context indicates otherwise.

Moreover, the Figures may show simplified or partial views, and the dimensions of elements in the Figures may be exaggerated or otherwise not in proportion for clarity. In addition, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a terminal includes reference to one or more terminals. In addition, where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements.

The present disclosure relates to a new and improved submersible pump-set for underwater use for supply of water. It is to be understood that being submerged in water, for example within a well, the submersible pump set of the present disclosure can be submerged in water for a variety of purposes/applications.

Referring to Fig. 1, a cross-sectional view of a motor 22 of the submersible pump-set of the present disclosure is illustrated. The portion of the motor 22 shown in Fig. 1 is mainly limited to features of the motor 22 which forms part of a submersible pump set. The motor 22 includes a generally cylindrical shaped casing 36. The casing 36 may be formed of any generally rigid and durable material.

The motor 22, thus, comprising a casing 36 that extends along an axial direction A and defines an interior chamber, a stator 38 enclosed by said casing 36, a rotor assembly 10 supported by a bearing housing sub assembly 48,46 and enclosed by said stator 38. A plurality of stator winding are coiled to form the stator 38. The stator stack is a bunch of electrical steel laminations being wounded with poly wrap copper wire.

A power supply is transmitted to the motor by a conductive line that communicates with an electrical outlet or other external source of electrical energy (not shown) to commutate and control the speed and torque of the motor during operation of the submersible pump set. When the motor is energized by the electrical energy, the motor operates the pump to impart sufficient force on the water source to pump the water or pipe out through a discharge conduit (not shown).

The embodiment shown in Fig. 1 includes a pair of bearing housing sub assemblies, i.e. an upper bearing housing sub assembly 48 and a lower bearing housing sub assembly 46. Each bearing housing sub assembly 48, 46 located at opposite ends of the motor 22 along the ends of an axial direction A and the rotor assembly 10 coupled to the rotor shaft 12 arranged in between bearing bushes 44 arranged therein. The bearing assemblies 48, 46 can be any type of bearing assembly that can rotatably support the rotor shaft 12. A thrust bearing housing 50 adjoins the lower bearing housing sub-assembly 46. A thrust bearing 42 is arranged within the thrust bearing housing 50. The thrust bearing 42 resists axial movement of the rotor shaft 12 i.e. the drive shaft during operation of the motor 22. Thrust bearing 42 of the disclosure include two elements wherein one is rotating and another is stationary. The rotating element which is of carbon material is in a disc form whereas the stationary element is of stainless steel material pivoted with the thrust bearing housing 50. A circular flexible diaphragm 54 extends across a circular opening 56 in the thrust bearing housing 50 which helps in balancing the pressure inside the motor 22 and external pressure in bore well. A cover plate over the diaphragm 54 retains the diaphragm 54 in a position which prevent leakage of fluid from the motor 22.

The upper bearing housing sub assembly 48 is connected to one end of the casing 36 and the lower bearing housing sub assembly 46 is connected to the other end of the casing 36. The sub-assemblies 48, 46 enclose the interior of the motor 22 at each end, an aperture 52 formed in at least one of the sub- assemblies 48, 46 which allows the rotor shaft 12 i.e. the drive shaft to extend from within the rotor chamber to the pump unit (not shown) which is arranged externally of the casing 36. The interior of the motor 22 can be filled with a liquid which is maintained at the same pressure as the liquid in which the motor 22 is submerged. One or more sealing rings 40 may be provided adjacent to the aperture 52 in the sub assemblies 48, 46 through which the rotor shaft 12 i.e. the drive shaft extends. The one or more sealing rings restrict the flow of water through the aperture 52 and into the interior of the casing 36 and it also retains the liquid inside the motor.

Referring now to Figs. 2A & 2B, a rotor assembly 10 for permanent magnet synchronous motors for use in the motor (22) of the submersible pump-systems is illustrated, the rotor assembly 10 comprising a rotor shaft 12 having opposite ends being integral therewith extending in an axial direction A, a rotor stack 14 press fitted on the rotor shaft 12, one or more permanent magnet bars 24 fixedly mounted within the rotor stack 14. The rotor shaft 12 including a drive shaft at the distal most top end. The rotor stack 14 having a bore 58 in center. The rotor shaft 12 is inserted with interference fit within the rotor stack 14 through the bore 58. The complete rotor stack 14 is coated with corrosion resistant paint. The rotor shaft 12 including the drive shaft end having spline teeth suitable for NEMA coupling and is a rotating element on which the rotor stack 14 is mounted. The rotor shaft 12 holds the rotor stack 14 centrally. Both the rotor shaft 12 and rotor stack 14 having a proximal end 16 and a distal end 18. One or more cavities 20 are provided on the rotor stack 14 passing internally therethrough the entire length of the rotor stack 14 and opening from both the proximal 16 and distal 18 ends thereof. The rotor assembly 10 supported within a rotor chamber such that the stator 38 extends around and is coaxial with the rotor assembly 10. It is to be understood that the rotor stack 14 is a bunch of electric steel laminations.

In the embodiment shown in Figs. 2A & 2B, the rotor stack 14 is provided with at least four cavities 20 being arranged in an equi-spaced manner from each other having an internal profile. Further, as can be seen the cavities 20 are arranged in pairs i.e. each pair of cavities 20 face each other being 90 degrees apart for the insertion of the permanent magnets. However, the position of cavities 20 are not limited to any such specific arrangement and may vary in alternative embodiments. At least four permanent magnet bars 24 are fixedly received within said holes or cavities 20 for the entire full length of the rotor stack 14. The magnet bars 24 create paths for magnetic field that interacts with stator winding to generate the torque during operation. The permanent magnet bars 24 are configured having a profile which corresponds with the internal profile of the cavities 20 ensuring a close-fit fitment of the permanent magnet 24 within the cavities 20. In one of the embodiments, the permanent magnet bars 24 are preferably neodymium magnets also known as NdFeB, NIB or Neo permanent magnets and are inserted within the cavities 20 considering and taking into account the poles of the motors. It is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. The permanent magnet of the present disclosure enables the motor 22 to generate torque at zero speed.

At least a pair of first 26 and second 28 sealing gaskets each having a central opening 30 are aligned on both the sides of rotor stack 14 through the proximal 16 and distal end 18 of the rotor shaft 12 is inserted to seal and hold the permanent magnet bars 24 within the cavities 20. The sealing gaskets 26, 28 being circular in shape are continuous filament woven fiber glass bonded with flame resistant epoxy resin gaskets which prevent the entry of moisture or water during use inside the cavities 20 where permanent magnet bars 24 are mounted ensuring a long life and effective use of the rotor assembly 10. The sealing gaskets 26, 28 are, thus, flame and water proof which protect the permanent magnet bars 24 from ingress of water or moisture. Alternatively, the sealing gaskets 26, 28 can also be made of Teflon. It is to be understood that the sealing gaskets 26, 28 are made of such materials which has excellent mechanical, electrical and physical properties at elevated temperature for example, at 130°C.

At least a pair of first 32 and second 34 balancing rings each having a central opening 30 are aligned on both the sides of sealing gaskets 26, 28 through the proximal 16 and distal end 18 of the rotor shaft 12 and shrink and/or interference fitted to seal and hold the sealing gaskets 26, 28 in place against the rotor stack 14 through the shrink and/or interference fitment of the sealing gaskets 26, 28. The balancing rings 32, 34 thus being arranged abuts the proximal and distal faces of the rotor stack 14 on both sides thereof. With the fitment of balancing rings 32, 34 the permanent magnet bars 24 are fully protected from water or moisture for a long life ensuring effective working of the rotor assembly 10. Both the ends of rotor stack 14 are sealed with sealing gaskets 26, 28 and the sealing gaskets are retained in position by shrink fitted balancing rings 32, 34. For ensuring a rotating shaft 12 being dynamically balanced unbalanced material is removed from balancing rings 32, 34. Alternatively, both the ends of rotor stack 14 may also be sealed through resin filling in the cavities 20 from both the sides thereof.

Thus, the rotor stack 14 of the present disclosure is sealed with sealing gaskets 26, 28 from both sides. In case of the motor facing any issues with the permanent magnet bars 24 impacting the working of the motor, the same can be easily removed, repaired and, if the need arises, replaced by another set of permanent magnet bars 24 during the servicing or repairing of the rotor assembly 10. The disclosed sealing arrangement, therefore, leads to an increase in the life of the magnet bars 24, avoid demagnetization of magnet bars 24 and makes the rotor assembly 10 reusable for magnet replacement.

As is known in the art of electrical motors, electrical energy conducted by the stator windings generates an electromagnetic force that induces rotation of the rotor within the rotor chamber. The rotor shaft 12 operatively coupled to the rotor stack 14 such that the rotation of the rotor stack 14 imparts a force causing rotation of the rotor shaft 12 i.e. the drive shaft, which extends through the aperture 52 in an end wall 50 of the motor 22.

A method of construction of the rotor assembly 10 according to the present disclosure includes the steps of inserting a rotor shaft 12 with interference fit within a rotor stack 14 through a bore 58 provided in center of the rotor stack 14. The rotor stack 14 having at least four uniform slots /cavities 20 at 90 degree apart for the insertion of permanent magnets. For the robustness of the fitment of the rotor shaft 12 few drops of a retaining adhesive for example, lubricant Loctite 638 is applied on the outer diameter of the rotor shaft 12. The rotor shaft 12 is, thus, now fitted with the rotor stack 14. Thereafter, the rotor fitted shaft 12 is machined to maintain outer diameter of rotor stack 14 as per the required dimension which is necessary to maintain the radial clearance between stator 38 stack and rotor stack 14 for free rotation. Since the rotor stack 14 is submerged in water in order to protect the outer surface of rotor stack 14 from corrosion a special paint process is followed. Prior to paint, outer surface of the rotor stack 14 is prepared with shot blasting process to clean the same from any oil, rust, dust etc which makes the surface of the rotor stack 14 more effective for adhesion of the paint. Thereafter, the duly painted rotor stack 14 is kept for a specified time at a specified temperature in an oven for the baking of paint.

Thereafter, the duly painted rotor shaft 12 is kept vertically on a fixture and all the magnet bars 24 are inserted in the cavities 20 of the rotor stack 14 in both the upper and lower ends thereof. A plurality of fiber made sunk keys are inserted at both sides of the magnets 24 to fill the cavities/slots in the rotor stack 14. In an embodiment, at least eight sunk keys are inserted at both sides of the inserted magnets.

In order to further seal the magnets 24 inserted in the rotor stack 14, a first and second sealing gaskets 26, 28 are inserted from upper and lower side of the rotor shaft 12 and kept in resting position facing the magnets 24. The sealing gaskets 26, 28 are preferably resign gaskets. Thereafter, a first and second balancing rings 32, 34 are inserted from the upper and lower sides of the rotor shaft 12 such that to rest on the first and second sealing gasket 26, 28 creating a sealed arrangement. Prior to inserting, the balancing rings 32, 34 are heated. The balancing rings 32, 34 are, thus, now shrink fitted on the rotor shaft 12. The balancing ring 32, 34 together with the sealing gaskets 26, 28 keep in retaining position and protect the magnets from the ingress of water / moisture from the both the sides of the rotor stack 14 of the rotor assembly 10.

Same process is thus followed for the fitment of sealing gaskets and balancing rings on both the ends of the rotor stack 14 where magnets inserted in the cavities are fully sealed and well protected from ingress of water/moisture.

The embodiments of the disclosure include removable connections which can be established with mechanical fasteners such as screws, bolts, compatible threaded portions, and other fasteners that can be removed and replaced.

From the foregoing description, it will be appreciated that new and improved motor of the submersible pump-set of the present invention represents a significant improvement over the prior art. While preferred embodiment(s) of the new and improved motor of the submersible pump-set and the process for manufacturing the same has been disclosed, it should be further appreciated that modifications may be made without departing from the scope of the present invention. In addition, while various features and components have been disclosed in an exemplary fashion, various other features and components may be employed. It is intended by the foregoing to cover these and any other departures from these disclosed embodiments which fall within the true spirit of this invention.

Thus, it is intended that the scope of the present invention herein disclosed should not be limited by disclosed embodiments described above but should be determined only by a fair reading of complete specification and claims to follow.

List of reference numerals

10 rotor assembly
12 rotor shaft
14 rotor stack
16 proximal end
18 distal end
20 cavity
22 motor
24 permanent magnet bars
26 first sealing gasket
28 second sealing gasket
30 opening
32 first balancing ring
34 second balancing ring
36 casing
38 stator with winding
40 oil seal
42 thrust bearing
44 bearing bush
46 lower bearing carrier sub-assembly
48 upper bearing housing sub-assembly
50 thrust bearing housing
52 aperture
54 diaphragm
56 circular opening
58 rotor stack bore
A axial direction
,CLAIMS:WE CLAIM:

1. A submersible pump-set for underwater use for supply of water comprising:
a motor (22) including a stator (38);
a rotor assembly (10);
a common casing (36) enclosing the stator (38) and the rotor assembly (10);
a power supply connected to the motor (22) to commutate and control the speed and torque of the motor (22) during operation of the submersible pump-set, wherein the rotor assembly (10) supported by a bearing housing sub assembly and enclosed by said stator (38).

2. The submersible pump-set as claimed in claim 1, wherein the rotor assembly (10) comprises a rotor shaft (12) having opposite ends being integral therewith, a rotor stack (14) having a bore (58) in center, a pair of sealing gaskets (26, 28) aligned on both the sides of rotor stack (14) and a pair of balancing rings (32, 34) aligned on both the sides of sealing gaskets (26, 28).

3. The submersible pump-set as claimed any of the preceding claims, wherein the bearing housing sub assembly comprising an upper bearing housing sub assembly (48) and a lower bearing housing sub assembly (46) located at opposite ends of the motor (22) along an axial direction A and wherein rotor assembly (10) coupled to the rotor shaft (12) arranged in between bearing bushes (44).

4. The submersible pump-set as claimed in claim 3, wherein the upper bearing housing sub assembly (48) connected to one end of the casing (36) and the lower bearing housing sub assembly (46) connected to the other end of the casing (36).

5. The submersible pump-set as claimed in any of the preceding claims, wherein a thrust bearing housing (40) adjoins the lower bearing housing sub-assembly (46) and wherein a thrust bearing (42) arranged within the thrust bearing housing (40).

6. The submersible pump-set as claimed in claim 5, wherein a circular flexible diaphragm (54) extends across a circular opening (56) in the thrust bearing housing (50) which helps in balancing the pressure inside the motor (22) and external pressure in bore well.

7. The submersible pump-set as claimed in claim 2, wherein the rotor stack (14) having one or more cavities (20) passing internally therethrough the entire length of the rotor stack (14).

8. The submersible pump-set as claimed in claim 2, wherein the cavities (20) are arranged in pairs in that each pair of cavities (20) face each other being 90 degrees apart.

9. The submersible pump-set as claimed in claim 2, wherein one or more permanent magnet bars (24) fixedly received in said cavities (20) wherein the permanent magnet bars (24) configured having a profile which corresponds with an internal profile of the cavities (20) ensuring a close-fit fitment of the permanent magnet bars (24) within the cavities (20).

10. A method of construction of the rotor assembly (10) comprising the steps of:
inserting a rotor shaft (12) with interference fit within a rotor stack (14) through a bore (58) provided in center of the rotor stack (14);
applying few drops of a retaining adhesive on the outer diameter of the rotor shaft (12);
machining the rotor fitted shaft (12) to maintain outer diameter of rotor stack (14) as per the required dimension to maintain the radial clearance between stator (38) stack and rotor stack (14) for free rotation;
cleaning outer surface of the rotor stack (14) with a shot blasting process;
painting the rotor stack (14) and keeping the rotor stack (14) for a specified time at a specified temperature in an oven for the baking of paint;
arranging the painted rotor shaft (12) vertically on a fixture;
inserting magnets (24) in the cavities (20) of the rotor stack (14) in both the upper and lower ends thereof and sealing the magnets (24) inserted in the rotor stack (14) from both the ends.

11. The method of construction of the rotor assembly (10) as claimed in claim 10, wherein the step of step of inserting magnets (24) includes insertion of a plurality of fiber made sunk keys at both sides of the magnet (24) to fill the cavities/slots in the rotor stack (14).

12. The method of construction of the rotor assembly (10) as claimed in claim 11, wherein the step of sealing magnets (24) includes insertion of a first and second sealing gaskets (26, 28) from upper and lower side of the rotor shaft (12) being kept in resting position facing the magnets (24).

13. The method of construction of the rotor assembly (10) as claimed in claim 11, wherein the step of sealing magnets (24) includes insertion of a first and second balancing rings (32, 34) from the upper and lower sides of the rotor shaft (12) such that to rest on the first and second sealing gasket (26, 28) creating a sealed arrangement.