TECHNICAL FIELD

The present invention relates to a rotor for an electric machine. For example the rotor can be used for synchronous machines, asynchronous machines, etc; in addition the electric machine can be a generator or a motor. In the following particular reference to a synchronous or asynchronous generator is made.

BACKGROUND

Rotating electric machines such as electric generators are known to comprise a stator and a rotor.

The rotor has an active part provided with coils and shafts extending from each of its two opposite ends. The shafts support the rotor via bearings and are connected to one or two prime movers such as for example gas or steam turbines; in addition the shafts can carry slip rings connected to an exciter.

Large machines such as large turbogenerators have the rotor (that includes the shafts and the active part) made out of either one monolithic forged piece, or a plurality of forged pieces connected (e.g. welded) together to define one monolithic piece. This single or monolithic piece is required for the rotor to withstand the large forces that urge it during operation; these forces are mainly: torque from the prime mover;

bending due to the rotor weight,

centrifugal forces due to the rotating coils.

Nevertheless, the rotors with the above-described structure are very expensive and time consuming to procure and manufacture.

To overcome these problems, US 2011/0 080 068 discloses a rotor having a laminated active part with shafts extending from its ends; the laminated part has slots that house coils.

One or more studs are provided to pack the laminations together and guarantee the required electrical and mechanical properties.

In addition, the laminated part is covered by a cylinder that helps to withhold the coils within the slots.

Mechanical forces (such as torque, bending and centrifugal forces) could be troubling for this rotor during operation (in particular for large rotors) .

In fact, transmission of the torque is achieved by friction between adjacent laminations (tanks to the compression exerted by the studs) .

It is anyhow clear that for large machines mechanical forces (in particular the torque) could be so large that the friction is not able to counteract them, causing the laminations constituting the laminated part to slide one above the other . SUMMARY

One aspect of the present disclosure is that of providing a rotor with a laminated part with a reduced risk that the laminations that constitute it slide one above the other .

This and further aspects, are attained by providing a rotor in accordance with the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will be more apparent from the description of a preferred but non-exclusive embodiment of the rotor illustrated by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a laminated part with shafts and discs of the rotor in an embodiment of the invention;

Figure 2 is a schematic perspective view of a cylinder to be applied around the laminated part and discs of figure 1;

Figure 3 is a schematic longitudinal cross section of the rotor;

Figures 4-7 show an enlarged cross section of one end of the laminated part in different embodiments of the invention;

Figures 8-10 show three possible embodiments of the rotor . DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The rotor 1 for an electric machine comprises a laminated part 2 with opposite ends 3, 4. The laminated part 2 has slots that house coils 5 (defining windings such as DC field windings for a synchronous machine, polyphase AC winding for an asynchronous machine, etc) .

In one example, the laminated part 2 includes a plurality of stacked laminations with press plates 6, 7 at its opposite ends 3, 4. The laminations have aligned holes defining seats for tightening bars 8 connected between the press plates 6, 7.

The laminated part 2 can also include concave shaped laminations 30 inserted at one (for example at an axial central position of the laminated part 2) or different axial positions. These concave shaped laminations 30 help to compensate for bending and ensure constant and uniform pressure in various operating conditions. In addition, these laminations 30 can be used for balancing, by choosing the thickness at the outside border sufficiently large for drilling balancing holes.

At each end 3, 4 of the laminated part 2 a shaft 9, 10 is provided; these shafts 9, 10 can be connected to a prime mover (for example a gas or steam turbine, in particular one or both shafts 9, 10 can be connected to a prime mover) or can be provided with slip rings, or can be connected to a different exciter, etc.

Each shaft 9, 10 has a disc 11, 12 connected to it; for example shafts and discs can be manufactured in one piece or can be manufactured in separated pieces that are then connected together.

Around the laminated part 2 a cylinder 15 is provided; advantageously, at each end 3, 4 of the laminated part 2, the cylinder 15 projects from the laminated part 2 and is connected to the disc 11, 12. In this respect the figures show that at the end 3 the cylinder 15 projects from the laminated part 2 and is connected to the disc 11 and likewise at the end 4 the cylinder 15 projects from the laminated part 2 and is connected to the disc 12.

The cylinder 15 is preferably made out of an electrically insulating material to limit eddy currents. For example the cylinder is made out of a composite material, such as carbon fibres impregnated with a resin that is then cured.

One or both discs 11, 12 can have the same diameter as the laminated part 2 (figures 4 and 5) or one or both discs

11, 12 can have diameter different (preferably smaller) than the diameter of the laminated part 2 (figures 6, 7) .

In order to connect the cylinder 15 to the discs 11,

12, preferably the discs 11, 12 have slots 17, and the ends of the cylinder 15 has protrusions 18 extending from its internal surface; the protrusions 18 are housed in the slots 17 of the discs 11, 12.

The slots 17 and the protrusions 18 preferably extend axially (i.e. parallel to the longitudinal axis 20 of the rotor 1.

In addition, the press plates 6, 7 can have slots aligned with the slots of the laminated part 2 and preferably also the slots 17 of the discs 11, 12 are aligned with the slots of the laminated part 2.

The number of slots 17 of the discs 11, 12 is preferably also equal to the number of slots of the laminated part 2.

In a preferred embodiment, the cylinder 15 has protrusions 18 extending over its whole length. Each protrusion 18 has a portion housed in a slot 17 of one disc 11, a portion housed in a slot 17 of the other disc 12, and a portion resting against a coil 5 in a slot of the laminated part 2.

Naturally also other kinds of connections between the cylinder 15 and the discs 11, 12 are possible, such as for example a shrunk connection or a connection by screws or bolts or glue (that could also be the impregnating resin of the carbon fibres) .

In addition, the laminated part 2 (i.e. one or both press plates 6, 7) can also be connected to spindles 22 in turn connected to the discs 11, 12. The spindles 22 can be made in a separate piece or in one piece with the press plates 6, 7 and/or discs 11, 12.

In this respect different embodiments are possible.

In a first example one end 3 or 4 of the laminated part 2 can be provided with the spindle 22 and the other end 4 or 3 is not provided with the spindle 22 (e.g. figure 8) .

In a second example both ends 3, 4 can be provided with the spindle 22 (e.g. figure 9) .

In a third example none of the ends 3, 4 has the spindle 22.

The spindle 22 can not be provided or when provided can have a small diameter because the cylinder 15 withstand the most of the mechanical forces; when present, the spindle 22 helps to assemble the rotor.

The coils 5 protrude from the ends 3, 4 of the laminated part 2 defining end windings 23 that are housed within the cylinder 15; since the coils 5 could need cooling, the zones within the cylinder 15 at the ends 3, 4 could need cooling.

For this reason, the discs 11, 12 can have apertures

25 for a cooling gas. The apertures 25 can be axial, axial- radial (preferably converging towards the laminated part 2) or axial tangential apertures or axial-radial-tangential apertures and can also have an aerodynamic shape to help gas circulation.

For the same cooling reason, the cylinder 15 can have its lateral surface provided with apertures 26 for a cooling gas either circulating within the laminated part 2 (for example according to a traditional cooling scheme) or not (i.e. the apertures 26 can be located at the ends 3, 4) .

The end windings 23 urge the cylinder 15 with large forces that, according to the particular kind of electric machine, can be concentrated in particular positions; for example in case the rotor 1 is part of a two-pole synchronous generator, the end windings are concentrated about the two poles and the forces that the cylinder 15 has to withstand are likewise concentrated about them.

For this reason, parts of the cylinder 15 encircling the end windings 23 can have additional stiffening elements .

The additional stiffening elements can be of different kind such as, for example, an enlarged part of the cylinder 15 or additional stiffening elements (for example increased carbon fibres) embedded within the cylinder 15; anyhow, the additional stiffening elements preferably include rings 27 applied onto the cylinder 15 around a zone of the cylinder housing or enveloping the end winding 23. These rings 27 can have the same structure as the cylinder 15 or a different structure.

The cylinder 15 can be mounted onto the laminated part

2 and discs 11, 12 in different ways. In a first example the cylinder 15 can be manufactured separately from and then shrunk on the laminated part 2 and discs 11, 12.

In a second example the cylinder can be manufactured directly above the laminated part 2 and discs 11, 12. In this case the laminated part 2 and discs 11, 12 can be wrapped by a foil onto which a reinforcing material such as carbon fibres are applied and then the whole assembly can be placed into a mould to impregnate the reinforcing fibres with a resin and then cure the resin.

The operation of the rotor is apparent from that described and illustrated and is substantially the following .

In the following reference to a synchronous or asynchronous generator connected to one prime mover is made .

The prime mover transmits a torque to one shaft (for example 9) that makes the laminated part 2 to rotate.

Since the discs 11, 12 are connected via the cylinder 15, the cylinder 15 transmits the most of or all the torque and the laminated part 2 has to withstand only a limited torque or no torque at all.

For this reason the rotor can also withstand a large torque, because it is the cylinder 15 (i.e. not the laminated part 2) to withstand it.

During operation the cooling can be achieved by a cooling gas that enters the inside of the cylinder 15 via the apertures 25, then passes into a cooling circuit of the rotor (for example of traditional type) and then moves out from the rotor via the apertures 26 of the cylinder 15.

Advantageously the cylinder 15 helps to:

increase the torsional stiffness,

increase the bending stiffness,

fix the coils 5 in the slots.

Naturally the features described may be independently provided from one another.

In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art.

REFERENCE NUMBERS

1 rotor

2 laminated part of 1

3 end of 2

4 end of 2

6 press plate

7 press plate

8 tightening bars

9 shaft

10 shaft

11 disc

12 disc

15 cylinder

17 slots of 11/12

18 protrusions of 15

20 longitudinal axis of 1

22 spindle

23 end windings

25 apertures of 11/12

26 apertures of 15

27 rings

30 concave shaped laminations