Embodiments of the present invention relate to a winding of a rotor for use in rotating electrical machines. More particularly, embodiments of the present invention relate to innovative half-coils used for the winding of the rotor. Moreover, embodiments of the invention pertain to a method for winding a rotor body of an electrical machine.
As well known, the conversion of rotating mechanical energy into electric energy and vice versa is done by generators and by motors, respectively.
Motors or generators comprise a stator and a rotor. The rotor of the machine rotates inside the stator bore of the stator. For the conventional synchronous machines, the magnetic field is excited typically through the current-carrying field windings placed in the rotor body made of magnetic material. The combination of the number of the rotor poles and the rotational speed in revolutions per minute (rpm) determines the frequency of the rotating magnetic field.
Rotors are generally manufactured with a certain number of coils, each embedded in the respective slot arranged in the rotor body. In particular, each coil comes in the form of a stack of conductors called turns, generally made of copper.
The rotor winding is made of a plurality of coils, each extending parallel to the rotor axis along the rotor body. Each coil comes normally in the form of two opposite symmetric substantially C-shaped half-coils. Each half-coil has at its axial ends, two diametrically opposed radius portions, which form the rotor end winding, each one joined with the respective radius portion of the opposed half-coil, thus forming a complete rotor coil with all coils making up the rotor winding.
Typically, the joining of the half-coils in correspondence of the radius portions is accomplished by a brazing process, wherein the turns to be joined, located at both ends of the coil, are individually or in stacks heated to the braze temperature after the brazing alloy is positioned in the joint area.
The turns used for the half-coils are usually hollow, having one or two channels running throughout their axial length. Such a channel is needed in order to guide a fluid within the conductor for cooling purposes, since the current flows generate heat which must be removed from the machine.
The conductors usually come in the form of single hollow conductors, having a sole axial channel, or double hollow conductors, having a couple of channels running internally. The hollow conductors can be solidly formed or made from C-Sections (single hollow conductor) or E-Sections (double hollow conductor). The choice of designing the rotor winding with single-hollow conductors or double-hollow conductors mostly depends on the required power that must be delivered and the required mechanical strength of the coils. Double-hollow conductors are usually installed for high-power machines, while single-hollow conductors can be suitable for machines of less power.
However, the manufacturing of the double-hollow conductors, required for high-power machines, is usually more complex and time-consuming compared to the production of the single-hollow conductors, which results in a higher manufacture cost. A double-hollow conductor is mechanically stronger and deforms less compared to a single hollow conductor of the same width.
Furthermore, it is known practise to manufacture half-coils wherein the radius portions are brazed at its corners.
Corner brazing is usually avoided; instead, the rotor winding, in which the half-coils have radius end portions obtained by bending, may be beneficial. In fact, the brazing process, besides being a time-consuming and expensive process, cannot fully guarantee during the whole life of the machine the integrity and stability of the rotor winding.
However, a suitable solution for replacing corner brazed rotor coils is challenged by limited axial space underneath the retaining ring.
On rotors where the original design has brazed joints (corner brazing or brazed-on bow section) in the rotor end winding, a rewind solution necessarily has to have brazed corner joints as well, in order to meet the spatial constraints, i.e. the available space in axial direction under the retaining ring. In fact, bent corners tend to occupy more room, in the axial direction, with respect to brazed corner designs, where a bow section with different/smaller section is brazed on to save axial space. As a consequence, replacing the old winding with bent corners in the rotor end winding implies the replacement of the old retaining ring with a larger one.
Nevertheless, supplying a new retaining ring with larger axial dimension is not always technically feasible and a disadvantage in terms of price competitiveness may be experienced.
The object of the present invention is to solve the aforementioned technical problems by providing an innovative C-shaped half-coil for the winding of a rotor body as substantially defined in herein. Furthermore, a method is provided for winding a rotor body as substantially defined herein.
According to embodiments of the invention, which will be described in the following detailed description only for exemplary and non-limiting purposes, the C-shaped half-coils, instead of being manufactured as double-hollow conductors, are provided in the form of two single-hollow conductors which are adjacently embedded within a respective slot of the rotor body.
In this way, the manufacturing process is improved because, as mentioned above, the production of single-hollow conductors is faster and cheaper versus the production of double-hollow conductors. In an embodiment, this leads to an improved process in the manufacturing of electrical machines having conductors which require two cooling channels.
Moreover, this solution further improves a rewind process of the rotor body, providing coils having bent corners (in place of the existing ones having brazed corners or brazed-on bow sections without the need of replacing the retaining ring).
In fact, as the half-coils are provided in the configuration of two separate single-hollow conductors, only one conductor runs all way through the bent part of the end winding, while the other one ends after leaving the rotor body.
It has been demonstrated that such arrangement works at least for the inner coils of the winding, which are shorter and thus have the thermal margins to reduce the cross section around their end winding portion.
The separate single conductors can be electrically contacted by different contact techniques, such as soldering, friction welding, riveting, screwing, crimping, contact sleeves, contact bridges, contact strips.
Therefore, according to aspects of the invention, costly and time-consuming corner brazing can be omitted and broader supplier base together with shorter delivery time for single-hollow conductors instead of double-hollow conductors are achieved.
According to embodiments, a proposed to secure electrical contact between adjacent separate single conductors features a radial arrangement utilizing the centrifugal force to facilitate and enhance the electrical (galvanic) contact between the adjacent upper and lower layer conductors lying one above the other forming a turn, thus the joining (e.g. brazing) of these two adjacent conductors can be spared, meaning less efforts and lower cost owing to without the need of joining (brazing) process, as it will be fully explained in the detailed description of embodiments of the invention.
Regarding this radial arrangement, the following aspects need to be noted: sufficiently good contact shall be maintained along all the defined areas of the conductors; dimensional tolerances shall be prevented from varying due to deformation during e.g. assembly and possible axial moving shall be avoided due to vibration.
Moreover, joining the conductors of one layer in the configuration top to bottom together to form a turn, the winding is subjected to less vibration during operation, and less effort is needed to deal with the joining points along the conductors, which are a relevant number as such conductors have lengths usually of several meters.
The foregoing objects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein:
Photo 1 is a perspective view of a winding mounted on a rotor body with bent corners belonging to the state of the art;
With reference to photo 1, it shows a state-of-the-art electrical machine 1. In particular, the photo 1 shows a view of a rotor body generally indicated with reference 2. The rotor body 2 comprises a plurality of axial slots 3. A state of the art C-shaped half-coil 4′ is embedded in a respective slot 3 of the rotor body 3. The C-shaped half-coil 4′ comprises an axial active portion 41′ running through the rotor slot 3 and two opposite bent radius winding end portions, which are positioned out of the slot, at different ends of the rotor body 3. In the photo only the bent portion 42′ is visible at one end of the rotor body 3. Each C-shaped half-coil 4′ is joined to a correspondent opposed C-shaped half-coil 5′, as clearly showed in the photo. Half-coils 4′ and 5′ form a complete coil. All coils wound around the rotor body 2 make up the rotor winding, generally indicated in the photo with numeral 100.
Still making reference to the half-coil 4′ according to the state of the art, the half-coil 4′ comprises a plurality of stacked conductors, called turns, usually made of copper. Each turn of the stack is electrically insulated from the adjacent turn belonging to the same half-coil.
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The C-shaped half-coil 8 comprises, in a similar manner, an active portion 81, configured to be embedded in a respective rotor slot, and two opposite bent radius winding end portions, of which only bent portion 82 is visible in the figure. The half-coil 8 comprises a stack of turns 5 electrically insulated from each other. Each turn 5 of the stack of turns of the half-coil 8 comprises two separate adjacent single first and second conductors 9 and 10. The term first conductor 9 is also referred to as first straight conductor 9, 31 in this whole disclosure. As described not all of the first conductors 9 of the rotor winding 20 are mandatorily designed as straight first conductors 9, 31 however. The first conductors 9 can be designed partially as straight first conductors 9, 31 without a bended portion, and partially as common first conductors 9 having a bended portion corresponding to the second conductors 10, 32, see Fig.7. The first straight conductors 9, 31 are conductors with cut out bended parts. Conductors 9 and 10 are electrically connected to each other in order to assure the flow of current between them. In this variant, first conductor 9, which is the outer conductor of turn 5, is a straight conductor having its axial ends protruding outside the respective rotor slot 3 when embedded within the rotor body (not shown), and located in the proximity of respective bent radius portions (in the figure only bent portion 82 is visible). As can be seen in
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More in particular, half-coil 30 comprises, in similar manner, an active portion 301, configured to be embedded in a respective rotor slot, and two opposite bent radius winding end portions, of which only bent portion 302 is visible in the figure. The half-coil 30 comprises a stack of turns 5 electrically insulated from each other. Each turn 5 of the stack of turns of the half-coil 30 comprises two separate adjacent single first and second conductors 31 and 32. Conductors 31 and 32 are electrically connected to each other in order to assure the flow of current between them. In this variant, first conductor 31 is a straight shorter conductor having its axial ends protruding outside the respective rotor slot when embedded within the rotor body (not shown), and located in the proximity of respective bent radius portions (in the figure only bent portion 32 is visible). Turns 5 are positioned in pairs, side by side. In the portion of the half-coil illustrated, two turns are shown, comprising, respectively, first single straight conductor 31 and second conductor 32 and first single straight conductor 31′ and second conductor 32′. In an embodiment, the arrangement is such that, for each pair of turns positioned side by side, first and second conductors are disposed on top of each other such that the first straight conductor 31 abuts on second conductor 32′ of the adjacent turn and second conductor 32 abuts on the first straight conductor 31′. Moreover, in an embodiment, the bent radius portions of second conductor 32 are arranged aligned with corresponding bent radius portions of second conductor 32′ of the adjacent turn.
Such arrangement may be beneficial as it allows compacting the room required by the stack of coils without exceeding in the axial direction, and at the same time it allows the particular disposition of having single conductors of each turn disposed on top of each other, thus exploiting the centrifugal forces for establishing a strong contact between them for ensuring the flow of current.
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Moreover, embodiments of the present invention are also directed, with reference to the described figures, to a method for winding a rotor body 2 of an electrical machine 1. The winding operation may also be a re-winding, that is removing the existing rotor winding and replacing it with a new one. The method according to an embodiment of the invention comprises embedding in each slot 3 of the rotor body a respective conductive C-shaped half-coil, the half-coil comprising an axial active portion running through the slot parallel to a rotating axis R of the rotor body 2, shown in
According to a first embodiment, the turns of at least one half-coil are disposed along a radial direction and the first and second conductors are positioned along a circumferential direction with respect to the rotating axis R of the rotor body 2.
According to a second embodiment, the first and second conductors of each turn are positioned along a radial direction and the turns of at least a half-coil are positioned, in pairs, along a circumferential direction, such that the first conductor of turn abuts on a second conductor of adjacent turn, wherein the pairs of turns are arranged within the respective slot along a radial direction.
The method further comprising providing a slot wedge 110 supporting the half-coils such that, during operation, first and second conductor are pressed to each other due to centrifugal forces.
Although the present invention has been fully described in connection with embodiments, it is evident that modifications may be introduced within the scope thereof, not considering the application to be limited by these embodiments, but by the content of the following claims.
Number | Date | Country | Kind |
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14164161.3 | Apr 2014 | EP | regional |
This is a national phase U.S. Patent application claiming priority to International Application No. PCT/EP2015/057227 having an International Filing Date of Apr. 1, 2015, and EP Application No. 14164161.3 having a Filing Date of Apr. 10, 2014, each incorporated herein in its entirety by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2015/057227 | 4/1/2015 | WO | 00 |