Patent Application
20140132109
Embodiments of the present invention relate generally to a rotating electrical machine, and in particular to a rotating electrical machine having a segmented stator. The rotating electrical machine may be a gearless mill drive (GMD) for a grinding mill such as an autogenous (AG) mill or a semi-autogenous (SAG) mill.
Large diameter, low speed, rotating electrical machines usually employ a rigid stator assembly and grinding mills are one example of this type of rotating electrical machine. Grinding mills are widely used in mineral processing applications and the most common types are the autogenous (AG) grinding mill in which the feed material itself acts as the grinding medium and the semi-autogenous (SAG) grinding mill in which supplementary grinding material, typically steel balls, is added to the feed material.
Grinding mills typically employ a gearless mill drive (GMD), also commonly known as a ring motor, in which the mill barrel acts as the rotor and a stator assembly surrounds the rotor. GMD stator assemblies typically have a segmented construction, with circumferentially adjacent stator segments being rigidly connected to each other.
Grinding mills are often subjected to transient loads in the radial, axial and circumferential directions, particularly during start-up if the material in the mill has settled and formed what is commonly referred to as a ‘frozen charge’, with translational and torsional shock loads being especially problematic. These transient loads have been known to cause fatigue damage to some of the component parts of the stator assembly of existing gearless mill drives.
There is, therefore, a need for an improved rotating electrical machine, such as a grinding mill, having an improved stator assembly.
According to an embodiment of the present invention, there is provided a rotating electrical machine comprising a rotor having an axis of rotation and a stator assembly surrounding the rotor, the stator assembly comprising a plurality of circumferentially arranged stator segments; and a plurality of link elements of which at least one link element extends between each of the circumferentially adjacent stator segments, wherein each link element provides a rigid circumferential connection between circumferentially adjacent stator segments so that the linked stator segments form a torsionally stiff annular stator and provides a radially flexible connection between circumferentially adjacent stator segments to permit relative movement between adjacent linked stator segments in the radial direction.
The terms ‘radial’, ‘circumferential’ and ‘axial’ are used herein to refer to directions relative to the axis of rotation of the rotor.
The link elements link together the circumferentially arranged stator segments to provide the resulting annular stator with controlled stiffness in the torsional direction so that the linked stator segments effectively form a torsionally stiff annular stator. Because the individual stator segments are capable of moving independently in the radial direction, the annular stator can deflect locally in the event that there is local deflection of the rotor, for example due to translational and/or torsional shock loads. The air gap between the rotor and the individual stator segments is, therefore, locally controlled. Fatigue stresses are also reduced with the result that the fatigue resistance of the stator assembly is improved. In addition, the segmented stator assembly has a lightweight construction and is easy to assemble on-site.
The link elements may be secured to axial faces of the stator segments. A first link element may extend between first axial faces of circumferentially adjacent stator segments and a second link element any extend between second axial faces of circumferentially adjacent stator segments. The axial faces may comprise axial face plates located on each stator segment.
The link elements may be elongate and each link element may extend in the circumferential direction between circumferentially adjacent stator segments. The link elements may, for example, comprise linear struts.
Opposite ends of each link element may be secured to circumferentially adjacent stator segments for pivotal movement about an axis parallel to said axis of rotation. This permits the relative movement between circumferentially adjacent linked stator segments in the radial direction.
In an embodiment, the circumferentially opposing faces of circumferentially adjacent stator segments may be spaced from each other. This may facilitate independent movement of each individual stator segment relative to the circumferentially adjacent stator segments. In an embodiment, the circumferentially opposing faces of circumferentially adjacent stator segments may contact each other. In this case, it may be configured so that one or more link elements extending between the circumferentially adjacent stator segments apply a preload to the contacting surfaces.
The circumferentially opposing faces of circumferentially adjacent stator segments can include a low friction material to facilitate sliding contact in the radial direction. This configuration can be applied in embodiments in which the circumferentially opposing faces of circumferentially adjacent stator segments are in contact with each other.
Each stator segment may include at least one rolling element which may cooperate with the rotor. This ensures that each stator segment is individually guided relative to the rotor, during rotation of the rotor. One or more of said rolling elements may be provided at the circumferentially opposite ends of each axial face of each stator segment. Each stator segment can be configured to be supported on the rotor by four rolling elements, one at each corner, for stability.
The rotor may include a circumferentially extending guide arrangement with which the rolling elements may cooperate. The guide arrangement axially constrains each of the plurality of stator segments. Two axially spaced circumferentially extending guide arrangements may be provided. Each guide arrangement may comprise a guide rail.
A mounting arrangement may be provided between at least one of the stator segments and a base structure to mount the stator assembly on the base structure.
The rotor may be a hollow rotatable body. The rotating electrical machine may be a gearless mill drive in which the hollow rotatable body is a mill barrel.
Embodiments will now be described by way of example only and with reference to the accompanying drawings.
Referring initially to
A plurality of permanent magnets (not shown) are affixed to an upper, and in use radially outer, surface of the pole bodies 12, for example by bonding, by way of mechanical fixings or by any other suitable means. In an embodiment, the permanent magnets could be located in a housing which could be secured to the upper, and in use radially outer, surface of the pole bodies 12.
A stator assembly 14 surrounds the rotor 10 and comprises a plurality of circumferentially arranged stator segments 16. Each stator segment 16 is mechanically connected to a circumferentially adjacent stator segment 16 by a pair of axially spaced link elements 18 (note that only one link element 18 of each pair is visible in the drawings) so that the circumferentially arranged stator segments 16 together form a torsionally stiff annular stator which surrounds the rotor 10. Each link element 18 comprises a linear strut which acts as a tie rod when under tensile stress and as a bracing strut when under compressive stress, thereby providing the aforesaid torsional rigidity. The circumferential faces 21 of the stator segments 16 are spaced from each other in the illustrated embodiment so that a small gap 19 is formed between adjacent stator segments 16.
In the illustrated embodiment, each stator segment 16 includes stator face plates 20 to which the link elements 18 are secured. Bushes 22 are provided at the opposite ends of each link element 18 and these provide flexibility in the radial direction by mounting the opposite ends of each link element 18 for movement about a pivot axis which is parallel to the axis of rotation of the rotor 10. The flexible bushes 22 thus enable circumferentially adjacent linked stator segments 16 to move relative to each other in the radial direction. The bushes 22 may also provide some limited flexibility in the axial direction, thereby permitting circumferentially adjacent linked stator segments 16 to move relative to each other by a limited amount in the axial direction.
Each of the stator segments 16 includes a plurality of rolling elements 24 in the form of wheels which cooperate with guide rails 26 that extend circumferentially around the rotor 10. The stator segments 16 are thus individually guided relative to the rotor 10 by virtue of the wheel/rail interaction and because the link elements 18 allow the stator segments 16 to move independently in the radial direction, the individual stator segments 16 can follow any local deflections of the rotor 10, allowing the air gap between the rotor 10 and individual stator segments 16 to be controlled and maintained during operation of the rotating electrical machine. In the illustrated embodiment, a pair of axially spaced wheels 24 mounted on radially inwardly projecting wheel support brackets 25 is provided at circumferentially opposite ends of the stator face plates 20 of each stator segment 16, so that each stator segment 16 is supported by four rolling elements 24 (note that only one rolling element 24 and wheel support bracket 25 of each pair is visible in the drawings). The guide rails 26 also constrain the axial movement of each of the stator segments 16, although some limited axial movement may occur and can be accommodated by the bushes 16 as discussed above.
A cooling duct 28 is provided on the radially outer surface of each stator segment 16 and a flexible conduit 30 such as a hose connects the cooling ducts 28 of adjacent stator segments 16. The cooling ducts 28 and flexible connecting conduits 30 carry a flow of cooling fluid across the radially outer surface of the stator segments 16 between a cooling fluid inlet 32 and a cooling fluid outlet 34.
Referring now to
Referring now to
In the grinding mill of
The arrangement of the hinged support links 52a, 52b and hinged connection points enables the stator segments 16 that are circumferentially aligned with the support arrangements 42 to move in the radial direction relative to the support arrangements 42 but not in the circumferential direction, thus decoupling the radial motion of the stator assembly 14 from the base structure 40.
Although embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described embodiments. Each feature disclosed in the specification, including the claims and drawings, may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise.
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12192653.9 | Nov 2012 | EP | regional |
