The invention relates to an electrical machine according to the preamble of claim 1, a rotor for the electrical machine according to claim 10, and a manufacturing method according to claim 15.
The invention relates especially to electrical machines for use in confined radial space like in narrow wells or tunnels. Applications for an electrical machine according to the invention are in oil and gas exploration and extraction (downhole), drilling applications in general, and any other applications where it is important to have a compact stator with axial channels.
In downhole applications it is often required to transport various substances like rock cuttings, water, oil, etc. through an electrical machine. Sometimes it is required to have cables going through the electrical machine as well. It is state of the art to use the gap between rotor and stator for transporting fluids, like oil, but the gap is very narrow, so the flow cannot be considerable. Moreover, solid particles or viscous fluids cannot be transported through the narrow gap. Therefore, having some extra passages through the machine is desirable.
There is a number of electrical machines where axial channels are integrated into iron cores of the electrical machine, but outside the zone directly involved in energy conversion. For accommodation of the channels, the iron cores are just made thicker and thus increasing the diameter of the electrical machine. Examples of such electrical machines are described in:
It is commonly known to provide channels in the stator for cooling. GB986682 is showing a typical configuration of holes for cooling a stator. In this design a relatively large part of the stator diameter is utilized for cooling. This may be suitable when a large mass stator is desirable for mechanical stability but in general such approach, when used for relatively long electrical machines with small diameter, leads to decrease of air gap diameter and corresponding decrease of torque density. In high torque electrical machines it is advantageous to have higher rotor diameter to have a longer torque arm, on which the force is applied. At the same time, when there is a limitation for outer diameter of the electrical machine, the rotor diameter cannot be increased too much, as there should be enough space for the stator laminations and the winding. So, the designer's task is to find optimal air gap diameter.
Common to the established methods is a failing to have optimal diameter of the air gap as the channels are taking considerable space at the periphery of the electrical machine and reduce the zone available for energy conversion. This may be reviewed e.g. in US2006066159 and in DE4103154. In US2006066159 the channels are arranged outside the active materials and therefore no optimal air gap diameter is achieved. In DE4103154 grooves in the outer part of the stator is used for channels, also without achieving optimal diameter of the air gap.
Contrary to US2006066159 and DE4103154, which have no channels integrated in the stator teeth, in the DE1090750 (B1) cooling channels are integrated in an oblique tooth. In addition to cooling the channels in the teeth are used for leveling the reluctance. It is noteworthy that in DE1090750 (B1) the channels are not prolonged into the back iron because almost all losses are considered to be in the teeth zone and the channels has the purpose of removing the heat from losses.
The type of electrical machine described in DE1090750 (B1) is characterized by too thick yoke (back iron), failing to achieve optimal air gap diameter. In U.S. Pat. No. 6,664,692 and NO324241 the back iron thickness is minimized due to the use of a special configuration of concentrated coils design and permanent magnet technology. This technology is especially favorable for integration of axial channels, as only each second tooth carries a coil and those teeth which do not carry coils have trapezoidal shape.
Therefore, the proposed new concept uses the technology described by patents U.S. Pat. No. 6,664,692 and NO324241 as a basis and a starting point.
The main object of the invention is to accommodate relatively large axial channels in a slim electrical machine without sacrificing its torque density and radial dimensions. It is particularly an object to provide a downhole electrical machine suitable for offshore use with high torque.
A further object is to provide stator channels allowing the inclusion of an integrated protector.
An electrical machine according to the invention is described in claim 1. Preferable features of the electrical machine are described in claims 2-9.
A rotor for an electrical machine according to the invention is described in claim 10. Preferable features of the rotor are described in claims 11-14.
A manufacturing method for an electrical machine according to the invention is described in claim 15. Preferable features of the manufacturing method are described in claims 16-21.
More specifically, the novel feature of the electrical machine is that there are axial channels protruding into some of the teeth which are not carrying coils and neighboring back iron, where the area of the channel inside the tooth is comparable to, or even larger, than the area of the channel in the back iron.
This electrical machine may be designed to provide an optimal diameter of the air gap based on the external diameter available and the need for axial channels given.
In addition to the optimal air gap diameter, a rotor structure is introduced which is maximizing the magnetic field in the machine and contributing to a higher torque. The optimal diameter is creating a substantially higher torque than at prior art machines. The particular rotor design also allows omitting the use of laminated back iron in the rotor.
The machine according to the invention is a permanent magnet synchronous machine (PMSM) with concentrated coils forming the winding. This implies a substantial reduction of the thickness of the stator yoke and provides high torque in a low volume.
The electrical machine preferably includes twelve slots, six coils, six teeth carrying coils, and six teeth not carrying coils.
The number of channels may be fewer than six as not all the teeth not carrying coils contain a channel.
The electrical machine preferably includes six or less teeth containing channels.
The slots are preferably closed by non-magnetic or semi-magnetic slot wedges.
The electrical machine is preferably at least partly filled with fluid for pressure compensation.
An outer shell of the electrical machine is preferably exposed to a cooling fluid circulating in the interior of the electrical machine.
Preferably, at least some of the channels form a flow path, extending through the stator, for the transmission of a fluid, for example a wellbore fluid.
The electrical machine preferably includes a rotor provided with means to provide the internal fluid circulation.
Preferably, at least one channel is used for accommodation of a motor protector.
The invention is particularly suitable for downhole applications with relatively narrow openings. The invention allows the design of machines with a high torque without demanding lengths creating mechanical problems.
The invention also comprises a novel rotor, with a shaft and with permanent magnets attached to the shaft, wherein the magnets are segmented and magnetized according to a special pattern, for example magnetized in alternating directions. The permanent magnets or permanent magnet segments are preferably attached to the shaft. The permanent magnets are further preferably provided with an anti-corrosion coating.
The shaft of the rotor is preferably hollow.
Finally, the invention comprises a manufacturing method for an electrical machine, wherein the stator is assembled from a main preassembled stack of laminations and a plurality of arced segments. Each segment preferably acts as a part of back iron.
The manufacturing method preferably includes first fitting the coils into the slots of laminated stack and next installing the arced segments.
The manufacturing method further preferably includes preforming the coils before fitted into the main preassembled stack.
The manufacturing method further preferably includes the use of arced segments made of radially stacked laminations, axially stacked laminations, sintered magnetic body or compacted magnetic powder body.
Further details of the invention will appear from the following description of example embodiments.
The invention will be hereafter described with reference to the accompanying drawings, where:
Reference is made to
In the proposed machine the number of slots 15 is twelve, the number of narrow teeth 16 is six, the number of wide teeth 17 is six and the number of channels 18 is six. In general case the number of teeth can be selected differently, adjusted to speed requirements.
The number of channels 18 may be fewer than six as not all the teeth 17 not carrying coils contain a channel 18.
The slots 15 accommodating the coils are closed by slot wedges 19 with relative permeability equal unity or higher than unity.
The channels 18 may have various shapes, as shown in
Reference is now made to
The electrical machine may have its own housing or be integrated into some tool. An alternative with “flower-like” lamination shape 21 with open channels 18 for further integration is shown in
Reference is now made to
In the machine rotor presented in
Reference is now made to
To strengthen the magnetic field some of the magnets 12 are magnetized in radial direction and some magnets 12—at a certain angle.
The magnets 12 may be mounted directly on the shaft 23A or on the back iron. Mounting the magnets 12 directly on the shaft 23A is advantageous as thicker shaft means lower radial deflections of the rotor which in turn allows production of longer machines.
The magnets 12 may be provided with an anti-corrosion coating.
In case the electrical machine is very long it may be difficult to insert the coils 20A-C into the stator slots 15 in traditional way. For such a case manufacturing of the electrical machine can be changed as described below.
As shown in
The coils 20B are first fitted into the slots 15 of laminated stack 21. Then arced segments 30 are installed afterwards. The coils 20B may be pre-formed before being fitted to the laminated stack 21.
The arced segments 30 may be made of axially stacked laminations, sintered magnetic body or compacted magnetic powder body.
An alternative to the arced segments 30 are segments 31 made of radially stacked laminations 21, as shown in
In the figure it is shown a flat segment 31 made of radially stacked laminations 21, but the segments 31 may also be made of axially stacked laminations, sintered magnetic body or compacted magnetic powder body (not shown in figure). This alternative will simplify the manufacturing and assembling.
As above, the coils 20C are first fitted into the slots 15 of the laminated stack 21. The flat segments 31 are installed afterwards. The coils 20C may be pre-formed before being fitted to the laminated stack 21.
An alternative for simplifying the insertion of coils 20A-C into the laminated stack 21 for long electrical machines will be described below.
To be able to insert the coils 20A-C into the slots 15 for long electrical machines with small inner diameter, the stator lamination stack 21 can be made of two or more circumferential sections where each section can comprise one or more coils 20A-C.
The coils 20A-C is first fitted into the slots 15 of the laminated stack 21. The stator sections are then joined together creating a circular stator 13.
Reference is now made to
The electrical machine can be used in generator mode as well as in motor mode. The electrical machine may have integrated speed or position sensor. The electrical machine may have hollow shaft for transportation of external substances.
The stator is shown with round closed channels in the examples, but it is obvious that the channels may have different shapes if desired.
The rotor is shown with threads to circulate cooling fluid inside the electrical machine, but it is obvious that fins, an impeller or other suitable means could be used for the same purpose.
The rotor is shown with a layer for retention and protection to protect the permanent magnets, but it is obvious that the layer can be made of a metallic layer.
Number | Date | Country | Kind |
---|---|---|---|
20093533 | Dec 2009 | NO | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/NO2010/000444 | 12/3/2010 | WO | 00 | 7/12/2012 |