Generator rotor with coil end-turn retention mechanism

A rotor assembly includes a rotor core having winding slots, and one or more coils, which have slot-inserted segments included in the winding slots, and first and second end-turn segments external to the winding slots and located around opposite axial ends of the rotor core, respectively. The rotor assembly further includes a first containment band located around at least a portion of the first end-turn segments and configured to prevent the first end-turn segments from moving away from the rotor core radially, a second containment band located around at least a portion of the second end-turn segments and configured to prevent the second end-turn segments from moving away from the rotor core radially, and one or more sticks mounted in one or more of the winding slots, respectively. The first and second containment bands are retained via the sticks against moving away axially.

FIELD OF THE INVENTION

The present disclosure generally relates to generators, and more specifically to retention mechanism of coil end-turn segments in generator rotors.

BACKGROUND OF THE INVENTION

Gas turbine engines are rotary engines that extract energy from a flow of combusted gases passing through the engine onto a multitude of turbine blades. A generator coupled with a gas turbine engine converts the mechanical power of the engine into electrical energy by using pressure spools of the engine to rotate the generator rotor, and thus, generate electricity.

Some generators are used with high rotational speeds. During the high speed rotation, high centrifugal forces may be imposed upon the generator rotors. The centrifugal force imposed upon a rotor may be strong enough to cause wire coils wound on the rotor to bend or get dislocated. Such bending, over time, may result in mechanical breakdown of the wires and compromise of the coil insulation system. Such dislocation may be a potential source of imbalance within the rotor.

SUMMARY OF THE INVENTION

A rotor assembly for a generator, includes a rotor core having winding slots, and one or more coils, which have slot-inserted segments included in the winding slots, and first and second end-turn segments external to the winding slots and located around opposite axial ends of the rotor core, respectively. The rotor assembly further includes a first containment band located around at least a portion of the first end-turn segments and configured to prevent the first end-turn segments from moving away from the rotor core radially, a second containment band located around at least a portion of the second end-turn segments and configured to prevent the second end-turn segments from moving away from the rotor core radially, and one or more sticks mounted in one or more of the winding slots, respectively. The first and second containment bands are retained via the sticks against moving away axially.

A generator includes a stator and a rotor assembly rotationally mounted at least partially within the stator. The rotor assembly includes a rotor core having winding slots, and one or more coils, which have slot-inserted segments included in the plurality of winding slots, and first and second end-turn segments external to the winding slots and located around opposite axial ends of the rotor core, respectively. The rotor assembly further includes a first containment band located around at least a portion of the first end-turn segments and configured to prevent the first end-turn segments from moving away from the rotor core radially, a second containment band located around at least a portion of the second end-turn segments and configured to prevent the second end-turn segments from moving away from the rotor core radially, and one or more sticks mounted in one or more of the winding slots, respectively. The first and second containment bands are retained via the sticks against moving away axially.

A method of assembling a rotor, includes: providing a rotor core having winding slots; winding one or more coils on the rotor core, with slot-inserted segments of the coils included in the winding slots, and first and second end-turn segments of the coils external to the winding slots and located around opposite axial ends of the rotor core, respectively; disposing a first containment band around at least a portion of the first end-turn segments to prevent the first end-turn segments from moving away from the rotor core radially; connecting one or more sticks to the first containment band, by inserting the one or more sticks into one or more of the winding slots, respectively, axially pushing the sticks into the first containment band and snap-fitting the sticks onto the first containment band; disposing a second containment band around at least a portion of the second end-turn segments to prevent the second end-turn segments from moving away from the rotor core radially; axially pushing the second containment band toward the sticks and snap-fitting the second containment onto the sticks; and holding the first and second containment bands by the sticks against moving away axially.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to a rotor assembly for a generator. The rotor assembly includes a rotor core defining a plurality of winding slots, one or more coils having slot-inserted segments included in the winding slots of the rotor core, and end-turn segments external to the winding slots and extending from opposite axial ends of the rotor core, respectively. Containment bands are used to hold the coil end-turn segments against from moving away radially, and one or more sticks are used to hold the containment bands against moving away axially.

FIG. 1illustrates an exemplary electric machine assembly, such as a generator1, which includes a first machine2having an exciter rotor3and an exciter stator4, and a synchronous second machine5having a main machine rotor6and a main machine stator assembly10. At least one power connection is provided on the exterior of the generator1to provide for the transfer of electrical power to and from the generator1. Power is transmitted by this power connection, shown as an electrical power cable7, directly or indirectly, to the electrical load and may provide for a three phase with a ground reference output from the generator1.

The generator1further includes a rotatable shaft8mechanically coupled to a source of axial rotation, which may be a gas turbine engine, about an axis of rotation9. The rotatable shaft8is supported by spaced bearings11. The exciter rotor3and main machine rotor6are mounted to the rotatable shaft8for rotation relative to the stators4,10. The stators4,10may be mounted to any suitable part of a housing portion of the generator1. The rotatable shaft8is configured such that mechanical force from a running turbine engine provides rotation to the shaft8. Alternatively, in an example of a starter/generator, rotation of the rotatable shaft8of the generator1during a starting mode produces a mechanical force that is transferred through the shaft8to provide rotation to the turbine engine.

FIGS. 2-5illustrate the exciter rotor3in greater detail, whereinFIG. 2is a perspective view showing the exciter rotor3in assembly and coupled to the shaft8,FIG. 3is an exploded view of the exciter rotor3, showing main parts of the exciter rotor3,FIG. 4is a close-up perspective view showing the exciter rotor3in a partially assembled state, andFIG. 5is a cross section view of an upper half of the exciter rotor3and the shaft8inFIG. 2.

The exciter rotor3, as shown, includes a generally cylindrical rotor core31. The cylindrical rotor core31includes a plurality of spaced posts311defining a corresponding plurality of spaced winding slots312therebetween, arranged in a circumferential direction of the core31. Each of the plurality of winding slots312is configured with an open top and may terminate in opposing open ends spaced axially along the core31. For instance, the ends of the winding slot312may axially terminate at the same length as the core31. The core31may be formed from a magnetic material, such as Cobalt-Iron (CoFe) alloy, which is magnetic in nature. It is generally manufactured by gluing and stacking thin stamps of the alloy together along the length the core.

As shown inFIG. 4, the exciter rotor3further includes a plurality of coils32(only a few are shown), that are wound about the core31, by inserting one or more segments321of each coil32into two separate winding slots312. The winding slots that each coil32is inserted into are, for example, non-adjacent, though it will be appreciated that the present disclosure is not limited to this scheme. The coil32extending the length of the winding slot312has two non-slot-inserted segments322,323, external to the winding slot312and extending from opposite axial ends of the rotor core31, respectively. These coil segments321inserted into the winding slots312are referred to herein as slot-inserted segments, whereas these non-slot-inserted segments322,323are referred to herein as end-turn segments, wherein the end-turn segments322located at a first axial end313of the rotor core31is referred to as first end-turn segments and the end-turn segments323located at a second axial end314of the rotor core31is referred to as second end-turn segments. In some embodiments, as shown inFIG. 4, each coil32is bent or twisted at the end-turn segments322,323thereof.

The coils32may be made from any suitable conductive materials, including conductive metals, such as copper, aluminum, zinc, brass, carbon, or iron. The coils32may have various cross-sectional shapes, such as round, square, or rectangle. For example, in the embodiment as illustrated inFIG. 4, the coils are rectangular in cross section. Moreover, each coil32may be constructed of a single conductor, or a plurality of conductors.

As the coil end-turn segments322,323are subject to radial loads when the exciter rotor31rotates, an end-turn retention assembly33including a first containment band331, a second containment band332, and one or more sticks333, as shown inFIGS. 3 and 4, is provided for retaining the coil end-turn segments322,323. The first containment band331is located around at least a portion of the first end-turn segments322and configured to prevent the first end-turn segments322from radially moving away from the rotor core31. In particular, the first containment band331includes an annular structure radially enclosing therein the first end-turn segments322. Similarly, the second containment band332is located around at least a portion of the second end-turn segments323and configured to prevent the second end-turn segments323from radially moving away from the rotor core31. In particular, the second containment band332includes an annular structure radially enclosing therein the second end-turn segments323. In some embodiments, the first containment band331has an axial length equal to or greater than that of the first end-turn segments322, such that the first end-turn segments322can be covered by the containment band331substantially in the entire axial length thereof, and the second containment band332has an axial length equal to or greater than that of the second end-turn segments323, such that the second end-turn segments323can be covered by the second containment band332substantially in the entire axial length thereof.

As shown inFIG. 5, each of the sticks333is inserted in one of the winding slots312, and thus sits above the slot-inserted segment321of the coil32in the same winding slot312. Each stick333includes a first stick-catch334and a second stick-catch335formed at opposite ends thereof, respectively. The first containment band331has a first band-catch336for engaging the first stick-catch334in a snap fit manner, and the second containment band332has a second band-catch337for engaging the second stick-catch335in a snap fit manner. In some embodiments, each of the stick-catches334,335includes an upward hook, and each of the band-catches336,337includes a downward hook. The stick-catch334(or335) and the corresponding band-catch336(or337), either or both, can bend radially to lock into each other, when they are axially pushed towards each other.

As shown inFIG. 3, there are four sticks333used to retain the first and second containment bands331and332. The four sticks may be equidistantly arranged in the circumferential direction of the core31. Band-catches336,337are provided at the first and second containment bands331and332corresponding to the positions of the sticks333. For example, the first containment band331may include at least four first band-catches336corresponding to the first stick-catches334of the four sticks333, and the second containment band332may include at least four second band-catches337corresponding to the second stick-catches334of the four sticks333. There is no limitation to the number of the sticks used. Less or more than four sticks may be used, depending on needs.

Referring toFIGS. 2 and 5, the first containment band331includes opposite axial ends, namely an inner end (a core-adjacent end)338adjacent to the rotor core31, specifically, adjacent to the first axial end313of the rotor core31, and an outer end339away from the rotor core31. Similarly, the second containment band332includes opposite axial ends, namely an inner end (a core-adjacent end)340adjacent to the rotor core31, specifically, adjacent to the second axial end314of the rotor core31, and an outer end341away from the rotor core31. The first band-catch336is formed around the core-adjacent end338of the first containment band331, and the second band-catch337is formed around the core-adjacent end340of the second containment band332. In some embodiments, the entire core-adjacent end of the containment band331or332may be shaped as a common band-catch for engaging the corresponding stick-catches of all the sticks.

In assembly, the first band-catch336is locked to the first stick-catch334of the stick333and the second band-catch337is locked to the second stick-catch335of the stick333, such that the first and second containment bands331and332are retained to the sticks333against moving away axially.

The first and second containment bands331and332may be made from metallic materials, including but not limited to metallic alloys such as a Titanium alloy. The sticks may be made from soft metallic/non-metallic materials such as Kapton or an Aluminum alloy, via conventional manufacturing techniques or additive manufacturing.

As shown inFIG. 5, in which only an upper half of the exciter rotor and the shaft is shown, the rotatable shaft8may be hollowed to provide a passage81therein for allowing cooling fluid such as cooling oil to pass. The rotatable shaft8may further define one or more radial holes82through a thickness thereof. The radial holes82is configured to allow the cooling fluid to flow from the passage81to impinge and cool the first and second end-turn segments322,323of the coils32. There is at least one axial gap defined between the rotor core31and at least one of the first and second containment bands331,332. In particular, as shown inFIG. 5, there is an axial gap between the rotor core31and each of the first and second containment bands331,332. The axial gap is configured to allow the cooling fluid that impinges and cools the first and second end-turn segments322,323to exit the exciter rotor3radially.

The matched stick-catch and band-catch may be shaped and sized to enable snap fit connection therebetween. Taking the stick-catch334as shown inFIG. 6as an example of the stick-catches, the shapes and sizes of the stick-catches will be described hereinafter. Referring toFIG. 6, the stick-catch334includes an arm351formed with an upward hook352at a distal end thereof. The arm351has a substantially horizontal upper surface353and an uptilted lower surface354. The uptilted lower surface354tilts up from a stick middle portion to the stick distal end where the upward hook352is formed. The upward hook352includes a sliding surface356configured to slide on a corresponding sliding surface of a downward hook of the band-catch336(shown inFIG. 5) in the process of assembly, and a retaining surface357configured to hold on a corresponding retaining surface of the downward hook of the band-catch336(shown inFIG. 5) upon assembly. In some embodiments, the retaining surface357is substantially perpendicular to the upper surface353. The hook352has a height h defined between a top of the hook352and the upper surface353of the arm351. The sliding surface356is at a certain angle (contact angle θ) to the upper surface353.

The sizes of the hook352, including the height h and the contact angle θ, basically depend on the overall size of the exciter rotor, as well as the available space for the hook352to enter the band-catch336(shown inFIG. 5) during assembly. It is expected to achieve good engagement between the stick-catch and band-catch upon assembly, without the need for the stick-catch and band-catch to deflect a lot during assembly. Thus the size of the hook352is designed to achieve an appropriated balance between reliable engagement upon assembly and deflection required during assembly. In the conditions of achieving reliable engagement, the sticks and containment bands are designed such that minimal load is required to assemble or snap the two. In some embodiments, the height h may be in a range from about 1 mm to about 8 mm. In some embodiments, the contact angle θ may be in a range from about 15 degrees to about 45 degrees.

Similar hooks are provided at the core-adjacent ends of the containment bands. In some embodiments, as shown inFIG. 5, the band catch336or337includes a downward hook similar to the upward hook of the stick-catch. The downward hook may have a shape and size the same as the upward hook352. For example, the downward hook may have a hook height and a contact angle the same as those for the upward hook352.

Embodiments of the present disclosure also relate to a method for assembling a rotor as described above. Referring toFIGS. 7-9, an exemplary assembling process will be described hereinafter. After coils32are wound on the rotor core31, as shown inFIG. 7, the first containment band331is held in position. Specifically, the first containment band331is placed to surround the first end-turn segments of the coils32to prevent the first end-turn segments against moving away from the rotor core radially. The sticks333(only one stick is shown inFIGS. 7-9) are inserted into the corresponding winding slots, one at a time. Then, as shown inFIG. 8, the inserted sticks333are pushed further into the first containment band331, and then are locked with the first containment band331. As shown inFIG. 9, after the sticks333are locked with the first containment band331, the second containment band332is placed to surround the second end-turn segments of the coils32to prevent the second end-turn segments against moving away from the rotor core radially, and then the second containment band332is pushed axially towards the free ends of the sticks333until it gets locked with the sticks333. As such, both the first and second containment bands331,332are locked with the sticks333and prevented against moving away from the rotor core31axially.

When the stick333is pushed into the first containment band331, a first axial end of the stick333bends radially inside the first containment band331, in order to make the first stick-catch334snap fitted to the first containment band331. When the second containment band332is axially pushed towards the sticks333, second axial ends of the sticks333bend radially inside the second containment band332, in order to make the second containment band332snap fitted to the sticks333.

The rotor assembly as described herein above enables safe operation of the rotor at high speeds and temperatures by using the containment bands to radially retain the coil end-turn segments in place and using the sticks to axially arrest the containment bands in place. Moreover, the rotor assembly also enables easy manufacturing, assembly and installation. The sticks used to retain the containment bands can be fabricated by conventional or additive manufacturing technologies, and can be easily inserted into the winding slots along an axial direction during assembly. The containment bands and sticks can easily get locked into each other via snap fit mechanism. The snap fit connection allows creation of axial gaps between the containment bands and the rotor core, which enables wet cavity cooling of the coils, as has been described above in detail.