Title:
SYSTEM AND METHOD FOR ADJUSTING CLEARANCE IN A GAS TURBINE
Kind Code:
A1


Abstract:
A system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets is disclosed. The system includes: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an elongated member extending from the turbine shell. The at least one shroud segment is attached to an end of the elongated member, the elongated member configured to move in response to a temperature change to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.



Inventors:
Wilson, Ian David (Simpsonville, SC, US)
Miller, Bradley James (Simpsonville, SC, US)
Scicchitano, Eric (Montreal, CA)
Application Number:
12/201174
Publication Date:
03/04/2010
Filing Date:
08/29/2008
Assignee:
GENERAL ELECTRIC COMPANY (Schenectady, NY, US)
Primary Class:
Other Classes:
415/1, 415/126
International Classes:
F01D11/22
View Patent Images:
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Primary Examiner:
FOURSON III, GEORGE R
Attorney, Agent or Firm:
Cantor Colburn LLP - General Electric (Hartford, CT, US)
Claims:
1. A system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets, the system comprising: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an elongated member extending from the turbine shell; wherein the at least one shroud segment is attached to an end of the elongated member, the elongated member configured to move in response to a temperature change to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.

2. The system of claim 1, wherein a coefficient of thermal expansion (CTE) of the elongated member is different than the CTE of the turbine shell.

3. The system of claim 1, wherein the elongated member extends through the turbine shell in a radial direction, the radial direction being normal to a major axis of the turbine rotor.

4. The system of claim 1, further comprising a tube extending through at least a portion of the turbine shell, the elongated member extending through the tube.

5. The system of claim 4, wherein a coefficient of thermal expansion (CTE) of the elongated member is different than the CTE of the tube.

6. The system of claim 1, wherein the elongated member is selected from a hollow rod and a solid rod.

7. The system of claim 1, further comprising a protrusion attached to an exterior of the turbine shell and attached to the elongated member, and an electric heat source in thermal communication with the protrusion for changing the temperature of at least one of the protrusion and the elongated member.

8. The system of claim 1, wherein the at least one segment includes an outer shroud attached to the turbine shell, an intermediate shroud attached to the elongated member, and an inner shroud attached to the intermediate shroud.

9. The system of claim 1, further comprising an inlet through at least one of the elongated member and the turbine shell for introducing a thermal source to the elongated member.

10. The system of claim 9, wherein the thermal source is selected from at least one of steam, air and gas.

11. The system of claim 1, wherein the shroud assembly includes a plurality of shroud segments configured to form a ring.

12. The system of claim 1, further comprising an adjustment device at a connection point between the elongated member and the turbine shell, the adjustment device configured to be engaged to move the elongated member relative to the turbine shell.

13. The system of claim 1, further comprising at least one additional elongated member extending from the turbine shell and attached to the at least one shroud segment, wherein both the elongated member and the at least one additional elongated member extend in an average direction parallel to a radial direction extending from a rotational axis of the gas turbine.

14. A method of adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets, the method comprising: disposing a shroud assembly on a turbine shell, the shroud assembly including a shroud segment attached to one end of an elongated member; extending the elongated member from the turbine shell and disposing the shroud segment in an interior of a turbine shell; and applying a thermal source to the shroud assembly to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.

15. The method of claim 14, wherein applying the thermal source includes applying the thermal source to the elongated member to elevate a temperature of the elongated member to cause the shroud segment to move radially toward an interior of the turbine shell.

16. The method of claim 14, wherein applying the thermal source includes applying the thermal source to the elongated member to reduce a temperature of the elongated member to cause the shroud segment to move radially away from an interior of the turbine shell.

17. The method of claim 14, wherein the shroud assembly includes a protrusion attached to an exterior of the turbine shell and attached to the elongated member.

18. The method of claim 17, wherein applying the thermal source includes applying the thermal source to the protrusion to cause the protrusion to thermally expand and move the elongated member radially away from the interior of the turbine shell.

19. The method of claim 14, wherein disposing the shroud segment includes determining a maximum pinch between the bucket tip and the shroud segment, and disposing the shroud segment at an initial radial location based on the maximum pinch.

20. The method of claim 19, further comprising retracting the shroud segment to the initial position upon a malfunction of the shroud assembly.

Description:

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to gas turbines and, more particularly, to methods and systems for adjusting clearance between bucket or blade tips and a shroud assembly connected to a turbine shell.

In order to improve efficiency, gas turbines, such as those used in power generation or aviation, utilize a turbine “shroud” disposed in a turbine shell. The shroud provides for a reduced clearance between the tips of buckets disposed on the turbine rotor and the shroud in comparison to a clearance between the bucket tips and the turbine shell. Such reduced clearance provides enhanced efficiency by maintaining a reduced threshold clearance between the shroud and tips of the buckets to prevent unwanted “leakage” of hot gas over tips of the buckets. Increased clearances can lead to gas leakage which can reduce turbine efficiency.

Current shroud systems employ solely segmented shrouds connected to the turbine shell and held together by, for example, turbine shell hooks. The clearance between the bucket tips and the shroud is simply driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Initial bucket tip/shroud clearances may be set high enough to prevent rubbing, but such clearances cannot be actively controlled in transient or in steady state conditions. Both turbine shell out-of-roundness and transient bucket/shroud rubbing play a major role in increased steady state clearances. Cold-built clearances, i.e., clearances set prior to operation, can be set high enough to mitigate rubbing, but, in effect, this will drive up steady state clearances, and thereby reduce engine efficiency and output. Accordingly, there is a need for improved systems and methods for controlling clearance between bucket tips and shrouds in a gas turbine, such as during transient and/or steady state operation of the turbine.

BRIEF DESCRIPTION OF THE INVENTION

A system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets, constructed in accordance with exemplary embodiments of the invention includes: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an elongated member extending from the turbine shell. The at least one shroud segment is attached to an end of the elongated member, the elongated member configured to move in response to a temperature change to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.

Other exemplary embodiments of the invention include a method of adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets. The method includes: disposing a shroud assembly on a turbine shell, the shroud assembly including a shroud segment attached to one end of an elongated member; extending the elongated member from the turbine shell and disposing the shroud segment in an interior of a turbine shell; and applying a thermal source to the shroud assembly to move the shroud segment and change a clearance between the shroud segment and at least one of the plurality of buckets.

Additional features and advantages are realized through the techniques of exemplary embodiments of the invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features thereof, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gas turbine in accordance with an exemplary embodiment of the invention;

FIG. 2 is a side view of an exemplary embodiment of a shroud assembly coupled to the gas turbine of FIG. 1;

FIG. 3 is a side view of another exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 4 is an axial and side view of another exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 5 is an axial and side view of another exemplary embodiment of the shroud assembly of FIG. 2, including exemplary values for clearance between a shroud and a turbine shell;

FIG. 6 is a side view of a further exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 7 is a side view of another exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 8 is a side view of another exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 9 is a side view of another exemplary embodiment of the shroud assembly of FIG. 2;

FIG. 10 is an axial view of an exemplary embodiment of a cooling configuration of the shroud assembly of FIG. 2;

FIG. 11 is an axial view of another exemplary embodiment of the cooling configuration of FIG. 10;

FIG. 12 is an axial view of another exemplary embodiment of the cooling configuration of FIG. 10;

FIG. 13 is an illustration of a system for controlling clearance between a shroud and a bucket tip in a gas turbine; and

FIG. 14 is a flow chart providing an exemplary method for controlling clearance between a shroud and a bucket tip in a gas turbine.

DETAILED DESCRIPTION OF THE INVENTION

There is provided a system and method for displacing a component in a turbine or other system. The system includes a thermally actuated member that is configured to move in response to a temperature change. In one embodiment, a coefficient of thermal expansion (“CTE”) of the thermally actuated member is different than the CTE of one or more structures attached thereto. A method is provided that includes heating or cooling the thermally actuated member to cause movement of the member. In one embodiment, the thermally actuated member is an elongated member such as a rod or cylinder.

In one embodiment, the system includes the thermally actuated member connected at one end to a turbine shell or other body, and connected at another end to a movable member such as a turbine shroud, to adjust a clearance between bucket tips and one or more shrouds located on a gas turbine. Although bucket tips are described herein, the system may be utilized with any type of bucket, blade or other device for causing movement of a turbine rotor. The elongated member is described herein as a generally cylindrical rod or tube, but may be any suitable shape having a dimension in the radial direction. As used herein, the term “radial” refers to a direction extending from the center of the turbine rotor or a rotational axis of the turbine rotor, and perpendicular to the major axis or the rotational axis of the turbine rotor. Although the thermally actuated member is described herein in conjunction with turbine assemblies, the thermally actuated member may be utilized in conjunction with any system or apparatus utilizing displacement of components.

With reference to FIG. 1, a gas turbine assembly constructed in accordance with an exemplary embodiment of the invention is indicated generally at 10. The gas turbine assembly 10 includes a turbine shell 12 which is held in place around a compressor 14 and a power turbine 16, which are connected by a rotor 18. A combustion chamber 20 is formed between the compressor 14 and turbine 16 sections of the assembly 10. A plurality of rotor blades or buckets 39 are connected to the turbine 16 via, for example, a rotor disk. The turbine shell 12 includes a plurality of shroud assemblies 30 attached to an interior portion of the turbine shell 12 and defining a clearance “C” between the shroud assembly 30 and the buckets 39.

Referring to FIG. 2, a shroud assembly 30 is disposed in the turbine shell 12. The shroud assembly 30 includes one or more shroud segments 31, each of which is removably attached to an elongated member 32 by any suitable mechanism, such as a bayonet attachment or a threaded attachment. The elongated member 32 extends radially from the turbine shell 12 toward the bucket 39. The shroud segment 31 is separated from the bucket 39, and the distance between a tip of the bucket 39 defines the clearance “C” between the inner shroud 40 and the bucket tip. The elongated member 32 has a coefficient of thermal expansion (“CTE”) that is different from the CTE of the turbine shell 12 and/or other components. In one embodiment, the elongated member 32 has a CTE that is greater than the turbine shell 12. The elongated member 32 is expandable and/or retractable by selecting a temperature of the elongated member to control the clearance C between the shroud segment 31 and the bucket 39.

Referring to FIG. 3, in one embodiment, the elongated member 32 extends radially from an exterior wall 42 and through a tube 44 formed through the turbine shell 12 and a protrusion 46 such as a boss. The radial length of the protrusion 46 is selected, in one embodiment, to increase the radial length of the elongated member 32 and thereby increase or adjust the amount of displacement of the elongated member 32 in response to changes of temperature. In this embodiment, the protrusion 46 is made from a material, such as an alloy, having a higher CTE than that of the elongated member 32. In one embodiment, an electric heater 48 is disposed in contact with the protrusion 46, so that heat can be applied to the elongated member 32 and/or the protrusion 46 to control the expansion of the elongated member 32 and/or the protrusion 46.

In one embodiment, the elongated member 32 has a coefficient of thermal expansion (“CTE”) that is different from the CTE of the protrusion 46 and or the turbine shell 12. For example, as shown in FIG. 4, the elongated member 32 has a CTE that is less than the CTE of the protrusion 46. By selecting the CTE of each component, the amount of extension of the inner shroud 40 is controllable relative to the amount of heating or cooling applied. For example, because the elongated member 32 has a CTE that is less than the CTE of the protrusion 46, heat can be applied to the protrusion 46 to control displacement of the shroud assembly 30 without the elongated member 32 providing any significant contribution to the displacement. In one embodiment, the elongated member 32 has a CTE that is sufficiently low so that displacement is substantially a result of heating the protrusion 46.

Referring to FIG. 4, another embodiment of the shroud assembly 30 is disposed in the turbine shell 12. In this embodiment, the one or more shroud segments 31 each include the elongated member 32, an outer shroud 34 attached to the interior wall 36 of the turbine shell 12, an intermediate shroud 38 attached to the elongated member 32, and an inner shroud 40 attached to the intermediate shroud 38. In one embodiment, the intermediate shroud 38 is removably attached to the elongated member by any suitable mechanism, such as a bayonet attachment or a threaded attachment. The inner shroud 40 is separated from a bucket 39, and the distance between a tip of the bucket 39 defines the clearance between the inner shroud 40 and the bucket tip.

In one embodiment, the shroud assembly 30 includes any number of segments 3 1, and each segment 31 includes at least one elongated member 32 and at least one of the shrouds, 34, 38, 40. In the example shown in FIG. 2, the shroud assembly 30 forms a ring shroud having four quadrants. Each segment 31 includes one elongated member 32, one outer shroud 34, one intermediate shroud 38, and six inner shrouds 40. The number and size of segments 31, and the number of elongated members 32 and shrouds 34, 3 8, 40 described in the embodiments herein is exemplary and is not limited.

In one embodiment, an inlet 50 is included to allow heated air or steam from the interior of the turbine shell 12 or allow other heating or cooling sources. Such sources may include air, gas and steam.

In one embodiment, a securing or adjusting mechanism 52 is attached to the elongated member 32. The mechanism 52 is connectable to the protrusion 46 to allow the elongated member 32 to be manually or mechanically moved or removed from the shroud assembly 30.

In another embodiment, insulation 54 is provided to thermally isolate the elongated member 32 from the protrusion 46, and heating or cooling sources can be applied to the elongated member 32 via the inlet 50. Alternatively, this embodiment allows for air from the interior of the turbine shell 12 to maintain the elongated member 32 at a specified temperature, and retract the elongated member 32 by applying heat to the protrusion 46 and causing the protrusion 46 to expand and thereby retract the elongated member 32. For example, during transient operation, the electric heater 48 is turned on at the time of maximum pinch between the bucket tip and the inner shroud 40 to expand the protrusion 46 and cause the elongated member 32 to retract. In this embodiment, the elongated member 32 has a CTE that is less than the CTE of the protrusion 46.

Referring to FIG. 5, another embodiment of the shroud assembly 30 is shown. In this embodiment, the elongated member 32 is a hollow cylindrical rod disposed in the tube 44. The tube 44 extends through the turbine shell 12, and is sealed from the exterior of the turbine shell by a cap 56. In one embodiment, the tube 44 extends partially through the interior of the wall of the turbine shell, and is thus sealed by the wall itself. The elongated member 32 is attached to the intermediate shroud 38 and is secured in position by a positioning mechanism 58. The elongated member 32 may be connected to the positioning mechanism 58 by a mechanical attachment, such as a threaded or bayonet attachment, or may simply act as a centering mechanism and protrude into the tube 44 to prevent the elongated member from moving about an axis of the tube 44. Heating or cooling sources can be applied to the inlet 50 to adjust the temperature of the elongated member 32.

In one example, the elongated member 32 has a radial height of nine inches, the turbine shell has a radial height of six inches, and the outer shroud has a radial height of three inches.

Referring to FIG. 6, another embodiment of the shroud assembly 30 includes the elongated member 32 that extends through the protrusion 46 and the turbine shell 12, and is attached to the intermediate shroud 38. The elongated member 32 is attached to the securing or adjusting mechanism 52. As shown in this embodiment, the intermediate shroud 38 forms a “u” shape that may be designed to define a distance by which the elongated member can be retracted. In addition to adjusting temperature and providing selected materials having selected CTEs, this feature provides another mechanism by which to control movement of the inner shroud 40. In one embodiment, the shroud assembly includes a purging system 60. The purging system includes a purge conduit to allow cooling air or other material to be applied to the intermediate and inner shrouds 38, 40.

Referring to FIG. 7, another embodiment of the shroud assembly 30 includes an elongated member conduit 64 extending through a portion of the length of the elongated member 32. This partially hollow elongated member 32 includes a solid portion at an end of the elongated member 32 located at or near an exterior of the turbine shell 12. In this embodiment, gas from the turbine shell interior and/or other thermal sources may be applied through the inlet 50 to the interior of the elongated member 32, with the exterior end of the elongated member 32 preventing the thermal source from escaping to the exterior of the turbine shell 12.

In another embodiment of the shroud assembly 30, the outer shroud 34 is pocketed and includes a pin 66 or other fastening mechanism that attaches the outer shroud 34 to the turbine shell 12. The pin 66 is removable in an axial direction, to in turn allow the outer shroud 34 to be removed axially so that components such as the inner shroud 40 can be accessed. Additional pins or other fastening mechanisms are included to attach the intermediate shroud 38 to the elongated member 32.

Referring to FIG. 8, yet another embodiment of the shroud assembly 30 includes a hollow elongated member 32 having a conduit 64 extending along the entire length of the elongated member 32. In this embodiment, discharge gas from the turbine 10, cooling air, gas or steam, or other materials can be applied to the interior of the elongated member 32 from an exterior of the turbine shell 12. In one embodiment, stabilizing protrusions 68, such as one or more individual protrusions or a ring, protruding toward the interior of the elongated member conduit are included to assist in stabilizing the elongated member 32 within the tube 44.

In another embodiment, the securing or adjusting mechanism includes a locking feature 70 attached to an alignment feature 71, which allows the elongated member to be mechanically or manually aligned within the tube 44 and/or allows the elongated member 32 to be advanced or retracted radially to adjust the clearance between the inner shroud 40 and the bucket tips. In another embodiment, the elongated member 32 is a solid elongated member.

Referring to FIG. 9, another embodiment of the shroud assembly 30 includes the locking/alignment cap 70, another embodiment of the stabilizing protrusions 68 which are separately constructed and attached to the turbine shell 12, and pins 66. An additional pin 72 is provided to secure the intermediate shroud 38 to the elongated member 32 and allow for axial removal of the pin 72 for removal of the intermediate shroud 38. In one embodiment, shroud conduits 74 are provided to allow gas from the interior of the turbine shell 12 or from other sources to enter the tube 44 and exit through the intermediate shroud 38.

FIGS. 10-12 provide configurations of the shroud assembly 30 including cooling applications for cooling the inner shrouds 40. In each of these configurations, the shroud assembly includes a plurality of intermediate shrouds 38 and a plurality of inner shrouds 40 forming a ring.

FIG. 10 illustrates a configuration including hollow elongated members 32 through which a cooling source 78 such as air, gas or steam can be introduced to the inner shrouds 40. In this embodiment, a single hollow elongated member 32 is associated with each intermediate shroud 38. The shroud assembly 30, for example, includes twenty intermediate shrouds 38 and one hundred inner shrouds 40.

Referring to FIG. 11, another embodiment of the shroud assembly 30 includes two hollow elongated members 32 per intermediate shroud 38, and also includes a cavity 80 in the intermediate shroud 38 through which the cooling source 78 can be introduced to the inner shrouds 40. In this embodiment, the cooling source 78 can enter and exit through the hollow elongated members 32, and can also enter through the cavity 80. The shroud assembly 30, for example, includes ten intermediate shrouds 38 and one hundred inner shrouds 40.

In one embodiment, if there are two or more elongated members 32 per shroud assembly 30, the elongated members 32 extend parallel to one another. The average of the angular deviation of each elongated member 32 from a radial line extending from the rotational axis is equal to zero. This orientation helps to prevent possible binding during operation. For example, if a third elongated member 32 is placed half way between the first two elongated members 32, the third elongated member 32 is oriented along the radial line, and all of the elongated members 32 are parallel to one another.

FIG. 12 shows another embodiment of the cooling scheme, including a single elongated member 32 per intermediate shroud 38, and a single cavity 80 per intermediate shroud 38. In another embodiment, any number of elongated members and/or cavities 80 are included with each intermediate shroud 38.

Referring to FIG. 13, there is provided a system 90 for controlling a clearance between a shroud 34, 38, 40 and one or more bucket tips. The system may be incorporated in a computer 91 or other processing unit capable of receiving data from users or from sensors incorporated with the shroud assembly. A displacement sensor 92 is also coupled to the computer 91 so that the computer 91 can control the shroud assembly 30 to achieve or maintain a desired clearance. In one embodiment, the shroud assembly includes or is operably connected to a heating mechanism such as the electric heater 48 and/or a relay or other switch connected to an electrical power source. The computer 91, in one embodiment, also is connected to and able to control sources of thermal energy, such as the electric heater 48 and gas, steam and/or air sources. The processing unit may be included with the shroud assembly 30 or included as part of a remote processing unit.

In one embodiment, the system 90 includes a computer 91 coupled to a device such as the displacement senor 92 to measure the clearance between the bucket tip and the shroud assembly 30. Exemplary components include, without limitation, at least one processor, storage, memory, input devices, output devices and the like. As these components are known to those skilled in the art, these are not depicted in any detail herein.

In one embodiment, the computer 91 is configured to automatically retract the inner shroud 40 to an initial position upon detection of a malfunction in the shroud assembly 30.

Generally, some of the teachings herein are reduced to instructions that are stored on machine-readable media. The instructions are implemented by the computer 91 and provide operators with desired output.

FIG. 14 illustrates an exemplary method 100 for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets. The method 100 includes one or more stages 101-104. In an exemplary embodiment, the method includes the execution of all of stages 101-104 in the order described. However, certain stages may be omitted, stages may be added, or the order of the stages changed. In the exemplary embodiments described herein, the method is described in conjunction with the shroud assembly 30 and the computer 91. However, the method 100 may be performed in conjunction with any type of processor or performed manually.

In the first stage 101, the shroud assembly 30 is disposed on the turbine shell 12. The elongated member 32 is extended through at least a portion of the wall of the turbine shell 12 and the inner shroud is positioned in the interior of the turbine shell 12.

In the second stage 102, the elongated member 32 is initially disposed to a selected radial distance from the interior of the turbine shell 12. In one embodiment, this is accomplished by disposing the shroud assembly 30 and designating the radial distance of the outer shroud 34, the intermediate shroud 38 and/or the inner shroud 40 so that a selected minimum distance is set. In one embodiment, this may be accomplished by moving the elongated member 32 radially through the tube 44. In one embodiment, the minimum distance is selected based on the maximum pinch between the bucket tip and the inner shroud 40, that is, the closest approach between the bucket tip and the inner shroud 40.

In the third stage 103, the turbine 10 is activated. Activation in turn causes rotation of the turbine rotor and the buckets 39.

In the fourth stage 104, a thermal source such as the electric heater 46, steam, air and gas is applied to the shroud assembly 30 to move the inner shroud 40 and change a clearance between the inner shroud 40 and at least one of the plurality of buckets tips. In one embodiment, a thermal source is applied to the elongated member 32 to raise the temperature of the elongated member, causing it to expand and advance the inner shroud 40 toward the interior of the turbine shell 12 to reduce the clearance between the inner shroud 40 and the bucket tips. In another embodiment, the thermal source is applied to the elongated member 32 to reduce its temperature to retract the inner shroud 40 away from the interior of the turbine shell 12.

In one embodiment, the electric heater 46 is activated to elevate the temperature of the protrusion 46 and/or the elongated member 32. In response, the elongated member expands and extends in the radial direction to decrease the clearance between the inner shroud and the bucket tip. In one embodiment, a thermal source is applied to the elongated member via the protrusion 46 and/or the inlet 50, to extend or retract the inner shroud 40. As discussed above, applying a heating source will raise the temperature of the elongated member and extend the inner shroud 40, and applying a cooling source will lower the temperature of the elongated member and retract the shroud 40.

In one embodiment, the elongated member is maintained at a selected temperature, such as by applying air from the interior of the turbine shell 12 through the conduit 50, and the elongated member 32 is retracted by applying heat to the protrusion 46 and causing the protrusion 46 to expand and thereby retract the elongated member 32. For example, during transient operation, the electric heater 48 is turned on at the time of maximum pinch between the bucket tip and the inner shroud 40 to expand the protrusion 46 and cause the elongated member 32 to retract.

Although the systems and methods described herein are provided in conjunction with gas turbines, any other suitable type of turbine may be used. For example, the systems and methods described herein may be used with a steam turbine or turbine including both gas and steam generation.

The system and method described herein provide numerous advantages over prior art systems. For example, the systems and methods provide the technical effect of allowing active control of the clearance between the bucket tip and the shroud, which will allow a user to run the turbine engine at tighter clearances than prior art systems. These systems and method are a simple and inexpensive means of moving the shrouds independently to control clearances and to account for manufacturing differences.

The systems and methods described herein allow for tighter clearances than prior art systems, which increases overall efficiency relative to prior art designs. Prior art systems employ solely segmented shrouds held together by turbine shell hooks. The clearance is simple driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Bucket tip/shroud clearances may be set high enough to prevent rubbing, but clearances may not be actively controlled in transient, nor in steady state conditions. The systems and methods described herein are advantageous in that they provide for active control of the shroud assembly during both transient and steady state conditions.

The capabilities of the embodiments disclosed herein can be implemented in software, firmware, hardware or some combination thereof As one example, one or more aspects of the embodiments disclosed can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has embodied therein, for instance, computer readable program code means for providing and facilitating the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately. Additionally, at least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform the capabilities of the disclosed embodiments can be provided.

In general, this written description uses examples to disclose the invention, including the best mode, 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 exemplary embodiments of the invention 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 language of the claims.