Method and apparatus for measuring turbine shell clearance

An apparatus for measuring turbine rotor-to-stator clearances and a method for assembling a turbomachine based on the measured clearances are disclosed. In an embodiment, at least one clearance sensor is inserted into a stator of a turbomachine. Using the sensor, tops-on clearance between a rotor blade tip and an inner surface of a stator is measured while an upper stator shell, a rotor, a lower stator shell are assembled together; and a tops-off clearance is measured while the lower stator shell and a rotor are assembled together. A tops-on/tops-off shift, i.e., a difference between the tops-on clearance and the tops-off clearance, is determined. The turbine can be assembled by adjusting a relative position of the rotor and stator to account for the tops-on/tops-off shift.

BACKGROUND OF THE INVENTION

The disclosure relates generally to turbo-machines such as steam and gas turbines, and more particularly, to an apparatus and method for measuring deflection between rotating turbine blade tips and their surrounding casing.

Turbomachines, such as gas and steam turbines, typically include a centrally-disposed rotor that rotates within a stator. A working fluid flows through one or more rows of circumferentially arranged rotating blades that extend radially outward from the rotor shaft. The fluid imparts energy to the shaft, which is used to drive a load such as an electric generator or compressor.

Clearance between radially outer tips of the rotating blades and stationary shrouds on an interior of the stator in, e.g., compressor and turbine sections of gas turbines strongly impacts efficiency of the gas turbine engine. The smaller the clearance between the rotor blades and the inner surface of the stator, the lower the likelihood of fluid leakage across blade tips. Fluid leakage across blade tips causes fluid to bypass a row of blades, reducing efficiency.

Insufficient clearance may also be problematic, however. Operating conditions may cause blades and other components to experience thermal expansion, which may result in variations in blade tip clearance. The specific effects of various operating conditions on blade clearance may vary depending on the type and design of a particular turbomachine. For example, tip clearances in gas turbine compressors may reach their nadir values when the turbine is shut down and cooled, whereas tip clearances in low pressure steam turbines may reach their nadir values during steady state full load operation. If insufficient tip clearance is provided when the turbomachine is assembled or re-assembled after inspection/repair, the rotating blades may hit the surrounding shroud, causing damage to the shroud on the stator interior, the blades, or both when operating under certain conditions.

During turbine assembly and re-assembly after inspection/repair, the lower stator shell is typically assembled first, then the rotor is set in place. Then the upper stator shell is assembled, including affixing the upper shell to the lower shell of the stator as shown inFIG. 1. This may typically be done by, e.g., bolting arm222of upper stator shell220to arm242of lower stator shell240together in a horizontal joint230.

Although rotor-to-stator clearances can be measured in the lower half prior to assembling the upper half (i.e., in the “tops-off” condition, seeFIG. 4), these values are not directly representative of the values in the fully assembled turbine (i.e., in “tops-on” condition, seeFIG. 3) because the turbine shell is supported differently when the upper shell220of the stator is affixed to the lower shell240. In the tops-on condition, support is shifted from the lower shell arm242to the upper shell arms222, the weight of the upper shell220of the stator is added, and when the horizontal joint230is bolted, the overall stator200structure stiffens. As a result of these and other changes, the rotor-to-stator clearance is different in the tops-on and tops-off conditions, by a factor which may not be readily predictable. In the tops-on condition, in which the turbomachine is operated, clearances cannot be measured directly, since the turbomachine is fully assembled, and the rotating blades and inner surface210of stator200are not accessible.

One way the tops-on/tops-off shift has been addressed has been to use clearances between the rotating blade tips and the inner surface of the stator that are sufficiently large as to include the tops-on/tops-off deviation. For reasons discussed above, however, this is detrimental to turbomachine performance and efficiency because it is likely to result in excessive clearances and leakage of working fluid across blade stages.

Another approach has been to use factory tops-on/tops-off data in the field. However, this presents a data management problem, as factory data may be taken years before the turbomachine is disassembled in the field and must be reassembled. Differences in conditions between the factory and the field further complicate this approach.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides an apparatus comprising: at least one sensor inserted in a stator, for measuring a tops-on clearance between a rotor blade tip and an inner surface of a stator while an upper stator shell, a rotor, a lower stator shell are assembled together, and a tops-off clearance between the rotor blade tip and the inner surface of a stator while the lower stator shell and a rotor are assembled together; and a computing device operably connected with the at least one sensor for determining a tops-on/tops-off shift, wherein the tops-on/tops-off shift is a difference between the tops-on clearance and the tops-off clearance.

A second aspect of the disclosure provides a turbomachine comprising: a rotor; and a stator surrounding the rotor, the stator including a lower stator shell and an upper stator shell. At least one sensor is inserted in the lower stator shell, for measuring a tops-on clearance between a rotor blade tip and an inner surface of the stator while the upper stator shell, the rotor, and the lower stator shell are assembled together, and a tops-off clearance between the rotor blade tip and the inner surface of the stator while the lower stator shell and the rotor are assembled together; and a computing device is operably connected with the at least one sensor for determining a tops-on/tops-off shift, wherein the tops-on/tops-off shift is a difference between the tops-on clearance and the tops-off clearance.

A third aspect of the disclosure provides a method for assembling a turbomachine, comprising: using at least one sensor inserted in a stator, measuring a tops-on clearance between a rotor blade tip and an inner surface of a stator while an upper stator shell, a rotor, a lower stator shell are assembled together, and measuring a tops-off clearance between the rotor blade tip and the inner surface of a stator while the lower stator shell and a rotor are assembled together; determining a tops-on/tops-off shift, wherein the tops-on/tops-off shift is a difference between the tops-on clearance and the tops-off clearance; assembling the lower stator shell; placing the rotor on the lower stator shell at a position shifted from a desired rotor position by a distance equal to the tops-on/tops-off shift; and assembling the upper stator shell to the lower stator shell.

These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

At least one embodiment of the present invention is described below in reference to its application in connection with the operation of a turbomachine. Although embodiments of the invention are illustrated relative to a turbomachine in the form of a steam turbine, it is understood that the teachings are equally applicable to other turbomachines, including but not limited to gas turbines. Further, at least one embodiment of the present invention is described below in reference to a nominal size and including a set of nominal dimensions. However, it should be apparent to those skilled in the art that the present invention is likewise applicable to any suitable turbine and/or generator. Further, it should be apparent to those skilled in the art that the present invention is likewise applicable to various scales of the nominal size and/or nominal dimensions.

As indicated above,FIGS. 1-8depict, and aspects of the invention provide, an apparatus for measuring deflection, andFIG. 9depicts a method for assembling a turbomachine using the same.

FIGS. 1-2show different aspects of turbine100(labeled inFIG. 2) in accordance with embodiments of the disclosure.FIG. 1shows an exploded perspective view of an outer shell of stator200, which includes upper stator shell220and lower stator shell240. Upper stator shell220includes an upper stator shell arm222; lower stator shell240likewise includes lower stator shell arm242. As shown inFIG. 2, stator200surrounds rotor120, which rotates about a longitudinal axis250within stator200.

As shown inFIG. 3, lower stator shell240includes at least one clearance sensor300inserted therein. Clearance sensor300may be inserted in lower stator shell240such that clearance sensor300is embedded in lower stator shell240with a radially outer edge of clearance sensor300substantially flush with an inner surface210of the stator200. In some embodiments, as shown inFIGS. 3-4, clearance sensor300is located at a bottom dead-center position in the lower shell240of stator200. In other embodiments, clearance sensor300may be offset from a bottom dead center position by a margin of degrees which may be accounted for in calculations. Clearance sensor300is used for measuring clearances310,320(FIGS. 3,4respectively) between a tip of blade140on rotor120(FIG. 5), i.e., the radially outermost point on rotor120, and an inner surface210of stator200. As shown inFIG. 5, the radially outermost point on rotor120blade140may be a blade seal tooth tip160.

In further embodiments, such as the embodiment shown inFIG. 6, clearance sensor300may comprise a plurality of clearance sensors300. In the embodiment inFIG. 6, clearance sensors300are separated by two stages of blades. In other embodiments, between about 3 and about 6 clearance sensors300may be axially spaced along stator200. In further embodiments, a plurality of clearance sensors300may be arranged such that one clearance sensor300is axially aligned with each of a plurality of stages of blades on rotor120. In such an embodiment, the number of clearance sensors300may be equal to the number of stages of blades on rotor120. In other arrangements, one clearance sensor300may be axially aligned with every other stage of blades on rotor120, such that the number of clearance sensors300may be equal to half of the number of stages of blades on rotor120. These arrangements are merely illustrative, however; other arrangements of clearance sensors300relative to stages of blades on rotor120are contemplated as other embodiments of the invention.

As further shown inFIG. 7, clearance sensor300may be mounted to stator200and held in place by means of sensor retainer member330. Sensor retainer member330may be substantially tube-shaped, with a passageway therein for clearance sensor instrumentation leads340, and a flange member331at a radially outward end relative to turbine200. In some embodiments, sensor retainer member330may comprise a single member; in other embodiments sensor retainer member330may comprise two separate members, each including a semi-annular portion and portion of flange member331such that they can be inserted into stator200separately and joined together to position clearance sensor300and contain clearance sensor instrumentation leads340. Bolts370may be used to affix flange member331of sensor retainer330to stator200.

In order to avoid a potential steam leakage path380along sensor retainer member330, clearance sensor300may be either permanently affixed in a manner that fully seals the interface (e.g., welded, brazed, cemented, etc.) or may be installed with enough contact surface area and contact force so as to prevent leakage along path380. In the embodiment shown inFIGS. 7-8, substantially annularly shaped sealing member385includes surface390, which acts as a sealing surface. Surface390is a substantially annularly shaped surface at the distal end, i.e., the end nearer clearance sensor300.

A proximal end305of clearance sensor300mates with a surface390(FIG. 7), and the surfaces are forced together to prevent leakage of working fluid in the turbine. Retainer member330and the bolts370or other method of affixation provide the force necessary to ensure a proper seal. Force may also be applied using other types of springs or fluid systems, e.g., hydraulic or pneumatic. Gaskets or other sealing devices may also be used to provide a seal.

In embodiments in which turbine100is single-shell construction, the clearance sensor300may be embedded in the shell or the nozzle ring. In either case, the clearance sensor300and related hardware (including, e.g., sensor retainer member330) would penetrate the shell. In embodiments in which turbine100has double-shell construction, the clearance sensor300could be embedded in the inner shell (or nozzle carrier), as shown here inFIG. 7, or in a nozzle outer ring. In such an embodiment, the inner shell would be penetrated by the clearance sensor300and related hardware, and clearance sensor instrumentation leads340would exit turbine100through an instrumentation port in the outer shell.

Referring back toFIG. 3, clearance sensor300may measure a tops-on clearance310, which is the clearance between rotor120and inner surface210as measured while upper stator shell220, rotor120, and lower stator shell240are assembled together. Clearance sensor300may also measure tops-off clearance320(FIG. 4), which is the clearance between rotor120and inner surface210as measured while lower stator shell240and rotor120are assembled together. In some embodiments, clearance sensor300may be a voltage drop sensor, and may measure a voltage drop across a clearance310,320between a tip of sensor300and a point on rotor120. Other types of sensors, either now known or later developed, may also be used.

Clearance sensor300may further be in signal communication with computing device350via clearance sensor instrumentation leads340. Upon measuring a clearance310,320, clearance sensor300may transmit a signal representing the clearance310,320to computing device350. As shown inFIG. 3, computing device350includes a processing unit346, a memory352, and input/output (I/O) interfaces348operably connected to one another by pathway354, which provides a communications link between each of the components in computing device350. Further, computing device350is shown in communication with display356, external I/O devices/resources358, and storage unit360. I/O resources/devices358can comprise one or more human I/O devices, such as a mouse, keyboard, joystick, numeric keypad, or alphanumeric keypad or other selection device, which enable a human user to interact with computing device350and/or one or more communications devices to enable a device user to communicate with computing device350using any type of communications link. Computing device350is shown in phantom inFIG. 4for purposes of brevity only.

In general, processing unit346executes computer program code362which provides the functions of computing device350. Modules, such as shift calculator module364, which is described further herein, are stored in memory352and/or storage unit360, and perform the functions and/or steps of the present invention as described herein. Memory352and/or storage unit360can comprise any combination of various types of computer readable data storage media that reside at one or more physical locations. To this extent, storage unit360could include one or more storage devices, such as a magnetic disk drive or an optical disk drive. Still further, it is understood that one or more additional components not shown inFIG. 3can be included in computing device350. Additionally, in some embodiments one or more external devices358, display356, and/or storage unit360could be contained within computing device350, rather than externally as shown, in the form of a computing device350which may be portable and/or handheld.

Computing device350can comprise one or more general purpose computing articles of manufacture capable of executing program code, such as program362, installed thereon. As used herein, it is understood that “program code” means any collection of instructions, in any language, code or notation, that cause a computing device having an information processing capability to perform a particular action either directly or after any combination of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form; and/or (c) decompression. To this extent, program362can be embodied as any combination of system software and/or application software.

Further, program362can be implemented using a module such as shift calculator364or set of modules366. In this case, calculator364can enable computing device350to perform a set of tasks used by program362, and can be separately developed and/or implemented apart from other portions of program362. As used herein, the term “component” means any configuration of hardware, with or without software, which implements the functionality described in conjunction therewith using any solution, while the term “module” means program code that enables a computing device350to implement the actions described in conjunction therewith using any solution. When fixed in memory352or storage unit360of a computing device350that includes a processing unit346, a module is a substantial portion of a component that implements the actions. Regardless, it is understood that two or more components, modules, and/or systems may share some/all of their respective hardware and/or software. Further, it is understood that some of the functionality discussed herein may not be implemented or additional functionality may be included as part of computing device350.

When computing device350comprises multiple computing devices, each computing device can have only a portion of program362fixed thereon (e.g., one or more modules364,366). However, it is understood that computing device350and program362are only representative of various possible equivalent computer systems that may perform a process described herein. To this extent, in other embodiments, the functionality provided by computing device350and program362can be at least partially implemented by one or more computing devices that include any combination of general and/or specific purpose hardware with or without program code, including but not limited to a handheld measuring device for stator-to-rotor clearance. In each embodiment, the hardware and program code, if included, can be created using standard engineering and programming techniques, respectively.

When computing device350includes multiple computing devices, the computing devices can communicate over any type of communications link. Further, while performing a process described herein, computing device350can communicate with one or more other computer systems using any type of communications link. In either case, the communications link can comprise any combination of various types of wired and/or wireless links; comprise any combination of one or more types of networks; and/or utilize any combination of various types of transmission techniques and protocols.

As noted, computing device350includes a shift calculator module364for analyzing a signal provided by clearance sensor300. Using a signal from clearance sensor300representing a tops-on clearance310and a signal representing tops-off clearance320, shift calculator module364may calculate a tops-on/tops-off shift. The tops-on/tops-off shift is equal to the difference between tops-on clearance310and tops-off clearance320, and represents the shift in position attributable to installing upper stator shell220to lower stator shell240.

Tops-on clearance310may be measured when turbomachine100is shutdown and cool. In further embodiments, rotor120may be rotated on a turning gear during measurement of tops-on clearance310. This allows clearance310to account for any variations in clearance related to variations in radially extending length of blades on rotor120. When measuring tops-off clearance320, a motor such as, e.g., an air motor, may be used to rotate rotor120for the same purpose. During measurement of tops-off clearance320, rotor120is rotated slowly. For example, rotor120may be rotated at a speed of one half of a rotation per minute.

The measurements of tops-on clearance310and tops-off clearance320as described above may be used in a method for assembling a turbomachine100. Referring toFIG. 9, in step S1, using clearance sensor (or sensors)300inserted in lower stator shell240of stator200, tops-on clearance310may be measured while upper stator shell220, rotor120, a lower stator shell240are assembled together (FIG. 3). In step S2, tops-off clearance320may be measured while lower stator shell240and rotor120are assembled together (FIG. 4). It is noted that steps S1and S2may be performed with either step S1prior to S2, or the reverse, with step S2prior to step S1.

In step S3, using computing device350, including shift calculator module364as described above, a tops-on/tops-off shift may be determined. The tops-on/tops-off shift is equal to the difference between tops-on clearance310and tops-off clearance320.

Where, for example, turbomachine100had been disassembled for maintenance and/or repair, it may be reassembled by first assembling lower stator shell240(step S4), and placing rotor120on lower stator shell240(step S5). As discussed above, however, rotor120is not placed such rotor120is in the desired rotor position relative to lower stator shell240, i.e., tops-off clearance320is not equal to the clearance that results in maximal efficiency of turbomachine100. Rather, rotor120is placed in position relative to lower stator shell240such that it is shifted from the desired rotor position by a distance equal to the tops-on/tops-off shift. Where a plurality of clearance sensors300are used, the relative positions of rotor120and lower stator shell240are adjusted such that at each axial location of a clearance sensor300, rotor120is shifted by the tops-on/tops-off shift as described above.

Adjustments in the relative positions of rotor120and lower stator shell240in order to achieve the appropriate shift from the desired rotor position may be made in a variety of ways. In one embodiment, the position of rotor120may be adjusted relative to lower stator shell240in accordance with the tops-on/tops-off shift. Such manipulation of rotor120may be accomplished by, e.g., adjusting the rotor bearings. In another embodiment, lower stator shell240may be adjusted. Lower stator shell240may be manipulated by, e.g., shimming or adjusting stator components including but not limited to nozzles180and other stator components. Each nozzle stage180(seeFIGS. 5-7) may be individually adjustable. Where nozzles180are not individually adjustable, a best fit may be used, based on measured data from clearance sensor300.

In step S6, upper stator shell220is assembled to lower stator shell240. As the weight of upper stator shell220is added, and horizontal joint230between upper and lower stator shells220,240is affixed by, e.g., bolts at horizontal joint230, rotor120is shifted such that it is positioned relative to inner surface210of stator200such that when operated, it will produce maximal efficiency without impacting inner surface210of stator200.

As previously mentioned and discussed further herein, the apparatus for measuring deflection, including clearance sensor300, has the technical effect of enabling measurement of the tops-on clearance310and tops-off clearance320between rotor120and stator using clearance sensor300. Using the measured tops-on310and tops-off320clearances, a tops-on/tops-off shift can be calculated. This tops-on/tops-off shift may be used to assemble or re-assemble turbomachine100by placing rotor120on lower stator shell240, shifted from the desired position (relative to lower stator shell240) by a distance equal to the tops-on/tops-off shift. When upper stator shell220is affixed to lower stator shell240, the resulting rotor120position will be as desired. It is understood that some of the various components shown inFIG. 3can be implemented independently, combined, and/or stored in memory for one or more separate computing devices that are included in computing device350.

As used herein, the terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 6, or, more specifically, about 3 to about 6 sensors,” is inclusive of the endpoints and all intermediate values of the ranges of “about 3 to about 6,” etc.).

While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.