Segmented Seating Plates And Anchoring Means For A Turbine Power Plant

Abstract

The invention relates to a segmented seating plate construction for providing a positive anchor for tandem-connected low pressure turbines of a turbine-generator power plant. Rectangularly arranged seating plate segments, which are not interconnected, are provided for each low pressure turbine. In both of the opposite central seating plate segments for the central low pressure turbine, located in a tandem arrangement between two other low pressure turbines having segmented seating plates, there is provided a keyway for restraining axial movements, such as those due to thermal expansion of the turbines. Each of the central seating plate segments is securely held in position by a vertically extending anchor embedded in the concrete foundation and connected to such segment by an eccentric bushing structure.

Description

BACKGROUND OF THE INVENTION

In a well known and typical tandem compound arrangement of steam turbine casings, three low pressure turbines are arranged in line and interconnected by push-pull tie beams. A generator and exciter are disposed adjacent one of the end low pressure turbines, and an intermediate pressure turbine and high pressure turbine with intermediate bearing pedestals are disposed adjacent the other end low pressure turbine. A steam condenser is disposed below the low pressure turbines and along the transverse centerline of the central low pressure turbine, while the axial center lines of the turbine and condenser are parallel.

In the prior art, an anchored point or point of fixity is established at the transverse centerline of the condenser and of the central low pressure turbine. The low pressure turbine casings respond to the same temperature increase due to changes in the heat power cycle and generally the casings exhaust into the same condenser. Therefore the casings and condensers expand uniformly in all directions. However, each low pressure turbine is positioned on its seating plate which is, in effect, a one piece unit. It is made up on interconnected parts which act as a single plate as the result of welding or doweling joints of adjacent seating plate segments. Keys are inserted into keyways to fix the seating plate to the central low pressure turbine and thereby to help prevent movement in the axial direction (parallel to the turbine rotor axis). Thus axial expansions of the central low pressure turbine are directed toward the adjoining low pressure turbine, intermediate pressure turbine and high pressure turbine in the direction of the governor, as well as toward the adjoining other low pressure turbine, generator and exciter in the opposite or generator direction.

Since low pressure turbines are interconnected by push-pull tie beams, axial expansion of the central low pressure turbines is translated thereby to either of the adjoining low pressure turbines, and from there, and through similar tie beams in bearing pedestals, they are translated, in the governor direction, through the intermediate pressure and high pressure turbines. These push-pull tie beams, therefore, enable a continual axial thrust between the low pressure turbines so that axial expansions of either of the end low pressure turbines are additive to motions imposed on it by expansion of the central low pressure turbine. Similarly, there are other push-pull thrust members located between the end low pressure turbine and the intermediate pressure turbine, the intermediate pressure turbine and inboard pedestal, the pedestal and the high pressure turbine, and the high pressure turbine and the governor pedestal. Therefore, axial expansions of the turbine casings act in a cumulative manner.

Likewise, there is an accumulation of the reaction forces due to friction sliding forces between the turbines and their seating plates and between the separate pedestals and their seating plates.

Because of the cumulative expansion of the casings, there is a cumulative axial thrust. Therefore the aforementioned keys and keyways must be capable of absorbing the total net axial thrust from axial thermal expansions or contractions of all the turbine components, including the casings and bearing pedestals.

The axial thrust or friction force arises as a result of the local coefficient of friction between the turbine components and their seating plates, the axial motions, and the respective normal forces (total vertical reactions) at each location.

The seating plates resist the above-mentioned axial thrust and anchor the turbine to the foundation in the following manner. The seating plates are supported on a layer of grout which, in turn, is supported on the basic turbine-generator foundation material (chiefly reinforced concrete).

In order to enable the seating plates to be effective in resisting movement of the turbine casings, the plates must resist slipping at the seating plate-to-grout interface. At this interface, there also acts an effective coefficient of static friction and a normal force which give rise to a stability force.

The normal force consists of three separate and distinct components (1) the low pressure turbine machinery weight; (2) the condenser weight reaction imposed on its supporting low pressure turbines, or, if an expansion joint is employed between the turbine and the condenser with the condenser bolted down solidly, an unbalanced pressure force acts on the seating plate which, in turn, conveys the force to the foundation; (3) the vertical clamping forces imposed as a result of prestressing the foundation bolts. One end of these bolts is embedded in the foundation members, and the other end protrudes through the seating plate. The exposed ends are screw threaded to nuts which, when tightened, apply a tensile stress to the foundation bolts, resulting in establishment of a clamping force on the seating plate, pressing it to the foundation.

Of the three components of the normal force described above, it will be seen that the last mentioned, namely, the foundation bolt clamping, is the only variable element. It can be varied by the degree of prestress, the diameter of the bolt, and/or the number of foundation bolts. The degree of prestress has been optimized as the result of many years of successful service. The diameter of the bolt has evolved to a single standard size which is related to commercially available concrete strength. Thus, the only controllable variable left is the number of foundation bolts. By varying the number of foundation bolts, the total normal force is adjusted, acting in conjunction with the static friction coefficient at the seating plate-to-grout interface, to provide the desired friction stability force. Occasionally, single foundation plate cannot be practically loaded with the necessary number of foundation bolts, in which event it becomes necessary to tie (such as by dowel pins, tap bolts etc.) adjacent seating plates together to obtain the combined friction stability effect of the three low pressure turbine seating plates acting in unison.

It would be desirable to design a seating plate structure which would reduce the large quantity of foundation structure which would reduce the large quantity of foundation bolts presently required, eliminate the necessity of tying the adjacent seating plates together while giving greater flexibility in aligning the low pressure turbine casings, and enable the substantial cost reductions and shortening of manufacturing time.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, segmented seating plates are provided for each of three adjoining tandem-connected low pressure turbines, there being no interconnection between the segments of the seating plates of any turbine. Keyways are provided in central seating plate segments of the central low pressure turbine, which segments are each positively anchored to the foundation by a novel vertical post embedded in the concrete and which, by an eccentric connection, is fitted to he segment so as to prevent any possible movement of the anchored segments. This arrangement eliminates the practice of tying the adjacent seating plates together and reduces the installation time and costs of installing a large number of foundation bolts. Furthermore, there is greater flexibility in aligning the low pressure turbine casings than is presently available.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view shown partially in cross section, of three tandem-connected low pressure turbines forming a portion of a steam turbine-generator power plant and supported on a segmented seating plate arrangement in accordance with the principles of the present invention;

FIG. 2 is a plan view of the novel, segmented seating plate arrangement for supporting the low pressure turbines shown in FIG. 1.

FIG. 3 is an enlarged plan view of the central seating plate segment of the middle, low pressure casing shown in FIG. 2;

FIG. 4 is a further enlarged, cross-sectional view taken along lines IV--IV of FIG. 3;

FIG. 5 is a cross-sectional view taken along lines V--V of FIG. 3 and on the same scale as FIG. 4; and

FIG. 6 is a cross-sectional view taken along lines VI--VI of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to FIG. 1 of the drawing, the letter T generally denotes a portion of a compound steam turbine-generator power plant including three low pressure turbine units connected in tandem with each other and anchored in accordance with the present invention. On one end of the low pressure turbines connected in tandem, is a generator and exciter and an intermediate pressure turbine and high pressure turbine are connected on the other as well known in the art.

FIG. 1 shows a low pressure turbine unit having an outer casing 1, a second or central low pressure turbine unit having an outer casing 2, and a third low pressure turbine unit having an outer casing 3, with their rotors (not shown) connected in tandem along a central longitudinal axis of rotation A--A' (See FIGS. 1 and 2).

Low pressure turbine casings 1, 2 and 3 are supported on segment seating plate groupings 4, 5 and 6, respectively, shown more clearly in FIG. 2.

Segmented seating plate grouping 5 comprises 12 segments 7 to 18, inclusive, made of steel in the form of rectangular blocks. An important distinguishing feature of the present invention, compared to seating plates of the prior art, is that the seating plate segments for any of the low pressure turbines are mutually spaced and not interconnected. The seating plate segments are preferably mutually spaced on the order of 4 inches apart.

Keyways 19 and 20 are machined in two corresponding portions in plates 8 and 14, respectively, and the foot portions 2a of the turbine 2 (FIGS. 2, 5 and 6). The keyways extend in a horizontal plane which is normal to the longitudinal axis A--A'. The keyways 19 and 20 are defined by the foot portion 2a of the turbine 2 and the central opposed seating segments 8 and 14. A key 19a is inserted horizontally into the corresponding keyway 19 and a corresponding key (not shown) is inserted into keyway 20. Keyways 19 and 20 and their respective keys receive the total net axial thrust force from axial thermal expansions or contractions of the turbo-generator unit. Normally the segments 8 and 14 of the segmented seating plate grouping 5 are too short to securely anchor the turbine in the manner accomplished by the external keyways in prior devices.

Assured anchorage of seating plates 8 and 14 is provided by vertically extending anchors or posts 21 and 22 of steel (see FIG. 3) embedded in the concrete foundation 23 as shown more clearly in FIG. 4. This assured anchorage is important because the point of fixity of the turbo-generator unit is at seating plates 8 and 14. Such posts 21 and 22 positively anchor the low pressure turbine cylinder 2 against moving in a longitudinal or axial direction (parallel to its rotor axis A--A'). The posts or anchors 21 and 22 are embedded in the concrete and during erection of the turbine casings 1, 2 and 3, the protruding ends 21a and 22a of the embedded posts are machined to a diameter denoted as M in FIG. 4. There is an opening of diameter N premachined in seating plate 8 (and 14).

Also there is an access hole 0 having a larger diameter than N which is machined in the foot 2a of the low pressure casing 2 (shown in a dot-and-dash outline). An eccentric anchor bushing 24, preliminarily formed as a circular plate or disc machined to a diameter N (less a small clearance for fitting) and of a thickness approximately equal to the thickness of seating plate 8, is provided. After final turbine alignment, the eccentricity of the center of diameter M on the exposed end 21a of the embedded axial post 21 is measured in relation to the center of the bore or diameter N in the seating plate. The prefitted disc or eccentric anchor bushing 24 is then bored to an inner diameter M (plus a small clearance for fitting) at the required eccentricity.

The eccentric anchor bushings 24 are then installed by introducing them through the access hole 0 in the low pressure turbine foot 2a. The plate segment 8 is provided with a welded-on retaining ring or washer 25 on its bottom surface which acts to maintain the proper vertical position of the eccentric anchor bushing 24 in relation to the seating plate thickness.

Finally, to protect the alignment of the various seating plate segments from motions imposed by friction forces resulting from differential values of coefficient of friction, a circumferential series of anchor discs 26 are attached to the underside of the seating plate segments. Such anchor discs 26 are solidly embedded in the layer of grout G under the seating plates and on the surface of concrete foundation 23 so as to interlock the plate segments and provide the desired resistance to motion in the horizontal plane.

Two keyways 27 and 28 (FIG. 2) are provided in the oppositely disposed segments 17 and 11, respectively, which keyways are located in parallel alignment with the longitudinal axis A--A' of the turbine-generator. Similarly, keyways 29 and 30 are provided in the segmented seating plate grouping 4 for casing 1 and keyways 31 and 32 are provided in the segmented seating plate grouping 6 for cylinder 3, all in parallel alignment with the longitudinal turbine rotor axis A--A'.

A plane B--A' transverse to the longitudinal axis A--A' of the central low pressure turbine contains the transverse or vertical center line 34 of the turbine, while transverse planes C--C' and D--D' contain vertical joint lines 35 and 36, respectively. Separately constructed sections 42, 43 and 44 are bolted together, along the vertical joint lines 35 and 36. Each section has a base portion and a cover portion. Section 43 is the central casing portion having a central inlet in the cover portion and sections 42 and 44 are the end casing portions. Through the base portions of sections 42, 43 and 44, the steam is exhausted downwardly to condensing equipment (not shown), as well known in the art. The centers of the gaps between the axially directed seating plate segments 7, 8, 9, 13, 14 and 15 are located approximately coincident with the above mentioned vertical planes C--C' and D--D'. Variations in the elevational setting of the low pressure turbine foot adjacent casing base sections are readily tolerated. This allows for much less precision machining of the casing sections 42, 43 and 44 since each seating plate segment can be adjusted vertically to support the corresponding casing section. As an example, up to 0.25 inches of vertical tolerance on turbine casing sections is allowable as compared to 0.001 inches previously allowable.

It should be noted that each of the seating plate segments 7 to 18, inclusive, is independently set to an elevation compatible with the turbine casing dimensions and the overall bearing alignment scheme. This allows various adjustable leveling devices, well known in the art, to position each seating plate segment to support the turbine casings with an optimum distribution of normal forces on the seating plates. Previously, with the unitary seating plate, concentrated forces at the turbine casing foot 2a and at the vertical joints 35 and 36 would result from any mismatch in elevation, and required expensive and time consuming hard finishing operations to preclude gouging of the seating plate and subsequent misalignment problems.

Foundation anchor bolts, such as 37, are disposed all along the longitudinal centerlines extending through all the segments of each of the seating plate groupings 4, 5 and 6.

To ensure cumulative expansion of the low pressure turbine units about the point of fixity at the center of the low pressure turbine unit 2, push-pull tie beams 38 and 39 are secured to the foot area of the adjacent end casing base portions of the units 2 and 3 and similar beams 40 and 41 are secured to the foot area of the adjacent end casing bases of units 1 and 2.

Variations may be made in the shape of the ends 21a and 22a of the anchor post 21 and 22, respectively, that is, they may be made rectangular or polygonal with corresponding shaped anchor bushings 24, instead of round as described.

Furthermore, the segmented seating plate construction described for this tandem arrangement of three low pressure turbines may be applied to any other tandem or cross compound arrangement of low pressure turbines to realize similar benefits and advantages to those herein enumerated. An additional advantage of the present structure is that it considerably reduces the required number of foundation anchor bolts resulting in savings on associated design details. Additionally, a major load reduction occurs because, whereas in the existing or well known design described above under Background of the Invention, the transverse anchor design load results as a function of a differential friction force at the seating plate-to-grout interface in the present invention the transverse anchor design load results as a function of a differential friction force at the turbine base-to-seating plate interface. The latter has an inherently lower coefficient of friction as well as the complete absence of foundation anchor bolt clamping forces in the normal or vertical direction. This tends to reduce transverse anchor loads by about one one-third.

Smaller plate sections will have the same relative movement to the grout due to differential thermal expansion, but this movement will no longer be cumulative, therefore, this should add measurably to stabilizing the turbine alignment throughout the operating life of the machinery.

Thus it is seen that a segmented seating plate structure with eccentric anchoring means is provided, which seating plate structure is unconnected, more reliable, less expensive, and which structure greatly reduces the number of foundation anchor bolts because it is no longer necessary to use them to augment the friction stability forces previously described, and provides more aligning flexibility than is presently available. Because of the increase in associated tolerances, the seating plates and turbine casings do not have to be prefitted before erection at the plant site and the eccentric anchors permit erection in less time than heretofore. Furthermore, the following are eliminated: welding and machining of dowel pinned and bolted lap joints in adjacent sections of seating plates; heat treating seating plates; machining the lower surface of the seating plates thereby reducing fabrication thickness; and finishing operation to custom fit the turbine keyways; the severe vertical tolerance limitation on turbine casings; and precise thickness matching at adjacent sections of seating plates.

Since numerous changes may be made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A large machine subjected to substantial differential thermal expansions between said machine and its foundation during operation,

said machine having a longitudinal centerline, a plane transverse to said longitudinal centerline and containing a transverse centerline of said machine, and a base portion supported on a foundation,

seating plates supported by said foundation and frictionally engaging said base portion of said machine,

said seating plates comprising a plurality of separate unconnected segments,

said segments including two opposed central segments having their transverse centerlines extending along said transverse plane of said machine,

anchoring means for anchoring each of said central segments to said foundation,

and means for securing said machine to said central segments to prevent movement of said machine in the longitudinal direction at said central segments.

2. The structure recited in claim 1 and further providing means for expansion of the machine in a horizontal plane.

3. The structure recited in claim 2 wherein the means for providing horizontal expansion and the means for securing the machine comprise

two keyways equally spaced on opposite sides of the longitudinal centerline, each keyway cooperatively defined by a central seating plate segment and the machine base portion,

and a key disposed in each of said keyways.

4. The structure recited in claim 3 wherein the keyways and keys are disposed in a horizontal plane, and are mutually normal to the longitudinal centerline of the machine.

5. The structure recited in claim 1 wherein the anchoring means comprise at least one post embedded in the foundation,

each central segment defining at least one opening therein corresponding to said post,

said post extending upwardly into said corresponding opening in the central segment,

said post having a smaller cross-sectional dimension than said opening and thereby defining a gap,

and means for bridging said gap in said opening between said post and the central segment to provide a rigid connection between the post and segment.

6. The structure recited in claim 5 wherein the bridging means comprises a bushing member which is fitted to the post, bridging the gap in the opening.

7. The structure recited in claim 1 wherein the anchoring means comprise at least one post embedded in the foundation,

each central segment defining at least one opening therein corresponding to said post,

said post extending upwardly into said corresponding opening in the central segment,

said post having a smaller cross-sectional dimension than said opening and thereby defining a gap,

a means for bridging said gap in said opening between said post and the central segment to provide a rigid connection between said post and segment,

said bridging means comprising a bushing member which is fitted onto the post bridging the gap in the opening,

said post being eccentrically disposed in said opening and said bushing member having a corresponding aperture which is eccentric with respect to its outer dimension.

8. The structure recited in claim 1 wherein the anchoring means comprise at least one post embedded in the foundation,

each central segment defining at least one opening therein corresponding to said post,

said post extending upwardly into said corresponding opening in the central segment,

said post having a smaller cross-sectional dimension than said opening and jointly defining a gap therewith,

means for bridging said gap in said opening between said post and said central segment, to provide a rigid connection between said post and segment,

said bridging means comprising a bushing member which is fitted to the post, bridging said gap in said opening,

said post being eccentrically disposed in said opening and said bushing member having a corresponding aperture which is eccentric with respect to its outer dimension, and

said post, said opening and said bushing member being circular in cross section.

9. The structure recited in claim 1 wherein the base portion of the machine is substantially rectangular in cross section and the seating plate segments are arranged in a substantially rectangular configuration to support the machine.

10. The structure recited in claim 1 wherein the seating plate segments are rectangular in cross section.

11. The structure recited in claim 6 wherein the base portion of the machine has access apertures of greater dimension than the dimension of the bushing member, one of said apertures corresponding to each opening in the seating plate.

12. The structure recited in claim 6 wherein each bushing member and the foundation are in spaced relation, and wherein a retaining washer is secured to the bottom of each central segment to assist in supporting the bushing member.

13. The structure recited in claim 1 wherein a layer of grout is placed between the foundation and the seating plates and wherein each central segment is provided with anchor discs embedded in said layer.

14. The structure recited in claim 1 wherein the machine is formed of a plurality of housing units.

15. The structure recited in claim 14 wherein the units are turbines heated by hot motive fluid which produces differential thermal expansion in the units.