TECHNICAL FIELD

The present invention relates to an equipment for supporting a shaft of a rotating machine, in particular a rotating machine of a plant for producing electric power, and to a method of repairing a rotating machine using such a supporting equipment.

BACKGROUND ART

As known, plants for producing electric power may comprise one or more rotating machines, which normally include a driving machine, in particular a gas turbine or a steam turbine, and an electric generator, e.g. an alternator .

The driving machine and the electric generator may be coupled to separate shafts or, more frequently, to a single shaft. In all cases, bearings which are coupled to respective shaft portions (generally named bearing coupling portions) must be provided to ensure appropriate support and friction levels during machine operation.

However, even if the bearings may be well designed and made, the weights involved, the rotation speeds and the almost uninterrupted operation over time may cause rubbing, local metal melting and, as a result, grooves on the bearing coupling portions of the shaft. Since even small mechanical imperfections are generally harmful for rotating machines, the bearing coupling portions need to be occasionally repaired by means of turning operations.

In order to perform the necessary work, the shaft needs to be extracted from the machine and sometimes arranged on special supports after having been transported to a specialized workshop. These special supports allow the shaft to be rotated at slow speeds, leaving the surface of the bearing coupling portions free.

However, disassembling the rotor of a rotating shaft of a plant for producing electric power is extremely complex, and normally requires very long downtimes. Therefore, the cost associated with the repair is high.

DISCLOSURE OF INVENTION

It is thus the object of the present invention to provide a supporting equipment for a rotor of a rotating machine, and a method of repairing a rotating machine of a plant for producing electric power which allow to overcome, or at least attenuate, the limitations described, and in particular allow to repair the damaged bearing coupling portions without necessarily needing to extract the shaft from the machine.

According to the present invention, a supporting equipment for a rotor of a rotating machine and a method of repairing a rotating machine of a plant for producing electric power are provided as set out in claims 1 and 15, respectively .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which show some non-limitative embodiments thereof, in which:

- figure 1 is a top plan view, taken along a horizontal longitudinal plane, of a rotating machine of a plant for producing electric power incorporating a supporting equipment according to an embodiment of the present invention;

- figure 2 is a partially sectional, enlarged side view of a portion of the machine in figure 1, housing the supporting equipment;

- figure 3 is a front view, with parts removed for clarity, taken along the plotting plane III-III in figure 2, of a portion of the rotating machine and of the supporting equipment in figure 1;

- figure 4 is a partially exploded, top perspective view of the supporting equipment in figure 1;

- figure 5 is an enlarged side section view, taken along the plotting plane V-V in figure 3, of a detail of the rotating machine and of the supporting equipment in figure 1;

- figure 6 is a simplified block diagram of the supporting equipment in figure 1;

- figure 7 is a side view of a portion of a rotating machine of a plant for producing electric power incorporating a supporting equipment according to a different embodiment of the present invention; and

- figure 8 is a front view of the portion of rotating machine and of the supporting equipment in figure 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows a gas turbine 1 of an plant for producing electric power as a whole.

Gas turbine 1 comprises a turbine casing 2 and a shaft 3, which extends along an axis A and has a compressor section 4 and an expansion or turbine section 5.

Shaft 3 is housed in the turbine casing 2 and is rotationally supported by a front bearing assembly 7, located close to the compression section 4, and a rear bearing assembly 8, located close to the turbine section 5. In particular, the bearing assembly 7 is coupled to a bearing coupling portion 10 of shaft 3, axially delimited by annular shoulders 11, 12 on the suction side and on the compressor side, respectively.

At a suction mouth of gas turbine 1, the turbine casing 2 comprises an outer casing 13 and a truncated cone shaped, inner casing 14, which is rigidly supported by the outer casing 13 through spokes 15 and houses the portion of shaft 3 in which the bearing coupling portion 10 and the bearing assembly 7 are defined.

The inner casing comprises a lower half-shell and an upper half-shell, which is removed in the views in figures 2 and 3 (as the bearing assembly 7) .

Figures 2-6 show a supporting equipment 18 in accordance with an embodiment of the present invention. The supporting equipment 18 is housed in the turbine casing 2 and rotationally supports shaft 3, as shown in figures 2 and 3. In particular, the supporting equipment 18 is housed in the lower half-shell of the inner casing 14 and supports shaft 3 in a region adjacent to, preferably immediately adjacent to, the bearing coupling portion 10. In an embodiment, the supporting equipment 18 supports the shoulder 12 of shaft 3, between the bearing coupling portion 10 and the compressor section 4.

The supporting equipment 18 comprises a frame 20, fastening elements 21 for connecting frame 3 to the turbine casing 3, and an insert 24 which defines a supporting seat 25 for shaft 3.

Frame 20 is shaped as a ring portion which extends along an arc of a circle corresponding to an angle of 180° or less, and rests against the lower half-shell of the turbine casing 2. On a radially outer surface (figure 5), frame 20 has a plurality of seats 26 for receiving respective centring wedges 27. The centring wedges 27 are also provided with adjusting screws 28 which engage respective holes on a face 20a of frame 20, as described in greater detail in the enlargement in figure 5.

Insert 24, which in one embodiment is made of aluminum alloy, is also shaped as a ring portion which extends along an arc of a circle and has opening equal to frame 20. Insert 24 is coaxially supported by frame 20. Moreover, frame 20 and insert 24 are coaxial in use with respect to shaft 3.

Tubs 30 arranged in sequence in the circumferential direction are obtained on a radially inner surface of insert 24, which defines the supporting seat 25. Tubs 30 are open on the radially inner surface of insert 24. In an embodiment, the area of tubs 30 differs as a function of the position along the radially inner surface of insert 24. For example, the area of the tubs 30 arranged at the ends of insert 24 is smaller than the area of the tubs 30 in more central positions.

A hydraulic circuit 31, which comprises a plurality of independent pipes 32, is integrated in insert 24. Pipes 32 have respective separate inlets 32a on a face 24a of insert 24 perpendicular to the axis A of shaft 3 in use and respective feeding outlets 32b at the bottom of respective tubs 30 (see figure 4) .

Figure 4 also shows the fastening elements 21, which comprise plates 35, at respective ends of frame 20, and screws 36, 37. Screws 36 are inserted through the respective plates 35 into holes 38 at the ends of frame 20. Screws 37 are inserted through the respective plates 35 into holes 39 for closing the upper half-shell of the turbine casing 2 onto the lower half-shell.

With reference to figure 6, the equipment 1 comprises a lubricant feeding device 40 for feeding a pressurized lubricant fluid to the tubs 30 of insert 24, which thus defines a hydraulic bearing for shaft 3.

The lubricant feeding device 40 comprises a tank 41, a pump 42 and a distributor 43, connected to the pipes 32 of the hydraulic circuit 31 and to the tubs 30 through pipes 44.

Pump 42 draws lubricant at atmospheric pressure from tank 41 and supplies a flow of lubricant at high pressure to tubs 30 through distributor 43, pipes 44 and hydraulic circuit 31. In an embodiment, pump 42 forms part of a lifting system 45 of the bearing assembly 7 and is connected to an inlet of distributor 43 by a quick connecting pipe (also not shown in detail) .

Distributor 43 has a plurality of outlets 43a connected to respective pipes 32 of the hydraulic circuit 31, as mentioned. Furthermore, the distributor is provided with adjusting valves 46 to adjust the pressure of each outlet 43a in an independent manner.

Figure 6 also shows a collection tank 47, which collects the lubricant fluid leaked from the gap between insert 24 and shaft 3. The leaked lubricant fluid is returned to tank 41.

Figures 7 and 8 show a different embodiment of the invention, according to which a supporting equipment 118 is used to support a shaft 103 of an alternator 100, which may be operated in service, for example but not necessarily, by a gas turbine or by a steam turbine.

The supporting equipment 118 comprises a frame 120; fastening elements 121 for connecting frame 120 to the alternator turbine casing 102 close to a bearing coupling portion 110 of shaft 103) ; and an insert 124, which defines a supporting seat 125 for shaft 103 and is substantially made as the insert 24 described with reference to figures 2-5.

Frame 120 comprises a plate which can be frontally fixed to a bearing support of alternator 100 by the fastening elements 121, which in the embodiment described herein comprises screws passing through the frame 120 itself. Frame 120 supports insert 124 coaxially with respect to the shaft 103 of alternator 100 (which extends along an axis A' ) . The centring of insert 124 is obtained by centring wedges 127 and adjusting screws 129. In an embodiment, the adjusting screws 129 act against a basement 101 of alternator 100 and are symmetrically arranged with respect to the vertical median plane of shaft 103. The centring wedges 127 are arranged between frame 120 and basement 101.

As mentioned, insert 124 is shaped as a ring portion which extends along an arc of a circle in use about shaft 103. Tubs 130 (figure 8) arranged in sequence in the circumferential direction are obtained on a radially inner surface of the 124, which defines the supporting seat 125. A hydraulic circuit (not shown in detail) is integrated in insert 124, comprising a plurality of independent pipes for feeding a lubricant fluid separately to respective tubs 130.

For this purpose, the equipment 118 is provided with a lubricant feeding device 140, which comprises a tank 141, a pipe 142 and a distributor 143, connected to the hydraulic circuit pipes and to the tubs 130 through pipes 144.

Pump 142 draws lubricant at ambient pressure from tank 141 and supplies a flow of high pressure lubricant to distributor 143, which has a plurality of outlets 143a connected to respective ducts of the hydraulic circuit and is provided with adjusting valves 146 for adjusting the pressures to each outlet 143a independently.

The described equipment advantageously allows to support the shaft of a rotating machine of a plant for producing electric power in a rotational manner. In particular, the equipment allows the machine bearings to be removed without extracting the shaft from the turbine casing of the rotating machine. The shaft can be thus accessed with a tool, e.g. a turning tool or a belt grinding machine, and to machine and repair the surface of the bearing coupling portion directly in the machine. Since the equipment according to the invention avoids the need to extract the shaft from the turbine casing, the intervention time and machine downtime are drastically reduced, especially in the case of the gas turbines. Indeed, in this case, the fluid connections for feeding fuel are particularly complex, and the disassembly and reassembly operations require very long execution times. Instead, the equipment according to the invention allows to perform the repairs directly on the machine and therefore to achieve major savings.

Moreover, the described centring systems allows the frame and insert to be aligned to the shaft axis with very high accuracy, in practice eliminating possible oscillations during the rotation for machining (the oscillations may be restrained within one hundredth of a millimeter) .

It is finally apparent that changes and variations can be made to the hydrostatic bearing and method described herein without departing from the scope of the present invention as defined in the appended claims.