TECHNICAL FIELD

The present invention relates to a gas turbine plant for the production of electric energy, provided with an apparatus for monitoring rotating parts.

BACKGROUND ART

In plants for the production of electric energy, the rate of availability of gas turbines is of primary importance, both for the legislation governing the supply of energy, and for the increasingly stringent demands of the markets. In order to maximize the rate of availability, it is essential, firstly, to extend the useful life of all components of the turbine and, secondly, to reduce the number of maintenance procedures, which generally impose long periods of downtime. In addition, there is an obvious need for avoiding failure and sudden breakage . In particular, it is essential to monitor the status of all critical components of the rotor, i.e. those parts that are most prone to thermo-mechanical stress during normal operation of the plant and that, as a rule, can be subjected to detailed verification of structural integrity only when work is scheduled for revision, when the rotor is disassembled.

For reliable monitoring, distributed measurement systems should be provided, which allow to detect parameters relating to critical components in a large number of positions. In particular, given the high thermal stress to which rotating parts of gas turbines are submitted, a decisive parameter is the temperature. The temperature is usually detected by thermographic systems based on infrared sensors, which are housed in specially prepared sites in the turbine case and focusing on respective portions of the rotor. The known systems have severe limitations, however, mainly due to the difficulty of placing many sensors and to the fact that temperature monitoring can be exclusively extended to portions of the rotor that are visualized by the sensors. Housing the sensors is problematic, since seats must be made within the case of the turbine. In other words, it is necessary, for each sensor, to drill holes in the case and provide sufficient space for the sensor itself and the required wiring. Consequently, the number of monitoring points can not be large. In addition, only the surfaces in the viewing angle of the sensors, i.e. a relatively small portion of the outer surface of the rotor can be subjected to thermographic measurements .

DISCLOSURE OF INVENTION

The aim of the present invention is therefore to provide a gas turbine plant for the production of electric energy, which is free of the limitations described.

According to the present invention, a gas turbine power plant for the production of electric energy is provided, as defined in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the annexed drawings, which illustrate a non limitative example of implementation, in which:

- Figure 1 is a side view longitudinally partially sectioned of a turbogas unit of a plant for the production of electric energy according to an embodiment of the present invention;

Figure 2 is a simplified block diagram relative to a temperature monitoring system incorporated in the plant of figure 1;

- Figure 3 is an enlarged three quarters perspective view from above of a first detail of the plant of figure 1;

- Figure 4 is an enlarged side view, longitudinally sectioned, of a second detail of the plant of figure 1;

- Figure 5 is an enlarged side view, longitudinally sectioned, of a second detail of the system of figure 1, in a different embodiment; and

- Figure 6 is an enlarged side view, longitudinally sectioned, of a third detail of the plant of figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows a portion of a plant for the production of electric energy, indicated as a whole with reference number 1. The plant 1 comprises a shaft 2, along which are arranged a compressor 3 and a gas turbine, hereinafter simply referred to as turbine 5. In addition, a combustion chamber 6 of an annular type is arranged around the shaft 2, between the compressor 3 and the turbine 5. The compressor 3, the combustion chamber 6 and the turbine 5 form a turbogas unit, which is housed in an external case 4.

The shaft 2 comprises a plurality of rotor discs 7, 8 arranged in a succession between a front hollow shaft 10 and a rear hollow shaft 11 and clamped by a central tie rod 12. A central hollow shaft 13 separates the rotor discs 7 in the region of the compressor 3 from the discs 8 in the region of the turbine 5 and extends through the combustion chamber 6. The rotor discs 7 and the rotor discs 8 present respective annular expansions 7a, 8a, which extend axially in opposite directions and are in contact with annular expansions 7a, 8a, of the adjacent rotor discs 7, 8. In addition, pairs of adjacent rotor discs 7, 8 define rotor cavities 14 between the respective annular expansions 7a, 8a and the central shaft 12.

Each of the discs 7 carries a respective array of compressor blades 15 while the rotor discs 8 carry a respective array of turbine blades 16.

Damping rings 17 are arranged around the tie rod 12, between pairs of adjacent rotor discs 7, 8, in order to reduce bending stress and dampen vibrations of the tie rod connected to its own frequencies. With reference to Figure 2, the plant 1 is provided with a temperature monitoring system 18, which comprises a processing station 19, a plurality of temperature sensors 20, 21 and a radio frequency coupling device 22.

The processing station 19 is configured to receive temperature signals ST from the temperature sensors 20, 21 and to carry out monitoring operations using the detected temperature signals ST.

As shown in Figures 1 and 3, the temperature sensors 20 are located on the surface of the tie rod 12 at respective axial positions. In particular, the temperature sensors 20 are arranged both along the compressor 3, and along the cylinder 13, and along the turbine 5.

The temperature sensors 21 are arranged on the faces of respective rotor discs 7, 8 of the shaft 2. The temperature sensors 21 are thus within respective rotor cavities 14.

In one embodiment, the temperature sensors 20, 21 are thermocouples. In a different embodiment, thermoresistive sensors are used.

The temperature sensors 20, 21 are fixed to the shaft 2 by welded metal strips 24 (Figure 3) and are connected to a movable portion of the coupling device 22 (as described in more detail below, Figure 6; see also Figure 1) by way of respective electric connection lines 25, 26.

As shown in Figures 1 and 3, the electric connection lines 25 extend axially on the surface of the tie rod 12. The electric connection lines 26 extend substantially in a radial direction on the rotor discs 7, 8, therefore running parallel to the electric connection lines 26 on the surface of the tie rod 12. The electric connection lines 25, 26 are also secured by welded metal strips 24. The metal strips 24 are of an elongated shape and are applied in a substantially perpendicular direction to the electric connection lines 25, 26 themselves. In particular, the strips 24 are applied to the faces of the rotor discs 7, 8 in the tangential direction, i.e. perpendicular to a radial direction. On the tie rod 12, the strips 24 are applied in a circumferential direction. This arrangement of strips 24 minimizes the risk that possible micro-cracks formed during welding extend, damaging the structure of the shaft 2.

Between the tie rod 12 and rotor discs 7, 8 are annular interspaces 29 (see Figures 4 and 5) , through which pass the electric connection lines 25, 26.

The damping rings 17 are instead in contact with the surface of the tie rod 12. In an embodiment (Figure 4), longitudinal grooves 28a for the passage of electric connection lines 25, 26 are made in the damping rings 17 on the face toward the surface of the tie rod 12. In this case, the surface of the tie rod 12 is integral and continuous.

In a different embodiment (Figure 5), longitudinal grooves 28b are made on the surface of the tie rod 12, through regions occupied by the damping rings 17. Referring once again to Figures 1 and 2, the coupling device 22 comprises a receiver 30, a transmitter 31 and a feeding device 32.

The receiver 30 is fixed and placed next to the processing station 19 and is connected to it for transferring temperature signals ST detected by the temperature sensors 20, 21 and transmitted in radio frequency by the transmitter 31.

As shown in Figure 6, the transmitter 31 is housed upon the shaft 2, more precisely on the head in a balancing cavity 34 of the front hollow shaft 10 and is connected to the electric connection lines 25, 26. In order to allow the connection, an oblique through hole 36 connects the surface of the tie rod 12 with the balancing cavity 34 where the transmitter 31 is arranged. The electric connection lines 25, 26 run throughout the through hole 36.

The feeding device 32 comprises an inductive power supply 38, a transformer 39 and an AC/DC converter 40. In turn, the transformer 39 has a primary winding 41, fixed to the outer case 4 and connected to inductive power supply 38, and a secondary winding 42, fixed to the shaft 2. The primary winding 41, in particular, is composed of a torus fixed to the inside of the bearing support of the shaft 2 (in this regard see Figure 6) .

The described system advantageously enables monitoring of the temperature of the rotating parts of the plant 1 in a large number of positions. The installation of temperature sensors 20, 21 and the necessary wiring, in fact, does not appreciably alter the mechanical properties of the rotating parts of the plant, specifically of the rotor discs 7, 8 and of the tie rod 12. Above all, fatigue resistance and the number of cycles that the material of the shaft 2 can withstand are not altered. The electric welding, in particular, is carried out so as to mainly extend transversely to the radial direction (on the rotor discs 7, 8) and in the circumferential direction (on the tie rod 12) . Thanks to this provision, the propagation of micro-cracks is prevented and the structural integrity is preserved, as well as the fatigue strength of the material. In addition, the arrangement and size of the masses does not alter the balance of the shaft 2. It is therefore possible to install a relatively large number of temperature sensors 20,

21, to perform an accurate and reliable monitoring of temperature distribution over a large part of the shaft 2. In addition the electric welding alters the surface area of the tie rod without undermining the structural integrity of the section of the component; furthermore the effect of temperature also involves in operation a tempering of the altered zone by electric welding. Another advantage is that monitoring can be done even on internal portions of the shaft 2, i.e. the central tie rod 12, the faces of the rotor discs 7, 8 and on the portions of the annular expansion 7a, 8a facing the tie rod 12. The interior surfaces of the shaft 2 are not visible from the outside of the shaft 2 and therefore are not accessible through remote sensing, such as thermographic sensors.

On the other hand, the use of sensors attached to the shaft 2 is compatible with measures of different types, in particular thermographic, which can be integrated in the same monitoring system for maximum flexibility and completeness.

It is finally clear that to the described method and plant modifications and variations can be made, without going beyond the scope of the present invention, as defined in the appended claims .

In particular, the placement of temperature sensors is not limited to the example described. The temperature sensors can be placed also in other parts of the shaft of the turbogas unit, including at least the annular expansion of the discs, both on internal surfaces, towards the tie rod, and on external surfaces.