Description of the Prior Art A gas turbine used in a stationary combined heat and power generation plant can be of an axial or radial type with one or more compressor and/or turbine stages, depending on the power and heat requirement, and available space. Different power requirements and heat outputs lead to different sizes and types of gas turbines. In bigger plants, e g with an electrical output of more than 150 kWe, gas turbine units of an axial type are often used. Smaller plants often have to fulfill not just demands on required output but also limitations in space and sound pollution due to their location, e g in hospitals, hotels, small industries and small scale district heating installations.

Smaller gas turbines can have a rotor unit with one (mono) or more shafts for at least one turbine wheel driving at least one compressor wheel.

One problem with earlier gas turbines having more than one shaft, e g one shaft for a turbine wheel driving a compressor wheel and another shaft for another turbine wheel driving a generator or the wheels of a car, is that a gearbox and a coupling have to be built in together with the gas turbine. This increases the weight, cost, and space for the stationary power plant and its emitted sound.

Another problem concerns the maintenance, replacement and balancing of these shafts, because their construction makes these operations more difficult with subsequent high costs,

in comparison with gas turbines having only one shaft, due to a more complicated replacement procedure when maintaining a shaft in an existing plant.

Summary of the Invention The main objects of the present invention are to simplify the construction, the balancing and the replacement procedure of rotor units in gas turbine units.

These objects are achieved for gas turbine units by a rotor unit according to the invention. The rotor unit has a mono-shaft, a compressor wheel, a turbine wheel, a tie bolt, and a tie bolt nut. The mono-shaft is essentially cylinder-shaped with a centre through hole for containing the tie bolt, and has a first supporting bearing arrangement detachably attached to a first end and a second supporting bearing arrangement detachably attached to a second end.

The compressor wheel and the turbine wheel constitute a detachable unit, which is attached by means of the tie bolt at the second end of the mono-shaft, forming a shaft overhang, the tie bolt protruding through the centre of the mono-shaft and into the centre of the turbine wheel, where one end of the tie bolt is detachably connected to the centre of the turbine wheel or the compressor wheel, and the tie bolt nut is detachably connected to the other end of the tie bolt at the first end of the mono-shaft.

These objects are also achieved by a method of balancing the rotor unit. The balancing is done step by step, i e the rotor unit is constituted by several detachable parts, which are mounted together in groups starting with the mounting and a first balancing step of a first part, then mounting another part onto the first part and balancing them together in a second step and so on until all of the parts forming the complete rotor unit have been mounted and balanced together. Each balancing step

concerns sub steps of mounting each part or group of parts together, then calibrating each part or group of parts by registering its unbalance. This is followed by balancing each part or group of parts by cutting away material corresponding to the unbalance until an unbalance below an approved value for the complete rotok,-unit is achieved. The last step concerns marking this"best"position or final balancing state on each rotating part of the complete rotor unit.

By providing a gas turbine unit with a rotor unit that is easily balanced, the following advantages are obtained: the construction of a gas turbine unit is simplified due to fewer parts, i e no gear is needed between the generator and the rotor unit, and the maintanence and replacement of a rotor unit is facilitated due to the fact that the balancing of it can be done in advance and it can be stored as a stock article, thereby reducing associated costs. Moreover, the time required when handling the rotor unit is reduced due to fewer parts.

Brief Description of the Drawings The present invention will now be described in further detail, reference being made to the accompanying drawings, in which: FIG 1 is a longitudinal side view in section showing a preferred embodiment of a rotor unit according to the invention mounted in a gas turbine, FIG 2 is a longitudinal side view in section showing a first preferred embodiment of a rotor unit according to the invention, FIG 3 is a longitudinal side view in section showing a second preferred embodiment of a rotor unit according to the invention,

FIG 4 is an enlarged longitudinal side view in section showing one end of any of the preferred embodiments of the rotor unit, FIG 5 is an enlarged longitudinal side view in section showing the other end of the first embodiment of the rotor unit in FIG 2, FIG 6 is an enlarged longitudinal side view in section showing the other end of the second embodiment of the rotor unit in FIG 3, FIG 7 is a side view of the rotor unit in FIG 3 illustrating the locations and planes on the rotor unit where unbalances are measured and compensated during a balancing procedure of the rotor unit according to the invention, FIG 8 is a side view illustrating a step in the balancing procedure in FIG 7, FIG 9 is a side view illustrating another step in the balancing procedure in FIG 7, and FIG 10 is a side view illustrating yet another step in the balancing procedure in FIG 7.

Detailed Description of the Invention FIG 1 shows a rotor unit 10 according to the invention mounted in a gas turbine unit 20. The gas turbine unit also comprises a housing 2, a combustion chamber 3 (only partly shown), a generator 4, and an air intake 5.

FIGS 2-3 show the rotor unit 10 according to the invention in two preferred embodiments. For clarity reasons no sectioning are shown in the following drawings. The rotor unit comprises a mono-shaft construction 30 below simply called a mono-shaft, i e a single shaft for a compressor wheel 40, a turbine wheel 50, and a generator rotor 80 in the generator 4, wherein the turbine wheel drives both the compressor wheel and the generator rotor.

The compressor wheel 40 is of a single-stage centrifugal

type and the turbine wheel 50 is of a single-stage radial- flow type. The mono-shaft 30 also comprises a tie bolt 60, a tie bolt nut 70 and a first bearing arrangement 100 at a first end, and a second bearing arrangement 110 and a rotor shaft 90 at a second end. The compressor wheel 40 and the turbine wheel 50 form a detachable unit, which is attached by means of the tie bolt 60 at the second end of said mono- shaft 30, creating a shaft overhang.

The tie bolt 60 is a solid, long and straight essentially cylinder-shaped axle and has at least one rest surface 60', seen in FIGS 2-6, for supporting the tie bolt against the inner walls of the centre through hole in the mono-shaft 30. This support is achieved due to the bigger diameter at the rest surface, whereby the portion or portions between the rest surface and respective ends of the tie bolt 60 have a smaller diameter forming a waist.

The ends of the tie bolt are threaded.

The mono-shaft 30 is essentially cylinder-shaped and is composed of the generator rotor 80 and the rotor shaft 90, each of them being cylinder-shaped and having a centre through hole for containing the tie bolt 60. The generator rotor has different constructions in the two embodiments, shown in FIG 2 and 3, by differently designed annular permanent-magnets 81a, 81b around its periphery giving certain features for the generator rotor 80a with permanent-magnets 81a in FIG 2 and other features for the generator rotor 80b with permanent-magnets 81b in FIG 3.

The second embodiment of the generator rotor 80b also comprises a runner retainer 61 and a screw 62 for attaching it to the first end of the generator rotor 80b, as shown in FIG 3. The runner retainer is equipped with magnets, which are placed so that they correspond to the poles of the magnets 81b on the generator rotor 80b, serving as a help when starting the gas turbine unit 20.

The generator rotor 80a or 80b and the rotor shaft 90 of the mono-shaft 30 are detachable from each other and guided at their contact ends by guiding pins 31, shown in FIGS 2-4. The rotor shaft 90 is detachably attached and guided by guiding pins 91, also shown in FIGS 2-4, at its other end to the compressor wheel 40. Preferably, the compressor wheel and the rotor shaft are two separate parts detachable from each other but may also be only one part, i e the rotor shaft may be integrated in the compressor wheel.

The tie bolt 60 protrudes through the centre of the generator rotor 80 and the rotor shaft 90, i e the mono- shaft 30, and into the centre of the turbine wheel 50 where it is connected with one threaded end to a turbine nut 52 shown in FIGS 2-4. The turbine nut is in turn detachably attached to the turbine wheel by means of a short threaded pin 51 pointing out from the centre of the turbine wheel 50. The tie bolt nut 70 is detachably connected to the other threaded end of the tie bolt 60. The turbine wheel is preferably detachably attached with guiding pins to the compressor wheel 40 by means of a turbine sleeve 53, which is detachably attached to the turbine nut. In another embodiment the turbine wheel, the turbine nut, and the turbine sleeve may be one part, i e these three parts are integrated into one part by welding or any other suitable method. This would reduce the number of parts in the rotor unit 10 considerably.

The tie bolt nut 70 holds the first bearing arrangement 100 against a shoulder 100'at the first end of each generator rotor 80a and 80b by means of a bearing clamp plate 102, shown in FIG 2,3,5 and 6. The first bearing arrangement 100 and the second bearing arrangement 110 have the same construction in each of the preferred embodiments of the generator rotor 80a and 80b. The second bearing arrangement 110 is held by means of the rotor shaft

90 against a shoulder 101'at the second end of respective generator rotor 80a and 80b shown in FIGS 2-4.

FIG 4 illustrates the second end of respective generator rotor 80a and 80b in which the second bearing arrangement 110 is shown in more detail. This second bearing arrangement comprises a roller bearing 111, a circlip 112 for holding the roller bearing and a non- rotating squeeze film sleeve 113 together, a labyrinth front sleeve 114 for sealing the generator rotor 80a or 80b against lubricant oil and/or dirt from the roller bearing, at least one O-ring 115 located on the periphery of a non- rotating rear bearing sleeve 116 for sealing the generator rotor from the surrounding when the complete rotor unit 10 is mounted in the gas turbine 20, and a rear labyrinth sleeve 117 for sealing the roller bearing 111 against dirt and sealing the compressor air from lubricant oil in the roller bearing.

FIGS 5 and 6 illustrate the first end of respective generator rotor 80a and 80b in which the first bearing arrangement 100 is shown in more detail. This first bearing arrangement comprises a ball bearing 101, the bearing clamp plate 102, which holds the ball bearing against the shoulder 100'on the generator rotor, a non-rotating labyrinth sleeve 103 and a labyrinth stator seal 104 for sealing the generator rotor from the lubricant oil in the ball bearing, a circlip 105 for holding the labyrinth sleeve and the labyrinth stator seal together, and at least one O-ring 106 located on the periphery of a non-rotating front bearing sleeve 107 for sealing the generator rotor from the surrounding when the complete rotor unit 10 is mounted in the gas turbine 20. In FIG 6 the runner retainer 61 and its screw 62 are shown attached to the first end of the generator rotor 80b.

A description will now be given of a method for balancing the rotor unit 10 according to the invention. One

principle when balancing is first to weigh all of the rotating parts to be balanced before starting the balancing procedure, then calibrating and measuring wobbling, unbalances and remaining unbalances for the concerned parts. Another balancing principle that may be used differs from the above-mentioned principle in that the weighing of the parts to be balanced is unnecessary, as is readily understood by a skilled person using a common balancing machine of today. All the other balancing steps in this second balancing principle are the same as in the first principle.

The balancing is first done for the generator rotor 80a or 80b and then together with the other rotating parts, which are mounted step by step forming groups up to the complete rotor unit 10.

Each step is documented regarding wobbling, unbalance, unbalance remaining after the calibration, and the result of the balancing in a balancing record. The calibration of each part and group of parts is done in an ordinary balancing machine available on the market (not shown). The balancing machine measures the unbalance at predefined planes and locations of the rotor unit 10, shown in FIG 7, by rotating the rotor unit at a certain rotation speed, in this application 2500 rpm, thereby defining the quantity of unbalance, and the location and the radius on which it is located. The balancing procedure may be performed at any other suitable rotation speed, e g at speeds lower than 2500 rpm, speeds higher than 2500 rpm, and even at full speed for the gas turbine when operating at full load, as is readily understood by a skilled person.

Preferably, the measured unbalance is compensated by putting adhesive material on the right radius, position and plane corresponding to the unbalance, i e spaced 180° from the location of the unbalance seen in a circle, until the unbalance is almost equal to zero or below an allowed

value. It is not necessary to put any adhesive on the parts during the balancing procedure due to the fact that the balancing machines of today may register the unbalance and its position, whereby the unbalance is easily compensated for by cutting away material correspondingly.

In the following procedure the balancing, i e the cutting away of material, can be done without being related to any weight of added adhesive material on the parts to be balanced. In other words, the cutting away of material can be done in direct relation to the measured and in the balancing machine registered unbalance data without using any adhesive material. Material is then cut away from the same position as the measured unbalance, i e at the position spaced 180° from where the added adhesive material may be put, until the corresponding weight of the unbalance, e g the same weight as the added adhesive material is cut away. Therefor each part may be weighed before and after cutting so that an as exact weight of material as possible is cut away. The unbalance is measured in gmm, which is a measure of the unbalance at a certain radius, e g an measured unbalance of 10 gmm is a product of mm radius and weight in gram, which can be compensated either by cutting away 10 g of material at radius 1 mm or cutting away 1 g of material at radius 10 mm in a linear relationship.

The tie bolt 60 is always prestressed when mounted together with the tie bolt nut 70 and the bearing clamp plate 102 during each mounting step explained below with a force of 47 kN, thereby having a protruding length of 26.5 mm in the non-prestressed state and about 28 mm in the prestressed state.

The method is explained with reference to FIGS 7-10.

FIG 7 shows the complete rotor unit 10 with the locations and planes where unbalance and wobbling are measured. The method involves the consecutive steps of first measuring

the wobbling of the generator rotor 80a or 80b manually with a dial indicator for controlling that there is no big wobbling. Then the ball bearing 101 is mounted at the first end of the generator rotor, the roller bearing 111 and a long balancing sleeve 120 are mounted at the second end, and the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102 are mounted at the first end, as shown in FIG 8. This is followed by a rough calibration in the balancing machine at plane C and D shown in FIG 7, and a rough balancing by cutting, here drilling away material at plane C and D at radius 24 mm with an inclination of 20°.

Remaining unbalance may be compensated for by putting adhesive material on the appropriate radius at plane C and D.

The long balancing sleeve 120 is removed, and the rotor shaft 90 and a short balancing sleeve 130 are mounted at the second end of the generator rotor 80a or 80b, and the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102 are mounted at the first end of the generator rotor as shown in FIG 9. These components are then calibrated as a group in the balancing machine at plane C and L shown in FIG 7, wherein unbalance may be compensated for by putting adhesive material on the right radius at plane L of the rotor shaft.

The short balancing sleeve 130 is removed, and the compressor wheel 40 and a balancing sleeve 140 are mounted at the second end of the generator rotor 80a or 80b, and the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102 are mounted as in the preceding step, as is illustrated in FIG 10. The generator rotor 80a or 80b, the rotor shaft 90, the compressor wheel 40, the balancing sleeve 140, the tie bolt, the tie bolt nut, and the bearing clamp plate 102 are calibrated as a group in the balancing machine at plane E and F shown in FIG 7. The compressor wheel 40 is mounted in four different positions, each

followed by a calibration and documentation, with a 90° division between them so that the"best"position can be chosen in relation to least wobbling and unbalance. The remaining unbalance in the"best"position may be compensated by putting adhesive material on the appropriate radius at plane E and F.

The balancing sleeve 140 is then removed, and the turbine wheel 50, the turbine sleeve 53 and the turbine nut 52 are mounted to the compressor wheel 40, and the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102 are mounted in the same above-mentioned way, as shown in FIG 7.

The wobbling at the turbine outlet near plane H is measured and documented, and the generator rotor 80a or 80b, the rotor shaft 90, the compressor wheel, the turbine wheel, the turbine sleeve, the turbine nut, the tie bolt, the tie bolt nut, and the bearing clamp plate are then calibrated together in the balancing machine at plane G and H. The turbine wheel 50 is also mounted in four different positions as the compressor wheel 40, each calibrated and documented, with a 90° division between them so that the "best"position can be chosen in relation to least wobbling and unbalance. The"best"position is marked on the turbine wheel 50, the compressor wheel 40, the rotor shaft 90 and the tie bolt 60, and the length of the protruding part of the tie bolt is measured and documented.

All of the balancing steps described above are performed so that the"best"position regarding least wobbling and unbalance for the compressor wheel 40 and the turbine wheel 50 can be determined. A small wobbling of the turbine outlet is given priority instead of cutting away less material. Most important is that the wobbling of the tie bolt 60 can be repeated in each mounting and dismounting step.

The turbine wheel 50, the compressor wheel 40 and the rotor shaft 90 are removed, and the long balancing sleeve

120 is mounted once again with the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102, wherein the tie bolt is mounted with the same length of the protruding part as in the preceding steps. The generator rotor 80a or 80b is then balanced by cutting away material, here drilling in an incrementally shaped pattern at radius 24 mm in plane C and D, shown in FIG 7, with a 20° inclination until the unbalance is below an allowed value of 1.0 gmm.

The next step is removing the long balancing sleeve 120, and mounting the rotor shaft 90 and the short balancing sleeve 130, the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102. The rotor shaft is balanced by cutting, i e drilling away material radially at plane L until an allowed unbalance below 3.0 gmm is achieved.

Then the short balancing sleeve 130 is removed, and the compressor wheel 40 and the balancing sleeve 140 are mounted together with the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102 again, wherein the tie bolt is mounted in the same way as in the preceding steps.

Material is first of all cut away from the compressor wheel in the axial direction at plane E and plane F, i e by drilling in the axial direction at plane E and grinding the surface at plane F. If large cuttings have to be done at plane E it is possible to cut away material at plane L on the rotor shaft 90, i e by drilling in the radial direction at plane L. The compressor wheel 40 is dismounted before each cutting step, which also ensures a repetition of the calibration. An unbalance of 5 gmm is allowed at plane E and an unbalance of 10 gmm is allowed at plane F. The balanced compressor wheel is controlled by checking how remaining unbalance affects the bearing points of the generator rotor 80a or 80b at plane A and B shown in FIG 7.

This is done by transferring the value of remaining

unbalance for the compressor wheel 40 to the calibration of the generator rotor 80a or 80b at plane C and D.

The balancing sleeve 140 is then removed, and the turbine wheel 50, the turbine sleeve 53 and the turbine nut 52 are mounted together with the tie bolt 60, the tie bolt nut 70 and the bearing clamp plate 102, wherein the tie bolt is mounted in the same way as in the preceding steps.

The wobbling of the outlet of the turbine wheel is measured and documented, and material on the turbine wheel 50 is cut away by grinding its surface at plane G and the surface at plane H near the outlet of the turbine wheel. Large amounts of material are cut away with the turbine wheel 50 dismounted, and an unbalance of 10 gmm is allowed at plane G and an unbalance of 5 gmm is allowed at plane H. A final cutting can be done with the turbine wheel mounted for achieving an approved balancing result. After the turbine wheel is balanced a control of the final balancing is done by transferring the value of the unbalance for the turbine wheel to the calibration planes of the generator rotor 80a or 80b, i e the unbalance at planes C and D has to be below an approved level. Then the complete bearing arrangements 100 and 110 are mounted, whereby the rotor unit is complete, for checking that possible remaining unbalance after the final balancing lies within the allowed interval.

The last step of balancing the rotor unit 10 concerns an accurate marking of the"best"positions for all of the balanced rotating components adherent to the rotor unit.

All of the balancing steps explained above are common for the two embodiments of the generator rotor 80a and 80b of the rotor unit 10 according to the invention. However, the balancing of the second embodiment of the generator rotor 80b differs from the procedure when balancing the first embodiment of the generator rotor 80a. The difference is a few additional steps in the balancing procedure before the last step of the accurate marking of the"best"

position for all concerned parts concerning the step of checking the final balancing for the complete rotor unit 10, i e when the two bearing arrangements 100 and 110, the runner retainer 61 and associated screw 62 are mounted in this second embodiment. These additional steps are the following: first the runner retainer 61 and its associated screw 62 are mounted at the first end of the generator rotor 80b after the control of the final balancing at the calibration planes of the generator rotor 80b at plane C and D. Then the wobbling and unbalance for the runner retainer are measured and documented. This is followed by removing the runner retainer and then balancing it by means of cutting away material on the runner retainer 61 at plane K, shown in FIG 7, on the side placed opposite its magnets until the unbalance is below an approved level. Then the two bearing arrangements 100 and 110 are mounted before the runner retainer and its screw, whereby the rotor unit 10 is complete, for checking that possible remaining unbalance for the complete rotor unit lies within the allowed interval and that the wobbling of the runner retainer is repeated after the final balancing. The last step of balancing the second embodiment of the generator rotor 80b concerns the accurate marking of the"best"position for all of the balanced rotating components adherent to the rotor unit 10.

Preferably, the allowed remaining unbalance for the calibrated parts should be between 0 and 100 gmm but more preferably between 0 and 50 gmm, and in these two embodiments between 0 and 20 gmm. The allowed unbalance depends mostly on the size of the gas turbine and its operation conditions.

Moreover, the balancing procedure described herein may change in response of any future changes in design and construction of the rotor unit 10. If the design and number of parts in the rotor unit changes the chronological steps in the balancing may be altered and/or existing balancing steps may be unnecessary. Furthermore, the position and number of balancing planes A-L may be changed for the same reasons.