Turbine generator and method of operating a turbine generator

Abstract

A turbine generator contains a turbine part and a generator part. The turbine contains a turbine wheel. A sealing arrangement is arranged between the turbine wheel and the generator part, the sealing effect of which varies during operation. The generator part further has a generator shaft, which is supported by an axial bearing configured as a magnetic bearing with two coils axially spaced apart from each other. A bearing ring is arranged between these coils with an axial distance from the coils. To ensure a safe operation, a setpoint value for the axial distance is varied to change the sealing effect of the sealing arrangement. Alternatively or additionally, it is provided that when a current threshold of a coil current is exceeded, a control signal is emitted to control the flow of the medium or the rotational speed.

Claims

1. A turbine generator for rotational speeds greater than 4,000 rpm, comprising: a turbine part having a turbine wheel, an inlet and an outlet for a medium; a generator part, the turbine generator extending along an axis of rotation from said turbine part to said generator part, wherein said generator part having a rotating part and a fixed part with a fixed housing part; a sealing configuration disposed between said turbine wheel and said fixed housing part; an axial bearing configured as a magnetic bearing; said generator part having a generator shaft with at least one bearing ring, said generator shaft is mounted via said magnetic bearing and, for this purpose, said magnetic bearing having two coils axially spaced apart from each other, between which said at least one bearing ring is disposed at a respective axial distance from said two coils; and a controller for controlling said axial bearing and configured in such a way that the respective axial distance between said at least one bearing ring and one of said two coils is regulated to a setpoint value and for this purpose said controller is set up to apply a coil current to said two coils during operation, said two coils being configured for a maximum coil current, wherein said controller is further configured in such way that said controller initiates at least one of the two following measures as required, namely: varying the setpoint value in such way that a sealing effect of said sealing configuration is changed; and/or if a current threshold for the coil current is exceeded, a control signal is emitted to control a flow of the medium or a rotational speed of the turbine generator.

2. The turbine generator according to claim 1, wherein a gap size between said turbine part and said fixed housing part in an area of said sealing configuration is changed by a change of the setpoint value.

3. The turbine generator according to claim 1, wherein: during operation axial forces are generated via said two coils respectively, which act on said at least one bearing ring; and said controller is configured in such way that the setpoint value is regulated in such way that an alignment of the axial forces generated by said two coils is effected.

4. The turbine generator according to claim 1, wherein a maximum permissible change in a range of +/−0.5 mm is specified for a change of the setpoint value.

5. The turbine generator according to claim 1, wherein said controller is configured in such way that a variation of the setpoint value is effected, if a difference between coil currents and/or an absolute value of at least one of the coil currents exceeds a predetermined threshold.

6. The turbine generator according to claim 1, wherein said controller is configured in such way that a variation of the setpoint value is effected, if a difference between coil currents is greater than 20%.

7. The turbine generator according to claim 1, wherein the current threshold for an output of the control signal is in a range between 60% and 85% of a maximum permissible coil current.

8. The turbine generator according to claim 1, wherein said controller is disposed in such way that when the current threshold is exceeded at least one of the following measures is initiated via the control signal: reducing a flow rate of the medium by controlling a flow valve for the medium; limiting and/or reducing a current rotational speed; and hanging pressure conditions at said inlet and/or said outlet.

9. The turbine generator according to claim 1, wherein said sealing configuration is formed as a labyrinth seal.

10. The turbine generator according to claim 1, wherein the turbine generator is configured for an operating at a rotational speed in a range between 4,000 and 40,000 rpm.

11. The turbine generator according to claim 1, wherein said turbine part has a diameter in a range between 50 mm and 500 mm.

12. The turbine generator according to claim 1, wherein said controller is configured in such way that a variation of the setpoint value is effected, if a difference between coil currents is greater than 30%.

13. The turbine generator according to claim 1, wherein said controller is configured in such way that a variation of the setpoint value is effected, if a difference between coil currents is a range between 20% and 60% of an averaged coil current of the two coils.

14. The turbine generator according to claim 1, wherein the current threshold for an output of the control signal is at 75% of a maximum permissible coil current.

15. A method for operating a turbine generator having a turbine part and a generator part and extending along an axis of rotation from the turbine part to the generator part, the generator part having a rotating part and a fixed part and the rotating part rotating at a rotational speed of more than 4,000 rpm, the generator part further having a generator shaft with at least one bearing ring, the turbine part containing a turbine wheel, an inlet and an outlet for a medium, and the medium flows in via the inlet and flows out via the outlet, which comprises the steps of: disposing a sealing configuration between the turbine part and a fixed housing part; mounting the generator shaft via the at least one axial bearing configured as a magnetic bearing and, for this purpose, the axial bearing containing two coils axially spaced apart from each other, between which the at least one bearing ring is disposed at a respective axial distance from the two coils; regulating the respective axial distance between the at least one bearing ring and one of the two coils to a setpoint value and for this purpose a coil current is applied to the two coils, wherein the two coils are configured for a maximum coil current; and carrying out at least one of the following measures: varying the setpoint value in order to change a sealing effect of the sealing configuration; and/or upon exceeding a current threshold for a coil current, emitting a control signal to control a flow of the medium or the rotational speed of the turbine generator.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, cross-sectional longitudinal view through a turbine generator according to the invention;

(2) FIG. 2 is an enlarged sectional view of the axial bearing area marked with the letter C in FIG. 1;

(3) FIG. 3 is an enlarged section view of the area marked with the letter D in FIG. 1 with a labyrinth seal; and

(4) FIG. 4 is a highly simplified schematic diagram of the turbine generator with the inlet and outlet for the medium.

DETAILED DESCRIPTION OF THE INVENTION

(5) In the figures, components with the same effect are marked with the same reference signs.

(6) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a turbine generator 2 that extends along an axis of rotation 4 in axial direction 6 and contains a turbine part 8 followed by a generator part 10. At its front end, the generator part 10 has an annular flange 12, by which it is attached to the turbine part 8.

(7) The turbine part 8 and the generator part 10 have a common continuous generator shaft 14. A turbine wheel 16 is attached to the shaft in the turbine part 8, which has blades distributed around the circumference and encloses 18 flow channels to a turbine housing. During operation, a medium M is fed in via inlet 20, flows through the turbine part 8 and leaves it via outlet 22. The turbine part 8 shown in FIG. 1 is a radial turbine, in which the inlet 20 is oriented radially and the outlet 22 axially. Alternatively, the turbine part 8 is configured as an axial turbine, where the inlet 20 and the outlet 22 are axially oriented.

(8) The turbine wheel 16 is sealed to the generator part 10 and to the fixed annular flange 12 by a sealing arrangement, which in the exemplary embodiment is designed as a labyrinth seal 24. As a result of leakage currents during operation, part of the medium M penetrates into an inner chamber 26 of the generator part 10. In this inner chamber 26 a pressure is built up, which is in the range between the pressure at the inlet 20 and the pressure at the outlet 22 of the medium M.

(9) The generator part 10 generally contains a fixed part 28 and a rotating part 30. The fixed part 28 contains, among others, a generator housing 32 with the annular flange 12 already described.

(10) The rotating part 30 is supported by a bearing arrangement, which in the exemplary embodiment contains an axial bearing 36 and two radial bearings 38. The axial bearing 36 is arranged between the annular flange 12 and the front radial bearing 38 on the turbine side. The rear radial bearing 38 supports the generator shaft 14 in its end part. A rotor 40 is arranged between the two radial bearings 38.

(11) In the exemplary embodiment, the axial bearing 36 and the two radial bearings 38 are each designed as magnetic bearings. Due to the design as magnetic bearings, the radial bearings 38 contains a fixed outer part 42 and an inner part 44 which is fixed to the generator shaft 14 and rotates during operation.

(12) The axial bearing 36 has two axially spaced coils 46, which are each enclosed in a coil housing 48. A bearing ring 50 is mounted on the generator shaft 14 and penetrates into the space between the two coils 46. A thin air gap is formed between one bearing ring 50 and each of the two coils.

(13) According to an alternative variant, which is not shown here in detail, the axial bearing is designed as a split axial bearing, in which each of the two coils 46 is assigned its own bearing ring, which are spaced apart from each other. Starting from the situation shown in FIG. 1, the second bearing ring is arranged, for example, downstream of rotor 40 and, for example, in the area of the rear radial bearing 38, viewed in axial direction 6.

(14) To check both the axial position and the radial position of the rotating part 30 relative to the fixed part 28, several position sensors are provided, namely at least one axial position sensor 52a, and in the exemplary embodiment at least two radial position sensors 52b. Said position sensors 52a,b each measure on a rotating measuring ring 54a,b of the rotating part 30. Preferably, two axial position sensors 52a, arranged offset to each other, are arranged on the circumference.

(15) The rotor 40 is surrounded by a stator 56. The stator—in a manner not shown in detail here—contains coil windings, which are wound around coil cores designed as sheet metal packages. On its circumference the stator 56 is surrounded by a cooling jacket 60, which in turn contains cooling channels 62 on its outer circumference, through which coolant flows during operation. The cooling channels 62 are closed off to the outside by a housing sleeve of the generator housing 32. The housing sleeve has a coolant inlet and a coolant outlet.

(16) The bearing arrangement further contains two axially spaced emergency bearings 66, which radially support the rotating part 30 to the generator housing 32, preferably at the opposite ends of the generator part 10, as shown in FIG. 1. They are used for emergency bearing, for example in case of a power failure. The right emergency bearing 66 shown in FIG. 1 is mounted in an end wall of the generator housing 32. This front wall contains a corresponding bearing bore hole, which is closed off to the outside by a cover 68. The cover is sealed to the front side of the generator housing 32, in particular by at least one O-ring 70.

(17) A gap 72 is formed between the rotating part 30 and the fixed part 28. A sealing tube 74 is arranged in the gap. The sealing tube 74 preferably extends over the rotor 40 between the two radial bearings 38. The sealing tube 74 preferably extends over almost the entire axial length of the rotating part 30. In particular, the sealing tube 74 extends from the axial bearing 36 to the front side of the generator housing 32. The sealing tube 74 is fixed during operation and therefore belongs to the fixed part 28. It is sealed in the radial direction at its opposite ends by means of seals, which are especially designed as O-rings 70. At the front end, it is sealed off from the coil housing 48. At the right end, the sealing tube 74 enters a recess in the front wall of the generator housing 32 and is sealed radially to a surrounding wall area of the recess. The sealing tube 74 hermetically seals the fixed part 28 against the interior 26. Furthermore, the components arranged on the generator shaft 14 are sealed against the interior as well.

(18) During operation, the medium M flows through the turbine part 8 and drives the turbine part as well as the generator shaft 14 and thus also the rotor 40 to generate electrical energy. The turbine wheel 16 rotates at a rotational speed in the range between 4,000 and 40,000 rpm. The turbine wheel has a diameter d which is between 50 mm and 500 mm, depending on the power rating. The entire turbine generator 2 has a length l, which is between 350 mm and 1500 mm, depending on the power rating.

(19) The design of the axial bearing 36 can be identified from in FIG. 2. The two coils 46 are each arranged in a—viewed in a cross-section—approximately U-shaped coil housing 48. The bearing ring 50 penetrates into the space between the two coils 46. A distance a is formed between the bearing ring 50 and a respective coil 46. The coil housings 48 also seal the space between them in a radial direction. In the exemplary embodiment, an intermediate piece 84 is arranged for this purpose, which is designed as a ring that is connected to the bearing ring 50 on the circumference. The intermediate piece 84 is arranged between the two coil housings 48 and sealed with sealing elements, especially O-rings 70. The left coil housing 48 is further sealed by an O-ring 70 to another housing part of the generator housing 32.

(20) The axial position sensor 52a records an axial distance value to the axial measuring ring 54a. This distance value is directly correlated to the distance a between the two coils 46 and the bearing ring 50. Due to the geometric conditions, the measured distance value can be clearly converted into the distance a, which is assumed by the turbine side coil 46 to the bearing ring 50 on the one hand and by the generator side coil to the bearing ring 50 on the other hand. The two distances can also differ. Under normal operating conditions, the distance is typically set so that the distance a to the two coils 46 is identical.

(21) The enlarged illustration according to FIG. 3 clearly shows the labyrinth seal arrangement 24 between the turbine part 8 and the generator part 10. Between the turbine wheel 16 and the annular flange 12 a sealing element is arranged, which contains annular webs projecting in the axial direction. These annular webs engage in corresponding annular grooves on the back of the turbine wheel 16 and form the labyrinth seal 24 already mentioned. The annular webs and the annular grooves are only arranged in the outermost circumferential area of the turbine wheel 16. Between the turbine wheel 16 and the generator housing 32, i.e. especially the annular flange 12, a further gap 86 with a gap size s is formed. During operation, a leakage flow of the medium M flows through the labyrinth seal 24 and enters the inner chamber 26 via the further gap 86. The sealing effect of the labyrinth seal 24 is defined by a gap between the annular flanges and the annular grooves, which is not shown in detail here. This gap varies with a change in the gap size s of the gap 86 and is therefore correlated with the gap size s.

(22) The simplified schematic diagram in FIG. 4 shows that a control unit 90 is assigned to the turbine generator 2, which is preferably a direct component of the turbine generator 2. A supply line 92 is connected to the turbine part 8 on the inlet side and a discharge line 94 for the medium M on the outlet side. As an example, FIG. 4 shows a flow valve 96 in the supply line 92. In general, such a valve can be arranged in addition or alternatively in the discharge line 94.

(23) During operation, a pressure build up on the rear side of the turbine wheel 16 on the generator side and a differential pressure ratio is established between the front side of the turbine and the rear side of the turbine wheel 16. Different pressures result in an axial force acting on the turbine wheel 16 and the generator shaft 14. The sealing arrangement 24 is preferably configured in such way that during normal operation the pressure ratios on the front and rear sides are the same or as equal as possible, so that no or as little differential pressure as possible is formed. As a result, no or as little as possible axial force is generated and the axial bearing 36 has to absorb no or only small axial forces.

(24) During operation, varying process parameters, such as varying rotational speeds, varying pressure ratios, varying flow rates, varying temperatures, etc., can cause the gap size s between the turbine wheel 16 and the annular flange 12 to vary. Varying process parameters, i.e. unsteady operating conditions, occur for example during start-up. These can lead to a slight bending of the turbine wheel 16, which has a direct influence on the gap size s and the sealing effect of the labyrinth seal 24. As a result, the leakage current flowing across the wider gap 86 changes, which leads to a change in the pressure conditions and especially in the pressure difference between the front and the rear of the turbine wheel 16 and finally to a resulting axial force on the generator shaft 14. In order to continue to ensure a reliable operation of the turbine generator 2 at the very high rotational speeds, such an axial force has to be absorbed by the axial bearing 36. For this purpose, a control unit 90 is first integrated in the control unit 90, which controls the coil currents of the two coils 46 accordingly, in order to adjust the distance a between the respective coils 46 and the bearing ring 50 to a desired setpoint value. The distance is preferably selected in such way that the bearing ring 50 is positioned exactly in the middle between the coils 46.

(25) In order to ensure a safe operation even if the gap size s is changed and the sealing effect of the labyrinth seal and thus the axial forces are changed, the switching to the optimized operating mode and, if necessary, also to the safety mode is provided. The control device 90 first switches from a normal operating mode to the optimized operating mode, if, for example, a difference in the coil currents of the coils 46 of the axial bearing 36 is greater than 20% or greater than 30% of an average value of the coil currents of the two coils 46. If this measure is not sufficient, the safety mode is preferably initiated when a special safety-critical operating situation is reached. In particular, the control device switches to the safety mode and emits the control signal S, if one of the two coil currents of the two coils 46 exceeds a predetermined threshold, also called current threshold, of e.g. 75% of a maximum permissible coil current.

(26) In the optimized mode, the setpoint for distance a is changed. As a result of the control algorithm, this leads to the fact that a change in the coil currents deliberately generates an axial force, so that the bearing ring 50 and thus the entire generator shaft 14 is displaced in—or against the axial direction 6 relative to the fixed part 28. This leads directly to an axial relative displacement between the turbine wheel 16 and the annular flange 12 and thus to a change in the gap size s. This has a direct influence on the sealing effect of the labyrinth seal 24 and thus on the pressure conditions. The change in the setpoint value for the distance a is such that—depending on the current operating situation—the gap size s is increased or reduced in such way that the coil currents of the two coils 46 match. If, for example, the operating situation causes the gap size s to increase initially, so that the pressure on the back side increases and an axial force is exerted against the axial direction 6, the new setpoint value a is set in such way that the gap size s is reduced again. This means that the bearing ring 50 is deliberately displaced by the axial bearing in the axial direction 6 to the turbine part 8.

(27) If a reduction of the gap size s occurs during normal operation, the method is reversed accordingly.

(28) This measure therefore directly influences the sealing effect of the labyrinth seal 24 by varying the setpoint value for the distance a, preferably in the direction of a bearing as free of axial forces as possible, or it is regulated to a maximum efficiency of the turbine generator 2.

(29) Alternatively to the optimized mode, only the safety mode is provided. However, the safety mode is preferably provided as a supplement. In this mode, a control signal S is emitted by the control device 90, with which, for example, the flow valve 96 is controlled in order to reduce the mass flow for the medium M, for example. Alternatively or additionally, the rotational speed of the turbine generator 2 is limited by the control device. By intervening in the flow of the medium M or in the rotational speed, a change in the critical pressure conditions at turbine wheel 16 is achieved and thus the axial forces caused by a differential pressure are also reduced.

(30) As mentioned above, both variants are used in particular in combination, wherein first—when the first trigger criterion is reached—the setpoint value is varied. As this can only be varied within a limited range, as a distance has to remain between the coils and the bearing ring 50, the additional measure according to the second variant may become necessary in unfavourable situations. Therefore, this additional measure is initiated in particular if the setpoint has already reached a maximum permissible value and additionally the second trigger criterion, i.e. the exceeding of the current threshold for the coil current, is exceeded.

LIST OF REFERENCE SIGNS

(31) TABLE-US-00001 2 turbine generator 4 axis of rotation 6 axial direction 8 turbine part 10 generator part 12 annular flange 14 generator shaft 16 turbine wheel 18 turbine housing 20 inlet 22 outlet 24 labyrinth seal 26 interior 28 fixed part 30 rotating part 32 generator housing 36 axial bearing 38 radial bearing 40 rotor 42 outer part 44 inner part 46 coils 48 coil housing 50 bearing ring 52a axial position sensor 52b radial position sensor 54a axial measuring ring 54b radial measuring ring 56 stator 60 cooling jacket 62 cooling channels 66 emergency bearing 68 cover 70 O-ring 72 gap 74 sealing tube 76 protective housing 86 further gap 90 control device 92 supply line 94 discharge line 96 flow valve l length d diameter a distance M medium s gap size S control signal