METHOD FOR COUPLING A STEAM TURBINE AND A GAS TURBINE AT A DESIRED DIFFERENTIAL ANGLE

Abstract

A method for coupling a rotational device, particularly a steam turbine, and a shaft device, particularly a gas turbine, the method including the following steps: accelerating the rotational device up to an output rotational speed that is below the rotational speed of the shaft device; detecting a differential angle between the shaft device and the rotational device; and accelerating the rotational device with an acceleration value that is derived from the target rotational speed difference, which is formed as a function of the detected differential angle, the acceleration and a desired target coupling angle. An associated arrangement couples a rotational device.

Claims

1. A method for coupling a rotational device and a shaft device, comprising: accelerating the rotational device up to an initial rotational speed which lies below the rotational speed of the shaft device wherein the shaft device and the rotational device are twisted in relation to one another by a differential angle () and an ideal differential angle () of 32 .sub.opt is obtained after the coupling; detecting the differential angle () between the shaft device and rotational device; wherein a rotational speed difference (n), which is formed from the difference of the rotational speed of the rotational device (n.sub.DT) and the rotational speed of the shaft device (n.sub.GT), is established; changing the rotational speed of the rotational device (n.sub.DT) with a rotational speed intended value (n.sub.DT), wherein an intended rotational speed difference (n.sub.intended) depends on the differential angle (), and the rotational speed intended value (n.sub.DT) is established from the dependence between the intended rotational speed difference (n.sub.intended) and the difference angle (), wherein the established rotational speed difference (n) is additionally taken into account when establishing the rotational speed intended value (n.sub.DT).

2. The method as claimed in claim 1, wherein the changing of the rotational speed of the rotational device (n.sub.DT) with the rotational speed intended value (n.sub.DT) is made available by an intended rotational speed (n.sub.intended,DT) of the rotational device as an input variable.

3. The method as claimed in claim 1, further comprising: providing a turbine regulator, having the rotational speed intended value (n.sub.DT) and a switching criterion as input variable.

4. The method as claimed in claim 1, wherein the initial rotational speed lies approximately 1 Hz below the rotational speed of the shaft device.

5. The method as claimed in claim 1, wherein the acceleration value is approximately 0.025 Hz/s to approximately 0.075 Hz/s.

6. An arrangement comprising a shaft device, and a rotational device, and a coupling for coupling the shaft device and rotational device, the coupling comprising: a device for detecting the differential angle between the shaft device and rotational device; a device for accelerating the rotational device by an acceleration value; means to obtain a desired target coupling angle between the shaft device and rotational device as a function of the detected differential angle () and the detected rotational speed difference (n).

7. The arrangement of claim 6, wherein the rotational device comprises a steam turbine, and the shaft device comprises a gas turbine.

8. The method of claim 1, wherein the rotational device comprises a steam turbine, and the shaft device comprises a gas turbine.

9. The method of claim 4, wherein the initial rotational speed lies approximately 0.5 Hz to approximately 1.5 Hz below the rotational speed of the shaft device.

10. The method of claim 4, wherein the initial rotational speed lies approximately 0.9 Hz to approximately 1.1 Hz below the rotational speed of the shaft device.

11. The method of claim 5, wherein the acceleration value is approximately 0.05 Hz/s.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Below, the invention will be described in more detail on the basis of figures. Here:

[0028] FIG. 1 shows the relationship between various coupling angles in the case of different relative accelerations proceeding from an initial rotational speed difference of 1 Hz and an initial angle difference of zero;

[0029] FIG. 2 shows the setpoint rotational speed difference as a function of the differential angle, proceeding from an initial rotational speed difference of 1 Hz and an initial angle difference of 3600;

[0030] FIG. 3 shows the profile of the rotational speed of the gas turbine and the steam turbine in an exemplary manner;

[0031] FIG. 4 shows the profile of the differential angle during coupling and the coupling twist angle;

[0032] FIG. 5 shows a diagram of a shaft run;

[0033] FIG. 6 shows the principle of coupling with a desired differential angle.

DETAILED DESCRIPTION OF INVENTION

[0034] FIG. 1 shows the differential angle during the acceleration of the steam turbine as a function of the respective rotational speed difference for various constant acceleration values. The rotational speed difference between gas turbine and steam turbine in hertz is plotted along the X-axis. The differential angle in degrees is plotted along the Y-axis, wherein the integer multiples of 360 are also added.

[0035] The uppermost dashed curve shows the relationship in the case of an acceleration value of 0.025 Hz/s, the central dotted curve shows the relationship in the case of an acceleration value of 0.05 Hz/s and the lower full line shows the relationship in the case of an acceleration value of 0.075 Hz/s. This is intended to be explained in more detail on the basis of the central curve.

[0036] The point at the left-hand, lower end of the curve is considered to be the initial point. The angle difference between the gas and steam turbine is zero; the rotational speed difference is 1 Hz. That is to say, the gas turbine rotates with one Hz more than the steam turbine. At this point, i.e. at this initial rotational speed difference of the steam turbine, the targeted approach of a coupling angle is intended to start.

[0037] The steam turbine is accelerated with an unchanging acceleration of 0.05 Hz/s relative to the gas turbine until both turbines have the same rotational speed. The gas turbine, which is quicker up until that point, passes over an angle that is greater than that of the steam turbine by 3600 up to the point in time at which the steam turbine has the same speed; that is to say, said gas turbine has experienced 10 more revolutions than the steam turbine in the time period. Reference is made to the fact that the time axis is not depicted here. What can be identified from the curve is that the differential angle change between gas and steam turbine reduces as the speeds approach, i.e. the smaller the rotational speed difference is. What can furthermore be seen from the different curves is that the passed-over angle up to the coupling start is larger the smaller the acceleration is. This effect is used essentially for actuating a selected target coupling angle. Quantitatively different relationships apply for different acceleration values and different start differential angles; however, the deliberations are otherwise analogous. By way of example, the target coupling angle for the start of coupling is 0 in the case of a start differential angle of 3600 and a relative acceleration of 0.05 Hz.

[0038] FIG. 2 is an inverse illustration of FIG. 1, with only the curve with an acceleration value of 0.05 Hz/s being depicted here. Here, compared to FIG. 1, the start differential angle was set to 3600 in order to nominally achieve a target coupling angle of 0. Plotted on the X-axis is the differential angle in degrees, wherein the integer multiples of 360 are also added. The Y-axis plots the rotational speed difference between gas turbine and steam turbine in Hz.

[0039] FIG. 2 therefore highlights how the rotational speed difference depends on the differential angle in the case of a constant relative acceleration of 0.05 Hz/s. Here, a differential angle of 0 is assumed in the case of a corresponding frequency between gas turbine and steam turbine. For a selected acceleration of 0.05 Hz/s, FIG. 2 represents the central setpoint value curve. Thus, for example, the speed difference between gas turbine and steam turbine should be 0.5 Hz in the case of an angle difference of 900 . That is to say that the steam turbine still is slower than the gas turbine by 0.5 Hz in the case of an angle difference of 900.

[0040] In an ideal case, FIG. 2 describes the relationship between passed-over angle and rotational speed difference between the steam turbine and gas turbine.

[0041] If the speed difference in the case of a measured differential angle of 900 is larger in the real installation, it is not the target angle of 0, but rather a larger target angle, that is reached when there is an unchanging acceleration of 0.05 Hz/s. In this case, the steam turbine is too slow; it must be accelerated more strongly.

[0042] Conversely, if the speed difference is smaller in the case of a measured differential angle of 900 in the real installation, it is not the target angle of 0, but rather a smaller target angle, that is reached when there is an unchanging acceleration of 0.05 Hz/s. In this case, the steam turbine is too quick; it must be decelerated.

[0043] The coupling procedure as such is depicted in FIG. 3. The time in seconds is plotted along the X-axis and the rotational speed is plotted along the Y-axis. Initially, the steam turbine is slower than the gas turbine but it is accelerated relative to the latter. The rotational speed of the gas turbine is constant at 50 Hz, as depicted by the dotted line. The speed of the steam turbine is plotted by means of the full line. The coupling procedure starts at the time at which the steam turbine has the same speed as the gas turbine. Thus, a start is made to enter the coupling. Initially, the steam turbine is accelerated further; it overtakes the gas turbine in the process and runs into the stop of the coupling. There is a deceleration at this position. Afterwards, the two turbine shafts rotate with the same rotational speed.

[0044] The effect of the coupling on the differential angle becomes apparent from FIG. 4. The X-axis once again plots the time in seconds and the Y-axis plots the rotational angle difference in degrees. The dashed line shows a setpoint value of the angle difference, which is at 0 in this case. The full line, initially extending below, highlights the time profile of the actual angle difference. Initially, the rotational angle of the steam turbine is 250 smaller than the rotational angle of the gas turbine. This rotational angle difference initially decreases quickly to a difference of zero degrees. Then, the rotational angle difference increases again, by approximately 20 in the present case. This is due to the fact that there is a backing of the steam turbine by the coupling twist angle when turning into the coupling sleeve. The profile of the coupling twist angle can be identified by the dotted line.

[0045] Thus, what should be taken into account when selecting the desired target coupling angle during coupling is that there is a change in the rotational angle difference by the coupling twist angle during coupling-in.

[0046] FIG. 5 shows a schematic illustration of a shaft run 1. It comprises a rotational device 2 which forms the shaft 3 of a steam turbine not depicted here. The shaft 3 is coupleable to a generator shaft 5 by way of a coupling 4. The generator shaft 5 is driven by the generator 6. By way of a further coupling 7, the generator shaft 5 is connected to a shaft device 8, which forms the shaft 9 of a gas turbine not depicted in any more detail.

[0047] The rotational speed and rotational angle of the shaft 3 are established by a key phasor 10. The rotational speed and rotational angle of the shaft 9 are established by way of a further key phasor 11. The signals from the key phasor 10 and the key phasor 11 are transferred to a unit 12. The differential angle AT and the rotational speed difference An are forwarded from the unit 12 to a turbine regulator 13.

[0048] The steam turbine is accelerated as per usual by way of a predetermined ramp up to a predetermined speed difference. In the case of a speed difference of 1 Hz, i.e. the initial rotational speed, there is a switchover to the target angle-regulated coupling. To this end, the current angle difference is detected in the range 0-360 and reduced by the angle range which the gas turbine would pass over up to the start of the coupling when the previous acceleration of the steam turbine is maintained. This should be clarified using an example: the rotational speed difference between the gas turbine and steam turbine is 1 Hz; the steam turbine is accelerated by 0.05 Hz/s. 20 seconds pass up until the time at which the gas turbine and the steam turbine have the same speed. The differential angle passed over in the process is 3600.

[0049] FIG. 6 describes the actual closed-loop control of the target coupling angle. The difference between the steam turbine twist angle and gas turbine twist angle, i.e. the differential angle, is transferred into a setpoint rotational speed difference between the steam and gas turbine by means of a characteristic. The setpoint rotational speed of the steam turbine is thus set depending on the gas turbine rotational speed and the differential angle. The factor K in this case provides the additional possibility for further increasing this setpoint rotational speed difference. Here, the factor K is the feedback factor of the system deviation, i.e. the deviation of the actual value from the setpoint value. Therefore, this is a P-controller. It should be analyzed and set separately in view of the properties of the resultant overall control loop. The standard prescription is K=1. The setpoint rotational speed of the steam turbine emerges by adding the gas turbine rotational speed.

[0050] The use of an adjustable offset renders it possible to design the whole computational prescription to a target angle of zero. A desired target angle deviating from zero is displaced by way of this offset in such a way that a standard curve is usable for the relationship between AT and n.sub.setpoint. Using this approach, it is then possible to restrict the considerations to a desired target angle of 0.

[0051] The differential rotational speed n is processed in a unit 14 in addition to the differential angle . Moreover, the rotational speed n.sub.DT is processed in the unit 14. An intended rotational speed n.sub.intended,DT is generated in the unit 14, said intended rotational speed being forwarded to an intended value guide 15. The signal n.sub.SV,DT is generated in the intended value guide and fed to a further intended value guide 16. A value for the rotational speed change n.sub.DT is generated at the output of the intended value guide 16 and forwarded to the turbine regulator 13. Moreover, the signal from the switching criterion 17 is connected to the turbine regulator 13. The signal from the switching criterion is then used to switch between the intended value guide 15 and the intended value guide 16.

[0052] In the case of an acceleration of the steam turbine relative to the gas turbine with a constant acceleration of k Hz/s, a time t=.sub.0/k is required to overcome an initial rotational speed difference of .sub.0. During this time, the system passes over a relative angle difference corresponding to (.sub.0).sup.2/(2*k) whole revolutions. Thus, if the differential angle at the start rotational speed difference .sub.0 randomly happened to be 360*(.sub.0).sup.2/(2*k), the constant acceleration k will be suitable to target the target angle 0. In the case of every other start angle difference, the acceleration needs to be modified in order to arrive at the target angle of 0. If the start angle is now set to 360*(.sub.0).sup.2/(2*k)+measured angle, this means that the turbine must experience a slightly increased acceleration relative to the acceleration k up to the initial rotational speed. A slight increase in the acceleration during the controlled approach of the target coupling angle was found to be more advantageous than a slight reduction in the acceleration. The selected approach of setting the differential angle at the start rotational speed difference as above always renders it possible to slightly increase the acceleration.

[0053] Using a numerical example: it is better to assume that the steam turbine must advance by 270 rather than be intended to fall back by 90.

[0054] Even though the invention was, in detail, described and illustrated more closely on the basis of the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by a person skilled in the art, without departing from the scope of protection of the invention.