JP2014114796A - Turbine overspeed prevention system and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbine overspeed prevention system which has high reliability by constantly securing the triplication of a measurement point.SOLUTION: A turbine overspeed prevention system 10 includes: a first overspeed prevention part 13 for controlling the number of revolutions of a steam turbine on the basis of speed signals (a, b and c) output from at least three first detectors 11 (11A to 11C) for detecting rotational speed of the steam turbine; a second overspeed prevention part 14 for receiving as input, speed signals (d, e and f) output from at least three second detectors 12 (12D to 12F) different from the first detectors in measurement points; an abnormality determination part 15 for determining whether or not the speed signals (a, b and c) output from the first detectors 11 are abnormal; and a signal complementing part 22 that selects the speed signals (d, e and f) output from the second detectors 12 in place of the speed signals (a, b and c) which are determined to be abnormal and output from the first detectors 11, and that thereby causes to perform control of the number of revolutions.

Description

  The present invention relates to a turbine overspeed prevention technique.

  A steam turbine such as a thermal power generation needs to stably control its rotation speed and stop its operation promptly in the event of an emergency such as exceeding the rotation speed.

  Conventionally, control of the rotational speed of the turbine has been performed by an emergency governor using a mechanical mechanism. Further, when the emergency speed governor fails, backup control is performed by an electric circuit using a rotation detector that detects the rotation speed of the turbine as a speed signal.

  In recent years, due to the difficulty of maintenance of equipment related to a mechanical mechanism, a method of controlling by an electric circuit based on a speed signal in which measurement points are multiplexed by a plurality of detectors has been proposed (for example, see Patent Document 1). .

Japanese Patent Laid-Open No. 11-82908

  The technique of Patent Document 1 maintains the control system by duplicating with the remaining detectors even if there is an abnormality in one detector by triplicating measurement points with three detectors. ing.

  However, there is a problem that the reliability of the control system is lowered when the measurement point triple configuration is shifted to the dual configuration. In addition, when performing abnormality determination of the detector, it is difficult to determine based on a large intermediate value deviation with the signals from the two detectors. For this reason, determination by upper / lower limit deviation and the remaining two signals are monitored and manual selection work is required, and there is a problem that it is difficult to perform highly reliable abnormality determination.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a highly reliable turbine overspeed prevention system by always ensuring triple measurement points.

  The turbine overspeed prevention system according to the present embodiment includes a first overspeed prevention unit that controls the number of rotations of the steam turbine based on a speed signal output from at least three first detectors that detect the rotation speed of the steam turbine. And a second overspeed prevention unit for inputting a speed signal output from at least three second detectors having different measurement points from the first detector, and the speed signal output from the first detector is abnormal. An abnormality determining unit that determines whether or not the speed signal output from the second detector is selected instead of the speed signal output from the first detector determined to be abnormal; And a signal complementing unit for controlling.

The block diagram of the turbine overspeed prevention system which concerns on this embodiment. The block diagram of the abnormality determination part applied to this embodiment. The block diagram of the abnormality determination circuit applied to this embodiment. The flowchart which showed the selection procedure of the speed signal to complement. The block diagram of the speed control circuit applied to this embodiment. The block diagram of the overspeed prevention circuit applied to this embodiment. The block diagram of an overspeed prevention circuit when many speed signals become abnormal. The block diagram which showed the 1st modification of the overspeed prevention circuit applied to this embodiment. The block diagram which showed the 2nd modification of the overspeed prevention circuit applied to this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  A turbine overspeed prevention system 10 (hereinafter, referred to as a system 10) shown in FIG. 1 includes speed signals (a, 1) output from at least three first detectors 11 (11A to 11C) that detect the rotational speed of a steam turbine. b, c) the first overspeed prevention unit 13 that controls the rotational speed of the steam turbine, and the first detector 11 includes at least three second detectors 12 (12D to 12F) having different measurement points. Abnormality determination for determining whether or not the speed signal (a, b, c) output by the first detector 11 and the second overspeed prevention unit 14 for inputting the speed signal (d, e, f) to be output are abnormal. A speed signal (d, e, f) output from the second detector 12 instead of the speed signal (a, b, c) output from the first detector 11 determined to be abnormal and the unit 15; And a signal complementing unit 22 for controlling the number of revolutions. In FIG. 1, three first detectors 11 and three second detectors 12 are configured, but the quantity, position, and arrangement of each component are not limited to those in FIG. 1.

The first detector 11 detects the rotational speed of a steam turbine (not shown) and generates speed signals (a, b, c), respectively. Then, the generated signal is output to the first overspeed prevention unit 13.
Similar to the first detector 11, the second detector 12 detects the rotational speed of the turbine and generates speed signals (d, e, f), respectively. Then, the generated signal is output to the second overspeed prevention unit 14. The second detector 12 and the first detector 11 are installed at different measurement points.

  The first detector 11 is an active type, the second detector 12 is a passive type, and different types of rotation detectors are used. The active type rotation detector has its own battery, or detects the number of rotations using radio waves or the like by external power feeding. On the other hand, the passive type rotation detector itself does not have a battery but detects the number of rotations using a magnetic field or an electric field generated by the rotation of the turbine.

  The first overspeed prevention unit 13 includes an abnormality determination unit 15, a first speed control circuit 17, a first overspeed prevention circuit 19, and a zero speed detection interlock 21. The abnormality determination unit 15 receives the speed signals (a, b, c) output from the first detector 11 and determines whether each signal is abnormal due to a failure of the first detector 11 or the like. When there is a signal determined to be abnormal, the backup signal is complemented from the second overspeed prevention unit 14 via the signal complementing unit 22.

  The signal complementing unit 22 selects the speed signal (d, e, f) from the first overspeed preventing unit 13 in place of the speed signal (a, b, c) determined to be abnormal, and sends it to the abnormality determining unit 15. Complement. Accordingly, the abnormality determination unit 15 outputs a normal speed signal (a1, b1, c1) that does not include an abnormal signal to the first speed control circuit 17 and the first overspeed prevention circuit 19.

The first speed control circuit 17 controls the rotational speed of the turbine based on the speed signals (a1, b1, c1) output from the abnormality determination unit 15.
The first overspeed prevention circuit 19 outputs a trip signal s for tripping the turbine when the speed signal (a1, b1, c1) exceeds a predetermined speed. The zero speed detection interlock 21 is an interlock that detects that the rotational speed of the turbine has fallen below a certain speed.

  The second overspeed prevention unit 14 includes an abnormality determination unit 16, a second speed control circuit 18, and a second overspeed prevention circuit 20. The abnormality determination unit 16 receives the speed signals (d, e, f) output from the second detector 12 and determines whether or not each signal is abnormal due to a failure of the first detector 12 or the like. The signal determined to be abnormal is excluded from candidates that the signal complementing unit 22 selects as the backup signal to the first overspeed prevention unit 13.

  Further, the backup signal can be supplemented from the first overspeed prevention unit 13 via the signal complementing unit 22 for the signal determined to be abnormal. Therefore, the first overspeed prevention unit 13 and the second overspeed prevention unit 14 can mutually complement the speed signal. Thus, the abnormality determination unit 16 outputs a normal speed signal (d1, e1, f1) that does not include an abnormal signal to the second speed control circuit 18 and the second overspeed prevention circuit 20.

  When the speed signals (a, b, c) output from all the first detectors 11 are determined to be abnormal, the switching unit 23 is controlled by the first overspeed prevention unit 13 through the second overspeed prevention unit 14. Switch to control.

  In this case, the second speed control circuit 18 performs the rotational speed control of the turbine based on the speed signal (d1, e1, f1) output from the abnormality determination unit 16. The second overspeed prevention circuit 20 outputs a trip signal s for causing a turbine trip when the speed signal (d1, e1, f1) exceeds a predetermined speed.

  FIG. 2 is a configuration diagram illustrating an outline of the abnormality determination unit 15 applied to the first overspeed prevention unit 13. Although the detector 11 and the like are omitted for explanation, the configuration is the same as that in FIG.

The abnormality determination unit 15 includes an A contact 25 and a B contact 26 corresponding to each speed signal (a, b, c), and an abnormality determination circuit 24.
The A contact 25 operates so as to close when the abnormality determination signal t is not input from the abnormality determination circuit 24 and open when the abnormality determination signal t is input. On the other hand, the B contact 26 is open when the abnormality determination signal t is not input from the abnormality determination circuit 24 and operates so as to close when the abnormality determination signal t is input.

  When the abnormality determination signal t is not input, that is, when the speed signals (a, b, c) are normal, the A contacts 25 corresponding to the respective signals are closed. Therefore, these signals are output as normal speed signals (a1, b1, c1). However, when any of the speed signals (a, b, c) becomes abnormal and the abnormality determination signal t is output from the abnormality determination circuit 24, the A contact 25 of the signal determined to be abnormal is opened, and the B contact 26 is close up. Thereby, the speed signal determined to be abnormal is blocked by opening the A contact 25.

  At this time, the signal complementing unit 22 selects one of the normal speed signals (d, e, f) from the second overspeed preventing unit 14 in order to complement the backup signal. Then, the selected signal is complemented through the closed B contact 26.

  For example, when the speed signal a becomes abnormal, the speed signal a is interrupted by opening the A contact 25. At this time, the signal complementing unit 22 selects the speed signal d from the normal speed signals (d, e, f) of the second overspeed preventing unit 14. Then, the selected speed signal d is complemented as a normal speed signal a1 through the closed B contact 26.

  The abnormality determination unit 16 (FIG. 1) has the same configuration as the abnormality determination unit 15. When any of the speed signals (d, e, f) becomes abnormal, the abnormality determination unit 16 transmits the speed signal (a, b, c) of the first overspeed prevention unit 13 via the signal complementing unit 22. Can be supplemented as a backup signal.

  The abnormality determination circuit 24 receives the speed signals (a1, b1, c1), and performs abnormality determination based on the upper / lower limit deviation, the large change rate, and the large intermediate value deviation for each signal.

  The abnormality determination based on the deviation from the upper and lower limits means that a predetermined upper limit value and lower limit value are set, and that the abnormality is determined when the speed signal (a1, b1, c1) is not within the upper and lower limit ranges. The abnormality determination based on the large change rate means that the speed change rate is calculated for the speed signal (a1, b1, c1), and it is determined as abnormal when the calculated value is larger than a predetermined value. The abnormality determination based on the large intermediate value deviation is a difference between the intermediate value of the three speed signals (a1, b1, c1) and one of the speed signals (a1, b1, c1), and the obtained value is a predetermined value. When it is larger, it means that it is judged as abnormal.

  The abnormality determination circuit 24 does not directly input the speed signal (a, b, c) generated by the first detector 11 but inputs the speed signal (a1, b1, c1) via the A contact 25 and the B contact 26. To do. Therefore, when two signals out of the speed signals (a, b, c) become abnormal, the abnormality determination circuit 24 performs an abnormality after complementing normal signals from the second overspeed prevention unit 14 for the two signals. Can be judged. As a result, at least two normal signals among the three signals are required for the abnormality determination, but even if two of the speed signals (a, b, c) are abnormal, the remaining one abnormality is detected. It becomes possible to judge.

  FIG. 3 shows a configuration diagram of the abnormality determination circuit 24. The abnormality determination of the speed signal a1 will be specifically described as an example. The differentiator 28 receives the speed signal a 1, calculates the rate of change of the speed signal a 1, and outputs the value to the upper limit setter 29. The upper limit setter 29 determines whether the input signal is within a predetermined upper limit value. If the upper limit value is exceeded, an establishment signal is output to the OR operator 33.

  The upper / lower limit setter 30 receives the speed signal a1 and determines whether the speed signal is within a predetermined upper limit and lower limit range. When it is not within the range, an establishment signal is output to the OR operator 33.

  The intermediate value selector 27 receives the speed signals a 1, b 1 and c 1, selects an intermediate value of these signals, and outputs it to the difference circuit 31. The difference circuit inputs a difference signal between the intermediate value and the speed signal a1 to the upper limit setter 32. The upper limit setter 32 determines whether or not the input difference signal is within a predetermined upper limit value. If the upper limit value is exceeded, an establishment signal is output to the OR operator 33.

  The OR operator 33 outputs the establishment signal to the OR operator 34 when the establishment signal is input from any one of the upper limit setting devices 29 and 32 or the upper and lower limit setting device 30. The OR operator 34 outputs the establishment signal when the establishment signal is input from either the signal output from the OR operator 33 or the signal output from the OR operator 34 itself.

  When the establishment signal is output from the OR operator 34, the speed signal a1 is determined to be an abnormal signal. Similarly, abnormality determination is also performed on the speed signals b1 and c1.

  Next, a procedure for selecting a speed signal (d, e, f) to be complemented as a backup signal in the signal complementing unit 22 when any of the speed signals (a, b, c) is determined to be abnormal will be described.

  FIG. 4 is a flowchart showing a complementing procedure by the signal complementing unit 22 when any of the speed signals (a, b, c) becomes abnormal. Here, a case where the speed signal d is complemented will be described. The abnormal speed signal (d, e, f) is excluded from the selection candidates.

  First, the speed signal d is selected (S10), and it is determined whether the first overspeed prevention unit 13 (FIG. 1) has already been supplemented as a backup signal. If the speed signal d is selected, the process ends (S11, Yes).

Next, consider the case where the speed signal d is not selected. (S11, No).
When the speed signal e is not selected as a backup signal (S12, No) and the speed signal f is not selected (S13, No), when the speed signal d is an intermediate value of the three signals (S14, Yes) ), The speed signal d is selected as a backup signal (S15).
If it is not an intermediate value, the process ends (S14, No).

When the speed signal e is not selected as the backup signal (S12, No) and the speed signal f is selected (S13, Yes), when the speed signal d is the maximum value (S17, Yes), the speed The signal d is selected as a backup signal (S15).
If it is not the maximum value, the process is terminated (S17, No).

When the speed signal e is selected as the backup signal (S12, Yes) and the speed signal f is not selected (S16, No), when the speed signal d is the maximum value (S17, Yes), the speed signal d is selected as a backup signal (S15).
If it is not the maximum value, the process is terminated (S17, No).
When the speed signal e is selected (S12, Yes) and the speed signal f is selected (S16, Yes), the speed signal d is selected as a backup signal (S15).

  A similar selection procedure is executed for the speed signals e and f to determine a backup signal. Therefore, the speed signal (d, e, f) is selected in the priority order of the intermediate value, the high value, and the low value.

  Here, the selection method when the speed signal of the second detector 12 is three is illustrated. Consider a case where the number of measurement points of the second detector 12 is N. In this case, when the speed signals of (2N−1) (N ≧ 2) units are normal, the intermediate value, the value one higher than the intermediate value, the value one lower than the intermediate value, -Select the value in the order of (N-1) values above the intermediate value and (N-1) values below.

  On the other hand, when the speed signals of the (2N) (N ≧ 2) second detectors 12 are normal, the (N + 1) th value from the low value, the (N) th value from the low value, and the low value ( N + 2) th value,..., Low value to (2N) th value, low value to first value.

  That is, the speed signal of the second detector 12 is selected in the order of the intermediate value and then the value gradually moving away from the intermediate value.

  Therefore, even when the speed signal (a, b, c) of the first overspeed prevention unit 13 becomes abnormal, the speed signal (d, e, f) of the second overspeed prevention unit 14 is complemented as a backup signal. Therefore, it is possible to always maintain the triple measurement point.

  FIG. 5 shows a configuration diagram of the first speed control circuit 17 and the second speed control circuit 18. Although only the first speed control circuit 17 and the second speed control circuit 18 are shown, the overall configuration is the same as that in FIG.

  The first speed control circuit 17 receives normal speed signals (a1, b1, c1) output from the abnormality determination unit 15 (FIG. 1). These signals are input to the intermediate value selector 35, and an intermediate value is selected from the three speed signals.

  Then, the intermediate value selector 35 outputs the selected intermediate value to the control setter 36. The control setter 36 compares the input intermediate value with a predetermined set speed and outputs the difference as a difference signal to the speed controller 37. The speed controller 37 controls the rotational speed of the turbine based on this difference signal.

  The second speed control circuit 18 has the same configuration as the first speed control circuit 17 and controls the rotational speed of the turbine based on the normal speed signal (d1, e1, f1) output from the abnormality determination unit 16. be able to.

  The first speed control circuit 17 and the second speed control circuit 18 are connected via the A contact 38, the B contact 39, and the switching unit 23. The switching unit 23 includes an AND operator 40. The AND operator 40 outputs a switching signal u when all of the speed signals (a, b, c) are determined to be abnormal signals by the abnormality determining unit 15.

  The A contact 38 installed in the first speed control circuit 17 operates so as to be closed when the switching signal u is not inputted and to be opened when the switching signal u is inputted. On the other hand, the B contact 39 installed in the second speed control circuit 18 operates to open when the switching signal u is not input and to close when the switching signal u is input.

  Therefore, when the switching signal u is not output from the switching unit 23, the first contact speed control circuit 17 performs speed control because the A contact 38 is closed. On the other hand, when the switching signal u is output, the second speed control circuit 18 performs speed control because the B contact 39 is closed.

  Thus, the first speed control circuit 17 is used for normal speed control. When all of the speed signals (a, b, c) become abnormal signals, the second speed control circuit 18 performs speed control as a backup. It can be performed.

  FIG. 6 shows a configuration diagram of the first overspeed prevention circuit 19 and the second overspeed prevention circuit 20. The overall configuration is the same as in FIG. Although only the first overspeed prevention circuit 19 and the second overspeed prevention circuit 20 are described, the overall configuration is the same as that in FIG.

  The first overspeed prevention circuit 19 receives normal speed signals (a1, b1, c1) output from the abnormality determination unit 15 (FIG. 1). These signals are input to the upper limit setter 41, respectively. The upper limit setter 41 determines whether the input signal is within a predetermined upper limit value. When the upper limit value is exceeded, an establishment signal is output.

  The 2/3 monitor 42 outputs an establishment signal when two signals are established among the three input signals. Therefore, the 2/3 monitor 42 outputs an establishment signal when two establishment signals are output from the three upper limit setting devices 41. This establishment signal is output as a trip signal s.

  The second overspeed prevention circuit 20 has the same configuration as the first overspeed prevention circuit 19 and trips based on the normal speed signals (d1, e1, f1) output from the abnormality determination unit 16 (FIG. 1). The signal s can be output.

  The first overspeed prevention circuit 19 and the second overspeed prevention circuit 20 are connected via the A contact 38, the B contact 39, and the switching unit 23. The A contact 38, the B contact 39, and the switching unit 23 are the same as those in FIG.

  Therefore, when the switching signal u is not output from the switching unit 23, the first overspeed prevention circuit 19 outputs the trip signal s because the A contact 38 is closed. On the other hand, when the switching signal u is output, since the B contact 39 is closed, the second overspeed prevention circuit 20 outputs the trip signal s.

  As a result, the first overspeed prevention circuit 19 is used for normal overspeed prevention. When all of the speed signals (a, b, c) are abnormal signals, the second overspeed prevention circuit 20 Speed prevention can be performed.

  The second overspeed prevention circuit 20 includes a backup overspeed prevention circuit 46. The backup overspeed prevention circuit 46 has an upper limit setter 47 whose set value is larger than that of the upper limit setter 41 and can independently output the trip signal s separately from the operation of the first overspeed prevention circuit 19.

  FIG. 7 shows the configuration of the first overspeed prevention circuit 19 and the second overspeed prevention circuit 20 when a large number of speeds become abnormal. The 2/3 monitor 42 of the first overspeed prevention circuit 19 outputs an establishment signal when two of the speed signals (a, b, c) become abnormal. On the other hand, the 2/3 monitor 43 of the second overspeed prevention circuit 20 outputs an establishment signal when two of the speed signals (d, e, f) become abnormal.

  The AND operator 44 outputs a trip signal s when the signals output from the 2/3 monitors 42 and 43 are both established signals.

  Accordingly, when two of the speed signals (a, b, c) of the first detector 11 become abnormal and two of the speed signals (d, e, f) of the second detector 12 become abnormal. Cannot maintain triple measurement points. At this time, the turbine can be forcibly tripped by outputting the trip signal s.

FIG. 8 shows a modification of the configuration of the first overspeed prevention circuit 19 and the second overspeed prevention circuit 20 shown in FIG.
The AND operator 44 provided in the first overspeed prevention circuit 19 takes a logical product of the output signal of the 2/3 monitor 42 and the output signal of the 2/3 monitor 43. If any of the output signals is a success signal, a trip signal s is output.

  Thereby, since 6 measurement points can be realized, the operation continuity of the system 10 can be improved.

FIG. 9 shows a modification of the configuration of the first overspeed prevention circuit 19 and the second overspeed prevention circuit 20 shown in FIG.
The OR operator 45 provided in the first overspeed prevention circuit 19 takes the logical sum of the output signal of the 2/3 monitor 42 and the output signal of the 2/3 monitor 43. When any output signal is the establishment signal, a trip signal s is output.

  Thereby, since 6 measurement points can be realized, it is possible to operate the system 10 to improve the overspeed detectability.

  According to the overspeed prevention system described above, at least three second detectors 12 having different measurement points from the first detector 11 are multiplexed, and the speed signals (a, b, c) of the first detector 11 are multiplexed. Becomes abnormal, it is supplemented by the speed signal (d, e, f) of the second detector 12 to always maintain the triple measurement point, thereby providing a reliable overspeed prevention system. It can be configured.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 Turbine overspeed prevention system 11 (11A, 11B, 11C) First detector 12 (12A, 12B, 12C) Second detector 13 First overspeed prevention unit 14 Second overspeed prevention unit 15, 16 Abnormality determination unit 17 1st speed control circuit 18 2nd speed control circuit 19 1st overspeed prevention circuit 20 2nd overspeed prevention circuit 21 Zero speed detection interlock 22 Signal complement part 23 Switching part 24 Abnormality determination circuit 25, 38 A contact 26, 39 B contact point 27, 35 Intermediate value selector 28 Differentiator 29, 32, 41, 47 Upper limit setter 30 Upper / lower limit setter 31 Difference circuit 33, 34, 45 OR operator 36 Control setter 37 Speed controller 40, 44 AND operator 42, 43 2/3 monitor 46 Backup overspeed prevention circuit a, b, c, d, e, f, a1, b1, c1, d1, e1, f1 Speed signal s Trip signal t Abnormality determination signal u Switching signal

Claims (7)

A first overspeed prevention unit that controls the rotational speed of the steam turbine based on a speed signal output by at least three first detectors that detect the rotational speed of the steam turbine;
A second overspeed prevention unit for inputting a speed signal output by at least three second detectors having different measurement points from the first detector;
An abnormality determining unit that determines whether or not the speed signal output by the first detector is abnormal;
A signal complement unit that selects the speed signal output from the second detector instead of the speed signal output from the first detector determined to be abnormal, and controls the rotational speed;
A turbine overspeed prevention system comprising: The turbine overspeed prevention system according to claim 1,
The signal complementing unit is a value that gradually moves away from the intermediate value and then the intermediate value among the values of the second detector when the velocity signals output by the plurality of first detectors are determined to be abnormal. The turbine overspeed prevention system, wherein the speed signal output by the second detector is selected in the following order. The turbine overspeed prevention system according to claim 1 or 2,
The turbine overspeed prevention system, wherein the abnormality determination unit determines whether or not the speed signal output from the first detector is abnormal based on a large intermediate value deviation, an upper / lower limit deviation, and a large change rate. . In the turbine overspeed prevention system according to any one of claims 1 to 3,
A switching unit that switches from the first overspeed prevention unit to the rotation speed control by the second overspeed prevention unit when the speed signals output by all the first detectors are determined to be abnormal. A turbine overspeed prevention system comprising: In the turbine overspeed prevention system according to any one of claims 1 to 4,
The first detector comprises an active type of the detector, and the second detector comprises a passive type of the detector. In the turbine overspeed prevention system according to any one of claims 1 to 5,
A turbine overspeed prevention system, wherein the speed signal output from the first detector and the speed signal output from the second detector are logically ANDed. Controlling the rotational speed of the steam turbine based on a speed signal output by at least three first detectors for detecting the speed of the steam turbine;
Inputting a speed signal output by at least three second detectors having different measurement points from the first detector;
Determining whether the speed signal output by the first detector is abnormal;
Selecting the speed signal output from the second detector instead of the speed signal output from the first detector determined to be abnormal, and controlling the rotational speed;
A turbine overspeed prevention method comprising:

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