JPS61265310A - Overspeed preventing equipment of steam turbine - Google Patents

Abstract

PURPOSE:To brake a turbine and reduce the overshoot by connecting a steam discharge passage to a preliminary nozzle chamber and opening the preliminary nozzle chamber to an outlet pipe at the same time when load is cut off. CONSTITUTION:A steam discharge passage 25 is connected to the preliminary nozzle chamber 19 of a steam turbine via a steam discharge valve 26. And the valve 26 is opened simultaneously with the load cutting-off time of have the preliminary nozzle chamber open toward the outlet pipe, whereby feeding back steam from a turbine a casing 2 toward the preliminarily nozzle chamber 19 to brake a turbine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overspeed prevention device for a steam turbine that drives a generator, etc., and particularly to an overspeed prevention device for a steam turbine that drives a generator, etc. The present invention relates to an overspeed prevention device for a steam turbine that suppresses the overshoot amount of the turbine rotation speed as much as possible.

[Prior Art] Generally, a steam turbine used in a thermal power plant or the like is constructed as shown in FIGS. 5 and 6.

That is, reference numeral 1 in the figure is a steam turbine in which an impeller 3 is rotatably supported within a turbine chamber 2, and a generator 5 is coaxially attached to a rotating shaft 4 of the impeller 3. A steam supply pipe 8 with a main steam valve 7 interposed in the middle is connected to a steam inlet 6 provided at one end of the steam turbine 1, and the impeller 3 is rotated once by the energy of the supplied high-pressure steam. It has become. Further, an outlet pipe 10 is connected to a steam outlet 9 provided at the other end of the steam turbine 1, and the steam that has finished its work is discharged.

The header part 11 of the steam inlet 6 and its lower part are provided with blades 3i provided around the impeller 3 as shown in FIG.
A plurality of nozzle chambers 12 are formed along the circumferential direction of the nozzle chamber 12, facing the
On the exit side of each nozzle chamber 12, the blade 3a.
A large number of nozzle groups (not shown) that inject steam directly into...
is formed. In addition, at the inlet 13 of each nozzle chamber 12, a plurality of flow rate regulating valves 15 are attached to a support 14 that is movable up and down to adjust the opening degree of each nozzle chamber 12. ... are provided, and the amount of incoming steam is adjusted by moving these multiple valves up and down as a unit.

Each of the flow rate regulating valves 15 is vertically movable relative to the support 14 within a certain predetermined tolerance range.

In the illustrated example, a total of five nozzle chambers 12 . This fifth nozzle chamber 12a
are connected to the relay nozzle chamber 12b formed in the upper part by connecting the respective openings 16 and 17 with a communication pipe 18, and constitute a preliminary nozzle chamber 19 as a whole.

During normal rated operation, this preliminary nozzle chamber 19 is kept in an unused state by blocking the inlet 13a with the flow rate regulating valve 15a on the steam supply side of the relay nozzle chamber 12b, as shown in FIG. Only during so-called overload operation, the flow rate regulating valve 15a of the relay nozzle chamber 12b is raised to open the inlet 13a, and steam is allowed to flow toward the fifth nozzle chamber 12a to be in use.

That is, in the event of an overload, as shown in FIG. 7, the fifth nozzle 11 is
The high pressure steam that has flowed into the nozzle 2a flows through the nozzle 2 as shown by the arrow.
The fuel is injected from zero toward the blades 3a of the impeller 3, flows into the inside of the turbine chamber 2, and contributes to the rotation of the impeller 3 in the forward direction.

In this case, it goes without saying that the first to fourth nozzle chambers 12 are all open and in use.

Incidentally, such a steam turbine is required to maintain a constant rotational speed at all times because it is necessary to keep the output voltage from the generator 5 constant at all times. Therefore, for example, the rotation speed is detected by a detector 21 provided on the rotating shaft 4 of the turbine, this detected value is transmitted to the governor 22, and a command signal from the governor 22 is used to control the flow rate provided in the header section 11 of the steam turbine. By moving the m adjustment valves 15 up and down, the steam flow rate was adjusted so that the turbine rotational speed remained as constant as possible.

[Problem to be solved by the invention 1 By the way, when the output on the power generation 1115 side suddenly decreases, that is, when load shedding occurs, the rotational speed of the turbine tends to increase rapidly in just a few seconds. . In this case, as mentioned above, since the governor 22 is provided to keep the rotation speed constant, the rotation speed will eventually settle to a predetermined predetermined speed, but the turbine will overshoot for a few seconds immediately after the load is cut off. I didn't like it. In particular, the control method using the governor 22 detects the speed of the rotating shaft 4, which causes a large delay in operation. For this purpose, an attempt has been made to provide a load shedding detector 23 in the generator 5 and directly input the detection signal to the governor 22 to eliminate the delay in operation.

However, even if this type of overspeed prevention device is installed,
There was a slight delay before the flow ω adjustment valves 15 were activated, and it was not possible to sufficiently suppress the overshoot, that is, the amount of over-rotation.

In particular, steam turbines with a large rate of increase in rotational speed per unit time (acceleration rate) also have a large overshoot meter, and there is an urgent need for a fundamental solution to this type of problem. .

[Purpose of the Invention J The present invention has been designed to address the above-mentioned problems and effectively solve them.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overspeed prevention device for a steam turbine that is capable of suppressing as much as possible the amount of overshoot of the turbine rotation speed by causing steam to flow backward into a preliminary nozzle during load interruption. .

[Summary of the Invention] The configuration of the present invention that achieves the above object includes connecting a steam release passage for discharging steam from the preliminary nozzle chamber, which is closed during rated operation, and opening this passage. A valve control unit is provided to open the steam release valve when the load is cut off, and by opening the steam release valve when the load is cut off, the steam flows back from the turbine room to the preliminary nozzle room. The main point is that the impeller is braked by applying a brake to the impeller.

[Embodiment] A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

Fig. 1 is a system diagram showing an overspeed prevention device according to the present invention installed in a steam turbine, Fig. 2 is a schematic cross-sectional view taken along the line If-I in Fig. 1, and Fig. 3 is an enlarged view taken in the direction of the arrow in Fig. 2. It is a diagram.

Incidentally, the same reference numerals as those in the conventional example will be used to omit the explanation.

First, as shown in FIGS. 1 and 2, 1 is a steam turbine. An impeller 3 is rotatably supported in a turbine chamber 2 of the steam turbine 1. The rotation shaft 4 of this impeller 3
A generator 5 is attached coaxially to the.

A plurality of divided nozzle chambers 12 are formed in the header part 11 of the steam inlet 6 and its lower part, facing the blades 3a provided around the impeller 3. On the outlet side of each nozzle chamber 12, there is provided the blade 3a.
A large number of nozzle groups (not shown) are formed to directly inject steam into the air. Inlet 13 of each nozzle chamber 12...
・Includes multiple flow rate adjustment valves 15 that are freely movable up and down.
... is provided, and each flow rate adjustment valve 15...
are vertically movable relative to the support 14 within a predetermined tolerance range.

In the illustrated example, a total of five nozzle chambers 12 . This fifth nozzle chamber 12a
is connected to a relay nozzle chamber 12b formed in the upper part via a communication pipe 18, and constitutes a preliminary nozzle chamber 19 as a whole. During normal rated operation, this preliminary nozzle chamber 19 is kept in an unused state by closing the inlet 13a with the fifth flow port regulating valve 15a on the steam supply side of the relay nozzle chamber 12b, as shown in FIG. Only during overload operation, the fifth flow rate regulating valve 15a is raised to open the inlet 13a, thereby bringing it into use. Therefore, this fifth
The allowable stroke of movement of the flow pot regulating valve 15a relative to the support 14 is the largest compared to other valves.

The overspeed prevention device 24 according to the present invention is attached to the steam turbine 1 configured in this manner.

This device 24 includes a steam discharge passage 25 for discharging steam from the preliminary nozzle chamber 19, a steam discharge valve 26 interposed in this passage 25 for opening and closing it, and a steam discharge valve 26 for discharging steam from the preliminary nozzle chamber 19 in response to load cutoff. It is mainly composed of a valve control section 27 that opens the discharge valve 26.

Specifically, the steam release passage 25 has one end 25a
is connected to the communication pipe 18 that communicates the relay nozzle chamber 12b and the fifth nozzle chamber 12a, and the other end 25b is connected to the outlet pipe 10 for discharging steam from the turbine chamber 2. By opening the interposed steam release valve 26, the relay nozzle chamber 12b and the fifth nozzle cavity 12a, that is, the preliminary nozzle chamber 19, are opened to the outlet pipe 10 side, that is, to the atmosphere, so that steam can be discharged. is being done.

In this case, the other end 25b of the steam release passage 25 is connected to the outlet pipe 10, but the present invention is not limited to this, and the steam may be released directly into the atmosphere.

Further, a valve control section 2 that controls the operation of the steam release valve 26 is provided.
7 is configured to receive a signal from the load shedding detector 23, and in response to the input of the load shedding signal, the valve controller 27 immediately directs the valve to the steam release valve 26. The valve is designed to output a valve opening signal.

Next, the operation of the present invention configured as described above will be explained.

During rated or steady operation, high-pressure steam that has flowed into the header section 11 from the steam inlet 6 first flows through the first to fourth channels.
It flows into the nozzle chamber 12, is vigorously injected from each nozzle group into the turbine chamber 2, acts on the blades 3a of the impeller 3, and drives them to rotate at a predetermined speed.

The steam pressure inside each open nozzle chamber 12 is, for example, about 55 atmospheres, and the pressure inside the turbine chamber 2 is about 45 atmospheres.
It's about atmospheric pressure. Therefore, the impeller 3 is rotated by a pressure difference of about 10 atmospheres FM.

The steam injected into the turbine chamber 2 sequentially passes through the blades at the later stages (
(not shown), and finally drops to about 10 atmospheres and flows out from the steam outlet 9 to the outlet pipe 10. Then, constant speed rotation is maintained by the action of the governor 22.

During this steady operation, the inlet 13a of the relay nozzle chamber 12b is closed by the fifth flow rate regulating valve 15H.
High pressure steam of about 55 atmospheres is prevented from flowing into it. Further, the steam release valve 26 provided in the steam release passage 25 is also closed7, so the preliminary nozzle chamber 19 is in an open state and in an unused state. However, even in this state, the fifth nozzle chamber 12a is connected to the turbine chamber 2.
Since it is always open to the copper, the steam in the turbine butt 2 flows into the relay nozzle chamber 12b via this fifth nozzle chamber 12a and the connecting pipe 18, and stagnates therein, almost the same as in the turbine chamber 2. The pressure is about 45 atmospheres.

During such steady operation, if a load cutoff occurs on the generator 5, the load on the steam turbine 1 will suddenly drop or become unloaded, and the rotational speed of the turbine will tend to increase rapidly. However, the effect of this embodiment makes it possible to suppress the amount of overshoot of the turbine as much as possible. That is, when a load shedding occurs, the fact is immediately detected by the load shedding detector 23, and a detection signal is transmitted to the valve control section 27. Upon receiving this detection signal, the valve control section 27 outputs an open signal to the steam release valve 26, thereby fully opening the steam release valve 26. In this case as well, the fifth flow mother regulating valve 15a1 of the relay nozzle chamber 12b. Of course, it is closed.

When the steam release valve 26 is fully opened as described above, approximately 45 atmospheres of steam in the relay nozzle chamber 12b and the fifth nozzle chamber 12a flows out to the outlet pipe 10 via the communication pipe 18 and the steam release passage 25. , is ejected.

That is, the steam in the 'fw nozzle chamber 19 is discharged through the steam discharge passage 25. Then, the pressure inside the fifth nozzle chamber 12a becomes lower than that inside the turbine chamber 2, so that the pressure inside the fifth nozzle chamber 12a, that is, the preliminary nozzle chamber 19, flows from the inside of the turbine chamber 2 to the fifth nozzle 12a, as shown by the solid line arrow in FIGS. 2 and 3. Steam flows backwards towards the This reverse flow of steam acts as a force to reverse the rotation of the impeller 3, which is rotating in the forward direction, so that the turbine is suddenly braked against the increasing rotational speed due to load shedding. This amount of overshoot can be suppressed to a minimum.

In this case, the full opening time of the steam release valve 26 may be about 2 to 3 seconds, and if the impeller 3 is controlled for this amount of time, the governor 22 operating When the predetermined rated rotational speed (represented by the hard line in Figures 2, 3, and 3) is 1°, there is no overload. Show flow 19 during operation, 1:
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Let me explain.

Similar to load shedding, the turbine rotational speed increases rapidly to an overspeed state, that is, to a tendency to overshoot. In addition, the broken line in the figure shows the turbine rotation speed according to the conventional example.

On the other hand, the steam release valve 26 is fully opened about 0.5 seconds later than when the load is cut off, and the flow G adjustment valve 15 is activated slightly later than when the steam release valve 26 is activated. At the same time as the steam release valve 26 is fully opened, the rotational speed of the turbine is rapidly suppressed, reaches a peak, and then decreases. After that, the effect of the flow control valve driven by the governor becomes effective, so the steam release valve is fully opened for about 2 to 3 seconds and then closed again. Then, the rotational speed of the targen will not pulsate around the rated rotational speed, but will gradually be maintained at the roundness rated rotational speed. At the same time as detecting a load cutoff, by opening the inside of the 7th chamber 19, which is used only during overload operation, to the outlet 10 side, the fifth nozzle chamber 12a is opened from the inside of the turbine chamber 2.
Since the steam is caused to flow back inward, braking is applied to the impeller 3, and the amount of overshoot can be reduced as much as possible.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects can be achieved.

(1) By opening the spare nozzle blank to the outlet pipe side at the same time as the load is cut off, steam flows backward from the turbine chamber to the spare nozzle chamber and the turbine is braked, compared to conventional feedback control using a governor. The amount of overshoot can be reduced as much as possible.

(Thus, the safety of turbines, generators, etc. can be improved as much as possible.)

(3) When installing the device according to the present invention, a pre-provided spare nozzle chamber is used, so it can be easily adopted without changing the design of the steam turbine.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing a preferred embodiment of the overspeed prevention device according to the present invention installed in a steam turbine, Fig. 2 is a schematic cross-sectional view taken along the line ■-■ in Fig. Figure 2 is an enlarged view of the arrow in Figure 4, and Figure 4 is the rotation speed. A graph showing changes in the flow rate adjustment valve and steam release valve. Fig. 5 is a system diagram showing a conventional overspeed prevention device installed in a steam turbine. Fig. 6 is a schematic cross-sectional view taken along the line VI-■ in Fig. 5. ,
FIG. 7 is a sectional view taken along the line ■--■ in FIG. In the figure, 2 is a turbine chamber, 3 is an impeller, 19 is a preliminary nozzle chamber, 25 is a steam release passage, 26 is a steam release valve, and 27 is a valve control section. Patent Applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Representative Patent Attorney Nobuaki Kinutani Yutan Yacho Figure 3: Distress and Distress Figure 4 (1) Figure 6

Claims (1)

[Claims] In a steam turbine having a preliminary nozzle chamber, which is opened only during overload operation and injects high-pressure steam introduced into the turbine chamber toward an impeller provided in the turbine chamber, and whose steam supply side is closed during steady operation, the preliminary nozzle chamber is , a steam discharge passage for discharging steam from this is connected, and a steam discharge valve is connected to the passage, and the steam discharge valve is opened to cause steam to flow backward from the turbine chamber into the preliminary nozzle chamber to apply braking to the impeller. 1. An overspeed prevention device for a steam turbine, comprising: a valve control section that opens the steam release valve in response to a load cutoff.