JPS6154921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the protection of steam turbines, and particularly to a method and apparatus for limiting exhaust pressure load on a turbine when exhaust pressure rises above a set pressure.

In a condensing turbine, the exhaust pressure may rise compared to the originally expected pressure due to changes in the amount of cooling water to the condenser and the water temperature. In this case, when the exhaust pressure rises, the exhaust temperature also rises, and the low-pressure casing There is a risk that it will affect. Therefore, in order to prevent the exhaust pressure from increasing further and tripping the turbine, an exhaust pressure load limiting device is often provided as a turbine protection device for operating the turbine with a reduced load. This is intended to reduce the turbine exhaust heat load by lowering the load when the turbine exhaust pressure increases, thereby recovering (lowering) the exhaust pressure.

The mechanism of a conventionally used exhaust pressure load limiting device is shown in FIG. In reality, these mechanisms will not function adequately unless they are equipped with a width increasing mechanism or a restoring mechanism, but only the necessary parts are shown for ease of understanding.

In FIG. 1, main steam 4 from a boiler flows into a turbine 1 from a steam control valve 2 via a main steam stop valve (not shown), performs work in the turbine, and then is discharged to a condenser 3.

Here, the pressure inside the condenser 3 may rise from the initially set pressure due to changes in the temperature or amount of cooling water, etc., and the exhaust pressure load limiting device 5 detects this and limits the turbine load. It is provided. Inside the exhaust pressure load limiting device 5 is a bellows-type pressure detection section (hereinafter abbreviated as bellows) 6, which is connected to the condenser 3 through a pipe 9.

When the pressure in the condenser 3 increases, the bellows 6 expands, pushing up a rod 8 connected to its upper part, which in turn pushes up the lever 10.

The lever 10 is pivotally supported at one end 11, and the other end 12 is pushed up around this end 11. This pushes up the end 16 of the link mechanism 15, and the link mechanism 15 is moved via the fulcrum 18. The structure is such that the steam control valve 2 is operated in the closing direction.

The normal operation of the steam control valve 2 is controlled by the command 1 of the control device.
9 is received in the middle of the link mechanism 15.

One feature of the device shown in FIG. 1 is that when the exhaust pressure increases and then decreases, the steam control valve 2 is not operated in the opening direction.

In the mechanism that operates the steam control valve 2 in conjunction with the exhaust pressure, the steam control valve 2 is activated due to the increase in exhaust pressure.
is operated in the closing direction, and if the turbine exhaust heat load decreases, the exhaust pressure recovers and decreases.
The steam control valve 2 will be operated in the opening direction. Since the turbine exhaust heat load will increase this time, the exhaust pressure will rise again and the steam control valve 2 may be operated in the closing direction. Repeat this operation,
In other words, a hunting phenomenon occurs. As a mechanism for this purpose, an example is used between the lever 10 and the link mechanism 15 as shown in FIG. be able to. When the exhaust pressure decreases and the bellows 6 is compressed by the spring 7, the rod 8 and lever 10
is lowered by the spring 14, and the female and male parts 13, 17
The bonding relationship between the two is becoming severed.

Also, the steam control valve 2 is controlled by the command 19 of the control device.
is already in the closing direction, the link mechanism 15 is at the 15' position shown by the two-dot chain line, and the male at the end 16 of the link mechanism 15 is already in the position 15', which is indicated by the two-dot chain line. Since the shaped portion 17 is located above, even if the exhaust pressure increases to some extent and the lever 10 is pushed up, the link mechanism 15 will not be affected at all, and the load will be limited only when the exhaust pressure increases further.

An example of this relationship is shown in FIG. As the load on the turbine decreases, restrictions on exhaust pressure become more relaxed. However, the numerical values in this figure are merely reference numerical values used to facilitate understanding.

On the other hand, in response to the recent trend toward larger capacity turbines, longer and longer final stage blades have been developed and are being used. This gives rise to the following problem.

Figure 3 shows the flow of steam at the tip of the final stage blade. That is, the steam flow V ₁ injected from the nozzle blade 20 becomes a flow V ₂ that flows into the blade blade 21 at an angle B in relation to the rotational speed W of the blade blade 21 . The speed triangle on the left side of FIG. 3 indicates the operating condition at high load or low exhaust pressure and is marked with the symbol H. The speed triangle on the right shows the operating condition at low load or high exhaust pressure and is marked with the symbol L.

Since the rotation speed W of the blade wing 21 is constant and the angle A is also determined by the exit angle of the nozzle 20, A _H and A _L are approximately the same value.

As is clear from the comparison between the two, under high load or low exhaust pressure operating conditions, the absolute steam velocity V _1H is high and the relative streamline V _2H takes a direction angle B _H that provides rotational force to the blade wing 21. When the load is low or the exhaust pressure is high, the absolute speed V _1L becomes low, so that the relative speed V _2L takes an angle B _L that causes streamline separation at the inlet of the blade wing 21.

The phenomenon of separation of the streamlines generates steam turbulence 22 on the back surface of the blade 21, and vibrations mainly caused by torsion occur at the tip of the blade 21. This phenomenon is called wing fluttering, and if left untreated, it will cause an infinite number of repeated vibrations in a short period of time, leading to wing destruction.

This fluttering phenomenon occurs because the longer the blade length, the faster the rotational speed W, and the relative steam speed V ₂
This is a noticeable tendency because the blades tend to change easily and the blades tend to twist. Therefore, especially in a turbine using long blades in the final stage, the blades 21 may be operated in an unfavorable state at the exhaust pressure limit value operated by the conventional exhaust pressure limiting device.

According to the example shown in Figure 2, the limit is 100mmHgabs. at 100% load, and 150mmHgabs. at minimum load.
It is possible to drive under the worst conditions.

In order to deal with such a situation, the purpose of the present invention is to set the limit value of the exhaust pressure of the turbine to allow operation to a high exhaust pressure when the load is high, and to limit the operation to a low exhaust pressure when the load is low, thereby preventing the blade from fluttering. It is an object of the present invention to provide a new turbine exhaust pressure load limiting method and device as a turbine protection technology to prevent the above.

The first feature of the present invention resides in that during low load operation, the exhaust pressure load limiting device is switched to a configuration in which it operates at a lower exhaust pressure than during high load operation, and this configuration causes the blade fluttering phenomenon. This method provides a method for limiting the turbine exhaust pressure load so that the turbine exhaust pressure does not increase.

The second feature of the present invention is that the exhaust pressure load limiting device is switched to a mode in which it senses and operates high exhaust pressure during high load operation of the turbine, and a mode in which it senses and operates low exhaust pressure during low load operation. This configuration provides a turbine exhaust pressure load limiting device that can reliably implement the method described above.

The present invention will be explained below based on the drawings.

One embodiment of the invention is shown in FIG. In the embodiment shown in FIG. 4 as well, like the prior art shown in FIG. 1 described above, the functions of the interlocking members are shown as mechanical link mechanisms for ease of understanding.

The embodiment shown in FIG. 4 includes an exhaust pressure load limiting device 5, a lever 10, and a link mechanism 1.
5. It has a connection 31 that connects the valve stem 29 of the steam control valve 2 and the exhaust pressure load limiting device 5.

The exhaust pressure load limiting device 5 has a bellows 6, a spring 7, and a rod 8 provided on the bellows 6. A condenser 3 is connected to the bellows 6 through a pipe 9.
Some of the pressure has been introduced. Further, the exhaust pressure load limiting device 5 has a turbine 1 installed in a fixed case 30.
The end of the rod 8 is housed so that it can move between a setting position where it is away from the lever 10 and a setting position where it approaches the lever 10 during high load operation and during low load operation.

The lever 10 is arranged so as to be able to rotate about one end 11, and has a female part 13 at the other end 12, so that when the bellows 6 is expanded,
The other end 12 side is lifted up by the rod 8 and returned by the spring 14 when the bellows 6 contracts.

The link mechanism 15 has a male part 17 formed at one end 16, and is linked to the other end 12 of the lever 10 through engagement between the male part 17 and the female part 13. The end is hinged to the valve stem 29 of the steam control valve 2. When the other end 12 side of the lever 10 is pushed up, this link mechanism 15 connects the female and male parts 13 and 17 to the one end 12 side.
When the valve 6 is pushed up, it rotates at the fulcrum 18 and acts in a direction to push down the steam control valve 2 through the valve stem 29.

The connection 31 has one end connected to the valve stem 29 of the steam control valve 2, and the other end connected to an arm 33 attached to the exhaust pressure load limiting device 5, and rotates about a fulcrum 32. It is set up so that it can be easily accessed. The connection 31 is interlocked with the valve stem 29 during low load operation of the turbine 1 when the valve stem 29 of the steam control valve 2 is operated downward by the operation command 19, and rotates clockwise in FIG. 4 about the fulcrum 32. , the exhaust pressure limiting device 5 is pushed up in the direction in which the rod 8 approaches the lever 10 and set at the setting position for low load operation, and the valve stem 29 of the steam control valve 2 is operated upward in the opposite direction according to the operation command 19. When the turbine 1 is operated under high load, it rotates counterclockwise in FIG. 4, and the rod 8 is configured to push down the exhaust pressure limiting device 5 in the direction away from the lever 10 and set it at the set position during high load operation. has been done.

In the device having the above configuration, during high-load operation, the exhaust pressure load limiting device 5 is set to a lower position than the position shown in FIG.
Detects the pressure inside.

During this high-load operation, when the pressure inside the condenser 3 rises above the set pressure, the bellows 6 of the exhaust pressure load limiting device 5 expands, the rod 8 is operated upward, and the lever 10 is moved to the one end 11. The link mechanism 15 is rotated by the other end 12 in the clockwise direction in FIG. The opening degree of
The flow rate of main steam 4 flowing to turbine 1 is throttled, and the turbine load is lowered.

Once the link mechanism 15 is rotated in the clockwise direction described above and the opening degree of the steam control valve 2 is reduced, the bellows 6 of the exhaust pressure load limiting device 5 is contracted, the rod 8 is operated downward, and the lever is opened. 10 is returned by the spring 14, the female part 13 of the lever 10
The link mechanism 15 is only disengaged from the male portion 17 of the link mechanism 15, and the link mechanism 15 does not return.

When the pressure of the condenser 3 further increases, the valve stem 29 of the steam control valve 2 is pushed up by the same operation as described above, the opening degree of the steam control valve 2 is further reduced, and the turbine load is further reduced. It will be done.

When the operation of the turbine 1 has returned to normal and the detected pressure in the condenser 3 has become normal, the valve rod 29 is operated upward by the operation command 19, and the link mechanism 15 is returned to its normal position.

Next, when the turbine 1 is operating at a low load, the valve rod 29 is pushed down by the operation command 19. Following this lowering operation of the valve stem 29, the connection 31 is rotated clockwise in FIG.
is set at the setting position for low load operation, as shown in FIG.

As a result, the rod 8 of the exhaust pressure load limiting device 5
occupies a position close to the lever 10, so that even if the bellows 6 expands slightly, the lever 10 and the link mechanism 15 will be interlocked, and the pressure in the condenser 3 during the low load operation will be reduced. Sensitively detects
In the event of an abnormality, the valve rod 29 of the steam control valve 2 can be reliably pushed down to reduce the turbine load.

Further, the method of the present invention is characterized in that the exhaust pressure load limiting device 5, which had a fixed operating position in the prior art, is switched to a mode in which it operates at a lower exhaust pressure during low load operation of the turbine 1 than during high pressure load operation. It is said that

That is, in the embodiment shown in FIG. 4, the exhaust pressure load limiting device 5 is located in a fixed case 30 and can be moved up and down, and the position of the steam control valve 2 is detected by the connection 31. However, the position of the exhaust pressure load limiting device 5 can be determined. Therefore, when the steam control valve 2 operates downward to reduce the load, the connection 31 rotates about the fulcrum 32 and pushes the position of the exhaust pressure load limiting device 5 upward. As a result, the rod 8 position will also be located upwards, and even if the exhaust pressure increases slightly, the lever 10 will be pushed up, so the linkage mechanism 15 can be operated and the Driving will be restricted.

According to the present invention, the exhaust pressure limit value for the turbine load can be set to a lower exhaust pressure limit value as the load becomes lower, as in the example shown in FIG. The numerical values in Fig. 5 are merely reference values for ease of understanding, but in the case of the minimum load, 75mm
Since the operation is limited to the exhaust pressure of Hgabs., low exhaust pressure is maintained even under low load, and the third
Corresponding to the left diagram of the figure, a relative streamline V _2H can be formed, and the blade wing 21 can be protected from operation that causes a fluttering phenomenon.

In the above explanation, when the load is lowered, there is a concern that pushing the exhaust pressure load limiting device 5 upward will further lower the load, and the load will be lowered one after another, causing the steam control valve 2 to operate to the fully closed position. However, as mentioned earlier, this is because the restoring mechanism and width increasing mechanism necessary for the actual mechanism are omitted from the illustration, and if the amount of movement of the exhaust pressure load limiting device 5 is set to an appropriate value for the load. , even if the exhaust pressure does not rise, the steam control valve 2 will not be sequentially closed and the operation will be delayed.

Also, during high load operation, the exhaust pressure reaches the limit value,
When the operation command 19 is issued to lower the load, the limit value of exhaust pressure becomes stricter as the load decreases, so the load must be gradually restricted to lower values, and finally the steam control valve 2 is set to the fully closed position. However, the purpose of the exhaust pressure load limiting device is to reduce the turbine exhaust heat load while lowering the load and wait for the exhaust pressure to recover. For example, the bellows 6 is no longer pushed down by the spring 7, so the rod 8
The lever 10 is also lowered, the relationship with the link mechanism 15 is released, and no further command to reduce the load is issued.

However, if the exhaust pressure does not recover or drop sufficiently even while the load is being lowered, the load will be lowered one after another and the steam control valve 2 will finally be fully closed, but this is in accordance with the present invention. As a turbine protection technique, the blade blade 21 can be protected from operation that may cause a fluttering phenomenon.

Furthermore, if the limiting pressure is set in a stepwise manner as shown by the broken line in FIG. 5, it is possible to prevent the load from decreasing like an avalanche.

FIG. 6 shows another embodiment of the invention.

The device shown in this embodiment includes a first pressure transmitter 4 connected to a condenser 3 via a pipe 9.
0, the second stage connected to 41 after the first stage of turbine 1
a pressure transmitter 42, a first operator 43 coupled to the second pressure transmitter 42, a first
an adder 44 connected to the pressure transmitter 40 and the first operator 43, a second operator 45 connected to the adder 44, a low position priority circuit 47 connected thereto, and a steam control valve 2. It has an operating section 48.

41 after the first stage of turbine 1 as turbine load
The pressure is detected and transmitted to the pressure transmitter 42.
It is set as an electrical value and sent to the first operator 43, and the first operator 43 determines the limit value of the exhaust pressure at that turbine load.

On the other hand, the pressure of the condenser 3 is also transferred to the pressure transmitter 40.
is replaced with an electrical value by , and sent to the adder 44 , and the adder 44 communicates the difference from the limit pressure value to the second operator 45 .

It is assumed that the second operator 45 issues the steam control valve closing signal 46 only when the condenser pressure is higher than the limit pressure, that is, only when the electric signal e becomes positive.

The low value priority circuit 47 is required to comply with the steam control valve closing signal 46 and the operation command 49 of the main control mechanism, and is provided to select the most severe condition and operate the operating section 48 of the steam control valve 2. ing.

In the above explanation, the pressure after the first stage of the turbine, which is generally employed, is detected and applied to the turbine load detection, but according to the gist of the present invention, the pressure before the final stage can be used. It is most desirable to measure. In addition, it goes without saying that it is also possible to detect the position of the steam control valve stem as described in connection with the mechanical linkage mechanism, or to directly detect the power generation end output and use it as a load for the turbine.

In the embodiment, the first and second pressure transmitters 40, 42, the first operator 43, the adder 44, and the second operator 45 constitute an exhaust pressure load limiting device. The exhaust pressure load limiting device has a function of sensing and operating a lower exhaust pressure during low load operation than during high load operation via the low value priority circuit 47.

Therefore, the method of the present invention can also be carried out using the apparatus of this embodiment as explained below.

FIG. 7 shows an example of the operating state of the turbine according to the embodiment shown in FIG. 6. The horizontal axis shows time t, and the vertical axis shows the limit pressure set value, turbine exhaust pressure, electric signal magnitude, and turbine load, respectively.

Now, assume that stable operation continued until T ₁ , but at this point the condenser pressure began to rise due to some reason, and at T ₂ the exhaust pressure finally exceeded the limit pressure. At this point, the electric signal e becomes positive, and the steam control valve 2 is closed to reduce the turbine load. As a result, the condenser pressure decreases, and by falling below the limit pressure until T ₃ , the electrical signal e becomes negative, and there is no longer a need to lower the turbine load, allowing stable operation at the load at T ₃ . can continue. Since the exhaust pressure relative to the turbine load has returned to a normal value by the time T ₄ , the operation command 49 returns to high-load operation from T ₅ . After stable operation continued from T ₆ to T ₇ , operation command 49 issued a command to lower the turbine load and the load started to be lowered, but the condenser pressure did not drop enough and the limit was reached at T ₈ . I exceeded the value. Here, the electric signal e becomes a positive value,
A command is issued to further reduce the load. By further reducing the load, the condenser pressure was sufficiently reduced by _T9 , so the electric signal e became negative, indicating that stable low-load operation continued after _T9 .

As is clear from Fig. 7, when the exhaust pressure exceeds the limit value, the steam control valve closes. It is set with .

The present invention has the structure and operation described above, and according to the method of the present invention, it is possible to avoid operation in a state where a severe blade fluttering phenomenon occurs on long blades, increase the reliability of the turbine, and improve the safety device. It has the effect of being able to fully fulfill its functions.

Furthermore, the apparatus of the present invention has the advantage of being able to reliably carry out the method described above.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the prior art, Fig. 2 is a diagram showing an example of the turbine load and limiting pressure obtained by the conventional technology, and Fig. 3 is a diagram showing a velocity triangle near the top of the turbine final stage blade. Fig. 4 is a system diagram showing one embodiment of the present invention, Fig. 5 is a diagram showing an example of turbine load and limiting pressure obtained by the same embodiment, and Fig. 6 is a diagram showing another embodiment of the present invention. The system diagram shown in FIG. 7 is a diagram showing an example of the operation of the turbine according to the same embodiment. DESCRIPTION OF SYMBOLS 1... Turbine, 2... Steam control valve, 3... Condenser, 5... Exhaust pressure load limiting device, 6... Bellows, 8... Rod, 9... Piping, 10... Lever, 15... ...Link mechanism, 19...Movement command, 3
0...Fixed case for exhaust pressure load limiting device, 3
1... Connection, 40, 41... 1st, 2nd
pressure transmitter, 43...first operator,
44...Adder, 45...Second operator, 46...
...Steam control valve close signal, 47...Low value priority circuit, 4
8...Operation unit of steam control valve, 49...Same operation command.

Claims (1)

[Scope of Claims] 1. In an exhaust pressure load limiting method in which when the exhaust pressure of a turbine rises above a set pressure, the steam control valve is operated in the closing direction to reduce the turbine load. pressure load limiting device,
A turbine exhaust pressure load limiting method characterized by switching to a mode in which the exhaust pressure is lower than that during high load operation. 2. When the exhaust pressure of the turbine rises above the set pressure, the exhaust pressure load limiting device operates the steam control valve in the closing direction to reduce the turbine load. 1. An exhaust pressure load limiting device for a turbine, characterized in that the operating mode is provided with switching means for switching the exhaust pressure load limiting device to a mode in which the exhaust pressure load limiting device senses low exhaust pressure during low load operation and operates.