JPS60233302A - Main steam pressure drop prevention device - Google Patents

Abstract

PURPOSE:To prevent a main steam pressure reduction while operating under pressure modulating mode by a control device for a steam turbine pressure modulating plant in which the adjusting valve is throttled upon comparing the main steam signal as well as the load signal with the set values. CONSTITUTION:In a main steam pressure reduction prevention device for a steam turbine pressure modulating plant having an electro-hydraulic governor, the set pressure Ls is determined as a primary function when the set load Ls is normally within the pressure modulating range, and the boiler main steam pressure is controlled in response to the load fluctuation, and the opening of the adjusting valve is maintained constant. The set pressure Ps relative to the set load Ls is determined by a set pressure calculator 22, and a pressure P90 which is 90% of the set pressure Ps and a pressure P80 which is 80% equivalent are determined by a throttle pressure setting unit 23. They are compared with the real pressure P in a comparator 24 while operating. When P<P90, the target load is lowered by a target load setting unit 25 in accordance with the predetermined characteristics, and the adjusting valve is throttled to prevent a main steam pressure reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a main steam pressure drop prevention device in a steam turbine variable pressure plant.

[Background of the invention]

Figure 1 shows the configuration of a standard steam turbine power plant. Main steam from boiler 1 is passed through main steam stop valve 2 (hereinafter referred to as M
(referred to as SV). It passes through a steam control valve 3 (SCV) and flows into a high pressure turbine 4 (hereinafter referred to as HPTb). H
The steam that has done work in the reheater 5 is heated by the reheater 5, and then the reheat steam stop valve 6 (hereinafter referred to as R8U). It passes through an intercept valve 7 (hereinafter referred to as ICV) and flows into an intermediate pressure turbine 8 (hereinafter referred to as ``P''). ■The steam leaving the PTl flows into the Takumi turbine 9 (hereinafter referred to as LPTb). Thereafter, the water is condensed in a condenser 10, and is heated to a low pressure heater 11. Deaerator 12, water pump 13. It is supplied to the boiler through the high pressure heater 14 and the like.

Figure 2 shows the relationship between the main steam pressure and the load of the transformer plant. In transformer plants, loads below Lt and loads I
,? In the following, the main steam pressure is constant for each of Pl and P2. The load is increased or decreased by changing the main steam pressure from L,1 to L2.

Fig. 3 shows the relationship between the load and main steam pressure with respect to the valve opening of the transformer plant. When variable pressure operation is performed from the main steam pressure P to P2, the Cv opening degree remains approximately constant at point X. The CV opening degree at point X takes throttle loss into consideration, and is generally selected near the valve full-opening point where loss is small.

FIG. 4 shows an example of a startup pattern in a voltage transformation plant. At the time of supplying steam to the turbine (during ventilation), the steam pressure is a% of the rated pressure, but b% of the rated load.
After Cv reaches near the full-open point at point Cv, the pressure is naturally increased to reach the rated pressure at point C% of the rated output.

Now, steam turbines are generally equipped with a main steam pressure drop prevention device. This system is designed to prevent main steam pressure from dropping rapidly due to boiler control abnormalities during turbine operation, causing water to flow into the steam turbine or the HPTb final stage to become wet.
Due to excessive thrust force being applied to the steam turbine,
It is installed to prevent abnormalities such as excessive thermal stress, thrust bearing wear/vibration, and static/rotor blade contact, and when the main steam pressure falls to a specified value, it starts to throttle the Cv ( In other words, if the main steam pressure continues to decrease (by reducing the load), it has the function of ultimately reducing Cv to no load on the turbine.

First, among conventional examples, a mechanical-hydraulic governor for a constant pressure steam turbine will be explained as an example. The main steam pressure drop prevention device is provided together with other turbine control devices in a turbine front bearing box in which the turbine control device is built.

The main steam pressure drop prevention device does not operate as long as the main steam pressure from the boiler maintains a normal value, and generally the pressure is approximately 90% below the rated pressure.
When it drops to 0% or less, it starts operating and begins to open the CV. The main steam pressure drop prevention device has a fixed rate of 7 to 13%, and when the main steam pressure reaches 83 to 71% of the rated value, Cv is closed to the no-load opening.

Such a sudden drop in main steam pressure is due to an abnormality occurring on the boiler side, such as water generation within the boiler tube, and at the same time, a drop in main steam temperature also occurs.

As mentioned above, water flowing into the turbine can cause extremely serious accidents for the turbine, such as erosion and thermal stress caused by local cooling. A device is provided to narrow down the results.

In FIG. 5, which shows a mechanical main steam pressure drop prevention device, the main steam pressure change passes through the pressure detector 15 converter 16 and is converted into a change in air pressure and enters the bellows 17. When the main steam pressure decreases, the bellows move downward in the pressure detection section incorporating the spring 18 and the bellows, causing the pilot piston 19 to move downward. Control oil is then supplied to the upper side of the unload piston 20, and the unload piston moves downward. The unload piston is connected to a rotary lever 21 installed in the middle of the rod that leads from the speed relay to the servo motor pilot piston that operates the turbine control valve, so the downward movement of the unload piston causes the servo motor to operate. Operate in the closing direction to narrow down the control valve.

As mentioned above, the normally used main steam pressure drop prevention device operates the unload piston by the balance between the spring and the bellows, so after setting the lever system to operate at the rated main steam pressure, The unload piston will only operate at the same pressure. That is, generally, as shown in FIG. 6, when the main steam pressure decreases to 90% of the rated pressure, Cv starts to be throttled, and when it further decreases to 80%, Cv is closed to a position corresponding to no load on the turbine.

Therefore, in a variable pressure plant that changes the main steam pressure from a% to 0% of the rated pressure as shown in Figure 4, the plant must be operated without the main steam pressure drop prevention device during variable pressure operation. did not become. This exclusion operation, as shown in FIG. 5, involves artificially applying pseudo pressure to the bellows during variable pressure operation to raise the bellows as if the unloading piston were to maintain the rated main steam pressure. Therefore, even if a boiler abnormality occurs and the main steam pressure decreases during variable pressure operation, there is a drawback that it is not possible to reduce Cv and protect the turbine.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a main steam pressure drop prevention device for detecting a main steam pressure drop and throttling a control valve during pressure variable operation.

[Summary of the invention]

The present invention detects changes in main steam pressure during variable pressure operation, and in the process of converting main steam pressure into air pressure, captures the generator output or turbine load signal, and predetermines changes in main steam pressure and load. , is characterized by controlling the narrowing of the adjustment valve by comparing it with a set value.

[Embodiments of the invention]

The present invention relates to a main steam pressure drop prevention device in an electro-hydraulic governor and a mechanical-hydraulic governor. First, the case of a voltage-hydraulic governor will be shown. FIG. 7 shows a signal processing block diagram of the electrohydraulic governor.

The main steam pressure is detected by a pressure detector installed upstream of the main steam stop valve, and is obtained as an electrical signal by a converter, while the load signal is obtained from the generator output in this example. As is well known, the turbine load is proportional to the steam pressure in the stages after the high-pressure first stage, so the load can be detected by measuring the pressure after the first stage of the high-pressure turbine or the steam pressure after the first stage of the intermediate-pressure turbine. It can also be obtained by doing.

The steam turbine normally operates with a determined load based on the power supply command (set load Ls). In a transformer plant, as shown in Fig. 2 mentioned above, when the set load Ls is in the transformer pressure region, the set pressure Ps is uniquely determined, and with respect to load changes,
By controlling the main steam pressure of the boiler, operation is performed with the opening of the control valve kept almost constant.

In an electro-hydraulic governor, speed control and load control are performed by inputting signals from detectors attached to various parts around the turbine into a control computer, performing calculations within the computer, and outputting a control valve opening signal, etc.

In the control computer, when the electric signals of the set load Ls, the actual pressure P, and the actual load Lo are input, the set pressure calculator 22
From the load-pressure diagram shown in Fig. 8, set load Ls
The set pressure Ps is determined. Next, in the throttling pressure setting device 23, a regulating valve throttling start pressure Peo (= 0, 9 Ps
) and the adjustment valve stagnation end pressure Pao (=0.8 Ps) equivalent to 80% of the set pressure Ps, and during operation, P2O is compared with the actual pressure P using the comparator 24 every unit time. . P
> P e.

When the following relationship holds true, the main steam pressure (actual pressure P) is higher than the regulating valve throttle start pressure, and there is no need to throttle the turbine generated load. Therefore, the subsequent signal processing calculation process is omitted. When the relationship P < P 90 is established, the turbine generated load is narrowed down. Target load setter 2
5, the set pressure is 8 with no load, as shown in Figure 8.
Adjustment valve throttle end pressure Pao (coordinates (
0, Pso)) and the set load Ls, the regulator valve throttling start pressure Pno (seat i1 (Ls, P2O)
) The load is controlled so that it moves on the straight line A that connects the

In the target load setter, the load is controlled using equation (CB), which is a modification of equation (A). That is, the actual pressure P taken into the control calculator from time to time is compared with P2O, and P
< P Substitute for P in formula B only when the condition of 90 is satisfied, and the load when narrowing down ■.

I put it on.

The narrowing load calculated by equation (B) can be applied to all operating ranges in the transformer plant. In other words, in Fig. 9, the operation of the target load setter during 100% rated operation moves on points a-b-c in the figure, and the over-transformation chamber, for example, 75%
During load operation, it moves on the d-e-f point, and moves to the low load area,
For example, at 25% load, it becomes g - h - i.

The target load signal ■ output from the target load setter is the actual load T-
PI calculation unit 26 calculates the difference (L − L o ) with
The signal is converted into a control valve control signal (ET-signal) and sent to the control valve drive unit 27. When L −Lo is negative,
The adjustment valve is narrowed down.

As another example, a main steam pressure drop prevention device in a mechanical hydraulic governor (Ml-IG) will be described.

In the mechanical hydraulic governor, the signal processing method up to the target load setter is the same as that of the electrohydraulic governor described above. The first diagram shows the main steam pressure drop prevention device in a mechanical hydraulic governor.
In Figure 1, a main steam pressure signal processing calculator 29 is installed between the steam pressure component from the pressure detector 28 that measures the upstream pressure of the main steam stop valve and the bellows that constitutes the main steam pressure drop prevention device. establish. An electro-pneumatic converter 30 is provided between the main steam pressure signal processing calculator and the bellows.

Part 1 showing the signal processing method in the main steam pressure signal processing calculator
In the signal processing block diagram of FIG. 1, the actual pressure P obtained from the main steam pressure detector is compared with the regulating valve throttling start pressure poo calculated from the set load Ls, and at 90% or less of the set pressure Ps, Start narrowing down the control valve and set the 90% point of the set pressure of the load signal (coordinates (L) in Figure 8).
s, Poo)) and 80% of the set pressure at no load
A target load signal is output from the target load setting device so as to move on a straight line connecting the points (coordinates (0, P2O) in FIG. 8).

The process up to this point is the same as in the case of the electrohydraulic governor described above.

Next, the target load is converted in a bellows operation signal generator into a bellows operation signal for the ratio to the set load Ps.

The bellows operation signal is converted into air/pneumatic pressure by an electro-pneumatic converter 30 shown in FIG. 10, and then enters the bellows.

The bellows actuate the load piston in response to the bellows operation signal in balance with a built-in spring. A certain constant value a is outputted as a bellows operation signal at L/Lo=O as a signal commensurate with the mounting load of the spring built into the bellows.

The movement of the bellows is connected via an unloading piston to a rotary lever provided in the middle of a rod leading from the speed relay to a servo motor pilot piston that operates the regulator valve of the turbine, thereby driving the regulator valve.

〔Effect of the invention〕

By applying the present invention, the main steam pressure drop prevention device was excluded during the pressure transformation process, which made it impossible to protect the turbine from water generation due to boiler abnormalities during the pressure transformation process, but now it can be used in all operating areas of the transformation plant. , the main steam pressure drop prevention device can be operated to protect the main engine.

[Brief explanation of drawings]

Figure 1 is a conventional plant system diagram, Figure 2 is a diagram of the relationship between load and steam pressure in a transformer pressure plant, Figure 3 is a diagram of the relationship between valve opening and load and steam pressure in a transformer pressure plant, and Figure 4 is a diagram of the relationship between load and steam pressure in a transformer plant. The figure is an explanatory diagram of the startup pattern of a transformer plant, Figure 5 is an explanatory diagram of the main steam pressure drop prevention device mechanism in a mechanical hydraulic governor, and Figure 6 is an explanatory diagram of the main steam pressure drop prevention device mechanism in a mechanical hydraulic governor.
8 is an explanatory diagram of the operation of the main steam pressure drop prevention device in a mechanical-hydraulic governor, FIG. 7 is a signal processing block diagram in an electro-hydraulic governor according to an embodiment of the present invention, and FIG. Fig. 9 is an explanatory diagram of signal processing, and Fig. 10 is a diagram showing the mechanical/hydraulic type control A/S.
A system diagram of the main steam pressure drop prevention device, FIG. 11 is a signal processing block diagram in the mechanical hydraulic governor. 25... Load setting device, 26... PI calculator, 27.
...Adjustment valve drive unit, 29...Signal processing calculator, 30.
...Electro-pneumatic converter. Agent Patent Attorney Akio Takahashi 1 Kasumi 2nd drawing 30 □ Toma degree - In short, Ren 几 1 hour envy 6 Kasumi Shun ii 80 φ load L 躬 9 m Q +00c%) @ load

Claims (1)

[Claims] 1. The steam turbine main steam pressure drop prevention device is characterized in that it is possible to narrow down the steam control valve over the entire main steam pressure range by comparing the main steam pressure signal and the load signal with a set value. Main steam pressure drop prevention device.