JPS6293405A - Speed control device - Google Patents

Abstract

PURPOSE:To prevent the overspeed at the time of load shutdown by providing a speed control device which quickly closes a steam turbine regulating valve at the time of special conditions in gas turbine speed, in a single-shaft combined plant. CONSTITUTION:In a single-shaft combined plant, a gas turbine, a steam turbine, and a generator are connected on one shaft. The speed deviation DELTAN is compared with a prescribed value by a comparator 104 to detect that DELTAN has become less than the prescribed value. The output of an analog switch 108 controls a regulating valve 7 via a servo-motor driver 109. A flip-flop 106 is reset after a lapse of a given time by means of a timer 110. The setting time of the timer 110 is set to the time in which the turbine speed becomes steady. As a result of the above, the regulating valve fully closes, and after a lapse of a given time opens, if once the speed deviation DELTAN becomes negative. Thus, the overspeed at the time of load shutdown can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling a combined plant, and more particularly to a speed control device that prevents overspeeding during load interruption.

[Background of the invention]

Figure 2 shows the main engine configuration of a single-shaft combined power generation plant. A feature of the single-shaft combined plan 1- is that a gas turbine and a steam turbine are coupled to one shaft, and a single generator coupled to the same shaft is driven. A steam turbine is an energy-saving plant that recovers heat from the gas turbine's exhaust gas using an exhaust heat recovery boiler.

Conventional control equipment for such plants.

Although not introduced in the literature, gas turbine control is discussed in the Hitachi Review.
ew) V o Q, 27 (1978), Na4
It is introduced on pages 201 to 207. Basically, this control method is used as is. Speed control in a combined plant is carried out by the speed control function on the gas turbine side, so the regulator valve of the steam turbine does not have a speed control function, and is fully open when the load exceeds a certain level. It becomes.

When a load cutoff occurs, the gas turbine's speed control function throttles the gas turbine's fuel adjustment valve to try to keep the speed to a specified value, but the output ratio between the gas turbine and the steam turbine is approximately 2:1. The steam turbine control valve must also be closed.

Conventional control systems detect that the speed of the steam turbine exceeds a specified value and close the control valve. This value is usually about 107% of the rated speed, and this value is less than 111%, which is the overspeed trip setting value according to the thermal power technical standards, and the speed is set by the speed adjustment rate (usually 4 to 5%)], 04
It is determined by setting it to 105% or more. The operation of the control valve by such a control device is shown in FIG. When load cutoff occurs and the turbine speed increases to the value indicated by the arrow, the control valve is fully closed to prevent the speed from increasing.

In this conventional example, the difference from the overspeed trip setting of 111% is only 4%, and there is a risk of an overspeed trip.

There is a concept of detecting load cutoff based on the electric power or the opening/closing conditions of the circuit breaker, and then closing the control valve.
As shown in the figure, the system configuration around the power plant is not uniform;
Standardization is difficult if conditions change for each delivery destination.

Furthermore, there may be cases where it is not necessary to close the control valve in partial load shutoff on the system side. Next, using electric power as a condition is complicated because it is necessary to consider increases and decreases in electric power during start-up and stop, as well as component load interruption.

As a result of the above, it is necessary to detect load interruption based on the conditions within the spontaneous molding facility.

[Purpose of the invention]

The purpose of the present invention is to use the conditions in a spontaneous molding laboratory to easily form H4
An object of the present invention is to provide an inexpensive control device that prevents overspeed.

[Summary of the invention]

The present invention prevents overspeed during load cutoff by obtaining a fully open command for a control valve using the speed deviation of a gas turbine speed control device as a determination value.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The gas turbine speed control device calculates the deviation (ΔN) between the speed/load set value and the actual speed (N) using a subtractor 101,
A gain of 102 is applied to obtain fuel proportional to the speed deviation. Adder 103 adds fuel bias FSNL for ensuring compressor power during no-load conditions, and generates gas turbine fuel flow rate request signal CFF. The fuel control of the gas turbine is not within the scope of this patent and will therefore be omitted.

As shown in FIG. 5, the speed control of the gas turbine is configured such that the load increases as the speed deviation increases. The speed/load setting value is the load command converted to speed, and since the turbine speed is 100% when the generator is operating in parallel,
When the speed/load setting value is 104%, the speed deviation (ΔN)
is 4%.

When the speed deviation is 4%, the gain is 10 as if it were due to 100% load.
When adjusting 3, it is called a 4% adjustment rate. In other words, 100
% load, the speed deviation is 4%.

Figure 6 shows the movement of speed deviation when the load is cut off.

During 100% load operation, the turbine speed is 100% and the speed deviation is 4%. When load shedding occurs, the turbine speed increases, but since the speed load set point remains at 104%, the speed deviation decreases and becomes 0 when the turbine speed reaches 104%, and then becomes negative.

Since the load is taken during normal operation, the speed deviation is always positive, and if it becomes even slightly negative, it can be determined that the load has been cut off, and the value is less than the speed deviation ΔN=-1%. If this value is used as a judgment value and the control valve is throttled down, it can be detected at a very early stage, so overspeed trips can be prevented. If the specific determination value is the speed deviation ΔN=-0, 5%, then the absolute value of the turbine speed is detected at 104.5%.

Figure 7 shows an example in which the load is cut off at 75% load. In this example, load cutoff is performed from a speed deviation of 3%, and the judgment value is speed deviation ΔN=-〇. If 5%, the turbine speed is 103
．． Detectable at 5%.

It may be possible to set the regulating valve to close at 104.5% of the absolute value of the turbine speed, but the speed adjustment range was previously 9.
5% to 107%, which is inconvenient because a control valve closing command is issued (although it is actually closed) during speed adjustment under no load.

Returning to FIG. 1, the specific circuit will be explained. Speed deviation (ΔN
) is compared with the set value by the comparator 104, and it is detected that ΔN has become the same as the specified value.This signal and the sequence completion signal 3 and A indicating that the turbine has once reached the rated speed
N I) and store it in a flip-flop. The analog switch 108 receives the control valve control signal CFV during normal operation.
F and full open bias 107 are switched by the flip-flop output signal. The output of the analog switch controls the control valve 7 via the servo valve driver 109. Flip-flop 106 is reset by timer 110 after a certain period of time has elapsed. The set time of the timer 110 is set to the time when the turbine speed is stabilized.

As a result of the above, once the speed deviation (ΔN) becomes negative, the control valve is fully closed and the operation is performed after a certain period of time.

〔Effect of the invention〕

According to the present invention, overspeed can be prevented because load cutoff is detected at a very early stage. In addition, it is simple and inexpensive with little increase in hardware.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a configuration diagram showing the main engine configuration, Fig. 3 is an explanatory diagram showing conventional control, and Fig. 4 is a configuration showing the power plant system configuration. Figure, Figure 5,
FIG. 6 and FIG. 7 are supplementary explanatory diagrams of the embodiment of the present invention. 10]...Subtractor, 102...Gain, 103...
- Adder, 104... Comparator, 105... AND gate, 106... Flip-flop, 107... Signal generator, 108... Analog switch, 1.09.
... Servo valve driver, ■... Compressor, 2... Combustor, 3... Gas turbine, 4... Generator, 5...
・Exhaust heat recovery boiler, 6...Steam turbine, 7...Gas turbine fuel adjustment valve, 8...Adjustment valve.

Claims (1)

[Claims] 1. In a single-shaft combined plant in which a gas turbine, a steam turbine, and a generator are connected to one shaft, the deviation between the speed/load setting value in the gas turbine speed control system and the actual turbine speed is below the specified value. A speed control device that detects the speed of the steam turbine and quickly closes the steam turbine control valve.