JPH0529761B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the operation of a steam turbine, particularly when the steam turbine is operated under conditions where the main steam and reheat steam temperatures rapidly decrease. , relates to a steam turbine protection method suitable for operating the turbine safely.

[Conventional technology]

Traditionally, as one of the methods of protecting steam turbines,
A “main steam temperature low trip device” is used.
This system detects boiler control abnormalities by monitoring the main steam, and trips the steam turbine when the steam temperature falls below a specified value. Note that related protection methods of this type include, for example, Japanese Patent Publication No. 45725/1983.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology is based on the fact that under normal plant operating conditions, an abnormality in boiler control, that is, an abnormality in the air-fuel ratio or an abnormality in the water-fuel ratio, first appears in a change in the state of the main steam. Therefore, no consideration has been given to operations in which the steam turbine continues to operate after a boiler trip, that is, operations in which the operating status of the reheat steam system changes more rapidly than in the main steam system, and the protection of the steam turbine is not considered. On the other hand, there was a problem that protection for medium and low pressure turbines was insufficient.

An object of the present invention is to provide a steam turbine protection method that can completely protect a steam turbine even under such severe operation.

[Means for solving problems]

That is, the present invention detects the reheat steam temperature and the rate of change in the reheat steam temperature in the reheat system, and detects when the reheat steam temperature is below a specified value or when the rate of change in the reheat steam temperature is above the specified value. In order to achieve the desired purpose, the turbine is tripped in the event of failure.

[Effect]

In other words, changes in steam conditions are most noticeable in changes in steam temperature, and the temperature of reheated steam rapidly decreases after the boiler is stopped. However, the present invention directly detects the temperature of reheated steam and changes the temperature of reheated steam. Since we are trying to capture the absolute value or rate of change of reheated steam,
It is possible to sufficiently respond to changes in the steam conditions of the turbine and protect the turbine.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Although FIG. 1 shows the logic for applying the present invention, such protection applies to one or more stage reheat plants such as that shown in FIG.

First, the reheat plant will be explained using FIG. 2. Main steam heated by the boiler 1 passes through the main steam stop valve 2 and the steam control valve 3, and flows into the high pressure turbine 4. The steam that has done work in each stage of the turbine returns to boiler 1 and is heated again.
The steam flows into the intermediate pressure turbine 7 through the reheat steam stop valve 5 and the intercept valve 6, and after performing work, flows into the low pressure turbine 9 through the crossover pipe 8, and is finally condensed in the condenser 10. be done. In this series of processes, the thermal energy of the steam is changed into kinetic energy, which is further converted into electrical energy by the generator 11. The condensate in the condenser 10 is pressurized by the pump 11, returns to the boiler 1, and is heated again.

In such reheat plants, if the steam turbine continues to operate after the boiler trips (stops),
A phenomenon as shown in Fig. 3 occurs. After boiler trip,
The steam turbine load is generally rapidly reduced to a very low load or no load after the generator is disconnected.
However, the boiler was tripped and the fuel
Since almost no water or air is supplied, the steam temperature drops extremely rapidly as shown in the figure. When such an operation is performed, the reheat steam temperature often rapidly decreases to a level higher than the main steam temperature, as shown in the figure.

Therefore, as shown in FIG. 4, a main steam temperature detector 13 is installed in the main steam system, and a reheat steam temperature detector 14 is installed in the reheat steam system.

For reference, we will first discuss protection for the main steam system using Figure 1. When the main steam temperature rises during the start-up process and reaches x [°C] or higher, the protection logic enters the set state, and the signal conditions of line 15 in the figure are subsequently established in series. Under these conditions, operate as described above until the main steam temperature reaches y.
If the main steam temperature drops below [°C] or the rate of change of the main steam temperature exceeds Z [°C/min], the steam turbine is tripped to protect it. In this way, complete protection for the main steam system is possible by monitoring not only the absolute value of the main steam temperature but also its rate of change, and tripping the steam turbine if either of them exceeds a specified value. becomes. This protects the turbine from changes in the high-pressure turbine casing due to changes in main steam conditions, erosion, changes in thrust force, etc. due to the final stage of the turbine entering the wet region. On the other hand, similar protection will be applied to the reheat steam system. That is, when the reheated steam temperature reaches or exceeds u [° C.], the protection logic 16 enters a set state so that the conditions are always satisfied. In such a state, if the above-mentioned operation etc. is performed and the reheat steam temperature falls below v [℃] or the rate of change in reheat steam temperature exceeds w [℃], the turbine will be tripped. , provide protection. This allows sufficient protection for medium and low pressure turbines. Among these set values, x [℃] and u [℃]
are generally defined by the boiler temperature rise characteristics at startup, y [°C], v [°C], z [°C/min], w [°C/min]
is defined by the strength and deformation surface of the steam turbine.

〔Effect of the invention〕

As explained above, the present invention detects the reheat steam temperature of the reheat system and the rate of change in the reheat steam temperature, and detects when the reheat steam temperature becomes below a specified value or when the reheat steam temperature decreases. Since the steam turbine is tripped when the rate of change exceeds a specified value, the medium and low pressure turbine can be more reliably protected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the application logic of the present invention, Fig. 2 is a system diagram of a known reheat thermal power plant,
FIG. 3 is a steam characteristic diagram when the steam turbine is continuously operated after the boiler is stopped, FIG. 4 is a diagram showing how the detection device is installed, and FIG. 5 is a block diagram showing another embodiment of the present invention. 1...Boiler, 2...Main steam stop valve, 3...Steam control valve, 4...High pressure turbine, 5...Reheat steam stop valve, 6...Intercept valve, 7...Intermediate pressure turbine, 8... ... Crossover pipe, 9 ... Low pressure turbine, 10 ... Condenser, 11 ... Generator, 12 ...
...Water pump.

Claims (1)

[Claims] 1. In a reheat power generation plant having one or more stages of reheating system, detecting the reheating steam temperature of the reheating system and the rate of change of the reheating steam temperature, A method for protecting a steam turbine, characterized in that the steam turbine is tripped when the temperature of the reheated steam falls below a specified value or when the rate of change of the reheated steam temperature exceeds a specified value.