JPS6045725B2 - Power plant protection equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a protection device for a thermal power plant.

Figure 1 shows the general system of a thermal power plant.

In Fig. 1, superheated steam generated in a boiler 1 enters a high-pressure turbine 2, where the expanded steam is guided to a reheater 3, where it is reheated to an appropriate temperature, and then introduced to a medium/low pressure turbine 4, where it is expanded. . The work of the turbine consisting of the high pressure turbine 2 and medium/low pressure turbine 4 becomes the output of the generator 5. The steam led to the turbine undergoes adiabatic expansion up to the exhaust pressure, which lowers its pressure and temperature, reducing its degree of superheating.

When the steam in the turbine changes from superheated steam to saturated steam and the humidity of the saturated steam increases, not only does the turbine efficiency deteriorate, but it also causes erosion and fatigue of the turbine blades, so a permissible humidity limit value is set for turbine operation. . As the main steam pressure and main steam temperature at the turbine inlet decrease, the degree of superheating of the steam inside the turbine decreases and it becomes saturated steam, which increases the humidity. When the main steam temperature is below a specified value, an alarm is issued or the turbine is tripped, and when the boiler outlet pressure falls below a specified value, the steam control valve at the turbine inlet is closed to reduce the steam pressure. A recovery device was provided. On the other hand, recently variable pressure operation has been adopted in which the boiler pressure is changed according to the generator load in order to improve thermal efficiency at low loads.

Because this variable pressure operation operates by changing the main steam pressure, the inlet steam pressure adjustment device of the type used in constant pressure operation cannot be used. The wet area of steam is determined by the pressure and temperature, so in the case of variable pressure operation, the generator output or
It is necessary to set a main steam temperature limit value corresponding to a moisture limit value in accordance with the main steam pressure, and to issue an alarm or trip for turbine protection when the main steam temperature is below this limit value. Conventionally, a method has been devised to set the main gate steam temperature limit value as a function of the main steam pressure at the turbine inlet. Since the internal efficiency of the turbine differs due to the difference, the humidity of the saturated steam that reaches the final stage of the high pressure turbine from the inlet of the high pressure turbine differs.

In this way, in order to perform a trip at the permissible moisture limit value and to avoid unnecessary trips when this limit value is not reached, it may not be sufficient to set the main steam temperature limit value only based on the main steam pressure. Ta. The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a protection device for a power plant that can prevent a turbine that performs variable pressure operation from operating in a humid region.

To achieve this objective, the present invention has developed two function generators: a function generator that takes the generator output as an input and gives the main steam temperature limit value, and a function generator that takes the main steam pressure as the input and gives the main steam temperature limit value. Depending on the operating condition of the turbine,
The present invention is characterized in that a function generator that provides a more accurate main steam temperature limit value is selected from both function generators.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram for detecting a main steam temperature drop using the generator output as an index. Comparator 7 for comparing main steam temperature T
is provided, and when the main steam temperature T is smaller than the limit value TLl, the comparator 7 sends a contact signal to the outside as shown by the dotted line. FIG. 3 is a block diagram of main steam temperature drop detection using main steam pressure as an index. Temperature T
of. A comparator 9 is provided for comparison, and when the main steam temperature T is smaller than the limit value TL2, a contact signal is sent from the comparator 9 to the outside as shown by the dotted line -C.

Figure 4 shows the main steam temperature using the generator output MW as input. 2 shows the function characteristics of the function generator 6 that provides the degree limit value τL1.

This functional characteristic is determined by the point where the high-pressure turbine final stage end point of the turbine expansion line corresponding to the steam pressure at the generator output MWl crosses the saturation line on the i-S diagram, that is, enters the wet region. This is a plot of the main steam temperature at the high-pressure turbine inlet, which is determined as the main steam temperature at one point, and is obtained by sequential numerical analysis for each stage from the final stage of the high-pressure turbine to the upstream stage. It is.
FIG. 5 shows the function characteristics of the function generator 8 which inputs the main steam pressure PR and provides the main steam temperature limit value τL2.

This function characteristic can be obtained by sequentially performing numerical analysis for each stage from the final stage of the high-pressure turbine to the upstream stage, in the same way as the function characteristic shown in Fig. 4. The difference is that the generator output is constant at a few percent of the rated output,
It also plots the main steam temperature obtained by taking into account the throttling loss of the high-pressure turbine inlet steam control valve.
FIG. 6 is a sequence circuit diagram, in which P-N is a DC power supply bus, and the a contact Aa is used by the comparator 7 in FIG. 2 to detect that the main steam temperature T is smaller than the main steam temperature limit value TLl. It is a contact that operates and closes when detected. The a contact Ea is a contact that is closed when the power plant is in normal operation. Here, during normal operation, after steam is supplied to the turbine,
In the relationship shown in Figure 7, the operating state in which the generator output MW and main steam pressure PR are increasing or decreasing, or the generator output at 100% rated power is supplied. Refers to the operating state. When the FCB described below occurs, the normal operation is stopped and the a contact Ea is opened. The a contact Ba is connected to the comparator 9 in FIG. This is a contact that operates and closes when it detects that it has become smaller.

A contact Fa is an operation mode in which the power generation plant is not in normal operation,
For example, it is a contact that closes during a special operation called FCB (Fast Cut Back), which is an isolated operation within a power plant. During the normal operation mentioned above, the a contact F
a is open circuit. When FCB occurs, the main steam pressure PR
Since the generator output MW rapidly decreases while the current value is almost maintained, the power generation plant is operated at a location away from the line shown in the relationship shown in FIG. A contact Aa (5 A series circuit of A contact Ea and a series circuit of A contact Ba and A contact Fa are connected in parallel, and this parallel circuit is connected to relay X.

Relay X (7) a contact Xa is a contact that causes the turbine to trip. Next, the operation of the protection device for a thermal power plant having such a configuration will be explained.

In variable pressure operation, the relationship between generator output and main steam pressure is generally as shown in FIG. This is a relationship determined from the plant operation plan. Here, the main steam temperature at the point where the last stage of the high pressure turbine enters the humid region is selected as the main steam temperature limit value for performing a turbine trip.

The point at which the final stage of the high-pressure turbine enters the humid region is generally given by the main steam pressure and main steam temperature at the turbine inlet, but even if the main steam pressure is the same, the final stage will be in the humid region. The main steam temperature entering is different. At 25% or less of the rated power in Figure 7, the main steam pressure is kept constant to ensure steam conditions, but due to the difference in turbine internal efficiency at each generator output, the final stage of the high-pressure turbine The main steam temperature at the point where it enters the wet region is different. When the turbine is operated in the relationship shown in Figure 7, the main steam temperature limit value is
It cannot be set as a function of main steam pressure, but it can be set as a function of generator output. The function generator 6 of FIG. 2 having the characteristics shown in FIG. 4 was provided with this intention in mind. In contrast to such normal operation, when FCB occurs, the generator output decreases to the station load and remains almost constant.

In this case, the generator output is constant and the main steam pressure is gradually decreased from the pressure at the time of FCB generation. In this case, conversely, the main steam temperature control value cannot be set as a function of the generator output, but can be set as a function of the main steam pressure.

The function generator 8 of FIG. 3 having the characteristics shown in FIG. 5 was provided with this intention in mind. In order to protect the turbine from wet operation regardless of the operating status of the power plant, a limit value set according to the generator output and a limit value set according to the main steam pressure are set. The feature is that two limit values are provided and used depending on the operating condition of the power generation plant. In Fig. 6, during normal operation, the a contact Ea is closed, When the comparator 7 in Fig. 2 detects a decrease in the main steam temperature, the a contact M closes and the relay X is energized.
Contact Xa closes to issue a trip signal.

During FCB operation, the a contact Fa is closed and the third
When the comparator 9 in the figure detects a decrease in the main steam temperature, the a contact? is closed, relay X is energized, and a contact X
a closes and issues a trip signal, and the turbine trip protects the turbine from wet operation. As explained above, according to the present invention, it is possible to automatically set the main steam temperature limit value regardless of the operating state, especially for power plants that operate under variable pressure. It is possible to provide a protective device that can provide stricter protection to avoid such damage.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a general system of a thermal power plant, Fig. 2 is a block diagram for detecting a main steam temperature drop using generator output as an index in an embodiment of the present invention, and Fig. 3 is a diagram showing an embodiment of the present invention. A block diagram for detecting a main steam temperature drop using the main steam pressure as an index in the embodiment, FIG. 4 is a diagram showing the characteristics of the function generator 6 that inputs the generator output in FIG. 2 and gives a main steam temperature limit value, FIG. 5 is a diagram showing the characteristics of the function generator 8 in FIG. 3 which inputs the main steam pressure and gives the main steam temperature limit value, FIG. 6 is a sequence circuit diagram showing an embodiment of the present invention, and FIG. The figure shows the relationship between the generator output and main steam pressure of a power generation plant that performs variable pressure operation. 1... Boiler, 2... High pressure turbine,
3... Reheater, 4... Medium/low pressure turbine, 5... Generator, 6, 8... Function generator, 7, 9... ...Comparator, MW5...
Generator output, PR... Main steam pressure, TLl, T
L2...Main steam temperature limit value, T...Main steam temperature.

Claims (1)

[Claims] 1. In order to prevent the humidity of the steam flowing into the turbine from deviating from the permissible limit value, a limit value for the turbine inlet main steam temperature is calculated based on the turbine inlet main steam pressure, and the turbine inlet main steam temperature is adjusted to the above limit value. A protection device that issues an alarm when the limit value is deviated from the limit value, and is configured to change the limit value in accordance with the change in the main steam pressure at the turbine inlet when the main steam pressure at the turbine inlet changes due to variable pressure operation of the boiler,
Means for calculating the limit value based on the generator output is provided, and the limit value calculated based on the generator output is selected during normal operation, and the turbine inlet main steam pressure is based on the turbine inlet main steam pressure during independent operation within the power plant. A protection device for a power generation plant, characterized in that the limit value calculated in accordance with the above is selected.