JPH0241261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for operating and controlling a power generation plant, which shifts the power generation plant to in-house isolated operation when a system accident occurs, and rejoins the system after the accident is restored.

[Technical background of the invention]

In recent thermal power plants, when an accident occurs in the power transmission system, until the accident is restored,
without separating from the system and extinguishing the boiler.
Increasingly, generators are equipped with a function to continue operation with only the on-site load on the generator. This is to immediately join the power generation plant to the grid and increase the load to ensure an early and stable supply of electricity after the grid fault is restored.This function is generally referred to as FCB (Fast Cut Back). . this
Implementation of FCB operations has greatly contributed to improving the reliability of power supply, such as by quickly restoring supply capacity while waiting for grid restoration, and by simplifying operations when restarting power plants. The current situation is that further improvements are desired in terms of operation and equipment.

Figure 1 shows a conventional example of a thermal power plant that performs such FCB operation.
The water sent out is heated by a high-pressure heater 2 and then passed through a economizer 3 to become high-temperature, high-pressure water and sent to an evaporator 4. On the other hand, the fuel in the fuel tank 5 is supplied to the fuel control valve 7 by the fuel pump 6.
At the same time, the air is sucked in from the atmosphere by an air fan 8, heated by an air heater 9, and then combined with air that is also sent to the evaporator 4 via an air flow control valve 10, where it is combusted. The water is then evaporated at high temperature and pressure. The combustion state in the furnace is maintained in a safe state by controlling the fuel control valve 7 and the air flow control valve 10. This control of the fuel flow rate or air flow rate is performed by a plant system control device (hereinafter referred to as APC) not shown. The steam generated in the evaporator 4 is superheated by a superheater 11, drives a high-pressure turbine 12, an intermediate-pressure turbine 13, and a low-pressure turbine 14, and turns a generator 15 directly connected to the turbines to generate electricity. . The low-temperature, low-pressure steam that has become the exhaust gas of the turbine is condensed into water in the condenser 16 and sent to the water supply pump 1 by the condensate pump 17 via the low-pressure heater 18 .

APC controls the entire plant.
During plant operation, the load increase/decrease of the generator 15 is controlled by giving the target power generation amount (load). In this case, the load on the generator 15 changes depending on the flow rate of steam flowing into the high-pressure turbine 12 per unit time;
It is controlled by a steam control valve at the inlet of 2. APC adjusts and controls the opening degree of this steam control valve to the target load.
5 loads can be controlled. Also, APC
has a function of controlling the steam pressure to an appropriate value by changing the water supply flow rate and fuel flow rate by an amount commensurate with the changing steam flow rate by operating the steam control valve. That is, when the amount of steam flowing into the turbine increases, the amount of fuel input is increased in order to increase the amount of evaporation in the evaporator 4, and the flow rate of water supply is also increased. Furthermore, when increasing the fuel flow rate, the air flow rate must be increased to maintain optimal combustion in the furnace, and this operation is also performed by the APC.

FIG. 2 is a block diagram showing the in-house electrical system in the power generating plant shown in FIG. The power transmission system 20 and the inside of the power plant are connected via a switchyard disconnector 21. Electric power generated by the generator 15 is sent to the power transmission system 20 via the main transformer 22, the main disconnector 23, and the in-house power transmission system side bus 24.
Power for the station is supplied from the station bus 25, which is supplied from the station power transmission system side bus 24 via the switching device 26, through the disconnector 27, and the startup transformer 28 when starting the power plant. The rest is supplied from the generator 15 through the station transformer 29.

Now, when the power generation plant is disconnected from the grid due to a grid fault, the main switch 23 opens, but in this case, the output of the generator 15 is instantaneously transferred to the starting transformer 2.
The in-house load is reduced to that of 8. The APC detects this condition and rapidly narrows down boiler inputs such as fuel, air, and water supply according to the required target load, and shifts to isolated operation within the plant. This narrowing operation is carried out rapidly while coordinating with each other, but in the event of failure, the boiler protection interlock of the plant is activated, tripping the boiler and turbine, and preventing the plant from falling into a dangerous state. This series of operations is shown in FIG.

First, if a system accident occurs in step 1,
The operation to narrow down the generator load to the station load is started. In order to prevent system accidents from spreading within the power plant, power transmission line protection relays operate, main changes occur, and circuit breakers open, and in response to sudden load drops, turbine steam control valves are suddenly opened. , suppresses the amount of steam flowing into the high-pressure turbine. In addition, the steam supplied to the intermediate pressure turbine is cut off by closing the reheat steam check valve (RSV) and intermediate check valve (ICV) at the inlet of the intermediate pressure turbine, suppressing the increase in turbine speed. It works like that. Furthermore, in step 3, as the load suddenly decreases, APC works to narrow down the boiler inlet and make the amount of steam generated commensurate with the load. Regarding combustion in the furnace, the amount of fuel input is reduced in order to reduce the amount of steam and suppress the rise in pressure in the boiler. As the burner oil pressure decreases as the amount of fuel input decreases, the burners are extinguished, leaving only the required number of burners. Also, to prevent excessive air flow due to fuel loss, the air supply is restricted. Through the above operations, the steam pressure corresponding to the suddenly reduced generator load (in-house load only) is maintained, and stable combustion within the furnace is maintained. However, if the steam pressure control cannot follow the above-described control operations due to sudden transient changes, the boiler pressure relief valve is urgently operated to suppress the pressure rise. On the other hand, the amount of water supplied to the boiler will be reduced to an amount commensurate with the sharply reduced generator load. In general thermal power plants, the water pump that supplies water to the boiler is a motor-driven water pump (hereinafter referred to as M-BFP).
It is equipped with one turbine-driven water supply pump (hereinafter referred to as T-BFP) and two turbine-driven water supply pumps (hereinafter referred to as T-BFP), and water is supplied by two T-BFPs during normal load operation.
T-BFP generally uses the steam generated by its own plant as a steam source, so M-BFP is used when starting up the plant.
Supply water with BFP. Switching between M-BFP and T-BFP is normally done at around 20% generator load, but
When an FCB occurs, the generator load is only the station load (approximately 5% of the rated load), so the T-BFP is stopped.
The M-BFP is activated and operated to ensure the minimum water supply flow rate. If the operation in step 3 is performed normally and there is no need to activate the boiler protection interlock operation in step 4, the FCB continues to operate independently within the plant as a success, and enters a standby state (step 5) waiting for system accident recovery. . In step 4, the control operation when FCB occurs (step 3) ends in failure, and the reheater (RH)
If the fuel cannot be reduced to the amount required for protection, if the burner oil pressure cannot be lowered to below the specified value, if the balance between the amount of fuel and the amount of air cannot be achieved and stable combustion cannot be ensured, If it is not possible to secure the minimum water supply flow rate to prevent the boiler from running dry, and furthermore, if the supply water and fuel are not sufficiently throttled, the steam pressure supplied to the turbine will exceed the specified value. If the pressure rises to such an extent, the boiler and turbine will be tripped as an FCB failure, and the plant will be shut down while waiting for the system fault to recover. Once the system accident has been recovered, the plant will be restarted in step 6. If the FCB is successful and has been on standby in isolated operation within the station, the restart operation involves turning on a main switch or disconnecting circuit, rejoining the grid, and increasing the load. On the other hand, if the FCB fails, a series of plant start-up operations such as boiler core purge, feed water pump start-up, boiler ignition, turbine start-up, and generator excitation are carried out after the accident. This must be done as a plant start-up before re-intake operations.

[Problems with background technology]

Above, we have described FCB operation in the event of a system accident in a conventional thermal power plant.
FCB operation has the following problems.

(a) When the FCB is operated under high load, the reheater protection interlock is activated due to a delay in fuel throttling.
FCB may fail and lead to a unit trip.

(b) Not only will the isolated operation time within the station become longer, but the steam temperature will change, increasing thermal stress on the turbine rotor.

(c) The rapid decrease in water supply flow rate makes control difficult, and low water supply flow rates may lead to plant trips.

(d) Recovery after an accident must be carried out quickly considering the social impact, so recovery operations are required especially when an FCB fails, placing a burden on operators to regenerate power in a short time.

[Purpose of the invention]

An object of the present invention is to provide a method for operating and controlling a power generation plant that can reliably shift to in-plant isolated operation when a system accident occurs, and that can quickly and easily rejoin the system after the accident is restored.

[Summary of the invention]

For this reason, the present invention configures a power generation plant with a plurality of power generation units. This power generation unit connects the shafts of a compressor, gas turbine, generator, and steam turbine to each other. The gas generated from the combustion machine rotates the gas turbine, and the exhaust heat is used to rotate the steam turbine to generate electricity. This is a power generation unit that performs The power generated from each generator of each power generation unit is transmitted to the power grid via a common main transformer and main switch, and if an accident occurs in the power grid, the main After the machine is opened, among the power generation units, the power generation unit that generates the power corresponding to the station load is left, the other power generation units are tripped, and the remaining power generation units are shifted to the station independent operation. It is characterized by

[Embodiments of the invention]

The present invention will be described below with reference to the embodiments shown in FIGS. 4 and 5.

FIG. 4 shows an internal electrical system diagram of a power generation plant according to an embodiment of the present invention. In the figure, the same symbols as in Figure 2 indicate the same or corresponding parts, and
The difference from the diagram is that the power generation plant is composed of n power generation units, and the generator 40 of each power generation unit is connected to the main transformer 22 and the station via a transformer 41 and a shield switch 42. This is the point where it is connected to the transformer 29.

FIG. 5 shows an example of the system configuration of the power generation unit, in which the shafts of the compressor 50, gas turbine 51, generator 40, and steam turbine 52 are connected to each other, and the gas generated from the combustor 53 is connected to each other. At the same time as the gas turbine 51 is rotated, the waste heat is used to convert the water from the condenser 55 into steam in the gas turbine exhaust heat recovery boiler 54, which rotates the steam turbine 52 and generates steam from the generator 40. It is a system that generates electricity.

In this way, one power generation plant is constructed by using n power generation units as shown in FIG. do. If an accident occurs in the in-house power transmission system bus 24, the power supply to the power system becomes impossible.In other words, since it is unnecessary to supply power, the output of the entire power generation plant must be reduced. . Therefore, for example, all but one unit is tripped, and the power generation output of that one unit is adjusted to output only the load power corresponding to the load within the station. For example, now,
If the rated capacity of the power generation plant is 1000MW and it is composed of 8 power generation units, the rated power distributed by each power generation unit during rated load operation is
This means that the maximum capacity of each power generation unit needs to be 125MW. While this plant was operating at a rated capacity of 1000MW, an accident occurred in the grid.
When shifting to in-house independent operation, first the main disconnector 23 is opened to isolate it from the grid, and seven of the eight power generation units are tripped. on the other hand,
The on-site load is usually about 5% of the rated capacity of the power plant, which is 50MW, so the remaining one
The load will rapidly follow the load from 125MW to 50MW, and the load will be maintained within the plant until the system fault is restored. In response to a sudden load increase, the amount of combustion gas generated in the combustor 53 in FIG. 5 flowing into the gas turbine 51 is reduced. To this end, the gas control valve at the gas turbine inlet is throttled at once due to the generation of FCB, and the flow rate of air supplied from the compressor 50 to the combustion 53 is throttled accordingly. In addition to restricting the combustion gas, the fuel is also restricted in order to prevent the pressure in the combustor 53 from exceeding a specified value, thereby maintaining a stable combustion state. In this way, when an FCB occurs, in order to maintain the necessary station load with one power generation unit, the target load can be rapidly lowered and the generator output can follow, by rapidly reducing the fuel flow rate of the gas turbine. Further, if necessary, the steam control valve on the steam turbine side is once fully closed to reduce the output of the turbine.

In this case, the station load is 50MW as mentioned above, which is 40% from the perspective of one power generation unit.
corresponds to If the station load exceeds 125MW, two power generation units will be left and each will share the station load.

Therefore, when FCB occurs, the flow rate of combustion gas, fuel, and air is reduced from 100% to 5% in the case of conventional thermal power plants.
In the case of the power plant in this example, 100% to 40%
This narrows down the narrowing span considerably. In addition, the operation at this time is simpler than in conventional thermal power plants, requires less coordination with other process quantities, and has good followability of gas, fuel, and air.
The probability of success is extremely high.

In addition, in conventional thermal power plants, the control targets are diverse, including steam (flow rate, pressure), fuel, air, and water supply, and the follow-up of the water supply flow rate when throttling the supply water is particularly poor, resulting in sudden reductions in water supply and agitation. Undershoot of the water supply flow rate was the biggest cause of FCB failure, but the power plant of this example uses only combustion gas (flow rate, pressure), combustion, and air, and there are no factors equivalent to conventional water supply, making it easy to control. Become.

〔Effect of the invention〕

As described above, according to the present invention, when a power grid accident occurs, it is possible to reliably shift the power plant to on-site isolated operation, and also to quickly and easily rejoin the power plant after the fault is restored. You will be able to do this.

[Brief explanation of drawings]

Figure 1 is a system configuration diagram of a conventional thermal power plant, Figure 2 is an internal electrical system diagram of a conventional thermal power plant, Figure 3 is an explanatory diagram of FCB operation of a conventional thermal power plant, and Figure 4 5 is an internal electrical system diagram of a power generation plant according to an embodiment of the present invention, and FIG. 5 is a block diagram showing one of its power generation units. 20...Power transmission system, 21, 27, 42...Shield disconnector, 22...Main transformer, main sheath disconnector, 24...
Station power transmission system side bus, 25... Station bus, 26...
...Switching device, 28...Starting transformer, 29...In-house transformer, 40...Generator, 41...Transformer, 50
... Compressor, 51 ... Gas turbine, 52 ... Steam turbine, 53 ... Combustor, 51 ... Gas turbine exhaust heat recovery boiler, 55 ... Condenser.

Claims (1)

[Claims] 1 Power generation in which the shafts of a compressor, gas turbine, generator, and steam turbine are connected to each other, and the gas generated from the combustor rotates the gas turbine, while the exhaust heat is used to rotate the steam turbine. In a power generation plant consisting of a plurality of plants, the power generated from the generators of each power generation unit is transmitted to the power system via a common main transformer, main transformer, and disconnector, When the power supply to the power system is no longer necessary, after opening the main disconnector, leave only the power generation unit necessary to produce the power generation output that matches the station load, and trip the others. 1. A method for operating and controlling a power generation plant, characterized in that the power generation plant is shifted to isolated operation within the plant.