JPH0850195A - Reactor pressure rise preventing device at load interruption - Google Patents

Abstract

PURPOSE:To keep a reactor pressure constant without suppressing a rise of steam turbine rotating speed more than it needs by outputting a power load unbalance(PLU) generation signal only for a prescribed time at load interruption. CONSTITUTION:At load interruption, two signals of an intermediate steam pressure signal 9 and a load sudden reduction signal 10 are inputted to the AND circuit 7 of a PLU circuit. An AND circuit 13 then inputs the output signal from an OR circuit 8 and the output of a timer 12 of inhibit signal, and outputs a PLU generation signal 14 only for a time determined by the timer 12 of the inhibit signal. Thus, the PLL circuit is operated up to a primary peak to suppress a rise of rotating speed of a steam turbine, but this is canceled on and after it. Further, a steam governor forced close signal is also eliminated on and after it. Thus, the whole steam quantity is most suitably distributed to the steam turbine and a condenser, respectively, by a steam governor and a turbine bypass valve, and the reactor pressure is never raised and can be kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of a steam turbine in a nuclear power plant using an electric hydraulic control device, and more particularly to a reactor pressure rise prevention device when a load is cut off.

[0002]

2. Description of the Related Art A steam turbine control device using an electrohydraulic control device in a nuclear power plant uses a speed deviation signal which is a deviation between an actual speed signal and a speed setting signal and a deviation between a main steam pressure signal and a pressure setting signal. With the pressure deviation signal and various interlock signals for steam turbine protection, steam turbine rotation speed control and reactor pressure control,
Alternatively, the steam turbine is protected by tripping the steam turbine.

As shown in the block diagram of FIG. 2, a conventional control circuit for a steam turbine and a turbine bypass valve (not shown) at the time of load cut-off is normally a load setting signal + speed deviation signal ( Δδ) 2
Then, the pressure deviation signal (ΔP) 3 is input, and the opening degree of the steam control valve is adjusted by the steam control valve flow rate command signal 4 output from the low value priority circuit 1 to control the steam amount to the steam turbine. Have control.

Further, the turbine bypass valve flow rate command signal 5
The deviation detector 6 obtains the difference between the pressure deviation signal 3 and the steam control valve flow rate command signal 4, and the degree of opening of the turbine bypass valve is adjusted by this, so that the turbine bypass flow rate to a condenser (not shown) is obtained. Are in control.

Since the pressure deviation signal 3 is normally equal to the steam control valve flow rate command signal 4, the output of the turbine bypass valve flow rate command signal 5 is 0%, so the turbine bypass valve is closed and the reactor is closed. All the generated steam is flowing into the steam turbine through the steam control valve.

When the load is cut off in the reactor in such a state, a power load imbalance (hereinafter abbreviated as PLU) occurs, the steam control valve is forcibly closed, and the steam control valve flow rate command 4 is also issued. Clear load setting signal,
It becomes 0% due to the increase of the speed deviation in the closing direction.

For this reason, the total amount of steam generated by the reactor has been delivered to the steam turbine through the steam control valve, but as shown in FIG. Bypass the steam turbine and let it flow into the condenser.

When the PLU is generated, the steam control valve is mechanically fully closed regardless of the steam control valve flow rate command 4, but this state continues while the PLU is generated.
If the steam turbine speed may fall below the speed setting value while the PLU is occurring in this way, an open command signal is output to the steam control valve and a close command is issued to the turbine bypass valve. A signal will be input to reduce the turbine bypass flow rate.

However, since the steam control valve is not closed because it is forcibly closed, as the turbine bypass flow rate is decreased, the outflow amount of steam is decreased and the reactor pressure is increased.

[0010]

P for controlling a steam control valve and a turbine bypass valve in a steam turbine control device.
The LU circuit is composed of an AND circuit 7 and an OR circuit 8 as shown in the logic diagram of FIG. 3, and the conditions for PLU generation are an intermediate steam pressure signal 9 (for example, 40% or more) and a sudden load decrease signal.
Two signals of 10 (for example, 40% / 10 msec) are AND circuit 7
When it is input to, the PLU generation signal 11 is output. In addition,
If the intermediate vapor pressure is above 40%, the PLU circuit will continue to operate.

The intermediate steam pressure is also the load cutoff, that is, P
In some cases, it may be reset several tens of seconds after the LU occurs. This PLU circuit is installed for the purpose of suppressing the rapid increase in the steam turbine speed due to load shedding.
Therefore, after the steam turbine speed exceeds the peak value, suppression of the increase in the steam turbine speed due to the operation of the PLU circuit cannot be expected.

That is, the turbine speed at the time of load shedding is determined as shown in the characteristic curve diagram of FIG.
At the same time as the generation of LU), the temperature rises and goes through the first peak and the second peak toward settling.

Therefore, the PLU circuit exerts an extremely effective effect in suppressing the steam turbine speed, which is its original purpose, for a few seconds after the load is cut off, and thereafter, the PLU circuit is unnecessary. Met.

Further, when the PLU circuit is operating and the steam control valve is mechanically closed forcibly, the steam control valve is opened even when the steam turbine speed falls below the set speed. Since the flow rate command signal 4 of the steam control valve that does not operate and produces the flow rate command signal 5 of the turbine bypass valve is subtracted from the flow rate command signal 5 of the turbine bypass valve, the turbine bypass valve closes. To do.

As described above, in the steam turbine control device, the function of keeping the reactor pressure constant by closing the turbine bypass valve by the amount that the steam control valve is originally opened has the function of keeping the reactor pressure constant. Didn't work well.

Further, if the PLU is canceled while the steam control valve opening command signal 4 is being output, the steam control valve may close suddenly, which may cause disturbance to the reactor. An object of the present invention is to operate a PLU generation signal only for a certain period of time when the load is cut off to prevent the steam turbine speed from being increased more than necessary and keep the reactor pressure constant when the load is cut off. It is to provide a pressure rise prevention device.

[0017]

In order to achieve the above-mentioned object, a reactor pressure rise preventing device at the time of load shedding according to the present invention is
The power load unbalance circuit in the steam turbine control device is characterized in that the power load unbalance generation signal is output for a predetermined time when the load is cut off.

[0018]

According to the present invention, the PLU circuit does not interfere with the function of suppressing the increase in turbine speed due to the original purpose of load shedding, and the PLU circuit operates at least after the first peak of the increase in turbine speed. Do not let

However, after that, since the steam control valve flow rate command signal and the turbine bypass valve flow rate command signal are controlled in cooperation with each other to optimally adjust the opening degrees of the steam control valve and the turbine bypass valve, the reactor pressure is increased. It is possible to suppress and keep the steam control valve constant at all times, and it is possible to prevent the steam control valve from being suddenly opened by canceling the PLU circuit during the steam control valve opening command output.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in the logic diagram of FIG. 1, the PLU circuit includes an AND circuit 7 and an OR circuit 8,
In addition to this, it is composed of a negative signal timer 12 and an AND circuit 13.

The operation of the above configuration is that when two signals of the intermediate steam pressure signal 9 (for example, 40% or more) and the load rapid decrease signal 10 (for example, 40% / 10 msec) are input to the AND circuit 7, OR By inputting the output signal from the circuit 8 and the output of the negative signal timer 12, the AND circuit 13 generates the PLU only for the time determined by the negative signal timer 12 (for example, until the first peak shown in FIG. 4 is exceeded). Output signal 14.

As a result, the rotation speed of the steam turbine is 1
Until the next peak, the PLU circuit operates to suppress the increase in the rotational speed of the steam turbine, but is canceled after that, and after this cancellation, the steam control valve forced closing signal also disappears.

Therefore, the steam control valve flow rate command signal 4
And the turbine bypass valve flow rate command signal 5 is controlled in a coordinated manner, the total amount of steam generated in the reactor thereafter is
Since the steam control valve and the turbine bypass valve are optimally distributed to the steam turbine and the condenser, respectively, it is possible to keep the reactor pressure constant without increasing the reactor pressure.

Even if the steam control valve forced closing signal due to the PLU cancellation during the output of the steam control valve opening signal disappears, the steam control valve is continuously adjusted by the steam control valve flow rate command signal 4, so that the steam control by PLU cancellation is performed. Since the rapid opening of the regulator valve is suppressed, it is possible to prevent the occurrence of a disturbance that affects the reactor pressure.

[0025]

As described above, according to the present invention, the increase of the turbine speed at the time of load shedding is suppressed, and the steam control valve flow rate command and the turbine bypass valve flow rate command are controlled in a coordinated manner, and the atom at the time of load shedding is controlled. Furnace pressure Prevents rise in furnace pressure. Further, there is an effect of preventing disturbance to the reactor pressure due to the steam control valve opening operation due to the PLU signal cancellation during the steam control valve opening command output.

[Brief description of drawings]

FIG. 1 is a logic diagram of a reactor pressure rise prevention device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a relationship between a steam control valve flow rate command and a turbine bypass valve flow rate command.

FIG. 3 is a logic diagram of a conventional power load unbalance circuit.

FIG. 4 is a behavior characteristic curve diagram of turbine rotational speed at the time of load shedding.

[Explanation of symbols]

1 ... Low value priority circuit, 2 ... Load setting signal + speed deviation signal,
3 ... Pressure deviation signal, 4 ... Steam control valve flow rate command signal, 5 ...
Turbine bypass valve flow rate command signal, 6 ... Deviation tester,
7, 13 ... AND circuit, 8 ... OR circuit, 9 ... Intermediate steam pressure signal, 10 ... Load rapid decrease signal, 11, 14 ... PLU signal, 12 ... Negative signal timer.

Claims (1)

[Claims] 1. A reactor pressure rise prevention device at the time of load cutoff, wherein a power load unbalanced circuit of a steam turbine control device outputs a power load unbalance generation signal for a predetermined time when the load is cut off.