JPS6042324B2 - Control valve opening detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control valve opening detection device that prevents malfunction of a drive device of a steam flow control valve used for controlling the rotation speed of a steam turbine in a power generation plant and ensures safe control. It is.

The present invention is suitable for control that detects abnormal rotation by a control valve of a control device in which a steam flow control valve with a dead zone rotates a rotating body to generate a desired driving force, and at the same time automatically corrects the amount of the dead zone. As an example, the rotation speed control of steam turbines installed in thermal and nuclear power plants will be discussed below. Figure 1 shows the steam flow control valve MSV (hereinafter simply referred to as control valve) and the steam engine driven by it (
(hereinafter referred to as a turbine). Steam 1 is supplied from a steam generator through piping, and this steam passes through a control valve 2.
It drives the turbine 5 and generates rotational force.

This steam passes through the control valve 2, drives the turbine 5, and generates rotational force. This control valve 2 is driven by a hydraulic piston 3 via an arm 51 driven by an electric motor 50. This piston is driven by the pressure of oil supplied through the oil control pipe 4. The control valve 2 driven by this oil has an unsteady zone, so the rotational force of the turbine 5 is not affected until the control valve 2 is fully closed to the position where the control valve 2 begins to open and steam begins to flow (referred to as the opening point). cannot be born. This relationship is shown in Figure 2. In FIG. 2, the vertical axis represents the fluid flow rate Q, and the horizontal axis represents the control valve lift X. In FIG. 2, below 1, the flow rate of steam 1 is 0, and above 12, the flow rate is saturated. When such a control valve 2 is adopted in a control device as shown in FIG. 3, the pressure switch PS shown in FIG.
6 (hereinafter simply referred to as PS6), open loop control is performed by a dedicated device 7 until the opening start point is detected by PS6. P.S.
6 is activated, the feedback shown in FIG. 3 begins. Until the PS 6 operates in the MSV drive device 21, it is sufficient to provide a constant drive amount using the dedicated device 7. However, in this control method, if there is a deviation in the operation of the PS6, that is, a deviation in the setting of the operating point or a delay in operation due to a failure, the control valve 2 will open excessively.
The turbine 5 is rapidly accelerated, causing vibrations and friction between the casing and the blades, which may damage the drive blades of the turbine 5.

It is an object of the present invention to provide a control valve opening detection device that can prevent such risks and perform stable control.

The details are described below.

In FIG. 3, the head x of the control valve 2 and the measured variable to be controlled (for example, the turbine speed) y are transmitted to the closed-loop control device 8. If the controlled object is not an integral characteristic, there is no particular risk of overspeeding, so it is assumed that the object is an integral characteristic. The operation of a controlled object having this type of integral characteristic can be expressed as follows. Here, X is the head of the control valve 2, y is the rotational speed which is the target measurement quantity, t is the total drive time of the control valve 2, t1 is the drive time until the control valve 2 starts to open, and α is the control valve 2 , and T is the time constant of the controlled object.

Now, from equations (1) and (2), in order to calculate the lift formula when the control valve 2 starts to open, the value before the rotation speed y reaches the critical speed after the control valve 2 opens, for example, the acceleration start point. Think about the point in time when you reach Y2. At this time, equation (2) can be derived. Here!
is the drive time of the control valve 2 up to the acceleration start point Y2. (
By modifying equation 3) and substituting it for equation (1), the lift height X2 when the control valve 2 begins to open can be calculated.

In addition, equation (5) is the lift height αT2 when the rotation speed reaches Y2.
Since control valve 2 begins to open, the rotation speed increases by Y2 minutes. The lift amount J of control valve 2 required to increase the speed? ■ Subtracting whether or not, what is the lift height of control valve 2 when it starts to open? It means to calculate.

By comparing X2 obtained in this way with the actual lift amount X1 at the time when PS6 operates, it is possible to predict the deviation in operation of PS6.

The following calculation is performed based on this comparison result, taking into account the differential of the rotational speed y (acceleration of the turbine 5). The operation is performed according to the set value of the control target setter 11 of the turbine 5 which is the controlled object in FIG. Ba, P
Assuming that there is no deviation in the operation of S6, the actual lift amount X1 is set as the start of the control valve opening.

Here, ar is the differential operator, and ε1 is the permissible acceleration deviation). On the other hand, in the case of
and X2, and perform the control again. The details of the device for detecting the start of opening of the control valve 2 will be explained with reference to the block diagram shown in FIG.

When the turbine 5 is started up, the dedicated device 7 performs the control valve opening operation through open loop control until the PS 6 is activated.
At this time, the contacts 51 and 55 are closed, and the contact 52 is open, and the lift amount of the valve is updated in the memory 46 from time to time. When PS6 operates, contact 51 opens and contact 52 closes, switching to closed loop control by closed loop control device 8. Further, by opening the contact 55, the lift amount at the time of PS6 operation is stored in the memory. On the other hand, calculation device 3
1, the time constant T1 is input from the turbine time constant T setter 32, the control start command a from the closed loop control device 8, the controlled object measurement signal, that is, the rotation speed y, and when the rotation speed reaches Y2, the equation (4 ) to calculate the lift amount X2.

This lift amount formula and the lift amount X1 during PS6 operation are input to the low value priority circuit 33 and the deviation calculator 34. Deviation calculator 34
Then, the lift amount X1 during PS6 operation is compared with the lift amount X2 calculated by equation (4), and if the deviation is large, the large lift deviation signal d is turned on. Further, the outputs of the differential circuit 36 for the rotational speed y of the turbine 5 and the setter 37 for the tolerance E1 are output from the comparator 38.
is input, and if these are equal or the value of the differentiating circuit 36 becomes large, an acceleration rate deviation large signal C is output.

The AND circuit 35 with hold receives the large head deviation signal d and the large acceleration rate deviation signal C, and if these AND conditions are met, that is, both the lift height deviation and the acceleration rate deviation are large, it is assumed that there is an abnormality in the operation of the PS6, and the valve is closed. Outputs a closed signal (XX).

When this signal is output, the contact 53 closes and the control valve 2
The valve closing signal from the closing operator 41 is sent to the MSV drive device 2.
1, and the valve is closed. By closing the valve, the lift amount gradually decreases, and this causes the low value priority circuit 33
The lift amount X1 during PS6 operation selected by and the lift amount calculated by equation (4)! When the smaller of the two values is reached, the comparator 39 outputs the close command reset signal b, and the valve close signal (XX) is turned off. At the same time, comparator 39
By outputting a closed loop control device reset signal (x), the contact 56 is closed so that the control balance signal e is sent from the control device balancer 42 to the closed loop control device 8. The closed loop control device receives this signal and starts closed loop control from the opening point again. In addition, the close command reset signal b is ANDed via the delay circuit 45.
Since it is sent to the circuit, the valve close signal (xx) is turned off after a while after the closed loop reset signal (x) is turned on, and the contact 57 is opened and the control balance signal e is turned on in a pulsed manner. Then, the closed-loop controller 8 enters closed-loop control.

Further, when performing this balance, an alarm may be generated by a (XX) signal. Further, in the above case, the following may be used. (1) Integrating circuit 36, setting device 37, comparator 38
Prepare another set and increase the setting on the setting device 37 to the mechanically permissible value.

In this case, if the differential value becomes even larger than the setting value of the setting device 37, it is possible to close the control valve directly from the closing device 41. This means machine protection. (2) When detecting the point at which the control valve 2 starts to open while the control valve 2 is in the closed state and the controlled object measurement signal y is falling, the following procedure is performed.

During the descent, the moat becomes 0? -Therefore, ,t-0
y (this is referred to as y1) is stored.

Using this y1 and using the same concept as equation (4), the lift amount equation at the beginning of opening of the control valve 2 can be calculated using the following equation.

Here, αT2 is the head when the rotation speed reaches Y2, and α is the head when the control valve 2 starts to open.
It means the increase in the lift amount of the control valve 2 during the speed increase from the rotational speed y1 at the time when the rotational speed reaches Y2.

To realize this function, a differentiating circuit 3 is used as shown in Figure 6.
6 with a zero detector 47 added? = o, a zero detection signal Y is output to the arithmetic unit 31, and the arithmetic unit 31 calculates j based on the above equation (5), setting the rotation speed at the time when this signal turns on as y1. You can just do the calculations. In particular, the above invention does not rely only on mechanical detection by the PS6, but also directly measures the amount of change in the controlled object, thereby suppressing malfunctions and excessive operations due to PS6 failures and mechanical deviations, and preventing both of these. This has the effect of backing up control operations by comparing and checking detected amounts.

Although the embodiments of the present invention are applied to a steam turbine in a power generation plant, the present invention is generally applicable to a control system having a dead zone.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining the principle of the drive mechanism of the control valve, Fig. 2 is a correlation diagram of fluid flow rate with respect to the lift of the control valve,
Fig. 3 is a block diagram showing a conventional control system, Fig. 4 is a correlation diagram showing control valve characteristics and characteristics of a controlled object, and Fig. 5 is a block diagram showing a control system of a control valve opening start detecting device according to the present invention. 6 are block diagrams showing another embodiment.

Claims (1)

[Claims] 1. In a steam plant where the rotational speed of a steam prime mover is controlled by a control valve, a detector for detecting the actual head of the control valve and a head of the control valve determined based on the characteristics and rotational speed of the steam prime mover. a calculation device; a deviation calculation unit that calculates a deviation between the lift amount and the actual lift amount and outputs a closing command for the control valve when the deviation exceeds a certain value; a comparator that detects excessive opening of the control valve and outputs a command to close the control valve, and compares the smaller of the actual lift amount and the lift amount with the actual lift amount obtained here. A control valve opening start detection device comprising: a comparator that outputs a reset signal for the closing command when the deviation is smaller than a certain value.