JPS6120683B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a so-called automatic turbine startup device for automatically speeding up a steam turbine of a thermal power plant from a stopped state or from a certain rotational speed to a rated rotational speed. FIG. 1 shows a conceptual diagram of automatic turbine control by an automatic turbine starting device. 1 is a steam turbine, and 2 is a regulating valve for adjusting the amount of steam flowing into the steam turbine. 3 is a rotational speed command value setting device. 4 is a change rate creation unit for changing the set value of 3 according to a certain change rate. 5 is an adder (subtractor). Reference numeral 6 denotes a regulating valve drive unit for opening and closing the regulating valve 2 according to the polarity and magnitude of input. 7 is a rotation speed detector for detecting the actual value of the rotation speed of the steam turbine 1. Reference numeral 8 denotes an opening degree detector that detects the actual opening degree of the regulating valve 2. 9 is a differentiator, and 10 is an adder. To briefly describe the operation of such a control system, the rotational speed setting value set by the rotational speed command value setting device 3 is gradually changed at a certain rate of change by the rate of change generator 4, and finally becomes a signal that reaches the rotation speed set value, and is subtracted from the actual rotation speed by an adder (subtractor). If the difference is positive, the adjustment valve drive unit 6 opens the adjustment valve 2. If the polarity is negative, it is driven in the closing direction. Therefore, the amount of steam flowing into the steam turbine 1 is increased or decreased, and the rotation of the steam turbine increases while being automatically controlled according to the rate of change created by the rate of change generator. However, what we need to consider here is the delay in the control system, and the one that is particularly problematic is the steam turbine 1.
This is a delay in the response itself, and in the case of commercial thermal power plants, the response delay is 5 to 10 seconds or more. As a means of correcting this delay in response, a method of predicting changes in rotational speed from the movement of the regulating valve 2 is often used. A specific example of this is the opening detector 8 of the regulating valve 2 shown in FIG. 1 and the differentiator 9 for detecting the amount of change in the opening. By adding the output of the differentiator 9, that is, the amount of change in rotational speed predicted from the amount of change in the opening degree of the regulating valve 2, to the actual value of the rotational speed, the addition point (subtraction point) with the rotational speed change command value is It appears that the rotational speed responded to the apparent speed. As a result, there is almost no delay in the response of the control system, resulting in better control. When there is a significant response delay in the control system as described above, a method of correcting the response delay of the controlled system from a responsive operating point is generally called a disturbance prevention circuit. Further, the output obtained by adding the differential value of the actual rotational speed and the adjustment valve opening degree is used for adjusting the initial value of the rate of change creation section 4 before the start of speed increase. This is indispensable when starting automatic control from an intermediate rotational speed or when increasing the speed again after a love check or rundown, and this initial value adjustment circuit is generally called a command value tracking circuit. Since the command value tracking circuit is always utilized except during automatic speed increase, the output of the rate of change generator 4 is always the same value as the actual rotation speed (the value to which the differential value of the opening degree of the regulating valve is added). . The rate of change generator 4 changes the set value at a certain rate of change, and when the rotational speed command signal V _R output from the rate of change generator approaches the set value V _S set by the rotational speed command value setter 3. It has a function that gradually reduces the rate of change. This is to prevent the rotational speed of the steam turbine from exceeding the target value, so-called overshoot. A typical example of this rate of change creation section 4 will be explained with reference to FIG. In FIG. 2, 41 is an amplifier, which has a gain of several tens to a hundred times. A limiter 42 limits the output so that it does not exceed a certain value. As mentioned above, 43 is a contact point for switching between automatic speed increase and the command value tracking circuit, and is connected to the output side of limiter 42 during automatic speed increase.
44 is an integrator whose output is the rotational speed command V
It becomes _R. The integration time constant of this integrator 44 is long during automatic speed increase, and is extremely short during command value tracking. Further, 45 and 46 are adders (subtractors). Here, when command value tracking is performed, that is, when the integrator input is connected to the adder 46, the integrator 44 input is V _O -V _R , and when V _O > V _R , the integrator integrates in the positive direction. Integration is stopped when _O = V _R , that is, V _O -V _R =0. Further, in the case of V _O <V _R , integration is performed in the negative direction, and the integration is stopped when V _O =V _R as well. Since this is done in an extremely short time, it can be considered that V _R =V _O at all times. That is, the integrator output V _R is always V _O . Furthermore, when the speed is automatically increased, that is, when the integrator input is connected to the limiter 42, the following occurs. The integrator input becomes the value set by the limiter 42 at most. For example, the integration time constant of the integrator 44 is 1
If the set value of the limiter is V _L , then when the input to the limiter 42 is greater than V _L , the limiter output is always V _L regardless of the magnitude of the input, so the output of the integrator 44 is V _L /min. changes at a rate of change. Also, when the limiter input becomes smaller than V _L , the integrator changes at a rate corresponding to the input at that time. Now, if we set V _S = 3000 rpm in the state of V _R = 0, the output of the adder 45 will be 3000 rpm and will be amplified by the amplifier 41, and the output of the amplifier 41 will be K ₄₁
×3000rpm. (K ₄₁ is the gain of the amplifier 41), where the set value of the limiter 42 V _L = 100 rpm
Then, K ₄₁ × 3000 rpm is clearly larger than V _L , so the limiter output becomes 100 rpm, which becomes the integrator input, and the integrator increases at a rate of change of 100 rpm/min. If the operation is continued as it is, the integrator output will gradually increase and V _R will approach V _S . Therefore, the output of adder 45 gradually approaches zero. Eventually, the input to the limiter 42 begins to become smaller than the V _L setting value of 100 rpm. In this way, since the integration operation is performed while gradually approaching zero, the rate of change in the integrator output V _R gradually decreases. The operation of such a circuit is so-called first-order lag, and when expressed as a transfer function,

[Formula] becomes. In this way, the rate of change creation section has two types of movements, and the changes are shown in FIG. In this way, when the integrator output, that is, the rotational speed command value V _R approaches the rotational speed set value V _S , the purpose of slowing down the rotational speed change rate is to control the rotational speed control system shown in Figure 1. This is to prevent the rotation speed of the steam turbine from overshooting the set rotation speed. The amount of overshoot increases as the rate of change increases, and decreases as the rate of change decreases. Therefore, the rotation speed command V _R is the rotation speed set value V _S
If it approaches , overshoot can be prevented by continuously decreasing the rate of change of the rotational speed command value _VR . The above is an overview of the operation of the steam turbine automatic starting device, and as explained above, it is possible to set the rate of change in several types in the actual device. This is to achieve a rate of change in rotational speed suitable for suppressing thermal stress in the steam turbine. Figure 4 shows the movements of several types of change rates.As can be seen in Figure 4, the rotation speed command value _V It can be seen that the time it takes to reach the command value V _S becomes abnormally long.The set value is reached only after a considerable amount of time has passed when the rotation speed would normally have been reached at the predetermined rate of change. This becomes more noticeable as the rate of change setting value is lower.Therefore, it is possible to consider setting the point above where the rotational speed command value V _R starts the first-order lag operation, but in this case, the rate of change becomes If the setting is too large, overshoot will occur.In conventional steam turbine starter systems, settings are made to choose between the two, or to take an intermediate setting between the two.In other words, overshoot occurs. In other words, it takes an unnecessarily long time to increase the rotational speed to the target value.This is a matter of concern in view of recent technological advances.The purpose of the present invention is to solve the above-mentioned problems. The main point of the present invention is that when the rate of change setting is large, the point at which the change in the rotational speed command begins to operate with a first-order lag is set large, and when the rate of change setting is small, the point at which the change in the rotational speed command starts to operate with a first-order lag is set to a large value. This is to keep the rotational speed command V _R small.
Focusing on the fact that the point at which the operation shifts to first-order lag operation is V _R -V _L /K ₄₁ , this can be realized by switching the gain K ₄₁ of the amplifier by setting the rate of change. Incidentally, V _L is a set value of the limiter 42 and can be switched by setting the rate of change. Specifically, as shown in FIG. 5, the gain of the amplifier 41 is switched by setting the rate of change. By doing this, the gain of the operational amplifier is
K ₄₁ can be switched. Reference numeral 50 denotes a changeover switch for changing the conversion rate setting, and the switch for changing the limit value of the limiter 42 has been conventionally used. According to the present invention, the gain of the amplifier 41 is switched. For convenience, the gain by changing the rate of change setting of the amplifier 41 is set to K.
_A , K _B , K _C ..., then K _A = R _A /R, K _B = R _B /
R, K _C = R _C /R, ... and K _A > K _B > K _C ..., the point at which the rotational speed command V _R shifts to the first-order lag is V _R - V _L /K _A <V _R -V _L /K _B <V _R -V _L
/K _C ..., and it can be seen that the larger the gain of the amplifier 41 is, the closer the point to the first-order lag is to the rotational speed set value. Therefore, when the rate of change is at the minimum setting, the gain of the amplifier 41 is K _A
As the rate of change becomes larger, K _B becomes larger.
In the case of K _C , as the setting of the rate of change increases, the point at which the change in the rotational speed command value V _R shifts to first-order lag moves downward. This situation is shown in FIG. The solid line is the minimum setting of the rate of change, and the point at which it shifts to first-order lag is the uppermost point. By doing this, overshoot can be prevented for each changed rate of change, and the time required to reach the rotational speed set value can also be minimized. As an embodiment of the present invention, the case where the rate of change setting is switched stepwise for convenience has been described above, but of course, even when the rate of change setting is a stepless continuous setting, the gain of the amplifier 41 can be changed continuously in the same way. It is possible. (The method of making the amplifier gain continuously variable is already generally known, so it will be omitted.)

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the control of the steam turbine automatic starting device, Fig. 2 is a diagram showing an example of the inside of the rate-of-change creating unit, Fig. 3 is a diagram showing the operation of the rate-of-change creating unit, and Fig. 4 is a diagram showing the operation of the rate-of-change creating unit.
The figure shows the operation of the conventional rate of change creation unit for several types of rate of change, Figure 5 shows an example of the improvements made by the present invention, and Figure 6 shows the changes resulting from the improvements made by the present invention. It is a figure showing the characteristic of rate. 1...Steam turbine, 2...(steam) regulating valve,
3... Rotation speed command value setter, 4... Change rate creation section, 5... Adder (subtractor), 6... Adjustment valve drive section, 7... Rotation speed detection section, 8... (Adjustment valve ) Opening degree detector, 9... Differentiator, 10... Adder, 41
... Amplifier, 42 ... Limiter, 43 ... Automatic speed increase/command value tracking switching contact, 44 ... Integrator, 45 ... Adder (subtractor), 46 ... Adder (subtractor), V _S ...Setting value of rotation speed command value setter 3, V _O ...Control system fieldback value (actual rotation speed + adjustment valve opening degree differential value), V _R ...Rotation speed command value (change rate creation part output), V _L ...set value of limiter 42, _K41 ...gain of amplifier 41,
R, R _A , R _B , R _O ...... operational resistance of the amplifier 41,
50...Change rate setting switch.

Claims (1)

[Claims] 1. In an automatic starting device for a steam turbine that allows selection of several types of rate of change in the process of automatically increasing the speed of a steam turbine in a power plant to a target value, and is equipped with a circuit to prevent overshoot of the rotation speed relative to the target value. An automatic steam turbine starting device characterized in that a plurality of overshoot prevention circuits are provided and the circuits are switched according to the selection of the rate of change setting.