JPH07174066A - Speed governing controller for water turbine - Google Patents

Abstract

PURPOSE:To dissolve the trouble that the opening degree instruction which is to be fixed at a load restriction value operates in an unstable manner, when the water turbine revolution speed signal or the guide blade opening degree signal varies, by restricting the integrated signal so as to be less than the load restriction value, at least during the load restricted operation. CONSTITUTION:The revolution speed of a water turbine is detected by a detection part 1, and the detection speed and the set speed are compared by a comparison part 2, and the speed reduction rate corresponding to the speed difference signal is set by a set part 5. While, the opening degree of a guide blade is detected by a detection part 3, and the detected opening degree and the set opening degree are compared in a comparison part 4, and the opening degree deviation is calculated in a calculation part 6. Further, the proportion, integration and differentiation of the opening degree deviation are calculated in each calculation part 7-9, and the result are added in an additional calculation part 10, and the PID signal is outputted. Further, the less value between the PID signal and the load restriction value is selected by a load restriction part 11, and outputted as opening degree instruction. Further, during the load restriction operation, the integration signal is restricted by an integration restriction part 15 so that the integration signal become less than the load restriction value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for a water turbine installed in a hydroelectric power plant.

[0002]

2. Description of the Related Art Generally, a speed control device for a hydraulic turbine is used for controlling the hydraulic turbine in a hydraulic power plant. Such a speed governor control device for a water turbine controls the rotational speed so that the rotational speed matches the speed setting value when the water turbine generator is disconnected from the power system. When operated in parallel with, it controls the opening of the guide vanes of the water turbine generator to match the load limit value and has a speed regulation rate or speed droop rate characteristic according to the frequency change of the power system. .

FIG. 5 shows the structure of a conventional speed governor control device for a water turbine. The speed detecting unit 1 detects a rotational speed FT of a hydraulic power generator (not shown) and a speed signal F proportional to the rotational speed FT. The speed comparison section 2 compares the speed signal F with the speed setting signal FR and outputs the speed deviation signal FD. The droop rate setting unit 5 multiplies the speed deviation signal FD by the reciprocal of the speed droop rate, and outputs it as a speed droop signal FP.

On the other hand, the opening detection unit 3 detects the guide blade opening GVT of the water turbine and outputs a guide blade opening signal GV proportional to the guide blade opening GVT, and the guide blade opening comparison unit 4
Outputs a guide blade opening deviation signal GVD by comparing the guide blade opening signal GV with the opening setting signal GVR.

The speed drooping signal FP and the guide vane opening deviation signal GVD are added by an opening deviation calculating unit 6 including an adder, and the opening deviation signal GD is calculated as a proportional calculating unit 7 and an integral calculating unit 8. It is output to the differential operation section 9.

The proportional calculator 7 multiplies the opening deviation signal GD by a proportional gain and outputs a proportional signal P. Further, the integral calculation unit 8 integrates the opening deviation signal GD and outputs an integral signal I. Further, the differential operation section 9 determines that the opening deviation signal GD
Is differentiated and a differential signal D is output.

The proportional signal P, the integral signal I, and the differential signal D are added in the adding section 10 and output to the load limiting section 11 as a (PID) signal PID. The load limiter 11 compares the signal PID with the load limit value PR and outputs a low value as the opening degree command GR. When the signal PID is larger than the load limit value PR, the load limit operation signal PD is output.

The opening comparison unit 12 compares the opening command GR with the guide blade opening signal GV and compares the guide blade operation signal GC.
Is output, and a servo motor (not shown) is driven according to the guide blade operation signal GC to drive the guide blades of the water turbine.

Further, the integral follow-up calculator 13 subtracts the proportional signal P and the differential signal D from the load limit value PR and outputs it as an integral follow-up signal IF. The integration tracking signal IF is replaced by the integration signal I by the integration signal switching unit 14 when the load limiting operation signal PD is output.

The operation of the speed governor control device for a water turbine constructed in this way will be described below, taking as an example the case where the water turbine generator is operating in parallel with the power system. The integration calculation unit 8 constantly causes the addition result of the speed droop signal FP and the guide blade opening deviation signal GVD, that is, the opening deviation signal GD, to be zero, and the opening command GR and the guide blade opening signal GV are They coincide with each other, and the guide blade operation signal GC is also zero.

In such a steady state, when the frequency of the electric power system, that is, the rotational speed FT of the water turbine generator increases, the speed deviation signal FD decreases, and the opening deviation signal GD shows a negative value accordingly.

Then, the proportional operation unit 7, the integral operation unit 8, and the differential operation unit 9 perform the PID operation of the opening deviation signal GD to reduce the opening command GR, so that the guide blade operation signal GC is reduced.
Becomes a negative value, and the opening command GR and the guide blade opening signal GV
The guide vane opening GVT is reduced until the two coincide with each other, and set at the point where the opening deviation signal GD becomes zero.

At this time, the reduction amount of the guide vane opening GVT is
It becomes equal to the value obtained by multiplying the change amount of the rotation speed FT by the reciprocal of the speed droop rate. On the other hand, in the speed control device of the water turbine, the guide blade opening GVT is controlled independently of the rotation speed FT, in addition to the speed droop rate operation in which the guide blade opening GVT is controlled by the function of the rotation speed FT as described above. It has a load control operation function.

That is, when the load limit value PR is made lower than the sum of the guide blade opening deviation signal GVD and the speed droop signal FP, the opening deviation signal GD becomes a positive value and the signal PID tries to increase. By the action of the load limiter 11, the opening degree command GR has the same value as the load limit value PR,
The guide vane opening GVT can be controlled regardless of the rotation speed FT.

In this state, the opening deviation signal G having a positive value
When the PID calculation of D is continued, the integrated signal I continues to increase,
As a result, the values of the integrated signal I and the signal PID go overshoot. In this way, if the integral signal I and the signal PID are overshooted, the integral signal I and the signal PID become appropriate values, that is, the values of the guide blade opening signal GV when the load limiting operation is changed to the speed drooping operation. It takes a long time to get back.

Further, when a load cutoff occurs in which the turbine generator is disconnected from the power system and the rotation speed FT sharply increases,
If the integrated signal I and the signal PID are overshooting, the closing of the guide blade opening GVT will be delayed, and the ability to suppress the increase of the rotation speed FT will be seriously affected. In order to prevent the integral signal I from overshooting, the integral tracking signal calculation unit 13 calculates the integral tracking signal IF by subtracting the proportional signal P and the differential signal D from the load limit value PR, and integrates the integral signal I during the load limiting operation. By replacing the tracking signal IF with the signal PID
Is made to follow the same value as the load limit value PR.

FIG. 6 is a waveform diagram showing the operation when the opening degree setting signal GVR is changed during the load limiting operation of the water turbine. As shown in the figure, when the opening setting signal GVR is reduced during the load limiting operation within a range not lower than the load limiting value PR, the opening deviation signal GD decreases and the sum of the proportional signal P and the differential signal D ( P + D) also decreases.

At this time, the integral signal switching unit 14 integrates the integral signal I so that the signal PID becomes the same value as the load limit value PR.
Is replaced by the integration tracking signal IF, but the proportional signal P
Even if the sum (P + D) of the differential signal D and the abrupt decrease, the integrated signal I does not abruptly increase, so the signal PID falls below the load limit value PR. Since the opening degree deviation signal GD has a positive value, the integration signal I is calculated by the integration calculation unit 8 as the signal PID.
Increases until it becomes equal to the value of the load limit value PR. During this time, the opening degree command GR becomes smaller than the load limit value PR even during the load limit operation.

Further, during the load limiting operation, the opening setting signal GV
When R is increased, the opening deviation signal GD increases and the sum (P + D) of the proportional signal P and the differential signal D also increases. This time,
The integrated signal I replaces the integrated signal tracking signal IF and decreases so that the signal PID becomes the same value as the load limit value PR. Then, when there is no change in the increasing direction of the opening degree setting signal GVR, the sum (P + D) of the proportional signal P and the differential signal D decreases by the differential signal D.

At this time, the integral signal switching unit 14 integrates the integral signal I so that the signal PID becomes the same value as the load limit value PR.
Is replaced by the integration tracking signal IF, but the proportional signal P
Even if the sum (P + D) of the differential signal D and the abrupt decrease, the integrated signal I does not abruptly increase, so the signal PID falls below the load limit value PR. Then, since the opening degree deviation signal GD has a positive value, the integral calculation unit 8 increases the integral signal I until the PID signal PID becomes equal to the load limit value PR. During this time, the opening degree command GR becomes smaller than the load limit value PR even during the load limit operation.

The opening deviation signal G during such a load limiting operation
The fluctuation of D is also seen by the fluctuation of the speed signal F and the guide blade opening signal GV, or the operation of the speed setting signal FR, and the opening command GR operates unstable like the above.

Next, a conventional control for parallelizing the system will be described. Generally, when paralleling to the system, the frequency setter is adjusted by the increase / decrease signal from the automatic synchronizer so that the system frequency and the rotational speed of the turbine are equal, the servo motor opening is adjusted and the desired rotational speed is adjusted. Control, and after paralleling, the output of the frequency setter is the specified value (rated frequency).
Runback control is performed with the normal time constant of the frequency setter.

FIG. 7 shows the structure of a conventional speed governor control device for a water turbine of this type. As shown in the figure, in the conventional speed governor control device for a water turbine, the output of the speed detection unit 21 and the frequency setting unit 2
The deviation from the output of No. 3 is calculated by the speed comparison unit 22 to obtain the speed deviation signal. Further, the load comparing unit 30 calculates a deviation between the output of the position detecting unit 29 and the output of the load setting unit 31,
The obtained load deviation signal is multiplied by the drooping rate setting device 32 to obtain the drooping load deviation signal.

The drooping load deviation signal is input to the control deviation signal calculating section 24 composed of an adder via the contact 33, and added with the speed deviation signal to obtain the control deviation signal. The signal is input to the PID calculator 25. The PID calculator 25 performs proportional, integral, and derivative calculations on the control deviation signal to obtain an opening command signal. Then, the opening deviation signal calculating unit 26 obtains an opening deviation signal which is a deviation between the opening command signal and the opening signal detected by the position detecting unit 29, and the opening deviation signal is electrically converted. / Servo motor 28 via mechanical conversion unit 27
To control the servo motor opening.

However, when such a speed governor control device for a water turbine is used, in a power plant where the start / stop is frequently performed and the difference between the rotational speed of the water turbine and the output of the frequency setting unit 23 immediately after being paralleled is large, There is a problem that the servomotor 28 is suddenly closed or suddenly opened due to the difference between the rotational speed of the water turbine and the output of the frequency setting unit 23 immediately after the parallel arrangement.

In particular, in the case of "turbine speed> output of frequency setting section 23", the servo motor 28 is suddenly closed, causing motoring. After that, the frequency setting section 2
Since the output of No. 3 is run back by the normal time constant of the frequency setting unit 23 so that it becomes the specified value (rated frequency), after paralleling, it is run back and the difference between the output of the frequency setting unit 23 and the turbine rotational speed is small. Until then, the motoring continued, and after being paralleled, there was a problem that load fluctuations were given to the system or the hydraulic machine was adversely affected.

[0027]

As described above, in the conventional speed governor control device for a water turbine, the opening deviation is caused by the fluctuation of the speed signal or the guide blade opening signal or the operation of the speed setting signal or the opening setting signal. When the signal changes, the problem that the opening command that should be fixed to the value of the load limit value operates unstable,
After paralleling, there was a problem that load fluctuations were given to the system and the hydraulic machine was adversely affected.

The present invention has been made in consideration of such a conventional situation, and an object of the present invention is to provide a speed control device for a water turbine which can perform more stable control than the conventional one.

[0029]

According to another aspect of the present invention, there is provided a speed control device for a water turbine, which includes a speed detection unit for detecting a rotational speed of the water turbine and outputting a speed signal, a speed setting signal and the speed signal. And a speed comparison unit that outputs a speed deviation signal, a speed drooping rate setting unit that outputs a speed drooping signal corresponding to the speed deviation signal, and a guide blade opening degree and outputs an opening degree signal. An opening detection unit, a guide blade opening comparison unit that compares the opening setting signal and the opening signal and outputs a guide blade opening deviation signal, the speed droop signal, and the guide blade opening deviation signal An opening degree deviation calculating section that outputs an opening degree deviation signal by adding the following, a proportional calculating section that outputs a proportional signal of the opening degree deviation signal, and an integral calculating section that outputs an integral signal of the opening degree deviation signal. , A differential operation section that outputs a differential signal of the opening deviation signal, and the proportional An adder for outputting a PID signal by adding the integrated signal and said differential signal and No., the PID
The load limiter that selects the lower one of the signal and the load limit value and outputs it as the opening command, compares the opening command and the opening signal, and outputs the guide blade operation signal. And an integration limiting unit that limits the integrated signal to be equal to or less than the load limiting value at least during the load limiting operation.

According to a second aspect of the present invention, there is provided a speed control device for a water turbine, which includes a speed detecting unit for detecting a rotational speed of the water turbine and outputting a speed signal, and a speed for adjusting the rotational speed of the water turbine. A frequency setting unit that outputs a command signal, a position detection unit that detects the opening degree of the servo motor that operates the guide vanes, and outputs an opening signal, and a load that outputs a load command signal for adjusting the output of the turbine. A setting unit, a speed comparing unit that outputs a speed deviation signal corresponding to the deviation between the speed signal and the speed command signal, and a load deviation signal corresponding to the deviation between the opening signal and the load command signal A load comparison unit, a droop rate setting unit that multiplies the load deviation signal by a drooping characteristic and outputs the drooping load deviation signal, and the speed deviation signal,
A control deviation signal calculation unit that adds the drooping load deviation signal and outputs the control deviation signal; As the signal for operating the servo motor opening, the opening instruction signal, and an opening deviation signal calculation unit that outputs an opening deviation signal according to the deviation between the opening signal, and a parallel condition, When a condition that the absolute value of the speed deviation signal is equal to or greater than a predetermined value is satisfied, a switching unit that switches the time constant of the frequency setting unit from the normal time constant to the runback time constant is provided.

Further, in the speed control device for a water turbine according to a third aspect of the present invention, there is provided a speed detection unit for detecting the rotational speed of the water turbine and outputting a speed signal, and a speed for adjusting the rotational speed of the water turbine. A frequency setting unit that outputs a command signal, a position detection unit that detects the opening degree of the servo motor that operates the guide vanes, and outputs an opening signal, and a load that outputs a load command signal for adjusting the output of the turbine. A setting unit, a speed comparing unit that outputs a speed deviation signal corresponding to the deviation between the speed signal and the speed command signal, and a load deviation signal corresponding to the deviation between the opening signal and the load command signal A load comparing unit, a drooping rate setting unit that multiplies the load deviation signal by a drooping characteristic and outputs the drooping load deviation signal, the speed deviation signal, and the drooping load deviation signal, and a control deviation Control output as a signal A difference signal calculation unit, a PID calculation unit that performs proportional, integral, and differential calculations on the control deviation signal and outputs it as an opening command signal, and the opening command as a signal for operating the servo motor opening. Signal, and an opening deviation signal calculation unit that outputs an opening deviation signal according to the deviation between the opening signal, the parallel condition, and the condition that the absolute value of the speed deviation signal is a predetermined value or more And means for replacing the output of the frequency setting unit with the speed signal from the speed detecting unit.

[0032]

In the speed control device for a water turbine according to the first aspect of the present invention having the above-described structure, the fluctuation of the input of the speed signal or the guide blade opening signal or the speed setting signal or the opening setting signal during the load limiting operation. Even if the opening deviation signal changes due to the operation, the opening command can be stably output. Therefore, more stable control can be performed as compared with the conventional case.

Further, in the speed control device for a water turbine according to the present invention having the above-mentioned structure, it is possible to shorten the time from immediately after the parallel operation until the output of the frequency setting section is run back to the specified value. The load fluctuation immediately after the parallel connection can be reduced, and the adverse effect on the hydraulic machine can be suppressed. Therefore, more stable control can be performed as compared with the conventional case.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the speed control device for a water turbine according to the present invention. The same parts as those of the conventional speed control device for a water turbine shown in FIG. 5 are designated by the same reference numerals. . As shown in the figure, in this speed control device for a water turbine, the integral calculating unit 8 is provided with an integral limiting unit 15 so that the integral calculating result of the integral calculating unit 8 does not exceed the load limit value PR. Is configured to output the integrated signal I.

FIG. 2 is a waveform diagram showing an operation when the opening degree setting signal GVR is changed during the load limiting operation in the speed governor control device for a water turbine having the above-mentioned configuration. When the turbine is in the load limiting operation, the load limiter 11 limits the opening degree command GR to the load limit value PR, so that the guide blade opening degree signal GV becomes equal to or lower than the opening degree setting signal GVR, and the opening degree deviation signal GD. Is a positive value. In this state, the integral calculating unit 8 always tries to increase the integral signal I, but the integral limiting unit 15 limits the integral signal I to the load limit value PR.

Since the opening deviation signal GD is always a positive value during the load limiting operation of the water turbine, the integral signal I indicates the load limiting value P.
Limited to the value of R, the sum of the proportional signal P and the differential signal D (P +
D) also has a positive value. In this state, be sure to use the signal P
Since the ID becomes a value equal to or larger than the load limit value PR, the opening command GR becomes the same value as the load limit value PR by the action of the load limiter 11.

Even when the opening degree setting signal GVR is increased or decreased during the load limiting operation within a range that does not fall below the load limiting value PR,
Since the opening degree deviation signal GD is a positive value, the signal PID is always a value equal to or greater than the load limit value PR, so the load limiter 11
By the action of, the opening degree command GR is stably limited to the load limit value PR.

As described above, in the speed control device for a water turbine of this embodiment, the opening command GR can be stably limited to the load limit value PR even if the opening setting signal GVR is changed during the load limiting operation. Further, the opening deviation signal GD due to the fluctuation of the speed signal F or the guide blade opening signal GV or the operation of the speed setting signal FR.
Similarly, the opening degree command GR can be stably limited with respect to the change of.

In the above embodiment, the case where the integral signal I is always limited to the load limit value PR or less has been described, but the integral signal I may be limited only during the load limiting operation. .

FIG. 3 shows the structure of a speed control device for a water turbine according to another embodiment of the present invention. The same parts as those of the conventional speed control device for a water turbine shown in FIG. It is attached. As shown in the figure, the speed control device for a water turbine of this embodiment is provided with a frequency setter time constant switching circuit 34 and a switching contact 35.

The frequency setter time constant switching circuit 34 is shown in FIG.
As shown in, the speed deviation signal output from the speed comparison unit 22 is taken in, the absolute value of the speed deviation signal is obtained by the absolute value 51, and whether or not the absolute value of this speed deviation signal is large enough to cause load fluctuation. It is determined by the speed deviation determiner 52. Then, the drive relay 54 is driven by the signal obtained by the logical product 53 of the determination result that the load fluctuation is given and the parallel condition, the switching contact 35 is switched, and the frequency setting unit 23
The time constant of is switched from the normal time constant to the runback time constant.

According to the present embodiment, when the absolute value of the speed deviation signal is large and the load fluctuation is given when paralleled, the time constant of the frequency setting unit 23 is set to a runback shorter than the normal time constant. Since it is switched to the time constant, it can be run back to the specified value (rated frequency) in a short time, load fluctuation can be reduced, and speed control can be performed quickly.
It is also possible to suppress adverse effects on hydraulic machinery.

Further, in the above embodiment, the frequency setting unit 23
However, instead of switching the time constant, the output of the frequency setting unit 23 is set to the speed signal from the speed detection unit 21 under the same conditions as the frequency setting unit time constant switching circuit 34 described above. The same effect as that of the above-described embodiment can be obtained even if the configuration is replaced with.

[0044]

As described above, according to the speed control device for a water turbine of the present invention, more stable control can be performed as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a speed control device for a water turbine according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the speed governing control device of the water turbine of FIG. 1 during a load limiting operation.

FIG. 3 is a diagram showing a configuration of a speed control device for a water turbine according to another embodiment of the present invention.

FIG. 4 is a diagram showing a main configuration of a speed governing control device for the water turbine of FIG.

FIG. 5 is a diagram showing a configuration of a conventional speed governor control device for a water turbine.

6 is a diagram for explaining the operation of the speed governor control device of the water turbine of FIG. 5 during a load limiting operation.

FIG. 7 is a diagram showing a configuration of a conventional speed governor control device for a water turbine.

[Explanation of symbols]

 2 Speed comparison unit 4 Guide vane opening comparison unit 6 Opening deviation calculation unit 10 Addition unit 12 Opening comparison unit FT rotation speed F Speed signal FR Speed setting signal FD Speed deviation signal FP Speed droop signal GVT Water turbine guide blade opening GV guide blade opening signal GVR opening setting signal GVD guide blade opening deviation signal GD opening deviation signal P proportional signal I integral signal D differential signal PID PID signal PR load limit value PD load limiting operation signal GR opening instruction GC guidance Blade operation signal

Claims (3)

[Claims] 1. A speed detection unit that detects a rotation speed of a water turbine and outputs a speed signal, a speed comparison unit that compares a speed setting signal with the speed signal and outputs a speed deviation signal, and the speed deviation signal A speed droop rate setting unit that outputs a speed droop signal according to the above, an opening detection unit that detects the guide blade opening and outputs an opening signal, and compares the opening setting signal with the opening signal. A guide vane opening degree comparison unit that outputs a guide blade opening degree deviation signal; an opening degree deviation calculation unit that adds the speed droop signal and the guide blade opening degree deviation signal and outputs an opening degree deviation signal; A proportional calculation unit that outputs a proportional signal of the opening deviation signal; an integral calculation unit that outputs an integrated signal of the opening deviation signal; a differential calculation unit that outputs a differential signal of the opening deviation signal; And the integrated signal and the differentiated signal are added to obtain a PID signal. An addition unit that outputs, a load limiting unit that selects the lower one of the PID signal and the load limit value and outputs the selected value as an opening command, and the opening command and the opening signal are compared. The water turbine includes an opening degree comparison unit that outputs a guide blade operation signal, and an integration limiting unit that limits the integrated signal to be equal to or less than the load limiting value at least during a load limiting operation. Speed control device. 2. A speed detection unit for detecting a rotation speed of a water turbine and outputting a speed signal, a frequency setting unit for outputting a speed command signal for adjusting the rotation speed of the water turbine, and a servo for operating a guide blade. A position detection unit that detects a motor opening and outputs an opening signal, a load setting unit that outputs a load command signal for adjusting the output of the water turbine, and a deviation between the speed signal and the speed command signal. A speed comparison unit that outputs a speed deviation signal according to the load, a load comparison unit that outputs a load deviation signal corresponding to the deviation between the opening signal and the load command signal, and the load deviation signal is multiplied by a drooping characteristic. Drooping portion load deviation signal output as a drooping load deviation signal, the speed deviation signal, the drooping load deviation signal is added, and a control deviation signal calculation unit that outputs as a control deviation signal, the control deviation signal , Proportional, product , A PID calculator that performs a differential operation and outputs as an opening command signal, and an opening according to a deviation between the opening command signal and the opening signal as a signal for operating the servo motor opening. When the opening deviation signal calculation unit that outputs the deviation signal, the parallel condition, and the condition that the absolute value of the speed deviation signal is a predetermined value or more are satisfied, the time constant of the frequency setting unit is changed from the normal time constant to A speed control device for a water turbine, comprising a switching means for switching to a time constant. 3. A speed detection unit for detecting a rotation speed of a water turbine and outputting a speed signal, a frequency setting unit for outputting a speed command signal for adjusting the rotation speed of the water turbine, and a servo for operating a guide blade. A position detection unit that detects a motor opening and outputs an opening signal, a load setting unit that outputs a load command signal for adjusting the output of the water turbine, and a deviation between the speed signal and the speed command signal. A speed comparison unit that outputs a speed deviation signal according to the load, a load comparison unit that outputs a load deviation signal corresponding to the deviation between the opening signal and the load command signal, and the load deviation signal is multiplied by a drooping characteristic. Drooping portion load deviation signal output as a drooping load deviation signal, the speed deviation signal, the drooping load deviation signal is added, and a control deviation signal calculation unit that outputs as a control deviation signal, the control deviation signal , Proportional, product , A PID calculator that performs a differential operation and outputs as an opening command signal, and an opening according to a deviation between the opening command signal and the opening signal as a signal for operating the servo motor opening. When the opening deviation signal calculation unit that outputs a deviation signal, the parallel condition, and the condition that the absolute value of the speed deviation signal is a predetermined value or more are satisfied, the output of the frequency setting unit is output from the speed detection unit. A speed control device for a water turbine, comprising: a means for replacing with a speed signal.