阅读说明：本技术 弗朗西斯式水轮机的起动方法以及弗朗西斯式水轮机 (Francis turbine starting method and Francis turbine ) 是由 中园昌彦 向井健朗 在原义贤 于 2021-06-18 设计创作，主要内容包括：本发明实施方式的弗朗西斯式水轮机的起动方法具备：旁通阀打开工序,关闭入口阀,并且打开旁通阀；入口阀打开工序,在旁通阀打开工序之后,打开入口阀；以及第一转速上升工序,在转轮的周围流动的回旋流的流速达到90m/sec之前以最大开度的50％以上的开度打开导流叶片,使转轮的转速上升。(A method for starting a Francis turbine according to an embodiment of the present invention includes: a bypass valve opening process of closing the inlet valve and opening the bypass valve; an inlet valve opening step of opening the inlet valve after the bypass valve opening step; and a first rotation speed increasing step of opening the guide vane at an opening degree of 50% or more of the maximum opening degree before the flow speed of the swirling flow flowing around the runner reaches 90m/sec, and increasing the rotation speed of the runner.)

1. A starting method of a francis turbine, the francis turbine including: an inlet valve provided to an inlet pipe guiding water to the housing; a bypass valve provided in a bypass pipe that bypasses the inlet valve and guides water to the housing; and a guide vane capable of adjusting a flow rate of water guided to a runner provided in the casing, wherein the francis turbine starting method includes:

a bypass valve opening process of closing the inlet valve and opening the bypass valve;

an inlet valve opening step of opening the inlet valve after the bypass valve opening step; and

and a first rotation speed increasing step of opening the guide vane at an opening degree of 50% or more of a maximum opening degree before a flow speed of the swirling flow flowing around the runner reaches 90m/sec, and increasing the rotation speed of the runner.

2. The starting method of a francis turbine according to claim 1,

the first rotation speed increasing step is performed after the inlet valve opening step.

3. The starting method of a francis turbine according to claim 1,

the first rotation speed increasing step is performed before the bypass valve opening step.

4. The starting method of a francis turbine according to claim 1,

the first rotation speed increasing step is performed between the bypass valve opening step and the inlet valve opening step.

5. A Francis turbine, comprising:

a housing;

an inlet pipe to guide water to the housing;

an inlet valve provided to the inlet pipe;

a bypass pipe bypassing the inlet valve to guide water to the housing;

the bypass valve is arranged on the bypass pipe;

the rotating wheel is arranged in the shell;

a guide vane capable of adjusting a flow rate of water guided to the runner; and

a control device for controlling the operation of the motor,

the control device controls the inlet valve, the bypass valve, and the guide vane to perform the following steps:

a bypass valve opening process of closing the inlet valve and opening the bypass valve;

an inlet valve opening step of opening the inlet valve after the bypass valve opening step; and

and a first rotation speed increasing step of opening the guide vane at an opening degree of 50% or more of a maximum opening degree before a flow speed of the swirling flow flowing around the runner reaches 90m/sec, and increasing the rotation speed of the runner.

Technical Field

Embodiments of the present invention relate to a francis turbine starting method and a francis turbine.

Background

When the francis turbine is in operation, water from the upper sump is directed from the inlet pipe through the inlet valve to the housing. The water flowing into the housing passes through the fixed blades and the guide blades, is adjusted in flow rate by the guide blades, and is guided to the runner. The runner is rotationally driven by the water flowing into the runner, and a generator connected to the runner via a main shaft is driven to generate power. Thereafter, the water flows out of the runner, and is discharged to a lower pool or a drainage path through a draft tube. In order to reduce the pressure difference between the upstream side of the inlet valve and the downstream side of the inlet valve (inside the housing) and facilitate opening and closing of the inlet valve, a bypass pipe is provided for bypassing the inlet valve, and a bypass valve is provided in the bypass pipe.

Such francis turbine is usually started as follows. The inlet valve, bypass valve and guide vanes are all closed when the francis turbine is stopped. In this state, first, the bypass valve is opened to raise the pressure in the housing to the same level as the pressure on the upstream side of the inlet valve. Next, the inlet valve is opened and water is introduced into the housing. Then, the guide vanes are opened at an opening degree in the range of 10% to 20%, and the runner is rotationally driven by the inflowing water to increase the rotational speed of the runner to a rated rotational speed.

However, when the guide vanes are opened at an opening degree within the above range at the time of starting the francis turbine, an annular flow path can be formed radially between the guide vanes and the runner. In this case, the water passing through the guide vanes flows through the annular flow passage, and a swirling flow can be generated around the runner. The swirling flow collides with the runner blade of the runner, thereby generating a stripping flow. In particular, in the case of a francis turbine having a large head drop, the swirling flow becomes faster, and a stronger separation flow can be generated. At this time, the pressure inside the runner may decrease to be equal to or lower than the saturated water vapor pressure. In this case, water evaporates to generate water vapor bubbles in the water, and an impulsive pressure rise can occur at the moment when the water vapor in the water vapor bubbles condenses. This may cause an impact load to be applied to the runner, which may damage the runner.

Disclosure of Invention

A francis turbine starting method according to an embodiment is a francis turbine starting method including an inlet valve provided in an inlet pipe that guides water to a casing, a bypass valve provided in a bypass pipe that bypasses the inlet valve and guides the water to the casing, and a guide vane that is capable of adjusting a flow rate of the water guided to a runner provided in the casing. A method for starting a Francis turbine, comprising: a bypass valve opening process of closing the inlet valve and opening the bypass valve; an inlet valve opening step of opening the inlet valve after the bypass valve opening step; and a first rotation speed increasing step of opening the guide vane at an opening degree of 50% or more of the maximum opening degree before the flow speed of the swirling flow flowing around the runner reaches 90m/sec, and increasing the rotation speed of the runner.

Further, the francis turbine according to the embodiment includes: a housing; an inlet pipe guiding water to the housing; an inlet valve provided at the inlet pipe; a bypass pipe for bypassing the inlet valve and guiding the water to the housing; the bypass valve is arranged on the bypass pipe; the rotating wheel is arranged in the shell; a guide vane capable of adjusting the flow rate of water guided to the runner; and a control device. The control device controls the inlet valve, the bypass valve and the guide vane to perform the following processes: a bypass valve opening process of closing the inlet valve and opening the bypass valve; an inlet valve opening step of opening the inlet valve after the bypass valve opening step; and a first rotation speed increasing step of opening the guide vane at an opening degree of 50% or more of the maximum opening degree before the flow speed of the swirling flow flowing around the runner reaches 90m/sec, and increasing the rotation speed of the runner.

Drawings

Fig. 1 is a meridional sectional view of a francis turbine of an embodiment.

Fig. 2 is a top sectional view of the francis turbine of fig. 1.

Fig. 3 is a diagram for explaining a starting method of the francis turbine according to the embodiment, and is a plan sectional view showing a state when the francis turbine is stopped.

Fig. 4 is a plan sectional view for explaining a first rotational speed raising process in the starting method of the francis turbine according to the embodiment.

Fig. 5 is a time chart showing the opening degree of the guide vanes and the rotational speed of the runner in the francis turbine starting method according to the embodiment.

Fig. 6 is a partially enlarged top sectional view showing the flow of water when the guide vanes are opened at the starting opening in the starting method of the general francis turbine.

Fig. 7 is a partially enlarged top-view cross-sectional view showing the flow of water when the guide vanes are opened at the starting opening in the starting method of the francis turbine of the embodiment.

Detailed Description

Hereinafter, a method of starting a francis turbine and the francis turbine according to an embodiment of the present invention will be described with reference to the drawings.

First, a francis turbine according to the present embodiment will be described with reference to fig. 1 and 2. In the following, the flow of water during operation of the hydraulic turbine will be described.

As shown in fig. 1 and 2, the francis turbine 1 includes an inlet system 2, a casing 3, a plurality of stationary blades 4, a plurality of guide blades 5, and a runner 6.

The inlet system 2 is configured to guide water from an upper tank, not shown, to the housing 3. The inlet system 2 includes an inlet pipe 21, an inlet valve 22 provided in the inlet pipe 21, a bypass pipe 23 bypassing the inlet valve 22, and a bypass valve 24 provided in the bypass pipe 23.

The inlet pipe 21 is connected to a hydraulic iron pipe extending from an unillustrated upper tank and the casing 3, and is configured to allow water from the unillustrated upper tank to flow and to guide the water to the casing 3.

The inlet valve 22 is provided in the inlet pipe 21 and is configured to be opened and closed to allow or block the flow of water in the inlet pipe 21. When the francis turbine 1 is stopped, the inlet valve 22 is closed. On the other hand, when the francis turbine 1 is operating, the inlet valve 22 is opened. The opening and closing of the inlet valve 22 may be controlled by a control device C described later.

The bypass pipe 23 is connected to a portion of the inlet pipe 21 on the upstream side of the inlet valve 22 and a portion of the inlet pipe 22 on the downstream side thereof, and is configured to bypass the inlet valve 22 and guide water to the housing 3.

The bypass valve 24 is provided in the bypass pipe 23 and is configured to be opened and closed to allow or block the flow of water in the bypass pipe 23. When the francis turbine 1 is stopped, the bypass valve 24 is closed. On the other hand, when the francis turbine 1 is operating, the bypass valve 24 is opened. The opening and closing of the bypass valve 24 may be controlled by a control device C described later.

The casing 3 is formed in a spiral shape, and is configured to allow water from the inlet system 2 to flow therein. A plurality of stationary blades 4, a plurality of guide blades 5, and a runner 6 are provided inside the casing 3.

The fixed blades 4 are provided inside the casing 3. The fixed blades 4 are configured to guide the water flowing into the casing 3 to the guide blades 5 and the runner 6. As shown in fig. 2, the fixed blades 4 are arranged at predetermined intervals in the circumferential direction. A flow path through which water flows is formed between the fixed blades 4.

The guide vanes 5 are provided on the inner side of the fixed vanes 4. The guide vanes 5 are configured to guide the inflow water to the runner 6. As shown in fig. 2, the guide vanes 5 are disposed at predetermined intervals in the circumferential direction. Flow paths through which water flows are formed between the guide vanes 5. Each guide vane 5 is configured to be rotatable, and the flow rate of water guided to the runner 6 can be adjusted by rotating each guide vane 5 to change the opening degree G. The opening degree G of the guide vane 5 may be controlled by a control device C described later.

The runner 6 is provided inside the guide vane 5. The runner 6 is configured to be rotatable about the rotation axis X with respect to the housing 3, and is rotationally driven by water flowing in from the guide vanes 5. The rotor 6 includes an upper crown (crown)8 coupled to the main shaft 7, a lower ring (band)9 provided on the outer peripheral side of the upper crown 8, and a plurality of rotor blades 10 provided between the upper crown 8 and the lower ring 9. As shown in fig. 2, the runner blades 10 are arranged at predetermined intervals in the circumferential direction. Each runner blade 10 is engaged with the upper crown 8 and the lower ring 9, respectively. A flow path (inter-blade flow path) through which water flows is formed between the runner blades 10. Water from the guide vanes 5 flows through the respective flow paths, and the runner vanes 10 receive pressure from the water, whereby the runner 6 is rotationally driven. Thereby, the energy of the water flowing into the runner 6 is converted into rotational energy.

A generator 11 is connected to the runner 6 via the main shaft 7. The generator 11 is configured to generate electric power by transmitting rotational energy of the runner 6 during operation of the hydraulic turbine.

A draft tube 12 is provided on the downstream side of the runner 6. The draft pipe 12 is connected to a lower pool or a drainage path, not shown, and the water rotated and driven by the runner 6 is discharged to the lower pool or the drainage path by recovering the pressure.

The generator 11 may have a function as a motor and be configured to rotationally drive the runner 6 by supplying electric power. In this case, the water in the lower pool can be sucked up through the suction pipe 12 and discharged to the upper pool, and the francis turbine 1 can be operated as a pump turbine (pumping operation). At this time, the opening degree G of the guide vane 5 is changed to an appropriate water pumping amount according to the pump head.

The francis turbine 1 of the present embodiment includes a control device C.

The control device C is configured to be able to control the inlet valve 22, the bypass valve 24, and the guide vane 5. The controller C controls the inlet valve 22, the bypass valve 24, and the guide vanes 5 so as to perform a bypass valve opening step, an inlet valve opening step, a first rotational speed increasing step, and a second rotational speed increasing step, which will be described later, when the francis turbine 1 is started. More specifically, the control device C first controls the bypass valve 24 to open the bypass valve 24 in the bypass valve opening step. Next, the control device C controls the inlet valve 22 so as to open the inlet valve 22 in the inlet valve opening process. Next, in the first rotation speed increasing step, the controller C opens the guide vane 5 at an opening G1 that is 50% or more of the maximum opening G0 before the flow velocity of the swirling flow 31 described later reaches 90m/sec, and controls the guide vane 5 so as to increase the rotation speed N of the runner 6. Thereafter, in the second rotation speed increasing step, the controller C controls the guide vanes 5 so that the guide vanes 5 are opened at an opening degree G2 that is 50% smaller than the maximum opening degree G0 to further increase the rotation speed N of the runner 6 to reach the rated rotation speed N0.

Next, a method of starting the francis turbine according to the present embodiment will be described with reference to fig. 3 to 7.

The method for starting the francis turbine 1 of the present embodiment includes: a bypass valve opening step of opening the bypass valve 24; an inlet valve opening process of opening the inlet valve 22; a first rotation speed increasing step of increasing the rotation speed N of the runner 6; and a second rotation speed increasing step of further increasing the rotation speed N of the turning wheel 6 so that the rotation speed N of the turning wheel 6 reaches the rated rotation speed N0. As shown in fig. 3, when the francis turbine 1 is stopped, the inlet valve 22, the bypass valve 24, and the guide vanes 5 are closed.

In this state, first, the bypass valve opening step is performed. In the bypass valve opening step, the bypass valve 24 is opened with the inlet valve 22 and the guide vane 5 closed. Thereby, the water from the upper tank flows from the inlet pipe 21 to the bypass pipe 23, and is guided into the housing 3 through the bypass valve 24. Therefore, the pressure of the water in the housing 3 rises, and the pressure difference between the upstream side of the inlet valve and the housing decreases.

After the bypass valve opening process, an inlet valve opening process is performed. In the inlet valve opening step, the inlet valve 22 is opened with the bypass valve 24 opened and the guide vanes 5 closed. Thereby, a large amount of water is guided from the upper sump through the inlet valve 22 into the housing 3.

After the inlet valve opening step, a first rotation speed increasing step is performed. In the first rotation speed increasing step, in a state where the inlet valve 22 and the bypass valve 24 are open, as shown in fig. 4, the guide vane 5 is opened at an opening degree G1 (start-up opening degree G1) that is 50% or more of the maximum opening degree G0 (mechanical maximum opening degree) to increase the rotation speed N of the runner 6. The guide vanes 5 are opened at a start opening G1 before the flow velocity of the swirling flow 31 described later reaches 90 m/sec. The first rotation speed increasing step includes an opening increasing step of increasing the opening G of the guide vane 5 to the starting opening G1, and a starting opening maintaining step of maintaining the opening G of the guide vane 5 at the starting opening G1.

Fig. 5 shows an example of a time chart showing the opening degree G of the guide vane 5 and the rotation speed N of the runner 6. In the graph of fig. 5 (a), the horizontal axis represents the time T, and the vertical axis represents the opening degree G of the guide vane 5. In the graph of fig. 5 (b), the horizontal axis represents the time T, and the vertical axis represents the rotation speed N of the rotor 6.

In the first rotation speed increasing step, first, as shown in fig. 5, the opening degree increasing step is performed between time T1 and time T2. In this step, the guide vane 5 is rotated so as to be opened, and the opening degree G of the guide vane 5 is increased from 0% (closed state) to the start opening degree G1. Thereby, the water flowing into the housing 3 flows through the respective flow paths between the guide vanes 5, and starts flowing into the runner 6. Here, at this time T2, the flow velocity of the swirling flow 31 described later does not reach 90 m/sec.

Next, as shown in fig. 5, the starting opening degree maintaining step is performed between time T2 and time T3. In this step, the opening degree G of the guide vane 5 is maintained at the start-up opening degree G1. During this time, the water flowing into the housing 3 flows in each flow path between the guide vanes 5 and continues to flow into the runner 6. The water flowing into the runner 6 flows through each flow path between the runner blades 10. The runner blades 10 receive pressure from the water flowing through the flow path, and the runner 6 is rotationally driven, so that the rotation speed N of the runner 6 increases. As a result, as shown in fig. 5, the rotation speed N of the turning wheel 6 can be increased to the predetermined target rotation speed N1 at time T3. Here, the target rotation speed N1 is smaller than the rated rotation speed N0 of the turning wheel 6 (the target rotation speed is reached), and may be, for example, 20% or more and 95% or less of the rated rotation speed N0 of the turning wheel 6.

Generally, when the francis turbine 1 is started, the guide vanes 5 are opened at a starting opening that is less than 50%, for example, 10% or more and 20% or less of the maximum opening G0. In this case, as shown in fig. 6, the annular flow passage 30 can be formed radially between the guide vane 5 and the runner 6. As a result, the water flowing through the flow paths between the guide vanes 5 flows through the annular flow path 30, and a swirling flow 31 can be generated around the runner 6. The swirling flow 31 collides with the runner blade 10, thereby generating a separation flow 32. In particular, when the flow velocity of the swirling flow 31 is 90m/sec or more, a strong peeling flow 32 is likely to be generated. At this time, the pressure inside the runner 6 may decrease to be equal to or lower than the saturated water vapor pressure. In this case, water evaporates to generate water vapor bubbles in the water, and an impulsive pressure rise can occur at the moment when the water vapor in the water vapor bubbles condenses. This causes an impact load to be applied to the runner 6, which may damage the runner 6.

In contrast, in the present embodiment, at the start-up of the francis turbine 1, the guide vanes 5 are opened at the start-up opening G1 that is 50% or more of the maximum opening G0 before the flow velocity of the swirling flow 31 reaches 90 m/sec. As a result, as shown in fig. 7, the distance between the guide vane 5 and the runner 6 in the radial direction can be reduced by the rotating guide vane 5, and the width of the annular flow passage 30 can be narrowed. That is, the annular flow passage 30 can be closed by the guide vane 5 before the flow velocity of the swirling flow 31 reaches 90 m/sec. Therefore, the water flowing through the respective flow paths between the guide vanes 5 can be suppressed from flowing through the annular flow path 30, and can smoothly flow through the respective flow paths between the runner blades 10 as shown by thick arrows in fig. 7. Thereby, the development of the swirling flow 31 is suppressed, and the generation of the peeling flow 32 is suppressed. As a result, the impact load accompanying the peeling flow 32 is suppressed from being applied to the runner 6, and damage to the runner 6 is suppressed.

After the first rotation speed increasing step, a second rotation speed increasing step is performed. In the second rotation speed increasing step, the guide vane 5 is opened at an opening degree G2 (no-load opening degree G2) that is less than 50% of the maximum opening degree G0, and the rotation speed N of the rotor 6 is further increased to reach the rated rotation speed N0. The second rotation speed increasing step includes an opening degree decreasing step of decreasing the opening degree G of the guide vane 5 to the no-load opening degree G2, and a no-load opening degree maintaining step of maintaining the opening degree G of the guide vane 5 at the no-load opening degree G2.

In the second rotation speed increasing step, first, as shown in fig. 5, the opening degree decreasing step is performed between time T3 and time T4. In this step, the guide vane 5 is rotated so as to be closed, and the opening degree G of the guide vane 5 is decreased from the start opening degree G1 to the no-load opening degree G2.

Next, as shown in fig. 5, the no-load opening degree maintaining process is performed between time T4 and time T5. In this step, the opening degree G of the guide vane 5 is maintained at the no-load opening degree G2. During this time, the runner 6 is rotationally driven by the water flowing into the runner 6, and the rotation speed N of the runner 6 further increases. As a result, as shown in fig. 5, the rotation speed N of the turning wheel 6 can be brought to the rated rotation speed N0 at time T5.

Here, as described above, the no-load opening degree G2 is an opening degree that is less than 50% of the maximum opening degree G0, but more specifically, may be an opening degree that is 5% or more and 15% or less of the maximum opening degree G0.

In the bypass valve opening step, the inlet valve opening step, the first rotation speed increasing step, and the second rotation speed increasing step, the opening and closing of the inlet valve 22, the opening and closing of the bypass valve 24, and the adjustment of the opening degree G of the guide vane 5 may be performed by the control device C. However, the operator may manually operate the control device C independently.

In this way, the number of revolutions N of the runner 6 reaches the rated number of revolutions N0, and the francis turbine 1 of the present embodiment is started. Thereafter, the francis turbine 1 performs a normal operation (load operation), the rotational energy of the runner 6 is transmitted to the generator 11, and power generation is performed by the generator 11.

As described above, according to the present embodiment, in the first speed-raising process at the start-up of the francis turbine 1, the guide vanes 5 are opened at the opening degree G1 that is 50% or more of the maximum opening degree G0 before the flow velocity of the swirling flow 31 reaches 90 m/sec. This makes it possible to close the annular flow passage 30 by the rotating guide vane 5 before the flow velocity of the swirling flow reaches 90 m/sec. This can suppress the water flowing through each flow path between the guide vanes 5 from flowing through the annular flow path 30, and can suppress the development of the swirling flow 31. Therefore, generation of the stripping flow 32 can be suppressed. As a result, the impact load accompanying the peeling flow 32 can be suppressed from being applied to the runner 6, and damage to the runner can be suppressed. Further, by opening the guide vane 5 at an opening degree G1 of 50% or more of the maximum opening degree G0, the flow rate of water flowing into the runner 6 can be increased. Therefore, the number of revolutions N of the runner 6 can be rapidly increased, and the startup time of the francis turbine 1 can be shortened.

(first modification)

In the above embodiment, the first rotation speed increasing step is performed after the inlet valve opening step. However, the present invention is not limited to this, and the first rotation speed increasing step may be performed before the bypass valve opening step. That is, in the starting method of the francis turbine 1 of the above embodiment, the bypass valve opening step, the inlet valve opening step, the first rotation speed increasing step, and the second rotation speed increasing step are performed in this order, and the first rotation speed increasing step, the bypass valve opening step, the inlet valve opening step, and the second rotation speed increasing step may be performed in this order.

In this case, in the first rotation speed increasing step, the guide vane 5 is opened at the starting opening G1 that is 50% or more of the maximum opening G0 with the inlet valve 22 and the bypass valve 24 closed. As a result, the water stored in the casing 3 when the francis turbine 1 is stopped is guided to the runner 6, and the runner blades 10 receive pressure from the water, whereby the runner 6 is rotationally driven. Therefore, the rotation speed N of the runner 6 increases.

Next, in the bypass valve opening step, the bypass valve 24 is opened with the inlet valve 22 closed and the guide vanes 5 opened. Thereby, the water from the upper tank flows from the inlet pipe 21 to the bypass pipe 23, and is guided into the housing 3 through the bypass valve 24. Therefore, the pressure of the water in the housing 3 rises, and the pressure difference between the upstream side of the inlet valve and the housing decreases.

Next, in the inlet valve opening step, the inlet valve 22 is opened with the guide vane 5 and the bypass valve 24 opened. Thereby, a large amount of water is guided from the upper sump through the inlet valve 22 into the housing 3. The water flowing into the housing 3 flows through the flow paths between the guide vanes 5 and is guided to the runner 6, and the runner vanes 10 receive pressure from the water, whereby the runner 6 is rotationally driven. Thereby, the rotation speed N of the runner 6 further increases.

Then, in the second rotation speed increasing step, the guide vane 5 is opened at a no-load opening degree G2 that is less than 50% of the maximum opening degree G0, and the rotation speed N of the runner 6 is further increased to reach the rated rotation speed N0.

In this way, even when the first rotation speed increasing step is performed before the bypass valve opening step, the development of the swirling flow 31 can be suppressed by opening the guide vane 5 at the opening degree G1 that is 50% or more of the maximum opening degree G0 before the flow velocity of the swirling flow reaches 90m/sec in the first rotation speed increasing step. This can suppress the generation of the stripping flow 32. As a result, the impact load accompanying the peeling flow 32 can be suppressed from being applied to the runner 6, and damage to the runner can be suppressed.

(second modification)

In the above embodiment, the first rotation speed increasing step may be performed between the bypass valve opening step and the inlet valve opening step. That is, in the starting method of the francis turbine 1 of the above embodiment, the bypass valve opening step, the first rotational speed increasing step, the inlet valve opening step, and the second rotational speed increasing step may be performed in this order.

In this case, in the bypass valve opening step, the bypass valve 24 is opened with the inlet valve 22 and the guide vanes 5 closed. Thereby, the water from the upper tank flows from the inlet pipe 21 to the bypass pipe 23, and is guided into the housing 3 through the bypass valve 24. Therefore, the pressure of the water in the housing 3 rises, and the pressure difference between the upstream side of the inlet valve and the housing decreases.

Next, in the first rotation speed increasing step, the guide vane 5 is opened at a start-up opening degree G1 that is 50% or more of the maximum opening degree G0 in a state where the inlet valve 22 is closed and the bypass valve 24 is open. As a result, the water stored in the casing 3 when the francis turbine 1 is stopped is guided to the runner 6, and the runner blades 10 receive pressure from the water, whereby the runner 6 is rotationally driven. Therefore, the rotation speed N of the runner 6 increases.

Next, in the inlet valve opening step, the inlet valve 22 is opened with the bypass valve 24 and the guide vanes 5 opened. Thereby, a large amount of water is guided from the upper sump through the inlet valve 22 into the housing 3. The water flowing into the housing 3 flows through the flow paths between the guide vanes 5 and is guided to the runner 6, and the runner vanes 10 receive pressure from the water, whereby the runner 6 is rotationally driven. Thereby, the rotation speed N of the runner 6 further increases.

Then, in the second rotation speed increasing step, the guide vane 5 is opened at a no-load opening degree G2 that is less than 50% of the maximum opening degree G0, and the rotation speed N of the runner 6 is further increased to reach the rated rotation speed N0.

In this way, even when the first rotation speed increasing step is performed between the bypass valve opening step and the inlet valve opening step, the swirl flow 31 can be prevented from progressing by opening the guide vane 5 at an opening degree G1 that is 50% or more of the maximum opening degree G0 before the flow velocity of the swirl flow reaches 90m/sec in the first rotation speed increasing step. This can suppress the generation of the stripping flow 32. As a result, the impact load accompanying the peeling flow 32 can be suppressed from being applied to the runner 6, and damage to the runner can be suppressed.

According to the above-described embodiments, damage to the runner can be suppressed.

While the embodiments of the present invention have been described above, these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

In the above-described embodiment, an example in which the francis turbine is a pump turbine capable of performing pump operation has been described. However, the francis turbine may not be operated, and the francis turbine may not be operated.