Francis turbine starting method, starting program, and control device

Abstract

To provide a starting method of a Francis turbine for maximizing a rotation rising rate of a runner while maintaining an impact load.SOLUTION: A startup method of a Francis turbine in an embodiment includes: a first step of controlling an opening degree of a guide vane in a minute time unit to obtain a post-change guide vane opening degree; a second step of deriving a swirling flow velocity of a swirling flow at the post-change guide vane opening degree; a third step of deriving a circumferential velocity of a runner at the post-change guide vane opening degree; a fourth step of deriving a relative flow velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; and a fifth step of comparing the relative flow velocity with a predetermined relative flow velocity threshold value and determining whether or not a rotation speed of the runner at the post-change guide vane opening degree reaches a predetermined speed when the relative flow velocity is equal to or less than the predetermined relative flow velocity threshold value.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a Francis turbine starting method, a starting program, and a control device. [Background technology]

[0002] A Francis turbine is a type of water turbine used for hydroelectric power generation. During operation, water from the upper reservoir is introduced into the casing through an inlet valve installed in the inlet pipe. The water then passes through stay vanes and guide vanes to adjust the flow rate, and is then introduced into the runner. When the water flows into the runner, it rotates, driving the generator connected to the runner via the main shaft, which then rotates together with the runner, generating electricity. The water then flows out of the runner and is discharged through the draft pipe into the lower reservoir or tailrace.

[0003] When a Francis turbine is stopped, the inlet valve and guide vanes are closed. To start a Francis turbine, the inlet valve on the inlet pipe is first opened to allow water to flow into the casing. The guide vanes are then opened to their starting position, allowing water to flow into the runner, driving it to rotate and increasing its rotational speed to its rated speed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-001741 [Patent Document 2] Patent Publication No. 2022-001742 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a Francis turbine is started, an annular flow path may be formed around the runner, particularly between the guide vanes and the runner, when the guide vanes are opened to their starting position. When water passes through the guide vanes and flows forcefully through this annular flow path, a fast swirling flow is generated around the runner. When the swirling flow collides with the runner blades, a separated flow is generated around the runner blades. In particular, in the case of a Francis turbine with a large head, the swirling flow becomes faster, which may result in a stronger separated flow.

[0006] When such swirling and separated flows occur, the water pressure inside the runner drops, and it is easy for the water pressure to fall below the saturated water vapor pressure. If the area inside the runner where the water pressure is below the saturated water vapor pressure expands, cavitation will occur inside the runner, and the impact load caused by the collapse of large-scale cavitation could damage the runner.

[0007] To address this issue, studies have been conducted to reduce the speed of the swirling flow and weaken the separated flow by reducing the starting opening of the guide vanes.

[0008] However, this method requires maintaining a small opening for a long period of time, and it may take some time for the runner rotation speed to reach the rated rotation speed.

[0009] The present invention addresses these circumstances, and the problem to be solved by the present invention is to provide a Francis turbine starting method, starting program, and control device that controls the guide vane opening in accordance with the runner rotational speed when starting up the Francis turbine, thereby maintaining the impact load caused by separated flow at a certain value or less and maximizing the rate of increase in the runner rotational speed. [Means for solving the problem]

[0010] In order to achieve the above object, a starting method for a Francis turbine according to an embodiment is a method for starting a Francis turbine including guide vanes that can adjust the flow rate of water introduced into a runner, and is characterized by comprising: a first step of controlling the opening of the guide vane in micro-time units to set a changed guide vane opening; a second step of deriving a swirling flow velocity of the swirling flow at the changed guide vane opening; a third step of deriving a circumferential velocity of the runner at the changed guide vane opening; a fourth step of deriving a relative flow velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; and a fifth step of comparing the relative flow velocity with a predetermined relative flow velocity threshold, and, if the relative flow velocity is equal to or less than the predetermined relative flow velocity threshold, determining whether the rotational speed of the runner at the changed guide vane opening has reached a predetermined speed.

[0011] In order to achieve the above object, a start-up program for a Francis turbine according to an embodiment is a start-up program for a Francis turbine including guide vanes that can adjust the flow rate of water introduced into a runner, and includes: a first command for controlling the opening of the guide vanes in minute time units to set a changed guide vane opening; a second command for deriving a swirling flow velocity of the swirling flow at the changed guide vane opening; a third command for deriving a circumferential velocity of the runner at the changed guide vane opening; a fourth command for deriving a relative flow velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; and a fifth command for comparing the relative flow velocity with a predetermined relative flow velocity threshold, and, if the relative flow velocity is equal to or less than the predetermined relative flow velocity threshold, determining whether the rotational speed of the runner at the changed guide vane opening has reached a predetermined speed.

[0012] In order to achieve the above object, the control device for a Francis turbine of an embodiment is a control device for a Francis turbine including guide vanes that can adjust the flow rate of water guided to a runner, and is characterized by including: an opening change unit that controls the guide vanes and changes the opening of the guide vanes; a derivation unit that executes calculation processing or analysis processing in controlling the guide vanes; a memory unit that stores data from the derivation unit or externally; a comparison unit that compares a plurality of different data from among the data in controlling the guide vanes; and an opening / closing command unit that issues a command to the opening change unit to change the opening of the guide vanes based on a judgment made by the comparison unit. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram of a Francis turbine 1 according to this embodiment when the guide vanes are in an open state. [Figure 2] FIG. 1 is a configuration diagram of a Francis turbine 1 according to this embodiment when the guide vanes are in a closed state. [Figure 3] 1A and 1B are explanatory diagrams of a Francis turbine 1 at the start of conventional operation; (a) is a time diagram showing the opening of the guide vanes 5; and (b) is an explanatory diagram showing the water flow when the guide vanes 5 are opened at the starting opening. [Figure 4] 1 is an explanatory diagram showing a control device C that controls a starting method 100 for a Francis turbine 1 according to this embodiment. [Figure 5] 1 is a flowchart showing a method 100 for starting the Francis turbine 1 according to the present embodiment. [Figure 6] 2 is a flowchart illustrating a method 200 for deriving a predetermined relative flow velocity threshold R0 in step S105 of the activation method 100. [Figure 7] 1 is an explanatory diagram of a method 100 for starting a Francis turbine 1 according to the present embodiment. [Figure 8] 1 is an explanatory diagram showing the relationship between the guide vane opening G and the swirling flow velocity R1 in the starting method 100 of the Francis turbine 1 of this embodiment. FIG. [Figure 9] 10 is an explanatory diagram showing the relationship between the relative flow velocity R3 and the stress N in the starting method 100 of the Francis turbine 1 of the present embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a Francis turbine starting method, a starting program, and a control device according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are merely examples of embodiments of the present invention and are not intended to limit the scope of the invention. Furthermore, in the drawings referred to in the embodiments, identical parts or parts having similar functions are denoted by the same or similar reference numerals, and their description may be omitted. Furthermore, the dimensional ratios of the drawings may differ from the actual ratios, and some components may be omitted from the drawings.

[0015] First, a Francis turbine 1 according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a configuration diagram of the Francis turbine 1 according to this embodiment when the guide vanes are in an open state, and Figure 2 is a configuration diagram of the Francis turbine 1 according to this embodiment when the guide vanes are in a closed state. The Francis turbine 1 in Figures 1 and 2 is connected to a generator (not shown) via a main shaft A, and includes an inlet system 2, a casing 3, stay vanes 4, guide vanes 5, a runner 6, and a control device C. Hereinafter, the axial direction centered on the main shaft A will be simply referred to as the axial direction, and the circumferential and radial directions centered on the main shaft A will be simply referred to as the circumferential direction and the radial direction.

[0016] The inlet system 2 is configured to guide water from an upper reservoir (not shown) to the casing 3. The inlet system 2 has an inlet pipe 7, an inlet valve 8, a bypass pipe 9, and a bypass valve 10.

[0017] The inlet pipe 7 has one end connected to a penstock (not shown) extending from the upper reservoir and the other end connected to the casing 3 , and guides the water flowing in from the upper reservoir to the casing 3 .

[0018] The inlet valve 8 is provided in the inlet pipe 7, and opens or closes the flow of water in the inlet pipe 7 by opening or closing the valve. Specifically, the inlet valve 8 is closed when the Francis turbine 1 is stopped, and is open when the Francis turbine 1 is operating. The opening and closing of this inlet valve 8 may be controlled by a control device C, which will be described later.

[0019] One end of the bypass pipe 9 is connected to a portion of the inlet pipe 7 upstream of the inlet valve 8, and the other end is connected to a portion of the inlet pipe 7 downstream of the inlet valve 8, bypassing the inlet valve 8 and directing water into the casing 3. Note that the upstream side / downstream side referred to here refers to the upstream side / downstream side in the flow direction of water flowing from the upper pond toward the casing 3.

[0020] The bypass valve 10 is provided in the bypass pipe 9, and opens or closes the flow of water in the bypass pipe 9 by opening or closing the valve. Specifically, the bypass valve 10 is closed when the Francis turbine 1 is stopped, and is open when the Francis turbine 1 is operating. The opening and closing of this bypass valve 10 may be controlled by a control device C, which will be described later.

[0021] The casing 3 is formed in a spiral shape and guides water that flows in from the inlet system 2 into the inside of the casing 3. Inside the casing 3, a plurality of stay vanes 4, a plurality of guide vanes 5, and a runner 6 are provided.

[0022] The stay vanes 4 are provided on the radially inner side of the casing 3 and guide water that has flowed into the inside of the casing 3 to the guide vanes 5 and runner 6. Specifically, a plurality of stay vanes 4 are arranged at regular intervals in the circumferential direction on the radially inner side of the casing 3, and are formed so that these intervals create flow paths through which water flows.

[0023] The guide vanes 5 are provided radially inward of the stay vanes 4 and guide the water that flows in from the stay vanes 4 to the runner 6. Specifically, a plurality of guide vanes 5 are arranged radially inward of the stay vanes 4 at regular intervals in the circumferential direction, and these intervals are formed to create flow paths through which water flows. Furthermore, the guide vanes 5 are configured to be movable via a guide ring (not shown) and have their opening adjustable to adjust the flow rate and flow velocity of the water that is guided to the runner 6. The opening of the guide vanes 5 may be controlled by a control device C, which will be described later.

[0024] The runner 6 is provided radially inward of the guide vanes 5 and is connected to the generator via the main shaft A. The runner 6 has a plurality of runner blades 11 spaced at regular intervals in the circumferential direction, and a flow path through which water flows is formed in these intervals. The runner 6 is rotated in the circumferential direction by the water flowing in from the guide vanes 5, and is configured to be able to convert the energy of the water flowing into the runner 6 into rotational energy for rotating the generator via the main shaft A.

[0025] The control device C is configured to be able to control the inlet valve 8, bypass valve 10, guide vanes 5, etc. As a result, for example, when starting up the Francis turbine 1, the control device C controls the openings of the inlet valve 8, bypass valve 10, guide vanes 5, etc., thereby controlling the process for increasing the rotation speed of the runner 6. Details of the control by the control device C will be described later.

[0026] According to the Francis turbine 1 of this embodiment, when the Francis turbine 1 is stopped, the inlet valve 8, the bypass valve 10, and the guide vanes 5 are closed. When the Francis turbine 1 is operating, the inlet valve 8 and the bypass valve 10 are opened under the control of the control device C, and water from the upper reservoir is guided into the casing 3 through the inlet system 2. The water guided into the casing 3 passes through the stay vanes 4 and is guided to the guide vanes 5. The flow rate and flow velocity of the water passing through the guide vanes 5 are adjusted by the opening degree of the guide vanes 5 under the control of the control device C, and the water is then guided to the runner 6. When the water flowing into the runner 6 drives the runner 6 to rotate, the generator connected to the runner 6 via the main shaft A rotates together with the runner 6, generating electricity. The water then flows out of the runner 6 and is discharged through a draft pipe (not shown) to the lower reservoir or a tailrace (not shown).

[0027] Next, a method 100 for starting the Francis turbine 1 of this embodiment will be described.

[0028] Here, in order to clarify the difference between this embodiment and the conventional method, we will first explain as a comparative example a case in which the Francis turbine 1 according to this embodiment is started using a conventional operation start-up method, and then explain the start-up method 100 of the Francis turbine 1 according to this embodiment.

[0029] (Comparative Example) A conventional method for starting up the operation of a Francis turbine 1 will be described using Figure 3. Figure 3 is an explanatory diagram of the conventional start-up of the Francis turbine 1, where (a) is a time diagram showing the opening of the guide vanes 5, and (b) is an explanatory diagram showing the water flow when the guide vanes 5 are opened at the starting opening.

[0030] When a conventional Francis turbine 1 is started, the inlet valve 8 is opened to start the inflow of water into the casing 3. Then, as shown in FIG. 3(a), the guide vanes 5 are opened to a startup opening G1 from time T1 to T2 to increase the rotational speed of the runner 6. The rotational speed of the runner 6 is then increased from time T2 to T3 until it reaches a predetermined rotational speed. Then, the guide vanes 5 are closed to a no-load opening G2 from time T3 to T4 to adjust the rotational speed of the runner 6 to the rated rotational speed. The startup opening G1 here refers to a predetermined opening that supplies a sufficient amount of water to the runner 6 for startup, and is, for example, 10% to 20% of the maximum opening of the guide vanes 5. The no-load opening G2 here refers to an opening smaller than the startup opening G1 that rotates the generator at the rated rotational speed under no load, and is, for example, 5% to 15% of the maximum opening of the guide vanes 5.

[0031] In this case, when the guide vanes 5 are opened to the starting position G1, an annular flow passage 20 is formed around the runner 6, particularly between the guide vanes 5 and the runner 6, as shown in FIG. 3(b). When water passes through the guide vanes 5 and flows forcefully into this annular flow passage 20, a fast swirling flow 30 is generated. When this swirling flow 30 collides with the runner blades 11, a separated flow 40 is generated around the runner blades 11. When such a swirling flow 30 and separated flow 40 are generated, the water pressure inside the runner 6 decreases, and the water pressure is likely to fall below the saturated water vapor pressure. If the area where the water pressure is below the saturated water vapor pressure expands inside the runner 6, cavitation will occur inside the runner 6, and the impact load caused by this cavitation could damage the runner 6.

[0032] (Starting method of the Francis turbine 1 according to this embodiment) The start-up method 100 of the Francis turbine 1 of this embodiment will be described with reference to Figures 4 to 9. Figure 4 is an explanatory diagram showing a control device C that controls the start-up method 100 of the Francis turbine 1 of this embodiment. Figure 5 is a flowchart showing the start-up method 100 of the Francis turbine 1 of this embodiment. Figure 6 is a flowchart showing a method 200 for deriving a predetermined relative flow velocity threshold R0 in step S105 of the start-up method 100. Figure 7 is an explanatory diagram of the start-up method 100 of the Francis turbine 1 of this embodiment. Figure 8 is an explanatory diagram showing the relationship between the guide vane opening G and the swirling flow velocity R1 in the start-up method 100 of the Francis turbine 1 of this embodiment. Figure 9 is an explanatory diagram showing the relationship between the relative flow velocity R3 and the stress N in the start-up method 100 of the Francis turbine 1 of this embodiment.

[0033] First, the control device C that controls the starting method 100 of the Francis turbine 1 of this embodiment will be described with reference to Fig. 4. As shown in Fig. 4, the control device C includes an opening change unit C1, a derivation unit C2, a measurement unit C3, a memory unit C4, a comparison unit C5, and an opening / closing command unit C6.

[0034] The opening change unit C1 is an opening change unit that controls the guide vanes 5 of the Francis turbine 1 and changes the opening of the guide vanes 5. For example, the opening change unit C1 receives a command to change the opening of the guide vanes 5 from an opening change unit C6, which will be described later, and changes the opening of the guide vanes 5. Details of the control related to the starting method 100 will be described later.

[0035] The derivation unit C2 is a unit for executing calculation processing, analysis processing, etc. when necessary to control the guide vanes 5 of the Francis turbine 1, and deriving a desired result. Details of the control related to the start-up method 100 will be described later.

[0036] The measurement unit C3 is a measurement unit for measuring the state of each component of the Francis turbine 1. Details of the control relating to the start-up method 100 will be described later.

[0037] The storage unit C4 is a storage unit for storing data measured or derived by the control device C itself (the derivation unit C2, the measurement unit C3, etc.) or an external device, etc. Details of the control related to the activation method 100 will be described later.

[0038] The comparison unit C5 is a comparison unit for comparing two different pieces of data measured or derived by the control device C itself or an external device, etc., in controlling the guide vanes 5 of the Francis turbine 1. Details of the control related to the start-up method 100 will be described later.

[0039] The opening / closing command unit C6 is a command unit that receives the determination by the comparison unit C5 and issues a command to the opening change unit C1 to change the opening of the guide vanes 5 of the Francis turbine 1. Details of the control related to the start-up method 100 will be described later.

[0040] Next, a starting method 100 for the Francis turbine 1 of this embodiment will be described with reference to Figure 5. This starting method 100 is a method for controlling the opening of the guide vanes 5 when starting up the Francis turbine 1. The starting method 100 described below can be applied to Francis turbines 1 with each effective head. In addition, to facilitate understanding, the following description will be made with reference to the symbols in Figure 7.

[0041] The processing steps of the Francis turbine 1 start-up method 100 of this embodiment begin when one or more processors (not shown) provided in the control device C execute a software program and / or an instruction set stored in a memory (not shown).

[0042] First, when the Francis turbine 1 starts up, the opening change unit C1 controls the opening of the guide vanes 5 in micro-time units to change the guide vane opening G to a changed guide vane opening Gn' (step S101, corresponding to the first step). Specifically, the opening change unit C1 controls a predetermined opening speed of the guide vanes 5 in micro-time units to change the guide vane opening G at a certain point in time to a changed guide vane opening Gn', which is a value obtained by adding an amount of change in the opening obtained by multiplying the micro-time unit and the opening speed to the guide vane opening G at that time. The micro-unit time here refers to a time unit that is set in advance depending on the accuracy of the guide vane opening control. For example, when the guide vane opening G is changed for the first time, the guide vane opening G is 0, so the value obtained by adding an amount of change in the opening obtained by multiplying the micro-time unit and the opening speed to 0 is set as a changed guide vane opening G0', and the opening of the guide vanes 5 is changed to this changed guide vane opening G0'.

[0043] Next, the derivation unit C2 derives the swirling flow velocity R1 at the changed guide vane opening Gn' changed in step S101 (step S102, corresponding to the second step). Specifically, based on a flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine 1, the derivation unit C2 derives the swirling flow velocity R1 of the swirling flow 30 corresponding to the changed guide vane opening Gn' as shown in Figure 8.

[0044] Next, the derivation unit C2 derives the circumferential speed R2 of the radially outer portion of the runner blades 11 based on the rotational speed of the runner 6 at the changed guide vane opening Gn' (step S103, corresponding to the third step). Specifically, using the simulation results at the start-up of the Francis turbine 1, the derivation unit C2 predicts the rotational speed of the runner 6 at each time at the changed guide vane opening Gn', and derives the circumferential speed R2 of the radially outer portion of the runner blades 11 based on this predicted value.

[0045] The circumferential speed R2 is not limited to being derived by the above-mentioned method. For example, when the Francis turbine 1 starts up, the measuring unit C3 may measure the circumferential speed of the radially outer portion of the runner blades 11, and this may be used as the circumferential speed R2.

[0046] Next, the derivation section C2 derives the relative flow velocity R3 of the swirling flow 30 colliding with the runner blade 11 based on the swirling flow velocity R1 derived in step S102 and the circumferential velocity R2 derived in step S103 (step S104, corresponding to the fourth step).

[0047] Thereafter, the comparison unit C5 compares the relative flow velocity R3 derived in step S104 with a predetermined relative flow velocity threshold R0 stored in the storage unit C4 (step S105). The predetermined relative flow velocity threshold R0 here refers to a stress threshold that serves as a reference for continuing to operate the runner 6 until the expected runner life is reached, and this predetermined relative flow velocity threshold R0 is a value that is derived in advance before performing step S101. An example of how this predetermined relative flow velocity threshold R0 is derived will be described later. If the comparison unit C5 determines that the relative flow velocity R3 is equal to or less than the predetermined relative flow velocity threshold R0 (Yes in step S105), it then compares whether the rotational speed of the runner 6 at the changed guide vane opening Gn' at the time of comparison has reached a predetermined speed (step S106, corresponding to the fifth step). The "predetermined speed" here refers to the rotational speed of the runner 6 that is a predetermined target value when starting up the Francis turbine 1 using the starting method 100 of this embodiment, and this target value is preferably a value that is equal to or less than the rated rotational speed of the runner 6. The "rated rotational speed" here refers to the rotational speed of the runner 6 when the frequency of the generator of the Francis turbine 1 is synchronized with the grid frequency. Note that this target value is set to, for example, 30% of the rated rotational speed depending on the operating conditions of the Francis turbine 1, but this target value may be configured to be changeable so that the operator can achieve more optimal operating conditions for the Francis turbine 1. If the comparison unit C5 determines that the rotational speed of the runner 6 at the changed guide vane opening Gn' has reached a predetermined speed (Yes in step S106), the comparison unit C5 determines to transition to normal operation control (step S107, corresponding to the sixth step). That is, in the startup stage of the Francis turbine 1, the startup method 100 ends, and the opening of the guide vanes 5 is opened by normal operation control until the runner 6 reaches the rated rotational speed. Note that the normal operation control here refers to operation control in which the rotational speed of the runner 6 reaches the rated rotational speed, for example, by opening the guide vanes at the startup opening G1 and then at the no-load opening G2 described in the comparative example.

[0048] On the other hand, in step S105, if the comparison unit C5 determines that the relative flow velocity R3 is not equal to or less than the predetermined relative flow velocity threshold value R0 (No in step S105), the opening / closing command unit C6 issues a command (guide vane close command) to the opening change unit C1 to change the opening of the guide vane 5 to a post-change guide vane opening Gn-1' that is smaller than the post-change guide vane opening Gn' (step S108, corresponding to the seventh step). Then, the process returns to step S101, and the opening change unit C1 again changes the opening of the guide vane 5 to the post-change guide vane opening Gn-1', which is the value obtained by subtracting the amount of change in opening obtained by multiplying the infinitesimal time unit and the opening speed from the post-change guide vane opening Gn'. After returning to step S101, the subsequent steps are the same as those described above.

[0049] Furthermore, in step S106, if the comparison unit C5 determines that the rotational speed of the runner 6 at the changed guide vane opening Gn' has not reached the predetermined speed (No in step S106), the opening / closing command unit C6 issues a command (guide vane open command) to the opening change unit C1 to change the opening of the guide vanes 5 to a changed guide vane opening Gn+1' that is larger than the changed guide vane opening Gn' (step S109, corresponding to the eighth step). Then, the process returns to step S101, and the opening change unit C1 again changes the opening of the guide vanes 5 to the changed guide vane opening Gn+1', which is the value obtained by adding the amount of change in opening obtained by multiplying the changed guide vane opening Gn' by the infinitesimal time unit and the opening speed. After returning to step S101, the subsequent steps are the same as those described above.

[0050] Next, an example of a method 200 for deriving the predetermined relative flow velocity threshold value R0 in step S105 of the start-up method 100 shown in Fig. 5 will be described with reference to Fig. 6. The method 200 for deriving the predetermined relative flow velocity threshold value R0 is a step that is executed in advance, for example, during a wet test of the Francis turbine 1.

[0051] First, the measuring unit C3 measures the stress N at the radially outer portion of the runner blade 11 of the runner 6 (step S201).

[0052] Next, the derivation unit C2 derives a predicted value of the swirling flow velocity R1 of the swirling flow 30 at each guide vane opening G as shown in Figure 8 based on flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine 1 (step S202).

[0053] Next, the measurement unit C3 measures the rotation speed of the runner 6 at each guide vane opening G, and the derivation unit C2 derives the circumferential speed R2 of the radially outer portion of the runner blades 11 from the measured value (step S203).

[0054] Next, the derivation unit C2 derives the relative velocity R3 of the swirling flow 30 colliding with the radially outer portion of the runner blade 11 based on the swirling flow velocity R1 predicted in step S202 and the circumferential velocity R2 derived in step S203 (step S204).

[0055] Thereafter, the derivation unit C2 derives the relationship between the stress N and the relative flow velocity R3 as shown in FIG. 9 based on the stress N measured in S201 and the relative flow velocity R3 derived in step S204 (step S205).

[0056] After these steps, the derivation unit C2 derives the relative flow velocity R3 corresponding to the predetermined stress N0 as the predetermined relative flow velocity threshold R0 from the relationship derived in step S205 (step S206). The predetermined stress N0 here refers to, for example, the stress N that becomes the starting point of fatigue fracture in the runner blade 11.

[0057] The method of deriving the predetermined relative flow velocity threshold value R0 is not limited to the above-described method. For example, the derivation unit C2 may derive the predetermined relative flow velocity threshold value R0 based on a stress analysis in the runner blade 11 when a pressure rise derived from a flow analysis that can simulate the occurrence and collapse of cavitation is applied to the runner blade 11.

[0058] As described above, according to the starting method 100 of the Francis turbine 1 of this embodiment, the guide vane opening G is controlled in minute time units in accordance with the rotational speed of the runner 6 so that the relative flow velocity R3 between the swirling flow velocity R1 of the swirling flow 30 and the circumferential velocity R2 of the runner blades 11 does not exceed a predetermined relative flow velocity threshold value R0 derived in relation to the stress N of the runner blades 11. As a result, it is possible to maximize the rate of increase in the rotational speed until the runner 6 reaches the rated rotational speed while maintaining the impact load caused by the separated flow 40, which is generated when the swirling flow 30 collides with the runner blades 11, at or below a certain value.

[0059] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0060] 1...Francis turbine, 2...inlet system, 3...casing, 4...stay vane, 5...guide vane, 6...runner, 7...inlet pipe, 8...inlet valve, 9...bypass pipe, 10...bypass valve, 11...runner blade, 20...annular flow path, 30...swirl flow, 40...separated flow, 100...start-up method, C...control device, C1...opening change unit, C2...derivation unit, C3...measurement unit, C4...storage unit, C5...comparison unit, C6...opening / closing command unit, G...guide vane opening, Gn'...changed guide vane opening, N...stress, N0...specified stress, R0...specified relative flow velocity threshold, R1...swirl flow velocity, R2...circumferential flow velocity, R3...relative flow velocity.

Claims

1. A method for starting a Francis turbine including guide vanes that can adjust the flow rate of water guided to a runner, comprising: a first step of controlling the opening of the guide vane in minute time units to set the changed guide vane opening; a second step of deriving a swirling flow velocity of the swirling flow at the changed guide vane opening; a third step of deriving a circumferential speed of the runner at the changed guide vane opening degree; a fourth step of deriving a relative flow velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; a fifth step of comparing the relative flow velocity with a predetermined relative flow velocity threshold, and determining whether or not the rotational speed of the runner at the changed guide vane opening degree has reached a predetermined speed when the relative flow velocity is equal to or less than the predetermined relative flow velocity threshold; 1. A method for starting a Francis turbine, comprising:

2. In deriving the predetermined relative flow velocity threshold, measuring stress in the runner; predicting a swirling flow velocity of the swirling flow at each opening degree of the guide vanes based on a flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine; measuring a rotational speed of the runner at each opening degree of the guide vane and deriving a circumferential speed of the runner; deriving a relative velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; deriving a relationship between the stress and the relative flow velocity based on the stress and the relative flow velocity; deriving the relative flow velocity corresponding to a predetermined stress as the predetermined relative flow velocity threshold value based on the relationship; 2. The method for starting a Francis turbine according to claim 1, further comprising:

3. 2. The method for starting a Francis turbine according to claim 1, wherein the predetermined relative flow velocity threshold is derived by a stress analysis in the runner when a pressure rise derived by a flow analysis simulating the occurrence and collapse of cavitation is applied to the runner.

4. In the second step, 2. The method for starting a Francis turbine according to claim 1, wherein the swirling flow velocity of the swirling flow at the changed guide vane opening is derived by flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine.

5. In the third step, 2. The method for starting a Francis turbine according to claim 1, wherein the circumferential speed of the runner at the changed guide vane opening is derived based on the rotational speed of the runner at the changed guide vane opening predicted from a simulation result at the start of the Francis turbine.

6. In the third step, 2. The method for starting a Francis turbine according to claim 1, wherein the circumferential speed of the runner at the changed guide vane opening is a circumferential speed measured at the runner when the Francis turbine is started.

7. 7. The method for starting a Francis turbine according to claim 1, further comprising a sixth step of transitioning to normal operation control when it is determined that the rotational speed of the runner has reached a predetermined speed.

8. a seventh step of issuing a command to change the changed guide vane opening to a smaller opening when it is determined that the relative flow velocity is not equal to or less than the predetermined relative flow velocity threshold; an eighth step of issuing a command to change the post-change guide vane opening to a larger opening when it is determined that the rotational speed of the runner has not reached a predetermined speed; The method for starting a Francis turbine according to any one of claims 1 to 6, further comprising:

9. A starting program for a Francis turbine including guide vanes capable of adjusting the flow rate of water directed to a runner, comprising: a first command for controlling the opening of the guide vanes in minute time units to set the changed guide vane opening; a second command for deriving a swirl velocity of the swirl flow at the changed guide vane opening; a third command for deriving a circumferential speed of the runner at the changed guide vane opening degree; and a fourth command for deriving a relative flow velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; a fifth command to compare the relative flow velocity with a predetermined relative flow velocity threshold, and, if the relative flow velocity is equal to or less than the predetermined relative flow velocity threshold, to determine whether the rotational speed of the runner at the changed guide vane opening has reached a predetermined speed; A Francis turbine starting program comprising:

10. In deriving the predetermined relative flow velocity threshold, instructions for measuring stress in the runner; a command to predict the swirling flow velocity of the swirling flow at each opening degree of the guide vanes by flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine; a command to measure the rotational speed of the runner at each opening degree of the guide vane and derive the circumferential speed of the runner; a command to derive a relative velocity of the swirling flow based on the swirling flow velocity and the circumferential velocity; instructions for deriving a relationship between the stress and the relative flow velocity based on the stress and the relative flow velocity; instructions for deriving the relative flow velocity corresponding to a predetermined stress as the predetermined relative flow velocity threshold based on the relationship; 10. The Francis turbine starting program according to claim 9, further comprising:

11. 10. The Francis turbine start-up program according to claim 9, wherein the predetermined relative flow velocity threshold is derived from a stress analysis in the runner when a pressure rise derived from a flow analysis simulating the occurrence and collapse of cavitation is applied to the runner.

12. In the second instruction:

10. The Francis turbine start-up program according to claim 9, wherein the swirling flow velocity of the swirling flow at the changed guide vane opening is derived by flow analysis using a calculation model having a flow path shape similar to that of the Francis turbine.

13. In the third order:

10. The Francis turbine starting program according to claim 9, wherein the circumferential speed of the runner at the changed guide vane opening is derived based on the rotational speed of the runner at the changed guide vane opening predicted from a simulation result at the start of the Francis turbine.

14. In the third order:

10. The Francis turbine starting program according to claim 9, wherein the circumferential speed of the runner at the changed guide vane opening is a circumferential speed measured by the runner when the Francis turbine is started.

15. 15. The Francis turbine start-up program according to claim 9, further comprising a sixth command for transitioning to normal operation control when it is determined that the rotational speed of the runner has reached a predetermined speed.

16. a seventh command to issue a command to change the changed guide vane opening to a smaller opening when it is determined that the relative flow velocity is not equal to or less than the predetermined relative flow velocity threshold; and an eighth command to issue a command to change the post-change guide vane opening to a larger opening when it is determined that the rotational speed of the runner has not reached a predetermined speed; and The method for starting a Francis turbine according to any one of claims 9 to 14, further comprising:

17. A control device for a Francis turbine including guide vanes that can adjust the flow rate of water guided to a runner, an opening degree changing unit for controlling the guide vanes and changing the opening degree of the guide vanes; a derivation unit for performing calculation processing or analysis processing in controlling the guide vane; a storage unit for storing data from the derivation unit or an external device; a comparison unit for comparing a plurality of different data among the data in controlling the guide vanes; an opening / closing command unit configured to issue a command to the opening degree change unit to change the opening degree of the guide vane in response to the determination by the comparison unit; A control device for a Francis turbine, comprising:

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