CN103498749B - A kind of small-scale mixed-flow pump turbine for low water head pumped storage power station - Google Patents

Abstract

The present invention relates to a kind of small-scale mixed-flow pump turbine for low water head pumped storage power station, it is characterized in that the cornerite of runner bucket is 105 ° ~ 124 °, the angle of inlet edge of runner blade and outlet edge is 54 ° ~ 86 °, runner bucket is space three-dimensional distortion curved surface, in vertical bone line direction, thickness is equal, the molded line of runner bucket is crescent shape, runner bucket inlet height B1 ratio under runner bucket thickness and hydraulic turbine condition is 0.06 ~ 0.11, runner bucket inlet height B1 under hydraulic turbine condition is equal with guide vane height B2, stator aerofoil profile is symmetrical whale shape, on label and be provided with three uniform vents, spiral case axial cross section is circular cross-section, draft tube is bending elbow type, its flat segments axial cross section is circular cross-section.The present invention both can meet the contrary pumping for water pump operating mode of twice water (flow) direction and water turbine generating operation mode, and can meet again pump turbine all can Effec-tive Function under two kinds of operating conditionss.

Description

A small Francis pump-turbine used in a low-head pumped storage power station

technical field

The invention belongs to the technical field of hydraulic machinery, in particular to a small mixed-flow pump-turbine used in a low-head pumped storage power station.

Background technique

With the rapid expansion and development of the power system, the functions of pumped storage power plants in the power system, such as peak regulation, frequency regulation, phase regulation and emergency backup, are becoming more and more significant. The pumped storage unit is the main unit of the pumped storage power station. The current pumped storage unit is mainly a reversible pump-turbine that can operate in both directions, and it has the functions of both a water turbine and a water pump. At present, there have been relatively in-depth researches on medium-high head and large-capacity pump turbines at home and abroad, and many experiences in design, optimization, and operation have been accumulated, and good results have been achieved. At the same time, the development of new energy sources such as solar energy, wind energy, and tidal energy is also vigorous, but the instability and discontinuity of these energy sources have brought great difficulties to comprehensive utilization and convenience of people's lives. In order to ensure the stability of the power system and the rational use of energy, in the small power system of comprehensive multi-energy utilization, pumped storage power stations can be used for regulation, and the water head will generally not exceed 50m. In the known technology, there is little research on the small-scale low-head Francis pump-turbine. Due to the hydraulic design of the flow path from the volute through the guide vane to the runner and then to the elbow-shaped draft tube, the design of the high-performance runner blade Due to the lack of experience in design and optimization of the overall structure and layout of the unit, this small mixed-flow reversible unit with simple structure, good hydraulic performance, convenient installation and maintenance, and less excavation of the upper and lower reservoirs has not been developed and promoted as it should be. .

Chinese patent application 200810010743.1 discloses a "pump turbine", which provides a micro-pump turbine with simple structure, low cost, small flow rate, and small volume. The runner needs to be replaced when the working conditions are interchanged, which brings great restrictions to continuous production and operation; second, the manufacturing process of the airfoil blade is extremely complicated, and the dimensional accuracy is difficult to guarantee, which directly affects the operating efficiency.

Chinese patent application 201310049897.2 discloses "a low-head shaft extension through-flow pump-turbine and its blades". Operating conditions, suitable for low head pumped storage power plants. However, there are still the following obvious deficiencies: first, the shaft-extension tubular-flow pump-turbine adopts a straight-bent draft tube, and the tail water energy recovery efficiency is low, resulting in a decrease in the efficiency of the entire unit; Difficulty and environmental noise, and inconvenient operation and maintenance, so it can only be applied to small units; third, the processing of runner blades and guide vanes is difficult, the structure is complicated and the cost is high.

How to overcome the deficiencies of existing technologies, make full use of my country's hydraulic resources, ensure the stable operation of the power grid, and further develop and promote low-head small mixed-flow reversible units have become one of the key problems to be solved in the field of hydraulic machinery technology.

Contents of the invention

The purpose of the present invention is to provide a small Francis pump-turbine used in a low-head pumped storage power station to overcome the deficiencies of the prior art. In other words, the same runner satisfies the dual needs of pumping water and power generation at the same time, and also satisfies the efficient operation of the pump turbine under both operating conditions.

According to the present invention, a small Francis pump-turbine used in a low-head pumped storage power station comprises a volute, a draft tube, a runner chamber, guide vanes, an upper cover, a runner, a seat ring and a bearing end cover, Among them: the volute, the guide vane, the runner and the draft tube are connected in sequence, the runner includes the runner blade, the lower ring, the upper crown and the discharge cone, the upper cover is set on the runner, the bearing end cover is set on the upper cover, It is characterized in that the wrapping angle of the runner blade is 105°～124°, the angle between the water inlet side and the water outlet side of the runner blade is 54°～86°, the runner blade is a three-dimensional twisted surface in space, and the thickness in the direction perpendicular to the bone line is equal, the profile of the runner blade is crescent-shaped, the ratio of the runner blade thickness to the runner blade inlet height B1 under the turbine working condition is 0.06-0.11, and the runner blade inlet height B1 to the guide vane height B2 under the turbine working condition equal, the airfoil of the guide vane is symmetrical whale-shaped, there are three evenly distributed decompression holes on the upper crown, the axial section of the volute is circular, the draft tube is elbow-shaped, and the axial section of the straight section is circular. shaped section.

The working principle of the present invention is that: in the operating unit of the low head pumped storage power station, the reversible motor and the small Francis pump-turbine of the present invention are included, the reversible motor has the dual functions of generator and motor, and the pump-turbine has both functions It has dual functions of water turbine and water pump. The operation of the pump turbine can be divided into two working conditions, that is, the turbine working condition and the water pump working condition. In the working condition of the water turbine, the water in the upper reservoir is put into the lower reservoir through the pump turbine, and the potential energy of the water is converted into electrical energy; the pump working condition Electric energy is used to lift the water in the lower reservoir to the upper reservoir to generate water level energy. The energy conversion process of the two working conditions is shown in Fig. 2 in detail. When other energy sources such as electric power are sufficient, the unit works in the water pump mode, and the water from the lower reservoir (17) is pumped to the upper reservoir (14) to be stored as water potential energy; When other energy sources are lacking, the unit works in the turbine mode to generate electric energy, thereby ensuring the stability of electric power supply.

Compared with the prior art, the present invention has the following remarkable advantages: First, in order to ensure that the low-head pumped storage power station can operate efficiently, flow smoothly, and have low flow channel resistance loss under both pump and turbine operating conditions, the present invention adopts a crescent Shaped line blade, the blade is a three-dimensional twisted surface in space, with equal thickness in the direction of the vertical bone line, and the guide vane airfoil is symmetrical whale-shaped; second, the runner can meet the requirements of two-way working conditions, that is, as much as possible under the water pump working condition Pump more water to the upstream reservoir to obtain more water level energy, and convert the water level energy into electric energy as much as possible under the working condition of the turbine; the third is to adopt the elbow-shaped draft tube, which has high tail water energy recovery efficiency. The comprehensive synergistic effect of the newly designed blade and guide vane makes the energy conversion efficiency of the water pump turbine of the present invention reach more than 85% under two working conditions; the fourth is that the structure of the blade and guide vane of the present invention is simple and easy to process And the cost is low, and the noise is very small and has no impact on the environment; fifth, the present invention is suitable for low-head pumped storage power stations of 10m to 15m, and the flow rate is small, and the required excavation of the upper and lower reservoirs is small, and the amount of civil engineering is small. The overall cost of the unit is reduced by more than 20% compared with the existing unit.

Description of drawings

Fig. 1 is a schematic cross-sectional view of the structure of a small Francis pump-turbine according to the present invention.

Fig. 2 is a schematic diagram of the energy conversion relationship under the two working conditions of water pumping and power generation in the operation of the present invention.

Fig. 3 is a schematic top view of the runner of the small Francis pump-turbine of the present invention.

Fig. 4 is a schematic top view of the runner blades of the small Francis pump-turbine of the present invention.

Fig. 5 is a schematic diagram of five sections of the runner blades of the small Francis pump-turbine of the present invention.

Fig. 6 is a schematic top view of the volute of the small Francis pump-turbine of the present invention.

Fig. 7 is a schematic top view of guide vanes of the small Francis pump-turbine of the present invention.

Fig. 8 is a schematic front view of the elbow-shaped draft tube of the small Francis pump-turbine of the present invention.

detailed description

The specific implementation manners of the present invention will be further described in detail below in conjunction with the drawings and examples.

In conjunction with Fig. 1, Fig. 3, Fig. 7, a kind of small-sized mixed-flow water pump-turbine used in the low-head pumped storage power station that the present invention proposes, it comprises volute (1), draft tube (4), runner chamber (5 ), guide vane (6), upper cover (7), runner (9), seat ring (12) and bearing end cover (13), of which: volute (1), guide vane (6), runner ( 9) and the draft tube (4) are connected sequentially, the runner (9) includes the runner blade (2), the lower ring (3), the upper crown (8) and the discharge cone (19), and the upper cover (7) is set on On the runner (9), the bearing end cover (13) is arranged on the upper cover (7), the wrap angle of the runner blade (2) is 105°～124°, and the runner blade (2) enters the water edge (11) The included angle with the water outlet edge (10) is 54°～86°, the runner blade (2) is a three-dimensional twisted curved surface in space, the thickness is equal in the direction perpendicular to the bone line, and the profile line of the runner blade (2) is a crescent shape, the ratio of the thickness of the runner blade (2) to the inlet height B1 of the runner blade (2) under the working condition of the water turbine is 0.06-0.11, the height B1 of the inlet of the runner blade (2) and the guide vane (6) under the working condition of the water turbine The height B2 is equal, the airfoil of the guide vane (6) is symmetrical whale-shaped, the upper crown (8) is provided with three evenly distributed decompression holes (18), and the shaft of the volute (1) The cross-section is a circular cross-section, and the draft tube (4) is elbow-shaped, and the axial cross-section of its straight section is a circular cross-section.

A further preferred solution of the present invention is: the runner blade (2) is a three-dimensional distorted curved surface in space, which means that five sections are equally divided and intercepted at the position of the runner blade (2) in the height direction, and ten curves of the five sections are The equation after fitting is as follows:

Section 1:

A: y＝-8.1873×10 ^-7 x ⁴ +3.3151×10 ^-4 x ³ -0.0550x ² +4.3443x-7.0786;

B:y＝-7.0371×10 ^-7 x ⁴ -2.8457×10 ^-4 x ³ -0.0477x ² +3.8439x+9.0093;

Section 2:

C:y＝-8.3253×10 ^-7 x ⁴ +3.3913×10 ^-4 x ³ -0.0569x ² +4.5383x-10.2586;

D:y＝-7.1166×10 ^-7 x ⁴ +2.8906×10 ^-4 x ³ -0.0490x ² +3.9749x+8.3510;

Section 3:

E:y＝-7.9770×10 ^-7 x ⁴ +3.2027×10 ^-4 x ³ -0.0532x ² +4.1926x+5.0454;

F:y＝-5.8482×10 ^-7 x ⁴ +2.3309×10 ^-4 x ³ -0.0403x ² +3.3553x+28.7474;

Section 4:

G:y＝-6.2045×10 ^-7 x ⁴ +2.4262×10 ^-4 x ³ -0.0409x ² +3.3220x+31.7707;

H:y＝-5.6279×10 ^-7 x ⁴ +2.2104×10 ^-4 x ³ -0.0376x ² +3.0802x+42.6535;

Section 5:

I: y＝-6.3436×10 ^-7 x ⁴ +2.4662×10 ^-4 x ³ -0.0410x ² +3.2495x+40.6523;

J:y＝-5.4378×10 ^-7 x ⁴ +2.0954×10 ^-4 x ³ -0.0351x ² +2.8187x+56.5296;

The number of runner blades (2) is 5-8; the ratio of the runner blade (9) height B3 to the diameter of the runner blade (2) inlet edge (11) under the hydraulic turbine working condition is 0.366- 0.407, the ratio of the diameter D4 of the outlet edge (10) of the runner blade (2) to the diameter D0 of the inlet edge (11) under the working condition of the water turbine is 0.538～0.578; the cross-sectional area of the volute (1) changes around the circumferential direction The equation is: y=-121.8016+4446.2x, the wrap angle of the volute (1) is 318° to 337°, as shown in Figure 6; the guide vanes (6) are evenly distributed on the seat ring (12) in a single row annular manner Among them, the ratio of the diameter of the distribution circle of the guide vane (6) to the diameter of the runner blade (2) inlet edge (11) under the working condition of the turbine is 0.855-0.861, the diameter of the throat of the guide vane (6) and the diameter of the runner blade (2) under the working condition of the turbine The diameter ratio of the water inlet side (11) of the wheel blade (2) is 0.124 to 0.131, the number of guide vanes (6) is 21, and the profile equation of the guide vanes (6) is y=-1.0185×10 ^-4 x ³ + 0.0115x ² +0.3339x+124.6627; The straight cone section divergence angle of described draft tube (4) is 13 °, as shown in Figure 8; Runner blade (2) water outlet edge ( 10) The ratio of the diameter D7 to the diameter D4 of the water inlet side (11) is 1.661-1.812; the upper crown (8) is provided with three uniformly distributed decompression holes (18) with a diameter of 10mm.

Combining with Figure 2, now taking the small Francis pump-turbine designed for both pumping and power generation as an example, the main components and design parameters of the unit and the small Francis pump-turbine in the two operating conditions of pumping water and power generation are: The unit includes a reversible motor MG (16), a small Francis pump-turbine PT (20), a valve (15), a water diversion mechanism, a diversion mechanism and a flow path, and the flow path includes a primary through-flow volute (1) flow Channel, through the flow channel of the guide vane (6), the runner (9) flow channel and the draft tube (4) flow channel; the reversible motor (16) is on the upper side of the pump turbine, connected with the pump turbine through the main shaft; The runner (9) is arranged in the runner chamber (5), above the runner is a loam cake (7), and the runner (9) includes runner blades (2), lower ring (3), upper crown (8) and The water discharge cone (19) is provided with three evenly distributed decompression holes (18) at the upper crown (8), and the shape of the runner blade (2) is equal in thickness in the vertical bone line direction, and the runner blade (2) Meet the design requirements of the Francis turbine and the Francis water pump, and take into account both the operating conditions of the turbine and the water pump; as shown in Figure 3, the diameter of the runner (9) is 250 mm, and the number of runner blades (2) is 6 The diameter of the guide vane (6) throat is 32.2mm, the number of guide vanes (6) is 21, the axial section of the volute (1) is a circular section, the diameter of the inlet section of the volute (1) is 250mm, and the tail The diameter of the inlet section of the water pipe (4) is 142 mm, and the diameter of the outlet section is 250 mm; as shown in Figure 4, the runner blade (2) is a three-dimensional distorted surface in space, using a crescent shaped line, and its spatial characteristics are represented by five sections , taking the rotation center of the runner as the reference, A, B, C, D, E, F, G, H, I and J represent curves, as shown in Figure 5, Ax, Bx, Cx, Dx, Ex, Fx, Gx , Hx, Ix and Jx are the abscissas of the corresponding points on the curve, Ay, By, Cy, Dy, Ey, Fy, Gy, Hy, Iy and Jy are the ordinates of the corresponding points on the curve, and the five sections are in the rectangular coordinate system The mid-position is represented by the partial point coordinates as follows:

Section 1

Numbering 1 2 3 4 5 6 7 8 9 Ax 42.5 45 55 65 75 85 95 105 115 Ay 101.8 104.4 112.9 118.9 123.3 126.1 127.5 127.7 127.3 Bx 40 50 60 70 80 90 100 110 120 By 103.51 112.88 119.67 124.58 127.96 129.99 130.78 130.36 128.71 Numbering 10 11 12 13 14 15 16 17 18 Ax 125 135 145 155 165 175 180 Ay 124.3 120.5 115 107.3 96.48 79.42 63.63 Bx 130 140 150 160 170 180 182.5 By 125.75 121.33 115.16 106.69 94.68 74.8 65.97

Section 2:

Numbering 1 2 3 4 5 6 7 8 9 Cx 42.5 45 55 65 75 85 95 105 115 Cy 103.93 106.71 115.76 122.21 126.69 129.13 130.96 131.02 129.75 Dx 40 50 60 70 80 90 100 110 120 Dy 106.3 116.16 123.24 128.31 131.73 133.71 134.37 133.75 131.83 Numbering 10 11 12 13 14 15 16 17 18 Cx 125 135 145 155 165 175 180 Cy 127.09 122.91 116.99 108.82 97.4 79.65 63.78 Dx 130 140 150 160 170 180 182.5 Dy 128.54 123.73 117.09 108.09 95.45 74.91 66.14

Section 3:

Numbering 1 2 3 4 5 6 7 8 9 Ex 42.5 45 55 65 75 85 95 105 115 Ey 110.07 112.41 120.4 126.16 130.13 129.55 133.62 133.36 131.79 Fx 42.5 45 55 65 75 85 95 105 115 Fy 115.11 117.33 124.68 130.03 133.73 136 136.95 136.64 135.08 Numbering 10 11 12 13 14 15 16 17 18 Ex 125 135 145 155 165 175 180 Ey 128.83 124.37 118.13 109.64 97.86 79.71 63.77 Fx 125 135 145 155 165 175 180 182.5 Fy 132.19 127.88 121.9 113.85 102.91 86.96 74.88 66.11

Section 4:

Numbering 1 2 3 4 5 6 7 8 9 Gx 42.5 45 55 65 75 85 95 105 115 Gy 116.55 118.3 125.26 130.31 133.74 135.75 136.43 135.83 133.94 Hx 42.5 45 55 65 75 85 95 105 115 Hy 121.35 123.26 129.65 134.31 137.47 139.3 139.87 139.22 137.33

Numbering 10 11 12 13 14 15 16 17 18 Gx 125 135 145 155 165 175 180 Gy 130.68 125.91 119.35 110.51 98.35 79.76 63.76 Hx 125 135 145 155 165 175 180 182.5 Hy 134.14 129.51 123.21 114.82 103.51 87.14 74.86 66.09

Section 5:

Numbering 1 2 3 4 5 6 7 8 9 Ix 45 55 65 75 85 95 105 115 125 Iy 124.35 130.32 134.66 137.54 139.09 139.38 138.43 136.21 132.63 Jx 42.5 45 55 65 75 85 95 105 115 jy 127.83 129.43 134.87 138.83 141.44 142.8 142.97 141.96 139.73 Numbering 10 11 12 13 14 15 16 17 18 Ix 135 145 155 165 175 180 Iy 127.53 120.64 111.43 98.86 79.82 63.75 Jx 125 135 145 155 165 175 180 jy 136.21 131.25 124.62 115.86 104.15 87.32 74.84

The ten curve fitting equations of the five sections are as follows:

Section 1:

A: y＝-8.1873e-07x ⁴ +3.3151e-04x ³ -0.0550x ² +4.3443x-7.0786;

B: y＝-7.0371e-07x ⁴ -2.8457e-04x ³ -0.0477x ² +3.8439x+9.0093;

Section 2:

C:y=-8.3253e-07x ⁴ +3.3913e-04x ³ -0.0569x ² +4.5383x-10.2586;

D:y＝-7.1166e-07x ⁴ +2.8906e-04x ³ -0.0490x ² +3.9749x+8.3510;

Section 3:

E:y＝-7.9770e-07x ⁴ +3.2027e-04x ³ -0.0532x ² +4.1926x+5.0454;

F: y＝-5.8482e-07x ⁴ +2.3309e-04x ³ -0.0403x ² +3.3553x+28.7474;

Section 4:

G:y＝-6.2045e-07x ⁴ +2.4262e-04x ³ -0.0409x ² +3.3220x+31.7707;

H:y＝-5.6279e-07x ⁴ +2.2104e-04x ³ -0.0376x ² +3.0802x+42.6535;

Section 5:

I: y＝-6.3436e-07x ⁴ +2.4662e-04x ³ -0.0410x ² +3.2495x+40.6523;

J: y=-5.4378e-07x ⁴ +2.0954e-04x ^{3-0.0351x 2} +2.8187x+56.5296.

The present invention has obtained satisfactory application effects through repeated tests. The small Francis-type pump-turbine described in the embodiment is suitable for a pumped-storage power station with a low head of 10-15m, and the running speed of the runner (9) is 1000r/min-1500r/min. It is actually measured that the power generation and the water pump under the turbine working conditions The energy conversion efficiency of pumping water under working conditions can reach more than 87%.

The above specific implementation methods and examples are specific support for the technical idea of a small Francis pump-turbine used in a low-head pumped storage power station proposed by the present invention, and cannot be used to limit the protection scope of the present invention. The proposed technical ideas and any equivalent changes or equivalent changes made on the basis of this technical solution still belong to the scope of protection of the technical solution of the present invention.

Claims (8)

1. A small Francis pump-turbine used in a low-head pumped-storage power station, which comprises a volute (1), a draft tube (4), a runner chamber (5), guide vanes (6), an upper cover (7 ), the runner (9), the seat ring (12) and the bearing end cover (13), wherein: the volute (1), the guide vane (6), the runner (9) and the draft tube (4) are connected in sequence, Wheel (9) comprises runner blade (2), lower ring (3), upper crown (8) and drain cone (19), loam cake (7) is arranged on the runner (9), bearing end cover (13 ) is arranged on the upper cover (7), and it is characterized in that the wrapping angle of the runner blade (2) is 105°～124°, and the included angle between the water inlet edge (11) and the water outlet edge (10) of the runner blade (2) is 54°～86°, the runner blade (2) is a three-dimensional distorted curved surface in space, and the thickness in the vertical bone line direction is equal, the profile of the runner blade (2) is crescent-shaped, and the thickness of the runner blade (2) is the same as that of the hydraulic turbine. The ratio of the inlet height B1 of the runner blade (2) is 0.06 to 0.11, and the inlet height B1 of the runner blade (2) is equal to the height B2 of the guide vane (6) under the hydraulic turbine working condition, and the airfoil of the guide vane (6) is symmetrical Whale-shaped, with three evenly distributed decompression holes (18) on the upper crown (8), the axial section of the volute (1) is a circular section, the draft tube (4) is elbow-shaped, and its straight section shaft The cross-section is circular; the guide vanes (6) are evenly distributed in the seat ring (12) in a single-row annular manner, and the distribution circle diameter of the guide vanes (6) is the same as that of the water inlet edge of the runner blade (2) under the hydraulic turbine working condition. (11) The ratio of the diameters is 0.855 to 0.861, the diameter ratio of the throat diameter of the guide vane (6) to the diameter of the runner blade (2) inlet edge (11) under the working condition of the turbine is 0.124 to 0.131, the number of the guide vanes (6) is 21, and the profile equation of the guide vane (6) is: y= ^-1.0185 × ^10-4x3 +0.0115x2 ⁺ 0.3339x+124.6627. 2. The small Francis water pump-turbine according to claim 1, characterized in that the runner blade (2) is a three-dimensional twisted curved surface in space, which means that the runner blade (2) is equally divided into five parts in the height direction position. section, the ten curve fitting equations of the five sections are as follows: Section 1: A: y＝-8.1873×10 ^-7 x ⁴ +3.3151×10 ^-4 x ³ -0.0550x ² +4.3443x-7.0786; B:y＝-7.0371×10 ^-7 x ⁴ -2.8457×10 ^-4 x ³ -0.0477x ² +3.8439x+9.0093; Section 2: C:y＝-8.3253×10 ^-7 x ⁴ +3.3913×10 ^-4 x ³ -0.0569x ² +4.5383x-10.2586; D:y＝-7.1166×10 ^-7 x ⁴ +2.8906×10 ^-4 x ³ -0.0490x ² +3.9749x+8.3510; Section 3: E:y＝-7.9770×10 ^-7 x ⁴ +3.2027×10 ^-4 x ³ -0.0532x ² +4.1926x+5.0454; F:y＝-5.8482×10 ^-7 x ⁴ +2.3309×10 ^-4 x ³ -0.0403x ² +3.3553x+28.7474; Section 4: G:y＝-6.2045×10 ^-7 x ⁴ +2.4262×10 ^-4 x ³ -0.0409x ² +3.3220x+31.7707; H:y＝-5.6279×10 ^-7 x ⁴ +2.2104×10 ^-4 x ³ -0.0376x ² +3.0802x+42.6535; Section 5: I: y＝-6.3436×10 ^-7 x ⁴ +2.4662×10 ^-4 x ³ -0.0410x ² +3.2495x+40.6523; J: y＝-5.4378× ^10-7 x ⁴ +2.0954× ^10-4 x ^{3-0.0351x 2} +2.8187x+56.5296. 3. The small Francis pump-turbine according to claim 1 or 2, characterized in that the number of runner blades (2) is 5-8. 4. The small Francis water pump turbine according to claim 1, characterized in that the ratio of the height B3 of the runner (9) to the diameter of the runner blade (2) inlet edge (11) under the working condition of the turbine is 0.366-0.407, The ratio of the diameter D4 of the water outlet side (10) of the runner blade (2) to the diameter D0 of the water inlet side (11) under the working condition of the water turbine is 0.538-0.578. 5. The small Francis water pump-turbine according to claim 1, characterized in that the trend equation of the cross-sectional area of the volute (1) around the circumference direction is: y=-121.8016+4446.2x, and the wrap angle of the volute (1) is 318 °～337°. 6. The small Francis pump-turbine according to claim 1, characterized in that the divergence angle of the straight cone section of the draft tube (4) is 13°. 7. The small Francis water pump turbine according to claim 1, characterized in that the ratio of the diameter D7 of the outlet side (10) of the runner blade (2) to the diameter D4 of the water inlet side (11) under the working condition of the turbine is 1.661～ 1.812. 8. The small Francis pump-turbine according to claim 1, characterized in that the upper crown (8) is provided with three evenly distributed decompression holes (18) with a diameter of 10mm.