A vortex belt control device for a water turbine tailwater tube

Abstract

The present invention provides a vortex belt control device for a tailwater pipe of a turbine, comprising a support rod that can be freely slidably installed in the tailwater pipe of the turbine in a vertical direction, a plurality of fan blades hinged on the support rod in an annular distribution, and an opening and closing mechanism for driving the fan blades to rotate around their respective hinge points to achieve an umbrella-like opening and closing to adjust the opening and closing angles of the fan blades. The opening and closing angles of the fan blades are adjusted by the opening and closing mechanism so that the fan blades pass through the shear layer area. When the shear layer encounters the fan blades, the fan blades can block the relative movement of the fluid at the interface, thereby blocking the fluid vortex filaments from converging into spiral vortex belts. The present invention adjusts the angle of the fan blades by regulating the up and down movement of the slider, and adjusts the height position of the fan blades by driving the support rod to move up and down through a power mechanism. The fan blades can be adjusted to the optimal use angle and height according to the actual working conditions of the turbine, thereby destroying the shear layer to the greatest extent and achieving the best vortex belt control effect.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy and hydropower engineering, and in particular relates to a vortex belt control device for a water turbine tail water pipe. Background Art

[0002] Hydropower is an important renewable energy source and the key to my country's green and low-carbon energy development and achieving the "dual carbon" goal. It is widely used in power generation and grid stabilization. In the new context of the integrated development of water, wind and solar power, the advantage of rapid start and stop of hydropower makes it an important grid regulation energy source. Mixed flow turbines are applicable to a wide range of heads and are widely used in large, medium and small hydropower stations. The water flow of the mixed flow turbine flows radially into the runner through the volute, fixed guide vanes and movable guide vanes in turn, driving the runner to drive the generator to generate electricity, and changes the flow direction to flow axially into the tailwater pipe. Since the runner blades are fixed and cannot be adjusted, the water flow cannot be guaranteed to flow into the runner at the optimal fixed angle after the movable guide vanes rotate. When the turbine deviates from the optimal operating condition, the tangential velocity component of the water flow often increases after passing through the runner. When the water flow enters the tailwater pipe below the runner, a strong vortex is formed inside the tailwater pipe, and the water flow inside the vortex moves upward along the axis of the tailwater pipe in the reverse direction, and the water flow outside the vortex moves downward in a spiral to form a shear layer, which then develops into a spiral vortex belt. A strong pressure pulsation phenomenon will occur inside the tailwater pipe, which will induce surge and reduce efficiency. In severe cases, resonance may occur, causing mechanical damage, shortened service life, equipment failure, etc. This pressure pulsation seriously affects the stable operation of the turbine unit.

[0003] Under the new situation, Francis turbines are increasingly operating under partial load or even extreme partial load conditions. Currently, there is still no good way to control the vortex belt in the draft tube and reduce the impact of the vortex belt in the draft tube. Therefore, it is urgent to develop a vortex belt control device for the draft tube of a turbine so as to achieve the purpose of controlling the vortex belt and its pressure pulsation by destroying the shear layer. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a vortex belt control device for a tailwater pipe of a turbine, which does not affect the operation of the turbine under normal working conditions, and can adjust the height position and angle of the fan blades according to the actual working conditions under partial load conditions to achieve maximum destruction of the shear layer, achieve the best vortex belt control effect, and reduce the impact of pressure pulsation. The present invention can be applied to different partial load conditions, and has a simple structure and is easy to operate.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A vortex belt control device for a water turbine tailwater tube, comprising:

[0007] A support rod is installed in the turbine tailwater tube so as to be freely slidable in the vertical direction;

[0008] A plurality of fan blades are distributed in a ring shape and are hinged on the support rod;

[0009] The opening and closing mechanism is used to drive the fan blades to rotate around their respective hinge points to achieve umbrella-like opening and closing, so as to adjust the opening and closing angles of the fan blades.

[0010] Furthermore, the opening and closing mechanism includes a regulating slider, a support frame and a linear motion mechanism. The regulating slider is driven by the linear motion mechanism and can slide freely up and down and is installed in the support rod. The middle part of each fan blade is hingedly connected to the regulating slider through a support frame.

[0011] Furthermore, the linear motion mechanism includes a first driving device installed on the top of the support rod and a screw rod fixedly connected to the first output shaft of the first driving device, and the screw rod extends into the support rod and is threadedly connected to the regulating slider.

[0012] Furthermore, a slide groove is provided in the range where the spiral screw rod extends on the support rod, and the regulating slider can be installed in the slide groove so as to slide up and down, and the support frame is hingedly connected to the regulating slider in the slide groove.

[0013] Furthermore, the bottom of the support rod is connected to a power mechanism that can drive the support rod to slide in a vertical direction. The power mechanism includes a second driving device, a meshing worm wheel and worm, and a power rod fixed on the worm wheel. The worm is connected to the second output shaft of the second driving device, and the power rod is threadedly connected to the bottom of the support rod.

[0014] Furthermore, the power mechanism also includes a machine box, the worm wheel and the worm are meshed in the machine box, the second driving device is located outside the machine box, and a second water stopper is provided at the connection between the second output shaft and the machine box.

[0015] Furthermore, an elastic sleeve is provided on the outer wall of the support rod, and two ends of the elastic sleeve are respectively fixed to the lower wall of the tailwater pipe and the top of the machine box.

[0016] Furthermore, the portion of the power rod located inside the machine box is provided with an external thread.

[0017] Furthermore, a fixed ring is installed on the top of the support rod, and the roots of the plurality of fan blades are symmetrically hinged to the fixed ring.

[0018] Furthermore, the linear motion mechanism also includes a motor housing made of waterproof material installed on the top of the support rod, the first drive device is arranged in the motor housing, and a first water stopper is provided at the connection between the first output shaft and the motor housing.

[0019] The beneficial effects of the present invention are:

[0020] 1. A plurality of fan blades of the present invention are hinged on the support rod in a ring-shaped distribution, and the fan blades are driven to rotate around their respective hinge points through an opening and closing mechanism to achieve umbrella-shaped opening and closing, so as to adjust the opening and closing angles of the fan blades. Since the inclination angles of the shear layer formed in the tailwater pipe are different under different working conditions, by setting angle-adjustable fan blades, the opening and closing angles of the fan blades can be adjusted according to different operating conditions, thereby destroying the shear layer to the greatest extent, directly blocking the breeding and development of the shear layer, thereby inhibiting the formation of vortex belts, and reducing pressure pulsation, thereby ensuring the stability of the internal flow of the mixed flow turbine and the operation of the hydropower station plant.

[0021] 2. The present invention arranges the support rod to be able to move freely in the tailwater pipe of the turbine in the vertical direction. When the turbine operates under the designed working conditions, the vortex control mechanism does not need to work, and the fan blades can be lowered to the bottom of the tailwater pipe by adjusting the position of the support rod in the vertical direction, thereby minimizing the influence of the vortex control device of the present invention on the internal flow of the tailwater pipe; when the turbine operates under the eccentric load condition, since the position height and angle of the shear layer are different under different working conditions, the position height of the support rod can be adjusted in the vertical direction according to different working conditions, thereby adjusting the position height of the fan blades, thereby maximally destroying the shear layer and achieving the best vortex control effect.

[0022] 3. The present invention can control the up and down movement of the support rod and the regulating slider only by controlling the first drive device and the second drive device, thereby adjusting the height position and opening and closing angle of the fan blades. The structural design is safe and reasonable, and the operation is convenient. The present invention sets an elastic sleeve between the support rod and the tailwater pipe and the outer wall of the machine box, and sets a water stop plug at the connection between the second output shaft and the machine box and at the connection between the first output shaft and the motor housing. Both settings play a role in stopping water, preventing water leakage from the tailwater pipe when the turbine is working, causing damage to the drive mechanism, and playing a multiple protection role for the drive mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the installation structure of a vortex belt control device of a water turbine draft tube according to the present invention;

[0024] Figure 2 It is a schematic diagram of the side structure of a vortex belt control device of a water turbine draft tube according to the present invention;

[0025] Figure 3 It is a schematic diagram of the top surface installation structure of the fan blade of the present invention;

[0026] Figure 4 It is a schematic diagram of the bottom surface installation structure of the fan blade of the present invention;

[0027] Figure 5 It is a structural schematic diagram of the power mechanism of the present invention;

[0028] Figure 6 Schematic diagram of vortex belt and shear layer.

[0029] Reference numerals:

[0030] 100-tailwater pipe, 200-support rod, 210-slideway, 220-elastic sleeve, 230-fixing ring, 300-fan blade;

[0031] 400-opening and closing mechanism, 410-regulating slider, 420-supporting frame, 430-linear motion mechanism, 431-first driving device, 432-first output shaft, 433-micro motor, 434-power supply, 435-screw rod, 436-motor housing, 437-first water stopper;

[0032] 500-power mechanism, 510-second driving device, 511-second output shaft, 520-worm gear, 530-worm, 540-power rod, 550-machine box, 560-second water stopper;

[0033] 700- vortex belt, 800- shear layer. DETAILED DESCRIPTION

[0034] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] like Figure 1As shown, the present invention provides a vortex belt control device for a water turbine tailwater tube, comprising:

[0038] The support rod 200 is installed in the tailwater pipe 100 so as to be freely slidable in the vertical direction;

[0039] A plurality of fan blades 300 are distributed in an annular shape and are hinged on the support rod 200;

[0040] The opening and closing mechanism 400 is used to drive the fan blades 300 to rotate around their respective hinge points to achieve umbrella-like opening and closing, so as to adjust the opening and closing angles of the fan blades 300.

[0041] The Francis turbine is provided with a tailwater pipe 100 to recover the kinetic energy and gravitational potential energy at the runner outlet to improve efficiency. Figure 6 As shown, when the turbine operates under partial load conditions, the tangential velocity component at the runner outlet increases, resulting in the formation of a strong vortex inside the tailwater pipe 100. The water flow inside the vortex moves upward along the axis of the tailwater pipe 100 in a countercurrent manner, and the water flow outside the vortex moves downward in a spiral, thereby forming a shear flow at the interface. The fluid vortex filaments roll up around the shear layer 800, nurturing and converging to form a spiral vortex belt 700 that rotates around the axis of the tailwater pipe 100.

[0042] The present invention hinges the roots of a number of annularly distributed fan blades 300 on the support rod 200, and drives the fan blades 300 to rotate around their respective hinge points through the opening and closing mechanism 400 to achieve umbrella-like opening and closing, so as to adjust the opening and closing angles of the fan blades 300, so that the fan blades 300 pass through the shear layer 800 area. When the shear layer 800 encounters the fan blades 300, the fan blades 300 can block the relative movement of the fluid at the interface, thereby blocking the fluid vortex from converging into a spiral vortex belt 700. Since the more the turbine deviates from the design working condition, the more the shear layer 800 deviates from the center position, so it is necessary to adjust the angle and position of the fan blades 300 according to the actual working condition of the turbine, so as to achieve the maximum destruction of the shear layer 800, inhibit the generation of the vortex belt 700, and reduce the pressure pulsation, so as to ensure the internal flow of the mixed flow turbine and the stability of the operation of the hydropower plant. The present invention drives the fan blade 300 to rotate around the support rod 200 through the opening and closing mechanism 400 to adjust the angle of the fan blade 300, and adjusts the height position of the fan blade 300 by moving the support rod 200 in the vertical direction in the tailwater pipe 100, thereby adjusting the fan blade 300 to the optimal use angle and height according to the actual working conditions of the turbine, thereby destroying the shear layer 800 to the greatest extent and achieving the best control effect of the vortex belt 700. Therefore, the vortex belt control device of the present invention can not only well control the vortex belt 700 in the tailwater pipe 100, but also can be used under different turbine working conditions, and can also be suitable for tailwater pipes 100 with different shapes.

[0043] In some embodiments, Figure 1 and Figure 2 The opening and closing mechanism 400 includes a regulating slider 410, a support frame 420 and a linear motion mechanism 430. The two ends of the support frame 420 are respectively hinged to the end of the regulating slider 410 and the middle position of the bottom surface of the fan blade 300. The regulating slider 410 is installed in the support rod 200 and is connected to the linear motion mechanism 430. Under the driving action of the linear motion mechanism 430, the regulating slider 410 can slide freely up and down along the support rod 200 to drive the fan blade 300 to rotate around the support rod 200, thereby realizing an umbrella-shaped opening and closing, and then adjusting the opening and closing angle of the fan blade 300.

[0044] In some embodiments, Figure 1 and Figure 2 As shown, the linear motion mechanism 430 includes a first driving device 431 installed on the top of the support rod 200 and a screw rod 435 fixedly connected to the first output shaft 432 of the first driving device 431, and the screw rod 435 extends into the support rod 200 and is threadedly connected to the regulating slider 410. After the support rod 200 drives the fan blades 300 to move to a suitable height according to the actual use condition of the turbine, the opening angle of the fan blades 300 needs to be adjusted, and the first driving device 431 is turned on, and the first output shaft 432 will drive the screw rod 435 to rotate. Since the screw rod 435 is threadedly connected to the regulating slider 410 in the support rod 200, the rotation of the screw rod 435 will drive the regulating slider 410 to move up and down along the support rod 200. Since the two ends of the support frame 420 are respectively hinged to the middle of the fan blade 300 and the end of the regulating slider 410, and the root of the fan blade 300 is hinged to the top of the lifting mechanism, when the regulating slider 410 moves upward along the support rod 200, the opening angle of the fan blade 300 will be increased through the support frame 420, thereby realizing the opening of the fan blade 300; when the regulating slider 410 moves downward along the support rod 200, the opening angle of the fan blade 300 will be reduced through the support frame 420, thereby realizing the retraction of the fan blade 300.

[0045] In some embodiments, the opening angle range of the fan blades 300 is set to 0-30° according to different operating conditions of the turbine, as follows: when the turbine is operating under design conditions, the vortex belt control device of the present application does not need to work, and the opening angle of the fan blades 300 is 0°; when operating under the condition of 0.75 times the design flow rate, the opening angle of the fan blades 300 is adjusted to 7.5° by controlling the regulating slider 410 to rise along the support rod 200; when operating under the condition of 0.5 times the design flow rate, the opening angle of the fan blades 300 is adjusted to 15°; when operating under the condition of 0.25 times the design flow rate, the opening angle of the fan blades 300 is adjusted to 22.5°. The present invention can further increase the opening angle of the fan blades 300 to 30° according to the reduction of flow rate in actual use conditions.

[0046] As a preferred embodiment, Figure 2 As shown, the first driving device 431 includes a micro motor 433 and a power supply 434. The power supply 434 is detachably mounted on the micro motor 433 to supply power to the micro motor 433. When the turbine is not working, the power supply 434 needs to be replaced regularly.

[0047] As a preferred embodiment, the linear motion mechanism 430 further includes a motor housing 436 made of waterproof material installed on the top of the support rod 200, and the first drive device 431 is arranged in the motor housing 436. The motor housing 436 is fixed to the top of the support rod 200 by fasteners such as bolts to provide waterproof protection for the first drive device 431. A first water stopper 437 is provided at the connection between the first output shaft 432 and the motor housing 436 to prevent water in the tailwater pipe 100 from flowing into the motor housing 436 and affecting the normal use of the first drive device 431.

[0048] In some embodiments, Figure 2 and Figure 4 As shown, a slide groove 210 is provided within the range where the screw rod 435 extends on the support rod 200, and the regulating slider 410 can be installed in the slide groove 210 so as to slide up and down, and the support frame 420 is hingedly connected with the regulating slider 410 in the slide groove 210. An internal threaded hole is provided in the middle of the regulating slider 410, one end of the screw rod 435 is fixed to the first output shaft 432, and the other end is threadedly connected to the internal threaded hole in the middle of the regulating slider 410, and both ends of the regulating slider 410 are hingedly connected with the supporting frame 420 on both sides in the slide groove 210. When the first driving device 431 drives the screw rod 435 to rotate, the regulating slider 410 will move up and down along the slide groove 210, thereby driving the fan blades 300 to open and close.

[0049] In some embodiments, Figure 1 and Figure 5As shown, the bottom of the support rod 200 is connected to a power mechanism 500 capable of driving the support rod 200 to slide in the vertical direction, the power mechanism 500 includes a second driving device 510, a meshing worm wheel 520 and a worm 530, and a power rod 540 fixed to the worm wheel 520, the worm 530 is connected to the second output shaft 511 of the second driving device 510, and the power rod 540 is threadedly connected to the bottom of the support rod 200. Specifically, the power rod 540 is provided with an external thread, and the lower end of the support rod 200 is provided with an internal thread matched with the power rod 540. When the height position of the fan blade 300 needs to be adjusted according to the actual working condition of the turbine, the second driving device 510 is turned on to start working, and the second output shaft 511 will drive the worm 530 to rotate. Since the worm wheel 520 is meshed with the worm 530, the worm 530 will drive the worm wheel 520 to rotate, and then drive the power rod 540 fixed at the center of the worm wheel 520 to rotate. Since the support rod 200 is threadedly connected to the power rod 540, the rotation of the power rod 540 will drive the support rod 200 to move up and down, thereby realizing the position height adjustment of the fan blade 300 hinged on the support rod 200. The present invention sets a power mechanism 500. When the turbine operates under the designed working condition, since the fan blades 300 do not need to work, the fan blades 300 can be lowered to the bottom of the tailwater pipe 100 through the power mechanism 500, thereby minimizing the impact of the present invention on the internal flow of the tailwater pipe 100; when the turbine operates under the eccentric load condition, since the position height and angle of the shear layer 800 are different under different working conditions, the height position of the fan blades 300 can be adjusted according to different working conditions through the power mechanism 500, thereby maximally destroying the shear layer 800 and achieving the best vortex belt 700 control effect.

[0050] As a preferred embodiment, the second driving device 510 is a driving motor.

[0051] In some embodiments, Figure 1 and Figure 5 As shown, the power mechanism 500 further includes a machine box 550, the worm wheel 520 and the worm 530 are meshed in the machine box 550, the second drive device 510 is located outside the machine box 550, and the second output shaft 511 passes through the machine box 550 and is connected to the worm 530, and a second water stopper 560 is provided at the connection between the second output shaft 511 and the machine box 550. When the water turbine is working, the draft tube 100 will be filled with water, and at this time, part of the water may flow out of the draft tube 100 along the support rod 200. By providing the machine box 550 and the second water stopper 560, the worm wheel is isolated from the second drive device 510, so as to prevent the water flowing out of the draft tube 100 from causing damage to the second drive device 510.

[0052] In some embodiments, Figure 1As shown, a section of elastic sleeve 220 is provided on the outer wall of the support rod 200, and the two ends of the elastic sleeve 220 are respectively fixed to the lower wall of the tailwater pipe 100 and the top of the machine box 550. The extrusion force between the elastic sleeve 220 and the support rod 200 can play a water-stopping role, which can avoid the leakage of water flow in the tailwater pipe 100 and prevent the leaked water flow from flowing into the machine box 550.

[0053] As a preferred embodiment, the first water stopper 437 and the second water stopper 560 can be configured as rubber water stoppers, and the elastic sleeve 220 can be configured as a rubber sleeve.

[0054] In some embodiments, Figure 1 As shown, only the part of the power rod 540 located in the machine box 550 is provided with an external thread. When the worm gear 520 drives the power rod 540 to rotate, the bottom of the support rod 200 will not leave the machine box 550, thereby avoiding the support rod 200 leaving the machine box 550 to cause a gap between the elastic sleeve 220 and the power rod 540, thereby causing the water in the tail water pipe 100 to flow out and affecting the normal operation of the power mechanism 500.

[0055] In some embodiments, the vortex belt 700 control mechanism further includes a fixed ring 230 installed on the top of the lifting mechanism, the fixed ring 230 is fixed to the top of the support rod 200 by welding or threaded fasteners, and the roots of the fan blades 300 are symmetrically hinged on the fixed ring 230. Figure 3 and Figure 4 As shown, three fan blades 300 are hinged on each side of the fixed ring 230, and the number of support frames 420 is the same as the number of fan blades 300 and are respectively hinged to the middle of the bottom surface of each fan blade 300. Specifically, a hinge groove with a hole is provided in the middle of each fan blade 300, and an opening is provided at one end of the support frame 420, and the opening is placed in the hinge groove. The fan blade 300 and the support frame 420 are connected by pins, and the other end of the support frame 420 is connected to the end of the regulating slider 410 in the same way. Based on this structure, the angle of the fan blade 300 can be adjusted according to the lifting and lowering of the regulating slider 410.

[0056] The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the scope of the claims of the present invention.

Claims

1. A vortex belt control device for a water turbine draft tube, characterized in that: include: A support rod is installed in the turbine tailwater tube so as to be freely slidable in the vertical direction; A plurality of fan blades are distributed in a ring shape and are hinged on the support rod; The opening and closing mechanism is used to drive the fan blades to rotate around their respective hinge points to achieve an umbrella-like opening and closing, so as to adjust the opening and closing angles of the fan blades; The opening and closing mechanism includes a regulating slider, a support frame and a linear motion mechanism. The regulating slider is driven by the linear motion mechanism and can slide freely up and down and is installed in the support rod. The middle of each fan blade is hingedly connected to the regulating slider through a support frame. The linear motion mechanism comprises a first driving device mounted on the top of the support rod and a screw rod fixedly connected to the first output shaft of the first driving device, the screw rod extends into the support rod and is threadedly connected to the regulating slider; The fan blade opening angle range is set to 0-30°; The bottom of the support rod is connected to a power mechanism that can drive the support rod to slide in a vertical direction. The power mechanism includes a second drive device, a meshing worm wheel and worm, and a power rod fixed on the worm wheel. The worm is connected to the second output shaft of the second drive device, and the power rod is threadedly connected to the bottom of the support rod.

2. A vortex belt control device for a water turbine draft tube according to claim 1, characterized in that: A slide groove is provided in the range where the spiral screw rod on the support rod extends, and the regulating slider can be installed in the slide groove so as to slide up and down, and the support frame is hingedly connected with the regulating slider in the slide groove.

3. The vortex belt control device of the water turbine draft tube according to claim 1, characterized in that: The power mechanism also includes a machine box, the worm wheel and the worm are meshed in the machine box, the second driving device is located outside the machine box, and a second water stopper is provided at the connection between the second output shaft and the machine box.

4. A vortex belt control device for a water turbine draft tube according to claim 3, characterized in that: An elastic sleeve is arranged on the outer wall of the support rod, and two ends of the elastic sleeve are respectively fixed to the lower wall of the tailwater pipe and the top of the machine box.

5. The vortex belt control device for the draft tube of a water turbine according to claim 4, characterized in that: The portion of the power rod located inside the machine box is provided with an external thread.

6. The vortex belt control device for the draft tube of a water turbine according to claim 1, characterized in that: A fixed circular ring is installed on the top of the support rod, and the roots of the plurality of fan blades are symmetrically hinged on the fixed circular ring.

7. The vortex belt control device for the draft tube of a water turbine according to claim 1, characterized in that: The linear motion mechanism also includes a motor housing made of waterproof material and mounted on the top of the support rod. The first drive device is arranged in the motor housing. A first water stopper is arranged at the connection between the first output shaft and the motor housing.

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