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Design and development of large-scale axially extended tubular turbine generator set

Abstract: at present, the axially extended tubular turbine generator set with speed increaser with the largest runner diameter in China has been put into power generation. This paper introduces the design idea and structural characteristics of the large-scale shaft extension tubular turbine generator set developed by Dongfeng Electric Machinery Co., Ltd

key words: axial through flow; Turbine generator unit; Structure; Design plan

1 overview

large shaft extension tubular turbine generator set is a model developed by Dongfeng Electric Machinery Co., Ltd. with simple structure, excellent performance and convenient installation and maintenance. It is suitable for the installation of low head and large flow power stations. Generally, it uses units with water head of 2.5 ~ 18m, diameter class of D1 ≤ 3M and single unit rated output of n=5mw. This type of generator moves out of the bulb body and is exposed outside the turbine. Various forms of speed increasing devices can also be used. Since conventional generators can be used, the economy of small and medium-sized units is significant. In the development of small and medium-sized hydraulic resources, the axial expansion tubular flow has less investment and better economy than the bulb tubular flow. It is more convenient to install, use, repair and maintain than the bulb tubular flow, and is close to the bulb tubular machine in terms of performance. The following table lists some of these models and typical power stations that have been put into operation by Dongfeng Electric Corporation

2 general layout

the shaft extends through the water turbine unit. The water flow is introduced from the inlet pipe and discharged to the tailrace channel through the water guide mechanism, runner and draft tube. The elbow tube behind the runner chamber is S-shaped, and the main shaft of the hydraulic turbine passes through the elbow tube horizontally and is connected with the conventional generator through the speed increaser. The water turbine generator set is equipped with 3 bearings, including 2 bearings at the turbine side. The radial bearing of the water turbine is arranged in the fixed support, and the radial thrust bearing is arranged on the plant floor between the elbow seal seat and the speed increaser; The radial bearing of the generator is arranged on the downstream side of the rotor. The generator and turbine bearings share an oil supply system for centralized oil supply. In order to ensure the stable operation of the unit, there is enough distance between the bottom of the generator pit and the flow channel

the shaft extended through flow turbine is arranged horizontally and axially, without volute, and the flow channel is also axial. The water flow is parallel to the axis of the turbine to the runner. The water guide mechanism can be arranged near the runner blade, so as to fully control the water flow conditions at the runner inlet, so that the runner has better cavitation resistance. The water guide mechanism adopts conical arrangement, and 16 guide vanes are conical arranged between the inner and outer water distribution rings, with a cone angle of 65 °. Considering the stability of the unit operation, most of the stay ring of the inlet pipe and the draft tube are buried in the concrete. A square hole is opened on the top of the water inlet pipe of the hydraulic turbine for loading and unloading the workpiece in the bulb body. For the hydraulic turbine part in the flow passage, there are four fixed pillars, of which the upper pillar is the inlet of oil, gas and water pipelines, and the lower pillar is the outlet of drainage pipes and oil drainage pipes, and the weight and dynamic load of parts and components in the hydraulic turbine flow passage are transmitted to the foundation through the fixed pillars. The governor and the oil pressure device are arranged separately, which are set at the upstream side of the turbine and connected with the water diversion mechanism of the turbine through the operating oil pipe and feedback steel wire rope. The high-level oil tank of the bearing is arranged in the auxiliary power house 8 ~ 10m away from the center line of the unit, and the hydraulic station of the oil return tank and the speed increaser is arranged in the turbine pit. The general layout is shown in the figure


main structural characteristics of hydraulic turbine

3.1 runner and main shaft

the parameter selection of shaft extension tubular turbine runner is different from bulb tubular runner. For example, the value of cascade density 1/t is an important factor affecting unit speed and unit flow. Choosing a smaller 1/t value, the runner has large overcurrent capacity and high unit speed. However, the "s" draft tube restricts the passage of excessive flow, and the hydraulic efficiency is reduced due to the insufficient water flow energy conversion due to the too small 1/t value. Therefore, a smaller 1/t value is used for the runner of the shaft extended through flow turbine, while a larger 1/t value is used near the hub. The average density of the blades is also large, and the inlet and outlet edges of the blades are curved. In addition, the relative torsion angle of the blade is slightly smaller than that of the bulb runner, so the runner designed by selecting parameters has excellent energy and cavitation characteristics

for the propeller type axial-extension tubular turbine, the propeller mechanism of the runner is a straight link mechanism with an operating frame. The blade recovery mechanism is set on the oil receiver and outputs the mechanical motion through the sector plate and steel wire rope. The sealing of runner blades adopts multi-layer "U" rubber. In order to facilitate the installation of the runner, the runner discharge cone is divided into upper and lower parts. The support mode of rotating propeller type axial-extension tubular turbine is the same as that of fixed propeller type, both of which are supported by two fulcrums. Due to the long length and large span of the main shaft, in order to increase the rigidity of the main shaft and reduce the weight of the main shaft, the main shaft adopts hollow forgings, or adopts thick wall seamless steel pipe and welded flange structure. According to the characteristics of the shaft extension tubular turbine, its support position, main shaft diameter and inner hole size should be determined through multiple scheme optimization

the shaft extension tubular turbine has complex structure, low generator speed, large size and heavy weight compared with small units, so it is required not to move the generator when disassembling the turbine. For this reason, setting a half split transition flange between the two shafts can easily disassemble and maintain the hydraulic turbine or generator independently

the main shaft of the shaft extended tubular turbine is very long, and the installation of its main shaft and runner is an important problem. Most of the shaft extension tubular turbine spindles are pulled out from the elbow tube, which will increase the width of the plant and move the speed increaser, thrust bearing, generator, etc. There are also runner chambers, straight taper tubes and elbow tubes that are horizontally separated according to the axis, which solves the hoisting problem of the main shaft, but increases the installation trouble of the casing and increases the manufacturing cost of the unit. Therefore, the runner chamber and the straight cone tube are adopted for half, and the expansion joint is set between the straight cone tube and the elbow tube. A half split transition flange is set between the main shaft of the hydraulic turbine and the main shaft of the generator. When disassembling the runner and the main shaft, the purpose of disassembly can be achieved without moving other parts. The main shaft and the runner can be hoisted directly from the half split runner chamber and the half split straight cone tube

3.2 diversion mechanism

the guide vane adopts integral cast steel and two fulcrum structure. The guide vane airfoil is a space twisted profile, and the upper and lower bearings are made of self-lubricating materials. The sealing part of the guide vane shaft head can be protected by hot sleeve stainless steel or chromium plating to prevent rust from affecting the performance of the sealing ring. In order to facilitate installation, the short shaft of the guide vane is set on the inner ring of the guide vane and fits with the shaft hole of the inner ring of the guide vane. Guide vane seal adopts "Y" type plus "O" type seal. The guide vane shaft and guide vane arm adopt cylindrical pin to transfer torque by half key. The clearance between the upper and lower end faces of the guide vane is adjusted by increasing the thickness of the specific gravity ring of the raw material product through the bolts and adjusting pads at the shaft end of the guide vane. In the closed state, the total clearance of the end face is 0.8 ~ 1.8mm, and the local clearance of the facade is less than 0.15mm in the range of 1/4 guide vane height. This requirement can not only ensure small water leakage, but also ensure the flexible operation of the mechanism. The 16 guide vanes are respectively equipped with shear pins and shear pin annunciators. When there is foreign matter between the guide vanes, the shear pins cut and send signals to protect other parts from damage. Due to the conical layout of the water guide mechanism of the tubular unit, the operation of the connecting plate is a three-dimensional movement in space, and the force of the shear pin is complex, with shear force and a certain torque, so it is easy to shear. Therefore, the design of connecting plate and shear pin is a key point

the guide vane facade adopts metal seal, and the head and tail can be overlaid with stainless steel on the sealing surface as required. The metal seal is used as the facade seal, which is simple and convenient in structure. The processing and manufacturing can fully ensure the tightness of the seal. At the same time, the water head of the tubular unit is low and the leakage is small. The metal seal form is also convenient for the installation and adjustment of the water diversion mechanism

with the application of new materials, anti-corrosion and wear-resistant composite sealing materials sprayed on the sealing surface of guide vane are also increasing, which has a good development prospect

the outer ring shell of the guide vane is obliquely and evenly distributed with 16 sub holes to install the upper fulcrum of the guide vane. The outer ring of the guide vane is a thin shell weldment with poor rigidity. In order to increase the overall rigidity of the water guide mechanism, it is necessary to properly arrange the circumferential or longitudinal stiffeners in the structural design. However, in order to solve the installation problems caused by the deformation of the integral hoisting, it is more important to design special integral hoisting and turning over positioning support tools

the control ring is a rolling friction ring bearing structure. The sliding surface of the control ring is equipped with steel balls, and nylon ball spacer columns are installed between the steel balls, which can reduce the friction between the steel balls, make the control ring have small friction torque, and ensure the flexible action of the control ring

the water guide mechanism is equipped with a pendulum servomotor. The big ear hole of the control ring is connected with the push-pull rod of the servomotor, and the small hole is hinged with the fork of the connecting plate of the guide vane. In addition, the control ring is also provided with a circular groove for installing the recovery steel wire. When the control ring makes circular reciprocating motion under the action of the servomotor, it drives the connecting plate, which then transmits the operating force to the hinged guide vane arm, so as to realize the control of the guide vane. In addition, based on the kinematic and mechanical analysis of the transmission of the spatial water guide mechanism, the single qhmac103 [1] is used as the control ring 141 ⑵ 01 ⑵ 005 the structure of accelerator pedal ear hole and single guide vane servomotor. This system has compact structure, clear layout and convenient installation and commissioning. When the unit stops, it is necessary to lock the spindle of the water guide mechanism, which is realized by the servomotor. The locking spindle has two aspects, that is, locking the control oil pipeline in principle and hard locking the servomotor push-pull rod in mechanism. There is no automatic locking ingot in the design of servomotor, and only manual locking ingot is set at the fully closed position of guide vane, which is a very reliable protective measure

standard plain bearings are used for connecting plate ball joints. In order to prevent dust from entering the bearing, the bearing is equipped with bearing gland and sealing copper. The bearing gland is equipped with an oil cup, which is regularly filled with lubricating oil to ensure the flexible action of the connecting plate crank arm. The joint bearing is used to make the coupling ball joint have a certain self-aligning effect, which can compensate the deviation of the water diversion mechanism in the process of manufacturing and installation

during site installation, the water diversion mechanism shall be hoisted as a whole. Before integral hoisting, all guide vanes shall be placed in the fully closed position, and then the adjacent two guide vanes shall be overlapped and welded with braces, so that 16 guide vanes form an integral support ring with sufficient stiffness

3.3 main shaft seal

there are three main shaft seals, the first is comb seal, the second is hydraulic piston working seal, and the third is maintenance seal

comb seal is mainly used to reduce pressure and prevent the entry of large particles of impurities, and to protect and reduce the amount of the second seal. In order to reduce wear, the comb seal is made of stainless steel

the working seal adopts hydraulic piston seal, and the sealing ring adopts medium hard rubber with good performance. Features: it can store lubricating water, which is conducive to the lubrication of the contact surface; The grooved water storage ensures that the water hole will not be blocked due to wear; A water inlet hole with appropriate size is arranged on the sealing piston to form an appropriate pressure difference between the upper cavity and the inner cavity of the piston; It has long service life and convenient installation, adjustment and maintenance. In order to control the amount of water leakage during design and processing, the dimensions of grooves, guide holes and water inlet holes should be strictly controlled. For sediment laden hydropower stations, when using piston type end face rubber seals, it should be noted that the sealing water pressure must be greater than the leakage pressure. In order to ensure the free movement of the piston, there should be a clearance of 0.05mm between the piston and the piston body during installation

packing seal or air shroud seal shall be used for shutdown maintenance seal according to the size of the unit. When packing is used for sealing, the packing is braided polytetrafluoroethylene impregnated

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