The single unit capacity of China's large hydro-generator units is gradually developing to giant units such as 500MW and 700MW, such as the completed Ertan (550MW) power station, the Three Gorges (700MW) power station under construction and the soon-to-be-launched Longtan (700MW). Power stations such as Xiaowan (7OMW) are both opportunities and challenges for hydroelectric generator manufacturers. How to solve the problems of processing, assembly and transportation of oversized and overweight hydro-generator components has been placed in front of our company.
Drawing on the successful experience of foreign companies, combined with their own situation, research and development of new processing and assembly processes, this is our only way.
2 Three Gorges Stator Seat The three-gear power station hydro-generator stator base has an outer diameter of 3,306 mm and a weight of about 170 t. It is welded by ring plates, vertical ribs and steel tubes of different thicknesses, and its overall shape is a circular structure. The steel tube between the ring plates of the machine base adopts a long structure, which is convenient for controlling the total height of the machine base.
The stator frame has no lower ring and consists of a middle ring and an upper ring (block structure, similar to a buttress). The middle ring consists of a large-toothed plate and an upper ring plate with a total of 8 layers of ring plates. The upper ring is welded to the central ring at the construction site.
The middle ring of the machine base is divided into 8 petals, and there is no joint plate between the two petals, and the assembly block is used for closing. The docking groove of the construction machine is welded to the full circle by the butt groove.
The stator base and the base plate are keyed to the base for thermal movement under thermal expansion (see illustration).
The pressure finger is made of non-magnetic steel. It is welded to the large-toothed 3rd-three-stooth stator frame. The design of the Three Gorges stator base is designed according to the design requirements. It mainly needs to process the stator large-toothed plate plane, the stator bolt hole and the stator radial keyway. Parts.
3.1 Siemens stator frame processing technology For the stator frame similar to the structure of the Three Gorges, according to our traditional processing methods, the main process flow is as follows: the whole round and large tooth pressure plate processing line, the vertical processing of the stator frame large tooth pressure plate plane , the whole round hole line, the keyway line, the boring machine is used to process the bolt hole, and the key groove is processed.
According to this processing scheme, the stator frame is processed, and the processing of the whole frame takes up a short period of large equipment, and is a familiar processing method, easy to operate, and the quality is easy to ensure.
However, due to the large size and heavy weight of the Three Gorges stator base, it has brought certain difficulties to the scribing and overall lifting. For example, in the vertical car processing, Fu on the vertical car to close, line, so that the machining cycle occupied by the stator frame on the large vertical car greatly increased, affecting production. For workpieces with low machining requirements such as stator stands, other machining methods should be considered.
In Siemens, because there is no large vertical car, the stator frame is mostly processed by CNC boring.
In order to ensure the horizontalness and roundness of the large tooth pressure plate after the stator frame is processed, the stator base can be welded in the whole state or in the split state, and the height of each seat can be large. Three horizontal alignment blocks are welded on the tooth pressure plate, and the horizontal level is used to level the blocks, and then the spot is welded firmly; the large tooth plate is drawn to process the round line and the line is viewed, and the boat shape of each valve base is marked on the line. Find the correct point.
On the raft, use the square box and jack 'é…£ level to find the positive block to level the frame relative to the guide rail of the machine tool. The tolerance is controlled at 0 2~03mm. Then use the ship shape horizontal aligning point to find the ship's ship shape level. The tolerance is controlled. . Within 2~03mm, then fixed. Through numerical control programming, the large tooth platen plane, the bolt hole and the keyway are processed at one time.
3.2 The possibility analysis of our company adopting CNC boring machine to process the stator seat of the Three Gorges. As the processing technology of the Siemens stator base is copied by our company, there are two problems: the width of the large toothed plate ring to be processed is 560mm, such as the square due to the Three Gorges The stator pressing finger is directly welded to the large tooth plate structure, and the stator bolt is used as the positioning reference of the welding finger tool. How to ensure the shape tolerance of the stator bolt hole is also a problem.
In order to solve the above two problems, in the processing technology of the Three Gorges stator base, we use the right angle milling head of the CNC wrong bed to process the large tooth plate plane, which solves the problem of making large diameter flying cutter discs (such as Shown).
In the processing of the bolt hole, we only draw the starting point of the NC machining of the hole on each seat of the valve during the scribing process, and verify the contour hole of the program, and use the high-precision characteristics of the CNC machine to process All the bolt holes are used to solve the problem of the accuracy of the bolt holes.
4 The Three Gorges stator core assembly of the Three Gorges hydro-generator stator base is transported to the construction site, and is welded into a full circle at the work Sk. In order to prevent the stator core from being thermally deformed, the iron core and the base are connected by a double dovetail floating positioning rib structure; the whole site is a round laminated piece; the core is pressed tightly by a tensioning screw, a through-thread screw and a butterfly spring. In order to ensure the long-term tightness of the core, the structure also uses the end of the iron core bond, the lower pressure finger is directly welded to the site of the stator frame welding, iron core loading and lowering, and the conditional stator machine of the grind 4.1 site. Seat welding and core lamination can be carried out either in the installation room or in the pit. If it is carried out in the installation room, a foundation plate is required to be fixed at the center of the assembly site to fix the center column. The base plate is also required to be placed at the position corresponding to the stator base plate. The total load of all the base plates should be considered to support the weight of the entire stator core. The base plate should be buried in the coordinate orientation; taking into account the stacking area of ​​parts and tools, hot pressing The equipment placement area and the worker's rest room are required to be occupied. The area of ​​the site should be at least about lm larger than the diameter of the frame. The environment of the site should meet the relevant standards. If it is carried out in the pit, it is necessary to build a platform in the pit for fixing the center column and placing the lamination frame, etc., and the base is placed on the foundation support pier (as shown).
4.2 Main Process The stator frame of the large hydro-generator is transported to the construction site, and is welded into a complete circle in the stator installation of the site, and then laminated; the double-find floating locating rib between the core and the frame is beneficial to both. Improve the integrity of the core, and improve the reliability of the long-term operation of the unit, and solve the problem of relative thermal expansion of the large-diameter core.
Our company's technical staff combined with long-term work experience, through self-development, has basically mastered the compression technology of this structural core, and has been adopted in small hydropower generating units such as Xiaolangdi 300MW unit, Lijiaxia 400MW unit and Dachaoshan 225MW unit. How to better master this technology is the key to solving the problem of how to install the 700MW stator core. To this end, based on the comparison of the double dovetail stator core technology with foreign countries, combined with the existing technology, our company proposed a possible iron core compression scheme.
4.2.1 Stator base assembly First, the support base and the wedge plate are arranged in the installation room, and the wedge plate is roughly leveled. The center column is placed on the center base plate, the base is erected, and the joint bolt, the first valve base and the first The joint direction of the two-blade base should be toward the upstream end of the power station. According to the process requirements, adjust the level of the base, the center column is vertical, the center column is concentric with the base, and fix the base and center column (as shown).
Install and adjust the center column to indicate. Frame level 2. Center column 3. Measuring pin 4. Stator base 5. Measuring arm 4.2.2 Stator base, lower pressure finger welding In order to ensure welding quality and reduce welding deformation, the base welding should be welded by qualified welders, according to Special welding processes require welding. After the welding of the machine base is completed, the machine base and the center column are again aligned; the special pressure finger welding jig is used for the welding work of the lower pressure finger, and the wave degree of the lower pressure finger is checked.
The lower pressing finger is directly welded to the large toothed plate structure and has only been developed in recent years. In order to ensure that the undulation of the lower pressure finger meets the requirements, we used the method of overall processing of the post-weld vertical vehicle, and the processing performance was extremely poor. For controlling the welding quality of the pressing finger, we can learn from the Siemens finger press welding fixture and the structure of the inspection tool. 4.2.3 Installation and adjustment of the positioning ribs The positioning ribs are drawn on the ring plates of the machine base, and the positioning ribs are temporarily fixed to the machine base. According to the principle of equal division and small division, the benchmark is first determined and adjusted. Reinforcement, lap the reference rib block in a certain welding sequence, then adjust the remaining locating ribs in each zone, then lap the bracket in a certain welding order, check the rib size, pass the welding, and press according to certain welding The positioning of the rib block is fully performed in sequence. Finally, the positioning ribs are inspected and the positioning ribs are welded.
The door company is slightly different from ours. They generally adopt two methods: adopting the three-stage process core section of the upper, middle and lower stacks in the height direction of the machine base, and adjusting the groove shape and inner diameter of the process core section. After that, the position of the positioning rib is determined, and then the positioning rib block is welded (as shown).
The first part of the reference positioning rib is installed, and then the lamination is carried out. After stacking to 300 mm, the punching piece is shaped, adjusted, etc. After the requirements are met, the remaining positioning ribs are inserted, and the first layer of positioning ribs are welded, and then the stack is continued. After the sheet is stacked and the height is flush with the second layer of the frame of the machine base, the punching piece is shaped, adjusted, etc., and after satisfying the requirements, the second layer of the positioning rib block is welded. Repeatedly.
It can be seen from this that the fundamental difference between Siemens and us is that we can ensure the quality of the stator core assembly after adjusting the size of the positioning ribs. However, Siemens has ensured that the stator core size is qualified before positioning the ribs. Block welding work.
In order to eliminate the positioning rib welding error caused by the traditional positioning rib pitch measuring tool, we absorbed the technology of GE Company and developed the ball chord distance measuring tool to measure and adjust the chord distance between the positioning ribs.
The positioning of the ribbed block is a key to ensure the size of the locating rib. The size difference of the locating rib caused by the welding deformation of the splicing block is an old problem in the welding of the locating rib. Therefore, in the welding method, our company adopted (: 02 gas shielded welding. At the same time, our company also made a deep research on the welding order of the pallet.
4.2.4 Stator core-loaded stator core lamination adopts a full-circle lamination method. During the lamination process, when the lamination is to exceed one layer of the ring plate, the temporary wedge between the positioning rib and the bracket is taken out.
Positioning, shaping, and inspection tools such as grooved rods, plastic rods, and grooved rods are used to ensure lamination groove tolerance.
As a positioning tool in the core lamination process, we generally use a stack of iron cores to lift the grooved rods in the axial direction to ensure that the grooved rods always function. Siemens uses the fixed grooved rods. In the way, when the iron core is stacked to a height exceeding one grooved rod, that is, another grooved rod is placed in the adjacent groove, and the two grooved rods overlap the height of one core segment in the height direction.
In order to ensure the tightness of the core, pre-pressing each stack of 500mm, the pre-compression of the core is carried out by using the pre-pressing tool, and the core is pressed with a torque wrench to ensure the tightness of the core and prevent the warping deformation of the core in the future.
We use pressure plates, tool bolts, support pipes, etc. for the core preloading tools we use at the construction site. Siemens uses a variety of tool bolts and tool pressers.
In order to further improve the tightness of the core, we use the iron core hot pressing process to heat the iron core to a certain extent after the cold pressing is completed, keep the iron core for a certain period of time, and then let the iron core naturally cool below a certain temperature, and then press the iron core again, using a hot pressing process. The core can be further pressed, and at the same time, the process of thermally bonding the first and last ends of the core into a whole can be adopted to improve the rigidity of the core and prevent the core from loosening. After the hot pressing is completed, the core magnetic circuit heat test is performed, and then the core is pressed again.
5 Conclusions In the manufacturing technology of large-scale hydroelectric generators, many advanced manufacturing manufacturers have many manufacturing experience and technology worth learning and learning from, but while digesting and absorbing, they also need to combine their own actual conditions to complement each other.
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