Preliminary study on the deviation accident of the

Preliminary analysis and reinforcement treatment of the deviation accident of the turbine volute of the flood control captive power station

Abstract This paper briefly introduces the major accident of serious wear and tear of the runner caused by the inclination of the turbine volute of the Panjiakou flood control captive power station during the no-load test run after installation After many times of analysis and research by relevant experts and engineering technicians, the cause of the accident was found out, and an appropriate reinforcement scheme was put forward, so that the problem could be properly solved quickly. A 100lb dynamometer was installed in a 1000lb mold frame, and the unit returned to normal operation

key words: reinforcement treatment of inclined spiral case of hydraulic turbine

I. overview

Panjiakou flood control self-contained power station, in order to solve the problem of flood control self-contained power supply, self raised more than 20 million yuan to build two 400KW hlz%w hydraulic turbine generator units, located at the downstream side of No. 1 hole of 29-31 flood bottom hole of Panjiakou Reservoir Main Dam, the unit is upstream, the maximum water level is 2247m, the downstream water level is 1 sm, and the maximum water head is 54100m, The annual generating capacity of the two units is about so0kwl, and the construction period is LLS months. The construction has been officially started since August 16, 1995, and completed in advance and conducted no-load trial operation on July 27, 1996

II. Accident occurrence and harm

at 3 p.m. on July 27th, 1996, the unit began its no-load test run, and began to hear the friction sound of rotation. Half an hour later, it smelled the smell of burning like leather, and immediately shut down. After disassembling the runner, it was found that the runner was worn at many places, the upper and lower 45 degrees of the main shaft seal ring were worn, and the sparse teeth of the runner were worn and deformed According to the above situation, the volute of the two units may be scrapped, which will cause greater economic losses If the water turbine cannot operate normally, the reason must be analyzed and reinforced

III. cause analysis

after nearly half a month of analysis and research, the designers, supervision engineers and relevant technicians of the manufacturer agree that if they are not handled properly, two spiral cases will be scrapped, with a loss of nearly ten million yuan At that time, two schemes were put forward. One is that the rigidity of the spiral case itself is not enough, so when filling water, it causes local deformation of the spiral case, and the spiral case must be reinforced However, there is a great risk in strengthening the spiral case. Another opinion is that the maximum section diameter of the spiral case is 12M, the material is 1 ~ 6m thick A3 steel plate, the maximum water head is 70zzn, and the water hammer pressure is 10m. When leaving the factory, he has been proud of the hydraulic test face of 16ipa, and he recognized that the strength and stiffness of the spiral case itself are sufficient. There are two main problems: first, the spiral case inlet adopts water inflow, and due to the limitation of the dam joint, An expansion joint must be set between the butterfly valve and the volute In this way, when the upper end of the spiral case is filled with water, it is similar to the free end, and all the water thrust is balanced by the foundation; Second, the lower support of the spiral case is very weak. Between the spiral case and the foundation, only two 35 thick steel plates are used to connect, and it is still upright. Its bending resistance is very poor, and it cannot withstand the action of large overturning torque from the upper end. When the unit is filled with water, it produces large elastic deformation, which makes the spiral case tilt an angle to the direction of water flow, resulting in the occurrence of the above accidents. In order to facilitate the analysis, 14 dial indicators are set around the spiral case, and the spiral case water filling test is carried out for many times to confirm that the analysis of the above reasons is correct

IV. treatment scheme

1. Theoretical basis

according to the above analysis, the causes of the accident are: first, the water inlet on the volute is similar to the free end, and the horizontal thrust at the water inlet end of the volute can only be balanced by the lower support. Second, the lower support of the spiral case has a small and upright section. Poor bending capacity in order to solve the above problems, it is necessary to carry out detailed structural calculation. It is best to use the spatial finite element method to calculate the deformation of each part and the stiffness of the spiral case accurately, and take appropriate treatment schemes. However, due to the tight construction period and long skip counting time, if simplified calculation can be adopted, the structural defects can be explained and the purpose of reinforcement can be achieved To ensure the safe operation of the unit, even if more reinforcement materials are used, so that the unit can be put into operation in advance, it is also economical. In line with this idea, for the convenience of analysis, the volute can be simply turned into a rigid body. After the installation of the whole volute, it is simplified into a special rod, one end is a free end, the other end is a fixed end, and the upper end has a horizontal thrust when the volute is filled with water. Under the push of this force, the volute is elastically deformed. After several water filling tests of the volute, it is confirmed that it is basically consistent with the reality

2. Treatment scheme

(L) increase and heighten the volute foundation

according to the calculation, when the unit bears the load rejection of the highest water level, the axial horizontal thrust is 16jr, and this force is mostly borne by the newly increased foundation. At this time, it is required that the foundation must be firm and reliable and have an appropriate safety factor However, due to the limitation of the site, the concrete foundation can only be lengthened by 90mm and raised by 10cm on the side close to the butterfly valve, and the concrete foundation can only be lengthened by 70cm and raised by 50cm on the side close to the governor, that is, the right side of the spiral case. Considering the concrete foundation, in order to make the new foundation close to the old concrete foundation, lay a thick foundation steel plate on the old concrete foundation, and then use 32 thread reinforcement to reinforce the foundation plate on the old concrete foundation, Then, three 30inm thick reinforced steel plates are used on each side, one end is welded on the spiral case, the other end is welded on the foundation plate, and the dowel bars are overlapped and welded into reinforcement grids. Each reinforcement is welded firmly with the three reinforced plates respectively, and then 5m thick steel plates are used around to make concrete formwork, and special concrete is poured in the middle (flowing, early strength, micro expansion, strong adhesion concrete). During the whole reinforcement process, Always monitor the volute deformation with a dial indicator to prevent excessive permanent deformation, resulting in the failure of the whole reinforcement project

(2) balance the horizontal thrust at the inlet of the spiral case

according to the formula "PL ground EI", in order to make up for the defect of insufficient foundation reinforcement height, try to reduce the horizontal thrust p value as much as possible A top bar is installed on the center line of the steel pipe at the inlet of the spiral case and the side wall of the plant to balance the horizontal thrust. One end is installed on the base of the concrete side wall, and the other end is connected with the spiral case The foundation plate is set on the wall and reinforced on the wall with dowel bars The connection with the spiral case is also reinforced with reinforcing plates and base plates

v. reinforcement construction

1. Foundation reinforcement

after nearly a month of intense reinforcement work, first drill 40 resistant dowel holes in the reinforced part, 24 holes on the left and 18 holes on the right, and the hole spacing and row spacing are 20 ~ 30. Insert dowel bars with screws around the foundation plate, and the rest are inserted into 32 threaded bars, and the depth of the old foundation concrete is 0 inl. At the inserted end, the steel bar is used as a wedge. When burying people, the hole is filled with mortar, and it is reinforced firmly with a sledge hammer. After the mortar reaches a certain strength, the foundation plate is cut and placed on the old concrete foundation according to the position of the dowel hole, and the fine aggregate concrete cushion is plastered. Then the foundation plate is covered with dowel bars and placed on the concrete cushion, and then the screw cap is used to compress the foundation plate, and leveling is used. When the concrete reaches its strength, a jack is used for tensile test. Each joint bar can withstand 20t tensile force. First, three reinforced steel plates are welded to the spiral case. Special attention should be paid to the welding process to prevent excessive welding deformation of the spiral case. The spiral case is welded first, and the other end is free, and intermittent welding is adopted. There is a gap on the steel plate at the weld joint, which should eliminate the welding stress. When the other end of the reinforced plate is welded with the foundation plate, In order to reduce the deformation of the spiral case, it is not directly welded to the foundation plate, but two backing plates are used. The lower end is welded with the foundation plate, and the upper end is welded with the reinforcing plate. The reinforcing plate is clamped in the middle, and the lower end of the reinforcing plate is still free. After monitoring, the whole spiral case is deformed up and down, and there is no deformation in other directions, which is within the allowable range of the specification

2. Top bar installation

in order to balance the horizontal thrust of the inlet part of the volute, which will maintain the same rigidity, a top bar is added at the center line of the volute inlet pipe. According to the force of the top bar is 16ot, 45 solid round steel with a diameter of 20mm is designed. One end is installed on the foundation plate against the wall, and the other end is installed on the base plate of the volute, which is supported by five triangular rib plates. Both ends of the top bar are free, When the British government announced to invest 50million pounds (1 pound or about $1.52) to support graphene research, the spiral case will be fastened with a wedge plate at one end

VI. reinforcement treatment effect

reinforce the foundation on both sides of the turbine, and only reinforce the reinforcing plate and reinforcement And add a top bar Before pouring concrete, the water filling test was carried out, and the observation effect was very significant, which could initially meet the operating conditions. When pouring concrete (special concrete), the stiffness of the spiral case foundation was further strengthened, and the inclined deformation of the spiral case was eliminated. Make the unit operate normally

VII. Conclusion

the spiral case of Panjiakou flood control captive power station tilted, and the most economical reinforcement scheme was adopted. In the shortest time,

less funds were used to restore its normal operation, and the reinforcement was successful at one time Thus three enlightenments are obtained:

1. For horizontal units, the volute is an upper water inlet. When designing the expansion joint, it must be located on the upstream side of the bee stuffy, and the horizontal thrust must be balanced with steel pipes

2. The anti overturning strength and stiffness of the spiral case support must be calculated

3. When dealing with the lack of pinch of the spiral case, try to reduce the amount of welding on the spiral case, pay special attention to the welding process, and monitor the deformation in the direction of rare earth functional materials, so as to prevent the permanent deformation of the spiral case caused by repair welding, which will cause the spiral case to be scrapped and cause undue large economic losses

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