New design method for water ring of the hottest pu

2022-07-27
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New design method for water environment of pumped storage units × 300 MW。 The power station has designed and realized the dispatching remote start-up and shutdown according to the principle of unattended operation, which puts forward higher requirements for the reliability and stability of the equipment. The water ring drainage pipe of the first phase unit of Guangzhou Pumped Storage Power Station has been cracked for many times. However, the defects and problems of the water ring of the first phase unit have been fully considered in the second phase design. New ideas have been adopted to improve the design and the water ring drainage pipe has been cancelled

1 function of water ring

in order to reduce the resistance moment of the runner and the loss of active power, the runner chamber should be filled with air pressure water to make the runner run in the dehydration state, and the power consumed by the runner rotating in the air is only 1/10 of that in the water. In order to prevent the compressed air from entering the volute from the runner chamber and increase the air consumption of pressurized water, a circle of cylindrical water curtain, namely water ring, is formed between the outside of the runner and the guide vane by the centrifugal force of the runner to seal the compressed air from entering the volute and keep the volute always full of water. If the water ring is too thin, it will not play a sealing role. If the water ring is too thick, it will be impacted and thrown back by the runner, resulting in harmful pressure pulsation and an increase in active power consumption. Therefore, the water ring should be kept at a moderate thickness

2 the formation and release of water ring in the original design

there are many ways to form the water ring. The original design is to take water through the ball valve bypass pipe and directly leak from the end clearance of the guide vane to the runner room. When the water ring is too thick, it is drained by the specially designed water ring drain pipe located on the stay ring to ensure that the water ring is maintained at a certain thickness

the original design mechanism of the water ring of Guangzhou Pumped Storage Phase I project is as follows: during the start-up of the runner by charging water, open the bypass hydraulic valve of the ball valve, decompress the upstream steel pipe through the throttle plate of the bypass pipe of the ball valve, and then fill water into the volute to maintain a certain pressure. The pressure reducing pipe of the volute is controlled by the hydraulic valve and connected with the tail water. The pressure of the volute can be reduced again through the throttle plate on the pressure reducing pipe, so that the pressure of the volute is slightly greater than the pressure of the runner chamber. At this time, although the guide vane is closed, However, part of the volute pressure water will leak into the runner chamber from the key technology touched in this subject, which has not been reported in the literature. Under the action of the centrifugal force of the runner, a water ring will be formed on the water surface of the guide vane. When the water ring becomes thicker and thicker to a certain extent, it will be discharged from the water ring drain pipe of the stay ring (controlled by the hydraulic valve) to the draft tube

the flow and pressure in the volute can be adjusted by changing the size and position of the throttling plate on the bypass pipeline of the ball valve. The bypass pipe of the ball valve is equipped with a bypass pneumatic safety valve to ensure safety, which is automatically closed when the protection of the flooded plant acts. See Figure 1 for the layout of pipelines related to the water ring. The tail water can reach the upper crown pressure chamber of the runner through the clearance of the upper labyrinth ring. In Figure 1, the head cover pressure relief pipe acts as a flat pressure, which can directly connect the tail water pressure with the upper crown pressure chamber of the turbine, ensure the upper and lower flat pressure of the turbine, and reduce the unit vibration and lifting capacity. The main shaft seal used to block the tail water is a double face mechanical seal. The lubricating water in the inner ring is automatically discharged to the water collecting well, and the lubricating water in the outer ring is discharged to the upper crown pressure chamber of the runner. 3. New design method for water ring

the water ring of the pump turbine of Guangzhou Pumped Storage Phase II still adopts the methods of ball valve bypass pipe, spiral case relief pipe and water ring drain pipe in the initial design. In view of the frequent vibration and cracking of the water ring drain pipe in the initial production stage of the phase I unit, the associated company of Guangzhou Pumped Storage Power station put forward a new idea for the formation and release of the water ring based on its experience in the design of the phase II unit. After the successful test of a small unit in Austria, the manufacturer applied this idea to the second stage unit of Guangzhou Pumped Storage Co., Ltd. and developed a special control system for the aerated and pressurized water operation of high head pump turbine

the phase II water ring improvement scheme adopts a new mechanism. The draft tube is filled with air pressure water, and the cooling water of the upper and lower labyrinth rings leaks to the runner room. Under the action of the centrifugal force of the runner, the leakage water forms a water ring at the surface of the guide vane of the runner room. The labyrinth covers an area of 8000 square feet, and the ring leakage water is used as the water source of the water ring water supply. It can be unpacked after being torn gently. The regulation of cooling water volume of labyrinth ring is very important, and the power consumption largely depends on the cooling water volume provided and how it is consumed. The design idea is to make use of the characteristics of the single guide vane servomotor adopted by the phase II unit, appropriately open one or two symmetrical guide vanes separately, throw the excessive thick water ring water into the volute by relying on the centrifugal force of the runner, increase the volute pressure, and then flow to the tailrace cone through the volute pressure reducing pipe, so as to achieve the dynamic balance of water ring water supply and drainage, and ensure the moderate thickness of the water ring. In the actual commissioning process, the excessively thick water ring can escape into the volute directly from the end clearance of the guide vane, without opening a single guide vane to drain the water ring. The clearance of guide vanes affecting the formation and release of water ring is shown in Table 1. The design requires that the vertical clearance of guide vane shall be less than 0.05 mm and the end clearance of guide vane shall be less than 0.30 mm

note: the vertical clearance of guide vane 1 refers to the vertical clearance between guide vanes 1 and 2, and so on. If the water ring thickness is too thin during commissioning, the cooling water flow of the upper and lower labyrinth rings can be appropriately increased or the water ring drainage can be appropriately reduced by adding throttling plates on the spiral case pressure reducing pipe. Because the volute is always full of water, a small amount of gas escaping into the volute through the guide vane gap will return to the draft tube through the volute pressure reducing pipe during the inflation and water pressure operation

in the original design scheme, the volute is full of pressure water, and the water ring is forcibly formed by taking water from the front of the ball valve and entering the runner chamber from the volute. In the improved design scheme, the leakage water from the upper and lower labyrinth rings is formed under the centrifugal force of the runner and thrown into the volute, which is also the biggest difference between the two design schemes

4 relevant technical parameters of water ring

the upper and lower labyrinth rings are comb shaped seals composed of upper and lower anti-wear rings connected to the top cover and bottom ring and 7 steps on the upper crown and lower ring of the runner. The unilateral axial clearance of the upper labyrinth ring is 1.20 ~ 1.35mm, and the diameter is 2.136 mm. The unilateral axial clearance of the lower labyrinth ring is 1.40 ~ 1.55mm. When the diameter is 2, the high molecular polymer is required to have necessary mechanical properties 2

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