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Analysis And Treatment Of Cooling Tower Fan Faults
Apr 19, 2018

First, cooling tower fan structure

       1. Hair dryer 2. Blade 3. Reducer base 4. Hub 5. Reducer 6. 8, Chain coupling 7. Drive shaft 9. Motor 10. Motor base 11. Cooling tower top

Second, the fault situation

      The pump operator heard two loud noises from the cooling tower in the duty room and immediately went to the local inspection and found that the 2# fan current (50A) on the control cabinet was lower than usual (about 58A in normal operation). 2 # fan out of the problem, immediately check the top of the cooling tower and found that 2 # fan has been stopped, but the motor is still turning, the operator immediately to the control cabinet stop 2 # fan, and notify the power distribution room to cut off the motor power. After the maintenance personnel arrived at the site, they carefully examined the fault site and found that one blade of the fan broke from the near root and landed on the ground 25m away from the north side of the fan 2#. The cross section of the fracture was uneven in thickness and the degree of corrosion was not the same. The five blades were bent to varying degrees and severely deformed. The aluminum alloy outer cover of the transmission shaft and the motor and fan coupling was broken, the chain of the coupling coupling broke off, and the refueling pipe of the reducer broke from the root of the near reducer. All of the oil flowed into the big pool. The air cylinder was covered with scratches and some places were scratched.

Third, failure analysis

       The fan has been in operation since 2004 and has been operating for almost 9 years. During the course of the operation, it is necessary to stop the lubrication of the coupling and the wear of the chain every six months or so. The chain and grease are replaced depending on the wear and tear. Before the machine was shut down, the operation of the fan was checked. Although there was corrosion, all the important components were in good operation, and no abnormal vibrations and noise were found in the spot inspection. The rotation was relatively stable. Since carbon steel is corroded relatively quickly in a wet environment and a treatment agent is added to the circulating water, the treatment agent is carried along with water vapor to the connecting pipe of the blade during the operation of the fan, which intensifies the corrosion speed of the connecting pipe. By observing the cross-section of the fault blade connecting pipe, it is found that the degree of corrosion is uneven, the thin place is less than 2mm, and the strength is greatly reduced. In the operation of the fan, the blade is subjected to strong centrifugal force, and the position where the corrosion is more severe cannot withstand the effect of centrifugal force. Firstly, it was torn, and with the operation of the fan, the split gradually expanded, causing the end of the vane to come into contact with the blower, causing a collision. During the collision process, the breakage speed of the split was accelerated, and the end of the vane fell and hit the drive shaft. Under the action of the huge impact force, it flies up again and hits the other five blades, causing the other five blades to deform to different degrees. At the same time, they fly out under centrifugal force and inertia, and the fan is still running, in this case, The balance of the hub was seriously damaged, the vibration of the reducer increased sharply, and the vibration of the base increased. As a result, the coupling chain of the reducer coupling was damaged, the drive shaft and the reducer were disengaged, and the reducer was stopped. At this time, the motor was still Operation, the current is reduced due to the reduced load.

Fourth, troubleshooting

       1. Due to the serious damage of the shaft coupling, chain, hub, and blades on the cooling tower fan reducer and motor, the transmission shaft may be deformed. All of them need to be replaced. The reducer tubing breaks from the root, and it takes a long time to repair. This will have a greater impact on production. In order to minimize the impact, it is decided to replace the spare fan as a whole. The spare fan's shape design adopts the most advanced wing shape and good pneumatic performance. The blades are molded from high-strength glass-fiber reinforced plastics and have the advantages of high strength, light weight, and corrosion resistance. Then, while disassembling the damaged fan, the new fan was assembled according to the installation requirements and the angle of the fan blade was adjusted according to the marking of the fan at the time of shipment. The tilt angle was about 8°. After the old wind turbine was hoisted, it was found that the rust of the reducer base was severe. The thickness of the two horns was uneven and could no longer be used. The two horns were reworked. Place the horn on the pedestal to check the horizontality, find that the pedestal is on the southeast side of the pedestal, lower the level of the horn again, lift the whole fan onto the pedestal, then find the positive motor and reducer, and add the lubricating oil after all the installation work is completed. Drive test.

       2. Stop the fan and adjust the blade tilt angle to 15°C. Start the test again after adjusting the blade angle. After starting the fan, the operating current is 61A, the vertical vibration of the fan motor base is 2.3mm/s, and the motor level is 2.4mm/ s, vertical 1.7 mm/s. After stable operation, the circulating water outlet tower temperature is 33.0°C, still not reaching the designed temperature.

       3. In order to solve the problem thoroughly, it was decided to replace an old reducer that had been repaired, and then the new fan was completely hung down. The hub was disassembled together with the fan blades. Because this speed reducer was faster, it would wind again. Adjust the angle of the blade to 12°, install it on the repaired reducer, then install the whole fan to the fan base, find the positive motor and reducer, and start the test after reloading. After the fan runs for 3 hours, the temperature of the circulating water out of the tower is 31.5 °C, to meet the design requirements, to meet the production needs, but at this time the vibration value of each vibration measurement point is relatively high, and again processed.

Fifth, through this troubleshooting, take appropriate preventive measures to reduce the occurrence of failures.

1) Strengthen equipment inspections, keep abreast of the operational status of wind turbines, and rationally arrange maintenance intervals;

2) When replacing spare parts, firstly check the technical data to avoid detours;

3) When troubleshooting, try to find the possible causes of the failure as far as possible so that a thorough investigation can be conducted;

4) Operate strictly in accordance with the operating procedures.