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May 25, 2020
What are the important reasons for the vibration of the hydro-generator set
As an important part of the hydroelectric power generation system, the hydroelectric generator is an important task for its maintenance. Once the hydro-generator runs abnormally or fails, it will affect the power supply guarantee and safety of the entire power system. In the abnormal operation of hydro-generators, vibration is a common phenomenon. How to deal with the vibration of the generator set?
1. Aircraft vibration identification
The guide vane opening of the water guide mechanism of the turbine is opened in sections of 20%, 40%, 60%, and 70%, and the vibration of the azimuth of the bearing end of the turbine, front and rear of the generator is measured according to each opening. After the measurement, analyze the data to distinguish whether the vibration source is caused by the turbine problem or the unbalanced force of the generator rotor.
Second, empty machine plus excitation identification:
According to the requirements of the formula, no result can be obtained. At the rated speed of the engine, the excitation current is added in sections, and the added value of the excitation current must not cause the engine to exceed the rated voltage. Then measure the end of the water generator when the excitation current is added in sections, and measure the vibration of the bearing seat in all directions before and after the engine. The data analysis is whether the magnetic circuit is caused by unevenness.
3. Identification with load
Increase the load in sections and measure the vibration of the above parts in sections. At this time, due to the increase in the active load of the generator, the opening of the guide vane of the water generator increases according to the increase of the load of the generator. The water volume is greater than that at no load. Whether the wheel blades are symmetrical, whether the amount of water between the guide vanes of the water guide mechanism is uniform, whether the gap between the top cover, the bottom ring and the runner is appropriate, the gap between the runner and the leak stop ring, etc.
Due to processing errors and improper gaps, the flow surface of the runner is asymmetrical, forming an asymmetrical vortex in the cavity of the turbine, resulting in vibration caused by hydraulic and unbalanced axial and radial vibration forces. At this time, the vibration value of the turbine end is greater than Generator side.
If the generator load increases and the generator end vibration is greater than the water generator end, it is the cause of the uneven rotor air gap of the generator, unstable excitation system operation, unbalanced three-phase load, and short circuit between coil turns.
4. Vibration caused by hydraulic factors
1. The impulse of the inlet flow of the runner is not uniform due to the uneven water intake of the volute and guide vanes.
Ideally, when the guide vane is open, the flow velocity and pressure on both sides of it are uniformly distributed. Each two guide vane flow channels have the same energy balance. At this time, the water flow is normal and smooth, due to uneven wear due to processing and installation. The reason is that when the shape and size of the blades and the flow channels have large errors or differences, the water flow is disturbed. When the disturbed water enters the runner area, it will impact with it, causing water pressure pulsation and vibration.
2. The unevenness and eccentricity of the leakage stop ring cause the water pressure pulsation in the gaps everywhere, causing the self-excited vibration of the rotating part.
3. Axial water thrust and decompression device.
The function of the decompression device is to reduce the axial water thrust on the runner, and the clearance between the runner, the top cover, the upper crown and the leak stop ring is adjusted. The adjustment can weaken the axial water pressure on the surface of the upper crown and the lower ring, reduce the force of the thrust bearing bush, and control the shoe temperature.
5. The axial position of the generator stator should be installed so that the magnetic center of the stator deviates from the center of the rotor and 1.5-2mm toward the end of the water machine. So that when the unit is moving, the rotor can bear the magnetic pulling force of the axial water thrust in the opposite direction, so as to reduce the load of the thrust tile and keep the temperature of the thrust tile not too high.
5. The quality requirements of the horizontal unit axis.
1. The dial indicator checks the swing of each rotating part,
(1) At the shaft diameter <0.03mm;
(2) The end face of the thrust disk jumps <0.02mm;
(3) Double swing of the outer circular surface <0.10mm;
(4) Double swing amplitude of the outer surface of the flywheel <0.20mm;
(5) Double swing amplitude of the outer circular surface of the generator slip ring <0.20mm;
2. The gap between the rotating part and the fixed part:
(1) The gap around the leakage stop ring of the runner is uniform around, the maximum deviation is not greater than the average gap
(2) The air gap of the generator is uniform and the maximum deviation does not exceed ± 10% of the average air gap.
These are the common factors that cause the vibration of the hydroelectric generator. When discovering the problem of vibration of the hydro-generator set, we must deal with it according to the plan, correct the cause of the vibration, and solve the problem scientifically and reasonably.