New problems encountered during turbine commissioning?
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1. During today’s testing of the small turbine manufactured by Yiliao, new problems arose. During the first test run, the vibration level at the steam inlet side was very high; at around 7000 rpm, the vibration value reached approximately 60 um, while the vibration level at the exhaust side was only about 20 um. Since two water seals were added at the shaft journals during this year’s overhaul, but no balancing was performed, it was suspected that these water seals affected the rotor’s dynamic balance; therefore, they were removed during the second individual test run to restore the condition to that before the overhaul. 2. The conditions for the second single-unit test are the same as before the maintenance, except that the carbon ring steam seal and the comb-tooth steam seal at one end are replaced with new parts. The problem that occurred during the second test run was high vibration at both ends; the vibration levels at the inlet and outlet sides increased continuously until they reached around 60 um, while the rotational speed was only a little over 6800 rpm. Could everyone please analyze what might be the possible causes?
Has the rotor been subjected to a dynamic balance test? At what speed was this dynamic balance test carried out? It should be noted that a successful low-speed dynamic balance test does not necessarily mean there are no issues with the rotor’s dynamic balance! We have learned lessons in this regard. Of course, high-speed dynamic balancing costs a lot of money. :lol
Of course we did. During the second single-unit test, we were worried that the water-blocking rings we had added on our own might have an impact, so we removed those rings. As a result, the vibration levels at both ends increased, while the shaft displacement remained stable with no changes. Then why did the vibrations at the steam inlet and exhaust sides increase simultaneously the second time? Vibration is lower at low speeds; there is almost no change in vibration between 1000 and 3000 rpm, while the vibration levels increase at both ends of the range from 4000 to 7000 rpm. If the rotor is unbalanced, it should show up within the range of 1000 to 3000. This post was last edited by zhangya*ong on 2009-2-22 23:00]
What type of dynamic balancing is being done? Full-speed dynamic balancing or low-speed dynamic balancing? Also, what is the precision?
High-speed dynamic balancing: vibration value of 1.0 mm/s; low-speed double-sided dynamic balancing G1.0
If dynamic balancing has been done and the accuracy is within normal limits, loose components may be a possibility.
Damage to the components causes imbalance, and that imbalance should be detectable; it doesn’t seem like it’s a rotor imbalance to me. Last edited by zhangya*ong on 2009-2-23 10:50.]
When is dynamic balancing done, before adding the retaining ring? After demolition? Is it possible to do online dynamic balancing? Doesn’t this unit have vibration monitoring equipment? This post was last edited by zhangya*ong on 2009-2-23 10:51]
It was done before adding the retaining ring. We don’t seem to have the facilities here for on-line dynamic balancing. When we used our Bently online condition monitoring system to inspect one of the shaft seal comb teeth, we found gaps axially in three of those teeth; in other words, they weren’t fully closed and had been pushed apart
The comb-tooth steam seal has been replaced with a new one; everything else remains the same as before the maintenance. The problem that occurred during the second test run was high vibration at both ends; the vibration levels at the inlet and outlet sides increased continuously until they reached around 60 um, while the rotational speed was only a little over 6800 rpm. I think it might be a problem with the gas seal. The difference between the gas seal radial clearance and the bearing shell clearance causes rotor wobbling; it should return to normal after running for some time to allow for wear leveling....
After inspecting the unit, no issues were found; therefore, another trial run is necessary to determine whether there are any problems with the operational procedures
Check the expansion situation; it would be easier to analyze if there are relevant plots available (such as Bode plots)
Yes, it would be more convenient if it were available. I encountered this issue during today’s single-unit test run; it’s probably a problem with the steam seal. I’ll keep investigating it tomorrow
Our factory also encountered a situation similar to what you described during the individual testing of the turbines in the high-pressure methamine pumps: during the major overhaul in 2008, an air baffle was installed on each side of the turbine, outside the gas seals, and no dynamic balancing was carried out. During the first test run of the turbine, its vibration was good ； Immediately, a second test run was conducted; when the speed reached around 5000 r/min, the turbine experienced abnormal vibration, so the turbine was stopped right away to check the front and rear bearing shells, which showed no significant problems ； The next day, a further turbine test start was conducted; the vibration levels were satisfactory, and the test was completed. During this major repair, the two carbon rings at the inlet side of the turbine gas seal were replaced with honeycomb seals, and one of the carbon rings at the outlet side was also replaced with a honeycomb seal; however, the effect was minimal, as the gas seal continued to leak. The specific cause of the turbine vibration is unknown.
Steam quality is an important factor to consider – is there liquid present? There is a high possibility of liquid at the intake side. How about aligning the unit? The lubrication condition is also a possibility.
The steam quality is definitely good – there is no liquid present, and the lubrication is adequate. The couplings have not yet been connected.
Could you describe the process conditions during the testing? Such as pressure, temperature, warm-up time, etc.
Are there any issues with the clearance and tightness of the bearing shells? How is the contact with the wafer?
The bearing clearances and the clearances of all levels of steam seals were checked, and no issues were found; only a gap of approximately 1.2 mm was detected where the four sections of the comb-type steam seal at the exhaust end did not close properly.
Could it be the steam seal causing the issue? Make sure to check whether the probe is intact.
Adjust the oil temperature and pressure to see if there are any changes