【JST-039】One-on-One Consultation Office for Difficult Issues in Turbine Maintenance

This post was last edited by strong1125 on 2014-4-10 at 22:36. I need some advice~ We use condensing steam turbines from Hangzhou Machinery to drive centrifuges. During the first maintenance check after the units started operating on their own, it was found that the probe was in contact with the gear disc, which caused severe wear on the speed sensor probe until it became unusable. The initial installation gap for the speed sensor probe was between 80 microns and 1 mm; later, this gap was increased to 1.2 mm, but neither approach solved the problem. There are a total of 6 speed measurement probes, which are evenly installed on the end face of the front bearing housing at the upper part; visually, wear is more severe on the upper 4 probes. 1. Since the signal disc of the rotor is located close to the bearings, with only a clearance of 35 units between the bearing shells, and given that the unit is operating well without any abnormal vibrations or other issues, it is believed that the vibration of the rotor will not cause the signal disc to come into contact with the probes ； Moreover, when the unit is turned by the turning gear, the runout of the rotor journal near the signal disc is also very small (just over 0.01 mm). 2. After parking, a gap measurement was taken of the probe that had suffered abrasion; the gap was around 1 MM. http://bbs.hcbbs.com/forum.php?mod=image&aid=1015664&size=300x300&key=4b06b00e5e7153f9&nocache=yes&type=fixnone http://bbs.hcbbs.com/forum.php?mod=image&aid=1015679&size=300x300&key=ec973a6783e0c889&nocache=yes&type=fixnone

Firstly, vibration as the cause can be basically ruled out; a vibration of 1 millimeter is sufficient to cause the machine to lift off in a short period of time. The distance between the speed sensing probe and the speed sensing gear disc is approximately 1 millimeter. In our company, it is our instrumentation team that is responsible for checking these data. Based on the phenomena you described, I think that during maintenance, there are certain parameters that need to be measured carefully: at the location where the speed gear is installed, a dial indicator should be used; rotate it 360 degrees and record the readings at 8 different points. It is also necessary to measure the amount of play in each tooth on the top surface of the gear May I ask: Have the data in this area been reviewed? We look forward to receiving the above actual measurement data from you! It’s really surprising that a gap of just 1 millimeter can cause wear.

This post was last edited by zhaoqingsheng on 2014-4-10 22:06. The top clearance of the nearby megawatts is only 35 wires. However, this does not mean that the runout of the speed gear disc is small when it is rotating. It’s completely different. It’s like swinging a ball attached to a string with your hand; even though your hand doesn’t move much, you can still make the ball rotate.

Also, is the connection between the speed measurement gear disc and the shaft on your machine a mated fit? The clearance between the gear disc and the shaft also needs to be checked. When analyzing complex issues related to steam turbines, it’s difficult to arrive at a definitive conclusion. A little investigation is needed.

After the speed of our company’s turbines is set to automatic mode, fluctuations in speed occur from time to time; however, such fluctuations do not happen when the mode is set to manual. What is the reason for this?

In the industry, the two most difficult problems related to turbines are: first, speed fluctuation (or load fluctuation). Often, the oscillation intensifies at a certain speed or load point. II. High vibration. What you mentioned falls under the first category. I have been working with steam turbines for over a decade and have been involved in dealing with such faults on many occasions; however, it was not until recent years that I truly learned how to analyze and handle them correctly. Generally speaking, for \"group valve lift plate type control valves,\" an inappropriate overlap rate between the various control valves often leads to fluctuations in speed. If your machine uses this type of control mechanism, it is necessary to carefully review the \"overlap rate.\" If you are not familiar with how to operate it, it is recommended that you contact the manufacturer’s staff to help adjust it for you. I’ve put in all the savings I’ve accumulated over more than a decade – I wonder if that will be of any help to you? Also, if you could upload the drawings of the control valve, it might be even more helpful for you!

We measured the play of the tachometer disc by tapping at a location near the shaft journal of the tachometer disc; since the tips of the teeth on the tachometer disc are worn out, tapping now isn’t useful. We adjusted the distance between the tooth and the probe while turning the disc – several points were adjusted during one full rotation, with the gap being roughly 1 mm in each case. I really didn’t check whether the tachometer disc was loose; I’m not quite sure how it should be installed either. Two fixing bolts can be seen, but I think the possibility of it being loose is very low – otherwise the vehicle would have stopped working long ago. My main hypothesis at the moment is that the rotor and bearing housing are not concentric, and combined with changes between cold and hot states, this might have reduced the clearance, leading to rubbing – but it’s just a hypothesis. The manufacturer has arrived and recommends disassembly for major repairs. . . . http://bbs.hcbbs.com/forum.php?mod=image&aid=1015675&size=300x300&key=b489fa9ec3d876f1&nocache=yes&type=fixnone It turns out it was installed there for grinding; we plan to try installing it at the lower side instead

Since our machine is equipped with probes for measuring the eccentricity of the main shaft, it is possible to clearly see the change in the center position of the main shaft before and after the machine is turned on. Of course, the machines from different manufacturers are not the same. I suppose you must have also contacted the personnel at the steam turbine factory, right? It is recommended that they send someone to the site to measure and collect the relevant data again.

The method of installing it below could indeed be tried. Because the center position of the main shaft is different in static and dynamic states.

I just mentioned one of the most likely causes of speed fluctuations. Moreover, there are many other possibilities as well. For example: oil quality issues, DEH problems, and so on.