steam turbine overspeed

I have a 12mw ge turbine i want to ask about overspeed system if the 3 sensors send a signal that everything is ok and the turbine speed is ok but actually the speed is increasing in the turbine. isn’t there any other system to add more protection on this situation??
i have a woodward 505 turbine governor system & the turbine is running from 2005
thank u all
morsy san,

You make some very difficult-to-understand claims, for example, you say three sensors (magnetic speed pick-ups--active or passive; or, ???) send a signal that everything is okay and the turbine speed is ok but actually the speed is increasing in the turbine. ... What does that mean--the speed is okay but the speed is increasing? Does that mean it's below rated speed but the speed is increasing? Is the speed increasing slowly or quickly? Does it mean the speed is above rated speed but below the overspeed trip setpoint and is increasing--quickly or slowly?

What is it that you want the automated control system to do that it's not doing? Do you want it to anticipate an overspeed based on the rate of change of the speed signals--which you said were okay...???

Per some widely recognized international standard, high-speed rotating machinery such as turbines should have two (2) independent means of protecting against overspeed. (I'm referring to an API specification which most large companies and insurance companies usually follow in most parts of the world. Some insurers won't insure a unit without two (2) independent means of detecting an overspeed condition--which is usually when the actual speed exceeds the overspeed speed setpoint, but not based on the rate of change of turbine speed.) Usually, when a 505 is used then another, independent overspeed protection system--with it's own dedicated speed pick-ups--is also used which is capable of tripping the turbine if the overspeed speed setpoint is exceeded. Most turbine control systems for smaller turbines, particularly, do not do any kind of speed anticipation--meaning they don't continually monitor the rate of change of speed and trip the turbine before it reaches to overspeed speed setpoint (that's done sometimes on very large steam turbines).

You need to be clear about what you think the turbine control should do--and when it should do it--and you need to also be clear about the conditions and the equipment supplying signals to the turbine control. The 505 manual is pretty good, though a little lacking in some clarifications; it is widely used for configuration and "programming" around the world so it has to be relatively good. You should consult the document for information about the capabilities of the 505, and then determine if it does what you want it to do or need it to do by comparing the configuration parameters to the possibilities in the manual.

And, when you are saying things like 'the speed is okay but in fact is increasing' you need to provide numbers--values--data for that to be clearly understood. What you have provided is called 'anecdotal data' which means it is not based on hard, verifiable, concrete data--it's just "word of mouth" and so it's not verifiable and not clear. You need to provide 'actionable data'--data in numerical format with some time context (in this case) to be clearly understood.

You also didn't say when this occurring--during starting, or loaded operation, or during shutdown. You didn't say what the steam turbine is driving (a generator; a boiler feed pump; a centrifugal compressor; etc.). For example, when the unit reaches rated speed is the speed increasing and not controllable by the operator? If so, how fast is it increasing? How much does it increase? Does it eventually stop before reaching the overspeed speed setpoint and results in a turbine trip? Or does it eventually just stop increasing but is at an excessively high speed for use for the process?

And, very importantly--when you write to a forum like this you need to tell what troubleshooting has been done, AND what the results were. We can try to make recommendations, but if you've already done that you're not going to be happy when we tell you to do it. How do we know what you did--and what the results were--UNLESS YOU TELL US???

Best of luck with your problem.
The way I interpreted the OP's post was more of a theoretical: "What if the my 3 speed pickups are 'healthy' but aren't accurately reporting the actual turbine speed - and the turbine is actually spinning faster than indicated. Shouldn't there be extra protection to prevent an overspeed in this situation?" (..I personally can't think of a non-malicious way this would occur, especially undetected and on a running unit, but there are backups for a reason )

Morsy San, if this is the case, take note of CSA's third paragraph.

Per some widely recognized international standard, high-speed rotating machinery such as turbines should have two (2) independent means of protecting against overspeed
There is probably a very good chance that in addition to your turbines 3 primary speed pickups that there is an emergency mechanical or hydraulic overspeed trip device, or 3 separate additional, speed pickups - acting as a backup if the primary tripping means were to fail. Do you have any operations manuals for the steam turbine operation from GE, Woodward or the installer? Any of those will likely have a section on overspeed protection, turbine safety or something similar which should discuss the how the turbine is protected against overspeed events.

IF you do NOT have a secondary independent overspeed tripping means, or you're are actually asking about an acceleration/anticipated overspeed trip. I'm sure GE, Woodward and many other turbine control companies would be more than willing to sell you and install such a device.

I actually read it several ways, as above in my response, as in yours, and wondering if the question wasn't that the unit speed was increasing when the control system should not be trying to increase the speed. I've been to sites where the control valve position feedback (from LVDTs) wasn't calibrated properly and the turbine control system though the valve was at 0% when it was really at 5% or 6%--so the steam (in one case) was flowing past the control valve and the unit was accelerating pretty quickly as soon as the stop valve opened. In this case, site management and operators were blaming the turbine control system for the problem when it was an instrument tech who hadn't done a proper calibration of the LVDTs. And even when the LVDT feedback was properly calibrated the mill manager still blamed the turbine control system and was demanding a written explanation of how the turbine control system didn't prevent an improper calibration from happening (I was later told the instrument tech was his cousin or second cousin or something like that).

I also went to a site many years ago where someone had unintentionally changed the scaling for the speed feedback signal from the magnetic speed pick-ups--making the turbine control system think the turbine was going much faster than it actually was. This was done while the unit was running, so, of course it tripped, and then couldn't be re-started (because it kept tripping at well below rated speed). It wasn't malicious, but it just goes to demonstrate that well-meaning people with good intentions can--and do--cause unintended results, and that changing operating parameters with the unit running and producing power is extremely risky and before it's done--if it has to be done--the person doing the on line changes should be checking and double-checking the points being changed (and forced, since the same thing applies to forcing signals).

But, this is just a really unclear post, and its doubtful we'll get any clarity. It's likely another case of assuming the turbine control system is all-knowing and does things it has never done and isn't capable of doing. It just "makes sense" at the time when there's a problem and someone perceives the problem to be caused by something that's not related at all. There's probably a steam leak, or a programming parameter was changed, or something similar. And, we almost never hear back about those things anyway.