Say what?.?.?!!!???!!!

These thermocouples do measure "high" temperatures, but if they're in the exhaust (the exhaust of the HP gas generator (gas producer)) then the temperatures they measure should be very uniform around the periphery of the turbine--because if they are not fairly equal (uniform) then that can indicate some kind of problem with the combustors or fuel nozzles (injectors), etc.

Just because the thermocouples measure temperatures which can change from ambient to several hundreds of degrees Celsius doesn't mean they should be anything less than accurate--which is what you seem to be saying, that it's okay for there to be high temperature spreads because of the high, varying temperatures being measured.

And that's just not so. Read the copyrighted write-up in Post #11 above; it explains why the temperatures should be uniform and how there is no mixing of hot combustion gases as they flow through the turbine section of a combustion (gas) turbine.

yes,they should be measuring the same but they are nnot doing that,I have yet to hear from the mechanics now,
Update:I heard from them and they have no explanation,so I guess it is a design problem

 

nikidi.control,

You didn't actually answer any of the questions which were posed in post #18....

How is the spread problem resolved on the aeroderivative units on the site when the spread becomes too large? Are the T/Cs replaced and the problem goes away? If so, that would indicate the problem is failed or failing T/Cs, possible poor quality T/Cs and/or interconnecting cabling/wiring. So, the method for solving the spread problem over time can tell us a lot about the nature of the problem.

Are individual fuel nozzles (sometimes called 'fuel injectors' on aeroderivative combustion turbines) replaced to reduce or eliminate the temperature spreads?

AND, precisely which thermocouple are you talking about??? The ones measuring the discharge temperature of the HP section of the gas turbine, or the discharge of the LP section of the gas turbine? If I recall correctly, the temperature in the discharge of the HP section (the gas generator/producer section of the aeroderivative turbine) is referred to as T54 temperature.

Aeroderivative turbines are not the same as heavy duty turbines, mostly because they have two or more shafts, the stator vanes of the axial compressors can have variable blades (sometimes called "vanes") and the combustor section of the HP shaft can also be very different from most heavy duty turbines.

Because, contrary to popular belief, there is very little mixing of hot combustion gases as they pass through the turbine section of a combustion turbine AND because it's not really possible to measure the temperature of the hot gases entering the turbine section looking at discharge temperatures of the turbine (HP, LP) can be a very good indication of the condition of the combustion section of the turbine. If fuel nozzles are plugged, that will cause cold spots in the discharge temperatures. If there is a crack in the combustion liner that can allow cooler compressor discharge air to enter the combustor(s) in that area and cause a cold spot in the turbine discharge temperature (and here I'm referring to the HP gas generator discharge). If a fuel nozzle is excessively worn that can allow more fuel to enter through that nozzle (or nozzles) and that can cause a hot spot in the turbine discharge temperature. Allowed to continue unchecked, these kinds of problems can lead to serious problems and even catastrophic damage to the turbine, and worse (explosion; serious injury or loss of life to people in the area of the turbine; etc.).

Because it's not possible to measure the temperature of the hot gases entering the turbine section (leaving the combustion section) and because there is very little mixing of gases as they flow through the turbine section temperature spreads (differentials) can be the only indication of combustion problems (fuel nozzle problems; cracked liners; etc.) and that's basically why they are monitored for differentials (IF they are monitored for differentials).

Some turbines have multiple thermocouples around the periphery of the discharge of the turbine sections BUT they aren't monitored for excessive differential by the turbine control system. BUT, they should be monitored over time by the operators, because if the spreads increase over time, and increase very quickly over time, that can be a very good warning of impending problems--potentially very serious problems.

MOST of the aeroderivative turbines I have worked on did not monitor turbine discharge temperatures (HP or LP) using the control system for protection. That was left to the operators (who often weren't aware of what to look for). For heavy duty gas turbines with can annular combustors the turbine exhaust temperatures ARE monitored for excessive temperature spreads because combustion problems can and often do lead to serious damage, either very quickly or over time--which can lead to forced outages and lost production, which means lost revenue. Which is how everyone gets paid--by producing electricity and/or steam or by pumping gases or fluids (particularly with aeroderivative turbines).

Design problem? Probably not. Installation problem? Certainly possible. Thermocouple quality problem? Certainly possible. Combustion or fuel nozzle problem? Yes, especially if the unit burns liquid fuel(s).

But design problem? Again, not likely. There are literally thousands of aeroderivative turbines used for various purposes on the ground around the world. And, the HP sections of the aeroderivative turbines ARE THE SAME HP sections as used on flying aircraft around the world. So, design issues? Think harder about that. These things are very expensive to purchase and maintain, and to warrant when they are new or rebuilt. Design issues keep lots of aircraft from flying every day--but they get fixed. And, I'm talking about engine design issues, too. The manufacturers do a LOT to keep their design issues out of the press/media, and they are very good at it, too. Because it can affect their sales and profits. So, they want to fix those problems--and quickly.

I really think your question is unclear, and the lack of answers also adds to the lack of clarity. And, you say the mechanics--are these certified aircraft powerplant technicians, or just wrench turners (some of whom are very knowledgeable and qualified in many respect) but probably not qualified to repair aeroderivative turbines without the supervision of a certified aircraft powerplant technician. So, consider your sources of information. And when asked for clarification, seriously consider providing the requested information. The quality of your answers will definitely surprise you.