Hi all,

In frame 9E in which 24 T/C were used, I need to know exactly how the average exhaust temp (TTXM) was Calculated.

Also, I know from the GE manual that the allowable spread TTXSPL is calculated from the equation  (0.145 TTXM- 0.08*CTDA + TTKSPL5), so in baseload all the parameters are known so why the allowable spread sometimes instantaneously raises up to a high valve and after that it begins decay out? By what factor it multiply? and when?

 

AhmedWaleed,

All of these questions have been asked and answered several times on control.com. All of the past threads are stored in the 'Archives' and can be accessed using the cleverly-hidden 'Search' feature at the far right of every Menu bar in the desktop version of control.com. (It's accessible from the 'Control.com' tab in the mobile version of control.com.)

It's recommended to use the Search 'Help' feature before beginning your search, and to refine your search using words and terms you discover as you search for your answer (just like you normally would when using your preferred World Wide Web search engine. While you may not find exactly the concise answer you are looking for, it's pretty certain you will learn more than you bargained for in the process by reading through the threads.

The Speedtronic controls community here at control.com has been going strong for more than a decade now, and most of the questions you can think of have been asked and answered more than once. And, the ability to read the questions--and, most importantly, the feedback provided by many of the posters--will help you to determine if the responses were helpful, or not. It's the feedback provided by the original posters, and others, that makes the posts and the archived threads here at control.com so valuable--something few other similar sites can claim.

Actually, you can look in the sequencing/application code to find the algorithm ("block") TTXMVn, where 'n' is a digit indicating the version of the algorithm in use in the control panel at your site. It's fairly easy to work through blocks (algorithms) once you become accustomed to them; they are very graphical in nature and most are written using a relay ladder diagram style.

If you have a Mark VI or Mark VIe turbine control panel, you can use Toolbox or ToolboxST and when you find the block you can right-click on it and find any 'Help' the designers felt nice enough to provide (most blocks have 'Help', but some do not, especially ones which have been converted to macros). If you have questions about the block or how to read it, we can try to help.

The calculated allowable exhaust temperature spread, TTXSPL, is biased during load changes--because it's expected that under some conditions the exhaust spread may increase temporarily while changing load.

You can also read the document provided with all Speedtronic turbine control panels, the Control Specification. Sect. 03 is the section regarding temperature control and exhaust temperature spreads.

Hope this helps!

If you're having a specific problem sometimes it's best to just describe the problem here-including when the problem started (after a maintenance outage; after a trip from load; etc.)--and in the process we usually provide some background information about how blocks work and general GE-design heavy duty gas turbine control philosophies.

While it's laudable to try to learn and understand the blocks/algorithms when you're having a problem sometimes it's easiest to just state your problem and what you think might be happening and we can help guide you in your journey of discovery and problem resolution.

Just, please--don't ask how many exhaust thermocouples the unit can run without (in other words, after how many exhaust thermocouples have failed (low) will the turbine trip). The answer is: Fix the failed thermocouples so you don't have to find out.

And one more thing--the calculation of the exhaust temperature spreads and the calculation of the median (average) exhaust temperature is <b>NOT</b> the same. One discards the high and the low, and one only discards values below a certain temperature--and that's to protect the turbine combustion section.

Many people mistakenly believe the two methods are the same (specifically, that the highest and the lowest are discarded from the calculation--but that's not the case at all, and a thorough analysis of the two situations will help to clear up what is a terrible and false rumor).

 

Send me an email at [email protected] and I can send you a document which will explain all.