Can anyone please explain the effect of compressor discharge pressure (bias) differential on Gas Turbine operation, and specifically on Gas turbine Protection system. When will it results in unit tripping.

Regards,
Dottey.

 

Dottey,

You likely found this site using one of many Internet search engines.

This site has it's own 'Search' feature, cleverly hidden on the right side of the band across the top of every page. There is a question mark (?) in a circle to the right of the search term entry box; best to look at the syntax for using this search feature to it's best.

A lot has been written about CPD-biased exhaust temperature control over the years. There have even been "pictures" put into responses to this very same question.

One of the things that makes this site, and others like it, so useful is that when people find answers to questions or solve the problems they have posted to this site they usually take a couple of minutes to post some feedback. That feedback lets others reading the post later (using the cleverly hidden 'Search' feature) know if the responses they received were helpful or not.

What that means is that when responses have been helpful (or not) and people post feedback to that effect, you can feel pretty confident that the information you are receiving is pretty good. Information from a site which cost you nothing to post your query, and which respondents get paid exactly the same: nothing.

All we get for our replies is some feedback to let us know if our effort was useful. So, the feedback does two things: It lets you and others reading the posts know if the information provided was useful or valid, and it's a polite gesture to those who provided the responses to let them know their efforts were useful and helpful.

But, if you will use the control.com 'Search' feature you will find CPD-biased exhaust temperature control explained about twenty different times, in several different ways, but all trying to convey the same information.

By the way, if you have a Speedtronic turbine control system, it should have been provided with a document called the 'Control Specification'. In Section 3 of the Control Specification, Exhaust Temperature Control is also explained pretty well.

Speedtronic turbine control- and GE-design heavy duty gas turbine-related threads have been posted on control.com for some 6+ years now, going on seven, I think it is. There have been a LOT of questions, many of them the same questions. If you have a question, it's very likely that it has already been asked and answered. And you can find that out for yourself using the cleverly hidden 'Search' feature of control.com.

However, if you find some answer needs clarification or is incomplete, you are free to tell us that a particular thread had some information that still have questions about (not doubts, but questions; we don't deal in doubt or anything that leads to doubt).

Now, the one part of your question that I didn't understand was something about when CPD bias will result in tripping the turbine.

Well, a loss of CPD feedback will generally not result in a trip <b>for most GE-design heavy duty gas turbines with conventional combustors (non-DLN turbines).</b>

Because DLN control is very keenly a function of many parameters, and CPD is a very critical one, a loss of CPD feedback from more than half of the CPD transmitters (it's so critical there are redundant CPD transmitters) will result in a turbine trip.

When the unit is running on CPD-biased exhaust temperature control (Base Load) if the actual exhaust temperature exceeds the CPD-biased exhaust temperature reference by more than 40 deg F the unit will be tripped on exhaust overtemperature. (This is also described in Section 3 of the Control Specification document.)

But I'm not sure if that answers your question, because I'm not really sure exactly what the question was about.

Happy searching!

 

Hi there,

I am not sure but it seems like you are making use of the discharge valve in the same way as what we use on our back pressure control valves.

I will give you a brief explination how that works but if it is not what you are looking for, send us more details on your application and ask more direct questions. Answering a general question like this is quite difficult since we have to make assumptions as we go along.

Say your plant pressure is running at normal 100bar pressure with one gas compressor and you now need to start a second one as well. You need to get to the same pressure before the back pressure control valve first, before you can allow the second compressor to contribute.

The compressor back pressure control valve therefore needs to stay shut until the differential pressure across the valve is equal. In other words the compressor have to build up enough pressure (100Bar) which must be the same as the plant pressure after the valve (100Bar). This is monitored by a DP Transmitter across the back pressure control valve.

Then there is also a timer involved this Diff pressure must be stable and only then will the valve start to open. There is also a limited time involved that the valve have to open and the PLC needs to see the valve open feedback signal within this time limit. If not the unit will trip and close the back pressure control valve.

If all goes well there will be no bump in the process the moment the second compressor comes on line and starts to contribute. The fist compressor will obviously from then one starts to slow down at a rate commanded by the load share controller.

 

Thanks CSA i can now understand better the relationship between Exhaust Temperature, CPD and FSR of our Gas Turbine program/operations. It has worked better for me.

 

CSA: Based on the acerbic nature of many of your responses on this site I'm inclined to think your name is Joe. Would this be correct ?

 

My apologies if any of my posts were harsh; it was not my intent to offend anyone. My cynicism has been in overdrive recently.

Any similarity to the attributes, faults, failings or disposition of any individual is purely coincidental, and unintentional.

Did you have something positive or informative to add to this thread, mogy?

 

I am sorry if i have hurt your senses in any way, but i have seen some worst thread here and your humble reply to them. We are learning.

Thanks.
dottey