In the application manual Appendix-B TCQA card definition, what is this SRV warmup time constant? Because it has been mentioned that, at startup with low level flow, the GCV is relatively closed and a small change in the SRV position produces a high rate of change of FSR. So interval time constant should be higher and vice versa in normal running condition.

Is this interval time constant the same as SRV warm-up time constant, and if this interval time constant to remain high during startup than what exactly happens?

Regards,
Satyanarayan Pradhan

 

What are the values of the SRV Warm-up Time Constant Gain and the System Warm-up FSR from TCQA Screen 12 in the I/O Configurator for your unit?

Are you experiencing some kind of problem with start-up? Please be specific. Your statement about low level flow and GCV position versus SRV position is not familiar. Was that taken from the App. Manual?

markvguy

 

no we have not faced any problem during start-up.
the value of SRV Warm-up time constant is 0.3601,gain is 0.0 and system warm-up FSR is 20.
i want to know what is the physical significance of this terms?why this time constant data are needed for the type-7 regulator.

about my last statement in which i mentioned that at start-up with zero to low fuel flow the gcv is relatively closed.so a small change in srv position produces a high rate of change in pressure P2.therefore the interval time constant is high under this condition,and when the turbine is running normally because gcv is in open condition so a small change in SRV'S position will produces a small rate of change of fsr and interval time constant is low.

the above mentioned statement is given in the application manual.and it also been mentioned that to compensate for these changing condition,an algorithm changes the interval time constant in linear fashion with respect to fsr.

i m not able to understand what it means and what is the significance of this interval time constant.

Regards
Satyanarayan Pradhan

 

The passage you "quoted" (the passage actually reads "...produces a high rate of change in the pressure P2....", not FSR) was located; doesn't make a lot sense, does it?

There's another line about SRV Warm-up function I/O Config. Constants that says these values must be supplied by the "Turbine Department" (meaning Gas Turbine Control Systems Engineering).

There's another little passage about this functionality (not much more info there, either...) in Sect. 7-5.2.2, Position Control Regulator Notes, Note #2 "...If the pressure control regulator includes the variable integrator time constant function (also known as the SRV Warmup function), I/O Configuration Constants must also be entered on a separate screen for each Type 7 regulator defined...." The separate screen is the TCQA screen 12, which is what was being described in Appendix B.

There's a little better pictorial representation of the functionality on Fig. 7-16, Type 7 Regulator Signal Flow Diagram. The FSR_WU, T_G, and T_C values that all acted on FSR2 (which is Gas Fuel FSR (GCV position reference) from the Fuel Splitter algorithm) all affected the ramping of the integrator's gain during firing.

IN GENERAL, the SRV Warm-up Time Constant Gains were all set to 0.00 by the "Turbine Department" (GE Gas Turbine Control System Engineering) as it was determined after this functionality was put in the Mark V that it wasn't really necessary, so it was effectively disabled by setting the gain to zero.

Again, GE-design turbine packagers/licensees had other ideas about functionality and settings, and GE shipped some early Mk V turbine control panels with gains and the other related I/O Config. Constants set to some calculated values. IT IS NOT RECOMMENDED TO CHANGE THESE VALUES WITHOUT CONSULTING GE!

In this author's experience, almost every Mk V-equipped unit he worked on didn't use this functionality--and there was never any reason to investigate it any further. It seems what they are trying to say is that it might possible for a condition to occur where a fluctuating gas fuel supply pressure (which would affect the P2 pressure) to cause problems during firing/initial acceleration. P2 pressure at light-off is "typically" in the range of 30-50 psig, so a fluctuating supply pressure (such as from an improperly sized natural gas compressor or an improperly sized natural gas fuel supply pressure regulator--both of which have been known to cause problems during firing and acceleration because there were sized for RATED flow, and the "designers" didn't account for the low flows required during firing and acceleration!!!) would cause problems because the GCV positions during firing and light-off are "fixed" (not regulated to maintain a flow reference using flow feedback--just a position reference with position feedback). The concept is that with a known (and stable!) gas fuel supply pressure upstream of the GCV, flow will be "relative" to position. If the P2 pressure is fluctuating (cause the SRV gains are usually high), then flow through the GCV will be erratic, also.

Hope this helps!

It's noted that firing and warm-up FSRs are biased by CTIM (TNHCOR), and you have just recently asked about TNHCOR.

markvguy

 

thank you very much for ur valuable replies.yes it may be for a fluctuating gas pressure during firing.
this term light-off period, what it is? actually i listen it for the first time. is it warm-up, firing or accelerating period?

thanks again.
regards
Satyanarayan

 

Apologies for using the term; it's one of those American English slang terms which this author really struggles hard not to use (but occasionally doesn't catch/correct it). It is particularly aggravating to encounter these slang terms when trying to troubleshoot technical problems...one individual complained, "We cain't spin dry the unit after the crank wash." He meant, they couldn't use the starting means to crank the unit to blow out the water it after an Off-Line Compressor Water Wash and rinse, but it took about five minutes of telephone conversation to get the whole story and determine what the problem was. His native language was American English, but a particularly "unique" dialect used by (self-described) technicians who call Texas home.

"Lighting off" comes from a term used to describe the light emitted when a flame is established, probably derived from the early days of boilers/combustion. ("Light-on" would have been a more apt term, but it was probably originated by another Texan.) The the term "light-off" when used in reference to combustion turbines generally refers to the initial firing and warm-up period during starting, when fuel is first introduced to the unit, the ignitors (spark plugs) are energized, and flame is being established. It can, and sometimes is, also considered to include the warm-up period after flame is initially detected when fuel is reduced for a period of time to reduce the thermal stresses on the machine.

markvguy