TTKOT1 is the ultimate over temperature tripping value. After conducting peak load test for several GT units on gas, some units had exhaust average temperatures above 585C which is TTXM values. The reference temperature (TTRXB) can be exceeded some times. As we know that TTRXB + 13.9 C or + 22.2 C alarm/trip will be initiated.
But we had no alarm prior to reach 591C. How can we understand this?

 

You haven't told us what the value of TTKOT1 is for your machines.

TTKOT1 is the "maximum" (ultimate?) over-temperature trip setpoint, and it's usually set for (TTKn_I + 40 deg F), so if TTKn_I is 1100 deg F, then TTKOT1 would be 1140 deg F. (I'm using Fahrenheit because that's how GE describes it in their Control Specifications documents. And I'm using TTKn_I because that's how the "isothermal" value was expressed for many years in various Speedtronic turbine control panels; I've seen it also listed as TTK_I[n], but it's always an _I value, and it's almost always the same value for any of the exhaust temperature control arrays, Base, Peak or Peak Reserve.)

I'm not clear if you are saying that you had TTXMs greater than TTKOT1, because that would be very unusual. Individual exhaust temperature T/C feedback values can be higher than TTKOT1 or TTRX, but TTXM should never be higher than TTKOT1 without a trip being initiated. And, it's not uncommon for "T/C bounce" to cause TTXM to be slightly greater than TTRX occasionally, but it should never be much more than a couple of degrees higher than TTRX (I can never remember if TTRX is the high-select of TTRXB and TTRXS or the low select of TTRXS and TTRXB).

So, we don't have enough information and the question is unclear (to me, at least).

 

Thanks CSA and sorry for delay, but since I'm still new I lost the thread.

First of all TTKOT1 value in our machine is 1095 deg F. While peak load test TTXM reached 1085 deg F without any prior over temperature alarm.
Is it normal not to have a prior alarm?

Regards,

 

I would really need to see the sequencing running in your Speedtronic panel to comment on how your unit is configured.

TTKOT1 is, as you said, a maximum upper limit, which is usually set to 40 deg F above the isothermal value. And you haven't told us what the isothermal value(s) is(are).

The overtemperature alarm should be set (TTRX + TTKOT2 (or -3, I can't remember which is the alarm or trip and I don't have access to any sequencing as I write this response)), then I would not expect an alarm to occur unless the average exhaust temperature was greater than 25 deg F above the exhaust temperature reference.

Peak Load is not intended to be a normal operating mode; it's intended for unusual operating circumstances. As such, the over temperature alarm might not always be programmed to occur as it might be a nuisance when operating on Peak Load.

But, again, it would be necessary to examine the sequencing or application code running in the Speedtronic at your site to say for certain how things are programmed.

If you're trying to say, "We've found an error with the GE-provided sequencing! It doesn't operate the same way in all conditions!" rest assured there are other sites, and even other situations in the sequencing running in your machine, that are not consistent for every operating condition.

And, many times the packagers of GE-design heavy duty gas turbines make modifications to the standard GE sequencing for any number of reasons.

And, lastly, the people commissioning GE-design heavy duty gas turbines can be under tremendous pressure to change things based on how some people believe the turbine should operate, and do so in an attempt to placate loud, boisterous, and blustery people so as to get off the job. (It happens more than anyone knows!)

Your unit is still protected; I would offer that it's not annunciating the alarm because it would be a nuisance, and erroneous, to do so when operating on Peak Load, when it is (or should be) understood that the unit is being "over-fired" because the situation demands it, and is being operated very close to the design limits of the machine.

But, that's just my personal opinion, and without being able to see the sequencing in your machine it's not possible to say for certain if it's "standard" GE sequencing or has been modified for some reason, which may or may not be known at this time.

If you're really concerned, you should contact the packager of the unit, or GE, for review and comment.