a gas turbine frame5 tripped by high exhaust temperature spread trip after 25MW going to the base load. at 25 MW it is ok. allowable spread and sp1, sp2, sp3 are acceptable. may you know what the problem comes from? if you need more information .pls ask me? thanks.

 

What fuel is being burned?

What is the allowable spread (TTXSPL) at Base Load?

What is TTXSP1 at Base Load?

What is TTXSP2 at Base Load?

What is TTXSP3 at Base Load?

What alarms (Process- and Diagnostic Alarms) are present immediately before the trip?

How long after reaching Base Load does the turbine trip?

Is the Speedtronic panel TMR or SIMPLEX or DUAL Redundant?

 

Dear Ibrahim,

Sometime, it may happen, if anyone exhaust thermocouple read very high temperature. Please look the trip history and see all the exhaust temperature parameters.

In your case it tripped after 25 MW, may be with spread issue.

take care
G.Rajesh

 

> What fuel is being burned?
the fuel is light diesel oil LDO.sorry GT is frame6

> What is the allowable spread (TTXSPL)
at Base Load?at base load about31MW allowable spread is 175

> What is TTXSP1 at Base Load?
555.6

> What is TTXSP2 at Base Load?
54.4

> What is TTXSP3 at Base Load?
46.8

> What alarms (Process- and Diagnostic Alarms) are present immediately before the trip?
first: combustion trouble then high exhaust temperature spread trip

> How long after reaching Base Load does the turbine trip?
if we selec load preslect the load can reachs to 29 but spread increase so we decrease the load ,when we select base load after 25MW just after 2 or 3 min alarm occurs and trip.

> Is the Speedtronic panel TMR or SIMPLEX or DUAL Redundant?
SIMPLEX

 

SIMPLEX panels are somewhat unique. If it's a typical Mark VI Speedtronic SIMPLEX panel then it's very likely at least some of the exhaust T/Cs are connected to the <P> core for a kind of back-up combustion monitor and OT protection.

The TTXSPL number you provided is unbelievable. When ever a unit is loaded (such as going from Pre-Select Load to Base Load by clicking on Base Load and then confirming the selection), the allowable exh temp spread is biased up to prevent tripping on transient temp excursions during loading (and unloading, also). Once the unit reaches Base Load, the allowable exh temp spread is ramped down to the normal calculated value.

That's likely why you are seeing a trip after a couple of minutes. When a unit reaches Base Load initially there is still usually some RAISEing and LOWERing going on for a minute or so, and when that all settles down then TTXSPL starts ramping back down to normal calculated value, which is usually slightly less than the 56 deg C value of your highest exh T/C values. Now, if the hottest and coldest T/C values are adjacent (next to each other), then when the allowable gets down it's normal value the unit will alarm "Combustion Trouble" and trip several seconds later if no action is taken.

The spreads you are listing (SP1, SP2, and SP3) are not "okay". They are borderline high.

Fix your spread problem and the tripping problem will magically disappear.

Since you're running on liquid fuel, it should be relatively easy to determine which combustors the high spreads are associated with. Use the manual selector valve and gauge assembly at the Liq. Fuel Flow Divider to scroll through the pressures at each of the combustors. The "rule of thumb" (loose rule) is all of the 10 pressures (positions 1 through 10) should be within approximately 10% of each other. Any pressures much higher or much lower than the others means the problem is associated with that combustor. It could be fuel nozzle problems (blockages; loose internal components; worn passages; etc.) or problems with the liquid fuel check valve upstream of the fuel nozzle, or leaking purge air check valve(s) if the unit is dual fuel (gas/distillate). If the unit is dual fuel (gas/distillate) and has purge air check valves, then you can go to the Tell Tale Leak-off to see if there is any liquid fuel coming out of the drain. If there is, then at least one of the purge checks is leaking, and it will be apparent from the flow divider pressure reading which one(s).

Please write back to let us know what you find.

 

thanks all.

we are going to solve this problem. we have started by fuel nozzles cleaning, and we will replace all the fuel oil check valves by new. and we will also purge the oi line from flow divider to the nozzle.

according to the purge air lines check valves we have isolated already so we don't concern by leaking of them.