hello every one
currently in one of our gas turbine (frame 6 mark 5 ) in start up ( utilizes Distillate fuel) when the rpm reaches to about 2200 to 2300 rpm, it seems the acceleration control loop do not perform properly and the control loop changes between temp control and acceleration control mode and the fluctuation in FSR between 14 to 20 appears then suddenly the gas turbine tripped due to over temp trip alarm (actually because excess fuel injection because lack of proper control). also all of the fuel line including the tubes, flow divider, check valves, servo valve, nozzles, bypass valve are checked and are OK, however the possibility of failure of 3 cards simultaneously is unlikely (also all cards have about one FSR in this situation)
also there is no problem in starting the gas turbine using gas fuel
also when the gas turbine goes to full speed even using Distillate fuel there is no problem.
I appreciate your guiding me regarding this.

 

hello every one
currently in one of our gas turbine (frame 6 mark 5 ) in start up ( utilizes Distillate fuel) when the rpm reaches to about 2200 to 2300 rpm, it seems the acceleration control loop do not perform properly and the control loop changes between temp control and acceleration control mode and the fluctuation in FSR between 14 to 20 appears then suddenly the gas turbine tripped due to over temp trip alarm (actually because excess fuel injection because lack of proper control). also all of the fuel line including the tubes, flow divider, check valves, servo valve, nozzles, bypass valve are checked and are OK, however the possibility of failure of 3 cards simultaneously is unlikely (also all cards have about one FSR in this situation)
also there is no problem in starting the gas turbine using gas fuel
also when the gas turbine goes to full speed even using Distillate fuel there is no problem.
I appreciate your guiding me regarding this.

Hello

When did the problem appear? Is that unit used to be operating on Distillate fuel?

Any job done around control system MarkV or other related Turbine control systems auxiliaries?

 

Hello

When did the problem appear? Is that unit used to be operating on Distillate fuel?

Any job done around control system MarkV or other related Turbine control systems auxiliaries?

the unit used to be operating on gas fuel for long time , then it stopped (normal stop) and after a few days we want to start the unit on distillate fuel and the problem suddenly appears and still continues.
we did not change the cards (TCQA & TCQC cards are direct interaction in servo valve output but i think failure of 3 cards simultaneously is unlikely

 

Was the unit either operated /commissioned on Distillate fuel previously and if yes was unit operating properly ?

 

The NUMBER ONE reason for tripping while starting/accelerating on liquid fuel is air in the liquid fuel supply system. This is ESPECIALLY true if the unit doesn't run very often on liquid fuel and suddenly needs to be started on liquid fuel. When there is air in the liquid fuel supply piping it will cause the liquid fuel control valve to fluctuate as the air passes through the liquid fuel flow divider--and the FSR will jump up and down to try to get steady fuel flow. Sometimes (often) once a slug of air gets through the piping the liquid fuel flow rate will very suddenly increase and cause the exhaust temperature to spike. Also air in the piping can cause the acceleration rate to slow and this will cause the liquid fuel control valve to try to increase the fuel flow-rate, also.

The air can be trapped in the piping between the liquid fuel storage tanks, or in the liquid fuel filter(s) in the system. Very often the liquid fuel supply piping to the Accessory Base inlet flange does not have the proper pitch or air vent valves in the piping to remove air.

You should start the liquid fuel forwarding pumps and open the stop valve (20FD-1) at the forwarding skid to pressurize the liquid fuel supply piping. Then you should attempt to vent all air from any liquid fuel canister(s) and ensure that the transfer fill valves are in the correct position(s). If the unit is not running on gas fuel when you do this, you can force open 20FL-1 to pressurize the high-pressure liquid fuel filter canister and vent any air from it. (The liquid fuel forwarding pump supply pressure should stabilize once most of the air is removed, and it should be about 4-5 barg, which is below the cracking pressure of the liquid fuel check valves so no fuel will flow into the combustors.) The liquid fuel supply pressure (if controlled by a pressure regulator) should be stable and at the pressure specified in the Device Summary for the machine. If the pressure is NOT stable during low-load or no load operation (or during purging when not running) then the cause needs to be identified and resolved. Sometimes, the strainers upstream of the liquid fuel forwarding pump(s) can get plugged and cause flow-rate restrictions as flow is increased during STARTing or liquid fuel transfers. So, don't overlook the fuel strainers as a possible cause of an inability to get required flow-rate. (Bacteria does grow in liquid fuel storage tanks, and liquid fuel piping, also, when the system is inactive for long periods of time.)

If the liquid fuel supply piping runs in any overhead pipe racks between the outlet of the liquid fuel forwarding skid and the inlet flange to the Accessory Base check to see if there any vent lines in the high points of the piping, and if there are, vent any air out of the lines. This may entail some liquid fuel coming out of the vents to ensure the air has been removed, so use buckets and care as necessary.

START the machine on gas fuel, and then when at FSNL initiate a transfer to liquid fuel. This usually helps to get enough flow in the liquid fuel system to dislodge any air. If there is air there is still a risk of tripping--but it will usually only happen once. You should be using the VIEW2.EXE utility on the HMI to monitor the liquid fuel flow divider feedback during the fuel transfer (and during any subsequent START attempt--it can provide useful information). You should be monitoring FSR1, TNH, TNHAR, TNHA, TTRX, TTXSPL1, TTXSPL2, TTXSPL3 and TTXM in addition to the feedback from the liquid fuel flow divider (three speed pick-ups)--at a minimum. You should save the data to a file (it will be in ASCII text form) and you can attach it to a subsequent post for help in analyzing it.

But again--when a dual fuel machine is not run regularly (the OEM recommends once per week!) on liquid fuel, by transferring to liquid fuel and then back to gas fuel after a few minutes, air WILL make it's way into the liquid fuel supply piping and components.

It sounds counter-intuitive to START the machine on gas fuel when you are having problems with STARTing on liquid fuel, but it's usually very helpful--especially if you're collecting data with VIEW2 at a high-speed rate (32 Hz). BUT, you should still do everything you can to remove any air from the piping before attempting this. And, again, there is no guarantee it won't trip--but it's probably the best way to get liquid fuel flow-rate up quickly to try to move any air along and get it out of the piping.

Write back to let us know how you fare--and share any data you collect.

 

Was the unit either operated /commissioned on Distillate fuel previously and if yes was unit operating properly ?

yes this unit work on Distillate and gas fuel for 20 years but, since 6 month ago just work on gas fuel

 

The NUMBER ONE reason for tripping while starting/accelerating on liquid fuel is air in the liquid fuel supply system. This is ESPECIALLY true if the unit doesn't run very often on liquid fuel and suddenly needs to be started on liquid fuel. When there is air in the liquid fuel supply piping it will cause the liquid fuel control valve to fluctuate as the air passes through the liquid fuel flow divider--and the FSR will jump up and down to try to get steady fuel flow. Sometimes (often) once a slug of air gets through the piping the liquid fuel flow rate will very suddenly increase and cause the exhaust temperature to spike. Also air in the piping can cause the acceleration rate to slow and this will cause the liquid fuel control valve to try to increase the fuel flow-rate, also.

The air can be trapped in the piping between the liquid fuel storage tanks, or in the liquid fuel filter(s) in the system. Very often the liquid fuel supply piping to the Accessory Base inlet flange does not have the proper pitch or air vent valves in the piping to remove air.

You should start the liquid fuel forwarding pumps and open the stop valve (20FD-1) at the forwarding skid to pressurize the liquid fuel supply piping. Then you should attempt to vent all air from any liquid fuel canister(s) and ensure that the transfer fill valves are in the correct position(s). If the unit is not running on gas fuel when you do this, you can force open 20FL-1 to pressurize the high-pressure liquid fuel filter canister and vent any air from it. (The liquid fuel forwarding pump supply pressure should stabilize once most of the air is removed, and it should be about 4-5 barg, which is below the cracking pressure of the liquid fuel check valves so no fuel will flow into the combustors.) The liquid fuel supply pressure (if controlled by a pressure regulator) should be stable and at the pressure specified in the Device Summary for the machine. If the pressure is NOT stable during low-load or no load operation (or during purging when not running) then the cause needs to be identified and resolved. Sometimes, the strainers upstream of the liquid fuel forwarding pump(s) can get plugged and cause flow-rate restrictions as flow is increased during STARTing or liquid fuel transfers. So, don't overlook the fuel strainers as a possible cause of an inability to get required flow-rate. (Bacteria does grow in liquid fuel storage tanks, and liquid fuel piping, also, when the system is inactive for long periods of time.)

If the liquid fuel supply piping runs in any overhead pipe racks between the outlet of the liquid fuel forwarding skid and the inlet flange to the Accessory Base check to see if there any vent lines in the high points of the piping, and if there are, vent any air out of the lines. This may entail some liquid fuel coming out of the vents to ensure the air has been removed, so use buckets and care as necessary.

START the machine on gas fuel, and then when at FSNL initiate a transfer to liquid fuel. This usually helps to get enough flow in the liquid fuel system to dislodge any air. If there is air there is still a risk of tripping--but it will usually only happen once. You should be using the VIEW2.EXE utility on the HMI to monitor the liquid fuel flow divider feedback during the fuel transfer (and during any subsequent START attempt--it can provide useful information). You should be monitoring FSR1, TNH, TNHAR, TNHA, TTRX, TTXSPL1, TTXSPL2, TTXSPL3 and TTXM in addition to the feedback from the liquid fuel flow divider (three speed pick-ups)--at a minimum. You should save the data to a file (it will be in ASCII text form) and you can attach it to a subsequent post for help in analyzing it.

But again--when a dual fuel machine is not run regularly (the OEM recommends once per week!) on liquid fuel, by transferring to liquid fuel and then back to gas fuel after a few minutes, air WILL make it's way into the liquid fuel supply piping and components.

It sounds counter-intuitive to START the machine on gas fuel when you are having problems with STARTing on liquid fuel, but it's usually very helpful--especially if you're collecting data with VIEW2 at a high-speed rate (32 Hz). BUT, you should still do everything you can to remove any air from the piping before attempting this. And, again, there is no guarantee it won't trip--but it's probably the best way to get liquid fuel flow-rate up quickly to try to move any air along and get it out of the piping.

Write back to let us know how you fare--and share any data you collect.

as the LP and HP filters checked there is no air in line and all the feed backs are true but it seems the control dosnt send a proper signal to servo valve and the behavior of by pass valve isn't normal and send excess fuel (in acceleration FSR control loop). for example when the turbine fired the rate of fuel (mass flow) is 2 times the normal state

 

The typical GE-design Frame 6B heavy duty gas turbine does not have position feedback from the liquid fuel control valve. The feedback to the liquid fuel control regulator is from the liquid fuel flow divider. The liquid fuel control valve is moved to whatever position is required (128 times per second!) to make the flow divider feedback equal to the flow-rate reference.

It’s not unusual for the exhaust temperature to get very close to or even reach the maximum allowable exhaust temperature during acceleration. This causes the fuel flow to be limited so as not to exceed the maximum allowable exhaust temperature. If the acceleration rate slows when the fuel flow is limited and the exhaust temperature drops below the limit the Mark* V will increase the fuel—sometimes very quickly.

Without the requested data it’s virtually impossible to help you any further. To the list of requested signals please add FSRT, FSRACC FSRWU, FQR and FQROUT.

You have said FSR is oscillating between 14% and 20%. But we don’t know how quickly it is oscillating or why it is oscillating. You didn’t mention if the liquid fuel supply pressure to the Accessory Base is stable or oscillating.

But without data there’s not much we can do. Have you tried replacing the servo valve? Or replacing the liquid fuel bypass valve? It’s possible the valve actuator is worn and needs replacement.

While it’s not likely since you say FSNL operation on liquid fuel is fine, but if the liquid fuel pump clutch is slipping that could cause problems.

I have nothing further to offer. You haven’t mentioned what Diagnostic Alarms are active or annunciated when this problem is occurring which would likely be VERY HELPFUL to know if the problem were the Mark* V or one of its cards. The Mark* V is a relatively robust turbine control system and the fact that the unit lights off on liquid fuel and is stable at FSNL on liquid fuel pretty much says the problem isn’t the Mark* V or one of its cards. It’s more likely it’s an input to the Mark* V that’s intermittent or most likely it’s something in the liquid fuel system or maybe the hydraulic system that’s causing this problem. (Have you checked the hydraulic accumulator recently? AND, what is the hydraulic system pressure doing when this oscillation in liquid fuel flow is occurring?) The speed pickups used on the liquid fuel flow divider are usually the same as the shaft speed pickups, and if there were differences in speed input signals from the liquid fuel flow divider that would most likely show up as Diagnostic Alarms.

You want more help? Give us data and answer our questions. Or, call someone knowledgeable to site who can see what you’re seeing and get data from the Mark* V and help resolve your problem. We’d like to help, but we need more information/data.

 

There have been posts (a long time ago--but they are ALL searchable on Control.com!!!) about using VIEW2 to gather data. It's a command line executable so it's not really user-friendly, but it IS the way to capture high-speed data using a Mark* V turbine control system. [The machine CANNOT BE TRIPPED using VIEW2, or any of the VIEW software "tools"!!! It's simply a way of capturing data--it either works or not, and if it doesn't work it's because the command wasn't properly configured (the options and specifications of the command as it is typed in weren't correct). If one is trying to troubleshoot controls-related problems on a Mark* V turbine control panel one had best learn and be comfortable with using the VIEW "tools"--and understanding that using them CANNOT TRIP THE TURBINE!!!]

It would also help to know what operator interface is being used to communicate with the Mark* V turbine control panel--an <I> or an HMI. VIEW "tools" have to be run from the command prompt ("DOS prompt") of both, but on an <I> running VIEW "tools" means the <I> being used to collect data can't be used to see the normal operator displays or the Alarm Display. A GE Mark V HMI uses MS-Windows so a command prompt can be opened and run in a separate window and the operator can still see or switch to the normal operator displays (including the Alarm Display).

 

Any progress ...a quick update is welcome here