i am an instruments technician and there is something i cannot handle

am facing a trip in a GE frame 7 B .. when the unit is in start up it reaches Fire and at 30% speed the unit trips without indication

can you help me with this problem?

 

You really haven't given us very much to go on. What fuel are you trying to start on: gas or liquid?

Are you having trouble establishing flame or is it taking a long time?

Is the flame flickering during firing?

Are the exhaust temperature spreads really high during firing?

If you're trying to fire on liquid fuel, is the fuel supply pressure to the turbine fluctuating or stable?

If you're trying to fire on gas fuel is the gas fuel supply pressure stable or fluctuating?

Is the fuel control valve stable or fluctuating?

What kind of control system? Speedtronic Mark II, -Mark IV, -Mark V, -Mark VI? TMR or SIMPLEX? PLC-based?

You really haven't given us anything to go on, come to think of it.

The only time I've seen this problem on a Speedtronic turbine control-equipped unit is when the Trip Oil Pressure switches are not valved in properly. There's a stoopid bit of logic that will allow the turbine to fire if there is low Trip Oil pressure without an alarm that the Trip Oil pressure is low (!!!), but will then trip the turbine (usually with a 'Loss of Flame Trip' Process Alarm) approximately one minute after the firing timer starts (or the expiration of the firing time) if the Trip Oil pressure is still low.

The valves which control the Trip Oil pressure flow to the Trip Oil Pressure switches were found in the wrong positions. I can't recall if they were draining the oil pressure or blocking the oil pressure to the switch, but the Mark IV (it was at the time) didn't even annunciate a low trip oil pressure, and it did allow the turbine to fire and as soon as the firing timer expired it would trip the turbine with no other alarm than 'Loss of Flame Trip'.

This same bit of stoopid code has been in almost every GE-design heavy duty gas turbine control system I've ever seen.

That's the only thing I can think of based on the information provided.

 

Need more information:

1. What type of control is on this (MK II, MK IV, etc.)? [This is a pretty old machine if it is a 7001B.]

2. What has changed between the last successful startup and now?

3. Has the unit been on turning gear between starts?
4. What are FSR (or VCE if Mark II), exhaust temperature and spreads, vibration levels between firing and trip?

5. What is configuration of machine - simple cycle or combined cycle; type of fuel, type of combustion system?

 

CSA;

I just read your post, and was curious about your statment about the turbine tripping on start up and the only alarm being loss of flame trip.

Today we had this happen twice, where the turbine ran up to 2700RPM and then tripped. We noticed all of the flame intensity detectors dropped out and then a loss of flame trip. We tried it a third time and the unit did start. We have a MKV and are running on gas.

I was hoping you could explain this trip you had mentioned before in a bit of detail, and why it would cause a loss of flame trip and possibly what to check, as I assume we may have this problem again.

Nothing has been touched on the pressure switches and it has been started everyday all week with no issue until today.

Thanks

 

sorry for not giving much information

first of all it's a Gas Turbine 7001B..

and the problem is that we get the flame in both detectors without fluctuating but it takes less than a minute and trip without any indication..

and the temp. isn't high because it's tripping in 30 percent only and i checked and everything good with the fuel system .. and i believe it's a problem with speedtronic

also i think it would be from the SLEH cards but cannot make sure

and our speedtronic is Mark II

 

Well, this is more information, but you didn't indicate if you'd even checked the trip oil pressure switch valve(s) or which fuel the unit is being started on.

High exhaust temperature spreads can exist even if the average exhaust temperature is not high.

You also haven't indicated if there is(are) any alarms when unit trips, and if there is(are) what they are.

If you believe the problem is in the Speedtronic, then you're going to have to find it. You're going to have to try to find a way to see if the fuel stop valve is closing before a signal to close it is being sent from the Speedtronic. Or, you're going to have find out why the current to the fuel control valve is shutting off the fuel flow.

Could it be that the unit is accelerating too quickly and the fuel is being driven too low and causing the flame to be extinguished? Or that the speed feedback is intermittent and causing something similar?

You haven't said what VCE is doing at the time the flame is lost.

I have seen flame detector modules fail intermittently like this shortly after flame is detected.

If you believe it's the SLEH, you can replace the card.

Best of luck. Please write back and let us know what you find.

 

Look at the sequencing and find L63HGL and L63HGLX and follow them through to L4POSTX. If there is a L2F or L2TVX permissive in the L4POSTX rung that has the L63HGL or L63HGLX, then if the trip oil signal is picked up when L2F picks up or L2TVX drops out then it's possible that at the end of the firing timer (L2F) L4 will be dropped out as soon as the L2F times out.

But, you should also look at the alarm sequencing to see if there would be any alarms if any of the Trip Oil pressure switch signals indicate low pressure before the firing timer expires.

But, if this is happening after the firing timer expires, then this wouldn't be the problem. If the Trip Oil signal goes low, there should be a sensor trouble alarm or a "Hydraulic Protective Trouble" (L86HD) alarm prior to the trip.

You could trend the trip oil pressure switch inputs during subsequent starts.

Since you didn't say what frame size machine is at your site, we can't know when the trip is occurring in the starting sequence (as a percentage of the rated speed).

 

OK, you have Mark II Speedtronic. Do you have the ITS exhaust temperature control? If not, do you have a combustion monitor?
It would seem that the trip is occurring right after the 2W warmup timer times out (based on the 30% speed at trip), although it might be after the 2F firing timer times out. The control blocks loss of flame trip while 2F is timing, but once it times out, you must have flame established or it will trip.

What type of flame detectors do you have? You say the flame is not fluctuating - how do you know? The flame detectors that were used on Mark II did not provide any intensity signal on the panel. There are indicating lights driven from the 28FD-1 and 28FD-2 relays, and if they are solid on the intensity is probably OK. What is VCE doing? Typical firing VCE is around 10. After flame is established, VCE should drop to the warmup setting, typically around 7 to 8. It then would begin ramping up after the 2W timer times out. You might also check to see that the minimum VCE setting is per the control specification.

Tough to believe you trip and there are no annunciator alarms, but stranger things have happened.

 

hi people thanx for giving such information..

i just started the unit and it's full speed

i found that 63FL-3 isn't on in the isolation card and found the card is damaged then i changed a SLEH card and it worked

thanx again

 

Thank you for the feedback. It helps others to know how you solved your problem.