We have speedtronic control for frame-1 GT control. Recently Gas Turbine was stopped for overhauling and after maintenance activities unit was started. however it is continuously tripping during startup at 82% HP speed as soon as 14HS signal appears. At the Same time PCD FAILURE ALARM also appears.
We have checked compressor discharge pressure transmitter PCD which is OK, speed picks, thermocouples and their groundings which are appropriate.
Please find below relevant parameters at the stage where unit trip.
Exhaust average temp = about 390 deg C
PCD = 4.5 bar
HP SPEED = 82%
LP SPEED = 71%
We have attempted to replace calibrated SSKC startup card, STKK cards and tried for startup various times, however results are same.
Please suggest failure cause and its rectification.
Please feel free in case of any query.
What was overhauled? What, if anything, was done to the control system during the overhaul? Is 82% HP SPEED the correct setting for 14HS? Can you provide the logic for the PCD FAILURE ALARM? Are there any other alarms appearing - both before and after the event? I am inclined to believe the problem is NOT with the control.
Note: It's been a really long time since I looked at a Frame 1 - early 1977, I think. The control originally supplied with the Frame 1 GT's was sort of a half breed. It used the Mark II analog control module, but retained the Mark I relay sequencing.
Yes, Nuovo Pignone called MK 1.5 just to confuse everyone. From memory, 14HS is around there, it is a twin shaft.
I don't have any MKII drawings at the moment. What is in the "PCD Failure" alarm rung. It looks like the system sees a PCD Failure when it hits 14HS, I know you have checked the transmitter but maybe you just have a rung problem in the alarm.
Thanks for ur response.
One important thing I want to share. We have replaced sensing point of PCD transmitter from its original tapping to another point of compressor discharge. same casing because original sensing point was badly choked. As per mechanical team the replaced point are same. Please advise if is ok?
Secondly, we have recorded PCD pressure from field gauge and control room indicator which is showing 4.5 bar till 14HS signal. Please advise how we can catch the problem.
No problem in changing the PCD tapping point. Yes, you are getting PCD pressure but you still haven't told us what the logic is for the Alarm?
Dear Control Gurus,
Further to above problem in Speedtronic Mark-II system.
We have checked the control system in detail and also carried out the "Dry run test" its a simulation with GE provided calibrator. Everything worked fine and complete sequence was achieved. However, in actual startup problem remains the same, and unit tripped as soon as 14HS signal was achieved. Detailed investigation carried out and following was observed.
1. When HP speed raised to 14HS (82% NHP) main protective signal "4" becomes "0" and unit tripped.
2. Verified the tripping logic by connecting the recorders at test points of VMPA cards. NO protection signal was generated.
3. In dry run test everything worked fine however, problem appeared in actual unit running condition.
4. there is SLEH card where two major inputs 14HS and 4 signal "AND" and latched. Before the 14HS signal 4 signal =1 , 14HS=0
5. As per requirement as soon as 14 HS achieved 14HS= 1 , 4 signal =1 and both latched to provide 14HSX = 1.
6. However, in our case as soon as 14HS=1 the 4 signal = 0 and unable to latch the 14HSX signal as well.
7. Please note that at 14HS signal bleed valve solenoid also operate at field.
In last startup we concluded that main master protective signal '4" becomes "0" as soon as 14Hs signal appeared. we have already replaced corresponding logic cards. The system tripped without any alarm . The PCD alarm discussed above appear after tripping as its value decrease below minimum set point. Hence, we are sure problem in not due to PCD.
We are unable to identify the signal which cause tripping of unit as no alarm is available at annanciator.
Further, please advice if we can bypass master protective signal "4" by providing external power source .
I would advise you to look into any external trip inputs to the Mark II panel. I don't know what the load equipment is, maybe a compressor? Typically there is at least one hardwired input from the load or other equipment external to the gas turbine that will trip the gas turbine. Sometimes these trips are enabled only after the gas turbine reaches a certain point in the startup sequence like 14HS or 14HSX. The fact that you were able to simulate a successful startup using the calibrator leads me to suspect the source of the problem is outside of the Mark II panel. I would also look at any outputs from the turbine control that are used in external logic that operates the external trip input to the turbine control.
Maybe there was work on the load equipment during your maintenance outage. I have personally witnessed and solved this type of issue before.