Two frame V gas turbines, one having Mark V while other having Mark VIe control system, are installed at our site. Both turbines were installed with Mark Mark V, but one of the Mark V was upgraded to Mark Vie in 2019. Mark V was initially configured with I but in 2008 I was upgraded to HMI (computer based and with cimplicity). Each gas turbine has its own HMIs, one in the GT compartment and the other HMI in the control room. The fuel used for the gas turbines is Natural Gas.
We are facing and issue with the turbine with Mark V. We faced the same problem four years ago and was shared in this forum as well. The link to that problem is given below
https://control.com/forums/threads/markv-l14hr-and-racheting-issue.47166/
I am mentioning the problem and the steps we have taken so far in this post.
We are using three magnetic pickups. Same pickups are used for R, S, T and P core. The speed pickups cables come to the R, S and T core from area, and are jumpered to P core from RST. Hard-wire jumpers are not installed at P cores’ PTBA-3 to -4, and -7 to -8, and -11 and -12 i.e. only -1 to 2, -5 to -6 and -9 to -10 are connected with three magnetic pickups.
Turbine was shutdown and was not under any maintenance. It was showing ready to start status. Turbine cooldown sequence was off. Turbine was at rest speed and L14HR was 1.
From last couple of days, L14HR is toggling its value after some random hours i.e. it changes to 0 for few seconds and then again came back to 1. It should be noted that the turbine was at rest speed. Due to the transition of L14HR, “PROTECTIVE MODULE ACCELERATION TRIP- HP” alarm appears and the ratcheting starts for 24 hours. However, as L14HR is toggling randomly and before 24 hours the timer (T62CD) for L62CD gets reset, therefore, we are unable to stop the ratcheting unless we force L62CD.
Following steps are taken to troubleshoot the problem
What else can be checked? I am unable to share the alarms as USB was not allowed at the site this time.
We are facing and issue with the turbine with Mark V. We faced the same problem four years ago and was shared in this forum as well. The link to that problem is given below
https://control.com/forums/threads/markv-l14hr-and-racheting-issue.47166/
I am mentioning the problem and the steps we have taken so far in this post.
We are using three magnetic pickups. Same pickups are used for R, S, T and P core. The speed pickups cables come to the R, S and T core from area, and are jumpered to P core from RST. Hard-wire jumpers are not installed at P cores’ PTBA-3 to -4, and -7 to -8, and -11 and -12 i.e. only -1 to 2, -5 to -6 and -9 to -10 are connected with three magnetic pickups.
Turbine was shutdown and was not under any maintenance. It was showing ready to start status. Turbine cooldown sequence was off. Turbine was at rest speed and L14HR was 1.
From last couple of days, L14HR is toggling its value after some random hours i.e. it changes to 0 for few seconds and then again came back to 1. It should be noted that the turbine was at rest speed. Due to the transition of L14HR, “PROTECTIVE MODULE ACCELERATION TRIP- HP” alarm appears and the ratcheting starts for 24 hours. However, as L14HR is toggling randomly and before 24 hours the timer (T62CD) for L62CD gets reset, therefore, we are unable to stop the ratcheting unless we force L62CD.
Following steps are taken to troubleshoot the problem
- Upon going through the alarms, events and SOEs history, we came to know that diagnostic alarm “Voter mismatch, R L12H_ACC” appears sometimes and “Voter mismatch, S L12H_ACC” appears other times, at regular but random intervals.
- Resistance of all the speed pickups was checked and was found 210, 209 and 197 ohms. Grounding of these wires was checked and they were not showing any resistance with ground. No AC or DC voltages were found on the speed pickups wires.
- On HMI, pre-vote value of speed for R, S and T was zero, however, when we checked the speed values on diagnostic counters screen for TCE1, we found that TCE1 for R was showing 60 Hz and 1.18% speed. The TCE1 or S and T were showing 0 Hz and 0% speed. Does pre-vote screen shows values of TNH (voted and pre-voted) and TCE1 on diagnostic counter shows TNH_OS?
- We connected the wires on all the cores and the readings on pre-vote screen and TCE1 screens were 0. When the “Voter mismatch, R L12H_ACC” alarm appears the value on both screen changes for few moments (up to 50%) and then returns to 0.
- Again the wires of all three pickups from PTBA card were removed, but pickups were still connected with the RST. As soon as the wires were removed diagnostic counters TCE1 screen for R started to show 60 Hz and 1.18% TNH, whereas, pre-vote screen was showing 0%. The voltage and Hz were checked on the terminals of PTBA. PTBA -1 to -2 was showing 60Hz and 75mVac. PTBA -3 to -4, -5 to -6 and -7 to -8 were showing 60 Hz and 8 mVac, but it should be noted that diagnostic counter TCE1 screen for S was showng 0 Hz and 0% TNH. PTBA -9 to -10 and -11 to -12 were showing 0 Hz and 0 mVac and its respective TCE1 was showing 0 as well.
- Ribbon cable JU connects speed signals from PTBA card to TCEB card. The ribbon cables JKX, JKY and JKZ connects the speed signals from TCEB to TCE1 of X, Y and Z respectively. We removed the ribbon cable JKX and the value on the diagnostic counters for TCE1 of R core changed to 0 Hz and 0% TNH.
- The JKX was connected back and the TCE1 again started to show the above mentioned values. This time the ribbon JU was removed from the PTBA card. The values changed to 0 on diagnostic counters. 60 Hz and mVac were still present on the terminals of PTBA in this condition.
- All the ribbon cables from PTBA were removed from one by one, but the mVac and Hz were still present on the PTBA terminals. RST and XYZ were powered down from power distribution core. The voltages and Hz could still be measured on the PTBA terminals. There were only BUS PT voltages coming on the PTBA this time.
What else can be checked? I am unable to share the alarms as USB was not allowed at the site this time.