Mark V TMR system is installed on our site for Frame V gas turbines. Mark V was initially configured with <I> but in 2008 <I> was upgraded to HMI (computer based and with cimplicity). Two gas turbines are installed at our site and each gas turbine has its own HMI in the GT compartment and we have one HMI in the control room for both the gas turbines for displaying data. The fuel used for the gas turbine is Natural Gas.
We are using three magnetic pickups. Same pickups are used for <R>, <S>, <T> and <P> core. 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.
On 23-June-2018 at 3:40:34 L14HR became 0 for few seconds and then again came back to 1. It should be noted that the turbine was at rest speed. No alarm was shown on HMI and ONLY ratcheting started. Due to the transition of L14HR the timer (T62CD) for L62CD was reset and again started from zero. We were unable to stop the ratcheting as L62CD was not set.
We started to monitor T62CD so that as soon as timer is completed and L62CD is set we can stop the ratcheting (L62CD sets when when timer T62CD reaches to 24 hours). On 23-June-2018 at 8:25:11 the timer was reset to zero again due to L14HR toggling from 1 to 0 and back to 1 again. Turbine was at rest and no alarm appeared on HMI.
At 8:32 we got the following alarms<pre>
23-JUN-2018 08:42:37.875 T1 1 Q 0287 ALM PROTECTIVE MODULE ACCELERATION TRIP- HP
23-JUN-2018 08:42:37.937 T1 1 L4T EVT Master Protective\Turbine Trip
23-JUN-2018 08:42:40.000 T1 1 C 2906 DIA Voter mismatch, <T> L12H_ACC
23-JUN-2018 08:42:43.000 T1 0 C 1850 DIA Voter mismatch, <R> L12H_ACC</pre>
These alarms cleared after master reset but T62CD was not restarted due to these alarms.
We started to monitor TNH1 on pre-vote data screen. TNH1 for <S>, <T> and voted remained at zero percent. TNH1 for <R> core was changing from 0 to 10%. As soon as the TNH1 for <R> increases beyond 5% we get the following alarm
DIA Voter mismatch, <R> L12H_ACC
However this does not result in toggling of L14HR and does not rest T62CD.
Due to varying value of TNH1 for <R> we checked the magnetic pickup connections of all the three cores. They were found Ok.
When we remove speed pickup from <R> and <S> core QTBA prevote value varies between 0.12% to 0.6%. When we remove speed pickup from <T> core QTBA its value on prevote data reads upto 63% that results in number of alarms. Is this the normal behavior?
L14HR is still toggling between 1 and 0 after every few hours and we are not able to stop the ratcheting. When L14HR toggles and timer is reset we are not getting any alarm on HMI. What can be the possible cause of this problem and how can we rectify it?
NOTE: We do not intend to force L62CD.
We are using three magnetic pickups. Same pickups are used for <R>, <S>, <T> and <P> core. 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.
On 23-June-2018 at 3:40:34 L14HR became 0 for few seconds and then again came back to 1. It should be noted that the turbine was at rest speed. No alarm was shown on HMI and ONLY ratcheting started. Due to the transition of L14HR the timer (T62CD) for L62CD was reset and again started from zero. We were unable to stop the ratcheting as L62CD was not set.
We started to monitor T62CD so that as soon as timer is completed and L62CD is set we can stop the ratcheting (L62CD sets when when timer T62CD reaches to 24 hours). On 23-June-2018 at 8:25:11 the timer was reset to zero again due to L14HR toggling from 1 to 0 and back to 1 again. Turbine was at rest and no alarm appeared on HMI.
At 8:32 we got the following alarms<pre>
23-JUN-2018 08:42:37.875 T1 1 Q 0287 ALM PROTECTIVE MODULE ACCELERATION TRIP- HP
23-JUN-2018 08:42:37.937 T1 1 L4T EVT Master Protective\Turbine Trip
23-JUN-2018 08:42:40.000 T1 1 C 2906 DIA Voter mismatch, <T> L12H_ACC
23-JUN-2018 08:42:43.000 T1 0 C 1850 DIA Voter mismatch, <R> L12H_ACC</pre>
These alarms cleared after master reset but T62CD was not restarted due to these alarms.
We started to monitor TNH1 on pre-vote data screen. TNH1 for <S>, <T> and voted remained at zero percent. TNH1 for <R> core was changing from 0 to 10%. As soon as the TNH1 for <R> increases beyond 5% we get the following alarm
DIA Voter mismatch, <R> L12H_ACC
However this does not result in toggling of L14HR and does not rest T62CD.
Due to varying value of TNH1 for <R> we checked the magnetic pickup connections of all the three cores. They were found Ok.
When we remove speed pickup from <R> and <S> core QTBA prevote value varies between 0.12% to 0.6%. When we remove speed pickup from <T> core QTBA its value on prevote data reads upto 63% that results in number of alarms. Is this the normal behavior?
L14HR is still toggling between 1 and 0 after every few hours and we are not able to stop the ratcheting. When L14HR toggles and timer is reset we are not getting any alarm on HMI. What can be the possible cause of this problem and how can we rectify it?
NOTE: We do not intend to force L62CD.