On the morning of July 25th we encountered an unfamiliar alarm in our Mark V system for our GE7EA. The diagnostic alarm indicated a xmit failure. The following is what was populated in our alarms window:
<pre>Process Alarms Window:

Alarm Id Core State Message
P0 Q Alarm Diagnostic Alarm <C><Q>

Diagnostic Alarm window:

Alarm Id Core State Message
D1068 C Alarm TCCA Status S page xmit faliure</pre>
Has anyone else seen this alarm and can give some some input on how to correct this issue? We would really appreciate some feedback if anybody has some advice.

Thanks!

 

The 'TCCA Status S page xmit failure' alarm refers to the communications link between the Mark V and the EX2000, which uses Status S over the ARCnet link between the Mark V and the EX2000.

The typical causes of this alarm are failed or failing coaxial and/or fiber optic cabling between nodes on the ARCnet. (Some sites use fiber optic devices to extend the distance between nodes. Refer to the Mark V Maintenance and -Application Manuals for more details on StageLink communications.) Many coaxial cable BNC connectors were very poorly installed and can become problematic over time.

Another cause is corrosion of BNC connections caused by heat and humidity and contaminants in the atmosphere. It's always advisable to periodically (usually during maintenance outages when the turbine is not running) disconnect and reconnect the BNC connections to the nodes (all of them--not just the Mark V and the EX2000--but also the back of the operator interface(s)) to try to prevent corrosion.

Another cause is sometimes the 93-ohm termination resistors do fail (usually because of heat, and/or corrosion). They can be removed (when the turbine is not running) and checked with an ohmmeter. Also, sometimes the wrong resistors were used (there are coaxial Ethernet termination resistors which look exactly like coaxial ARCnet termination resistors), and some have worked just fine for years, and then suddenly they started causing intermittent problems.

But, the usual causes for this alarm are communication cabling issues. Sometimes, the EX2000 communication port fails, but this is not common, and is usually accompanied by other alarms (Diagnostic and -EX2000 alarms).

There was also a TIL (Technical Information Letter) many years ago that dealt with PROM upgrades that also helped with alleviating these alarms (but sites which needed this PROM upgrade usually had a LOT of these alarms, along with some other power supply-related Diagnostic Alarms).

Hope this helps!

 

Well replied by CSA

take care
g.rajesh

 

We really appreciate your help, we will be investigating your suggestions.

Thank you

 

mbaviche,

Another thing I'd like to mention is that if this is the first time you've encountered this particular Diagnostic Alarm you are pretty lucky--because some Mark Vs encounter this problem fairly frequently.

Second, if this is the first time it could just be an anomaly (I'm presuming the alarm was annunciated for a brief period of time, and then it cleared--which isn't clear from your posts). If the Mark V uses a GE Mark V HMI--the one which runs MS-Windows and some version of CIMPLICITY--they can occasionally cause quite a "storm" on the StageLink which can lead to some nuisance errors and Diagnostic Alarms, such as the one you are inquiring about. GE Mark V HMIs (as opposed to the previous Mark V <I> operator interfaces) ask the Mark V for every point in the CIMPLICITY database at least once per second and if there are multiple GE Mark V HMIs this can lead to a LOT of network traffic and sometimes network errors.

Also, if users have one or more Logic Forcing Displays and/or Prevote Data Displays open on the HMI for long periods of time they can contribute to the network traffic and nuisance Diagnostic Alarms. Even leaving the Control Constant Adjust display open for long periods of time on a GE Mark V HMI can lead to nuisance network issues and Diagnostic Alarms.

So, if your site is using GE Mark V HMIs try to keep the number of open displays (CIMPLICITY and TCI) to a minimum, and especially don't leave Logic Forcing Displays and/or Prevote Data Displays open for long periods of time.

Please write back to let us know how you fare in resolving this issue. Also, please let us know if the Diagnostic Alarm cleared shortly after being annunciated, or if it persisted for several hours or longer.