Hey Folks,

Just curious if anyone has experienced problems arising from moisture in the CPD pressure transmitter sensing lines.

We recently experienced a trip when two of the three CPD sensors stopped tracking and slowly trended upwards until we reached the trip point. The unit is a frame 7AE. The consensus after the fact was that 2 of the 3 lines froze off (ambient temps were low in the building that day).

After restarting the unit we gently blew down the sensing lines while the unit was in operation and found a bit of water in the dead legs.

Do any of you blow down these transmitters regularly? And is there an issue taking them out of service one at a time while on the run? My understanding is that the MarkVIe selects the median CPD reading as the control variable, so isolating one temporarily shouldn't cause an issue, but we weren't brave enough to try.

Thanks!

 

How old is/are the unit(s)?

Conventional combustors or DLN-I/I+?

Where are the CPD transmitters located?

 

Hi,
The unit is roughly 20 years old with DLN combustors.

The CPD lines run outside the enclosure and the transmitters are located near the exhaust frame blowers

 

That is an old design. Newer units (much to the chagrin of owners/operators) have the CPD transmitters mounted on the turbine compartment roof (which is a PITA when the turbine compartment has to be removed for maintenance). Mounting them on the roof, or above the compressor discharge casing, allows for drainage of any condensation back into the unit.

It should be standard operating procedure to blow down these lines, especially in cold weather. But, if they run outside of the turbine compartment over to the JB where they are mounted, it might be a good idea to heat-trace the tubing lines if blowing down isn't an option.

It would be necessary to see the application code to know for sure if CPD is median-selected. But it's not just the CPD, there is also (usually) some sensor checking on the CPD transmitters since they are so critical for DLN which might also trip the turbine. You say you have a Mark* VIe; is it a Mark* V-to-Mark* VIe Life Extension, or a full Mark* V replacement? If it's the latter, I've seen some VERY questionable app code (which came from South Asia). It's really a crap-shoot what some sites are getting these days with Mark* turbine control upgrades.