Dear all GE Gas Turbine Gurus,

What is the purpose of barometric pressure transmitter in Gas Turbine?
To be specific, the gas turbine is:
GE Frame 6 couple with GEC Alsthom Generator
Mark V
Diesel starter

What will be the effect if the transmitter drift or not properly calibrated?

Thank you

 

You will have to look at the CSP of your machine to see what purpose it serves in the monitoring and/or control and/or protection of the unit at your site.

Many newer GE-design heavy duty gas turbines use atmospheric pressure transmitters for extremely accurate calculation of axial compressor discharge pressure. Newer Speedtronic control schemes calculate an axial compressor discharge pressure ratio that is used for exhaust temperature control purposes, so the accuracy of the calibration and output of the transmitter(s) is very critical to optimizing output and hot gas path parts life.

In general, redundant atmospheric pressure transmitters are used for the above purpose, because it is so critical to the turbine.

Some turbines were equipped with a 'performance monitoring system' which attempts to calculate axial compressor air flow, and even exhaust flows, and atmospheric pressure transmitter(s) were used for that application, also.

But, the answer to the question of what an atmospheric pressure (barometric) pressure transmitter does at <b>your</b> site does lies in the CSP running in the Mark V at your site. Without being able to examine that CSP, it's virtually impossible for anyone to say exactly how that transmitter (or transmitters) is(are) being used. It's entirely possible that it's just for display purposes, for monitoring the atmospheric pressure, and not used for any control or protection purposes.

A lot of the atmospheric pressure transmitters used on GE-design heavy duty gas turbines were not properly installed and are not properly maintained. To be precise, the transmitter sensing line must be open to atmospheric pressure. Sometimes the turbines were installed inside buildings which were "pressurized" by ventilation fans (very large ones). Sometimes the air flows from these fans impinged on the sensing lines adversely affecting the reading. Other times, the sensing lines were not unblocked by removing tubing caps and covers used during shipping. Other times, the materials used to prevent ingress of insects and dirt were not installed properly or were not installed at all, and sometimes they actually served to block proper sensing.

So, proper installation and maintenance (cleaning of sensing line covers, etc.) is very, very critical to proper operation and sensing.

 

Barometric pressure is used in the airflow calculation. Airflow is used in (optional) performance monitoring software. If you have the performance monitoring software, then if the sensor drifts or goes out of calibration you can get erroneous results from the performance monitoring software.

If there are multiple barometric pressure sensors, the airflow calculation may be used in DLN control.

Another possible use for airflow is in a CEMS, although most air quality authorities require stack flow measurements instead of the turbine control system measurements.