Instrumentation

Hello again from T2E3.  It's hard to believe it's November already.  I hope your year has been a successful one to date.  The theme for my work this year seems to be Instrumentation.  I've heard from many gas turbine plants this year where performance deficiencies were identified, and finding the root cause led us back to problems with instrumentation.

Instrumentation is not just used to define safe control of your equipment, it's also used to define the limits for efficient, reliable operation.  When instrumentation is not reading correctly, your equipment could be limited to a false condition.  For example, if exhaust gas temperature indications are reading higher than actual, your gas turbine will operate at some point below base load and you will be under-firing your gas turbine.  Not only does this limit your power output, it also could lead to higher heat losses and higher heat rates at what should be base load (but isn't, due to instrumentation errors).

The GE LM6000 has some unique instrumentation issues.  Being an aeroderivative gas turbine, some parts were designed by aerospace engineers, who like to operate in absolute units (such as PSIA), while much of the unit package was designed by more traditional land-based-power engineers who utilize relative units (i.e. PSIG).  Knowing which units the control system is expecting is critical to proper sensor calibration, and the resulting unit operation.
 
If, for example, the compressor discharge pressure (PS3) is calibrated to report pressure in units of PSIG, when the control system expects a value in PSIA, the control system will get erroneous information and assume there is insufficient pressure for turbine blade cooling and (for LM6000 SPRINT units) SPRINT water atomization.  This will cause a significant drop in available gas turbine output.

These are just a few examples out of the many instrumentation issues available around a power plant.  One method being used to track instrumentation issues is with Advanced Pattern Recognition systems (APR).  These systems track the "normal" statistical relationships between plant data at various operating conditions.  When a piece of data starts to act 'abnormal', the system will flag the user to the abnormal data for investigation.  Many of these investigations result in finding faulty instrumentation providing readings which have either failed or drifted.  

Keeping your instrumentation in top shape and reading correctly will not just make the accountants (and engineers) happy to have accurate data, it will also reduce the number of outages and derates of your equipment due to bad information being used in the controls.  Good, accurate instrumentation leads to more safe, reliable, efficient and profitable operation.  

As we enter outage season, I encourage you all to review the instrumentation on your "to be calibrated" lists, and verify that all the instrumentation that may effect your operation in any small way is on that list.

Best regards,
-Tina
 

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