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Detectable Problems 203
Running
Running problems associated with fuel controls consist of the
inability to accelerate (or increase load), or accelerate too rapidly.
There are also numerous running problems (such as miscellaneous
trips, aborts, etc.) that are specific to the type of control method
employed. Pneumatic and hydraulic controls are very susceptible to
leaks and contamination. In addition pneumatic controls are sensitive
to moisture in the lines, that can result in erratic operation. This often
leads to erratic or otherwise unstable operation. Mechanical and
electric controls are subject to wear and leaks in bellows and capillary
sensors. In addition, accuracy deteriorates over a period of time.
Computer or electronic controls are generally the most problem free,
once the unit has been commissioned and all the programming logic
fully and completely implemented.
Acceleration problems, either a lack or too much of, usually
result from governor malfunctions (although the malfunctions may
not be specifically with the governor mechanism). These malfunctions
may result from faulty governor input signals such as speed,
compressor discharge pressure, temperature, or fuel flow. Overspeed
could be the result of a governor malfunction, electrical upsets (generator
drives), or coupling failure. Overspeed is detrimental not only
to the gas turbine but also to the driven load. Redundant systems
(usually two electrical and one mechanical) are installed to protect
against overspeed. The electrical systems should be checked periodically
(simulation test) and the mechanical fly-bolt should be cleaned.
It is not possible to check the operation of the mechanical fly-bolt
mechanism in the field.
References
1. “Gas Turbine Parameter Interrelationships,” Louis A. Urban, 1969.
2. American Society of Mechanical Engineers Power Test Code 22, 1974.
3. Sawyer’s Turbomachinery Maintenance Handbook, First Edition, Vol 1, p
12-25.
4. “How Lightweight And Heavy Gas Turbines Compare,” Anthony J. Giampaolo,
Oil & Gas Journal, January 1980.