Gas Turbine Handbook : Principles and Practices

84 Gas Turbine Handbook: Principles and Practices
Temperature protection is provided to protect against excessively
high temperatures, but it can also be used to protect against
excessive temperature spread. The use of multiple temperature sensors,
as in the case of turbine inlet temperature (intermediate turbine
temperature or exhaust gas temperature), provides protection should
the spread from minimum to maximum temperature (or minimum
and maximum compared to the average) become excessive.
Because turbine inlet temperature is the most frequently activated
limiting factor, one level is set for base load operation and a
higher level is set for peaking operation. However, direct measurement
of turbine inlet temperature is too risky, because a responsive
temperature probe can not live in that environment and a robust
probe would not be responsive. Therefore, temperatures are measured
in a cooler part of the compressor-turbine, and sometimes
between the compressor-turbine and the power extraction turbine.
A predetermined temperature schedule is then prepared by the gas
turbine manufacturer to ensure operation within safe temperature
limits.
References
1. “Controls: The Old vs the New”, Power Engineering, April 1996.
2. “Speedtronic* Mark II For Pipeline Applications,” SOA-17-73, T.R.
Chamberlin, General Electric.