Gas Turbine Handbook : Principles and Practices

50 Gas Turbine Handbook: Principles and Practices
Turbine Efficiency
Tracking or trending turbine efficiency would be an excellent
method to monitor the health of a unit. However, as turbine inlet temperatures
(TIT) have climbed higher and higher, they have become
virtually impossible to measure on a long term basis. In fact, many
manufacturers measure an intermediate turbine temperature for gas
turbine control. Where this is the case the turbine inlet temperatures
are calculated.
η t = 1–T EXH
TIT
s
1–R t
(4-14)
where
T EXH
= Turbine total exhaust temperature, °R
TIT = Turbine total inlet temperature, °R
R t
= Turbine total inlet pressure/Turbine total
exhaust pressure
Turbine efficiency can be closely approximated by substituting
1
R c
= R t
η t =
1– T EXH
TIT
1– 1 R c
σ
(4-15)
Turbine Horsepower (Produced)
This is the total horsepower produced by the turbine. It includes
the horsepower to drive the compressor and, for single shaft machines,
the power used by the driven load. For units with separate
power turbines, this horsepower should equal the power absorbed by
the compressor plus losses.