58 HANDBOOK OF ELECTRICAL ENGINEERING
2.6.1.8 Combustion and turbine dynamics
After the fuel valve moves from one position to another the flow rate of the fuel delivered to the
combustors changes, but a delay due to the inertia of the fuel occurs. The fuel enters the combustor
and burns along its length at a finite burning rate. Completion of the combustion takes time and
adds a further delay to the energy conversion process. A finite time is required for the burnt gas to
pass through the power turbine and transfer part of its energy to the turbine. The ‘turbine lead-lag’
block approximates these conversion processes. The number of lead and lag terms varies from one
gas turbine type to another.
In a single-shaft gas turbine the turbine lead-lag block represents the amount of energy or power
that is convertible to mechanical power for accelerating the output shaft masses and to balance the
electrical power demand.
In a two-shaft gas turbine the situation is slightly more complicated. Part of the convertible
power is required to drive the separate compressor. The compressor has its own dynamic response
and is shown as a parallel branch in Figure 2.17. This illustrates the fact that the resulting mechanical
Table 2.7. Typical data for simulating gas-turbine control systems
Parameter Low Values Typical High
H note i) 1.2 1.5 2.0
Gh 0.25 0.33 0.42
Cw 1.0 1.0 1.0
Kg 1 1.0 1.0 1.0
Tg 1 0.05 0.01 0.015
Kg 2 note ii) 10.0 20.0 40.0
Tg 2 0.02 0.04 0.15
Kdg 0.02 0.04 0.08
Tg 3 0.25 0.50 0.75
Tg 4 1.0 1.50 1.75
Tf 1 0.01 0.02 0.05
fmax 1.2 1.35 1.5
fmin −0.2 −0.15 0
Kt 1 1.0 1.0 1.0
Tt 1 0.3 0.6 0.9
Tt 2 1.2 1.4 2.0
Kt 2 0.4 (1.0) 0.5 (1.0) 06 (1.0)
Kc 1 0.4 (0) 0.5 (0) 0.6 (0)
Tc 1 Tt 2 (0) Tt 2 (0) Tt 2 (0)
Cmax 1.1 (0) 1.2 (0) 1.3 (0)
Cmin 00 0
Ka 1 2.0 (0) 2.5 (0) 3.0 (0)
Ca 2 0.38 (0) 0.4 (0) 0.42 (0)
Cz 1 0.38 (0) 0.4 (0) 0.42 (0)
Cz 2 0.48 (0) 0.5 (0) 0.52 (0)
Notes:
i)Gh=^1.^0
2 H
ii)Kg 1 xKg 2 a constant value
iii) Data in brackets ( ) apply to the single-shaft mathematical model.