20-12-2012, 03:20 PM
Modeling of Gas Turbine and Its Control System
1Modeling of Gas.pdf (Size: 3.35 MB / Downloads: 406)
Brayton Cycle
• Air is first compressed in an adiabatic process with constant
entropy within the compressor (process 1–2), usually an axial
compressor. Pressure of 13–20 times that of atmospheric is
achieved after the compression stage.
• Fuel, either liquid of gas is then mixed with the compressed
air and burnt in the combustor (process 2–3). After which, the
hot gasses is allowed to expand through the turbine (process
3–4). This gas expansion drives the blades of the turbine and
consequently the shaft of the generator connected to it.
GT Controls modelled
• There are four blocks related with speed/load
control, temperature control, fuel control, and
air control.
• Speed/load control : determines the fuel
demand according to the load reference and the
rotor speed deviation
• Temperature control: restricts the exhaust
temperature not to injure the gas turbine. The
measured exhaust temperature is compared with
the reference temperature. The output is the
temperature control signal .
GT Controls
• The fuel demand is compared with the
temperature control signal in the fuel control
block. The lower value is selected by the low
value selector, and it determines the fuel flow
• The air control block adjusts the airflow
through compressor inlet guide vanes (IGV)
so as to attain the desired exhaust
temperature. The exhaust temperature is kept
lower than its rated value (say 1 %).
Outer Loop Control : pf/VAr Controller
• Many gas turbine units are equipped with a
pf/VAr controller which is in service whenever
the unit is on‐line. This is an outer‐loop control,
which monitors generator stator reactive current
and controls to a fixed VAr or pf set‐point.
• The controller is often used in pf mode,
controlling to unity power factor.
• The control structure is an “integrator with gain”
feedback to the AVR set‐point.