What percentage of maximum speed must a gas turbine be rotated to before fuel is turned on?

In gas turbine operation, it is critical to reach a specific rotational speed before introducing fuel to ensure safe and efficient ignition and operation. The correct choice indicates that a gas turbine must typically be rotated to 20-30% of its maximum speed prior to the fuel being turned on. This range is crucial because it allows the turbine to develop sufficient centrifugal force and air flow to stabilize combustion and prevent issues like flame blowout or unburnt fuel emissions, which could occur if the turbine was started at too low a speed.

At speeds below this threshold, the airflow through the combustor is insufficient to ensure a stable and complete combustion process, which can lead to low combustion efficiency and possible damage to the turbine components. Therefore, starting fuel flow within the 20-30% range helps facilitate a smooth and reliable ignition process, paving the way for the turbine to achieve full speed and output capacity safely.