tần số là thường được dùng bởi GTC, bởi một sự thay đổi nhanh chóng trong việc tăng tải trọng, kể từ tua-bin hơi nước không thể đáp ứng đủ nhanh. Đối với một tần số ngày càng tăng, tuabin khí và tuabin hơi nước đều có thể đáp ứng, do đó, như thể hiện trong hình, tua bin khí (60% tải) và tuabin hơi nước (40% tải) thay đổi thích hợp trong tải. | Control Systems and Instrumentation 641 frequency is usually taken up by the GTC by a fast change in increasing the load since the steam turbine cannot respond fast enough. For an increasing frequency the gas turbine and the steam turbine both can respond thus as shown in the figure the gas turbine 60 load and the steam turbine 40 load take their appropriate change in load. The startup and shutdown of a typical gas turbine is shown in figures 19-5 and 19-6 respectively. The time and percentages are approximate values and will vary depending upon the turbine design. The gas turbine during the start-up is on an auxiliary drive initially it is brought to a speed of about 1200-1500 RPM when ignition takes place and the turbine speed and temperature rise very rapidly. The bleed valves are open to prevent the compressor from surging. As the speed reaches about 2300-2500 rpm the turbine is declutched from its start-up motor the first set of bleed valves are closed and then as the turbine has reached near full speed the second set of bleed valves are closed. If the turbine is a two or three shaft turbine as is the case with aero-derivative turbines the power turbine shaft will break loose at a speed of about 60 of the rated speed of the turbine. The turbine temperature flow and speed increases in a very short time of about three to five minutes to the full rated parameters. There is usually a short period of time where the temperature may overshoot. If supplementary firing or steam injection for power augmentation is part of the plant system these should be turned on only after the gas turbine has reached full flow. The injection of steam for power augmentation if done before full load could cause the gas turbine compressor to surge. The shutdown of a gas turbine first requires the shutdown of the steam injection and then the opening of the bleed valves to prevent the compressor from Figure 19-5. A typical startup curve for a gas turbine. 642 Gas Turbine Engineering .
