Control system for single shaft combined cycle gas and steam turbine unit

Method for starting and controlling a combined cycle turbine of the type having a gas turbine with a fuel flow control valve and a steam turbine with at least one steam control valve both disposed on a single shaft and having a heat recovery steam generator heated by said gas turbine and connected to supply steam to said steam control valve, said combined cycle turbine having a unified control system and driving a load, and also having an auxiliary steam source connected to said steam control valve, said method comprising:

• controlling of steam from the auxiliary steam source with said steam control valve to crank said combined cycle turbine for starting,
• initiating and controlling fuel flow to the gas turbine with said fuel flow control valve and initiating combustion,
• controlling initial acceleration of said combined cycle turbine with said steam control valve on auxiliary steam,
• transferring control during acceleration of the combined cycle turbine to said fuel flow control valve and reducing the opening of said steam control valve to a minimum value when the turbine reaches rated speed,
• connecting said combined cycle turbine to a load,
• transferring steam supply from said auxiliary source to said heat recovery steam generator,
• opening said at least one steam control valve fully to increase power output to said load, and
• controlling load applied to the combined cycle turbine by varying a command signal to said fuel flow control valve.

Method for starting and controlling a combined cycle turbine of the type having a gas turbine with a fuel flow control valve and a steam turbine with at least one steam control valve both disposed on a single shaft and having a heat recovery steam generator heated by said gas turbine and connected to supply steam to said steam control valve, said combined cycle turbine having a unified control system and driving a load, and also having an auxiliary steam source connected to said steam control valve, said method comprising:

• controlling of steam from the auxiliary steam source with said steam control valve to crank said combined cycle turbine for starting,
• initiating and controlling fuel flow to the gas turbine with said fuel flow control valve and initiating combustion,
• controlling initial acceleration of said combined cycle turbine with said steam control valve on auxiliary steam,
• transferring control during acceleration of the combined cycle turbine to said fuel flow control valve and reducing the opening of said steam control valve to a minimum value when the turbine reaches rated speed,
• wherein said fuel flow is controlled partially in accordance with a gas turbine acceleration error signal determined by comparing a gas turbine acceleration reference to actual acceleration, wherein the steam flow is controlled partially by a steam turbine acceleration error determined by comparing a steam turbine acceleration reference with actual acceleration, and wherein said transferring step comprises setting said steam turbine acceleration reference lower than said gas turbine acceleration reference, whereby increasing acceleration of the combined cycle turbine will first be controlled by the steam valve until the gas turbine is capable of supplying acceleration torque and then controlled by the fuel flow control valve.

Method for starting and controlling a combined cycle turbine of the type having a gas turbine with a fuel flow control valve and a steam turbine with at least one steam control valve both disposed on a single shaft and having a heat recovery steam generator heated by said gas turbine and connected to supply steam to said steam control valve, said combined cycle turbine having a unified control system and driving a load, and also having an auxiliary steam source connected to said steam control valve, said method comprising:

• controlling of steam from the auxiliary steam source with said steam control valve to crank said combined cycle turbine for starting,
• initiating and controlling fuel flow to the gas turbine with said fuel flow control valve and initiating combustion,
• controlling initial acceleration of said combined cycle turbine with said steam control valve on auxiliary steam,
• transferring acceleration control during a smooth acceleration of the combined cycle turbine to said fuel flow control valve and gradually reducing the opening of said steam control valve to a minimum value when the turbine reaches rated speed, wherein the step of controlling steam from the auxiliary steam source further includes controlling auxiliary steam flow in accordance with a speed error signal determined by comparing a steam turbine speed reference with actual speed and positioning said steam control valve in accordance with said speed error signal, and
• setting said steam turbine speed reference first at gas turbine purging speed and subsequently lowering the steam turbine speed reference to gas turbine ignition speed.