Abstract: The majority of a number of relays is held in a quiescent state, without power, in a local maintenance controller preparatory to assumption of control of a gas turbine power plant. Control transfer may be manually requested or may occur automatically in response to failure of the plant's primary control system. Regardless of the cause of transfer, a time delay relay is utilized to allow the quiescent relays sufficient latching time. The time delay period is chosen to reflect the maximum period of time for which a lack of trip availability can be safely tolerated.The relay sequencing arrangement is adapted so that when the quiescent relays are energized, alarm circuitry for predetermined plant parameters is automatically reset for on-line transfers, thereby allowing more rapid and efficient transfer and minimizing the need for operator intervention. Alternative means for manually resetting the alarm circuitry is also provided.

Abstract: A combined cycle electric power plant includes two gas turbines, a steam turbine, and a digital control system with an analog or manual backup. Each of the gas turbines has an exhaust heat recovery steam generator connected to a common header from which the steam is supplied by one or both of the steam generators for operating the steam turbine. The digital/analog system includes a steam throttle pressure limiting control, which maintains a minimum steam throttle pressure as a function of steam flow to limit the maximum steam velocity through the steam generators, and reduce the probability of water carryover into the steam turbine. In response to a reduction in the number of steam generators in service, the pressure flow relationship is transferred from one characterization to another, and during such transfer, the analog system operates the steam turbine control valves to limit the rate of steam pressure decay as a function of steam flow.

Abstract: A steam turbine is provided with inlet throttle and governor valves which are positioned by an electrohydraulic control. A digital computer includes a speed control and a load control which respond to turbine speed and load signals and an electrical load signal to generate position control setpoints for the valves. A load reference is generated from an input load demand, and the reference is modified by a speed correction and selectively acted upon by a megawatt control and an impulse pressure control in the generation of the valve position setpoints. On the insertion of the megawatt control or the impulse pressure control into service, or on its removal from service, the computer instantly resets control parameters as required to provide for bumpless control loop switching.

Abstract: A combined cycle electric power plant includes two gas turbines, a steam turbine, and a digital control system with an analog or manual backup. Each of the gas turbines has an exhaust heat recovery steam generator connected to a common header from which the steam is supplied by one or both of the steam generators for operating the steam turbine. Both the digital and the analog systems provide a digital input to an interface for controlling the steam turbine valves. The analog system is controlled to operate a respective valve by an input to its interface which determines valve position in accordance with its duration. The digital system is controlled to operate a respective valve by an input to the interface in accordance with the repetitive duration of the signal. The analog system input and digital system input is applied to an interface for each valve.

Abstract: A local maintenance controller permits continued power generation during maintenance or failure of a primary gas turbine control system by manually for maintenance purposes or automatically for failure purposes assuming turbine control to thereby insure continued operation. The local maintenance controller set forth is particularly suitable for use in conjunction with a computer implemented gas turbine control system.Transfer between the local maintenance controller and the primary control system is effected in a bumpless manner so that load swings are absent. However, if the turbine was operating at system reserve at the time of transfer, the local maintenance controller reduces the load to peak value until primary control is resumed. Operation at any other load at the time of transfer is maintained by the controller. Transfer back to primary control is also effected in a bumpless manner.